Reassessing Risk Factors for High Defibrillation Threshold: The EF-SAGA Risk Score and Implications for Device Testing.

OBJECTIVES: To reevaluate risk factors for high defibrillation threshold (DFT) and propose a risk assessment tool. BACKGROUND: Controversy exists over routine DFT testing during implantable cardioverter defibrillator (ICD) placement. METHODS: We retrospectively analyzed 1,642 consecutive patients who received an ICD and underwent DFT testing. RESULTS: The incidence of high DFT requiring addition of a subcutaneous array was 2.3%. Five significant independent variables predictive of high DFT were identified, including younger age, male gender (hazard ratio 1.99), left ventricular (LV) dysfunction, secondary prevention (hazard ratio 2.33), and amiodarone use (hazard ratio 2.39). Each 10-year increase in age was indicative of a 0.35-times lower chance of high DFT. Each 10% increase of LV ejection fraction (EF) was indicative of a 0.52-times lower chance of high DFT. These five variables form the EF-SAGA risk score (LVEF < 20%, Secondary prevention ICD indication, Age < 60 years, male Gender, Amiodarone use). Cumulative risk of high DFT increased incrementally; patients with four or more variables had an 8.9% likelihood of high DFT. Importantly, primary prevention patients with LVEF > 20% had a negative predictive value for high DFT of 99.3%. CONCLUSION: We identified five independent predictors of high DFT. We propose the EF-SAGA risk score to help decision making. Primary prevention patients with an LVEF > 20% had an exceedingly low incidence of high DFT suggesting that testing could be avoided in these patients. Careful assessment of the risk-benefit ratio of testing is important in high-risk patients.

Intercostal muscle twitching from right ventricular apical pacing.

A patient with a dilated cardiomyopathy underwent successful implantation of a cardiac resynchronization therapy defibrillator. The device system included an active fixation lead placed at the right ventricular (RV) apex. Pacing from the RV apex unexpectedly led to left-sided intercostal muscle stimulation and twitching. This intercostal muscle twitching resolved completely with movement of the lead to the RV outflow tract.