Study: MG Patients Not at Increased Risk for Atrial Fibrillation

People with myasthenia gravis (MG) are not at a higher risk of developing atrial fibrillation, a potentially serious heart condition that causes the heart to beat irregularly and often faster than normal, a study from Taiwan reports.

The study, “Risk of subsequent atrial fibrillation in patients with myasthenia gravis,” was published in the journal Medicine.

MG is an autoimmune disease that often is associated with other conditions, including rare tumors in the thymus gland (thymoma), and heart disease. Atrial fibrillation (AF) is a form of heart arrhythmia, in which the heart beats faster than normal and at an irregular pace. This may lead to life-threatening complications, such as heart failure and stroke.

A recent study reported the occurrence of AF in eight patients with late-onset MG that diminished when MG activity was stabilized. Other studies have found that MG patients, with and without thymoma, are susceptible to developing heart arrhythmia. However, very little is known about the presence of AF in MG patients.

So, a group of researchers decided to investigate the relationship between MG and the risk of AF in an Asian population.

They evaluated 5,528 patients who had a history of MG, and 5,528 individuals who did not have a history of the disease, based on a hospitalization claim dataset that was part of the Taiwanese National Health Insurance Research Database (NHIRD). Both groups were matched by age, gender, year of disease diagnosis and presence of additional medical conditions (comorbidities).

Participants were followed until the date of AF onset, withdrawal or death, or until Dec. 31, 2013.

In the MG group most participants were diagnosed before age 50 (47%) and the mean age at diagnosis was 50.1. Both MG and non-MG participants were followed for about six years.

Statistical analyses showed that patients age 50 and older had a higher risk of developing AF compared with those younger than 50. However, men were not at a higher risk of developing the condition compared with women.

The risk of developing AF was higher in patients who had several comorbidities, such as chronic kidney disease, with an adjusted hazard ratio (HR) of 2.08. This means that patients who had chronic kidney disease had a 2.08 times higher risk of developing AF than those who did not have a chronic kidney condition.

A higher risk of developing AF also was seen in patients who had: high blood pressure (HR of 1.48); hyperlipidemia, or high levels of fatty molecules in the blood (HR of 1.66); heart failure (HR of 1.85); and chronic obstructive pulmonary disease (HR of 1.56).

However, after comparing the MG and non-MG group, researchers found that MG patients were not at an increased risk of developing AF, regardless of age, gender, or comorbidities.

Likewise, investigators found no differences in the cumulative incidence of AF between the two groups. (Cumulative incidence represents the number of new AF cases divided by the total number of participants at risk during a certain time interval.)

No increased risk for AF was observed in MG patients who had been followed for more or less than five years. Likewise, MG patients who had undergone a thymectomy (surgical removal of the thymus), or had been treated with plasmapheresis (plasma exchange), were not at an increased risk of developing AF.

“Although the results for our cohort [group] did not detect a higher risk of developing AF in MG patients, it is still possible that occult [asymptomatic] AF exists among MG patients without diagnosis,” the team wrote. According to study authors, it also is unknown if people with MG may experience paroxysmal AF, which occurs when the heart rate returns to normal within seven days.

The team also acknowledged the study had several limitations, including the fact that most patients in the study were Taiwanese, implying that results might not be valid in other populations.

“Our population-based cohort showed that individuals with MG had no higher risk of subsequent development of AF than the general population in Taiwan,” the researchers wrote. “However, we still need to be aware of occult AF, especially when hemodynamical instability [unstable blood pressure] or cardiac involvement occurs in MG patients,” they concluded.