Remote monitoring and inappropriate therapies in ICD patients: The THORN registry

Background Inappropriate shocks (IS) are a major side effect of implantable cardioverter defibrillators (ICD). Remote monitoring (RM) may reduce inappropriate diagnoses (ID) and subsequent inappropriate therapies (IT). Purpose The purpose of THORN study was to determine the ability of ICD RM to early identify ID of ventricular arrhythmias and prompt physician reaction, in order to reduce the risk of recurrent IT. Methods THORN is an observational multicenter study of RM ICD patients, separated in a retrospective cohort (R), issued from a large RM database collected since 2007 by Biotronik SE & Co.KG and a prospective cohort (P) of patients implanted since 2012. The primary objective was to determine: 1/in the retrospective cohort, the relative proportion of patients experiencing at least one IT during a 15-month follow-up period, and, 2/in the prospective cohort, the medical reaction time (MRT) and ID recurrence after an initial ID. Results A total of 1891 patients (R: 1379, P: 512), implanted with a CRT-D (28.1%) or conventional ICD, (single chamber: 45.1%; dual chamber: 26.8%) were enrolled (83.6% men, 62.9 ± 12.8 y), 31.8% in primary prevention. During 13.7 ± 3.5 months of follow-up, 8.6% (R: 9.2%, P: 6.9%, P = 0.05) of the patients experienced at least one ID, of whom, 75.3% suffered at least one IT (R: 74%, P: 80%, P = NS) and 35.8% at least one IS. The median MRT was 9 days (0 to 145 days). It was 4 times longer for ID due to supraventricular tachyarrhythmias (16 days) compared to those due to abnormal sensing (4 days) (P = 0.04). ID recurrence occurred in 37% of ID patients, with a substantial part (25.7%) within the MRT. Among the 6.5% of patients experiencing at least one IT, 36.1% had an IT recurrence. Conclusions The rate of patients experiencing ID/IT and recurrences seems to decrease over time. Though RM is intended to take action earlier, the MRT is sometimes long and could be reduced as ID/IT recurrences are not infrequent within the MRT period.