Heart rate decline after exercise in patients with hypertrophic cardiomyopathy

To evaluate the heart rate recovery, submaximal exercise, echocardiographic examination, and Holter monitoring were performed on 30 patients with hypertrophic cardiomyopathy and 11 controls. The time constant of heart rate decline after exercise was calculated. Spectral analysis was performed on Holter recordings. The time constant did not correlate with heart rate, left ventricular end-diastolic pressure, ejection fraction, or wall thickness. There was no correlation between the time constant and any mean spectral indices over 24 hours in patients. However, the time constant correlated with high frequency component in the night. Nocturnal high frequency component in patients with short time constant was significantly less than in those with long time constant, but did not significantly differ from that in controls. In conclusion, the heart rate decline after exercise does not primarily reflect the severity of hypertrophy or hemodynamic impairment but is associated with nocturnal parasympathetic modulation in patients with hypertrophic cardiomyopathy.