Supraventricular tachycardias: Clinical Guidelines

List of Abbreviations

AAD – antiarrhythmic drugs

AAT – antiarrhythmic therapy

AV – atrioventricular

AVRT – atrioventricular reentrant tachycardia

AVNRT – atrioventricular nodal reentrant tachycardia

WPW – Wolff-Parkinson-White syndrome (phenomenon)

CHD – congenital heart disease

AP – accessory pathway

AAP – accessory atrioventricular pathway

LV – left ventricle

LBBB – left bundle branch block

RBBB – right bundle branch block

Reentry – excitation wave reentry

RFA – radiofrequency catheter ablation of arrhythmogenic zones

SVT – supraventricular tachycardia

SR – sinus rhythm

ST – sinus tachycardia

SA – sinoatrial node

AFL – atrial flutter

LCE – level of confidence of evidence

GRS – grade of recommendation strength

EF – ejection fraction

AF – atrial fibrillation

HM – Holter (ambulatory) cardiac rhythm monitoring

CHF – chronic heart failure

HR – heart rate

VHR – ventricular heart rate

APR – atrial contraction rate

TEEPS – transesophageal electrophysiological study of the heart

ECG – electrocardiogram

EP study – electrophysiological study

EchoCG – echocardiography

** – the drug is included in the list of vital and essential drugs

# – off-label use of the drug is possible

*** – medical device implanted in the human body when providing medical care within the framework of the state guarantee program for free medical care to citizens

Terms and Definitions

Paroxysmal tachycardia – paroxysmal increase in heart rate with a sudden onset and termination of the episode.

Non-paroxysmal (chronic) tachycardia – persistent tachycardia or incessantly recurrent tachycardia occupying the majority of the day.

Reciprocal tachycardia – tachycardia via the reentry mechanism (macro-reentry).

Focal tachycardia – tachycardia caused by the generation of frequent pathological impulses from a small limited area of the myocardium—a "point source" functioning via abnormal automaticity / triggered activity / micro-reentry.

Sustained tachycardia episode – an episode of tachycardia lasting more than 30 seconds.

Tachycardia-induced cardiomyopathy – dilatation of the heart chambers and decreased myocardial contractility resulting from myocardial remodeling caused by tachycardia.

1. Brief information on the disease or condition

1.1 Definition of the disease or condition

Supraventricular tachycardia (SVT) – three or more consecutive heartbeats with a rate exceeding the upper limit of the age-specific normal range in children, provided the origin of the arrhythmia is supraventricular: in the sinus node (SA), atrial myocardium, muscle sleeves of the pulmonary and venae cavae, atrioventricular (AV) junction, as well as involving accessory pathways (APs) in the arrhythmogenic mechanism.

Typically, a rapid regular rhythm with narrow QRS complexes is recorded during SVT. Atrial tachycardias with variable AV conduction are characterized by an irregular rhythm. SVT with wide QRS complexes includes: antidromic AV reentrant tachycardia, other SVTs with antegrade conduction via an AP, and SVT with aberrant conduction (with RBBB or LBBB).

1.2 Etiology and pathogenesis of the disease or condition (group of diseases or conditions)

Several pathophysiological mechanisms may be involved in the development of SVT: enhanced automaticity, abnormal automaticity, triggered activity, and reentry (from English reentry).

Enhanced (accelerated) automaticity – impaired impulse formation in SA node cells or latent pacemaker cells as a result of an increased rate of diastolic depolarization. Enhanced SA node automaticity leads to chronic sinus tachycardia, while that of latent pacemaker cells leads to accelerated escape beats and accelerated rhythms. Enhanced automaticity occurs in pacemaker cells with an inherently characteristic function of spontaneous diastolic depolarization. This category differs from abnormal automaticity in this regard.

Abnormal automaticity – impaired impulse formation resulting from spontaneous diastolic depolarization in atrial, ventricular, and cardiac conduction system myocardial cells that do not normally possess this property. As a result, ectopic centers of a rapid pathological rhythm arise. In children, pathological foci of automaticity may appear due to impaired formation of specialized cardiac conduction tissue during cardiogenesis. The abnormal automaticity mechanism is the primary cause of focal atrial tachycardia.

Triggered activity – the occurrence of secondary depolarizations associated with a preceding action potential. If additional premature excitations occur before cell repolarization is complete, they are called early afterdepolarizations. They can appear during phase 2 (type 1) or phase 3 (type 2) of the action potential. Delayed afterdepolarizations occur after the completion of cell repolarization, i.e., in phase 4 of the action potential. Triggered activity may play a certain role in the genesis of focal tachycardias (atrial and junctional).

Reentry – an arrhythmia mechanism consisting of the re-excitation of a myocardial area by the same impulse traversing a circular path. Two conduction pathways are required for this mechanism to occur, with impulse propagation impaired in one of them due to a localized unidirectional block. Depending on the size of the loop, this mechanism is subdivided into macro-reentry and micro-reentry. In macro-reentry, circulation occurs along an anatomically defined pathway, for example, involving an accessory AV connection (AAVC) in Wolff-Parkinson-White (WPW) syndrome. In micro-reentry, impulse circulation occurs along functional pathways. Tachycardias based on the reentry mechanism are conventionally called reciprocating tachycardias.

SVT is found in 95% of cases in children with structurally normal hearts. The manifestation of SVT requires an arrhythmogenic zone where the pathophysiological mechanism arises and is maintained. Risk factors and triggers for SVT in children include: burdened perinatal history, immaturity of cardiac structures in infants, impairment of neuroautonomic regulation of cardiac rhythm, personality traits in the form of psychoemotional lability and high levels of neurotization, extracardiac pathology (central nervous system disorders, endocrine pathology, metabolic diseases, acute and chronic infectious diseases), fever, metabolic and electrolyte disorders, and poisoning. In rarer cases, the onset of SVT is associated with organic heart disease (congenital and acquired heart defects, cardiomyopathies, inflammatory heart diseases). During postnatal structural development of the heart in infants, spontaneous disappearance of the arrhythmia frequently occurs, for example, due to the cessation of AAVC functioning [1-6].

1.3 Epidemiology of the Disease or Condition

The incidence of SVT in children is 0.1-0.4%. The incidence of various electrophysiological variants of SVT depends on the child's age. AV reentrant tachycardias involving an AAVC predominate in the structure of SVT across all age groups. This type of tachycardia accounts for up to 80% of all SVT under 1 year of age and 60-70% in older age groups.

