Influences of the adrenergic nervous system on the repolarization phase of the electrocardiogram

Coronary adrenergic hyperreactivity in patients with syndrome X and abnormal electrocardiogram at rest

Syndrome X is characterized by an abnormal vasomotility of coronary microvessels. It is unknown whether the presence of an ischemic-like pattern in the electrocardiogram at rest (T-wave inversion) reflects a more severe vasomotion disturbance. Changes in coronary sinus flow (thermodilution) and epicardial vessel diameter (quantitative angiography) during adrenergic activation were measured with a standard cold pressor test in patients with syndrome X whose electrocardiogram at rest was normal (group 1: 17 patients) or showed stable, symmetrically inverted T waves (group 2: 22 patients). Cold pressor test increased mean blood pressure and rate-pressure product to a similar extent in both groups, increased coronary sinus flow in group 1 (88 +/- 29 to 119 +/- 36 ml/min; p less than 0.05) and not in group 2 (109 +/- 37 vs 104 +/- 36 ml/min; p = not significant), and decreased coronary resistance in group 1 (1.38 +/- 0.42 to 1.19 +/- 0.38 mm Hg/ml/min; p less than 0.05) and augmented it in group 2 (1.06 +/- 0.32 to 1.28 +/- 0.43 mm Hg/ml/min; p less than 0.02). During cold stimulus, the proximal and middle segments of epicardial arteries showed negligible changes in their lumen, whereas the distal segment dilated in group 1 (1.81 +/- 0.27 to 2.01 +/- 0.32 mm; p less than 0.05) and constricted in group 2 (1.82 +/- 0.12 to 1.62 +/- 0.20 mm; p less than 0.05). Differences in coronary hemodynamic and angiographic responses between the groups were statistically significant (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

T wave abnormalities in top-ranking athletes: effects of isoproterenol, atropine, and physical exercise

Eight cases of top-ranking athletes with "repolarization disorders" are reported. All subjects were asymptomatic and were otherwise suited for excellent cardiovascular performances. Seven athletes did not show any evidence of heart disease. Seven had MVP (mitral valve prolapse). Umprompted variability of ECG tracings was observed in three cases. Both isoproterenol infusions (IS) and maximal physical effort (EX) normalized T wave (abnormalities in 100% of cases, while atropine (AT) was ineffective despite an increase in heart rate greater than that caused by IS. The authors emphasize the usefulness of combined use of the EX and IS tests in ascertaining the clinical significance of T wave changes in healthy athletes. A "neurogenic" mechanism is proposed by the authors for the pathogenesis of these T wave abnormalities. This hypothesis may explain the umprompted variability of ECG tracings and T wave normalization after maximal physical effort and isoproterenol infusion.