Ultrasound may offer nonionizing, contrast-free way to assess coronary flow reserve

To date, clinicians have lacked a noninvasive technique for the assessment of coronary flow reserve, but a new study offers a promise of just such a technique.

The study’s stated aim was to determine the potential of coronary ultrafast Doppler angiography (CUDA) to noninvasively image the intramyocardial coronary vasculature and to measure coronary blood flow dynamics—and to do so with high sensitivity.

The results were published online Aug. 16 in the American College of Cardiology’s JACC: Cardiovascular Imaging.

“To date, the epicardial coronary vasculature is the only compartment that can be imaged in vivo in humans with current angiography techniques such as x-ray, computed tomography (CT) scan or [MRI],” wrote the authors of the new study, led by David Maresca, with the Institut Langevin in Paris.

This limited ability to observe the coronary vasculature, they explained, has meant that clinical cardiology has centered on focal macroscopic coronary artery disease (CAD), that is, the functional assessment of epicardial stenoses based on fractional flow reserve. Subsequent treatment has entailed either pharmacological therapies or invasive treatments, percutaneous interventions or surgery.

In contrast, the research team’s work opens new possibilities for assessing microvascular dysfunction, including dysfunction of the pre-arterioles.

The researchers performed CUDA in vivo in open chest procedures done on nine pigs. The team was able to obtain ultra-sensitive cine loops of venous and arterial intramyocardial blood flows within one cardiac cycle. They found that their quantification of the coronary flow changes during hyperemia agreed well with gold standard methods of measurement.

The team subsequently assessed the feasibility of using CUDA on four human volunteers, two adults (29 and 39 years of age) and two children (4.5 and 9.7 years of age). The researchers were thus able to present the first transthoracic images of coronary vasculature in humans that were obtained with CUDA.

“These results demonstrate that it is possible to detect coronary veins and arteries in a transthoracic clinical in vivo setting,” they wrote.

The authors concluded that their work opens new possibilities for the noninvasive characterization of intramural CFR in patients with microvascular angina. They stated that CUDA could also have an important role in enlarging current understanding of the venous myocardial drainage, which remains somewhat murky.

“In a final effort toward clinical translation, we demonstrated that our method could be readily used to image intramural coronary flow in pediatric cardiology,” wrote Maresca and colleagues.