Introduction: Hypertrophic cardiomyopathy (HCM) is a heterogeneous disease associated with sudden cardiac death (SCD) mainly due to ventricular tachycardia (VT) or fibrillation even though life-threatening bradycardia occurs. Risk stratification takes several variables into consideration including non-sustained VT (NSVT). An implantable cardioverter defibrillator effectively prevents SCD. Atrial fibrillation (AF) is common among patients with HCM and warrants anticoagulation even without conventional risk factors according to European guidelines. Routinely, the evaluation of arrhythmias using a 48-hour ambulatory external monitor takes place every 6-24 months if patients do not report palpitations. The remaining time the potential burden arrhythmia is unknown. Therefore, the aim of the present study is to assess NSVT and AF incidence during 18 months by an insertable cardiac monitor (ICM).
Methods: Adult patients, aged 18-65 years, with a validated diagnosis of HCM are eligible for the study. The study sample is planned to include 30 patients. A Confirm Rx is implanted at the level of the fourth rib on the left side subcutaneously after local anaesthesia. The application for monitoring is installed in the patients' smartphone and symptoms registered by the patient activation and VT detection programmed as 160 bpm during >= 8 intervals. An AF episode is recorded based on >= 2 min duration. Bradycardia is recorded at <= 40 bpm or pause >= 3.0 s. The patients are followed during 18 months before explant.
Ethics and dissemination: The study was approved by The Regional Ethical Committee in Umea (protocol number 2017/13-31). The study protocol, including variables and prespecified research questions, the study was registered at Clinical Trial Registration NCT03259113. Each patient is informed about the study in both oral and written form by a physician and included after written consent.