Is heart rate variability a reliable method to assess autonomic modulation in left ventricular dysfunction and heart...

Autonomic dysfunction seems to be involved in the progression and prognosis of congestive heart failure. Measurement of heart rate variability (HRV) provides a noninvasive method to obtain reliable and reproducible information on autonomic modulation of heart rate, but there is a difficulty in using HRV as a quantitative estimate of autonomic dysfunction in heart failure. This study was aimed at testing the hypothesis that abnormal modulation of heart rate assessed by power spectrum analysis may be present also in asymptomatic patients with left ventricular dysfunction and progress in patients with overt symptoms of congestive heart failure. HRV was measured in three groups of subjects: Group 1: 30 patients with chronic heart failure; Group 2: 21 patients with asymptomatic left ventricular dysfunction; and Group 3: 25 healthy volunteers as control group. HRV was evaluated by autoregressive spectral analysis with 600-beat ECG samples, while subjects were quietly recumbent (BSI), in conditions of controlled breathing (15 acts/min) (RSC) and passive orthostatism after tilting (80 degrees) (TLT). Patients in group 1 showed a reduction in the standard deviation of the R-R intervals (SDRR) (p<0.0003) and in the low frequency component (LF) (p<0.0001) compared to normal subjects. Low frequency component was not detectable in 11 patients of group I (p<0.0008). On RSC and TLT, group 1 failed to show any modification in the low frequency and high frequency components (HF) under any stimulation. Group 2 showed no modification at baseline evaluation, no increase in the high frequency component on RSC and in LF during TLT compared to controls (p<0.01 and p<0.0001 respectively). At baseline, group 1 had a lower SDRR (p<0.03) and LF (p<0.0001) vs. group 2, whereas during stimulation the two groups exhibited the same behaviour. In conclusion, reduced heart rate variability is specific for both asymptomatic and symptomatic post-ischemic left ventricular dysfunction. Our results suggest that frequency domain analysis of heart rate variability during a stimulation test allows a more accurate definition of the degree of autonomic control of heart rate.