Calculation of the index of microcirculatory resistance without coronary wedge pressure measurement in the presence of epicardial stenosis.
OBJECTIVE
This study sought to investigate a novel method to calculate the index of microcirculatory resistance (IMR) in the presence of significant epicardial stenosis without the need for balloon dilation to measure the coronary wedge pressure (P(w)).


BACKGROUND
The IMR provides a quantitative measure of coronary microvasculature status. However, in the presence of significant epicardial stenosis, IMR calculation requires incorporation of the coronary fractional flow reserve (FFR(cor)), which requires balloon dilation within the coronary artery for P(w) measurement.


METHODS
A method to calculate IMR by estimating FFR(cor) from myocardial FFR (FFR(myo)), which does not require P(w) measurement, was developed from a derivation cohort of 50 patients from a single institution. This method to calculate IMR was then validated in a cohort of 72 patients from 2 other different institutions. Physiology measurements were obtained with a pressure-temperature sensor wire before coronary intervention in both cohorts.


RESULTS
From the derivation cohort, a strong linear relationship was found between FFR(cor) and FFR(myo) (FFR(cor) = 1.34 × FFR(myo) - 0.32, r(2) = 0.87, p < 0.001) by regression analysis. With this equation to estimate FFR(cor) in the validation cohort, there was no significant difference between IMR calculated from estimated FFR(cor) and measured FFR(cor) (21.2 ± 12.9 U vs. 20.4 ± 13.6 U, p = 0.161). There was good correlation (r = 0.93, p < 0.001) and agreement by Bland-Altman analysis between calculated and measured IMR.


CONCLUSIONS
The FFR(cor), and, by extension, microcirculatory resistance can be derived without the need for P(w). This method enables assessment of coronary microcirculatory status before or without balloon inflation, in the presence of epicardial stenosis.
Department of Cardiovascular Medicine, Stanford University Medical Center, Stanford, California, USA.
Andy S
AS
Yong
Jamie
J
Layland
William F
WF
Fearon
Michael
M
Ho
Maulik G
MG
Shah
David
D
Daniels
Robert
R
Whitbourn
Andrew
A
Macisaac
Leonard
L
Kritharides
Andrew
A
Wilson
Martin K
MK
Ng
D000368:Aged; D001315:Australia; D001794:Blood Pressure; D002140:California; D006328:Cardiac Catheterization / Q000295:instrumentation; D062906:Cardiac Catheters; D003326:Coronary Circulation; D023921:Coronary Stenosis / Q000175:diagnosis* / Q000503:physiopathology; D005260:Female; D053805:Fractional Flow Reserve, Myocardial; D006801:Humans; D016014:Linear Models; D008297:Male; D008833:Microcirculation; D008875:Middle Aged; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D014160:Transducers, Pressure; D014655:Vascular Resistance