Coronary flow reserve measurement in the coronary sinus in pre and post CABG status
ABSTRACT Background: Coronary flow reserve (CFR) is defined as a maximal(hyperemic) to resting ratio of coronary blood flow. It is a physiologicparameter of coronary circulation and depends on the patency of the epicardialcoronary arteries and integrity of the microvascular circulation.CFR measurement has many clinical applications including functional assessmentof intermediate stenosis, detection of critical stenosis monitoring of coronaryflow in the post angioplasty period, assessment of post infarct blood flow andassessment of coronary graft patency. The aim of this study was to measure CFRin the coronary sinus through the transthoracic echocardiographic approach, inpatients who were candidate for coronary artery bypass graft surgery (CABG)before and one month after operation.Patients and Methods: The present study included 19 patients (meanage=56±9.1) including 15 males and 4 females, admitted for CABG. All patientshad a sinus rhythm, normal wall thickness, normal RV systolic pressure, andtricuspid valvular regurgitation equal or less than grade 2. The antegrade phaseof coronary flow in the coronary sinus moving into the right atrium was analyzedin two phases (systolic and diastolic). Each wave was determined considering thepeak velocity and velocity time integral (VTI). The volumetric blood flow in thecoronary sinus calculated at the baseline and then in hyperemic phase was usedfor determination of CFR both before and after CABG.Results: There was a significant increase in the diameter of the coronarysinus after CABG (9.4±1.2mm) compared with that of before CABG values (8.6±1.05mm). Also there was a trend of increasing the diameter in the hyperemicphase before and after CABG. The absolute increase in mean coronary sinusdiameter was 0.5 mm before and 1.5 mm after CABG. Coronary flow reserve (CFR)was significantly higher after surgery, despite a significant increase insystolic velocity ratio (hyperemic/baseline) after CABG. This is also true forsystolic velocity time integral (VTI) and diastolic VTI ratios, but there was aninsignificant increase in diastolic velocity ratio.Conclusion: Our study in accordance with previous studies, denotes thattransthoracic measurement of the coronary flow reserve can be used as a feasibleand reproducible method to monitor the changes in cardiac perfusion afterrevascularization.
87 Iranian Cardiovascular Research Journal Vol. 1, No. 2, 2007
Coronary flow reserve measurement in the coronary sinus in pre
and post CABG status
M Hajaghaei, M Maleki, HR Salehi, Z Ojaghi, F Noohi
Department of Echocardiography, Shaheed Rajaei Cardiovascular Medical and Research Center, Tehran, Iran.
M. Maleki, MD,
Department of Echocardiography, Shaheed Rajaei Cardiovascular
Medical and Research Center, Mellat Park, Vali Asr Avenue, Tehran,
Iran. Tel: (021) 22055594
Background: Coronary flow reserve (CFR) is defined as a maximal (hyperemic) to resting ratio of coronary
blood flow. It is a physiologic parameter of coronary circulation and depends on the patency of the epicardial
coronary arteries and integrity of the microvascular circulation.
CFR measurement has many clinical applications including functional assessment of intermediate stenosis, de-
tection of critical stenosis monitoring of coronary flow in the post angioplasty period, assessment of post infarct
blood flow and assessment of coronary graft patency. The aim of this study was to measure CFR in the coronary
sinus through the transthoracic echocardiographic approach, in patients who were candidate for coronary artery
bypass graft surgery (CABG) before and one month after operation.
PATIENTS AND METHODS: The present study included 19 patients (mean age=56±9.1) including 15 males
and 4 females, admitted for CABG. All patients had a sinus rhythm, normal wall thickness, normal RV systolic
pressure, and tricuspid valvular regurgitation equal or less than grade 2. The antegrade phase of coronary flow in
the coronary sinus moving into the right atrium was analyzed in two phases (systolic and diastolic). Each wave
was determined considering the peak velocity and velocity time integral (VTI). The volumetric blood flow in
the coronary sinus calculated at the baseline and then in hyperemic phase was used for determination of CFR
both before and after CABG.
