Branch-to-branch ventricular tachycardia due to primary non-ischemic cardiomyopathy

ECG 5A: This tracing shows a monomorphic, regular tachycardia of 155 bpm with a pattern of left bundle branch block; atrial activity is difficult to identify; clinical history indicates that this patient had undergone an ablation of the bundle of His and thus presents a complete anterograde atrioventricular block; the only possible diagnosis in the presence of a tachycardia with spontaneous QRS complexes (no ventricular pacing) is therefore ventricular tachycardia;  clinical history can sometimes influence the interpretation of a tracing (a history of infarction suggests ventricular tachycardia but does not guarantee its diagnosis) but can sometimes allow a diagnosis of certainty (as in this case when there is a complete atrioventricular block); probable branch-to-branch reentry tachycardia;

ECG 5B:

ECG 5B: ECG after termination of the tachycardia, showing low-voltage atrial fibrillation, biventricular pacing (narrow QRS, negative in lead I and positive in V1); presence of a polymorphic ventricular triplet attesting to the arrhythmogenic setting;

Comments: Branch-to-branch reentry is a ventricular tachycardia resulting from a macro-reentry between the two branches. This type of tachycardia represents a significant percentage (in the order of 20 to 40%) of ventricular tachycardias observed in patients with idiopathic non-ischemic cardiomyopathy. A number of cases have also been described in the context of valvular or ischemic cardiomyopathies, in patients with myotonia and in some patients without cardiac disease. The occurrence of near-syncope, syncope or sudden death is frequent as the tachycardia is often rapid and occurs in myocardial alterations. The right branch constitutes the anterograde pathway in the majority of cases, one of the fascicles (anterior or posterior) of the left branch constituting the retrograde pathway thus explaining the left bundle branch block pattern. The reverse circuit (right bundle branch block pattern) is a rarer occurrence.  The initiation of reentry occurs when a premature atrial or ventricular complex is blocked in one of the branches, conducted in the other in anterograde direction and then penetrates the initially blocked branch in a retrograde manner inducing a sustained reentrant tachycardia. The sinus rhythm electrocardiogram frequently reveals a first-degree atrioventricular block, an aspecific distal conduction disorder, infrequently with a left bundle branch block. The prerequisite for the occurrence of branch-to-branch reentry is the presence of a conduction delay in the His-Purkinje system resulting in the measurement of a prolonged HV interval (80 ms on average). In this patient, ablation of the atrioventricular node does not allow analyzing the spontaneous ventricular activation sequence. Antiarrhythmic treatments are rarely effective in this setting. Removal of the right branch often solves the problem, even if an implantable defibrillator remains indicated due to left ventricular dysfunction.

Take-home message: Branch-to-branch reentry occurs preferentially in heart failure patients with a frequent tachycardia pattern of left bundle branch block.