Quantification of myocardial blood flow reserve in patients with CAD using real-time myocardial contrast echocardiography (RTMCE) has been demonstrated to further improve accuracy over the analysis of wall motion and qualitative analysis of myocardial perfusion.

Conventional stress echocardiography compares wall motion during rest and stress. The FDA has approved a contrast agent for use in patients with suboptimal echocardiograms, which accounts for up to 20% of resting echo studies. A "suboptimal image" is one in which at least two of six myocardial segments of the left ventricle cannot be visualized in the apical views. Contrast is used to opacify the LV chamber and to improve the delineation of the left ventricular endocardial border. Patient with suboptimal echoes include technically difficult patients, such as obese patients; patients undergoing mechanical ventilation; or patients with pulmonary hypertension.

Thomas R. Porter, MD, Chair of Cardiology at the University of Nebraska Medical Center, and colleagues have been evaluating RTMCE to improve LV opacification and permit real-time assessment of perfusion and wall motion (WM), potentially improving detection of CAD and the predictive power of stress echo. However, no prospective comparison has been made of RTMCE versus conventional stress echo.

They studied 2,063 patients referred for suspicion of CAD and at intermediate risk who underwent either conventional stress echo or RTMCE using perflutren lipid microsphere injectable suspension (known as DEFINITY® Vial [Lantheus Medical Imaging Inc.; North Billerica, MA]), the first approved ultrasound contrast agent in the United States. In each group, the decision to perform exercise-stress or dobutamine-stress echocardiography was left to the referring physician. The continuous intravenous microbubble infusion was used for all real-time studies to examine myocardial perfusion (MP) and WM, and the same contrast agent was used for conventional echo only when endocardial border delineation was inadequate, which was the case in 46% of all studies.

Of the patients studied, mean age was 60 years, 52% were women, 26% had diabetes, and mean ejection fraction was 59%. An abnormal test was obtained in 26%, and 12% had a resting WM abnormality. Despite the fact that RTMCE revealed more abnormal results in patients with suspected CAD, it didn't beat conventional stress echocardiography for predicting event-free survival, which was similar with both approaches.

Among patients undergoing RTMCE, absence of a WM abnormality predicted event-free survival (p < 0.001), although among patients undergoing conventional stress echo, absence of a wall motion abnormality did not predict event-free survival (p = 0.71).

Interpretation of RTMCE was better for experienced readers (>1,000 studies) than less experienced readers.

Importantly, the authors noted, RTMCE had excellent predictive value and could be performed at bedside with no radiation risk. Besides the advantage of being portable, the results are more immediate.

Updates at ACC.13

RTMCE has been utilized to detect MP and WM abnormalities during both dobutamine and dipyridamole stress echo, although the comparative prognostic value of the two stressors is unknown.

At the recent ACC Scientific Sessions in San Francisco, Dr. Porter and colleagues compared the incremental prognostic value of MP imaging during dobutamine and dipyridamole stress echo. They analyzed the outcome (death/nonfatal MI) of patients referred to two experienced institutions for either dipyridamole (n = 1,355) or dobutamine (n = 1,514) stress echo.

With a median follow up of 1,113 days, abnormal MP (fixed or inducible) was seen in 496 (33%) of the dobutamine and 632 (47%) of the dipyridamole stress echo studies, while abnormal wall motion was seen in 25% versus 39% respectively (both p < 0.005). Overall, RTMCE assessments of myocardial perfusion using either dipyridamole or dobutamine add equivalent, significant predictive value over wall motion analysis, leading the authors to conclude that MP imaging "should be strongly considered during either test to improve its predictive value."

Keywords: Follow-Up Studies, Respiration, Artificial, Microbubbles, Disease-Free Survival, Contrast Media, Prognosis, Dobutamine, Endocardium, Hypertension, Pulmonary, Microspheres, Heart Ventricles, Dipyridamole, United States, Diabetes Mellitus, Echocardiography

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