SAN FRANCISCO — Echocardiography provides a great deal of information to help determine a patient's risk following a myocardial infarction, Dr. Thomas Ryan said at a cardiovascular imaging conference sponsored by the American College of Cardiology.
Echo and stress echo are not the only ways to risk stratify patients, acknowledged Dr. Ryan of Duke University, Durham, N.C.
“There are a lot of ways we can do it, but I think our goals should be to do it in the most efficient, the most effective, and the most cost-responsible fashion possible,” he said.
Echocardiography provides a variety of perspectives on left ventricular function. It allows for a calculation of ejection fraction. Doppler plus the principle of continuity of flow allows for the measurement of stroke volume across both valves, which in turn allows for the calculation of cardiac output. The contour of the mitral regurgitation depth can be used to measure the rate of change in left ventricular pressure (dP/dt). And finally, one can generate a wall-motion score.
“All of these different approaches to left ventricular systolic function have been shown to be prognostically important … to identify patients at risk and to manage them accordingly,” Dr. Ryan said.
Together, the degree of left ventricular dysfunction and the presence and severity of mitral regurgitation are the most powerful predictors of early risk after acute MI.
The results of a study of more than 3,000 patients in the Duke database show that an echo score derived from these two factors neatly stratifies patients into three categories.
Patients get no points for a good ejection fraction or good mitral regurgitation. They get 2 points each for poor ejection fraction and poor mitral regurgitation, and they get 1 point each for intermediate values. The echo score is the sum of the ejection fraction and mitral regurgitation scores.
Patients with an echo score of 0 have better than 90% 2-year survival. Those with an echo score of 3 or 4 have about a 50% 2-year survival, and those with a score of 1 or 2 have about a 75% 2-year survival.
Diastolic function has prognostic implications as well. If the deceleration time of the mitral P wave is 115 milliseconds or more, then the 30-month survival is 100%. Those with mitral deceleration times of less than 115 milliseconds have a 30-month survival rate of about 40%.
The combination of these measures means that the physician will get a great deal of information even before resorting to stress echocardiography.
Dr. Ryan said that he favors an algorithm based on echocardiography for the predischarge evaluation of patients following an MI. Those with ejection fractions of less than 40% should go to the catheterization laboratory.
If left ventricular function is preserved after an MI, then the management decision can often be made on the basis of the presence or absence of inducible ischemia.
Stress testing allows physicians to distinguish between those patients who should be sent to the catheterization laboratory for consideration for revascularization and those who can be treated medically.