Medtronic's External ICD Meets Safety, Efficacy Endpoints in Pivotal Trial

Paul Friedman, MD

Results of a single-group, premarket clinical study suggest a major advance in implantable cardioverter-defibrillators (ICD) could be on the horizon.

Sponsored by Medtronic, results of the study, which were presented at the European Society of Cardiology (ESC) Congress 2022, provide insight into the use of an external ICD system, including the proportion of event-free patients at 6 months and lack of intraprocedural complications observed with the system.

"This study is encouraging. By placing the lead in this new position behind the sternum, the uncommon but serious risks associated with transvenous ICDs, such as lung collapse, damage to heart valves and heart perforation, can be avoided. Limitations of the subcutaneous ICD are also overcome. Since the lead is behind the sternum and close to the heart, pacing can be delivered, and defibrillation requires less energy with a longer battery life than with the subcutaneous ICD," said lead investigator Paul Friedman, MD, a cardiac electrophysiologist, in a statement.

After a 3-month pilot study examining use of an extravascular ICD demonstrated safety and efficacy of the device, the current study was conducted with the intent of examining the extravascular ICD . Named the global Extravascular ICD Pivotal Study, the current study was designed as a prospective, global, multicenter, single-group, nonrandomized, premarket approval study with the aim of enrolling up to 400 patients with a class I or II indication for an ICD for primary tr secondary prevention at up to 60 sites.

The primary efficacy outcome of interest for the trial was successful defibrillation at implantation, which was defined as the termination of an induced sustain shockable ventricular arrhythmia either with one 20-j shock or with 30 J on 2 consecutive episodes. The primary safety outcome of interest was freedom from major system- or procedure-related complications at 6 months. Investigators determined their efficacy objective would be met if the lower boundary of the one-sided 97.5% CI for percentage of patients with successful defibrillation was greater than 88%. For the safety objective, investigators determined the safety objective would be met if the lower boundary of the one-sided 97.5% confidence interval for the percentage of patients free from such complications was greater than 79%.

From September 2019-October 2021, a total of 356 patients from 46 centers in 17 countries were enrolled in the trial. A total of 316 underwent an implantation attempt. This cohort had a mean age of 53.8±13.1 years, 25.3% were female, the mean BMI was 28.0±5.6 kg/m2, and the mean left ventricular ejection fraction was 38.9±15.4%. Of the 316 who underwent an implantation attempt, the lead was placed successfully in 315 patients and a total of 307 patients underwent defibrillation testing. Regarding the implantation procedure, investigators pointed out implantation was performed by a total of 45 physicians. For these procures, the median time from first incision to final lead position was 35.5 minutes (IQR, 25 to 50), and the median time from first incision to final suture, inclusive of defibrillation testing, was 66 minutes (IQR, 50 to 93).

Upon analysis, the percentage of patients with successful defibrillation was 98.7% (lower boundary of the one-sided 97.5% CI, 96.6%; P <.001 for the comparison with the performance goal of 88%) and 94.6% were discharged with a working ICD system. Kaplan-Meier estimate of the percentage of patients free from major system- or procedure-related complications at 6 months was 92.6% (lower boundary of the one-sided 97.5% CI, 89.0%; P <.001 for the comparison with the performance goal of 79%). Investigators pointed out there were no major intraprocedural complications were reported.

In the 6-month analysis, 25 major complications were observed in among 23 of the 316 patients included in the trial. Investigators pointed out the success rate of antitachycardia pacing, which was assessed with generalized estimating equations, was 50.8% (95% CI, 23.3 to 77.8). Investigators noted a total of 29 patients received 118 inappropriate shocks for 81 arrhythmic episodes and 8 systems were explanted without extravascular ICD replacement during the follow-up period, which lasted a mean of 10.6 months.

"While encouraging, these results reflect an early experience, and there is more to be learned with longer follow-up and greater usage," Friedman added, in the aforementioned statement. "The rates of inappropriate shock are higher than with current devices but similar or lower than the early experience with other types of defibrillators, and steps have already been taken to lower it. Additionally, this new device is not for everyone. Patients with previous open-heart surgery were excluded from the study and would not be candidates for this treatment at present."

This study, “Efficacy and Safety of an Extravascular Implantable Cardioverter–Defibrillator,” was published in the New England Journal of Medicine.