Appropriate and Inappropriate Electrical Therapies Delivered by an Implantable Cardioverter-Defibrillator: Effect on Intracardiac Electrogram

Abstract

Local injury current (LIC) seen after induced ventricular fibrillation rescue implantable cardioverter-defibrillator (ICD) shock predicts heart failure progression. We sought to determine the frequency of LIC after spontaneous events in patients receiving ICD therapies. Near-field (NF) right ventricular (RV) EGM during 10 seconds after delivered ICD therapy was compared with baseline EGM in 420 events that occurred in 134 patients (mean age 60.8 ± 14.8, 106 [79%] male). The magnitude of elevated or depressed potential immediately after the major fast EGM deflection was defined as LIC, and its ratio to the peak-to-peak EGM amplitude was defined as relative LIC. LIC of at least 1 mV or relative LIC of at least 15% was considered significant. LIC was observed in 121 events (28.8%) and was detected more frequently after appropriate (43 [60.6%] events) and inappropriate (56 [64.4%] events) ICD shocks, as compared with appropriate (8 [9.2%] events) and inappropriate (3 [4.7%] events) antitachycardia pacing (ATP) or nonsustained ventricular tachycardia (11 [9.9%] events) [ANOVA P < 0.0001]. Type of ICD therapy (ICD shock vs ATP) was the most significant predictor of LIC (ATP β coefficient -0.81; 95%CI-1.19 to 0.44); P < 0.0001), along with cycle length of tachycardia (β coefficient -0.0117; 95%CI -0.0167 to -0.0068, P < 0.00001) and shock energy (β coefficient 0.024; 95%CI 0.003-0.045, P = 0.025). Appropriate and inappropriate ICD shocks are frequently characterized by the development of LIC in patients with structural heart disease. Type of electrical ICD therapy, shock energy and cycle length of ventricular arrhythmia are important determinants of LIC.