Chronic follow-up from the pilot study of a novel substernal extravascular implantable cardioverter-defibrillator

Abstract

Background The investigational Extravascular Implantable Cardioverter Defibrillator (EV ICD) is an implantable defibrillator with defibrillation and pacing therapies, including the potential for antitachycardia pacing (ATP). Purpose To characterize chronic EV ICD system performance through 12 months of follow-up. Methods The first-in-human EV ICD Pilot study was prospectively conducted at four centers in Australia and New Zealand. Patients with Class I or IIa indications for ICD were enrolled between July and December of 2018. A defibrillation lead was inserted into the substernal space under radiologic guidance and a device was positioned close to the left midaxillary line. Figure 1 illustrates the implanted EV ICD. Defibrillation testing was conducted at implant and chronically in 5 patients. Follow-ups were conducted at pre-hospital discharge, 2 weeks, 4–6 weeks and 3 months post-implant, and every 6 months thereafter. Results A total of 26 patients were enrolled and 21 underwent the EV ICD implant procedure with no intraprocedural complications. Median energy for defibrillation at implant was 15 J; mean R-wave amplitude was 3.4±2.0 mV; mean pacing capture threshold was 5.1±2.0 volts. Seventeen of 21 implanted patients entered into chronic follow-up after successful system placement and implant testing, and 14 patients continue to be followed, representing >180 patient-months of total follow-up. Multiple episodes of spontaneous ventricular tachycardia (VT) were detected in one patient and either self-terminated or successfully cardioverted following unsuccessful ATP. One patient received an inappropriate shock secondary to lead tip displacement with subsequent P-wave oversensing. Elective chronic defibrillation testing was performed at physician discretion and converted 5 of 5 patients with ≤40 J (maximum energy of device). Three patients had the system electively removed due to 1) inappropriate shock after lead displacement, 2) recurrent VT without ATP termination, and 3) inadequate chronic safety margin for defibrillation. Conclusions The EV ICD is a novel platform for delivering high voltage therapy. Chronic system performance has generally remained stable during 12 months of follow-up and the device has demonstrated the ability to detect and treat VT. Fluoro images of implanted system Funding Acknowledgement Type of funding source: Private company. Main funding source(s): Medtronic plc

The development of the extravascular defibrillator with substernal lead placement: A new Frontier for device‐based treatment of sudden cardiac arrest

“…Fluoroscopic guidance and medical judgment were used to center the lead over the right ventricular cardiac silhouette, and the device was placed in a left midaxillary tissue pocket. Induced ventricular arrhythmias were terminated in 18 of 20 patients (90.0%) with ≥10‐J safety margin, consistent with prior clinical studies of existing ICDs, 36–38 and had a median lowest demonstrated energy for defibrillation of 15 J. Pacing capture was achieved in 19 of 20 patients (95%) at implant with a mean pacing threshold of 5.4 ± 2.2 V and remained stable over time, including 5.8 ± 1.8 V at 6 months and 4.9 ± 1.5 V at 12 months among patients tested in the supine posture 35,39 …”

“…Pacing output was subsequently increased and among four later episodes of VT, two self-terminated and two showed ATP reset without termination, requiring appropriate and successful shocks. 35,39 Mean R-wave amplitude in the ring-to-ring vector was 3.4 ± 2.0 mV at implant and remained stable over time (3.5 ± 2.0 mV at 6 months and 4.4 ± 2.2 mV at 12 months among patients evaluated in the supine posture). 35,39 Mean VF amplitude at implant was 2.8 ± 1.7 mV, and VF was detected at a sensitivity of ≥0.3 mV in all patients tested clinically (representing a two-fold safety margin over nominal).…”

“…35,39 Mean R-wave amplitude in the ring-to-ring vector was 3.4 ± 2.0 mV at implant and remained stable over time (3.5 ± 2.0 mV at 6 months and 4.4 ± 2.2 mV at 12 months among patients evaluated in the supine posture). 35,39 Mean VF amplitude at implant was 2.8 ± 1.7 mV, and VF was detected at a sensitivity of ≥0.3 mV in all patients tested clinically (representing a two-fold safety margin over nominal). 35 Postural effects on sensing performance were robustly evaluated.…”

“…In the first episode, intermittent pacing capture was observed; VT was terminated successfully with appropriate shock by the device. Pacing output was subsequently increased and among four later episodes of VT, two self‐terminated and two showed ATP reset without termination, requiring appropriate and successful shocks 35,39 …”

“…Induced ventricular arrhythmias were terminated in 18 of 20 patients (90.0%) with ≥10-J safety margin, consistent with prior clinical studies of existing ICDs, [36][37][38] and had a median lowest demonstrated energy for defibrillation of 15 J. Pacing capture was achieved in 19 of 20 patients (95%) at implant with a mean pacing threshold of 5.4 ± 2.2 V and remained stable over time, including 5.8 ± 1.8 V at 6 months and 4.9 ± 1.5 V at 12 months among patients tested in the supine posture. 35,39 One patient experienced five episodes of monomorphic VT outside the hospital setting, which were successfully detected and treated by the EV ICD system. In the first episode, intermittent pacing capture was observed; VT was terminated successfully with appropriate shock by the device.…”