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 >16mV, baseline QTc and the sum of amplitudes of the R waves at supine >30mV 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.