A pair of studies, published in the Journal of the American College of Cardiology found two novel forms of cardiac magnetic resonance imaging (MRI) can noninvasively and accurately detect microvascular coronary artery disease (CAD)

Both studies were led by Alexander Liu, MBBS, from the University of Oxford. Liu and his team found that cardiac magnetic resonance (CMR) stress T1 mapping outperformed the gadolinium-based imaging technique in using visual, semi-quantitative or quantitative analysis techniques.  

In the study of 60 patients with angina and 30 healthy control subjects, a change in T1 of 1.5% detected obstructive CAD with 93% sensitivity and 95% specificity, while a threshold of 4% detected microvascular dysfunction with 94% percent sensitivity and 94% specificity.

“Furthermore, stress T1 mapping accurately detected coronary microvascular dysfunction defined invasively by a high IMR value (≥25 U) downstream of nonobstructive (FFR >0.8) coronary arteries,” they added.

The second part of that conclusion, according to the researchers, could be key in increasing the utility of T1 mapping.

“Although these patients with ‘microvascular angina’ are often reassured as having no significant CAD or are treated empirically with antianginal medication, they experience reduced quality of life and adverse long-term prognosis," they wrote.

"Therefore, a noninvasive test to accurately detect CMD can improve clinical risk stratification and guide targeted therapy in patients with microvascular angina,” they added.

In an accompanying editorial, Theodoros D. Karamitsos, MD, PhD, pointed out the superiority of T1 mapping is this study is based on per-vessel data. That doesn’t necessarily mean the T1 technique would allow for better diagnosis at the patient level for either single-vessel or multivessel CAD, he said.

In addition, the study analyzes only one T1 mapping technique, and results may be different using one of the many other methods—even for a similar patient population.

“Streamlining of the various T1 mapping protocols and developing a unified approach to T1 mapping is one of the most important challenges for the CMR community,” wrote Karamitsos, with the Aristotle University of Thessaloniki, AHEPA Hospital in Greece.

Myocardial perfusion reserve index (MPRI)

Liu et al. performed another study in which a measure of myocardial perfusion accurately assessed the presence of CMD. Specifically, an MPRI of 1.4 detected impaired perfusion related to CMD with a specificity of 95% and sensitivity of 89%.

The study’s goal was to validate the use of CMR for this purpose in 50 patients with nonobstructive CAD, who were compared to 20 control individuals. The average age of the study population was 65.

The MPRI was derived from CMR, while subsequent invasive angiography within seven days provided the measurement of microvascular resistance. Now validated, the authors believe MPRI has the potential to noninvasively assess microvascular angina.

“Integration of MPRI and (myocardial blood flow) assessment into the clinical CMR workflow can provide a noninvasive approach for evaluating both epicardial and microvascular CAD in patients with angina, which deserves further validation in an all-comers population,” they wrote.

Nevertheless, Karamitsos said “the authors should be commended for performing 2 important studies that open new frontiers for myocardial ischemia testing.”

“There is no doubt that these novel, noncontrast CMR techniques offer important pathophysiological insights in myocardial ischemia and have a significant diagnostic potential that justifies the conduction of a large-scale study,” Karamitsos wrote.