Prognostic Value of Dobutamine Stress Echo

ABSTRACT & COMMENTARY

Synopsis: Dobutamine stress echocardiography provides added value over clinical parameters for predicting late clinical events during long-term follow-up and helps separate high- and low-risk patients with suspected or overt coronary artery disease.

Source: Poldermans D, et al. Circulation 1999; 99:757-762.

The long-term prognostic value of dobutamine stress echocardiography (DSE) is poorly defined. Thus, Poldermans and associates evaluated 1734 consecutive patients referred for DSE and followed them for 6-96 (mean, 36) months. Excluded were 74 patients who had revascularization within three months and one patient lost to follow-up. Subsequent clinical events were assessed by physicians unaware of the DSE results. DSE with atropine, if necessary, was done in the standard fashion without stopping the patient’s cardiac drugs. In 366 patients, 428 cardiac events occurred and included cardiac death in 108, nonfatal infarction in 128, and late revascularization in 192. There were no deaths or infarctions associated with DSE and only 4% of the patients developed severe hypotension. DSE was inconclusive (suboptimal heart rate and no ischemia) in 6%. The annual cardiac death or infarction event rate was 1.2% over five years in patients with a normal DSE and 5.4% in those with new (N) wall motion abnormalities (WMA) and 6.8% in those with both new and resting (R) WMA. Multivariate analysis showed that NWMA was the strongest predictor of all cardiac events (risk ratio [RR], 3.5). Cardiac death alone was best predicted by extensive RWMA (RR, 3.9) and only age added anything to the prediction (RR, 1.04). Revascularization alone was best predicted by hypercholesterolemia (RR, 4.0), then NRWA (RR, 3.3) and presence of angina (RR, 2.4). Poldermans et al conclude that DSE provides added value over clinical parameters for predicting late clinical events during long-term follow-up and helps separate high- and low-risk patients with suspected or overt coronary artery disease.

Comment by Michael H. Crawford, MD

The prognostic value of DSE and stress echocardiography in general has been a perceived weakness of this technology that has been used by the proponents of stress nuclear perfusion imaging (NPI) to denigrate stress echo. Stress NPI is generally believed to be more sensitive, but less specific, than stress echo for the diagnosis of ischemia. The proponents of stress NPI have pointed out that a negative test is associated with a low incidence of future cardiac events (2.2%), whereas several studies have shown that a negative DSE is associated with a higher event rate (6.6-8.5%/yr). The definition of a negative stress NPI in these studies was a normal resting and stress NPI. When the same analysis was done in this study, the event rate for DSE was 1.3%/yr. Thus, the prognostic value of the two stress imaging techniques is similar and this should not be a basis for test selection.

Another perceived advantage of NPI is its ability to localize the coronary artery territory involved with ischemia better than stress echo. Interestingly, in this study, ischemia location by DSE was not predictive of long-term outcome. On the other hand, the extent of ischemia was weakly predictive of outcome—one segment, RR = 2.9; two segments, RR = 4.0. This makes sense since the extent of ischemia would roughly correlate with postinfarction left ventricular dysfunction if infarction occurred in the ischemic area. Also, extensive RWMA correlated with left ventricular ejection fraction, which is related to survival. Thus, for long-term cardiac event prediction, the severity of ischemia and the extent of prior infarction may be more valuable than the location of ischemia. Consequently, the presumed ischemia localization superiority of NPI may not be critical for prognosis.

The 6% incidence of inconclusive studies is of concern with regard to the use of DSE, but it was mainly due to inadequate heart rate achievement in patients on beta blockers. Many physicians withhold beta blockers if feasible. Also, NPI studies have considered this a deficiency. In fact, NPI is touted to be highly accurate even in the event of suboptimal heart rate during stress. Whether this is a real advantage of NPI is difficult to tell. The new arbutamine delivery system may minimize inadequate heart rate responses and reduce inconclusive studies with DSE. Finally, harmonic imaging and contrast echocardiography may further enhance image quality and allow for more accurate stress echo studies.