Paroxysmal AV nodal reentrant tachycardia accounts for 13-24% of all SVT cases in children, and its occurrence has a clear age dependence—ranging from isolated cases in infants to up to 30% of all SVTs in adolescents. Atrial tachycardia is less common: in 15-25% of children under 1.5 years of age and in 4-6% of older children, occurring more frequently in patients with congenital heart defects. Atrial fibrillation rarely occurs in childhood.

Up to 30–50% of SVTs detected in the neonatal period spontaneously resolve by the age of 18 months. The prognosis is particularly favorable in children with Wolff-Parkinson-White syndrome: if paroxysmal AV reciprocating tachycardia involving an accessory pathway occurs in the first months of life, spontaneous resolution of the condition occurs in the majority of cases by the first year of life, though in one-third of patients the arrhythmia recurs in later childhood. When SVT occurs at an age older than 5 years, spontaneous recovery is rare [7-8].

1.4 Features of Coding the Disease or Condition

I45.6 – Pre-excitation syndromes.

I47.1 – Supraventricular tachycardia.

I47.9 – Paroxysmal tachycardia, unspecified.

I48 – Atrial fibrillation and flutter.

1.5 Classification of the disease or condition

1. Sinus tachycardias:

1.1. Physiological sinus tachycardia

1.2. Non-physiological (chronic) sinus tachycardia

1.3. Sinus node reentrant tachycardia

2. Atrial tachycardias:

2.1. Focal (ectopic) atrial tachycardia

2.2. Multifocal (chaotic) atrial tachycardia

2.3. Intra-atrial reentrant tachycardia (incisional atrial tachycardia)

2.4. Atrial flutter

2.5. Atrial fibrillation

3. Atrioventricular nodal tachycardias:

3.1. Atrioventricular nodal reentrant tachycardia

3.1.1. Typical

3.1.2. Atypical

3.2. Focal (ectopic) junctional tachycardia

3.2.1. Congenital

3.2.2. Postoperative

3.2.3. "Adult" variant

4. Atrioventricular tachycardias:

4.1. Atrioventricular reciprocating tachycardia utilizing an accessory pathway (AP, etc.)

4.1.1. Orthodromic

4.1.2. Antidromic

1.6 Clinical presentation of the disease or condition

Paroxysmal SVT is characterized by a sudden onset and termination of the episode, lasting from several seconds to several hours (more rarely, days). In newborns and young children, SVT episodes are accompanied by agitation or lethargy, refusal to feed, tachypnea, and in severe cases, acute heart failure and cardiogenic shock. School-age children complain of palpitations, chest "fluttering", a feeling of fear, air hunger, weakness, dizziness, sweating, and precordial pain. The child and their parents should be asked about the measures that help terminate the tachycardia episode. These may be standard vagal maneuvers or other successful techniques, such as drinking cold water, breath-holding, the effective use of which supports the diagnosis of SVT.

In 15% of patients, presyncopal or syncopal states develop at the time of the tachycardia episode. Severe clinical manifestations are characteristic of children with a high heart rate during the tachycardia episode: 250–300 bpm in infants under one year of age, and 200–250 bpm in older patients. Triggering factors for a tachycardia episode in young children include agitation, fever, and intoxication, while in older children they include psychoemotional stress and physical exertion. An SVT episode may occur at rest without any triggering factors.

In non-paroxysmal (chronic) SVT, children are often asymptomatic, and the arrhythmia is detected incidentally during routine check-ups and evaluations for intercurrent illnesses. The heart rate during chronic tachycardia is usually lower than in paroxysmal tachycardia, but in young children it can also be high, reaching 220–250 bpm. If present chronically for a long time, SVT is complicated by the development of tachycardia-induced cardiomyopathy, ultimately leading to heart failure. Following the restoration of sinus rhythm, the dimensions of the heart chambers and myocardial contractility return to age-norm quite rapidly, usually within a few weeks at most [14-17].

2. Diagnostics, medical indications and contraindications for diagnostic methods

Diagnostic criteria:

The diagnosis of SVT is established based on patient complaints, medical history, physical examination, and the results of laboratory and instrumental investigations. The basis for the diagnosis and differential diagnosis of SVT is its ECG recording, the method of which is determined by the frequency and duration of palpitation episodes, the presence of hemodynamic disorders, and other features of SVT [9-11].

2.1 Complaints and Anamnesis

see section "Clinical Presentation"

It is necessary to evaluate the history of the disease: age of onset of arrhythmia, association with past illnesses, vaccination, presence of cardiovascular diseases, congenital heart disease (CHD), methods of cardiac surgical correction of CHD, and the presence of syncopal episodes. Evaluation of the family history is also important to identify cases of arrhythmia, episodes of loss of consciousness, and sudden death among family members of the child under evaluation.

2.2 Physical Examination

In patients with existing or suspected SVT, it is necessary to assess anthropometric parameters (height and weight measurements), the presence and extent of cyanosis and edema. General thermometry, pulse examination, peripheral blood pressure measurement, respiratory rate measurement, and assessment of the state of the jugular veins (engorgement, pulsation), liver size, and thyroid changes are performed in children. Palpation, percussion, and auscultation are carried out (percussion for heart and pericardial pathology, auscultation for heart and pericardial pathology).

2.3 Laboratory Diagnostics

If SVT is a complication of any cardiovascular disease (myocarditis, congenital heart disease, cardiomyopathy, etc.), laboratory investigations must correspond to the diagnostic work-up for the underlying condition.

(LoE 5, GoR C)

(LoE 5, GoR C)

Comments:

The investigation must include the determination of blood electrolyte levels (potassium, sodium, total calcium, total magnesium), as hypokalemia, hyponatremia, hypocalcemia, and hypomagnesemia themselves exert an arrhythmogenic effect, reduce the efficacy of antiarrhythmic therapy (AAT), and create conditions for proarrhythmias. Target potassium values are 4.5–5 mmol/L.

When heart disease is suspected, determination of myocardial injury markers (blood troponin I, T levels) is required [18].

(LoE 5, GoR C)

2.4 Instrumental Diagnostics

• In cases where the medical history, complaints, or physical findings suggest SVT, its presence is recommended to be confirmed by recording an ECG or using another technique that records the cardiac electrical signal (Holter heart rhythm monitoring, recording of the electrical activity of the cardiac conduction system (A05.10.001)) [9-11, 18-23].

