Cardiac MRI helps to identify persons at risk for atrial fibrillation

A multi-ethnic study to investigate the association of left atrium (LA) function and new onset atrial fibrillation (AF) using cardiac MR imaging has determined that elevated LA volume and decreased LA reservoir and conduct functions were associated with the incident AF. Feature-tracking cardiac MRI may aid in identifying asymptomatic individuals at risk of AF and enable early intervention.

The U.S. Centers for Disease Control and Prevention estimates that between 2.7 and 6.1 million people in the United States have AF, the most common cardiac arrhythmia.¹ It is associated with cardiovascular and cerebrovascular morbidity and mortality. Cardiac MRI is increasingly being recommended as a reference method to measure atrial and ventricular volume. A multi-national, multi-institutional research team designed a case-cohort study of participants in the Multi-Ethnic Study of Atheroscloerosis (MESA) to validate or refute the hypothesis that reduced LA function, assessed as decreased LA emptying fractions (LAEF) and longitudinal LA strain, is associated with incidence of AF. Their findings have been published in Circulation: Cardiovascular Imaging.

MESA was initiated in July 2000 to investigate the prevalence, correlates, and progression of subclinical cardiovascular disease in a population based sample of 6,814 men and women aged 45-84 years who were free of any clinically apparent cardiovascular disease. They represented four different racial/ethnic backgrounds and lived in six communities representative of the main geographic regions of the U.S. The majority had a baseline cardiac MRI. Participants were followed through 2008 for identification and characterization of CVD events, including myocardial infarction and other coronary heart disease, stroke, peripheral vascular disease, and congestive heart failure.

The research team identified 179 MESA participants (3.6%) out of 4967 who developed incident AF after having a baseline MRI. They randomly selected a subcohort of 400 participants, of whom 18 (4.5%) had incident AF. The subcohort group had similar demographics, baseline characteristics, and incidence of cardiovascular events compared to the MESA population.

Lead author Mohammadali Habibi, MD, a second year cardiology fellow at Montefiore Medical Center/Albert Einstein College of Medicine in New York City, and co-authors, used Multimodality Tissue Tracking software (MTT version 5.0, Toshiba Medical Systems) to quantify LA strain and volume from baseline 4- and 2- chamber cine CMR images. Maximum, minimum, and pre-atrial contraction LA volumes were extracted from volume curves that were created using the area-length method from apical 4- and 2- chamber views. The software calculated global longitudinal atrial strain by averaging longitudinal strain of all LA segments in 2- and 4-chamber views during each cardiac cycle. Global peak longitudinal LA strain was measured from the global longitudinal strain curve

The authors reported that in multivariable analysis showed that an elevated LA maximum volume index and decreased peak LA strain, and passive and total LA emptying fractions and hazard ratio for active LA emptying fractions were associated with incident AF. Parallel to enlarged LA size, passive and total LAEF, and peak LA strain were lower at baseline in participants who developed AF. This association was independent of traditional cardiovascular risk factors, LV mass, and NT-proBNP.

“Measurement of LA function using cardiac MR in addition to clinical risk factors might be useful to detect individuals at risk of AF to start early preventive interventions,” they wrote.

REFERENCES

1. Atrial Fibrillation Fact Sheet. Division for Heart Disease and Stroke Prevention. Centers for Disease Control and Prevention website. http://www.cdc.gov/dhdsp/data_statistics/fact_sheets/fs_atrial_fibrillation.htm.
2. Bild DE, Bluemke DA, Burke GL, et al. Multi-ethnic study of atherosclerosis: Objectives and design. Am J Epidemiol. 2002 156;9: 871-881.
3. Habibi M, Samiei S, Venkatesh BA, et al. Cardiac magnetic resonance-measured left atrial volume and function and incident atrial fibrillation. Cir Cardiovas Imaging. 2016 9:e004299. doi: 10.1161/CIRCIMAGING.115.004299.
4. Schwitter J. Understanding the risk to develop atrial fibrillation: And what cardiac magnetic resonance can add. Cir Cardiovas Imaging. 2016 9:e005328. doi: 10.1161/CIRCIMAGING.115.005328.