VT Ablation to Reduce ICD Shocks

Abstract & Commentary

By John P. DiMarco, MD, PhD Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville Dr. DiMarco is a consultant for Novartis, and does research for Medtronic and Guidant.

Source: Reddy VY, et al. Prophylactic catheter ablation for the prevention of defibrillator therapy. N Engl J Med. 2007; 357:2657-2665.

This paper gives the results of the substrate Mapping and Ablation in Sinus Rhythm to Halt Ventricular Tachycardia (SMASH-VT) study. This study was designed to test the hypothesis that early prophylactic catheter ablation in patients with implantable cardioverter defibrillators (ICD) would decrease the frequency of ICD shocks during follow-up. Reddy and colleagues recruited patients with prior myocardial infarction who had either a planned or recent ICD implantation for spontaneous or electrically-induced ventricular tachycardia or a prior ICD implantation for primary prophylaxis, and subsequently received appropriate ICD therapy for a single event. Patients were excluded if they were receiving class I or class III antiarrhythmic drugs. Most patients were on beta blockers and ACE inhibitors. Smaller proportions were on statins and aspirin. Ventricular tachycardia ablation was performed using a 3-step protocol. First, programmed electrical stimulation was used to induce ventricular tachycardia, and the ECG morphology of all the ventricular tachycardias induced was recorded. Substrate 3 dimensional mapping then was used to define the localization and extent of any myocardial scar. Finally, pace mapping was used to locate probable exit sites for ventricular tachycardia from the areas of the scar. Mapping was performed using an electrical anatomical 3-dimensional mapping system (CARTO) using either a retrograde or combined retrograde transseptal approach.

The study group included 128 patients who were randomly assigned to VT ablation or no further therapy. The mean age was 67 years, and a large majority were men. Approximately 80% were New York Heart Association functional class I or II. The mean left ventricular ejection fraction was 31%. Two patients assigned to the ablation group did not undergo the procedure, and in three patients, no endocardial scar was visualized and no ablation lesions were placed. The number of VTs induced per patient, and the success of the ablation procedure in suppressing VT induction, was not reported. There were three significant complications related to the ablation procedure: one patient developed a pericardial effusion without tamponade; a second patient had an exacerbation of congestive heart failure, which required a prolonged hospitalization; and one patient developed a deep venous thrombosis.

Patients were followed for a mean duration of 22.5 ± 5.5 months. During follow-up, 8 patients in the ablation group (12%) and 21 patients in the control group (33%) received appropriate ICD therapy at least once. In 6 of the 8 ablation patients, and in 20 of the 21 control patients, at least one appropriate ICD shock was delivered. Mortality was 9% in the ablation group, compared to 17% with the control group; this difference was not statistically significant. Episodes of multiple ICD shocks ("VT storms") were noted in 4 patients assigned to the ablation group and in 12 control patients. In both groups, there was no change in the overall New York Heart Association functional class.

Reddy et al concluded that substrate-based catheter ablation reduces the incidence of ICD therapy in patients with a prior history of arrhythmias.

Commentary

The results of the SMASH-VT study confirm that catheter ablation of ventricular tachycardia can be a useful adjunct in patients with implantable defibrillators. Most electrophysiologists use drug therapy as the initial approach to decrease VT shock frequency in ICD patients. In SMASH-VT, the control group was not treated with antiarrhythmic drugs, and catheter ablation did prove to be better than no therapy. The most relevant randomized trial to compare to SMASH-VT is the OPTIC trial (JAMA. 2006; 295:165-171). In that study, ICD patients were randomized to treatment with either beta blockers, sotalol alone, or beta blockers plus amiodarone. Sotalol resulted in a 30% reduction in ICD therapy, and amiodarone resulted in a greater than 70% reduction in ICD therapy. Therefore, it appears that the results of catheter ablation are similar to drug therapy, but it is likely that catheter ablation is more expensive and may have more early complications.

It is also interesting that most of the catheter ablations were apparently carried out in the single non-US site. The reason for this is unexplained in the paper, but is probably due to pre-enrollment bias at the two US sites.

I don't think that SMASH-VT will change the approach of most electrophysiologists to the use of catheter ablation. Catheter ablation will remain an effective and useful tool, but most patients will receive a course of drug therapy before being referred for the procedure.