Figure 3.

Ladder diagram illustrates our proposed mechanism for intermittent right bundle branch (RBB) block and atrioventricular (AV) block seen on electrocardiogram. A His extrasystole that conducts retrogradely through the AV node to the atrium but blocks antegradely in the RBB will give rise to a QRS with RBB block. A shorter coupled His extrasystole that conducts retrograde into the slow AV node pathway to the atrium and into the fast AV node pathway, causing the preceding sinus beat to block in the AV node, will give rise to an inverted P wave without QRS, mimicking AV block.