‍Introduction

• A right bundle branch block (RBBB) may be incomplete or complete

• Incomplete RBBB - delayed conduction through the right bundle branch. The QRS complex is only slightly prolonged between 100 to 120ms

• Complete RBBB - is the result of a total block of impulse conduction along the right bundle branch. There is a delayed and abnormal activation of the right ventricular myocardium occurring through the septum from the left-sided Purkinje system

• The left ventricle depolarizes first in a normal way and then this wave of depolarization spreads slowly across to the right ventricle, myocyte to myocyte. This delay in right ventricular activation causes interventricular dyssynchrony

ECG findings

• QRS duration > 120ms 
• RsR’ pattern in leads V1 to V2 – M shaped, “rabbit-ear” pattern
• Deep, broad S wave in leads I, aVL and V5 to V6.
• ST segment depression and/or T wave inversion in leads V1 – V3 - altered sequence of repolarization
• RBBB does not lead to axis deviation

Figure 1 QRS complex morphology in lead V1

• QRS duration 130ms
• typical rSR’ morphology of the QRS complex
• inverted T wave – opposite to the slurred R’ wave
• the delay in right ventricular activation causes it to occur after left ventricular activation > altering the terminal portion of the QRS creating a late prominent R wave in V1 (R’)

Figure 2 QRS complex morphology in lead I

• wide slurred S waves in leads I, aVL and V5 to V6

The initial part of the QRS complex is normal – activation of the septum and left ventricle is unaffected. Because of this, abnormalities of the left ventricle can still be recognized (acute and chronic myocardial ischemia/infarction, LV hypertrophy, pericarditis).

Causes

The right bundle branch is vulnerable to stretch and trauma for two-thirds of its course when it is near the subendocardial surface. 

• Structural heart disease – right ventricular hypertrophy, cor pulmonale, myocardial ischemia/infarction, myocarditis, cardiomyopathy
• Iatrogenic RBBB – caused by procedures and interventions (catheter trauma, septal ethanol ablation in hypertrophic cardiomyopathy,..)
• Rate-related RBBB – Ashman’s phenomenon – functional RBBB as a result of a long preceding R-R interval following by a short cycle

ECG 1  Isolated RBBB

• sinus rhythm with RBBB, rate 75 bpm
• QRS duration 130 ms
• rSR’ pattern in lead V1
• ST depression and inverted T wave in leads V1, V2 – altered repolarization
• slurred S waves in leads V5, V6 and I, aVL
• normal heart axis

ECG 2  Isolated RBBB

• sinus rhythm with RBBB pattern, rate 75 bpm
• QRS duration 120 ms
• rsR’ pattern in V1
• M shaped QRS in lead V3
• ST depression and inverted T wave in leads V1, V2, V3 – altered repolarization
• slurred S waves in I and aVL, S waves preset in leads V5, V6

Management

• In a patient with a new RBBB, a careful history should be taken focused on potential causes of RV stretch/strain (pulmonary hypertension, obstructive sleep apnea, pulmonary embolism)
• Patients with isolated chronic RBBB (complete or incomplete) are generally asymptomatic and do not require further diagnostic evaluation for RBBB or placement of a pacemaker or any other specific therapy. 

References

1. CAMM, A. J., LÜSCHER, T. F., & SERRUYS, P. W. (2009). The ESC textbook of cardiovascular medicine. Oxford, Oxford University Press.
2. Houghton, A. (2019). Making Sense of the ECG: A Hands-On Guide (5th ed.). CRC Press.
3. William H Sauer, MD (2020). Right bundle branch block In I. Susan B Yeon, MD, JD, FACC (Ed.), UpToDate. Retrieved February 5, 2021 from: https://www-uptodate-com.ezproxy.is.cuni.cz/contents/right-bundle-branch-block?search=right%20bundle%20branch%20block&source=search_result&selectedTitle=1~146&usage_type=default&display_rank=1
4. https://litfl.com/right-bundle-branch-block-rbbb-ecg-library/