SPECT imaging scans show that abnormalities in blood flow to the muscle of the heart indicate higher cardiovascular disease risk in African-Americans and Hispanics than similar abnormalities in white patients, according to a new study (PDF) in the May 3, 2005, issue of the Journal of the American College of Cardiology.
“SPECT imaging can effectively risk-stratify ethnic minority patients. The event rates for ethnic minorities by the extent and severity of perfusion abnormalities are much higher than for our Caucasian, non-Hispanic patients. Thus, even mild abnormalities are associated with up to a 2-fold higher risk of death or heart attack when compared to a Caucasian, non-Hispanic patient,” said Leslee J. Shaw, Ph.D., at Cedars-Sinai Medical Center in Los Angeles.
SPECT (gated single-photon emission computed tomographic) imaging is frequently used to evaluate blood flow in coronary arteries, but this is the first study large enough to link abnormalities seen on SPECT images to important health outcomes, including heart attacks and death, in white, African-American and Hispanic patients. Five study centers across the country enrolled a total of 1,993 African American, 464 Hispanic, and 5,258 Caucasian non-Hispanic patients. The study subjects underwent SPECT imaging after exercise or drugs that put stress on their hearts. The participants, who had chest pain or other symptoms and at least one risk factor for heart disease, were referred to scanning in order to investigate possible coronary artery disease.
“SPECT imaging is highly accurate at the detection of cardiovascular risk in ethnic minority patients. Of note, for our largest group of minority patients, African-Americans, it appears that evidence of reduced blood flow in one or more areas of the heart following a stress test is very predictive of near term outcome. In fact, these flow abnormalities may become an optimal method applied to risk-stratify minority patients. And this data is consistent with other evidence noting that abnormalities in coronary artery flow are predictive of outcome in African-Americans,” Dr. Shaw said.
Dr. Shaw said the researchers included ethnicity data in the study in order to take into account different rates of recruitment at the study centers. She said the results were surprising.
“When the study was first finished and I started analyzing the data, I was seeing much higher event rates among minority participants, and I started to look for reasons. I had no idea that the prognostic results would vary so dramatically for ethnic subsets of the population. It was surprising to me and really drove home and supported the idea that our minority patient populations are very high-risk and require more intensive care,” Dr. Shaw said.
Dr. Shaw pointed out that in this study African-American patients with mild abnormalities in blood flow as seen on SPECT images had cardiovascular death rates equivalent to white patients who had severe abnormalities.
“I believe that there is growing evidence that there are true ethnic differences in the pathophysiology of atherosclerotic disease. This data supports the notion that blood flow, in other words, stress perfusion, coronary flow reserve, and endothelial function, is a prominent risk factor for certain minority populations. That is, abnormalities in blood flow or vascular function are key to identifying at-risk patients,” Dr. Shaw said.
She said these results have important implications for clinicians.
“Take care to treat a patient's residual ischemic risk. And be careful to focus on more aggressive care of your minority patients even those with only mild perfusion abnormalities,” Dr. Shaw said.
In addition to possible ethnic differences in cardiovascular disease itself, Dr. Shaw also emphasized that quality of care, socioeconomic differences and other factors are linked to disparities in health outcomes like those seen in this study.
Dr. Shaw noted that this type of observational study has limitations, including possible bias in the referral of patients for SPECT imaging. She said the results apply to this specific population and do not necessarily apply to healthy people or to African-Americans or Hispanics in the general population.
James E. Udelson, M.D., F.A.C.C., at the Tufts-New England Medical Center in Boston, Mass., who was not connected with this study, said it is an important article and one of the first of its type to include large numbers of African-American and Hispanic patients.
"It demonstrates in a way never shown as clearly before that SPECT works well in these populations. There are two major messages from the study. Within each of the ethnic racial groups, SPECT imaging can tell clinicians whether patients have low or high risks for a poor prognosis. The other message is that, consistent with other data, other ethnic groups seem to have higher risks of bad outcomes than white patients,” Dr. Udelson said.
Although this study does not explain why those differences exist, Dr. Udelson said the results imply that clinicians should pay more attention to aggressively treating African-American or Hispanic patients who have cardiovascular risk factors or who have had a stress test that indicates abnormalities in heart blood flow.
Site enrollment for this study was 20 percent from Duke University Medical Center in Durham, North Carolina, 18 percent from Georgetown University Medical Center in Washington, D.C., 18 percent from Emory University Veterans Administration Hospital in Atlanta, Georgia, 14 percent from Rush University Medical Center in Chicago, and 30 percent from the University of California at Los Angeles Medical Center.
The American College of Cardiology, a 31,000-member nonprofit professional medical society and teaching institution, is dedicated to fostering optimal cardiovascular care and disease prevention through professional education, promotion of research, leadership in the development of standards and guidelines, and the formulation of health care policy.