THE MECHANISM OF SYMPATHOVAGAL IMBALANCE IN PATIENTS WITH MYOCARDIAL-ISCHEMIA

To investigate the mechanism of sympathovagal imbalance due to myocard ial ischemia, we studied 42 consecutive patients undergoing successful percutaneous transluminal coronary angioplasty by correlating frequen cy domain and time domain measures of heart rate variability with para meters such as echocardiography, stress thallium scanning and radionuc lide angiography before, immediately after and 2 months after the proc edure. Of these, 20 patients (Group N) had normal and 22 patients (Gro up A) had abnormal regional wall motion. A control group of 20 healthy subjects (Group C) underwent echocardiography and examination of hear t rate variability twice at 2-month intervals to check for spontaneous variations. At baseline, frequency domain measures such as low and hi gh frequency power and time domain measures such as SDANN index (the m ean of the standard deviations of the average of RR intervals) were lo wer in Group A than in Groups N and C, whereas no differences were det ectable in ultra low and very low frequency, total power, SDNN index ( the mean of the standard deviations of the mean of normal RR intervals ), and r-MSSD (the root mean square of successive RR differences). The re was high association between the diastolic wall stress index and bo th high frequency (r = - 0.82) and low frequency power (r = - 0.77). T here were similar findings for the systolic wall stress index (r = - 0 .72 for high frequency and r = - 0.64 for low frequency power). After successful coronary angioplasty, regional wall motion, left ventricula r wall stress indices and all measures of heart rate variability were unchanged in Group N. In Group A the mean summed segment score improve d from 15.9 +/- 2.6 to 12.2 +/- 1.7 (P < 0.0001), and mean low frequen cy, mean high frequency power (logarithmic units), and SDANN index (ms ec) increased from 6.10 +/- 0.23 to 6.36 +/- 0.28 (P < 0.005), from 5. 36 +/- 0.40 to 5.70 +/- 0.39 (p < 0.01) and from 70 +/- 18 to 83 +/- 1 8 (p < 0.01) respectively. In addition, low and high frequency power a nd SDANN index, lower at baseline in Group A than in the other two gro ups, were comparable in the three groups after coronary angioplasty. T he evolution of diastolic and systolic wall stress indices paralleled that of the above three parameters. In conclusion, diastolic and systo lic wall stress indices, in addition to segmental left ventricular dys function, were synergistically involved in determining sympathovagal i mbalance in patients with significant coronary artery disease; the rev ersal of left ventricular dysfunction and wall stress indices improves the profile of heart rate variability. Alterations in cardiac geometr y and wall stress influence mainly the discharge of afferent sympathet ic and efferent parasympathetic innervations and also principally the long-term heart rate variations instead of short-term modulation.