Risk of ventricular tachyarrhythmias following improvement of left ventricular ejection fraction in patients with implantable cardiac defibrillators implanted for primary prevention of sudden cardiac death

Purpose: In patients who undergo implantable cardiac defibrillator (ICD) implantation for primary prevention of sudden cardiac death (SCD), data is unclear whether their ICD generator needs to be replaced at end of life if their left ventricular ejection fraction (EF) improves. Despite improvement in EF, the underlying scar may represent a potential substrate for ventricular arrhythmias. Methods: Data on 280 patients who underwent ICD implantation for primary prevention of SCD was obtained from two centers. Patients were followed for any improvement in EF to ≥35%. All arrhythmic events during follow-up, including appropriate and inappropriate shocks/ATP, were recorded. Results: Thirty percent (n = 86/280) of patients improved their EF to >35% of which 41% (n = 37) underwent a generator change by the study ending period with the rest not yet at ERI. Mean baseline EF in patients with and without target EF improvement was 26 ± 7 and 23 ± 7% (p = 0.2). After excluding patients whose arrhythmic events data were unavailable, the final sample consisted of 62 patients in the EF improvement group and 156 patients in the group without EF improvement. In the group with EF improvement, appropriate events (shock + ATP) were noted in 19% of patients (n = 12/62) and inappropriate shocks and ATP in 6% of (n = 4/62) patients after their EF improved to >35%. Four patients received appropriate therapies when their EF was low prior to improvement. In contrast, in patients who had no improvement in EF, 27% (n = 43/156) received an appropriate therapy (p = 0.6) while 11% (n = 18/156) (p = 0.2) received inappropriate shocks and ATP. All-cause mortality was higher in patients without subsequent improvement in EF versus those with EF improvement (31 vs. 15% (p =.005). Conclusions: There was no significant difference in the number of appropriate therapies received by each group. Patients continue to be at high risk for sudden cardiac death despite improvement in EF.