(LoE 4, GoR C)

Comments:

A 12-lead ECG with SVT recording allows for the differential diagnosis of arrhythmia based on the assessment of the regularity, number, and ratio of P waves and QRS complexes (Appendix B2). An interictal ECG makes it possible to detect signs of ventricular pre-excitation, concomitant heart rhythm and conduction disturbances, and changes characteristic of heart diseases.

Holter heart rhythm monitoring (HM) rarely allows for the recording of paroxysmal tachycardia (except in children with frequent paroxysms), but it helps assess the representation of chronic tachycardia in the structure of the diurnal heart rhythm, as well as detect concomitant rhythm and conduction disturbances.

Recording the electrical activity of the cardiac conduction system (via transesophageal electrophysiological study of the heart (TEEPS)) allows for the scheduled induction and recording of paroxysmal tachycardia with verification of its electrophysiological variant. TEEPS allows for the evaluation of the electrophysiological properties of the sinus node, AV node, and accessory pathway. An effective refractory period (ERP) of the accessory pathway of 250 ms or less is an additional criterion for determining indications for catheter ablation of the accessory pathway.

• In patients receiving antiarrhythmic therapy, it is recommended to regularly record a 12-lead ECG and/or HM to evaluate its efficacy and safety [9-11].

(LoE 5, GoR C)

Comments: When prescribing antiarrhythmic therapy, moderate drug-induced bradycardia and moderate changes in ECG intervals are acceptable as part of the electrophysiological effects of the drugs used. When prescribing #propafenone**, the duration of the PQ interval and the width of the QRS complex should not increase by more than 25%; when prescribing #amiodarone**, the duration of the corrected QT interval should not exceed 500 ms. Exceeding these parameters may lead to proarrhythmias [18].

• To assess the dimensions, chamber volumes, and contractile function of the heart in patients with SVT, a transthoracic echocardiography is recommended [9-11, 22].

(LoE 4, GoR C)

Comments: The purpose of echocardiography is to diagnose structural heart disease, organic myocardial pathology, signs of myocardial dysfunction, and to assess the hemodynamic significance of the arrhythmia. Tachycardia-induced cardiomyopathy refers to secondary, reversible myocardial dysfunction caused by tachyarrhythmia, manifested by dilation of the heart chambers, reduced ventricular myocardial contractility, relative mitral regurgitation, and the development of congestive heart failure. Timely detection of these complications helps correctly determine the management strategy for a patient with arrhythmia. Restoring rhythm in children without organic heart disease leads to the normalization of morphofunctional parameters, and echocardiography serves as the primary method for monitoring the dynamics of these changes [22-23].

2.5 Other Procedures

Other cardiac imaging methods, such as contrast-enhanced cardiac magnetic resonance imaging and contrast-enhanced cardiac computed tomography, are performed when heart disease is suspected, according to their respective indications.

Performing a single-stage incremental exercise test (stress tests: bicycle ergometry, treadmill test) makes it possible to establish a connection between rhythm and conduction disorders and physical activity. However, it is quite rare during the test, if performed according to a standard protocol, to provoke an SVT paroxysm, even if spontaneous tachycardia attacks are associated with physical activity.

• In cases of presyncope and unexplained syncope suspected to be caused by SVT, a tilt table test is recommended—which can provoke a syncopal state while evaluating the patient's physiological parameters (ECG, EEG, blood pressure)—or the implantation of a loop recorder for long-term monitoring of the electrical activity of the cardiac conduction system (implantable cardiac monitor***), which stores and subsequently analyzes the ECG during an attack if other diagnostic methods prove ineffective [9-11].

(LoE 5, GoR C)

(LoE 5, GoR C)

3. Treatment, including drug and non-drug therapies, diet therapy, and pain management

Treatment of SVT includes measures to restore sinus rhythm during a tachycardia paroxysm, long-term pharmacotherapy for the prevention of tachycardia recurrence, and surgical (interventional) treatment [10, 11, 18].

3.1. Emergency Treatment

Emergency therapy falls within the professional competence of an anesthesiologist-resuscitologist and should be performed in the intensive care unit or critical care unit of a pediatric medical facility under the monitoring of ECG, blood pressure, respiration, oxygen saturation, and other vital functions. If SVT persists despite the standard SVT termination protocol, a pediatric cardiologist should be consulted regarding the patient's further management strategy.

The main factors determining the pharmacological treatment strategy for patients with SVT include: hemodynamic status (stable or unstable), form of tachycardia (paroxysmal or non-paroxysmal), electrophysiological variant of the arrhythmia, child's age, and cardiac contractility. Incorrect clinical interpretation of clinical and electrocardiographic changes—such as the erroneous diagnosis of a paroxysmal tachycardia pattern in children with chronic SVT—leads to inappropriate therapy. Attempts to terminate chronic tachycardia with rapid administration of high doses of antiarrhythmic drugs are associated with complications up to hemodynamic collapse and cardiac arrest. SVT with bundle branch block and antidromic AV re-entry tachycardia must be differentiated from ventricular tachycardia. Termination of paroxysmal tachycardia should be performed under ECG and blood pressure monitoring.

• For emergency therapy of an SVT paroxysm with unstable hemodynamics (clinical signs of heart failure, low blood pressure, syncopal state), external electrical cardioversion (synchronized cardioversion) is recommended [10, 11, 18, 24].

(LoE 5, GoR C)

Comments: Defibrillator electrode placement scheme for children: one electrode is placed to the right of the sternum below the clavicle, and the second – in the projection of the left mid-axillary line. If such electrode placement is impossible due to a small chest size, the following positions can be used in emergency situations: the first electrode – over the cardiac silhouette, and the second – on the lateral chest wall at the level of the first electrode. The shock energy for children with SVT is 0.5-1-2 J/kg.

Electrical cardioversion is effective when the tachycardia mechanism involves re-entry (atrial fibrillation and flutter, AV re-entry tachycardia involving an accessory pathway, AV nodal re-entry tachycardia, atrial re-entry tachycardia), but does not terminate tachycardias caused by abnormal automaticity (focal atrial and junctional tachycardias). Electrical cardioversion is the method of choice for neonatal atrial flutter, after the termination of which antiarrhythmic therapy is unnecessary in most cases.

