Lead author Martin Burke, University of Chicago Hospitals, USA, presented a study at HeartRhythm 2012 that showed the subcutaneous implantable cardioverter defibrillator (S-ICD) to be an effective treatment for patients with ventricular tachyarrhythmias.
Burke explained that the new device “senses, detects, and treats malignant ventricular tachycardias from a completely subcutaneous system.” He said that the non-randomised, multicentre study had two primary endpoints. The first was the rate of acute ventricular fibrillation conversion (two consecutive successes out of four attempts at 65 joules, with a performance goal of 88%) and the second primary endpoint was the 180-day complication-free rate after the S-ICD was implanted (with a performance goal of 79%). Patient criteria for the study included age ≥18 years, meeting guidelines for ICD implantation or replacement of an existing ICD, and having an appropriate pre-operative ECG. Key exclusion criteria included having prior ventricular tachycardia that was reliably terminated with anti-tachycardia pacing, having existing epicardial patches or subcutaneous array, having a unipolar pacemaker, or having severe renal dysfunction.
Of the 330 patients enrolled in the study, 321 were implanted with the device. Burke said: “The implant was very successful. Ninety-five per cent of patients were implanted using only anatomical landmarks-no medical imaging was used at all. No electrode or pulse generator movement was seen in 99% of implanted patients throughout the follow-up period.”
Burke reported that acute ventricular fibrillation conversion was successful in 100% of the 304 patients who completed the testing protocol (95% of those who received the device). He said: “That is well above the predicted 88%” and added that in a sensitivity analysis that included some of the patients who did not complete the testing protocol (providing a cohort of 315 patients), the conversion rate was 96%. Also, according to the results of the study, unnecessary therapy was avoided due to the sensing algorithm in 63% of patients who spontaneously terminated ventricular tachycardia/ventricular fibrillation rhythms after “meeting criteria to charge without any reports of syncope.”
The study’s safety endpoint was also met. Burke explained: “The 180-day, type one, complication free rate was 99%. Type one complications were defined as device-related complications that required invasive action.” He added that the 180-day device, labelling and procedure-related complication free rate was 92.1%, still beating the performance goal of 79%. Burke said that there were 18 “suspected or confirmed” infections during the follow-up period and most of these were superficial or incisional infections that could be managed with antibiotics and local care. However, four infections did require the S-ICD to be explanted, which Burke commented was “consistent with recent transvenous trials”. Furthermore the rate of inappropriate shocks (38 patients received a shock not related to a ventricular tachycardia or ventricular fibrillation event) were also consistent with that seen in transvenous ICD trials.
Concluding his presentation, Burke said that acute ventricular fibrillation conversion testing was “exceptionally successful” and chronic conversion testing was consistent with acute endpoint data. He added: “This has been an exciting study. The most interesting thing that I can tell you is that 13% of patients actually had a prior transvenous ICDs system and 10% of them had prior transvenous infections. When they were consulted about having a transvenous system or an S-ICD system, which is no small feat for a patient to have a new system, they always chose the S-ICD system.”