Exercise Echo: Bicycle vs. Treadmill
abstract & commentary
Synopsis: Supine bicycle exercise has a higher sensitivity for detecting ischemic heart disease and is preferred by patients and technicians, making it a valuable stress echo technique.
Source: Badruddin SM, et al. J Am Coll Cardiol 1999;33:1485-1490.
Exercise echocardiography is a useful technique for diagnosing ischemic heart disease. The two most popular methods of exercise are the treadmill, with imaging immediately after exercise, and supine bicycle, with imaging during exercise. Treadmill exercise has the advantage that higher workloads are achieved making ischemia more likely, but the disadvantage that the echos are done after exercise during recovery. Supine exercise has the advantage of imaging during peak stress, but the disadvantage of lower achieved workloads. Results seem comparable in separate studies, but the two techniques have not been directly compared. Thus, Badruddin and colleagues studied 74 patients referred for cardiac catheterization by both techniques in random order at least four hours apart. Digitized images were interpreted by a blinded observer. Maximal heart rate was higher with treadmill exercise. However, systolic blood pressure was higher with the supine bicycle, resulting in similar but statistically different double products at peak exercise (23,095 treadmill vs 22,059 bicycle; P < 0.001). Quantitative coronary angiography showed significant coronary lesions (> 50%) in 57 patients. Ischemia was detected in 47 patients by supine exercise and in 38 by treadmill (P < 0.001). Overall sensitivity was 82% for bicycle and 75% for treadmill. Specificities were 80 and 90%, respectively. Image quality was similar by both techniques and concordance between the two studies was 80%. The patients and technicians preferred bicycle exercise by about 2 to 1. Badruddin et al concluded that supine bicycle exercise has a higher sensitivity for detecting ischemic heart disease and is preferred by patients and technicians, making it a valuable stress echo technique.
Comment by Michael H. Crawford, MD
The debate over the relative merits of supine bicycle vs. treadmill exercise echo has gone on for years. More laboratories probably use the treadmill because of the ready availability of the equipment. Supine bicycle exercise requires special equipment that is not cheap. Interestingly, in this well-done, head-to-head comparison, supine bicycle was clearly superior, especially if you consider that the study protocol was tipped in favor of the treadmill study. Since a blinded comparison of the two techniques was done, only the peak exercise bicycle images were analyzed. The images done during bicycle exercise were not used but likely contain information that would have increased the accuracy of the bicycle technique.
Overall sensitivity was higher for bicycle (82% vs 75%), but this was inflated by the presence of resting wall motion abnormalities in about 10% of the patients. If these patients are eliminated, the corresponding sensitivities for detecting ischemia are 75% and 61%. Sensitivity is higher by both techniques for multivessel disease (88 vs 81%) as compared to single-vessel disease (67 vs 60%). Specificity was greater with treadmill, as might be expected from the sensitivity data (90 vs 80%). Interestingly, the study was done with no echo pre-screening and only one patient was eliminated for poor images.
The higher sensitivity of supine bicycle is somewhat surprising since double product was significantly higher with treadmill. After exercise, heart rate and blood pressure can decline rapidly, but usually ischemia persists long enough to diagnose it by echo immediately after exercise. Badruddin et al suggest that the higher left ventricular volumes during supine exercise may increase wall stress and thus oxygen demand. Also, higher end-diastolic pressures during supine exercise may reduce the driving pressure to coronary bloodflow. In support of the idea that there is more of a stimulus to ischemia during supine exercise, it was noted that the number of ischemic segments was higher with supine exercise (3.3 vs 2.3 segments; P < 0.001).
Regardless of the mechanism, the superior results and greater patient preference for supine bicycle exercise echo should lead to serious consideration of switching to this technique in those labs doing treadmill echo. The only barrier is the cost of the supine bicycle equipment.
Supine bicycle exercise echo is superior to treadmill because of:
a. higher sensitivity.
b. higher specificity.
c. higher patient preference.
d. a and c.
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