Dobutamine Stress Echo
Source: Weissman NJ, et al. J Am Coll Cardiol 1997;29:526-530.
Debate over the necessity of adding atropine to achieve ³ 85% maximal predicted heart rate during dobutamine stress echocardiography to detect coronary artery disease continues. Atropine proponents argue that it increases sensitivity, and there are data to support their view. The down sides to atropine are increased cost, risk, and the complexity of the test. Atropine opponents make the point that dobutamine enhancement of myocardial contractile state (often visible at 5 mcg/kg/min) counterbalances the relatively lower heart rate acceleration, making the results vs. atropine similar. This is especially the case if dobutamine is infused for longer periods than the usual three minutes and if beta-blockers are withheld. To test this hypothesis, Weissman et al studied 84 patients referred for diagnostic dobutamine stress echo, which was performed in the usual manner (3 min stages) until 40 mcg/kg/min. If an end point such as new wall motion abnormalities or achieving 85% of maximum predicted heart rate was not met, the dobutamine infusion was continued for another two minutes. If there was no end point at this time, 1 mg of atropine was administered. In 26%, an end point was met with the standard protocol. The additional 2 mm of dobutamine in the rest increased heart rate from 100 to 107 beats/min, and 20 patients achieved an end point. Of the remaining 42 who got atropine, 23 never reached an end point, and one developed non-sustained ventricular tachycardia. The authors conclude that many patients who do not achieve a stress echo end point after the standard dobutamine protocol may safely reach an end point by prolonging the dobutamine infusion and avoiding the potential toxicity of atropine. It should be pointed out that other laboratories have achieved similar results by going to 50 mcg/kg/min of dobutamine. These modifications raise the percent achieving end points from roughly 25% to 50%, atropine adds about another 25%, and 25% never achieve an end point. These results are important for patients with contraindications to atropine use (narrow angle glaucoma, obstructive uropathy, etc.), but only a large randomized trial comparing different testing strategies could determine the comparative value of different pharmacologic stress testing protocols.mhc
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