Coronary flow reserve

Coronary Flow Reserve (CFR) is a term used in cardiology to describe the maximum increase in blood flow through the coronary arteries above the normal resting volume. It is an important physiological parameter that reflects the ability of the coronary circulation to meet increased demands of the myocardium for oxygen and nutrients during increased activity or stress. The concept of CFR is crucial in understanding various cardiac conditions, particularly those related to coronary artery disease (CAD).

Overview

The heart muscle, or myocardium, requires a constant supply of oxygen and nutrients to function effectively. This supply is delivered through the coronary arteries. Under normal conditions, the coronary blood flow adjusts to meet the myocardial demand. However, in the presence of conditions such as atherosclerosis, the arteries' ability to dilate and increase blood flow is compromised, potentially leading to myocardial ischemia and angina.

CFR is measured as the ratio of maximum blood flow to the heart muscle after vasodilation (widening of the arteries) to the flow when at rest. A reduced CFR indicates impaired coronary artery function and can be a predictor of cardiac events.

Measurement

The measurement of CFR can be performed using various techniques, including Doppler ultrasound, positron emission tomography (PET), and magnetic resonance imaging (MRI). Doppler ultrasound is a common method, where a probe is used to measure blood flow velocity in the coronary artery during rest and after a stressor (such as exercise or pharmacological agents that mimic exercise) has been applied.

Clinical Significance

A normal CFR value is typically above 2.0 to 2.5, indicating that the coronary blood flow can increase two to two and a half times above the resting level. Values below this threshold suggest the presence of significant coronary artery disease. CFR is particularly useful in the evaluation of patients with chest pain but no significant coronary artery stenosis on angiography, as it can identify those with microvascular dysfunction.

Limitations

While CFR provides valuable information about the coronary circulation's functional capacity, it has limitations. It does not specify which coronary arteries are affected or the exact location of the obstruction or dysfunction. Moreover, CFR can be influenced by various factors, including blood pressure, heart rate, and myocardial contractility, which can affect its accuracy and interpretation.

Conclusion

Coronary Flow Reserve is a vital parameter in cardiology, offering insights into the functional capacity of the coronary arteries to increase blood flow in response to increased myocardial demand. Its measurement is essential in diagnosing and managing patients with coronary artery disease, particularly in cases where traditional diagnostic methods may not fully reveal the extent of the disease.