When terminating a paroxysm of atrial fibrillation lasting more than 48 hours, the risk of thromboembolic complications increases; therefore, transesophageal echocardiography is advisable prior to electrical cardioversion, and if thrombi are suspected, warfarin** is prescribed for 4 weeks at a dose of 0.1 mg/kg/day once daily (target international normalized ratio of 2.0-3.0). In urgent situations, unfractionated heparin** is administered intravenously at a dose of 100 IU/kg prior to electrical cardioversion [25].

• In hemodynamically stable patients, vagal maneuvers are recommended to terminate SVT [10, 11, 18].

(LoE 5, GoR C)

Comments: in infants, the diving reflex is used (applying an ice pack or a rubber glove filled with ice and chilled water to the face for 5-10 seconds), nasogastric tube insertion, or holding upside down; in school-age children, the Valsalva maneuver is used (deep breath, straining, abdominal muscle tension); pressing on the root of the tongue. The efficacy of these maneuvers, provided they are performed correctly, is 19-54%. Many of these techniques carry a minimal risk of complications and can be performed by the patient themselves, the child's parents, or medical personnel. Patients and their parents must be trained in the technique of performing these maneuvers. Vagal maneuvers have both therapeutic and diagnostic value because they terminate re-entrant tachycardias involving the AV node [26].

• If vagal maneuvers are ineffective, transesophageal pacing is recommended to terminate sustained SVT [10, 11, 18].

(LoE 5, GoR C)

Comments: Transesophageal pacing is most effective in terminating paroxysms of AV re-entrant tachycardia and atrial flutter.

• If vagal maneuvers are ineffective, intravenous administration of #triphasadenin is recommended to terminate sustained SVT [9-11, 27-29].

(LoE 5, GoR C)

Comments: The following dosage of #triphasadenin is used (1% solution, 1 ml ampoule – 10 mg ATP): the drug is administered intravenously in escalating doses of 0.1-0.2-0.3 mg/kg, but not exceeding 12 mg under electrocardiographic monitoring (each subsequent dose is administered if the previous one is ineffective after 1-2 minutes); in infants under one year of age, the first dose is 0.15 mg/kg [28, 29]. The efficacy is 90-100%, but due to the very short half-life (5-10 seconds), tachycardia may recur in 1/3 of cases [9, 12].

#Triphasadenin is administered via rapid intravenous bolus injection (into a large vein) over 1-2 seconds, immediately followed by an injection of 0.9% sodium chloride solution**. This technique is known as the "double-syringe technique." It requires an intravenous catheter and a two-way stopcock with two syringes to ensure the effective administration of adenosine and 0.9% sodium chloride solution**. A single-syringe technique is acceptable: 1 ml of #triphasadenin is diluted in a syringe with 0.9% sodium chloride solution** to a volume of 10 ml (the concentration of #triphasadenin in the prepared solution is 1 mg/ml), and then the calculated dose of the drug is injected intravenously [29].

Although the administration of #trifosadenine causes a rhythm pause due to transient AV block and SA node depression, prolonged bradycardia is not observed; nevertheless, the drug should be used with caution in patients with sick sinus syndrome. Immediately after administration, a feeling of warmth, flushing, and dyspnea may occur, but these symptoms are also short-lived [30].

• If vagal maneuvers are ineffective and there are no signs of ventricular pre-excitation on the ECG (during and between episodes), intravenous administration of #verapamil** is recommended in children over 1 year of age for the termination of sustained SVT [9-11].

(LoE 5, GoR C)

Comments: #Verapamil** is a calcium channel blocker (C08: Calcium channel blockers). It depresses sinus node automaticity and AV nodal depolarization. It is administered intravenously at a dose of 0.1 mg/kg over 2 min [9,10]. When administered intravenously, the drug is rapidly metabolized and exerts a depressant effect on myocardial contractility. Intravenous administration of #verapamil** terminates SVT paroxysms in 64-98% of cases, but is associated with the development of arterial hypotension. Therefore, the drug should not be used in patients with hemodynamic instability or heart failure with a low LV ejection fraction. #Verapamil** is not used in infants under one year of age, as it can cause uncontrolled hypotension in this age group. #Verapamil** is contraindicated in patients with Wolff-Parkinson-White syndrome, as well as in wide-complex tachycardia of unknown etiology [18, 31-33].

• If vagal maneuvers, #trifosadenine, and/or #verapamil** are ineffective, intravenous administration of #amiodarone** is recommended [9-11].

(LoE 5, GoR C)

Comments: #Amiodarone** is a class III antiarrhythmic drug (C01BD: Antiarrhythmics, class III). It prolongs action potential duration and refractoriness in myocardial cells, including accessory pathways, due to potassium channel blockade, inhibition of the fast inward sodium current, local antiadrenergic (both alpha- and beta-blocking) activity, and calcium channel blockade. This leads to a decreased heart rate, slowed AV nodal conduction, and dilation of peripheral and coronary vessels. The drug is administered intravenously at a loading dose of 5-10 mg/kg over 40-60 min, followed by a maintenance dose of 5-15 mcg/kg/min (prepared in 5% dextrose solution**) [9]. Rapid administration and exceeding recommended doses can lead to hemodynamic collapse, especially in young children with myocardial dysfunction. Peak serum concentrations are reached within 30 min. If necessary, maintenance infusion can be continued for several days (up to 5 days). If oral #amiodarone** is subsequently planned as long-term antiarrhythmic therapy, oral loading with #amiodarone** at recommended doses (see Section 3.2) can be initiated concurrently with intravenous administration if the infusion needs to be continued (e.g., in frequent tachycardia recurrences). If another continuous antiarrhythmic therapy is planned (e.g., #propafenone**), it should preferably be prescribed after the intravenous #amiodarone** infusion is completed. ECG and blood pressure monitoring are required during #amiodarone** administration [34-38].

3.2. Pharmacotherapy

Long-term antiarrhythmic therapy is prescribed for frequent, clinically and hemodynamically significant episodes of SVT, or for chronic SVT with a risk of tachycardia-induced cardiomyopathy when interventional treatment is not feasible (child's body weight less than 15 kg, proximity of the arrhythmia substrate to normal conduction system structures or coronary arteries, patient refusal of catheter ablation, and other reasons).

