Abstract & Commentary
Synopsis: Beta-blocker pretreatment may underestimate the presence and severity of CAD by dipyridamole sestamibi SPECT.
Source: Taillefer R, et al. J Am Coll Cardiol. 2003; 42:1475-1483.
Although beta-blockers are known to reduce the sensitivity of exercise and dobutamine sestamibi SPECT imaging for the detection of coronary artery disease, little is known about their effects on vasodilator stress scintigraphy. Thus, Taillefer and colleagues studied 21 patients with catheter proven coronary artery disease during 3 different treatments on different days assigned in a random fashion: placebo, IV administration of low-dose metoprolol, and high-dose metoprolol. The high-dose metoprolol was predetermined in each patient by titration to predefined end points. Low dose was 50% of the high dose. After each pretreatment, dipyridamole SPECT was performed and interpreted by blinded experienced observers. The resting comparison study for the stress studies was done on a different day.
The sensitivity of SPECT was 86% on placebo vs 71% with low- and high-dose metoprolol. Also, the summed stress score, a measure of ischemic severity, was significantly lower on metoprolol (12 vs 8.7 vs 9.3; P < .001). Metoprolol lowered the pretreatment heart rate and blood pressure product (RPP). Dipyridamole increased heart rate and decreased blood pressure in each treatment setting, but RPP at peak stress was significantly lower on low- or high-dose metoprolol (10,470 vs 9440 vs 9480; P < .01). Taillefer et al concluded that beta-blocker pretreatment may underestimate the presence and severity of CAD by dipyridamole sestamibi SPECT.
Comment by Michael H. Crawford, MD
Beta-blockers have been proven in double-blind, placebo-controlled studies to reduce objective evidence of exercise-induced ischemia, and they are highly effective therapy for angina pectoris. Therefore, it is not surprising that they have been shown to reduce the sensitivity of exercise and dobutamine stress tests for the detection of CAD. Since dipyridamole usually does not induce frank myocardial ischemia, many believe it is impervious to beta-blockade. This study clearly shows otherwise, although the reasons are not clear. There are several caveats, however. This was acute beta-blockade in patients off antianginal drugs for 24-48 hours. Whether chronic beta-blockade would be similar is likely but not certain. Also, the effects of adenosine vs dipyridamole are not known but would probably be similar. In addition, this was a small group of highly selected patients who could safely be off antianginal drugs and undergo 3 stress tests over several weeks. The data suggest that beta-blockers should be withheld prior to all stress testing for the purpose of detecting CAD, if possible.
Dr. Crawford, Associate Chief of Cardiology for Clinical Programs, University of California, San Francisco, is Editor of Clinical Cardiology Alert.