Subcutaneous implantable cardioverter defibrillator insertion for preventing sudden cardiac death

5.1 Death was reported in 1% (2/140) of patients in the subcutaneous implantable cardioverter defibrillators (ICD) group (1 from a non-cardiac cause and 1 from a cardiac cause) and in 4% (6/140) of patients in the transvenous ICD group (3 from non-cardiac causes, 2 from cardiac causes and 1 for an unknown reason) in a retrospective propensity-matched cohort study of 280 patients with a 5‑year follow-up. Death from congestive heart failure was reported in 1 patient in the subcutaneous ICD group in a matched-controlled study of 138 patients comparing 69 patients with subcutaneous ICDs and 69 matched patients with transvenous ICDs (average follow-up 217 days). All-cause mortality rate was 3% (26/882) in a case series of 889 patients with a mean 22‑month follow-up that combined patients from a prospective case series and from an international registry (Effortless). There was only 1 known arrhythmic death due to Loeffler's syndrome. The 3‑year Kaplan–Meier estimate was 5% (95% confidence interval [CI] 1 to 9%), with 26 deaths (3%). Death was reported in 5% (48/985) of patients in an international registry of 985 patients, within a 3.1‑year follow-up. The primary cause was cardiac-related in 44% (21/48) of these patients: 1 was arrhythmic and the other deaths related to pump failure (14 deaths), ischaemic events (2 deaths) or other cardiac causes (4 deaths), and 98% (47/48) of deaths occurred outside the perioperative window of 30 days. No deaths were associated with the subcutaneous ICD system procedure.

5.2 Inappropriate shock rate was 21% in the subcutaneous ICD group (17% because of oversensing and 4% because of supraventricular tachycardia) compared with 19% in the transvenous ICD group (1% because of oversensing and 18% because of supraventricular tachycardia) in the retrospective propensity-matched cohort study of 280 patients. In the same study, inappropriate sensing rate was 3% in the subcutaneous ICD group and zero in the transvenous ICD group. The estimated 3‑year inappropriate shock rate was 13% in the case series of 889 patients. The causes were T‑wave oversensing in 39%, supraventricular arrhythmia above the discrimination zone in 24%, low amplitude signal in 21%, non-cardiac oversensing in 8%, oversensing of ventricular tachycardia and fibrillation below the rate zone in 4%, other or combined types of cardiac oversensing in 2%, supraventricular arrhythmia discrimination errors in 1%, and committed shock for ventricular tachycardia and fibrillation in 1%. Inappropriate shocks were reported in 8% (15/985) of patients during the first year and in 12% (115/985) of patients within a mean 3.1‑year follow-up in the international registry of 985 patients (some of these patients were also included in the case series of 889 patients). The causes were oversensing in 11 of the patients and supraventricular tachycardia above the discrimination zone (normal device function) in 2 of the patients (no cause reported for the other 2 patients). Inappropriate shocks were reported in 4% of patients (range 0 to 15%) in the systematic review of 5,380 patients. The most common cause was T‑wave oversensing. Inappropriate therapy due to supraventricular tachycardia, and artefact from noise or myopotentials were rare.

5.3 Pulse generator replacement due to battery depletion did not differ between the groups at 5‑year follow-up in the retrospective propensity-matched cohort study of 280 patients (p=0.18). Premature battery depletion was reported in 5 patients in the case series of 889 patients. Rapid battery depletion causing premature elective replacement of the device was reported in 9% (5/55) of devices, with a mean service time of 1.5 years, in a case series of 55 patients; 71% of devices were still in service at 5‑year follow-up. Premature battery depletion was reported in 1% of patients (range 0 to 9%, 16 events, 1,384 patients from 10 studies) in the systematic review of 5,380 patients.

5.4 Failure to communicate with the device was reported in less than 1% of patients (range 0 to 1%, 4 events, 1,249 patients from 8 studies) in the systematic review of 5,380 patients.

