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November 29, 2004
Study: Tall people at higher risk for atrial fibrillation
BY Sherry Baker
Data presented recently at the American Heart Association’s (AHA) scientific sessions by Emory cardiologist Jonathan Langberg show that tall people have a higher risk than their shorter counterparts for the heart arrhythmia known as atrial fibrillation (AF).
“I was inspired to look at this question because I have three patients who at one time played basketball professionally, and all have AF,” said Langberg, professor of medicine and director of cardiac electrophysiology at Emory Hospital. “It also has been known for some time in veterinary medicine that small animals rarely have AF, but large animals are plagued by it. For example, horses have a tremendous amount of trouble with atrial fibrillation, but it is less common in dogs and cats. So it seemed reasonable to presume that the same phenomenon applies to humans—and we found it does.”
This study evaluated the relationship between height and AF in more than 25,000 patients in the National Registry to Advance Heart Health. The patients were grouped according to whether they had a history of AF and, if so, whether it was paroxysmal (periodic) AF or permanent AF. To correct for gender differences, men and women were separately divided into quartiles of height.
“We found that AF prevalence was lowest in patients in the first height quartile and increased with each quartile,” Langberg said. “Patients’ risk of AF increased progressively with height; someone 6 feet tall was 35 percent more likely to have AF than someone who is 5-2.”
According to the AHA, about 2 million Americans suffer from AF, which occurs when multiple circuits of chaotic electrical activity in the top chambers of the heart (the atria) replace the organized electrical activity normally generated by the heart’s sinus node. This produces a quivering of the atria instead of regular heartbeats. Although not directly life threatening, this sometimes debilitating condition produces a fast, irregular heart rhythm and can cause fatigue, contribute to additional heart problems over time, and increase the risk of stroke.
Why are tall people more likely to have AF? Langberg said the reason is that taller people have larger atria. “You need to have six to eight simultaneous areas of electrical activation to have atrial fibrillation persist,” he said. “If there’s a smaller number than that, they simply run into each other and die out. Atria are physically larger in tall people, so more activation wavefronts can exist—just as a larger pond can have more ripples when a stone is thrown in than a small pond.”
He added that researchers have recognized for some time that men are more like to have AF than women. “But when we did a multivariable analysis of our data, we found that gender was not an independent predictor of the arrhythmia,” Langberg said. “So the difference between the risk of atrial fibrillation between men and women appears to be accounted for by the average difference in height.”
Although there are no immediate clinical applications to these findings, Langberg said they are important in several ways. “When researchers are designing or interpreting a trial of atrial fibrillation, they need to take height into consideration,” he said. “For example, when you are testing a new medication for AF and comparing the treatment to placebo, you need to see if the two groups are comparable according to height. Having more short people in one group could skew the data.
“In addition, we hope our research will people more aware of the need to aggressively treat larger patients in particular. Dose adjustments are important; one size doesn’t necessarily fit all.”