Massive myocardial hypertrophy in hypertrophic cardiomyopathy: a risk factor for sudden death and high defibrillation threshold during cardioverter-defibrillator implantation

Two cases of hypertrophic cardiomyopathy with massive hypertrophy and high defibrillation threshold (DFT) are described. A 14-year-old boy, whose single risk factor for sudden death was extreme hypertrophy with maximum interventricular septum (IVS) thickness of 43 mm, survived an episode of ventricular fibrillation. During ICD implantation DFT testing showed energy requirements >30 J and the procedure was aborted. Amiodarone and verapamil treatment was discontinued and treatment with oral sotalol was instituted. After a period of amiodarone washout the procedure was repeated and DFT of 24 J was encountered. An 18-year-old female with massive hypertrophy (IVS thickness=35 mm) and other risk factors for sudden death underwent ICD implantation for primary prevention. During the procedure DFT=20 J and ICD with 30 J maximal output was implanted. An increase in DFT to more than 20 J was encountered during pre-discharge test. Lack of 10 J safety margin warranted ICD system revision and upgrade; during the second procedure DFT was 24 J and ICD with 35 J maximal output was implanted. In summary, in both cases ICDs with 35 J maximal output were successfully implanted.