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A newly approved, totally subcutaneous implantable cardioverter-defibrillator was nearly 100% effective in detecting and treating ventricular arrhythmias, without the need for transvenous leads.
This exceeded the prespecified effectiveness goal of 88% in an 11-month safety and efficacy analysis of 314 patients who were eligible for an ICD and did not require pacing, Dr. Raul Weiss and colleagues reported in the August 26 issue of Circulation.
The device had a mean time to therapy of about 15 seconds, with some intervals as long as 18 seconds or more, noted Dr. Weiss of Ohio State University, Columbus, and his coinvestigators. There were no clinically relevant consequences for this and, in fact, they said, "a slightly longer time to therapy has the benefit of allowing spontaneous self-termination of many [tachycardia/fibrillation episodes]."
The subcutaneous implantable cardioverter-defibrillator (S-ICD) by Cameron Health/Boston Scientific was approved by the Food and Drug Administration in September 2012. It is the first ICD that can be placed without transvenous leads, which are associated with numerous complications, mechanical failure, and complicated extraction procedures. The subcutaneous pulse generator and electrode are placed extrathoracically, without the need for fluoroscopic guidance.
The company contends that this design spares the risks associated with an intravascular location or mechanical stresses caused by cardiac contractions. The authors noted, however, that "avoiding the intravascular space has its own limitations because the first-generation S-ICD lacks the ability to provide antitachycardia pacing, advanced diagnostics, or radiofrequency interrogation with remote monitoring."
As such, they said, the device should be considered as an add-on to other "tools available to combat sudden death."
The multicenter study examined the device’s efficacy and safety for the treatment of ventricular tachycardia/fibrillation (VT/VF) in a cohort of 314 patients. Of these, 276 (88%) had more than 180 days of follow-up; there were three deaths.
The patients had a mean of age of 52 years, and most (74%) were male. Most implantations (79%) were for primary prevention indications. The patients’ mean baseline ejection fraction was 36%. Congestive heart failure was the most common pathology (61%); others included hypertension (58%), prior myocardial infarction (41%), and atrial fibrillation (15%). Thirteen percent had previously had a transvenous ICD that was extracted because of infection, vascular injury/clot, or device/lead failure.
By 180 days, there were no device-related complications in almost all patients (99%). There were no lead failures, cases of endocarditis or bacteria, cardiac tamponade or perforation, pneumothorax or hemothorax, or subclavian vein occlusion (Circulation 2013;128:944-53 [doi:10.1161/CIRCULATIONAHA.113.0]).
Eight patients died during the study. Five were noncardiac, nonsudden, and not related to device implantation. Two patients died unwitnessed. Of these, interrogation showed successful treatment of a single arrhythmic interval. The other device was not interrogated because the patient wasn’t immediately discovered, but this patient had been diagnosed with atypical pneumonia and hypoxia before he died. The last death occurred outside the United States and there was no additional information available.
In 304 patients who completed the full testing protocol, there was a 100% conversion rate of spontaneous VT/VF episodes. Acute conversion of VF was successful after one or two shocks in 265 of these patients. Seventeen patients were unevaluable because of clinical issues that precluded testing; when these 17 patients were imputed as clinical failures, the efficacy rate dropped to 95%.
Among 21 patients, there were 119 spontaneous VT/VF episodes, 38 of which were discrete and the rest of which occurred during VT/VF storms. Among the 38 discrete episodes, the devices delivered 43 appropriate shocks, all of which were successful in resolving the arrhythmias. Most (35) converted after the first shock; two more required more than one shock. One episode of monomorphic VT did not convert with shocking but did spontaneously terminate while the device was recharging.
Inappropriate shocks occurred in 25 patients, all caused by oversensing. Of these, 22 had oversensed T waves or broad QRS complexes and three experienced oversensing due to external noise while working with electrical equipment. Most of the patients (32) were treated noninvasively with system reprogramming or medication changes.
A programming change resulted in a 56% relative reduction of inappropriate shocks caused by oversensing and a 70% relative reduction in shocks caused by supraventricular tachycardia.
Nine patients had an invasive procedure to deal with the problem: two of these had the device removed, two had it turned off, one had the electrode repositioned, and one pulse generator was repositioned. There was one Maze surgery, one ablation, and one electrophysiology study without ablation.
Dr. Weiss and his colleagues noted that the follow-up time in the study was relatively short – not long enough to account for the possibility of progression of conduction disease, which could happen in unknown degrees over time, depending on the patient and the substrate.