PR Interval Behavior During Exercise Stress Test

OBJECTIVES The PR interval on the electrocardiogram represents conduction time from the onset of atrial activation through His-Purkinje conduction system during a normal cardiac cycle. While its behavior at rest and during exposure to various cardioactive drugs is well documented, there exist few reports which describe PR interval variations during exercise in normal control and patient groups. In the present study, we examined the behavior of the PR intervals during various stages of exercise, and at the same time we observed whether the changes of PR interval during exercise could suggest that implanted cardiac pacemaker algorithms may be constructed to maximize hemodynamic benefits in patients requiring physiological cardiac pacemaker. METHODS A retrospective analysis of the exercise treadmill test was performed on 148 healthy control group (148 males, mean age of 42.7 +/- 11.7) and 134 patient group (95 males & 39 females, mean age of 47.1 +/- 11.7) which had complained of non-specific chest symptoms but were identified as normal in the exercise treadmill test. During the test, we used the standard Bruce protocol. The results were expressed as mean +/- standard deviation, and differences in the mean value of each standard deviation, and differences in the mean value of each group were evaluated by the student's t-test. A P value of less than 0.05 was regarded as significant. RESULTS 1) The control group showed 6.9msec reduction rate of the PR interval whenever their heart rate increased by 10 beats per minute. 2) The entire patients group showed 5msec reduction rate of the PR interval whenever their heart rate increased by 10 beats per minute. 3) The male patients group showed 5.2msec reduction rate of the PR interval whenever their heart rate increased by 10 beats per minute. 4) The female patient group showed 4.3msec reduction rate of the PR interval whenever their heart rate increased by 10 beats per minute. 5) There were significant differences of the PR interval changes between the entire or male patient group and the control group within the same range of heart rates. CONCLUSIONS This study shows that PR interval changes corresponding to heart rate increments were linearly decreased. These changes of PR interval during exercise suggest that implanted cardiac pacemaker algorithms may be constructed to maximize hemodynamic benefits in patients requiring physiological cardiac pacemakers.