We examined the incidence of appropriate shocks in 91 consecutive patients with ICDs for primary prevention of sudden death who underwent generator replacement. Improved EF was?defined as both EF >35 % at generator replacement and increase in EF by ¡Ý10 % since original implantation. Patients were 70 ¡À 11 years old, and 76 % had ischemic cardiomyopathy. At generator replacement, 25 patients (27 % ) had improved EF (0.49 ¡À 0.08 vs 0.31 ¡À 0.07 at baseline; P < .0001). Over 6.2 ¡À 2.2 years of follow-up after original implantation, 9 patients (36 % ) with improved EF versus 19?(29 % ) with unchanged EF had appropriate ICD shocks (P?= .51). Incidence of appropriate ICD shocks was similar between the two groups before (P?= .90) and after (P?= .97) generator replacement. Of the 9?improved EF patients with appropriate shock, 4 had shocks before generator replacement, 2 had shocks before and after generator replacement, and 3 patients, who never had shocks before, had their first shock after generator replacement.
Some ICD patients whose EF improves to >35 % at generator replacement remain at risk for appropriate ICD shocks.