Substrate Mapping and Ablation in Sinus Rhythm to Halt Ventricular Tachycardia - SMASH-VT

Description:

The goal of this trial was to evaluate the rate of defibrillator therapy among high-risk patients after prophylactic radiofrequency catheter ablation of arrhythmogenic tissue.

Hypothesis:

The use of radiofrequency ablation of arrhythmogenic ventricular tissue in patients with prior myocardial infarction (MI) and an unstable ventricular rhythm will reduce the need for subsequent defibrillator therapy.

Study Design

  • Randomized

Patients Screened: N/A
Patients Enrolled: 128
NYHA Class: I or II: 80%, and III or IV: 20%
Mean Follow Up: 22.5 months
Mean Patient Age: 67 years
Female: 13
Mean Ejection Fraction: 32%

Patient Populations:

Eligible patients had a history of MI at least 1 month prior to randomization and had a defibrillator placed within 6 months (or planned) due to an arrhythmic event. Qualifying arrhythmic events included: 1) VF, 2) unstable VT, 3) syncope and an electrophysiologic study that demonstrated VT, and 4) an appropriate defibrillator shock from a device that had been placed for primary prophylaxis. The last indication was instituted after the trial began to facilitate enrollment.

Exclusions:

Significant exclusion criteria included: 1) patients who were treated with a class I or class III antiarrhythmic drug, 2) ventricular arrhythmia thought to be due to active ischemia or an etiology other than infarction, and 3) incessant ventricular arrhythmia requiring immediate antiarrhythmic drug therapy.

Additional exclusion criteria included: 1) age less than 18 years, 2) inability to provide informed consent, 3) stroke within 30 days of randomization, 4) contraindication to anticoagulation therapy, and 5) any condition (medical or otherwise) that would impair the ability of the patient to complete the trial.

Primary Endpoints:

The primary endpoint was freedom from any appropriate defibrillator therapy, defined as a shock or antitachycardia pacing.

Secondary Endpoints:

The secondary endpoints were freedom from any appropriate defibrillator shock, death, or defibrillator storm. A defibrillator storm was defined as three or more shocks within a 24-hour period.

Drug/Procedures Used:

Patients with prior MI and an unstable ventricular arrhythmia who had a defibrillator implanted were randomized (1:1) to prophylactic catheter ablation of arrhythmogenic ventricular tissue during sinus rhythm versus control (defibrillator only).

Principal Findings:

The qualifying arrhythmic event was ventricular fibrillation (VF; 18%), unstable ventricular tachycardia (VT; 49%), syncope with inducible VT (21%), and defibrillator implanted for primary prophylaxis (12%). Baseline characteristics were well matched except for severe left ventricular (LV) dysfunction, which was marginally more common in the ablation group (25% vs. 11%, p = 0.06). There were three complications in the ablation group: 1) pericardial effusion without tamponade, 2) congestive heart failure exacerbation, and 3) deep venous thrombosis that required prolonged anticoagulation.

At 22.5 months of follow-up, appropriate defibrillator therapy occurred in 12% in the ablation group, compared with 33% in the defibrillator only group (hazard ratio [HR], 0.35; 95% confidence interval [CI], 0.15-0.78; p = 0.007). There was progressive separation of the Kaplan-Meier curves over the extent of follow-up. There was a consistent benefit in all subgroups that favored ablation.

Defibrillator shocks occurred in 9% of the ablation group versus 31% in the control group (HR, 0.27; 95% CI, 0.11-0.67; p = 0.003), defibrillator storms in 6% versus 19% (HR, 0.30; 95% CI, 0.09-1.00; p = 0.06), and death in 9% versus 17% (HR, 0.59; 95% CI, 0.22-1.59; p = 0.29), respectively. LV function and functional status remained stable in both groups during the extent of follow-up.

Interpretation:

This trial revealed that in carefully selected patients, the use of prophylactic catheter ablation of arrhythmic tissue while in sinus rhythm reduces the need for subsequent defibrillator shocks or antitachycardia pacing. This is important since defibrillator therapy, especially defibrillator storms, can result in significant morbidity and impaired quality of life. There were only three complications in the ablation group with no long-term adverse events noted, such as decline in LV function or functional status. Although the trial was not designed to study survival, there was no suggestion of increased early or long-term mortality in the ablation group.

This trial was conducted at three specialized centers by highly skilled operators; therefore, the applicability of this therapy in community hospitals will need to be evaluated. The current treatment of patients who experience defibrillator shocks is antiarrhythmic drug therapy, coupled with defibrillator re-programming and antitachycardia pacing. This trial did not assess quality of life or address the role of catheter ablation versus antiarrhythmic drug therapy, which is still considered first-line therapy.

References:

Reddy VY, Reynolds MR, Neuzil P, et al. Prophylactic catheter ablation for the prevention of defibrillator therapy. N Engl J Med 2007;357:2657-65.

Clinical Topics: Arrhythmias and Clinical EP, Heart Failure and Cardiomyopathies, Pericardial Disease, Vascular Medicine, Implantable Devices, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Acute Heart Failure

Keywords: Myocardial Infarction, Follow-Up Studies, Ventricular Fibrillation, Syncope, Electrophysiologic Techniques, Cardiac, Tachycardia, Ventricular, Quality of Life, Heart Failure, Venous Thrombosis, Confidence Intervals, Catheter Ablation, Pericardial Effusion, Defibrillators, Implantable


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