Clinical Pearls & Morning Reports
In the presence of structural heart disease, ventricular tachycardia is typically monomorphic and is usually due to a reentrant mechanism resulting from the formation of an abnormal electrical circuit in the myocardium. Myocardial scars from previous myocardial infarction or surgical procedures set the stage for the discontinuous propagation of myocardial electrical impulses, which results in reentry. Myocardial scars can also be seen in patients with nonischemic cardiomyopathy. Read the latest Review Article here.
Q: What are causes of ventricular tachycardia in a structurally normal heart?
A: In a structurally normal heart, ventricular tachycardia can be idiopathic or due to genetic arrhythmia syndromes. Idiopathic ventricular tachycardias, which are the most common type, are typically monomorphic (having a single QRS structure on ECG), indicating that they originate from a single discrete focus. The focus is most often located in the outflow region of one of the ventricles, either supravalvular or infravalvular.
Q: What is the primary approach for ablation of focal ventricular tachycardia?
A: The primary approach for ablation of focal ventricular tachycardia involves mapping (localizing) the site from which the ventricular tachycardia originates. In “activation mapping,” the electrical signal recorded during ventricular tachycardia from a catheter positioned in the heart can be timed in relation to the earliest point of onset of the body-surface QRS complex; the earlier the recorded signal, the closer the catheter tip is to the site of origin of the ventricular tachycardia. In “pace mapping,” the 12-lead ECG recorded during pacing at a specific site can be compared with the 12-lead ECG recorded during ventricular tachycardia; when the two QRS patterns are similar, the pacing site is likely to be near the site of origin of the ventricular tachycardia. Once the focus of origin of the ventricular tachycardia has been identified, radiofrequency current can be delivered through the catheter, resulting in ablation of that focus. This approach is very effective for premature ventricular contractions (PVCs) and idiopathic ventricular tachycardias.
A: Sustained ventricular tachycardia due to a reentry circuit involving a myocardial scar tends to involve a large area of the myocardium and to have a defined exit site from the scar into the rest of the myocardium, which can be mapped (if the patient is hemodynamically stable) to identify a suitable ablation site. One scar may have several exit sites, resulting in ventricular tachycardia with different ECG patterns and making ablation of multiple sites necessary. One approach to ablating reentrant ventricular tachycardia is called “entrainment mapping,” which involves use of a pacing catheter to identify areas of a reentrant ventricular tachycardia circuit. The pacing rate is set slightly faster than the rate of the tachycardia, and the pacing catheter is moved from point to point until pacing “captures” the ventricular tachycardia circuit, establishing that the paced location is part of that circuit. Termination of ventricular tachycardia is then achieved by radiofrequency ablation of critical parts of the ventricular tachycardia circuit that can be characterized by this approach.
A: Catheter ablation for ventricular tachycardia is effective in patients with and in patients without structural heart disease. In the absence of structural heart disease, success rates of more than 80% have been reported for both sustained ventricular tachycardia and PVCs. The overall success rate with ablation is higher for patients with postinfarction ischemic cardiomyopathy (56 to 77%) than for patients with nonischemic cardiomyopathy (38 to 67%). Recurrent ventricular tachycardia after ablation in patients with structural heart disease is associated with a decreased chance of survival.