ECG criteria
- Type 1 (diagnostic): J-point elevation ≥2 mm with a coved ST elevation gradually transitioning into a negative T wave in one or more of leads V1–V2 in standard or high intercostal spaces
- Type 2 (suspicious, but not diagnostic on its own): J-point elevation (high ST takeoff) ≥2 mm, followed by a saddleback ST elevation ≥1 mm and a positive or biphasic T wave
- In cases of clinical suspicion in selected patients at an experienced center, a provocative test with a sodium channel blocker (ajmaline, flecainide, procainamide) can be performed; the appearance of the type 1 pattern, rather than the fact of provocation itself, has diagnostic value
- The pattern is transient — it may appear and disappear spontaneously or upon provocation
- Before the test and before interpreting a questionable pattern, fever and electrolyte disturbances are corrected, and contraindications to the test are taken into account
- Brugada syndrome is diagnosed in the presence of a type 1 pattern in ≥1 right precordial lead V1 or V2, including recording in the 2nd–4th intercostal spaces, spontaneous or induced by a sodium channel blocker, after exclusion of phenocopies; clinical events (syncope, documented VT/VF, family history of sudden death under 45 years) are not mandatory for the diagnosis, but clarify the risk and management strategy
- QRS may be normal or widened; incomplete RBBB-like morphology and intraventricular conduction disturbances occur, but are not mandatory for diagnosis; QTc usually has no specific changes and is evaluated separately
- The electrical axis of the heart (EAX) is generally without specific changes
What it looks like on ECG
Key changes are localized in the right precordial leads V1–V2, sometimes V3. In type 1, the J point is elevated ≥2 mm, the ST segment has a convex coved shape and descends smoothly into a negative T wave. In type 2, after a J-point elevation (high ST takeoff) ≥2 mm, there is a slight dip, and then the terminal part of the ST segment remains elevated in a saddleback manner ≥1 mm transitioning into a positive or biphasic T wave.
| Parameter | Type 1 | Type 2 |
|---|---|---|
| ST shape | Coved | Saddleback |
| J-point elevation | ≥2 mm | ≥2 mm |
| ST elevation | Coved, merges with T | Saddleback, ≥1 mm |
| T wave | Negative | Positive/biphasic |
| Diagnostic significance | Yes, spontaneously | No, suspicious pattern |
When clinically suspected, V1–V2 are recorded sequentially not only in the standard 4th, but also in the high 2nd–3rd intercostal spaces — the type 1 pattern may be detected only in one of these positions. The other leads are usually unchanged, EAX is normal, although some patients exhibit PQ interval prolongation as a reflection of concomitant conduction disturbance. QRS is most often of normal width, but intraventricular conduction slowing and RBBB-like morphology with widening of the complex are possible; this does not exclude the syndrome.
Mechanism
The underlying mechanism is dysfunction of cardiomyocyte sodium channels (most commonly SCN5A gene mutations), leading to a reduction in the inward sodium current in the epicardium of the right ventricle against the background of a pronounced transient outward potassium current ($I_{to}$). This creates an electrophysiological substrate in the region of the right ventricular outflow tract, manifesting as ST elevation in V1–V2. Two complementary models are debated: the repolarization model, in which dispersion of refractoriness creates conditions for phase 2 re-entry and triggers polymorphic VT/VF, and the depolarization model, associated with conduction slowing and a structural-functional substrate in the right ventricular outflow tract. Neither model is considered exclusive. Manifestations are enhanced by vagotonia, fever, or sodium channel-blocking drugs.
Causes
- Inheritance is usually autosomal dominant with incomplete penetrance. A pathogenic SCN5A variant is identified in approximately 20–30% of patients; for most other proposed genes related to sodium and calcium channels, the causative role remains uncertain. A negative genetic test does not exclude the syndrome
- Subtle structural-electrophysiological changes of the right ventricular outflow tract in some patients; significant structural pathology is atypical and requires the exclusion of other diagnoses (e.g., arrhythmogenic cardiomyopathy)
Triggering factors (unmask or enhance the pattern, without being the cause of the disease itself): fever, vagotonia and sleep (most VF episodes occur at night), alcohol and cocaine abuse, sodium channel-blocking drugs.
