MMD patients have risk of conduction abnormalities, left ventricular dysfunction
More than 20 percent of patients with type I and type II myotonic muscular dystrophy (MMD) had critically prognostic conduction abnormalities, according to a small study at Johns Hopkins Hospital in Baltimore. In addition, more than 10 percent of the patients had left ventricular dysfunction.
Lead researcher Tanyanan Tanawuttiwat, MD, of Johns Hopkins University, and colleagues published their results online Nov. 9 in JAMA Cardiology.
The trial included patients with type I and type II MMD who were referred to the electrophysiology service at Johns Hopkins. The researchers retrospectively analyzed data on 136 patients with type I MMD and 28 patients with type 2 MMD who were diagnosed between January 1997 and August 2014. All patients underwent an electrocardiogram (ECG) at baseline. During the follow-up period, each patient had a mean 5.2 ECG examinations.
The researchers defined conduction abnormalities as PR of at least 240 milliseconds and QRS of at least 120 milliseconds and defined left ventricular dysfunction as ejection fraction less than 55 percent.
Patients with type 1 MMD had significantly longer PR and QRS intervals at baseline. During a mean follow-up period of 5.54 years for the type 1 MMD patients, the incidence of PR of at least 240 milliseconds was 19.2 percent and the incidence of QRS of at least 120 milliseconds was 11.7 percent. Patients with type II MMD had similar incidence of QRS abnormalities but no incident PR abnormalities.
Patients with type II MMD had a higher incidence of hypertension, while the rates of dyslipidemia, diabetes and coronary disease were similar between the groups. Although there was a trend toward higher prevalence of left ventricular dysfunction at baseline in patients with type II MMD, those patients had no incident left ventricular dysfunction compared with 2 percent of patients with type I MMD.
A multivariable analysis found that left ventricular dysfunction was independently associated with atrial fibrillation and age at diagnosis. Meanwhile, a longitudinal model found that an incident 10-millisecond increase in QRS duration was associated with a 3.5 percent decrease in ejection fraction in the subsequent year.
The researchers mentioned the study had a few limitations, including its retrospective design and potential for selection bias. The subgroups also had different follow-up assessments. In addition, the imaging studies could have been subject to interobserver bias.
“Based on these findings, yearly ECG examinations and symptom/QRS prolongation–prompted [left ventricular] function evaluation should be considered,” the researchers wrote.
Executive Editor
Tim Casey joined TriMed Media Group in 2015 as Executive Editor. For the previous four years, he worked as an editor and writer for HMP Communications, primarily focused on covering managed care issues and reporting from medical and health care conferences. He was also a staff reporter at the Sacramento Bee for more than four years covering professional, college and high school sports. He earned his undergraduate degree in psychology from the University of Notre Dame and his MBA degree from Georgetown University.