Marked differences in ICD therapy frequencies between phenotypes

Abstract Background Implantable cardioverter defibrillators (ICD) are implanted due to a broad range of cardiac conditions according to guidelines. Purpose The aim of this study was to compare the distribution of ICD therapies across different cardiac diseases. Methods In this descriptive study, we included patients from Eastern Denmark with an ICD implanted up until November 2021. Data was obtained from the national ICD registry and the diagnosis leading to implantation of the ICD was registered. ICD interrogations and number of episodes of appropriate ICD therapies (shock/anti-tachycardia pacing (ATP)) were obtained. End of follow-up was November 8, 2021 or date of death or heart transplantation. Cumulated numbers of therapies were calculated for each patient during the follow-up period (shock/ATP therapies per 1,000 patients per year). Results Data on 3,068 patients (median (IQR) age at implantation 65 years (56-72)) across 10 cardiac disorders was obtained (Figure). A total of 1,403 patients had the ICD implanted as primary prophylaxis and 1,554 as secondary prophylaxis and in 111 patients it was unclear. Mean follow-up time of 595 years per diagnostic subgroup (210-12,911 years). The median (IQR) shock/ATP rate per 1,000 patients per year was 1.47 (0.70-2.62). The numerically highest shock/ATP rate of 28.9 therapies per 1,000 patients per year was seen in patients with arrhythmogenic right ventricle cardiomyopathy and the lowest shock/ATP rate of 0.05 therapies per 1,000 patients per year was seen in patients with ischemic heart disease. In patients with ischemic heart disease, the shock/ATP rate per year was 0.06 in patients with an ICD implanted as primary prophylactic and 0.15 in patients with an ICD as secondary prophylactic. Conclusion The frequency of ICD shock/ATP therapy varies several-fold between cardiac disorders, with the highest rate in patient with arrhythmogenic right ventricle cardiomyopathy and the lowest rate in the major group of patients, i.e. patients with ischemic heart disease. These findings may indicate a need for adjustments of patient selection for ICD implantation.