Bidirectional fascicular tachycardia with alternating axis deviation following acute myocardial infarction

Abstract

A 46-year-old male without past medical history presented to the emergency department complaining of severe chest pain. Blood pressure was 100/70 mm Hg, heart rate was 66 bpm, and the oxygen saturation was normal. The 12-lead ECG showed ST segment elevation in leads I, avL and throughout the precordial leads (Fig. 1A). Urgent coronary angiography was performed and demonstrated a complete thrombotic occlusion of the mid left anterior descending artery (LAD) as well as a more proximal 70% luminal narrowing of the LAD. Percutaneous transluminal coronary angioplasty and stent implantation of the mid LAD was successfully performed with restoration of grade TIMI 3 flow in the LAD. The patient was admitted to the cardiac intensive care unit after successful stent implantation. ECG performed 1 h after reperfusion (Fig. 1B) showed a wide complex tachyarrhythmia with right bundle branch block (RBBB) morphology and alternating axis deviation. This arrhythmia spontaneously resolved to normal sinus rhythm (Fig. 1C). The patient was discharged with medical therapy including a beta blocker and without any complications. The 12-lead ECG recording demonstrates a bidirectional tachycardia in which all the beats have features of RBBB and the QRS axis in the frontal plane alternates between right and left axis deviations (Fig. 1B). The width of the QRS complex is only 110 ms, thus corresponding to a tachycardia originating within the left bundle branch (LBB) or its fascicles. The illustration (Fig. 2) is based on the assumption that the focus of the tachycardia was situated in the left bundle just above the division into the left posterior fascicle (LPF) and the left anterior fascicle (LAF) with impulses conducting to the myocardium using the LAF and LPF alternately, hence the alternating axis. Even though His bundle potentials were not recorded during the bidirectional tachycardia, the relatively narrow width of the QRS and the alternating axis together with RBB leaves no doubt regarding the location of the automatic focus in the territory of the LBB. This concept was documented by His bundle recordings by Massumi back as 1973 [1] and by clinical observations since 1977 [2]. The QRS morphology and rate of arrhythmia corresponds to the majority of the cases of reperfusion arrhythmias also known as accelerated idioventricular rhythm (AIVR) [3]. However, the unique feature is the alternation of the QRS axis in the frontal plane suggesting functional block in the two fascicles. As is usually the case, the tachycardiawas self-limited and resolved spontaneously. The majority of the AIVR cases have rates under 120/min and do not cause hemodynamic deterioration. However, it is important to distinguish the reperfusion AIVR from the more dangerous type of bidirectional ventricular tachycardia (VT) seen in the course of digitalis intoxication [4] and severe myocardial damage such as myocarditis [5]. This patient had no history of digitalis use and the arrhythmia occurred during the reperfusion period making bidirectional VT very unlikely. Bidirectional VT has not been reported in the setting of acute myocardial infarction. It should also be noted that the early publication of cases of AIVR emphasized the point that the occurrence of AIVR usually indicated restoration of flow to the infarcted region [3]. In recent publications, it has been reported that AIVR also appears in several drug intoxications [3], post-resuscitation [6] and idiopathic dilated cardiomyopathy [7]. There is general agreement that the electrophysiological mechanism of AIVR is enhanced automaticity of the His bundle and/or its divisions. To the best of our knowledge, this is the first report of alternating LAF and LPF block in the setting of the RBBB and fascicular rhythm in a patient with acute anterior myocardial infarction. The authors of this manuscript have certified that they comply with the Principles of Ethical Publishing in the International Journal of Cardiology [8].