ECG Clues for Diagnosing Ventricular Tachycardia Mechanism

Abstract

Three mechanisms underlie the initiation and maintenance of ventricular tachycardia: automaticity, triggered activity, and reentry. As straightforward as these mechanisms are, assessing which mechanism is operative in a particular patient's ventricular tachycardia can be difficult. The optimal treatment strategy for ventricular tachycardia in a given patient can be influenced by the mechanism underlying the ventricular tachycardia. Appropriately counseling patients, choosing the optimal pharmacologic agent that maximizes efficacy while minimizing undesirable side effects, risks, and toxicities, as well as recommending and timing ablative therapy all hinge on identifying the probable mechanism of ventricular tachycardia. Much has been published regarding invasive electrophysiologic maneuvers that allow for correct diagnosis of ventricular tachycardia mechanism. The aim of this clinical review is to provide insight into VT mechanisms based on ECG clues of spontaneous arrhythmia events and the response to pharmacologic manipulation prior to invasive electrophysiologic evaluation.

Two Ventricular Tachycardias with Cycle Length and QRS Alternans: Insights into the Mechanism from Mapping and Ablation of the Tachycardias

“…Repeat electrophysiologic evaluation was performed after elimination of the presenting VT. A second VT of a different morphology was inducible with atrial overdrive pacing at 400 ms after an infusion of isoproterenol. This induction sequence is most consistent with triggered activity as the mechanism of the second tachycardia 2,3 . The second VT also manifested QRS and cycle length alternans.…”

“…During episodes of spontaneous initiation of the tachycardia, the coupling interval from the normal sinus beat to the first tachycardia beat was fixed at 400 ms. Ventricular overdrive pacing often caused termination of the tachycardia but entrainment could not be demonstrated. The induction characteristics and response to ventricular overdrive pacing were felt most consistent with triggered activity as the tachycardia mechanism 2,3 …”

“…The induction characteristics and response to ventricular overdrive pacing were felt most consistent with triggered activity as the tachycardia mechanism. 2,3 After confirmation that the tachycardia was VT, mapping of both the left and right ventricles was undertaken utilizing the NavX mapping system (St. Jude Medical, Minnetonka, MN, USA). The site of earliest ventricular activation was found along the mid inferior right ventricular (RV) septum.…”

“…This induction sequence is most consistent with triggered activity as the mechanism of the second tachycardia. 2,3 The second VT also manifested QRS and cycle length alternans. Two particularly interesting electrocardiogram (ECG) findings were As can be seen in the anterior precordial leads (V1 to V3), there was some variability between the different long cycle length and different short cycle length intervals.…”

The Persistent Sodium Current Blocker Riluzole Is Antiarrhythmic and Anti-Ischaemic in a Pig Model of Acute Myocardial Infarction

“…Re-entrant arrhythmias require unidirectional conduction, conduction block, and a region of slow conduction such that the cycle length of the arrhythmia is longer than the longest refractory period in the circuit [37]. All these factors can result from myocardial damage and in particular the loss of gap junctions, impaired cell coupling and myocardial heterogeneity which occur during Phase 1b and Phase 2 [36].…”