Case report

The patient was a 20-year-old male with hypertrophic cardiomyopathy whose electrocardiogram showed an abnormal T-wave. He was diagnosed at 6 years of age by echocardiography. A p. Ala63Val mutation in the Tropomyosin alpha-1 gene, which is one of the sarcomere genes, was detected through genetic analysis of the patient. The patient’s family history revealed that his elder brother, father, and grandmother also had hypertrophic cardiomyopathy and his paternal uncle died suddenly; however, it is unclear whether the death was associated with hypertrophic cardiomyopathy. The elder brother had an episode of syncope at 18 years of age while running, but was resuscitated using an automated external defibrillator by a bystander.

Before the insertion of the implantable cardioverter-defibrillator, the patient had none of the five major classical risk factors (non-sustained ventricular tachycardia, a maximum left ventricular wall thickness ≥30 mm or a z-score ≥6, family history of sudden cardiac death associated with hypertrophic cardiomyopathy, unexplained syncope, and abnormal blood pressure response to exercise) associated with sudden cardiac death, ^{Reference Gersh, Maron and Bonow1} except the elder brother’s near-miss event, which was considered a possible risk factor. Thus, the patient was deemed a low-risk case. In contrast, the patient’s late gadolinium enhancement-MRI results showed an increasing late enhancement area of 1–16% of left ventricular mass over 2 years between ages 10 and 12. We considered this an indication of increased risk. However, to reduce the probability of complications due to implantable cardioverter-defibrillator insertion, we decided to wait until growth slowed down. When the patient turned 16 years of age, we applied the risk prediction model from the 2014 European Society of Cardiology for hypertrophic cardiomyopathy over 16 years of age at the time, ^{Reference O’Mahony, Jichi and Pavlou2} and the risk of sudden cardiac death was assessed at 4.8% per 5 years, which means that implantable cardioverter-defibrillator insertion was still an option. Ultimately, although aggressive conclusion that should be inserted an implantable defibrillator was not obtained, we obtained informed consent from the patient and his family and implantable cardioverter-defibrillator insertion was planned for the primary prevention of sudden cardiac death. ^{Reference Yamazawa, Takeda, Takei and Furukawa3} The patient underwent the transvenous insertion of a dual chamber implantable cardioverter-defibrillator at 17 years of age after achieving maximum growth in height. The device was programmed with two zones: a ventricular fibrillation zone with the lower detection rate of ≥220 bpm and a ventricular tachycardia zone with a rate of ≥180 bpm. In the ventricular tachycardia zone, two sequences of anti-tachycardia pacings and subsequent shocks were included. Three years later, the patient experienced a syncopal episode due to a ventricular tachycardia attack when he was having lunch at the university cafeteria. He had a sinus rhythm of 94 bpm before this episode. Initially, monomorphic ventricular tachycardia with rates between 160 and 180 bpm occurred and sustained for approximately 4 minutes. Subsequently, it accelerated above 180 bpm and anti-tachycardia pacing therapies were given, which failed to terminate ventricular tachycardia. 21 J shock was then delivered, which terminated the episode. However, polymorphic ventricular tachycardia with a rate of about 200 bpm recurred immediately, and 41 J shock was delivered, which restored sinus rhythm.