Case Report: ventricular fibrillation and concurrent sinus arrest
Background Hypertrophic cardiomyopathy (HCM) is an important inherited cardiomyopathy. Morphologically, it is characterized by an increased left ventricular (LV) wall thickness and mass and functionally by enhanced global chamber function and myocellular contractility, diastolic dysfunction and development of myocardial fibrosis. Typically, patients with HCM experience atrial fibrillation, syncope and ventricular arrhythmia (VF) causing severe symptoms and cardiac arrest. In contrast, sinus node dysfunction (SND) in the setting of HCM is uncommon and, in particular, during VF it has not described so far. Case Summary Here, we report an 18 years-old female with sudden cardiac arrest (SCA) due to VF and successful cardiopulmonary resuscitation as first clinical manifestation of non-obstructive HCM. Subsequently, a subcutaneous ICD (S-ICD) implanted for secondary VF prophylaxis. However, additional episodes of VF occurred. During these, device interrogation revealed a combined occurrence of VF and bradycardia and sinus node arrest (SND) requiring a device exchange into a dual-chamber ICD.  A heterozygous, pathogenic variant in the MYH7 gene (c.2155C>T; p.Arg719Trp) was identified as causative for HCM. Discussion First published in 1994, the particular MYH7 variant (p.Arg719Trp) was described in HCM patients with a high incidence of premature cardiac death and a reduced life expectancy. Electrophysiological studies in HCM patients are mainly performed for the treatment of atrial fibrillation and ventricular tachycardia; only in a few HCM patients, prolonged sinus-node recovery times (>1,500 ms) and sinoatrial conduction times (>120 m) were reported. Taken together, the present case with documented co-existing VF and SND is rare and also emphasises to address presence of sinus node dysfunction (in particular during VF episodes) in HCM patients when a distinct ICD device is considered for implantation.