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
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).
The right bundle branch is vulnerable to stretch and trauma for two-thirds of its course when it is near the subendocardial surface.
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
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.
CAMM, A. J., LÜSCHER, T. F., & SERRUYS, P. W. (2009). The ESC textbook of cardiovascular medicine. Oxford, Oxford University Press.
Houghton, A. (2019). Making Sense of the ECG: A Hands-On Guide (5th ed.). CRC Press.