Myocardial scars are often unrecognized by cardiac MRI and clinical evaluation

A population-based cohort study of U.S. adults who did not have cardiovascular disease at baseline found that more than three-quarters of their myocardial scars were unrecognized by electrocardiography, cardiac MRI and clinical evaluation. 

After 10 years, 7.9 percent of the participants had myocardial scars, although 78 percent were unrecognized.

Lead researcher Evrim B. Turkbey, MD, of the National Institute of Biomedical Imaging and Bioengineering in Bethesda, Md., and colleagues published their results online in JAMA on Nov. 8.

“The clinical significance of unrecognized myocardial scar remains to be defined, although prior myocardial scar has been noted pathologically in more than 70 percent of patients with sudden cardiac death but without prior known coronary artery disease,” the researchers wrote.

In this study, the researchers evaluated 1,840 participants from the MESA (Multi-Ethnic Study of Atherosclerosis) trial, which enrolled men and women who were between 45 and 85 years old and were free of cardiovascular disease. The participants were from Baltimore City and Baltimore County, Md.; Chicago; Forsyth County, N.C.; Los Angeles County, Calif.; northern Manhattan and the Bronx, New York City; and St. Paul, Minn.

All participants enrolled from 2000 through 2002 and underwent cardiac MRI from April 2010 until February 2012. They also underwent an LGE cardiac MRI 15 minutes after administration of a 0.15-mmol/kg dose of a gadolinium-based contrast agent. In addition, they had a physical examination, laboratory tests, clinical history and other evaluations.

The researchers defined myocardial scar as “focal LGE either in 2 adjacent short-axis slices or in 1 short-axis and a long-axis image at a corresponding location using QMass (version 7.2, Medis).”

Participants with a myocardial scar at 10 years were more likely to be older, male and a smoker and have hypertension and slightly lower cholesterol levels. They also had greater common carotid intima-media thickness and higher 10-year Framingham Global Risk score, 10-year American College of Cardiology/American Heart Association risk score and coronary artery calcium scores.

The researchers found the prevalence of previously unrecognized myocardial scar was 6.2 percent and the prevalence of clinically recognized MI was 1.7 percent.

Of the unrecognized myocardial scars, 38 percent were typical and 62 percent were atypical. Of the recognized myocardial scars, 84 percent were typical and 16 percent were atypical.

The researchers defined typical scars as “myocardial scars that involved subendocardium in a coronary artery distribution” and atypical scars as “myocardial scars predominantly affecting midwall or subepicardium without subendocardial involvement in a noncoronary artery distribution.”

The researchers cited a few limitations, including that the MESA study enrolled healthier participants than the general population. They also mentioned typical and atypical cardiac MRI patterns are defined by animal studies and patients with clinically overt disease.

“These scar patterns may represent an oversimplification of scar etiology in asymptomatic individuals and are of unknown clinical significance,” they wrote. “Cardiac magnetic resonance is relatively sensitive for detection of myocardial scar, although a minimum scar size of at least 1 g of tissue is generally accepted as the lower limit of detection. The changes in C statistics that we observed were also small. The prevalence of myocardial scar is low, resulting in small sample sizes and limited power for comparisons by scar subtype.”