Three-Dimensional MRI Models in Two Patients with Moderate Structural Remodeling in Patients with Atrial Fibrillation. Image source: Robert S. Oakes, et al. Circulation 2010;119(13):1758-1767.

Delayed-enhancement MRI (DE-MRI) detection of left atrial fibrosis is associated with an increased risk of thromboembolism and may improve risk stratification when paired with existing risk stratification measures, according to a study published online Feb. 8 in the Journal of the American College of Cardiology.

Patients with atrial fibrillation (AF) are two to seven times more likely to suffer a stroke, but risk varies based in individual clinical features and preventive therapy with warfarin is costly and risky. Although existing risk stratification measures including the CHADS2 index suffice for high-risk patients, physicians often rely on clinical judgment when assessing risk in moderate-risk patients.

Researchers led by Nassir Marrouche, MD, executive director of the Comprehensive Arrhythmia and Research Management Center and director of cardiac electrophysiology laboratories at the University of Utah in Salt Lake City, undertook the study “to ascertain the association of LA [left atrial] fibrosis and its association with the CHADS2 score variables and stroke prediction.”

Marrouche and colleagues prospectively enrolled 387 patients from the University of Utah and Clinical Center Coburg in Coburg, Germany, to undergo DE-MRI. Nearly 10 percent of the cohort presented with a history of stroke.

After quantitative analysis of LA remodeling, patients were assigned to four quartiles, with groups defined as the 25th, 50th and 75th percentile limits of the percentage of LA wall enhancement distribution. Patients with Q1 remodeling were defined as those with less than 8.5 percent enhancement, Q2 as 8.6 to 16 percent, Q3 as 16.1 to 21 percent and Q4 as more than 21 percent, according to the researchers.

Marrouche and colleagues found that patients who had suffered a prior stroke had a significantly higher percentage of LA fibrosis than those without a stroke history. In addition, Q1 patients had a 2.8 percent rate of thromboembolism whereas 52.8 percent of Q4 patients had experienced an ischemic event.

The researchers observed a correlation between LA fibrosis and CHADS2. AF patients with higher CHADS2 scores (> 2) had a significantly larger amount of LA fibrosis compared to patients with a low or moderate risk profile, according to the researchers.

When the researchers conducted multivariate regression analyses that controlled for significantly different comorbidities and known stroke predictors, with the exception of CHADS2, “DE-MRI-quantified LA structural remodeling was independently associated with strokes [and] … patients with Stage I (Q1) remodeling had a protective odds ratio for strokes and those patients with Stage IV (Q4) remodeling had nearly four times the odds to have a stroke,” wrote Marrouche.

Marrouche and colleagues then developed a novel clinical stroke prediction index based on combined clinical and MRI data, factoring in LA structural remodeling, congestive heart failure, hypertension, age and diabetes. The model improved the performance of clinical variables alone (CHADS) and the addition of LA fibrosis into the model offered further improvements, increasing the area under the curve from 0.58 to 0.72.

“[T]his study provides plausible evidence that LA substrate analysis is an independent risk factor and could possibly be used in addition to standard clinical values... Clinician use of both a CHADS2index and a quantified measure of AF has the potential to provide a more rigorous risk assessment and improve future risk stratification schemes,” summed Marrouche and colleagues, while calling for additional studies.