Largest Study of its Kind Shows Blacks With Hypertension Have Greater Thickening of Heart Muscle Than Whites After Accounting for Blood Pressure Levels
Thicker Heart Muscle Is Known To Increase Risk of Heart Attack, Stroke
May 17, 2004
New York, NY
New Study Emphasizes Importance of Lowering Blood Pressure in African-Americans
U.S. blacks with high blood pressure are about twice as likely to have an enlarged heart and a thicker heart muscle wall than their white counterparts independently of the degree of hypertension, report NewYork-Presbyterian Hospital/Weill Cornell Medical Center researchers in the American Heart Association's journal Hypertension.
Many studies have found that left ventricular hypertrophy increased muscle weight of the heart's main pumping chamber is an independent predictor of illness or death due to cardiovascular disease, including stroke, heart attack, and heart failure. And it is known that African-Americans with high blood pressure are 50% more likely to die of stroke and 80% more likely to die of heart disease than whites.
There's been a long series of studies that have documented that American blacks with high blood pressure in whom the prevalence of high blood pressure is greater than for blacks in Africa or the Caribbean have higher rates of stroke, heart attack, and heart failure than whites with hypertension, said lead study author Dr. Jorge Kizer, Assistant Professor of Medicine and Public Health at Weill Cornell Medical College and Assistant Attending Physician at NewYork-Presbyterian Hospital/Weill Cornell Medical Center, in New York City.
While some studies have suggested that blacks with high blood pressure are more likely to have an enlarged heart than whites, others have not.
The problem has been that a whole host of other factors, including body mass index (a measure of obesity), duration of hypertension, severity of hypertension, and even socioeconomic status can influence left ventricular mass, said Dr. Kizer, a cardiologist in the Greenberg Division of Cardiology at Weill Cornell.
In the study of 1060 black and 580 white patients with mostly treated hypertension, Dr. Kizer and colleagues used ultrasound to examine the heart's structure, and also took into account many factors that can influence blood pressure and heart enlargement. They looked at heart-muscle mass and at concentric geometry a thickening of the heart walls that does not necessarily affect the overall size of the heart.
The study found that after adjusting for a number of factors, there was nearly a two-fold greater prevalence of left ventricular hypertrophy among the black group than among the white group, and when we looked at concentric geometry, this showed a 2.3 fold greater prevalence in blacks than whites, said Dr. Kizer. Previous studies have shown that if you have left ventricular hypertrophy with concentric geometry, this carries a worse prognosis; those who have concentric left ventricular hypertrophy tend to do worse than other patients.
The study could not determine why there was a difference between blacks and whites.
One possibility is that this reflects different genetic determinants of left ventricular hypertrophy, but it would be hasty to jump to that conclusion. This study can't address that issue at all, said Dr. Kizer. It's possible that African-American patients had hypertension for longer than whites did before they were diagnosed.
We know African-Americans often don't have access to the same health care as whites, so it's possible that we are underestimating how long they have lived with high blood pressure, he said. Also, the researchers were unable to measure blood pressure around the clock, which requires special ambulatory equipment that patients take home and wear for a 24-hour period, even at night.
In whites there tends to be a decrease in blood pressure at night during sleep, and that same phenomenon is not always observed in African-Americans, said Dr. Kizer. It's possible that the difference in heart size could be related to such blood pressure patterns.
However, the study has several strengths, said Dr. Kizer. It is the largest study of its kind. And it looked at patients recruited from communities, so it avoided referral bias. Studies that look only at patients referred to a specialist for treatment may not be representative of all patients with high blood pressure, he noted.
Also, the researchers took into account several factors that affect blood pressure. For example, they adjusted for peripheral vascular resistance, or the amount of resistance the heart encounters when it tries to pump blood through the vessels.
This is basically the tone of the arteries, and earlier studies have shown that African-Americans tend to have a higher peripheral vascular resistance than whites, though the reason why is unclear, he said. We figured if we could adjust for this factor, we might be able to get at the things that are different between the two groups that might explain the difference in left ventricular mass.
After taking this and other factors into account, the researchers found that blacks were still at greater risk for heart-muscle thickening than whites.
The main implication of this study is that, whatever the cause of the differences, we have to be more aggressive about treating high blood pressure, said Dr. Kizer. We have to be very vigilant about reaching blood pressure targets in African-Americans.
The study's co-authors are Richard Devereux, Jennifer Liu, and Mary Paranicas, Weill Medical College of Cornell University; Donna Arnett, University of Minnesota, Minneapolis; Jonathan Bella, Albert Einstein College of Medicine, New York; D.C. Rao and Michael Province, Washington University in St. Louis, Missouri; Albert Oberman, University of Alabama, Birmingham; Dalane Kitzman, Wake Forrest School of Medicine, Winston-Salem, North Carolina; and Paul Hopkins, University of Utah, Salt Lake City.
The study was supported by grants and a Career Development Award from the National Heart, Lung, and Blood Institute.