Purpose To assess the relationship between exercise-induced myocardial ischemia and changes in atrial activity. Several investigators have postulated that inadequate ventricular output due to exercise-induced ischemia can lead to altered atrial contractility. These changes may be accompanied by measurable changes in P wave amplitude (Py) in patients with normal (N) and abnormal (+) exercise tests.
Methods Retrospective analysis of Py was conducted by selecting 87 consecutive patients who underwent exercise stress tests (EST) according to the Bruce protocol. All patients were required to reach 85% of their target heart rate for inclusion in this study. Baseline measurements of Py were recorded in the supine position in leads II, aVF, V1, V5 and V6 using a 5x magnifier. These measurements were repeated at maximum exercise in each lead. Subjects were then classified as having either a “+” (n=36) or “N” (n=48) EST based on changes in their ST segment morphology. Independent sample, one-tailed t-tests were then conducted to see if “+” patients had greater increases in Py percent change from supine to exercise than “N” patients. Three patients were eliminated from the final analysis due to missing values.
Results The mean Py exercise values were significantly greater than the supine values in all leads (p≤0.0001). The mean Py percent change from supine to maximum exercise was greater in patients with a “+” EST than in patients with a “N” EST (52.4% greater in V1, 52.5% in V5, 59.2% in V6, 6.7% in II, and 10.9% in aVF). This increase was statistically significant in leads V1, V5 and V6 (p=0.0479, 0.0197, and 0.0155 respectively), however, the mean difference between “+” and “N” patients in leads II and aVF was not significant (p= 0.3308 and 0.2843).
Conclusions Py typically increases in response to exercise. Patients with a “+” EST have greater increases in Py in leads V1, V5 and V6, than patients with a “N” EST. The atrial response to decreased left ventricular function associated with exercise-induced ischemia may be reflected in Py increases. Further assessment of P wave changes in response to exercise may add diagnostic and prognostic value to the EST.
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