he major causes of death of patients with hypertrophic cardiomyopathy (HCM) include sudden death, progressive heart failure, and HCM-related stroke associated with atrial fibrillation. Of these, sudden cardiac death is the most common in young patients. [1][2][3][4] Sudden death in HCM is associated with many factors: a family history of sudden death, the presence of an obstructive region, abnormal blood pressure (BP) response during exercise, increased left ventricular wall thickness, and the presence of an increased QT interval, ventricular arrhythmia, or myocardial bridging of the left anterior descending artery. 1,[3][4][5] A study on sudden death in patients with HCM and a mean age of 28 years demonstrated a circadian pattern over a 24-h period, with a prominent midmorning peak and a less striking early-evening peak. 5 The peak frequency of sudden death after awakening in the morning is similar to adult subjects with or without coronary artery disease. [6][7][8] Circulation Journal Vol.68, August 2004 The data regarding circadian variability suggest that the autonomic nervous system plays an important role in the genesis of sudden cardiac death, not only in coronary artery disease, 6,9,10 but also in HCM. [11][12][13][14][15][16] Many indices using 24-h Holter monitoring have been evaluated in HCM and those reports have described altered sympathetic and/or vagal activity; 2,5,[10][11][12][13][14][16][17][18][19] the results, however, are controversial, and the data for children are scant, despite the fact that sudden death primarily occurs in children and adolescents.An abnormal BP response during exercise has been reported as one of the predictive factors of sudden cardiac death in HCM, 20-22 especially in young patients, 23 but sudden death also occurs during sedentary periods or mild activity. 5 Recently, ambulatory BP monitoring has been used to manage childhood hypertension, [24][25][26][27][28] with results showing that BPs in childhood are quite different for the various time periods (resting, at school, at home, and sleeping). 26 These results suggest that the BP response to daily life activities should be investigated in children with HCM. Therefore, the purpose of this study was to determine the presence or absence of altered autonomic activity and abnormal BP response to daily life activities, and to predict sudden cardiac death in young patients with HCM.
Methods
SubjectsAll patients with a diagnosis of HCM made before 19 years of age, and who were being treated at the Depart- Background Sudden cardiac death commonly occurs in young patients with hypertrophic cardiomyopathy (HCM); however, their heart rate variability (HRV) and blood pressure (BP) response to daily life activities is not well known. Methods and Results HRV and ambulatory BP monitoring were performed in 20 patients (age range: 7-21 years) and 57 age-matched healthy volunteers (age range: 10-22 years). Time domain variables and spectral data were obtained at hourly intervals throughout the day. To determine the BP response to d...