5.5 Twiddler syndrome rate was 1% in both groups in the retrospective propensity-matched cohort study of 280 patients.

5.6 Device failure rate was 1% in the subcutaneous ICD group and none in the transvenous ICD group in the retrospective propensity-matched cohort study of 280 patients. Failure of the device to convert during the procedure was reported in 7 patients in the US registry of 1,637 patients. Failure of the device to cardiovert ventricular arrhythmia was reported in 1 patient out of 69 patients in a propensity-matched case-control study of 138 patients within a mean 31‑month follow-up.

5.7 Explantation of the subcutaneous ICD for pacing was reported in 4 patients because of the need for ventricular pacing in the case series of 889 patients: 1 patient developed a new bradycardia indication; in 1 patient, the device was explanted because of the need for anti-tachycardia pacing; and 1 patient with 3 ventricular tachycardia storm events had replacement with a transvenous ICD in an attempt to suppress ventricular arrhythmias using overdrive pacing. In addition, 1 device was extracted for a cardiac resynchronisation therapy upgrade. Device replacement was reported in 47% (26/55) of patients and device explantation (permanent removal) was reported in 9% (5/55) of patients during a median 5.8‑year follow-up in the case series of 55 patients. The indications for device replacement or explantation were battery depletion in 81% (25/31) of patients, replacement with a transvenous ICD system in 13% (4/31), infection in 1 patient and 'other' in 1 patient. The median time for device replacement was 5 years (first quartile–third quartile, 4.4 to 5.6 years) and the event-free rates for device replacement were 94% (95% CI 83 to 98%) after 2 years, 89% (95% CI 76 to 96%) after 4 years and 30% (95% CI 15 to 46%) after 6 years. Device explantation was reported in 4% of patients (range 0 to 12%, 57 events, 1,514 patients from 11 studies) in the systematic review of 5,380 patients. The explant indications were pocket infection (2%, 29 events, 1,585 patients, number of studies not reported), need for pacing, inappropriate shocks and unsuccessful defibrillation threshold testing. Generator repositioning or explant for erosion were needed in 2% of patients (total number of patients not reported).

5.8 Erosion rate was 3% in the subcutaneous ICD group and 2% in the transvenous ICD group in the retrospective propensity-matched cohort study of 280 patients. Erosion was reported in 1% (11) of patients in the case series of 889 patients.

5.9 Infection needing device removal or revision was reported in 2% (14) of patients in the case series of 889 patients. In the same study, incision or superficial infection were reported in 3 patients. Pocket infection was reported in 3% of patients (range 0 to 19%, 44 events, 1,654 patients from 14 studies) in the systematic review of 5,380 patients.

5.10 Haematoma was reported in less than1% of patients (range 0 to 3%, 22 events, 5,044 patients from 10 studies) in the systematic review of 5,380 patients.

5.11 Delayed wound healing was reported in less than 1% of patients (range 0 to 19%, 7 events, 1,145 patients from 7 studies) in the systematic review of 5,380 patients.

5.12 Suboptimal electrode position was reported in 7 patients in the case series of 889 patients. In the same study, suboptimal pulse generator position was reported in 2 patients and, suboptimal pulse generator and electrode position were reported in 4 patients.

5.13 Electrode movement was reported in 5 patients in the case series of 889 patients. The lead complication rate was statistically significantly lower in the subcutaneous ICD group than in the transvenous ICD group in the retrospective propensity-matched cohort study of 280 patients (1% versus 12%; p=0.03). The only lead complication reported in the subcutaneous ICD group was lead movement, which occurred in 1 patient out of 140.

5.14 Pleural effusion was reported in 1 patient in the US registry of 1,637 patients.

5.15 Pneumothorax was reported in 1 patient in the US registry of 1,637 patients.

5.16 In addition to safety outcomes reported in the literature, specialist advisers are asked about anecdotal adverse events (events which they have heard about) and about theoretical adverse events (events which they think might possibly occur, even if they have never done so). For this procedure, specialist advisers listed the following anecdotal adverse event: discomfort around the device. They did not identify any theoretical adverse events.

5.17 Seven commentaries from patients who had experience of this procedure were received, which were discussed by the committee.