ECHONOMY
Tools for Echocardiographic Calculations

Muhamed Saric, MD, PhD
New York University

## Definition

CFR stands for coronary flow reserve and is a measure of total coronary resistance epicardial + intramyocardial).

## Technical Hints

 Vmax distal to a coronary stenosis is measured by Doppler wire at rest and after maximal hyperemia (e.g. after adenosine infusion at 140 µg/kg/min) Doppler wire uses a tip- or side-mounted crystal and pulsed wave (PW) Doppler technique to measure Vmax. Vmean is calculated as 1/2 * Vmax Vmean is a measure of total coronary resistance if one assumes that the cross-sectional area of coronary vessels does not change from rest to maximal hyperemia.

## Calculator

Vmean at rest

cm/sec

Vmean at maximal hyperemia

cm/sec

CFR

Interpretation

The more severe the coronary stenosis, the lower the increase in hyperemic Vmean.

 Normal CFR Absolute for vessel (e.g. LAD) >2.0 Relative to reference vessel (e.g. LAD vs. RCA) >0.8

## Formulas

V in the CFR formulat refers to Vmean.

## References

Wilson RF, Laughlin DE, Ackell PH, Chilian WM, Holida MD, Hartley CJ, Armstrong ML, Marcus ML, White CW. Transluminal, subselective measurement of coronary artery blood flow velocity and vasodilator reserve in man. Circulation. 1985 Jul;72(1):82-92. [This article has a nice drawing of an early Doppler wire with a side-mounted 20 MHz crystal.]

Doucette JW, Corl PD, Payne HM, Flynn AE, Goto M, Nassi M, Segal J. Validation of a Doppler guide wire for intravascular measurement of coronary artery flow velocity. Circulation. 1992 May;85(5):1899-911. [This article has a nice drawing of a modern Doppler wire with a tip-mounted 12 MHz crystal.]