Heart Paradox Found in Blacks
Despite worse outcomes for heart failure, arrhythmia rate is lower than whites
WEDNESDAY, Feb. 4, 2004 (HealthDayNews) -- While black heart failure patients tend to fare worse than their white counterparts, researchers have found that, paradoxically, they also have significantly lower rates of a dangerous heart condition.
A new study by researchers at the Kaiser Permanente medical system and the University of California at San Francisco (UCSF) found blacks have sharply lower rates of the most common form of the condition, known as atrial fibrillation (AF), which is a disturbance in the electrical signals that tell the heart when to beat.
Since AF is linked to more severe heart failure, researchers thought higher rates of the disorder might be seen among blacks, which in turn might help explain why blacks with heart failure tend to have poorer outcomes than whites.
Their results, however, showed just the opposite, since the black patients in the study were much less likely to suffer from AF.
The finding appears in the Feb. 4 issue of the Journal of the American College of Cardiology.
"It is a little surprising," acknowledges Dr. Alan S. Go, a UCSF professor of epidemiology, "especially since we have seen higher risk factors for AF in that group, and then found they had such lower rates -- 50 percent lower."
The researchers combed through information on 1,373 heart failure patients treated at 16 Kaiser hospitals in northern California, including 223 blacks and 1,150 white patients.
All of the patients had similar health care insurance coverage and were treated by Kaiser Permanente providers using similar methods, to minimize socioeconomic and treatment differences.
"We found that even after you accounted for those differences, blacks with heart failure had about a 50 percent lower risk of atrial fibrillation. It was a very robust finding; no matter what we adjusted for, it remained consistent," Go says.
Typically, AF is a kind of an electrical storm that travels in spinning wavelets across both atria (the upper chambers of the heart), causing them to vibrate, or fibrillate, at 300 to 600 times per minute, instead of beating effectively. The disturbances can last anywhere from a few seconds to a lifetime.
Some specialists say the findings, while intriguing, are part of a complex issue and caution should be used when interpreting them.
"I think AF is very much population-dependent and it's all complicated, too. There are multiple factors that can influence AF," says Dr. Roosevelt Gilliam, clinical director of cardiac electrophysiology at Duke University Medical Center. "You have to ask: how do the populations compare, is the sample size big enough, is 223 enough. Maybe this group got to treatment later than other groups. What about the ones who didn't get to the trial at all?"
The study shows that "we have a lot to learn about this condition," Gilliam adds. "There may be something. Maybe there is a difference, and once you can understand the ethnic differences maybe you can exploit those differences. Maybe there is some genetics in this, but it's hard to say at this point."
In an accompanying joint editorial in the journal, Drs. Edward P. Havranek and Frederick A. Masoudi of the Denver Health Medical Center and the University of Colorado Health Sciences Center stress the need to address the socioeconomic and cultural issues of race.
"Most papers in the medical literature don't address that issue properly," they wrote. "They tend to assume that there are big biological or genetic differences between blacks and whites, but there really aren't."
But they praised the study, writing that it did a "reasonably good job of controlling for those socioeconomic factors" and "maybe this is one of those unusual situations where there really is some genetic reason" for the differences."