Atrial scarring seen on cardiac MRI may predict irregular heartbeat in healthy adults
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Key takeaways:
- A post hoc analysis of the MESA cohort study shows left atrial scarring seen on MRI may predict incident atrial fibrillation.
- Those with more than 2% scarring were twice as likely to develop AF during follow-up.
Data suggest that left atrial scarring observed with 2D long-axis MRI is associated with adverse atrial remodeling and incident clinically detected atrial fibrillation, researchers reported.
In an analysis of data from the Multi-Ethnic Study of Atherosclerosis (MESA) cohort, researchers found that left atrial fibrosis was prevalent and increased with advanced age, male sex, diastolic BP, HbA1c level and a history of congestive HF, according to Healio | Cardiology Today Editorial Board Member Joao A.C. Lima, MD, director of cardiovascular imaging and professor of medicine at Johns Hopkins University, and Tarek Zghaib, MD, a junior investigator at Johns Hopkins Medicine when the study was performed and now an electrophysiology fellow at the Hospital of the University of Pennsylvania. Participants with at least 2% of the total area left atrial late gadolinium enhancement (LGE) were twice as likely to develop AF compared with participants with an absence of left atrial LGE (HR = 2.01; 95% CI, 1.17-3.45; P = .01). The study serves as a proof of concept for research with dedicated 3D left atrial imaging to further characterize the correlation and its significance, they said.
Healio spoke with Lima and Zghaib about the importance of getting ahead of an AF diagnosis, the potential role of cardiac MRI in AF prevention and what the data suggest about atrial scarring and AF risk. Their paper was recently published in Radiology: Cardiothoracic Imaging.
Healio: What led you and your colleagues to conduct this study?
Zghaib: MRI is used in people who already have AF before they undergo an ablation procedure or other AF treatment. MRI data always showed that the worse your atrium is, the worse AF you have; however, this has never been demonstrated in people without documented AF or in a general population. There are many different “flavors” of AF. Some people develop AF at a younger age; some after an MI, for example. But AF is hard to predict and very common, so a predictor for it would be very valuable.
In this secondary post hoc analysis, we used available MRI images with contrast from the MESA study conducted at the fifth exam (2010-2012), with close to 1,700 participants. This was an hypothesis-generating study because this technique was designed for the ventricle, not the atrium. It was also a limited evaluation of the atrium, done on two cuts as opposed to 3D MRI, which covers the entire atrium. Regardless, we were interested in exploring this and seeing if we could observe a signal that would show there may be a predisposition for AF on top of known risk factors.
Healio: Looking at the MRI data, what did you and your colleagues observe?
Zghaib: We looked at these 1,700 patients and we were surprised to see that there was a pretty significant number of patients with LGE in the heart — 61%. We found that older people had a higher likelihood of scarring in the atrium, as did people with hypertension, obesity or diabetes. While this might be expected with those comorbidities, these findings were still novel and validated our hypothesis.
During follow-up, 4.4% of participants developed AF over a median of 3.95 years. After adjusting for the variables in the Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) AF score, left atrial LGE independently helped predict incident AF (HR = 1.46; 95% CI, 1.13-1.88; P = .003). The highest tertile (LGE > 2%) was twice as likely to develop AF.
These are participants who were healthy at baseline, so the incidence ratio of AF is not as high as other studies. Among those who developed AF, the predictor was this atrial scarring.
Healio: Did the 2% number surprise you?
Zghaib: That did surprise me, but when you look at the distribution, most had zero [scarring]. Understanding the limitation of our technique, we wanted to explore, is there a correlation between looking at two cuts of the atrium vs. a 3D MRI image? So, we looked at a subset of 10 patients, reconstructed their MRIs and compared only two cuts vs. a comprehensive evaluation. The comparison with 3D LGE demonstrated underestimation of scar burden, indicating that left atrial LGE is likely greater than that reported in our study. So yes, 2% is a low number, but it is likely an undermeasurement of the scarring they probably have. We also adjusted for known risk factors and atrial function, which is already known to predict AF, and this enhancement was still associated with AF incidence.
Healio: Most people without CVD are not going to undergo cardiac MRI, so how might these findings be applicable to daily practice?
Lima: Lately, there has been increased attention paid to the left atrium, so while we say disease of the ventricle is cardiomyopathy, atrial myopathy is something that only more recently has been focused on. I was surprised by these data. And while it is possible that our technique is including people who do not have atrial fibrosis, these data suggest that, in fact, we are actually underestimating this. A patient could undergo MRI with gadolinium to see if they have atrial scarring. If they do, it would be important to prevent AF.
Zghaib: Yes, we acknowledge there are limitations with this. One such limitation raised was that we may be including pericardial fat in our analysis. Pericardial fat sits near the muscle and is a known risk factor for CVD and is being studied in large populations. Sequences used did not have fat saturation, so we cannot rule out that areas of fat were included in measurements. In the short term, it is important to validate what we found with a good technique to image the atrium.
The value from a clinical standpoint is AF is so common, and the consequences of AF are so detrimental but also so preventable. A stroke is devastating and many people show up with stroke because of unrecognized AF. Cardiac MRI to detect atrial scarring could raise awareness. For those at risk, perhaps encourage more frequent ECGs to monitor for this very common arrhythmia as someone gets older.
The next issue is prevention. For someone with risk factors like hypertension, diabetes or smoking, we can be more aggressive. Just like a coronary artery calcium scan or a lipid panel, cardiac MRI could serve as a risk marker for us to intervene and prevent AF.
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