Relation Between Depressed Cardiac Response to Exercise and Autonomic Nervous Activity in Mildly Symptomatic Patients With Idiopathic Dilated Cardiomyopathy

We investigated whether the depressed cardiac response to adrenergic stimulation is accompanied with impaired autonomic function in mildly symptomatic patients with idiopathic dilated cardiomyopathy (DCM). Twenty-seven patients with DCM (New York Heart Association class I or II) and 7 normal control subjects underwent exercise radionuclide ventriculography and 24-h ambulatory ECG. The following frequency components of heart rate variability were calculated: the areas under the low (low frequency component [LF], 0.04 to 0.15 Hz), high (high frequency component [HF], 0.15 to 0.40 Hz), and total frequency portions of the spectrum. HF and HF% (the ratio of HF to total power) were calculated as indexes of specific vagal influences, and LF% (the ratio of LF to total power) and the ratio of LF to HF were of sympathetic tone. The left ventricular ejection fraction (LVEF) increased by more than 5% in all normal control subjects during exercise, whereas 17 (63%) of patients failed to show more than a 5% increase in LVEF. The profile of the mean hourly HF% and LF/HF showed circadian variations in normal control subjects but not in patients. The HF and HF% during sleep were significantly lower and the LF/HF during sleep was higher in patients than in normal control subjects. In patients, the LVEF during exercise minus LVEF at rest was significantly correlated with HF, LF%, and LF/HF during sleep, and with the ratios of the mean values during early morning to the mean daytime values for those spectral indexes. Our results demonstrated that mildly symptomatic patients with DCM showed an attenuated cardiac response to exercise and altered autonomic function, and their close relationship, suggesting that autonomic nervous activity contributes to cardiac desensitization in DCM.