Results: There was a significant increase in the diameter of the coronary sinus after CABG (9.4±1.2mm) com-
pared with that of before CABG values (8.6 ±1.05mm). Also there was a trend of increasing the diameter in the
hyperemic phase before and after CABG. The absolute increase in mean coronary sinus diameter was 0.5 mm
before and 1.5 mm after CABG. Coronary flow reserve (CFR) was significantly higher after surgery, despite
a significant increase in systolic velocity ratio (hyperemic/baseline) after CABG. This is also true for systolic
velocity time integral (VTI) and diastolic VTI ratios, but there was an insignificant increase in diastolic velocity
Conclusion: Our study in accordance with previous studies, denotes that transthoracic measurement of the coro-
nary flow reserve can be used as a feasible and reproducible method to monitor the changes in cardiac perfusion
Key words: Coronary Flow Reserve, Coronary Artery Disease, Coronary Sinus.
ormally, blood flow in the coronary arter-
ies can increase 4 to 6 fold to overcome
myocardial oxygen demand. This effect is me-
diated by dilation of arteriolar bed, thereby re-
ducing resistance and accelerating the flow.
Coronary flow reserve (CFR) is defined as
a maximal (hyperemic) to resting ratio of coro-
nary blood flow. It is a physiologic parameter
of coronary circulation and depends on the
patency of epicardial coronary arteries and
www.icrj.ir M Hajaghaei, et al.
Iranian Cardiovascular Research Journal Vol. 1, No. 2, 2007 88
integrity of microvascular circulation. Even in
the absence of stenosis in epicardial coronary
arteries, the CFR is decreased in such com-
promised microcirculation as arterial hyperten-
sion, left ventricular hypertrophy, syndrome X,
diabetes mellitus, hypercholesterolemia and
CFR measurement has many clinical ap-
plications including functional assessment of
intermediate stenosis, detection of critical ste-
nosis monitoring of coronary flow in post PTCA
period, evaluation of post infarct blood flow and
assessment of coronary graft patency.
Several methods have been used for as-
sessment of coronary flow reserve, including
invasive intracoronary Doppler flow wire, PET
scan with limited clinical use imposed by high
cost, and new non-invasive echocardiographic
There are several echocardiographic ap-
proaches including transthoracic Doppler
of coronary arteries mostly LAD and LCX in
decreasing degree of RCA, transesophagial
Doppler of coronary arteries, transthoracic and
transesophagial measurement of coronary si-
nus (CS) receiving blood flow from left coro-
The aim of this study was to measure CFR
in coronary sinus from trans thoracic approach
in patients scheduled for CABG before and
one month after operation.
Patients and Methods:
The present study comprised 19 patients
(mean age=56±9.1) including 15 males and 4
females, admitted for CABG. All patients had
a sinus rhythm, normal wall thickness, normal
RV systolic pressure, tricuspid valvular regur-
gitation equal or less than grade 2. Those with
unstable angina including angina at rest, sig-
nificant valvular disease and history of asthma
were excluded from the study. The drugs were
continued as prescribed.
Echocardiography was done by vivid sev-
en system GE machine. CS was visualized in
long axis from modified RV inflow view while
trying to reduce θ angel for accurate Doppler
measurement of flow. Diameter of coronary si-
nus was measured at baseline status at 1 cm
distance from the mouth in the end diastolic
phase before the P wave on ECG. Sample vol-
ume was used and advanced about 1 cm from
After baseline measurement of CS diam-
eter and flow, dipyridamole (0.56 mg/Kg) was
infused over a 4 min period. An additional in-
fusion of 0.28 mg/Kg over 2 min was used if
there was no increase in heart rate (10% from
After termination of infusion, Doppler profile
of CS was continuously recorded up to 10 min
for detection of hyperemic flow. Diameter of CS
was measured in 3 to 5 min after completion of
infusion. Blood pressure and heart rate were
measured automatically. Echocardiography
was repeated one month after CABG using the
Analysis of coronary blood flow in CS
The antegrade phase of coronary flow in CS
moving into the RA was analyzed in two phases
of systolic and diastolic waves. Peak velocity
and VTI of each wave were determined. The
volumetric blood flow in the CS was calculated
using the following formulas:
CABG related coronary reserve flow www.icrj.ir
89 Iranian Cardiovascular Research Journal Vol. 1, No. 2, 2007
Volume of blood /min =π × D² /4 ×(S VTI +D VTI)×HR
Volume of blood /beat=π × D² /4 ×(S VTI +D VTI)
Where D was the diameter of CS ,S the sys-
tolic velocity time interval, D VTI the diastolic
velocity time interval and HR the heart rate.
This measurement was done in baseline
and then in hyperemic phase for calculation of
CFR both before and after CABG. CFR was
calculated as the ratio of volumetric hyperemic
blood flow to the volumetric baseline blood
flow. The level of CFR < 2 was diagnostic of
low CFR according to previous studies with
sensitivity=89% and specificity =77%3,4.
