Right Bundle Branch Block

Right bundle branch block (RBBB) occurs when the right bundle no longer conducts, and the signal must pass to the right ventricle via myocyte-to-myocyte conduction. This pattern of conduction is slower than via the specialized conduction system, and results in a wide QRS complex (>120 ms). The criteria are:

QRS > 120 ms
rSR’ pattern in V1-3 (‘M-shaped’)
Wide/slurred S wave in the lateral leads (I, aVL, V5-6)

Note that there is no right axis deviation associated with RBBB as there is a left axis deviation associated with left bundle branch block.

RBBB is common and generally not a powerful indicator of disease by itself. This is because the right bundle often has a singular blood supply as opposed to the left bundle which has a more diverse blood supply and therefore is more consistent with significant disease. However, a new RBBB in a patient with unexplained respiratory symptoms should be viewed as right ventricular outflow obstruction until proven otherwise. RBBB can be caused by right ventricular hypertrophy/cor pulmonale, pulmonary embolism, ischemic heart disease, rheumatic heart disease, myocarditis or cardiomyopathy, degenerative disease of the conduction system, or congenital heart disease (e.g., atrial septal defect).

Expected repolarization abnormalities in the setting of RBBB include T wave inversions in V1-3 and slight discordant ST depressions. ST elevation in these leads is never normal; even slight ST elevations in V1-3 may represent STEMI.

Direction of depolarization in right bundle branch block. The septum first depolarizes from left to right (blue arrow), followed by left ventricular depolarization (pink arrow), and, finally, right ventricular depolarization (green arrow). The result is an rSR’ pattern in V1, and a wide S wave in the lateral leads (I, aVL, V5, V6). SA, sinoatrial node; AV, atrioventricular node; RB, right bundle; LB, left bundle; CB, common bundle; RV, right ventricle; LV, left ventricle; red dash represents a block of the right bundle.

Examples

Right Bundle Branch Block

This right bundle branch block pattern has a bit of an atypical appearance. The rsR' in V1 can have a qR appearance in some right bundle branch blocks. The expected wide S is present in the lateral leads (I, V5, V6).

Incomplete Right Bundle Branch Block

This is an example of an incomplete right bundle branch block. There is a morphology similar to a complete right bundle branch block including an rSR' in V1, but the width of the QRS is less than 120ms; therefore, it is considered incomplete.

Right Bundle Branch Block

The rhythm is atrial fibrillation and there is an associated rate-dependent right bundle branch block. At higher rates, diseased fascicles can fail.

Right Bundle Branch Block

Classic right bundle branch block pattern with rsR' in V1 and a wide S wave in the lateral leads (I, aVL, V5, V6).

Right Bundle Branch Block

In addition to the right bundle branch block, the left anterior fascicular block, and atrial fibrillation, the patient was also hyperkalemic.

Right Bundle Branch Block

Classic RBBB pattern with first degree atrioventricular block in a patient with right heart failure from obesity hypoventilation syndrome.

Bifascicular Block

There is a right bundle branch block and a left anterior fascicular block.

Trifascicular Block

Right bundle branch block and left anterior fascicular block with a prolonged PR interval. This represents disease of all three fascicles, so called "trifascicular block."

ST-elevation Myocardial Infarction

Anterior STEMI in the setting of a right bundle branch block. Typically, with a right bundle branch block, the ST-segments are slightly depressed in leads V1-3; therefore, any degree of ST-segment elevation in these leads is concerning for anterior STEMI.

Trifascicular Block

Right bundle branch block, left anterior fascicular block, and PR prolongation representing trifascicular disease.

Trifascicular Block

This patient had known trifascicular disease with a right bundle branch block, left anterior fascicular block, and PR prolongation. During tachycardia, even when sinus, trifascicular disease can mimic ventricular tachycardia. At a slower rate, sinus conduction was confirmed.

Bifascicular Block

Right bundle branch block and left anterior fascicular block.

Second Degree Atrioventricular Block 2:1

Right bundle branch block, left anterior fascicular block, and 2:1 atrioventricular block. This representing Mobitz II conduction given the extent of infranodal disease. This patient was admitted for a permanent pacemaker.

Bifascicular Block

Right bundle branch block and left anterior fascicular block with atrial fibrillation. This patient ultimately progressed to complete heart block.

ST-elevation Myocardial Infarction With Right Bundle Branch Block

Typically, a right bundle branch block has either isoelectric or slight ST-segment depressions in the anterior precordial leads (V1 through V3). Any degree of ST-segment elevation in V1 through V3 in the setting of a right bundle branch block is worrisome for acute occlusion. This patient had a left anterior descending artery occlusion.

References

Kusumoto FM, Schoenfeld MH, Barrett C, et al. 2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhyth. Circulation. 2019;140(8):e382-e482.
Costa D Da, Brady WJ, Edhouse J. Bradycardias and Atrioventricular conduction block. British Medical Journal. 2002;324(March):535-538.
Ibanez B, James S, Agewall S, et al. 2017 ESC Guidelines for the management of acute myocardial infarction in patients presenting with ST-segment elevation. European Heart Journal. 2018;39(2):119-177.