ECG signs of right bundle branch block

Formation of the right bundle branch block pattern in extrasystole

The classic picture resembling complete right bundle branch block is clearly manifested in left ventricular extrasystoles. This is due to a specific mechanism of electrical signal propagation in the myocardium.

When an ectopic focus generates an impulse directly in the left ventricular tissue, this part of the heart depolarizes first and very rapidly. However, the excitation wave reaches the right ventricle with a significant delay, propagating through the working myocardium rather than the specialized conduction system. It is this physiological delay that forms the characteristic right bundle branch block pattern on the ECG.

Key ECG criteria for left ventricular extrasystole (right bundle branch block pattern):

• The maximum changes are localized in the right precordial leads (leads V1 and V2).
• The ventricular complex is significantly deformed, widened, and characterized by high amplitude.
• In lead V1, the main wave is directed upward (a tall, deformed R wave is recorded).
• There is a discordant (oppositely directed relative to the main wave) shift of the ST segment and T wave in the right precordial leads.

Brugada syndrome: a deadly mimic

The right bundle branch block pattern can be part of a formidable hereditary disease—Brugada syndrome. Its pathogenesis is based on a genetic mutation affecting cardiomyocyte sodium channels (specifically, a defect in the SCN5A gene). The disease has a pronounced familial inheritance pattern.

The uniqueness of the syndrome lies in the fact that patients completely lack any organic lesions of heart structures, yet they are at the highest risk of sudden cardiac death. Most often, the tragedy occurs at night, and young men are at the maximum risk group.

Diagnosis and management:

• The ECG shows ST-segment elevation in leads V1–V3.
• These changes are often accompanied by a picture of right bundle branch block (complete or incomplete).
• Medical therapy does not yield reliable results. The only proven method for preventing sudden death in a patient is the surgical implantation of an implantable cardioverter-defibrillator (ICD).

Comparison with right ventricular extrasystole

For accurate ECG interpretation, it is necessary to clearly distinguish the right bundle branch block pattern from the picture resembling complete left bundle branch block. The latter is characteristic of right ventricular extrasystoles.

When an impulse originates in the right ventricle, the picture changes in mirror image:

1. Deformation, significant widening of the complex, and its high amplitude are recorded in the left precordial leads (V5 and V6).
2. In lead V1, the main vector is directed downward (a deep S wave is formed).
3. Discordant displacement of the ST segment and T wave is observed precisely in the left precordial leads, which is directly opposite to the changes in left ventricular extrasystole.

Additional signs involving the right ventricle

When analyzing changes associated with the right chambers of the heart, it is important to consider signs of right ventricular hypertrophy (RVH), which are also reflected in the left leads and affect repolarization processes.

Changes in the left precordial leads (V5-V6): A fundamental sign of right heart hypertrophy is the dominance of the S wave over the R wave. Mathematically, this criterion is expressed as the amplitude ratio $R/S < 1.0$. Crucial condition: this criterion is considered reliable exclusively in the absence of scar changes (prior myocardial infarction) of the anterior wall and the absence of left anterior fascicular block.

Secondary repolarization abnormalities: They are localized in the right precordial (V1-V2) and inferior leads (III, aVF). They are typically characterized by arc-like ST-segment depression and the appearance of a negative, asymmetric T wave.

What else to study on this topic

• Mechanisms of onset and termination of paroxysmal arrhythmias in pre-excitation syndromes
• The danger of atrial fibrillation in the presence of accessory pathways
• Differential diagnosis of arcuate ST depression in various pathologies
• Genetic testing for SCN5A mutations in cardiology

Other topics in the "Cardiovascular system" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.