Long-term antiarrhythmic therapy is most commonly used in neonates and young children. The goal of antiarrhythmic therapy in this patient population is to prevent recurrent tachycardia episodes, which are difficult to monitor at an early age but frequently lead to heart failure if prolonged. Therefore, antiarrhythmic therapy is prescribed immediately after the first documented episode of SVT for a duration of 4-12 months, depending on the clinical presentation and ECG dynamics [18].

Treatment efficacy is assessed based on changes in the clinical course of the disease and objective documentation of arrhythmia severity using modern non-invasive ECG diagnostic methods (absence of tachycardia episodes, reduction in the burden of chronic tachycardia). Continuous monitoring of antiarrhythmic therapy safety is required by evaluating the electrophysiological effects of antiarrhythmic drugs on the ECG (changes in PQ and QTc intervals, QRS duration) and tracking potential arrhythmogenic and extracardiac complications. Special attention should be paid to monitoring thyroid function during chronic #amiodarone** therapy. When selecting therapy, antiarrhythmic drugs are prescribed sequentially, starting with agents having a shorter half-life. The effective dose of antiarrhythmic drugs, with the exception of #amiodarone**, is determined by titration (gradual increase). If monotherapy is ineffective, combination antiarrhythmic therapy is used. Once stable pharmacological remission of the arrhythmia is achieved, scheduled discontinuation of therapy is performed. A follow-up cardiac evaluation is conducted before discharging the patient from clinical follow-up [18, 33, 39-45].

Information on antiarrhythmic drug dosages and potential adverse effects is presented in Appendix A3.1.

• #Propranolol** is recommended for the treatment of symptomatic patients with SVT [9-11, 18, 43].

(LoE 5, GoR C)

Comments: #Propranolol** is a non-selective beta-blocker with membrane-stabilizing activity that decreases heart rate, reduces sinus node automaticity, and slows AV conduction. It is administered orally at a dose of 1-3 mg/kg/day divided into 3-4 doses [9].

• #Atenolol** is recommended for the treatment of symptomatic patients with SVT [9-11, 46, 47].

(LEL 4, GR C)

Comments: #Atenolol** is a selective beta-blocker without membrane-stabilizing activity. It decreases heart rate, reduces sinus node automaticity, and slows AV conduction. It is administered orally at a dose of 0.3-1.3 mg/kg/day in a single daily dose [18]. #Atenolol** has a less pronounced effect on the smooth muscles of bronchi and peripheral arteries compared to propranolol. However, the cardioselectivity of #atenolol** decreases at higher doses [18, 47].

• #Propafenone** is recommended for the treatment of symptomatic patients with SVT [9-11, 18, 48-50].

(LEL 4, GR C)

Comments: #Propafenone** (C01BC: Antiarrhythmic drugs, class Ic) blocks fast sodium channels, which slows impulse conduction through the atria, ventricles, AV junction, and accessory pathways. It possesses anticholinergic (muscarinic receptor blocking) and weak beta-blocking effects. The drug is administered orally at a dose of 5-15 mg/kg/day in 3 divided doses, or 200-600 mg/m² per day in 3 divided doses [9, 50]. The starting dose is 5-7 mg/kg/day with subsequent titration to an effective dose [50].

In patients with atrial macro-reentrant tachycardias, #propafenone** is not recommended as monotherapy. #Propafenone** prolongs refractoriness in atrial cells, thereby lengthening the atrial tachycardia cycle (decreasing the atrial rate), which can eliminate functional AV block and significantly increase the ventricular rate (e.g., atrial flutter with an atrial rate of 300 bpm and 2:1 AV block resulting in a ventricular rate of 150 bpm; under the influence of #propafenone**, the atrial rate decreases to 240 bpm, enabling 1:1 AV conduction, which increases the ventricular rate to 240 bpm). To prevent this, #propafenone** can be used in combination with drugs that suppress AV conduction (#propafenone** plus beta-blockers). Furthermore, #propafenone** is contraindicated in patients with myocardial disease who have severe ventricular dysfunction, low ejection fraction, marked myocardial hypertrophy, or severe fibrosis [10-11, 18, 49-50].

• #Sotalol** is recommended for the treatment of symptomatic patients with SVT [9-11, 18, 51-53].

(LEL 4, GR C)

Comments: #Sotalol** is classified as a beta-blocker in the ATC classification and as a class III antiarrhythmic agent in the Vaughan-Williams classification. It non-selectively blocks beta-adrenergic receptors and potassium channels (at high doses), prolonging action potential duration and the effective refractory period in the atria, ventricles, AV node, His-Purkinje system, and accessory pathways. The drug is administered orally at a dose of 2-8 mg/kg/day in 2 divided doses [9, 18]. The initial dose is 2 mg/kg/day, followed by cautious titration to an effective dose under ECG and blood pressure monitoring. The maximum dose typically does not exceed 4-6 mg/kg/day [53].

• #Amiodarone** is recommended for the treatment of symptomatic patients with SVT [9-11, 18, 37, 54, 55].

(LoE 5, GoR C)

Comments: #Amiodarone** – (C01BD: Antiarrhythmic drugs, class III) is usually prescribed when beta-blockers and #propafenone** are ineffective. It is the drug of choice in children with reduced left ventricular ejection fraction. The loading dose is 10 mg/kg per day orally in two divided doses for 10 days (the duration of loading is determined by the clinical picture and the degree of QTc prolongation). The maintenance dose is 5 mg/kg/day orally once daily. The drug is not used in patients with initially increased or borderline QTc intervals. During therapy, the QTc interval should not increase by more than 500 ms [9, 18].

• #Verapamil** is recommended for the treatment of symptomatic patients older than 1 year with SVT without ECG evidence of ventricular pre-excitation (during tachycardia and on resting ECG) when other antiarrhythmic drugs are ineffective [9-11, 18].

(LoE 5, GoR C)

Comments: #Verapamil** is a calcium channel blocker. The drug acts on slow inward calcium currents, suppressing sinus node automaticity and AV node depolarization. It exerts a negative inotropic effect and lowers blood pressure. It is rarely used in children, usually when other antiarrhythmic drugs are ineffective or contraindicated. It is not used in infants under one year of age or in patients with Wolff-Parkinson-White syndrome. #Verapamil** may be useful for controlling ventricular rate in atrial tachycardias, including atrial fibrillation. The drug may be effective in children with paroxysmal AV nodal reentrant tachycardia. Recommended doses are 4-8 mg/kg per day orally in 3 divided doses [18].

