Mitral Annular Calcification Associated with Increased Risk of Atrial Fibrillation

A new analysis of insurance claims and medical records indicates that people with mitral annular calcification (MAC) may face a greatly elevated risk of incident atrial fibrillation (AF).

The authors of the paper, which appears in the journal Europace, tallied data for 6,641 people who participated in the Multi-Ethnic Study of Atherosclerosis (MESA).

None of the patients had ever received a diagnosis for cardiovascular disease or AF before the study began, but they were otherwise a very heterogeneous bunch: 53% female, 27% Black, 22% Hispanic and 12% Chinese-American. The mean age, at the beginning of the study, was 62 ± 10 years.

Only 619 patients (9.3%) had been diagnosed with MAC via cardiac computed tomography (CT) when the study commenced, and only 308 patients (4.6%) developed AF during a median follow up of 8.5 years, but the association between the 2 groups was very significant.

Multivariate analysis found that patients who started off with MAC were nearly twice as likely as those who did not to receive an initial AF diagnosis during the study period (hazard ratio [HR] = 1.9; 95% confidence interval [CI] = 1.5 - 2.5).

“This association was consistent across subgroups of age, sex, race/ethnicity (Whites vs. non-Whites), hypertension, diabetes, and left atrial enlargement,” the study authors wrote. “Potentially, these findings suggest a usefulness of cardiac CT to identify individuals at risk for AF.”

The study authors suggest the possibility of adding information about a MAC diagnosis to the risk scores developed by either the Framingham Heart Study and CHARGE AF study, noting that doing so for the patients in their study would have boosted C-statistics for the former from 0.769 to 0.776 (P = 0.038) and the latter from 0.788 to 0.792 (P = 0.089).

The new analysis supports and extends the conclusions of several earlier studies.

A cohort analysis published a decade ago in Atherosclerosis, for example, found a slightly lower, but still very significant, association between MAC and AF. After adjusting for age and sex, the authors of that study found that people with MAC received 362 diagnoses of AF per 10,000 person-years while people who did not have MAC received 185 diagnoses of AF per 10,000 person-years. In multivariable-adjusted analyses, MAC was associated with an increased risk of AF (HR 1.6, 95% CI 1.1-2.2).

An even earlier analysis, this one based directly on data from the Framingham Heart Study and published in Circulation, also found that patients with MAC were significantly more likely to develop non-rheumatic AF, but warned that the relatively small number of people who began the study with MAC limited the strength of the conclusion.

MAC is a chronic degenerative process that affects the mitral valve ring. It is extremely rare in people under 40 but may afflict more than half of all people who are over 80 years old.

Oddly, despite the new study’s finding that the association between MAC and incident AF is roughly the same for people of all races, the chances that a patient will develop MAC in the first place seems highly associated with that patient’s race. One analysis has concluded that non-Hispanic whites are nearly twice as likely as African-Americans and more than twice as likely as Chinese-Americans to be diagnosed with it.