Young Keun On, MD, PhD Division of Cardiology, Department of Medicine Cardiac & Vascular Center, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea Inappropriate implantable cardioverter-defibrillator shocks in a patient with hypertrophic cardiomyopathy ABSTRACT A 47-year-old man presented with hypertrophic cardiomyopathy (HCM) and syncope. He had a family history of sudden cardiac death (father and brother). He had an implantable cardioverter-defibrillator (ICD) for primary prevention of sudden cardiac death. The patient complained of 2 ICD shocks after implantation and electronic analysis revealed that the arrhythmia was atrial fibrillation at a heart rate of 207 bpm. The ICD had been reprogrammed to prevent inappropriate shock, and he was medicated for treatment of the atrial fibrillation. The ICD provides a significant reduction in mortality in survivors of sudden cardiac arrest and high-risk patients with cardiovascular disease. However, inappropriate shocks are painful, psychologically disturbing, potentially arrhythmogenic and could increase mortality. The causes of inappropriate ICD shocks include supraventricular tachycardia, oversensing of P or T waves as R waves, double counting of R waves, and an artifact from lead fractures or electromagnetic interference. Early detection of asymptomatic AF can facilitate early treatment via ICD reprogramming or medications adjustments to reduce the risk of inappropriate shocks and morbidity. Key words: implantable cardioverter-defibrillator shocks hypertrophic cardiomyopathy Received: January 25, 2012 Revision Received: March 12, 2012 Accepted: March 30, 2012 Correspondence: Young Keun On, MD, PhD, Division of Cardiology, Department of Medicine Cardiac & Vascular Center, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50 Irwon-dong Gangnam-gu, Seoul, Korea, 135-710 Tel: 82-2-3410-3420, Fax: 82-2-3410-3849, E-mail: yk.on@samsung.com 32 The Official Journal of Korean Heart Rhythm Society

Figure 1. Surface electrocardiogram showed normal sinus rhythm and left ventricular hypertrophy. VOL.13 NO.1 33

Figure 2. Transthoracic echocardiogram showed asymmetric septal hypertrophy, compatible with hypertrophic cardiomyopathy. 며, 부적절한 ICD 전기충격도 사망률을 증가시키는 것으로 보고하였다.3, 4 실제로 대규모 ICD 임상 연구 결과 부적절한 ICD 전기충 격이 매우 흔한 것으로 보고되었다.5 1,544명의 ICD 환자에 서 79%가 남성이었고, 평균 연령은 61±13세, 56%에서 일 차 예방으로 ICD를 시술하였고, 64%은 허혈성 심질환이었 다. 평균 41±18개월의 추적관찰 중 13%에서 1회 이상의 부 적절한 ICD 전기충격을 경험하였고,첫 번째 부적절한 ICD 전기충격까지의 경과기간은 평균 17±16개월이었다. 부적절 한 ICD 전기충격의 누계는 1년에 7%, 3년에 13%, 5년에 18%까지 증가하였다. 부적절한 ICD 전기충격에 대한 독립 적인 예측인자는 심방세동의 과거력(위험비 2.0, p 0.01) 과 70세 미만의 연령(위험비 1.8, p 0.01)이었다. 단심강 Figure 3. A 47-year-old man with hypertrophic cardiomyopathy and syncope had taken implantable cardioverter-defibrillator for primary prevention of sudden cardiac death. (single chamber) ICD는 dual-chamber ICD (24% vs, 8%, p=0.02)에 비하여 빈맥의 오진에 의한 부적절한 ICD 전기충격을 더 많이 경험하였고, 부적절한 ICD 전기충격이 발생한 경우 사망률이 60% 증가하였다(위험비 1.6, 95% 신 뢰구간 1.1~2.3, p=0.01). 34 특히 ICD 전기충격이 부적절한 경우 통증과 더불어 매우 심 이러한 부적절한 ICD 전기충격의 원인으로는 심실상성 한 스트레스를 유발하여 오히려 부정맥을 촉진시키는 것으 빈맥, P 또는 T파의 oversensing, R파의 이중 감지, 전극 로 알려져 있다. SCD-HeFT (Sudden Cardiac Death in 유도 골절 또는 전자파 방해에 의한 요인을 들수 있다. 따라 Heart Failure Trial), MADIT-II (Multicenter 서 무증상 심방세동의 조기 진단 및 치료와 ICD 프로그램 Automatic Defibrillator Implantation Trial II) 연구의 의 조정 등을 통하여 부적절한 ICD 전기충격을 줄이는 것 하부 분석에서 ICD 전기충격은 사망률에 나쁜 영향을 미치 이 필요하다. The Official Journal of Korean Heart Rhythm Society

A B C Figure 4. ICD analysis showed 7 episodes of arrhythmia including 2 events of ICD shock. (A) Intracardiac electrocardiogram during normal sinus rhythm and (B) Intracardiogram during tachycardia of 207 bpm. (C) The intracardiac electrocardiogram showed burst antitachycardia pacing for termination of tachycardia and ICD shock of 20 J after failure. VOL.13 NO.1 35

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