• #Digoxin** is recommended for the treatment of symptomatic patients with SVT without ECG evidence of ventricular pre-excitation (during tachycardia and on resting ECG) [9-11, 18, 43].

(LEL 4, GR C)

Comments: #Digoxin** is usually used in children with atrial tachycardias as part of combination antiarrhythmic therapy. #Digoxin** increases parasympathetic activity and stimulates type 2 muscarinic receptors. As a result, heart rate and AV conduction slow down. The goal of #digoxin** administration is ventricular rate control.

#Digoxin** is not prescribed to patients with Wolff-Parkinson-White syndrome due to shortening of the accessory pathway effective refractory period and the risk of life-threatening arrhythmias in the event of atrial fibrillation.

#Digoxin** is prescribed orally at a maintenance dose (Table 1) divided into 2 doses [56].

Table. Maintenance doses of digoxin** in children

3.3. Surgical (Interventional) Treatment

The safety and high efficacy of catheter ablation of arrhythmogenic zones (radiofrequency ablation, RFA) have made it the treatment of choice for most patients with SVT. The efficacy of RFA is assessed intraoperatively based on electrophysiological criteria, as well as in the early and late postoperative periods based on the disappearance of tachycardia and signs of ventricular pre-excitation according to ECG and Holter monitoring. In young children, the risk of complications is higher than in older age groups, and there are technical specifics to performing the procedures. Therefore, a "reasonable" conservatism is adhered to when determining indications for RFA in young children, which is also associated with a high probability of spontaneous resolution of SVT by 18 months of age. However, arrhythmia subsequently recurs in 30% of them, requiring monitoring and decision-making on further management. In children with a body weight <15 kg, preference is given to medical therapy, and RFA is performed for vital indications in the most specialized clinics. The efficacy of RFA in children ranges from 77% for atrial tachycardias to 97-100% for AV nodal reentrant tachycardia and Wolff-Parkinson-White syndrome. In some cases, to limit the lesion zone and reduce the risk of damage to the cardiac conduction system, the cryoablation technique for arrhythmogenic zones is used, which is based on the application of low temperatures [18, 57-65].

1.

1.1. Wolff-Parkinson-White syndrome with a history of sudden cardiac arrest at any age.

1.2. Wolff-Parkinson-White syndrome with a history of syncope and predictors of sudden cardiac arrest: multiple accessory pathways, antegrade effective refractory period of the accessory pathway ≤250 ms, or an RR interval ≤250 ms during a paroxysm of atrial fibrillation with AV conduction via the accessory pathway at any age.

1.3. Recurrent symptomatic atrial tachycardia in patients with congenital heart disease (no earlier than 3-6 months after cardiac surgery correction), when medical therapy is ineffective and/or associated with side effects at any age.

1.4. Incessant or recurrent SVT unresponsive to antiarrhythmic therapy, including drug combinations, or when antiarrhythmic drug administration is accompanied by side effects at any age.

1.5. Incessant or recurrent SVT in the presence of ventricular myocardial dysfunction in patients with a body weight ≥15 kg.

1.6. Incessant or recurrent SVT with hemodynamic instability (hypotension, syncope) in patients with a body weight ≥15 kg.

1.7. Recurrent SVT terminated using synchronized cardioversion (for patients with a body weight ≥15 kg).

1.8. Incessant or recurrent SVT upon the request of the patient and their parents (legal representatives) to discontinue long-term antiarrhythmic drug therapy (for patients with a body weight ≥15 kg).

2.

2.1. Wolff-Parkinson-White pattern in the presence of predictors of sudden cardiac arrest (multiple accessory pathways; antegrade effective refractory period of the accessory pathway ≤250 ms, or an RR interval ≤250 ms during an induced paroxysm of atrial fibrillation with AV conduction via the accessory pathway) in patients with a body weight ≥15 kg.

2.2. Myocardial dysfunction due to intraventricular dyssynchrony associated with the presence of an accessory pathway (for patients with a body weight ≥15 kg).

2.3. Wolff-Parkinson-White pattern in the presence of syncope and absence of predictors of sudden cardiac arrest in patients with a body weight ≥15 kg.

2.4. Wolff-Parkinson-White pattern in patients with a body weight ≥15 kg when pre-excitation is a contraindication to sports and associated with occupational restrictions.

2.5. Presence of isolated ectopic foci triggering atrial fibrillation paroxysms, located in the atria or at the ostium of one of the pulmonary veins.

(LoE 5, GoR C)

Comments: Despite the cautious attitude towards RFA in children with a body weight ≤15 kg, there is a category of young children with drug-refractory and life-threatening SVT for whom this treatment method is indicated. The RFA procedure in children with a body weight ≤15 kg is performed by specialists experienced in treating patients of this age group. It is safer to perform RFA in arrhythmology centers with cardiac surgery backup available to manage potential complications [59].

(LoE 4, GoR C)

Comments: The administration of low-dose #acetylsalicylic acid** (2-5 mg/kg per day) for 6-8 weeks after RFA is justified when the procedures were performed in the systemic ventricle/atrium, as well as in the presence of intracardiac shunts [66].

4. Medical Rehabilitation and Sanatorium-Resort Treatment

The need for rehabilitation in patients with SVT is determined by the presence and severity of the underlying cardiovascular disease and comorbid conditions. Accordingly, necessary medical rehabilitation services are provided to patients with cardiovascular diseases and other pathologies. In most cases, rehabilitation is not required for children with SVT; only certain restrictions on physical activity apply.

• Restriction of physical activity for 3 months is recommended for all patients who have undergone successful RFA for SVT. In the absence of complications, special rehabilitation measures are not required [9].

(GoR C, LoE 5)

Comments: In cases of any complications after RFA, including delayed ones, prompt hospitalization in a specialized cardiology/cardiac surgery inpatient facility is indicated to perform necessary diagnostic and therapeutic measures [18].

