Chest
Volume 109, Issue 4, April 1996, Pages 925-932
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Clinical Investigations: Cardiology
Relation Between Depressed Cardiac Response to Exercise and Autonomic Nervous Activity in Mildly Symptomatic Patients With Idiopathic Dilated Cardiomyopathy

https://doi.org/10.1378/chest.109.4.925Get rights and content

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.

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Subjects

We studied 27 mildly symptomatic patients with DCM (14 men, 13 women; 58±10 years of age) and 7 normal control subjects (4 men, 3 women; 60±6 years). Normal control subjects had no history, symptoms, or signs of cardiovascular disease and had normal 12-lead ECGs at rest and during exercise and normal M-mode, two-dimensional, and Doppler echocardiograms at rest. None of the control subjects had a history of hypertension, diabetes mellitus, or hyperlipidemia. In the group with DCM, 10 patients

Hemodynamic Measurements at Rest and During Exercise

The resting systolic BP and the resting heart rate were similar in both groups (Table 1). The systolic BP during exercise was also similar in both groups, but the heart rate during exercise was significantly lower in patients than in normal control subjects (p<0.05). The maximum workload was significantly lower in patients than in normal control subjects. LVEF increased during exercise by more than 5% in normal control subjects, but 17 (63%) of 27 patients failed to show a greater than 5%

Discussion

The cardiac response to exercise was attenuated in patients with DCM with mild symptoms. Resting clinical and hemodynamic parameters did not appear to be associated with the residual myocardial contractile reserve. Autonomic function was significantly different in the two groups, as indicated by a blunted circadian rhythm, and accelerated sympathetic activity and reduced vagal tone during sleep in patients with DCM with mild symptoms. The left ventricular response to exercise, which reflects

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