SMASH-VT Published: Ablation Reduces Incidence of Future ICD Therapy in Post-MI Patients

Michael O'Riordan
December 27, 2007 — A small, randomized study of post–myocardial infarction (MI) patients who received an implantable cardioverter defibrillator (ICD) after a first arrhythmic event has shown that substrate-based catheter ablation can be performed to reduce the incidence of future ICD therapies [1]. Compared with control patients, radiofrequency catheter ablation guided by electronanatomic mapping of the ventricular arrhythmia substrate reduced the incidence of future shocks by 73%, report investigators.

Results of the study, known as the Substrate Mapping and Ablation in Sinus Rhythm to Halt Ventricular Tachycardia (SMASH-VT) trial, which was first presented at the Heart Rhythm Society 2006 Scientific Sessions by Dr Vivek Reddy (Massachusetts General Hospital, Boston), the lead author of the study, are now published in the December 20, 2007 issue of the New England Journal of Medicine.

Although the findings leave open the future possibility that ventricular tachycardia-substrate ablation might be considered a clinical prophylactic option in post-MI patients who already have multiple ICD shocks, an editorial accompanying the published study stresses that option is still distant [2].

"Clinicians should mind the gap between the current practice and the promise of curing ventricular tachycardia with ablation techniques," writes Dr NA Mark Estes III (Tufts University School of Medicine, Boston, MA). "To bridge this gap, additional trials are needed to assess the comparative benefit of catheter ablation and antiarrhythmic 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. Until such data are available, catheter-ablation therapy should not be considered clinically indicated as prophylaxis to prevent ICD therapy."

Ablation of VT is a significant procedure

As previously reported by heartwire, the SMASH-VT investigators randomized 128 patients at three hospitals, two in Boston and one in the Czech Republic, to undergo or not undergo radiofrequency substrate ablation. The patients were required to have a history of MI and be scheduled for ICD implantation or to have had an ICD put in recently. Their device indication could be an occurrence of cardiac arrest, an episode of hemodynamically significant VT, or inducible VT plus syncope at an electrophysiologic (EP) study.

By design, the patients were not taking arrhythmia medication, which is commonly taken by ICD patients to reduce the risk of shocks. All patients in the ablation group underwent mapping (CARTO, Biosense-Webster, Diamond Bar, CA) followed by ablation performed with the patients in sinus rhythm.

SMASH-VT: Clinical end points

End point	Ablation group (n = 64), n (%)	Control group (n = 64), n (%)	Hazard ratio (95% CI)
ICD events	8 (12)	21 (33)	0.35 (0.15 - 0.78)
ICD shocks	6 (9)	20 (31)	0.27 (0.11 - 0.67)
ICD storm	4 (6)	12 (19)	0.30 (0.09 - 1.00)
Death	6 (9)	11 (17)	0.59 (0.22 - 1.59)

Patients in the ablation group showed significantly greater rates of two-year survival free of delivered ICD therapy, the primary end point. They also had higher rates of survival free of shocks.

"Ablation of VT is a significant enough procedure that I think only experienced centers should be doing it, initially," Reddy previously told heartwire. He noted the teams performing ablations in the study became better at it as time went on. "As centers get more experience doing VT [substrate] ablation on patients who already have had multiple ICD shocks, they may want to consider doing ablation on this kind of prophylactic basis."

Promise vs practice

As Estes notes in his editorial, the safety and efficacy of catheter ablation depend on the skill of the operator and the selection of patients. "The principal disadvantage of this invasive procedure is the risk of complications," he writes, adding, "It is not clear whether outcomes of catheter ablation would be similar for unselected patients or in less experienced centers."

Estes also writes that while the reduction in ICD therapies is convincing, the study does not address the more clinically important question of the relative efficacy of therapy with antiarrhythmic drugs, the standard front-line therapy for ICD discharges. In addition, he writes that more than 90% of VT episodes can be terminated with antitachycardia pacing, thus reducing the frequency of shocks, with the appropriate use of beta blockers, statins, and contemporary ICD programming.

"As the field of ventricular tachycardia ablation evolves, it is important that we continue to adhere to the fundamental principle of evidence-based medicine, with relevant clinical and economic data derived from human clinical trials forming the foundation for clinical practice," concludes Estes. "The health and well-being of our patients with ICDs who have a history of myocardial infarction are at stake."

Five of the study authors have disclosed various financial relationships with the National Institutes of Health, Biosense Webster, St. Jude Medical, Boston Scientific, Medtronic, Cameron Health, and InnerPulse. The remaining study authors have disclosed no relevant financial relationships. Dr. Estes has disclosed receiving lecture fees from Medtronic, St. Jude Medical, and Boston Scientific.

Sources

1. Reddy VY, Reynolds MR, Neuzil P, et al. Prophylactic catheter ablation for the prevention of defibrillator therapy. N Engl J Med 2007; 357:2657-2665.
2. Estes NA. Ablation after ICD implantation—bridging the gap between promise and practice. N Engl J Med 2007; 357:2717-2719.