Catheter ablation reduced the number of shocks delivered to patients who have defibrillators implanted after heart attacks, a study published Thursday in the New England Journal of Medicine concluded.

While implantable cardioverter defibrillators (ICDs) are a mainstay of therapy to prevent sudden death for people who have a ventricular tachyarrhythmic event, the shocks are painful, can cause clinical depression, and do not offer complete protection against death from arrhythmia, according to the study authors.

“Since no device is likely to be fully protective against ventricular tachycardia or fibrillation, it would be clinically valuable to adopt an approach that reduced the absolute incidence of ventricular tachycardia or fibrillation so that the ICD served solely as a backup device,” the authors wrote in the report.

Ablation is a technique of identifying and eliminating cardiac tissue that can generate the kind of abnormal rhythm that sets the heart beating irregularly, so that a defibrillator shock is needed to restore normal heart rhythm.

Mark Josephson, MD, chief of cardiology at Beth Israel Deaconess Medical Center and a professor of medicine at Harvard Medical School (both Boston), led the Substrate Mapping and Ablation in Sinus Rhythm to Halt Ventricular Tachycardia (SMASH-VT) study.

SMASH-VT included 128 people who had defibrillators implanted after heart attacks. Half of them underwent ablation, half did not. In an average follow-up period of 22.5 months, just eight of those who had ablation experienced defibrillator shocks, compared to 21 – a full third – of the group that did not have ablation.

Ablation was performed with the use of a substrate-based approach in which the myocardial scar is mapped and ablated while the heart remains predominantly in sinus rhythm. The primary end point was survival free from any appropriate ICD therapy.

The authors noted in the study discussion that as compared with the control population, patients in the ablation group had a 65% reduction in the risk of receiving ICD therapy during the subsequent two years. When anti-tachycardia pacing therapy was excluded from this analysis, there remained a 73% reduction in the risk of receiving subsequent ICD shocks.

“This effect may be clinically important, not only because of the reduction in the unpleasant experience of device discharge, but also in terms of subsequent adverse cardiovascular events,” the authors wrote.

There also was a reduction in deaths among those in the ablation group, the authors noted. Eleven of those who did not have ablation died, while there were just 6 deaths in the ablation group. The numbers were too small to reach statistical significance.

But radiofrequency ablation is not without its disadvantages. The principal disadvantage with the procedure is its risk of complications, noted N.A. Mark Estes III, MD, author of an accompanying editorial in the NEJM. Estes is the director of cardiac arrhythmia center at Tufts New England Medical Center (Boston).

According to the latest guidelines of the American Heart Association (Dallas), the American College of Cardiology (Washington), and the European Society of Cardiology (Sophia Antipolis, France), catheter ablation is indicated as adjunctive therapy in selected patients who have an ICD and who receive multiple shocks as a result of sustained ventricular tachycardia that is not manageable by reprogramming of the ICD or drug therapy, Estes wrote.

The SMASH-VT study did not address the issue of drug treatment to keep abnormal heart rhythm under control, Estes wrote, noting that none of the participants were given anti-arrhythmia drugs.

Clinicians should mind the gap between current practice and the promise of curing ventricular tachycardia with ablation techniques, according to the editorial.

“To bridge this gap, additional trials are needed to assess the comparative benefit of catheter ablation and anti-arrhythmic drugs, to identify which subgroups of patients are most likely to benefit, to evaluate the effect of operator expertise, and to assess quality of life and cost,” Estes wrote.

Still, the study is noteworthy for several reasons, he said.

“SMASH-VT convincingly demonstrates that highly selected patients undergoing ICD implantation over a period of almost four years without antiarrhythmic treatment in three experienced centers have fewer ICD therapies when prophylactic substrate-based catheter ablation is used,” Estes wrote.

The study may also be of interest to clinicians in light of recent concerns over certain ICD leads – the thin wires connecting the defibrillator to the heart. In October, Medtronic (Minneapolis) pulled its Sprint Fidelis family of ICD leads because they may break inside the body (Medical Device Daily, Oct. 16, 2007).

Soon after the recall, St. Jude’s (St. Paul, Minnesota) Riata leads came under heavy scrutiny as rumors quickly began to surface about the devices being next in line for a recall. The company attempted to discredit those rumors during a Bear Stearns conference call, citing data from three large St. Jude registries on 121,000 implants and pointing out significant design differences between the Riata and Fidelis leads (MDD, Oct. 31, 2007).

Then, an editorial published last month in the medical journal Pacing and Clinical Electrophysiology (PACE) didn’t do St. Jude any favors as it detailed four cases of the Riata leads poking holes through patients’ hearts rather than remaining attached to the heart wall. But St. Jude stood behind its product, saying that the rate of perforation with Riata is below or at the low end of what has been reported in clinical literature (MDD, Nov. 15, 2007).

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