5. Prevention and Dispensary Observation

(GoR C, LoE 5)

Comments: In patients receiving long-term antiarrhythmic therapy (AAT), a 12-lead ECG is recorded at least once every 3 months. Echocardiography and Holter ECG monitoring are performed at least once every 6 months, and in infants, at least once every 2–3 months. The development of new, previously undocumented cardiac arrhythmias, QTc interval prolongation, or the appearance of intraventricular and atrioventricular blocks during antiarrhythmic drug (AAD) therapy serves as an indication for treatment adjustment. When #amiodarone** is prescribed for long-term use, blood tests for thyroid-stimulating hormone (TSH), free thyroxine ($fT_4$), and antithyroid peroxidase (anti-TPO) antibodies, along with a general clinical blood chemistry panel, should be performed at least once every 6 months.

In infants under one year of age, AAT is prescribed after SVT is documented and is usually continued for 4–6 months, after which, provided it is effective, it is discontinued followed by a follow-up evaluation. Beta-blockers, #propafenone**, and #sotalol** are discontinued gradually by reducing single doses over 3–7 days. Amiodarone is discontinued abruptly. If SVT recurs, AAT is resumed.

In cases of successful catheter ablation of arrhythmogenic zones and in the absence of procedure-related complications, patients without structural heart disease do not require long-term follow-up care. Following complicated catheter ablation of arrhythmogenic zones, patients with SVT require careful follow-up care by a pediatric cardiologist/cardiovascular surgeon, the frequency of which is determined by the nature of the complication.

If indications arise for high-tech diagnostic and treatment methods at any stage of follow-up care, patients with SVT are referred for a consultation with a pediatric cardiologist at a specialized arrhythmology center [9].

(GoR C, LoE 5)

Comments:

If there are complaints of palpitations not captured on the ECG, transesophageal electrophysiological study (TEEPS) is performed. If there is no evidence of arrhythmia, the patient is discharged from follow-up registry.

Following catheter ablation of atrial tachycardia, evaluations (12-lead ECG, echocardiography, Holter monitoring) are performed at 3, 6, and 12 months. If there is no evidence of arrhythmia recurrence, the patient is discharged from follow-up registry. The presence of SVT in a patient without inflammatory heart disease is not a contraindication to vaccination.

6. Organization of Medical Care

Indications for emergency hospitalization in a medical organization:

1. Clinically significant SVT paroxysm with unresponsiveness to emergency care at the prehospital stage.

2. Newly diagnosed SVT in a previously unexamined child.

3. Adverse and arrhythmogenic effects of AADs.

Indications for scheduled hospitalization in a medical organization:

1. Provision of specialized cardiological care requiring continuous medical observation and therapeutic procedures.

2. Provision of high-tech medical care.

3. Inability to perform diagnostic and therapeutic procedures in an out-patient setting.

4. Geographical remoteness of the patient from the hospital (taking into account the potential risk of disease progression).

5. Failure of outpatient treatment in patients with SVT.

Scheduled hospitalization is carried out if the patient has the results of diagnostic tests that can be performed in an outpatient setting (according to the list of mandatory examinations for patients referred for scheduled hospitalization), and if the required diagnostic methods can be performed in the medical and preventive institution. The maximum waiting time is determined by the waiting list for scheduled hospitalization.

Indications for discharging a patient from a medical organization:

1. Upon patient recovery.

2. Upon sustained improvement, when the patient's health status allows them to continue treatment on an outpatient basis under the supervision of a general practitioner without detriment to their health.

3. In the absence of indications for further inpatient treatment.

4. When the patient needs to be transferred to another medical institution.

5. At the request of the patient or their legal representative.

6. In cases where the patient violates prescriptions or internal regulations of the medical and preventive institution, provided this does not threaten the patient's life or the health of others.

7. Additional Information

SVT in most cases is not classified as a life-threatening arrhythmia. High-risk conditions include: SVT with hemodynamic instability, SVT complicated by tachycardia-induced cardiomyopathy, atrial fibrillation and atrial flutter in children with Wolff-Parkinson-White syndrome and high ventricular response rates, and SVT in children with underlying heart disease. Hemodynamic instability, up to and including cardiogenic shock, is typical for newborns and infants with prolonged episodes of tachycardia leading to reduced myocardial contractility. Tachycardia-induced cardiomyopathy is also characteristic of chronic SVT. When paroxysmal SVT occurs in infants during the first months of life, the prognosis is favorable with medical control—in most cases, spontaneous resolution of the disease occurs by the first year of life, allowing discontinuation of AAT. If SVT episodes appear in school-age children, they will in most cases not resolve spontaneously, but this age group has fewer restrictions for radical treatment—catheter ablation—which also indicates a favorable disease outcome [18].

Criteria for Evaluating the Quality of Medical Care

References

Appendix A1. Working Group Composition

1. Kruchina T.K., MD, Member of the Association of Pediatric Cardiologists of Russia (Working Group Leader)

2. Kolbasova E.V., PhD, Member of the Association of Pediatric Cardiologists of Russia (Working Group Executive Secretary)

3. Bereznitskaya V.V., PhD, Member of the Association of Pediatric Cardiologists of Russia

4. Ivanitsky E.A., MD, Member of the "All-Russian Scientific Society of Clinical Electrophysiologists, Arrhythmologists and Pacing Specialists"

5. Kandinsky M.L., PhD, Member of the "All-Russian Scientific Society of Clinical Electrophysiologists, Arrhythmologists and Pacing Specialists"

6. Kovalev I.A., MD, Professor, President of the Association of Pediatric Cardiologists of Russia

7. Kravtsova L.A., PhD, Member of the Association of Pediatric Cardiologists of Russia

8. Svintsova L.I., MD, Member of the Association of Pediatric Cardiologists of Russia

9. Tatarsky B.A., MD, Member of the "All-Russian Scientific Society of Clinical Electrophysiologists, Arrhythmologists and Pacing Specialists"

10. Termosesov S.A., Member of the Association of Cardiovascular Surgeons of Russia, Member of the "All-Russian Scientific Society of Clinical Electrophysiologists, Arrhythmologists and Pacing Specialists"

11. Khamnagadaev I.A., PhD, Member of the Association of Cardiovascular Surgeons of Russia, Member of the "All-Russian Scientific Society of Clinical Electrophysiologists, Arrhythmologists and Pacing Specialists"

12. Shkolnikova M.A., MD, Professor, Honorary President of the Association of Pediatric Cardiologists of Russia

The authors declare no financial support or conflicts of interest that need to be disclosed.

