Time course of sympathovagal imbalance and left ventricular dysfunction in conscious dogs with heart failure.

To elucidate the time course of sympathovagal balance and its relationship to left ventricular function in heart failure, we serially evaluated left ventricular contractility and relaxation and autonomic tone in 11 conscious dogs with tachycardia-induced heart failure. We determined a dynamic map of sympathetic and parasympathetic modulation by power spectral analysis of heart rate variability. The left ventricular peak +dP/dt substantially fell from 3,364 ± 338 to 1,959 ± 318 mmHg/s (P< 0.05) on the third day and declined gradually to 1,783 ± 312 mmHg/s at 2 wk of rapid ventricular pacing. In contrast, the time constant of left ventricular pressure decay and end-diastolic pressure increased gradually from 25 ± 4 to 47 ± 5 ms (P < 0.05) and from 10 ± 2 to 21 ± 3 mmHg (P < 0.05), respectively, at 2 wk of pacing. The high-frequency component (0.15–1.0 Hz), a marker of parasympathetic modulation, decreased from 1,928 ± 1,914 to 62 ± 68 × 103ms2(P < 0.05) on the third day and further to 9 ± 12 × 103ms2(P < 0....