Electrocardiographic Eligibility for Subcutaneous Implantable Cardioverter Defibrillator: Evaluation during Bicycle Exercise

Background The subcutaneous implantable cardioverter-defibrillator (S-ICD) is used in patients at risk of sudden death. Our aim was to assess clinical predictors of electrocardiographic ineligibility for S-ICD, and the impact of exercise on S-ICD eligibility in an unselected series of patients requiring ICD therapy. Methods 102 patients at risk of sudden death were evaluated at rest and during exercise. Electrocardiograph screening using limb lead electrodes (to simulate the S-ICD sensing vectors) was performed at rest and during bicycle ergometer exercise. Results R wave amplitude in lead D3 during exercise >16 mV, baseline QTc and the sum of amplitudes of the R waves at supine >30 mV were predictors of ineligibility for S-ICD. Eligibility increased from 90% to 100% of patients when evaluated with an “any of the three leads” criterion compared to current recommendations. A more restrictive criterion based on two of three ECG leads caused an eligibility drop at 66%, that further decreased to 56% during exercise; these figures improved to 79% and 81%, respectively, when an “any 2 of 3 leads” criterion was used. Conclusions Huge ECG amplitude and QTc duration are associated with ineligibility in the current S-ICD release. By performing exercise testing, lead suitability changes in one patient out of 14 (7% of tested patients) and eligibility is decreased by use of a more stringent criterion for eligibility (ECG criteria satisfied in two of three leads). A dynamic selection of sensing vectors aiming at situation-specific suitability (any of three leads) would increase S-ICD eligibility to 100% of patients.