BOLD MRI Detects Blocked Arteries, No Stress Needed

Blood oxygen-level dependent (BOLD) magnetic resonance imaging (MRI) can detect myocardial ischemia without putting the heart under physiological or pharmacological stress, researchers found.

The range of BOLD signals at rest for each patient was indexed to create a score that correlated with presence of coronary artery disease, with an average index of 22.6% in those with versus 15.4% for those without ischemia (P=0.038).

Further analysis defined a 16.1% cutoff score that identified ischemia-causing blockages with 72% sensitivity and 78% specificity (AUC 0.72, P=0.0078) compared with quantitative coronary angiography as the reference standard, J. Ranjit Arnold, BM BCh, DPhil, of John Radcliffe Hospital in Oxford, England, and colleagues reported in JACC: Cardiovascular Imaging.

Upon validation, this model picked up those blockages with 88% sensitivity, 58% specificity, and 75% overall diagnostic accuracy. It performed similarly for diagnosing anatomically-significant CAD -- defined as 50% or greater stenosis -- at 82%, 61%, and 75%, respectively.

This form of MRI performed comparably at stress and at rest (AUC 0.80 versus 0.74, P=0.34).

"These data indicate that BOLD imaging detects anatomically and functionally significant CAD without the need for physiological or pharmacological stress," the authors concluded.

"Our findings are pertinent to alternative imaging modalities with the potential to identify microvascular heterogeneity, and advance the concept of a functional assessment of CAD being performed at rest. The inability of resting myocardial blood flow to discriminate the presence of CAD indicates that the favorable diagnostic performance of resting BOLD assessment is not dependent on changes in resting myocardial blood flow."

"The data suggest that rest-only BOLD may have a role in selected patient populations -- those unable to tolerate stress testing," Paul Schoenhagen, MD, of the Cleveland Clinic, told MedPage Today. However, "the data is interesting but not conclusive. It justifies further evaluation, but does not justify to change clinical practice."

Moreover, "if eventually better validated, this would be a relatively complex test for myocardial ischemia," said Schoenhagen, who was not involved with Arnold's study. "One should keep in mind that an exercise stress test -- with or without imaging -- provides important information about functional capacity and impairment of the patient."

The study was a secondary look at data published in 2012 that focused more on segment-based analysis of BOLD, whereas the new analysis focused on whole-slice analysis. There were 25 CAD patients and 20 healthy volunteers in the derivation group; another 57 patients with suspected CAD were included in the validation phase.

Although segment-based analysis is the "current standard" across imaging modalities, as Schoenhagen noted, BOLD signal intensity varied widely among segments in individual patients and performed poorly in a segment-based approach to identify blockages (AUC 0.52, P=0.71).

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