Chronotropic incompetence in clinical exercise testing

Chronotropic incompetence has been found to be an important predictor of obstructive coronary artery disease (CAD). However, few data define the normal heart rate response to progressive exercise and allow a clear definition of chronotropic incompetence. In this study, 312 patients who underwent an exercise stress test and coronary angiography were evaluated. The exercise heart rates of 140 normal subjects were used to define the normal mean heart rate at progressive work loads. Two standard deviations of the mean were chosen to represent a normal response at various levels of exercise. Analysis of the exercise heart rates in 172 patients who had CAD revealed 16 patients who had a peak exercise heart rate below 2 standard deviations of the mean. Of the 16 patients, 5 had 1-vessel, 5 had 2-vessel and 6 had 3-vessel CAD. Of 65 patients who had no significant ST-segment shift and who did not reach 85% of age-predicted heart rate, 13 (20%) had an inappropriately low heart rate for the work load performed. Each of the 13 patients had CAD. Of the 172 patients with CAD, those with chronotropic incompetence exercised further than the patients who did not have chronotropic incompetence (9.4 +/- 2.1 vs 7.0 +/- 3.4 METs, p less than 0.01). In conclusion, chronotropic incompetence is a relatively infrequent occurrence in an exercise test population; however, this finding, when present, is relatively specific for CAD, and may be useful in detecting patients with CAD who have an indeterminate exercise test.