Use of atropine in patients with chronotropic incompetence and poor exercise capacity during treadmill stress testing

Background Treadmill stress testing (TMST) is a valuable diagnostic test for ischemic heart disease. However, the inability to achieve the target heart rate because of either chronotropic incompetence or poor exercise capacity is a major limitation to its utility. We evaluated the usefulness of atropine in decreasing the number of tests with inconclusive results in patients with a poor chronotropic response or exercise capacity during TMST. Methods The study comprised 126 patients undergoing TMST. In subjects experiencing fatigue at submaximal exercise, atropine was administered in doses of 0.5 mg per minute until the test conclusion (positive test results or target heart rate achieved) or until a maximum dose of 2 mg was administered. Results Thirty-three of the 126 patients (26%) required atropine (mean dose, 1 mg) during the study; 23 of the 33 patients (70%) proceeded to achieve their target heart rate (n = 17) or positive test results (n = 6). The mean increase in heart rate after atropine administration was 25 beats/min (range 3-53 beats/min). Atropine was required in 39% of patients receiving β-blockers, versus 21% of patients not receiving β-blockers (P = .02). Among patients receiving atropine, a conclusive test was achieved significantly more often in patients not receiving β-blockers (94% vs 46%, P = .01). No adverse events were associated with the use of atropine. Atropine administration resulted in conclusive tests more often in subjects with poor chronotropic response than in subjects with poor exercise capacity (78% vs33%, P = <.001). Conclusion The use of atropine as an adjunct to standard TMST can help decrease the number of inconclusive tests, even in patients taking β-blockers. Larger studies are warranted to further define the role of atropine in diagnostic TMST.