Reed Miller

June 18, 2012

June 15, 2012 (Nice, France) — Rates of inappropriate shocks as well as other serious complications with a subcutaneous implantable cardioverter defibrillator (S-ICD) (Cameron Health/Boston Scientific) appear to be declining as electrophysiologists in Europe gain more experience with the device, data from the EFFORTLESS registry show [1].

"The S-ICD system is emerging as a feasible and promising alternative to conventional ICD therapy in patients without a need for antitachycardia pacing, including patients with both primary and secondary prevention for a variety of indications," Dr Lucas Boersma (St Antonius Hospital, Nieuwegein, the Netherlands) said during a presentation of the latest EFFORTLESS registry data here at Cardiostim 2012. EFFORTLESS has been collecting data on the "real-world" experience with the S-ICD in Europe since the device received a CE Mark two years ago and is planned for 1000 patients. "EFFORTLESS is ongoing and will be the key to understanding the real-world implant behavior in a wide variety of patients," Boersma said.

The rate of inappropriate shocks in EFFORTLESS is about 7%, and these were clustered in patients who received the device in the early months of the study, Boersma said. This rate is about 50% less than the rate seen in the 330-patient, 33-center investigational device exemption (IDE) trial that earned the device a favorable review from an FDA advisory panel in April. In EFFORTLESS, there have been no inappropriate shocks for AF or supraventricular tachycardia in patients with a device that has been programmed with both a shock zone based on rate and a conditional shock zone with additional rhythm discriminators that determine whether the device should deliver therapy. "That is a very important tool to prevent inappropriate shocks," Boersma said.

In the same session, one of the investigators for the IDE study [2], Dr Michael Gold (Medical University of South Carolina, Charleston), pointed out that in early experience with the S-ICD, many physicians were not using this dual zone programming, and therefore the device was "oversensing" by about 50% and delivering many inappropriate shocks. But electrophysiologists who program the device with this feature will find the rates of inappropriate shock rate "will be vanishingly low," Gold said.

In a different session at Cardiostim [3], Dr Gust Bardy (University of Washington, Seattle), who is credited with inventing the S-ICD, explained that unlike ICDs with transvenous leads that detect individual heart beats, "the S-ICD behaves more like an AED. It is a rhythm detector, not a beat detector." The S-ICD "validates and certifies" a detected rhythm with "noise discrimination" before deciding whether or not to deliver a shock.

Bardy also pointed out that many of the inappropriate shocks delivered by the S-ICD in the early days of clinical experience with the device were the result of physicians "cheating" on important parts of preimplant ECG screening. The device comes with a simple plastic template that the physician puts over a surface ECG to make sure the QRS and T waves fall within the appropriate range for successful therapy with this device. "If they do, the device almost never has trouble. If you cheat and try to sneak a patient in that doesn't pass this test, you'll have false-positive shocks," Bardy said.

EFFORTLESS Data Show "Real-World" Matches Trials

So far, all of the EFFORTLESS data are from the UK and the Netherlands, but more countries are being added. The average age of the patients in the registry is 49, and the study includes patients indicated for an ICD for cardiomyopathies as well as channelopathies.

Unlike the IDE trial, EFFORTLESS includes pediatric patients and patients with renal disease. EFFORTLESS also requires specific implant testing that was not part of the IDE protocol: two successful conversions at 65 J. In the IDE trial, 79% of the patients were getting an ICD for primary prevention of sudden cardiac death and 61% had congestive heart failure. In EFFORTLESS, 65% of the patients are getting the device for primary prevention and only 29% have congestive heart failure. Boersma attributed this difference to the increasing acceptance of the device among people who have already had a life-threatening arrhythmia. "Even people with a secondary-prevention indication are amenable to this therapy because people have become used to the [S-ICD] and trust that it will work," he said.

So far, the registry has implant test data from 219 patients, and the device worked on the first test try in 216 patients. In the registry, there have been 19 discrete ventricular tachycardia (VT) or ventricular fibrillation (VF) episodes in a total of 14 patients. As in the IDE study, the rate of successful spontaneous conversion of VT or VF is 100%. Two of the episodes were converted late after a single shock, and there were three episodes that needed multiple shocks for successful conversion. Two patients had VT storm, but all were successfully treated.

The infection rates in the CE Mark trial and the earlier Dutch registry were 3.6% and 7.6%, respectively. In the IDE study, there were four system infections requiring explants and 14 incisional/superficial infections not requiring explants, a rate the company claimed was competitive with that of standard transvenous-lead ICDs. EFFORTLESS suggests that the infection rate can be driven even lower with S-ICDs, as there were only six infections (2.5%) in the registry, an improvement Boersma attributed to physicians' learning curve with the device. One patient had to have the electrode removed, and the whole system was explanted from six patients. Of these, a new S-ICD was later implanted in three patients. Overall, the device-related complication rate was 2.2% and the procedure-related complication rate was 12.2%.

Slower Response? Not a Problem

During the meeting in which they voted to recommend that the FDA approve the S-ICD, some of the agency's advisors said they were concerned that the S-ICD's arrhythmia-detection and diagnosis algorithms work too slowly. In the IDE trial, the device never failed to save the patient's life, but it responded within 18 seconds in only 88% of events, suggesting it responds more slowly to arrhythmias than standard ICDs.

But faster isn't necessarily better, according to Dr Derek Exner (University of Calgary, AB), who is not involved in the S-ICD's development. After one of the sessions at Cardiostim devoted to subcutaneous-lead ICDs, Exner told heartwire that he believes that electrophysiologists are beginning to finally learn that the appropriateness of the ICD's response is far more important than the speed of that response. "If this study [of the S-ICD] were presented five years ago, everyone would say, 'We'd never program our devices that way; this is going to kill people,' but now we're seeing that we're treating a lot of patients who don't need to be treated and getting these huge rates of inappropriate therapy, and now the mindset has switched and says that longer is better. These data fit in nicely with that," he said.

"[Studies show that] if AED therapy can be administered within three minutes, the success rate is extremely high. So we know that three minutes is relatively safe," he said. "It was just a few years ago that everyone was all about really short detection times . . . [but] there has been a complete paradigm shift."

The session featuring Gold's and Boersma's presentations was sponsored by an educational grant from Cameron Health.

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