ABSTRACT
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. When a QRS complex had a RBBB configuration, therefore, the RBB was not depolarized; the ensuing sinus impulse found the RBB fully responsive as a consequence of the long period intervening between two successive depolarizations, and resulted in normal intraventricular conduction. With right ventricular afterload decrease, the recovery of RBB anterograde and retrograde excitability was asynchronous, since the retrograde RP became normal earlier than the anterograde one. In accordance with the relatively short retrograde RP, the RBB was retrogradely invaded by the transseptal impulse coming from the left ventricle; this "shifted to the right" the anterograde RP of the RBB. The RBB, thus, was still refractory to the next sinus impulse, and RBBB again occurred; the RBB, thus, was once more depolarized retrogradely, and this led to perpetuation of RBBB. Finally, intraventricular conduction became normal owing to full normalization of RBB anterograde and retrograde refractoriness.
Subject(s)
Bundle-Branch Block/etiology , Bundle-Branch Block/physiopathology , Electrocardiography/methods , Pulmonary Embolism/complications , Pulmonary Embolism/physiopathology , Acute Disease , Humans , Male , Middle Aged , Pulmonary Embolism/diagnostic imaging , Pulmonary Embolism/therapy , Thrombolytic Therapy , Tomography, X-Ray ComputedABSTRACT
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. Short literature review is done on the CRT implantation in patients with RBBB.
