Intraatrial conduction disturbance

Position in the classification of rhythm and conduction disorders

Cardiac functional disorders are divided into three major categories based on their mechanism of development. Intraatrial conduction disturbance belongs to the group of blocks.

1. Automatism disorders:
2. Nomotopic (impulse originates in the sinus node): sinus tachycardia, bradycardia, arrhythmia.
3. Heterotopic (ectopic sources): extrasystole, paroxysmal and non-paroxysmal tachycardias, atrial and ventricular flutter and fibrillation.
4. Conduction disorders (blocks):

Depend on the level of the lesion. These include sinoatrial, intraatrial, atrioventricular (AV block), and intraventricular blocks.

1. Combined arrhythmias:

Associated forms, such as sick sinus syndrome (SSS), atrioventricular dissociation, and ventricular pre-excitation syndromes.

Pathogenesis and premorbid background

The fundamental cause of rhythm and conduction disorders is instability of the myocardium and conduction system. This condition is accompanied by the depletion of cardiac functional reserves and dysregulation of the sympathoadrenal system.

In pediatric patients, history taking often reveals a characteristic background:

• Family history burdened with cardiovascular diseases.
• Perinatal complications.
• Presence of chronic infection foci and frequent acute respiratory viral infections (ARVI).

Physical examination may reveal concomitant syndromes: connective tissue dysplasia (CTD), psychovegetative dysfunctions, residual neurological symptoms, hypertensive-hydrocephalic syndrome, and sometimes delayed motor or pubertal development.

Clinical presentation and age-related features

Clinical manifestations of arrhythmias and blocks (including intraatrial ones) in children differ radically from adult patients:

• Asymptomatic course: About 40% of cases are completely asymptomatic and discovered as an incidental finding on an ECG or following an ARVI.
• Scarcity of complaints: Children rarely complain of palpitations or heart "skipped beats," even during severe disorders.
• Pubertal features: In prepubertal and pubertal children, psychovegetative disorders lead to cardialgia (chest pain), insomnia, weather sensitivity, and increased excitability.
• Hemodynamic disorders: If a block or arrhythmia leads to reduced cerebral blood flow, weakness, dizziness, and fainting (syncope) occur. This is most typical for AV blocks, SSS, and sinus bradycardia.

Differential diagnosis

The presence of intraatrial and intraventricular blocks, as well as other rhythm disorders on an ECG, is a key criterion for distinguishing isolated myocarditis from pericarditis (both dry and exudative).

In rheumatic processes, the heart membranes are affected together (myopericarditis develops), but in isolated myocarditis, conduction disorders come to the fore. In chronic exudative pericarditis, despite cardiomegaly and low voltage on an ECG, signs of chamber overload, arrhythmias, and blocks are generally absent.

Instrumental diagnostics of the structural background

Conduction and rhythm disorders often require a comprehensive assessment of target organs. Using a patient with atrial fibrillation (heterotopic disorder) as an example, the following parameters are evaluated:

• ECG: Allows recording the rhythm disorder itself (e.g., tachy-systolic variant with a heart rate of 100–142 bpm) and concomitant blocks (e.g., incomplete left bundle branch block).
• Echocardiography: Reveals the structural substrate. Left atrial dilation (indexed volume >40 mL/m²) maintains arrhythmia persistence. Left ventricular hypertrophy (LVH), diastolic dysfunction, and pulmonary artery pressure are also evaluated. Thrombi in the left atrial appendage must be ruled out.
• Chest X-ray: Confirms cardiomegaly (cardiothoracic ratio >0.5) and the absence of pulmonary venous congestion.
• Tolerance tests: The 6-minute walk test determines the functional class of heart failure.
• Additional studies: Ultrasound of brachiocephalic and renal arteries, renal and thyroid ultrasound (to rule out thyroid-origin genesis), and fundus examination (to rule out hypertensive retinopathy) help exclude symptomatic causes of the pathology.

Class and exam questions

What else to study on this topic

• Clinical presentation and ECG criteria for constrictive pericarditis
• Differential diagnosis of chronic exudative pericarditis and cardiomyopathies
• Psychovegetative disorders as a background for arrhythmias during puberty
• Echocardiographic criteria for left ventricular diastolic dysfunction
• Interpretation of the 6-minute walk test in heart failure

Other topics in the "Additional Topics" section

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