False-Positive Exercise Echoes
Abstract & Commentary
Synopsis: A hypertensive response to exercise is associated with a high incidence of false-positive echocardiographic responses.
Source: Ha JW, et al. J Am Coll Cardiol. 2002;39: 323-327.
Despite the proven usefulness of exercise echocardiography, false-positive results can occur in up to 10% of subjects. Thus, identification of potential causes of false-positive responses is important. Ha and colleagues at the Mayo Clinic Rochester identified 548 patients from their 6686 patient exercise echo database who had coronary angiography within 4 weeks of exercise echo. All patients underwent treadmill exercise echo using standard protocols. A hypertensive response was defined as systolic blood pressure > 220 mm Hg for men and > 190 mm Hg for women or an increase in diastolic pressure of > 10 mm Hg or > 90 mm Hg. In 132 of the 548 patients a hypertensive response was documented (24%). The only baseline characteristics more likely to occur in those with a hypertensive response were previous myocardial infarction and beta-blocker therapy. Resting blood pressure was higher in the hypertensive response patients and they achieved higher heart rates and double products during exercise. A resting or stress wall motion abnormality was seen in 363 of the 441 patient with significant coronary artery disease (CAD) on angiography (82% sensitivity). Of the 107 patients without CAD, 42 had a negative stress echo (39% specificity). Of the 132 patients with a hypertensive response, 108 had positive exercise echoes. Of these 108, 24 (22%) had normal coronary arteries. In those with a normal blood pressure response and a positive exercise echo, 12% had no CAD. Overall, the specificity of exercise echo decreased as blood pressure increased with exercise, but sensitivity was unchanged. Often the false-positive exercise echo wall motion abnormalities were extensive, erroneously suggesting left main or severe 3-vessel disease. Ha et al concluded that a hypertensive response to exercise is associated with a high incidence of false-positive echocardiographic responses.
Comment by Michael H. Crawford, MD
In this study, a hypertensive response to exercise increased the false-positive rate 2-fold. Also, the higher the blood pressure the greater the false-positive rate, which suggests pressures near the cut-off for a hypertensive response used in this study need to be considered. False-positive exercise echoes are known to be more common in those with resting wall motion abnormalities, dilated cardiomyopathy, and technically poor studies. This study suggests that a hypertensive response should be added to the list. Theoretically, marked increases in blood pressure could cause subendocardial ischemia because of excess demand vs. supply.
It is difficult to assume a test is falsely positive based solely on the blood pressure. Usually other clinical features are considered such as pretest likelihood, angina during exercise, or a positive electrocardiographic response. Unfortunately, none of these data were provided so it is difficult to tell the effect of the clinical picture on decision making. Also, all the patients in this report went on to cardiac catheterization, so this select group must have been considered true positives by the clinicians. Ha et al suggest that when a false-positive response is suspected, the test could be repeated after blood pressure control. There are several problems with this approach. Many agents that treat blood pressure would decrease the sensitivity of the test, ie, beta and calcium blockers. Physicians rarely repeat the same test, but rather move on to a new test, especially one where blood pressure is less of a factor such as dipyridamole perfusion scanning or cardiac catheterization.
The sensitivity in this study ranged from 79-87% depending on the blood pressure response quartile and is similar to other studies. The specificity is disappointingly low and ranged from 27-64%. This may reflect the cath referral bias of this study. In my experience, the specificity of exercise echo is superior to nuclear perfusion scanning in those with a lower likelihood of CAD, perhaps because such patients rarely have a hypertensive response to exercise, resting wall motion abnormalities, or dilated cardiomyopathy. For all these reasons those with a high likelihood of CAD may have more false-positive studies by exercise echo.
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