ECG predictors of T wave oversensing in subcutaneous implantable cardioverter defibrillators.

Background: T wave oversensing (TWOS) is the commonest cause of inappropriate shocks in subcutaneous implantable cardioverter defibrillators (S-ICDs). We hypothesise that predictors of TWOS can be derived from surface ECG parameters.

Methods: In a cohort of SICD recipients in two UK centres, all patients who had TWOS (study group) were compared to all those who had not (control group). The pre-implant screen was scanned and the R wave, T wave amplitudes, QRS interval, time to peak T wave, QT interval and R:T ratio was measured using digital callipers. Logistic regression was performed to identify ECG predictors of TWOS.

Results: One hundred one patients were studied. Six (5.9%) had TWOS. The mean age of the population was 58.6±18years and the median follow-up was 19.5months. By univariate analysis, the predictors of TWOS are QRS duration (140.7±28.7 vs. 105.9±24.6, P=0.007), time to peak T wave (corrected for heart rate, pTc) (403.9±22.6 vs. 347.8±41.4, P=0.006), QTc interval (500.4±41.2 vs. 446.8±49.7, P=0.021), and R:T ratio (3.5±1.1 vs. 9.5±13.2, P=0.034). By multivariate analysis, time to pTc is the most predictive of TWOS. A time to pTc of 390ms cut-off point provided a sensitivity 38.5%, a specificity of 98.9%, a positive predictive value for TWOS of 83.3%, and a negative predictive value of 91.6% (AUC=0.687).

Conclusion: In this study, time to pTc is the most powerful ECG predictor of TWOS.