Right bundle branch block on alternate beats during acute pulmonary embolism.

The electrocardiogram of a patient with acute pulmonary embolism showed right bundle branch block (RBBB) on alternate beats; following thrombolysis, the pattern evolved to persistent RBBB and eventually to normal conduction. Analysis of serial tracings suggested that the mechanism of RBBB alternans was tachycardia-dependent bidirectional bundle branch block, caused by prolongation of both anterograde and retrograde refractory periods (RPs) of the right bundle branch (RBB). The sinus impulse found the RBB refractory, and was conducted over the left bundle branch only, depolarizing the left ventricle and then attempting to penetrate retrogradely the RBB; at that time, however, the RBB was still refractory.

Last ditch CRT: right is not always wrong!

Cardiac resynchronization therapy (CRT) has become the mainstay of refractory heart failure treatment. Usually the patients having right bundle branch block (RBBB) on electrocardiogram are considered as relative contraindication as there is no or minimal dyssynchrony in them. We present a case where CRT was put in as last resort in a patient with RBBB and was successful.