Appendix A2. Methodology for Developing Clinical Guidelines

Target audience for these clinical guidelines:

1. Pediatricians

2. Pediatric cardiologists

3. Cardiovascular surgeons

4. General practitioners (family physicians)

Table 1. Levels of Evidence (LoE) grading scale for diagnostic methods (diagnostic interventions)

Table 2. Scale for grading levels of evidence certainty (LEC) for prevention, treatment, and rehabilitation methods (preventive, therapeutic, and rehabilitative interventions)

Table 3. Scale for grading grades of recommendation (GR) for prevention, diagnostic, treatment, and rehabilitation methods (preventive, diagnostic, therapeutic, and rehabilitative interventions)

Procedure for updating clinical guidelines.

The mechanism for updating clinical guidelines provides for their systematic revision at least once every three years, as well as upon the emergence of new evidence-based medicine data on the diagnosis, treatment, prevention, and rehabilitation of specific diseases, or in the presence of justified additions/comments to previously approved clinical guidelines, but no more frequently than once every 6 months.

Appendix A3. Reference Materials

1. Order of the Ministry of Health of the Russian Federation No. 103n dated February 28, 2019 "On approval of the procedure and timeframe for the development of clinical guidelines, their revision, the standard template for clinical guidelines, and requirements for their structure, composition, and scientific validity of the information included in clinical guidelines."

2. Order of the Ministry of Health of the Russian Federation No. 440n dated October 25, 2012 "On approval of the Procedure for the provision of medical care in the field of 'pediatric cardiology'."

3. Order of the Ministry of Health of the Russian Federation No. 203n dated May 10, 2017 "On approval of criteria for assessing the quality of medical care."

4. Methodological guidelines for assessing the reliability of evidence and the certainty of recommendations. FSBI CECKMP of the Russian Ministry of Health, 2018.

5. Decree of the Government of the Russian Federation No. 3053-r dated December 31, 2018 "On approval of the list of medical devices implanted in the human body when providing medical care under the state guarantee program of free medical care for citizens, as well as the list of medical devices dispensed upon prescriptions for medical devices when providing a set of social services."

6. Decree of the Government of the Russian Federation No. 2406-r dated October 12, 2019 "On approval of the list of vital and essential drugs, as well as lists of drugs for medical use and the minimum assortment of drugs required for the provision of medical care."

Appendix A3.3. Antiarrhythmic drugs registered in the Russian Federation.

Appendix A3.2. Recommendations for sports participation for athletes with cardiac arrhythmias and arrhythmogenic diseases [67-69]

Note. * – sports with a high risk of syncope (auto racing, diving, equestrianism, motorsports, bobsleigh, luge, mountaineering, water skiing, windsurfing, alpine skiing, snowboarding, cycling, triathlon)

Appendix B. Physician Action Algorithms

Appendix B1.

Appendix B2. Differential ECG Diagnosis of SVT Variants

Appendix C. Patient Information

Supraventricular tachycardia (SVT) is a form of arrhythmia caused by congenital or acquired factors, characterized by a rapid heart rate originating outside the sinus node, which is the normal pacemaker. During an SVT episode, which can last several hours, the heart beats rapidly, and the pulse is often "too fast to count." The heart rate reaches 180–250 beats per minute, and sometimes even higher. In a healthy heart, every contraction is initiated by an electrical impulse from the sinus node (the cardiac pacemaker) located in the right atrium. The impulse then travels to the second node (the atrioventricular node), which conducts it to the ventricles. In SVT, the sinus node does not control the heart contractions: due to the presence of abnormal conduction pathways through which an electrical impulse constantly circulates, or due to the formation of an ectopic focus of electrical activity that "overrides" the normal pacemaker, preventing it from setting the normal rhythm.

SVT most often first appears in infants under one year of age or in adolescents, although this condition can occur at any age. In some cases, the cause of SVT is a congenital disorder of the cardiac conduction system. There are two main forms of SVT: paroxysmal and non-paroxysmal. In the paroxysmal form, the tachycardia attack begins and ends abruptly. Attacks usually start for no apparent reason, but they can be triggered by physical exertion, agitation, fever, caffeine, and alcohol. The child perceives the attack as a sudden onset of severe palpitations and a "fluttering" sensation in the chest; after some time, if the heart rate is high (180 bpm and above), weakness, dizziness, and "cold sweat" occur. However, with a lower heart rate (140-150 bpm), the child may tolerate the attack well, experiencing only a rapid heartbeat.

A complication of SVT is heart failure (fatigue, shortness of breath, decreased appetite leading to food refusal (in infants under one year of age)). In some cases, a prolonged SVT episode can drop blood pressure to dangerous levels.

If a physician suspects SVT, the patient is referred for ECG examinations (standard ECG and Holter ECG monitoring). Additional tests may be performed to detect tachycardia, such as transesophageal electrophysiological study of the heart. It is necessary to document an episode of tachycardia, as only then can the physician develop a treatment plan. Therefore, when an episode occurs, medical assistance should be sought immediately to obtain an ECG (school medical office, any nearby medical facility, or emergency medical services). A patient with suspected SVT also undergoes echocardiography to assess cardiac structure, function, dimensions, presence or absence of congenital heart defects, signs of heart disease, and the impact of the arrhythmia on cardiac function.

Prolonged and severe SVT episodes require urgent inpatient treatment. In the hospital, the episode is terminated and normal rhythm is restored using medications or other methods. To terminate an episode, children typically require admission to a pediatric intensive care unit for continuous clinical observation, ECG monitoring, blood pressure and blood oxygen saturation tracking, and targeted medication administration. In some cases, synchronized cardioversion is performed to restore normal heart rhythm.

Patients with short and infrequent SVT episodes can terminate the attack and restore normal rhythm on their own, without medication. This is called vagal nerve stimulation. Older children can be instructed to take a deep breath and strain, thereby increasing intrathoracic pressure and slowing down the heart rate. However, only a physician, taking into account the child's age and condition, can provide professional guidance on these stimulation methods. Severe SVT attacks can be treated with a prolonged course of antiarrhythmic drugs. Radiofrequency ablation, performed during electrophysiological studies, is also used to treat SVT. This procedure destroys pathological conduction pathways and foci of abnormal electrical activity. In most cases, SVT does not affect life expectancy.

Appendix G. Assessment Scales, Questionnaires, and Other Evaluation Tools

Not applicable within the scope of these clinical guidelines.