October 20, 1998
The tiniest blood vessels nourishing the heart are at risk of damage not only during a heart attack but also after normal blood flow returns through the region, a Johns Hopkins-led animal study has found.
The study used magnetic resonance imaging (MRI) for the first time to measure the extent and time course of capillary blockage following simulated heart attacks in laboratory animals. Researchers found that the obstruction is uneven in these vessels and increases up to threefold during the 48 hours following return of blood flow. The consequences can affect nearly 10 percent of the left ventricle -- the heart's main pumping chamber.
Results of the study, supported by the American Heart Association and the National Heart, Lung and Blood Institute, were published in the Sept. 8 issue of Circulation: Journal of the American Heart Association.
During a heart attack, dying blood cells and debris can clog the heart's capillaries -- the body's narrowest blood vessels. If the vessels stay clogged for a long time, the capillaries remain blocked, preventing return of normal blood flow even after the body recovers from a heart attack. This can put a patient at risk for later complications, such as another heart attack, congestive heart failure or stroke.
In treating heart attack patients, physicians try to reperfuse -- or return blood flow -- to the area using drugs, angioplasty or surgery.
"But reperfusion is not uniform," says Carlos E. Rochitte, M.D., lead author of the study and a postdoctoral cardiology fellow at Hopkins. "The core area affected by the attack may be damaged so badly that the capillaries remain blocked."
Identifying the extent of obstruction early could aid in the development of new medications to open up the blocked vessels, according to Jo o A.C. Lima, M.D., and David A. Bluemke, M.D., Ph.D., senior authors of the study.
Researchers studied vascular obstruction in animal models by blocking the coronary arteries for 90 minutes to simulate a heart attack. Then they observed the region of the heart attack two hours, six hours and 48 hours following return of blood flow. At two hours, vascular obstruction affected an average of 3.2 percent of the left ventricle. At six hours, obstruction affected an average of 6.7 percent of the left ventricle; at 48 hours, the obstruction affected an average of 9.9 percent of the left ventricle.
Further study is necessary to determine why some people have more obstruction than others, Rochitte says.
The study's other authors were Scott B. Reeder, Ph.D.; Elliot R. McVeigh, Ph.D.; Toshiya Furuta, M.D.; and Lewis C. Becker, M.D., of Hopkins; and Jacques A. Melin, M.D., of the University of Louvain, Brussels, Belgium.