Researchers examined data on 2,631 patients with hypertrophic cardiomyopathy (HCM) without a history of persistent or permanent atrial fibrillation at baseline, including 96 individuals who had a total of 197 major atrial fibrillation events over a mean follow-up period of 33.5 months.
Overall, the risk of major atrial fibrillation events significantly increased with each 5-point increase in BMI (hazard ratio 1.38), and every 5% increase in left atrial volume index percent (HR 1.11), as well as with mitral regurgitation grade II/III (HR 1.33), and a history of arrhythmia (HR 1.56).
"All of these predictors in HCM are similar to those in a non-HCM population but mitral regurgitation and dilated, poorly contractile left atrium are more common in HCM due to left ventricular outflow tract obstruction and diastolic dysfunction, which are both quite prevalent," said lead study author Dr. Christopher Kramer, chief of the cardiovascular division at the University of Virginia Health System in Charlottesville.
For patients 32 years old or younger, obesity was the strongest predictor of atrial fibrillation events based on the risk associated with each 5-point increase in BMI (HR 2.06).
"The other risk factors take time to develop, and so obesity is a driver in younger patients," Dr. Kramer said by email.
However, a history of arrhythmia was the strongest predictor of atrial fibrillation events in middle-aged individuals 33 to 52 years old (HR 2.10) and 53 to 62 years old (HR 1.54).
And, mitral regurgitation grade II/III was the strongest predictor of atrial fibrillation events in people older than 62 (HR 1.21).
Major atrial fibrillation events included episodes treated with electrical cardioversion or a catheter ablation procedure, episodes that resulted in hospitalization longer than 24 hours, and clinical determination of permanent atrial fibrillation in patients previously in sinus rhythm.
Limitations of the study include the reliance on hospital records and patient reports to identify major atrial fibrillation events, which might lead to under-reporting, the study team notes in JACC: Clinical Electrophysiology.
"The low number of atrial fibrillation endpoints is somewhat surprising, since it's estimated that about 20% of patients with HCM have atrial fibrillation," said Dr. Eric Buch, director of the Electrophysiology Labs and Specialized Program for Atrial Fibrillation at the David Geffen School of Medicine at the University of California, Los Angeles.
It's also possible that atrial fibrillation events that didn't meet the study criteria might still lead to thromboembolism and influence clinical decisions about long-term anticoagulation, the authors point out. An additional limitation is that stroke wasn't assessed in the study because it wasn't possible to uniformly attribute stroke to atrial fibrillation.
However, risk factors identified in the study have also been seen in the broader population of atrial fibrillation patients without hypertrophic cardiomyopathy, Dr. Buch, who wasn't involved in the study, said by email.
"For clinicians taking care of patients with hypertrophic cardiomyopathy, they should expect more clinically significant atrial fibrillation in those HCM patients who are older, obese, and have hemodynamic evidence of left atrial stretch," Dr Buch said.
SOURCE: https://bit.ly/2TGWcd3 JACC: Clinical Electrophysiology, online June 30, 2021.
By Lisa Rapaport
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