Coronary flow reserve (CFR) is the ratio of resting coronary blood flow to maximum coronary blood flow. As a descriptor of myocardial blood supply, CFR suggests the ability of the coronaries to increase blood flow under stress. It’s a non-invasive test that could help rule out or measure multi-vessel ischemic Coronary Artery Disease (CAD).
Physicians primarily consider coronary flow reserve studies for cardiac patients who continue to be symptomatic after standard imaging and studies. Two factors that cardiologists often weigh when considering offering CFR are the frequency of which you’ll require the study and the overall clinical value of the data. In this post, we’ll take a look at these two dynamics and explore the benefits and limitations of offering coronary flow reserve studies.
The current approaches to evaluate myocardial blood flow include Intracoronary Doppler Ultrasound, echocardiography transesophageal sampling or transthoracic sampling with doppler, Cardiac SPECT, Cardiac PET, and pressure tipped catheters that can be used during diagnostic cardiac catheterization.
Frequency of CFR studies and diagnostic confidence
Coronary flow reserve studies are generally reserved for more unique cases that require greater clarification rather than ordered on a routine basis. It’s estimated that less than 10% of patients would benefit from CFR and the study provides a marginal amount of information which rarely cements a clinical diagnosis.
Typically, CFR is considered an additional data point that can confirm suspicions of triple vessel disease or poor dilation during stress, for example. However, many variables can affect the quality of the results.
When the images appear normal but the CFR result is contradictory or inconclusive, the coronary flow reserve results are often in question. Many cardiologists are more apt to lean towards what they can see or place more trust in other tests. CFR can be valuable, especially when it’s consistent with other findings, but when the results are called into question, a coronary flow reserve study may not create the diagnostic confidence to override other tests.
Evaluating the full picture
Although Cardiac PET is getting a lot of buzz for Coronary Flow Reserve studies, many cardiology practices have to step back and consider the full spectrum of their imaging needs. Given the small subset of cardiology patients who might qualify for CFR—especially under the stricter appropriate use guidelines— and given that several other diagnostic approaches are available, the ability to obtain CFR is not the determining factor in whether or not to invest in a Cardiac PET program in your office.
A substantial patient panel would be necessary to justify the purchase of a Cardiac PET imager for the ability to obtain CFR, and while the current reimbursement landscape is favorable to PET, changes could be on the horizon that greatly affect the rates and red tape associated with the studies.
The coronary flow reserve calculation can be an important component in certain diagnoses, but it’s critical to weight the full picture before making an investment that will affect your practice.