Subjects receiving the ICD for primary or secondary prevention experienced successful defibrillation in 98.7% of 316 implantation attempts, the lower limit of the confidence interval that allows the device to meet the performance target of 88% in detecting and terminating induced ventricular arrhythmias. Freedom from major system- or procedure-related complications was 92.6% at 6 months, and the device also met the safety goal of 79%, Ian Crozier, MB, ChB, of Christchurch Hospital in New Zealand, reported in European Society of Cardiology meeting (ESC). The results were published simultaneously in the New England Journal of Medicine. The extravascular ICD has a single lead implanted substernal so that the device can provide arrest prevention pacing and antitachycardia pacing without leads in the veins or the heart, unlike the conventional transvenous ICD. The extravascular device is also smaller than subcutaneous ICDs and delivers shocks with about half the energy. “Despite concerns or the perception that this may be a dangerous procedure,” there was no cardiac injury during implantation, no deaths from the procedure, and no unique complications not already seen with intravenous and subcutaneous ICDs, according to the Crozier. No cases of extravascular ICD-related mediastinitis, sepsis, or endocarditis were observed. However, there were four extravascular ICDs transplanted due to infection during a mean follow-up of 10.6 months, suggesting a risk similar to that seen with subcutaneous ICDs. In addition, there were 29 subjects who received 118 inappropriate shocks for 81 episodes of arrhythmia. “The incidence of inappropriate shock of 8.5% at 6 months exceeds that of current ICDs but is similar to that of early-generation transvenous and subcutaneous systems,” the authors noted. Their observation that P-wave hypersensitivity accounted for many of the inappropriate shocks in the study cohort led to new ICD programming recommendations and continued development of a specific P-wave algorithm to reduce these events, Crozier said. During the Q&A portion of the presentation, ESC participant Maged William, PhD, of Gosford Private Hospital in North Gosford, Australia, raised the issue of extracardiac stimulation and its potential discomfort for patients. Crozier acknowledged that there was patient awareness of pacing, which varied from mild to moderate with “some patients” experiencing greater sensations. The number of people with disability due to discomfort reached 5%, he said. The EV ICD was a follow-up to a 2019 pilot study that reported short-term safety and efficacy of the device. Crozier and colleagues conducted the present study at 46 participating sites in 17 countries with 356 subjects with a class I or IIa indication for primary or secondary ICD prevention. Exclusion criteria included evidence of chronic pacing including cardiac resynchronization therapy. Of those who signed up, 316 eventually went ahead with an implant attempt, which was performed by several dozen specialist implanters. The mean age was 53.8 and 25.3% were female. About four out of five people got the extravascular ICD for primary prevention. Almost half of the cohort had ischemic heart disease. Crozier reported that 302 device recipients completed the defibrillation trial protocol and were counted in the primary efficacy analysis. Extravascular ICD antitachycardia pacing, as assessed by generalized estimating equations, was 50.8% successful in terminating spontaneous arrhythmia episodes. No significant intraprocedural complications were reported. By 6 months, the rate of major complications reached 7.3%. There was one patient with a device software problem that required device replacement. The software was revised and the problem did not recur in other patients. There were two late lead fractures, one at 7 months and one at 11 months, attributed to sub-xiphisternum implantation and significant flexion contingencies. The study sponsor responded by changing the implant instructions. “Implantation of the extravascular ICD requires access to the substernal space, an anatomic location not traditionally accessed by cardiologists,” Crozier and colleagues wrote. “In our study, which included a dedicated training program and initial collaboration with a cardiac surgeon, implantation procedures were performed safely in electrophysiology laboratories, which supports both the importance of a comprehensive training program and the generalizability of the practice. The researchers acknowledged that there was no comparison group receiving intravenous and subcutaneous ICDs in the study. They also cautioned that the relatively young patient population may limit the generalizability of the study results to older, sicker patients.
Nicole Lou is a reporter for MedPage Today, where she covers cardiology news and other developments in medicine. Follow along
Revelations The study was supported by Medtronic. Crozier disclosed support and relationship with Medtronic.
