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The subcutaneous implantable cardioverter defibrillator (S-ICD) approved by the FDA in September is not ready for widespread use, a researcher said.
Robert Hauser, MD, of the Minneapolis Heart Institute of Abbott Northwestern Hospital in Minneapolis, wrote that the non-inferiority of the S-ICD to conventional transvenous ICDs has not been shown.
For example, the efficacy endpoint of the 330-patient, single-arm study that helped the device gain approval was terminated because of induced ventricular fibrillation (VF) rather than spontaneous VF.
"This surrogate [endpoint] might be appropriate for transvenous ICDs, but its applicability to S-ICDs is unknown. Thus by design, [the] study did not demonstrate the efficacy of the S-ICD in ambulatory patients," Hauser argued in a viewpoint in the Jan. 8 issue of the Journal of the American College of Cardiology.
He noted the S-ICD was not tested in a diverse population and only had 180 days of follow-up, whereas conventional ICDs are backed by 30 years of "proven safety and efficacy."
Until there are data "showing equivalency -- much less superiority -- in patients at high risk for sudden cardiac death," this device is not a better choice than a conventional transvenous ICD, Hauser said.
The S-ICD is indicated for patients who are at risk of VF and who do not need a pacemaker or anti-tachycardia pacing. Its single lead is placed just under the skin, compared with conventional ICD leads that are threaded transvenously to the heart under x-ray guidance.
Conventional ICDs provide three functions: defibrillation, anti-tachycardia pacing, and bradycardia pacing. And they do does so with half the weight (about 70 g versus 145 g), half the energy required for a shock (<40 joules versus 80 joules), and a longer battery life compared with S-ICD, Hauser pointed out.
This is important, Hauser said, because many patients with ventricular tachycardia (VT) can be painlessly brought back into rhythm with anti-tachycardia pacing.
"Without anti-tachycardia pacing, a conscious patient will receive painful 80-J shocks for ventricular tachycardia," he wrote.
In fact, 64% of the patients in the pivotal S-ICD trial received the 80-J shocks because they had a spontaneous VT or VF during follow-up, despite the fact that researchers excluded patients where it was known their VT could be terminated with pacing therapy.
Also, emerging evidence suggests that inappropriate shocks are associated with morbidity and mortality.
In particular, the Multicenter Automatic Defibrillator Implantation Trial -- Reduce Inappropriate Therapy (MADIT-RIT) study, presented in November at the American Heart Association meeting, showed a survival benefit when ICDs where programmed to ignore tachyarrhythmias under 200 beats per minute and delay discharge for 60 seconds versus 2.5 seconds.
Although not conclusive, researchers suggested the increase in survival could be due to the decrease in anti-tachycardia therapy.
Hauser concluded his editorial by saying the S-ICD should be confined to certain patient subgroups until "critical questions in regard to safety and efficacy in primary and secondary prevention are addressed."
From the American Heart Association:
- Focused Update for Device-Based Therapy of Cardiac Rhythm Abnormalities
- Interventions for Patients and Families with ICDs
The review was supported by grants from the Minneapolis Heart Institute Foundation and the Abbott Northwestern Hospital Foundation.
Journal of the American College of CardiologySource Reference: Hauser R "The subcutaneous implantable cardioverter-defibrillator: should patients want one?" J Am Coll Cardiol 2013; 61: 20-22.