The subcutaneous implantable cardioverter defibrillator (S-ICD) has been considered as a comparable alternative to transvenous ICD in a wide array of patients (pts) without pacing indication. Recent data have reported high rates of inappropriate (inap) therapies with S-ICD, mostly due to T wave or noise oversensing.

Our aim was to assess the predictive factors of inap therapies over a mid-term follow-up (FU) period after SICD implantation.

All pts implanted with an S-ICD and a FU above 6 months were included in a cross-sectional monocentric study. Data from preoperative screening with a thorough ECG study (amplitude of QRS complex, T wave and QRS:T ratio in leads I, II and III) has been collected. Pts were followed by remote monitoring.

One hundred and twenty-four pts (50±14 years old, male 84%) were included. Indications were: primary 73% and secondary prevention 27% (ischemic cardiopathy 39%; hypertrophic 8%; dilated 36%; channelopathy 2%). During a mean FU of 25±16 months, 29 pts (23%) experienced at least one therapy: 15 pts with appropriate (12%) and 15 pts with inap shocks (12%). A total of 22 inap shocks have been observed after a mean FU period of 15±18 months (1.5±1 inap shock per pt, several shocks for 4 pts). Causes were: supraventricular arrhythmias (33%), T wave (20%) and noise (53%) oversensing. The number of eligible vectors during preoperative screening was correlated with the occurrence of inap shocks (−0.23; P<0.05). ECG criteria measured in lead I were significantly correlated with inap therapies: QRS and T wave amplitude, respectively −0.23 and 0.3 (P<0.01), and the QRS:T ratio in lead I (−0.34; P<0.01). Of note, the untreated events related to T wave or noise oversensing during the FU were correlated with inap shocks (0.32; P<0.01) (Fig. 1).

Inap therapies remain frequent with S-ICD. Preoperative screening (number of eligible vectors) and ECG data may be taken into consideration to identify patients at high risk for inap shocks.