Assessment of Global Myocardial Perfusion Reserve Using Coronary Sinus Flow Measurements

Myocardial perfusion reserve is the ratio of global myocardial blood flow at stress vs.
rest. Traditionally, it has been measured non-invasively using quantitative positron
emission tomography (PET) or cardiac magnetic resonance (CMR). Several recent studies have
suggested that measurement of myocardial perfusion reserve provides significant additive
prognostic information during stress perfusion imaging in patients with known or suspected
coronary artery disease. Myocardial perfusion reserve depends not only on trans-stenotic
pressure gradient of the epicardial arteries and thus stenosis severity but even more on the
ability of the coronary microvasculature (especially the pre-arterioles) to dilate.
Therefore, coronary microvascular dysfunction, which impairs pre-arteriolar function,
reduces myocardial perfusion reserve independently of the presence of epicardial coronary
stenosis. Hence, the ability to measure myocardial perfusion reserve allows a more
comprehensive assessment of the entire coronary circulation, beyond the current paradigm of
the epicardial arteries.

However, both PET and current CMR techniques are cumbersome, and in the case of PET require
radiation as well as on-site Rubidium-82 generators. Therefore, they are challenging for
routine clinical practice and have been limited to specialized research centers. An
alternative, simple CMR method for measurement of myocardial perfusion reserve by
quantifying change in coronary sinus flow has been described. The coronary sinus drains
approximately 96% of total myocardial blood flow and provides a potentially convenient
location for measurement of global myocardial blood flow. This method has been validated
against both invasive and PET techniques. The investigators hypothesized that measurement of
coronary sinus flow at stress and rest may provide a simple and rapid assessment of
myocardial perfusion reserve during regadenoson stress perfusion CMR.

This study will use phase contrast images obtained from patients during their clinically
indicated CMR stress study to calculate myocardial perfusion reserve as the ratio of maximum
myocardial blood flow to baseline blood flow - at the coronary sinus. Coronary sinus flow
will be calculated by post-processing of images after the patient has left the scanner. In
brief, the contour of the coronary sinus will be traced on the flow images throughout the
cardiac cycle. Coronary sinus flow is calculated by integrating the momentary flow rate
values from each cardiac phase over the entire cardiac cycle and multiplying by the mean
heart rate during the acquisition. Patients will be followed for the occurrence of major
adverse cardiac events (death, myocardial infarction, late revascularization,
hospitalization for heart failure or unstable angina).

Inclusion Criteria:

- Age ≥18

- Male or Female

- Referred for clinical cardiac magnetic resonance stress testing (with Regadenoson) at
the University of Illinois Hospital & Health Sciences System by their healthcare
provider as part of their routine clinical care for known or suspected coronary
artery disease.

Exclusion Criteria:

- Presence of metallic implants contraindicated with cardiac magnetic resonance (e.g.
implantable cardiac defibrillator, pacemaker)

- Glomerular Filtration Rate (GFR) <30ml/min

- High degree atrio-ventricular block

- Hypersensitivity to Regadenoson

- Severe active wheezing from asthma

- Severe claustrophobia