Differential diagnosis
- Early repolarization syndrome — ST elevation without a coved shape, usually in lateral and inferior leads, T wave is positive
- Acute anterior/septal myocardial infarction and its phenocopies — ischemia can mimic or unmask the Brugada pattern; reciprocal changes and typical troponin dynamics are not always present, therefore, in the presence of appropriate clinical symptoms, ischemia is ruled out by serial ECGs, high-sensitivity troponin, and imaging, rather than by the formal absence of reciprocity
- Right bundle branch block — complete RBBB: QRS ≥120 ms, rsR′/rSR′ in V1–V2 and wide terminal S in I, aVL, V5–V6; incomplete RBBB: similar morphology with QRS 110–119 ms in adults, with corresponding terminal S. Neither of these signs alone excludes the Brugada pattern, as an RBBB-like shape can also occur with it — the shape and dynamics of ST-T in the right leads are evaluated precisely, rather than just the QRS width
- Right ventricular overload/hypertrophy — ST elevation combined with signs of hypertrophy and right axis deviation
- Myocarditis/pericarditis — diffuse ST changes, clinical picture of inflammation
- Brugada syndrome phenocopies — these are considered if a coved or saddleback pattern is explained by a reversible condition (hyperkalemia, hypocalcemia, other electrolyte disturbances, ischemia, drug toxicity) and disappears after its correction without other evidence of the syndrome. Fever occupies a special place: it more often unmasks a true Brugada pattern than creates a phenocopy, so fever is treated and a follow-up ECG is performed after temperature normalization, without rushing to conclude it is a phenocopy. Hyperkalemia is additionally accompanied by a tall T wave and QRS widening
Clinical significance and management
Brugada syndrome is an important cause of sudden cardiac death in some young people without significant structural heart disease, most often during sleep; its contribution is especially significant in certain regions of Southeast Asia. When a type 1 pattern is detected, it is important for the physician to exclude phenocopies (electrolyte disturbances, ischemia, fever, drugs) and evaluate the clinical context: syncopal episodes, family history of sudden death under 45 years, documented ventricular arrhythmias. In type 2, clinical suspicion in selected patients may require a provocative test with a sodium channel blocker in an experienced center, under ECG monitoring and with readiness for defibrillation, after correction of fever and electrolyte disturbances and taking contraindications into account. An ICD is recommended after survived cardiac arrest due to VF/polymorphic VT or documented spontaneous sustained life-threatening ventricular tachyarrhythmia, after exclusion of a reversible cause; in spontaneous type 1 and unexplained syncope, likely arrhythmic, implantation should be considered. In vasovagal or otherwise explained syncope, an ICD is not indicated. For asymptomatic carriers of the pattern — dynamic monitoring, treatment of fever with antipyretics, and avoidance of drugs hazardous in this syndrome: ajmaline, flecainide, propafenone, procainamide, pilsicainide, and other agents with pronounced sodium channel blockade; quinidine, conversely, can be used as therapy in individual patients under specialist supervision. First-degree relatives are recommended genetic counseling and clinical evaluation with ECG recording (including in high leads); genetic testing is most informative when a pathogenic variant is known in the proband, and the provocative test is performed according to indications in an experienced center, especially cautiously in children.
Common interpretation errors
- Mistaking the saddleback type 2 for a diagnostic sign on its own
- Confusing the Brugada pattern with incomplete right bundle branch block due to similar morphology in V1
- Failing to account for the transient nature of the pattern — a single normal ECG does not exclude the syndrome
- Recording precordial leads only in the standard position, missing a pattern visible only in high intercostal spaces
- Failing to exclude phenocopies and not correcting fever/electrolyte disturbances before interpreting the pattern
Coved ST with inverted T — type 1, diagnostic; "saddleback" — type 2, suspicious
1. Which ECG sign is diagnostic for Brugada syndrome without additional provocation?
Type 1 pattern (coved ST ≥2 mm with an inverted T wave in V1–V2) is diagnostic on its own, unlike the saddleback type 2.
2. Which class of medications is used for provocation testing when Brugada syndrome is suspected?
Sodium channel blockers exacerbate the ionic current imbalance in the right ventricular epicardium and unmask a concealed type 1 pattern.
3. What is the strongest indication for implantable cardioverter-defibrillator (ICD) placement in Brugada syndrome?
ICDs are recommended primarily after cardiac arrest due to VF/polymorphic VT or documented spontaneous sustained ventricular tachyarrhythmia, after excluding a reversible cause; unexplained, likely arrhythmic syncope with spontaneous type 1 is an indication for consideration, not a blanket rule for any syncope.
Frequently asked questions
How to distinguish Brugada type 1 pattern from type 2?
Type 1 is a coved ST elevation transitioning smoothly into an inverted T wave, diagnostic in its own right. Type 2 is a J-point elevation ≥2 mm with a saddleback ST elevation ≥1 mm and a positive or biphasic T wave — a suspicious, but not diagnostic pattern.
Is an asymptomatic Brugada pattern dangerous?
Asymptomatic carriers of the type 1 pattern have a lower, but non-zero risk of arrhythmic events compared to symptomatic patients. They are advised to undergo observation, avoid triggering medications, and manage fever; the decision for defibrillator implantation is made on an individual basis.
Why can the Brugada pattern disappear on a standard ECG?
The prominence of ECG changes depends on the tone of the autonomic nervous system, body temperature, and the intake of certain drugs, which is why the pattern can appear and disappear. To unmask it in selected patients at an experienced center, a provocation test with a sodium channel blocker is used.
Which medications are dangerous in Brugada syndrome?
Drugs with pronounced sodium channel-blocking activity are dangerous: ajmaline, flecainide, propafenone, procainamide, pilsicainide, certain tricyclic antidepressants, and cocaine — they can unmask or worsen the pattern and trigger arrhythmia. Quinidine, conversely, can be used to treat individual patients under specialist supervision.
Do relatives of a patient with Brugada syndrome need to be screened?
Yes, first-degree relatives are recommended to undergo genetic counseling and clinical evaluation with an ECG, as the syndrome is inherited in an autosomal dominant manner with incomplete penetrance. Genetic testing is most informative when a pathogenic variant is known in the proband, and provocation testing is performed by indication at an experienced center.
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Related terms
More in the «Channelopathies and Cardiomyopathies» section
Sources
- Surawicz B., Knilans T. Chou's Electrocardiography in Clinical Practice
- Hampton J. The ECG in Practice
- AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram, 2009
- Clinical Guidelines of the Russian Ministry of Health on Ventricular Arrhythmias
Educational material for medical students and physicians. Does not replace clinical guidelines and physical examination; the ECG must always be interpreted in conjunction with the clinical picture.