Right Bundle Branch Block on Alternate Beats during Acute Pulmonary Embolism

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.

Can Body Surface Microvolt T‐Wave Alternans Distinguish Concordant and Discordant Intracardiac Alternans?

“…Second, our model allows to investigate APD alternans at physiological heart rates, whereas most experimental research on APD alternans induced the phenomenon by steady pacing at very high heart rates. Finally, alternans of depolarization rather than repolarization exists: it was reported in patients as an indicator of myocardial and arrhythmic disease . In a computer modeling study, Engelman et al show that tortuous conduction across a region of patchy fibrosis is sufficient to give rise to APD alternans and eventually initiate reentry, without the need for regional heterogeneity in cellular electric properties that cause primary repolarization alternans.…”

Atrioventricular reentrant tachycardia with a 2:1 right bundle branch block

“…A 2:1 bundle branch block is reported in patients with AV nodal reentrant tachycardia, sinus tachycardia, atrial flutter, atrial fibrillation, and pulmonary embolism [1][2][3][4][5]. This phenomenon can be attributed to multiple mechanisms including first-and second-degree bundle branch blocks (prolonged refractory period of bundle branch block), aberrancy, or supernormal conduction [7][8][9][10].…”

“…The occurrence of bundle branch block during supraventricular tachycardia may aid in the differential diagnosis of the mechanism of supraventricular tachycardia. The phenomenon of a 2:1 bundle branch block is reported during atrioventricular (AV) nodal reentrant tachycardia, sinus tachycardia, atrial fibrillation, and atrial flutter [1–5]. A 2:1 bundle branch block is attributed to first‐ and second‐degree bundle branch block, linking, electrical alternans, aberrancy, or supernormal conduction.…”

AV nodal reentrant tachycardia with a 2:1 right bundle branch block missed as bidirectional ventricular tachycardia in the first superficial evaluation

“…Because in this kind of aberrancy, with an increase of heart rate, the bundle branch block persists in the continuous beats, except for the heart rate that changes intermittently. This pattern may be explained by some other rare mechanisms such as bradycardia-dependent bundle branch block or supernormal conduction, but these mechanisms are the least probable [5][6][7].…”

“…A 2:1 bundle branch block was reported in patients with AV nodal reentrant tachycardia, AV reentrant tachycardia, sinus tachycardia, atrial flutter, atrial fibrillation, and pulmonary embolism [6][7][8].…”