Heart rate variability and functional severity of congestive heart failure secondary to coronary artery disease

To investigate the behaviour of heart rate variability (HRV) with the advancing severity of heart failure (CHF) we studied 20 normal subjects and 80 coronary artery disease (CAD) patients in sinus rhythm. CAD patients were selected consecutively in order to form four equal groups of 20 subjects with different degrees of CHF according to the New York Heart Association (NYHA) functional classification. In each subject a 24 h ECG Holier tape was recorded and subsequently analysed to obtain measures of heart rate and HRV. We used several measures of HR and both spectral and non-spectral measures of HRV. Among these we employed the width of the R-R interval distribution over 24 h at three different heights (TV, 10%Var, 50%Var). The CAD group showed significantly lower HRV counts and smaller spectral components tlxan controls. However, these differences were due to the presence of CHF rather than to CAD. Indeed, a progressive and significant increase in heart rate and a contemporary decrease in HRV was observed with the advancing severity of CHF. Class IV patients had the smallest HR variation; the spectral composition in this group was barely detectable. The decrease in time domain measures of HRV followed the increase in NYHA Class in a progressive and regular pattern, while the low frequency and high frequency spectral power showed the largest reduction from NYHA Class I to NYHA Class II patients. No significant diange was demonstrated in NYHA Class I patients as compared to Controls. A significant direct correlation was found between left ventricular ejection fraction (EF) and all the measures of HRV examined (EF vs SDNN, r=0.77, P<0.0001). However, this relationship was not evident when both Controls and the single CHF Classes were considered separately. Both EF and the clinical status significantly and independently affected HRV (multiple regression analysis; NYHA Class vs EF, P<0.002 and vs 10%Var, P<0.0001). These data show that the extent of HRV reduction in CAD is related to the severity of the functional impairment and it is significantly affected by the degree of left ventricular dysfunction.