The Ideal End Point for Ablation in Postinfarction Ventricular Tachycardia

Abstract

T he end point of ventricular tachycardia (VT) ablation studies should ideally predict the target outcome-freedom from VT recurrence. VT in patients with previous myocardial infarction is often due to scar-related re-entry. This is supported, although not proven, by the fact that VT can be initiated by programmed electric stimulation (PES). Entrainment and resetting with fusion are strong arguments for re-entry but can be only performed during hemodynamically tolerated VT. Article see p 677The substrate for re-entry is characterized by regions of slow conduction, unidirectional conduction block that allows initiation of re-entry, and areas of conduction block that can define parts of the re-entry circuit. Conduction block can be anatomically fixed but also functional and thus only present during VT or at rapid rates. Catheter ablation aims to transect the critical isthmus of the re-entry circuit.The ideal ablation candidate is inducible for the clinically documented, hemodynamically tolerated VT. This allows for detailed analysis of the mechanism involved and accurate delineation of the underlying substrate. Unfortunately, this scenario applies only to a minority (albeit an important number) of patients.This first patient category was accepted for ablation in the early 1990s. Only the clinical VT was targeted and of importance, was, without exception reproducibly inducible from the right ventricle.1 Outcome was favorable if the clinical VT was abolished, a result achieved in 75% of the patients. Remarkably, 82% of them were noninducible for any VT after ablation. In 16% of these noninducible patients, ventricular arrhythmia (VA) recurred; in half of the patients early and often with the same VT morphology, perhaps due to lesion recovery. Patients presenting with a late recurrence either died suddenly, presumably (but not definitively) arrhythmic, or had a not previously documented VT. Patients with VA recurrence were more likely to be inducible for nonclinical VT.The second patient category was patients presenting with stable VTs but had multiple inducible VTs, of which all tolerated VTs were targeted.2 In 85%, the clinical VT could be abolished, but only 31% were rendered uninducible, despite a more extensive ablation approach. The difference in acute outcome may be partly explained by the more impaired ejection fraction (EF) in this second category. VT recurred in only 9% of noninducible patients but in 47% of patients with inducible nonclinical VTs after ablation. The latter had more inducible VTs, and the remaining VTs were faster than the ablated VTs.With the widespread use of implantable cardioverter defibrillators (ICDs), a third patient category has entered the electrophysiology laboratory. The majority have advanced heart failure and not tolerated VTs. For unstable VTs and for VTs that are documented but not inducible, it is impossible to verify the mechanism and to prove a causal relationship between the arrhythmia and the targeted substrate. It is important to remember that much of our knowledge about...