THE RELATIONSHIP BETWEEN CARDIAC AUTONOMIC TONE AND T-WAVE MORPHOLOGYDURING AMBULATORY MONITORING

Intermittent T-wave inversions are known to occur during ambulatory mo nitoring in the absence of myocardial ischemia. The purpose of this st udy was to determine if T-wave inversions are associated with alterati ons in cardiac autonomic nervous system tone by examining the power sp ectrum of heart rate variability (HRV) during ambulatory monitoring. T wenty-eight episodes of T-wave inversions were analyzed from 17 youthf ul patients (8 men, 9 women; mean age 33.7 +/- 7.3 years) who had no c linical evidence of coronary disease. Mean heart rate and total HRV (s tandard deviation of mean heart rate) increased during T-wave inversio n from 83 +/- 13 to 90 +/- 13 bpm, p < 0.05, and from 56.6 +/- 29.6 to 73.6 +/- 36.8 ms, p < 0.015, respectively. The power spectrum of the HRV showed an increase in the low frequency components (9.28 +/- 6.70 bpm(2) before vs. 16.45 +/- 11.63 bpm(2) during T-wave inversion; p < 0.05). In contrast, the high frequency components did not change signi ficantly during T-wave inversion (3.46 +/- 3.52 bpm(2) before vs. 3.53 +/- 4.30 bpm(2) during T-wave inversion). Three patients experienced dizziness, dyspnea or palpitations during T-wave inversion. In conclus ion, T-wave inversions, recorded during ambulatory monitoring in patie nts with a low probability of coronary disease, are associated with an increase in the HRV which is predominantly due to augmentation of the low frequency components without significant change in the high frequ ency components of the power spectrum. These data suggest that augment ation in cardiac sympathetic tone may influence T-wave morphology in t he absence of myocardial ischemia.