The statistical analysis was done by SPSS
software package version 11.5. The data were
analyzed by one way analysis of variance
(ANOVA), paired T test and repeated mea-
surement. The data were expressed as mean
EF before CABG (%)
EF after CABG(%)
Table 1: Patients’ age in relation to EF and CABG.
S velocity ratio
D velocity ratio
S VTI ratio
D VTI ratio
CFR: Coronary Flow Reserve, VTI: Velocity TimeIntegral.
Table 2: Echocardiographic data of the study population.
value ±SD. P vlaue less than 0.05 consider sig-
Table 1 demonstrates the patients’ age and
ejection fraction before and after CABG. At
baseline, the heart rate did not differ before
and after CABG (Table 2). There was a sig-
nificant increase in CS diameter in post CABG
status (9.4±1.2 vs 8.6 ±1.05) compared with
the pre CABG baseline. Also there was a trend
towards increasing diameter of CS in hyper-
emic phase before CABG. This increment was
higher in post operative status.
All patients exhibited an increase in the
coronary blood flow before CABG during
dipyridamole stress test (mean CFR/beat
=1.38±0.2, mean CFR/min=1.54 ±0.18). CFR
was significantly higher after surgery (mean
CFR/beat=2.25±0.45, mean CFR/min=2.55
±0.43). Also there was a significant increase (P
=0.007) in mean systolic velocity ratio (hyper-
emic/baseline) before and after CABG (1.21
±0.1 and 1.34 ±0.15 respectively). As shown
in Table 2, this was also true about systolic and
Iranian Cardiovascular Research Journal Vol. 1, No. 2, 2007 90
www.icrj.ir M Hajaghaei, et al.
diastolic VTI ratios, but increase in diastolic ve-
locity ratio was not significant (P = 0.54).
Coronary flow reserve is defined as a maxi-
mum to resting blood flow ratio. Normally, in-
crease in the coronary blood flow is mediated
by dilation of arteriolar bed.
CFR measurement is a very helpful clinical
tool in several conditions including assessment
of intermediate stenosis especially in patients
with chest pain syndrome, detection of critical
stenosis, and in-stent restenosis, as well as
evaluation of graft patency after CABG.
There are two major vasodilators for mea-
surement of CFR, adenosine and dipyridam-
ole. In this study we used dipyridamole as a
vasodilator and stressor test, mostly because
of its prolonged action compared with adenos-
ine5,6. Dipyridamole blocks the intracellular re-
transport of adenosine and inhibit adenosine
deaminase responsible for intracellular break-
down of adenosine7. Thus dipyridamole acts
as an indirect coronary arteriolar vasodilator.
Although assessment of CFR via intracoro-
nary Doppler wire is accurate, but this method
is invasive with radiation exposure; and makes
the follow up study relatively impossible. PET
scan is another method with radiation exposure
and highly expensive. In the passed decade,
there were several attempts for measurement
of CFR by echocardiography as non-invasive
and reproducible results, and mostly performed
on coronary arteries by transthoracic or trans-
esophageal approach. Although the coronary
arteries (mostly leftanterior descending artery)
was detected with Doppler and 2-D images,
these lacked sufficient clarity for accurate
measurement of vessel diameter, thus only the
coronary blood velocity could be measured.
The flow velocity variation is proportional to to-
tal blood flow if vessel lumen is kept constant.
Thus, estimation of CFR can be accurate if the
coronary artery functions only as a conduit4.
CFR measurement of the coronary arteries
by Doppler echocardiography is therefore limit-
ed to the coronary blood velocity. CFR and cor-
onary flow velocity were closely correlated1,8,
because most of the vasodilation was located
in microcirculation and arterioles, but in this
study measurement of blood velocity and VTI
was done on venous side of the coronary sys-
tem. Similar to other veins, coronary sinus has
a thin wall and highly extensible structure; so
the coronary blood velocity is no longer closely
related to CFR.
As a result, for measuring CFR in the coro-
nary sinus, measurement of CS diameter at
baseline and hyperemic phase is mandatory
and ignoring this step may lead to significant
error in estimation of CFR. In another study9
with focus on CS diameter in baseline status
before and after CABG, there was no signifi-
cant increase in CS diameter after surgery.
Another difference in CFR estimation on ar-
terial and venous side was based on different
shape of flow in the cardiac cycle. Regarding
the coronary arteries, there was predominantly
diastolic flow with gradual diastolic slope and
respective peak diastolic and systolic veloci-
ties of 28±9 cm/sec and 17±4 cm/sec10. How-
ever, in CS, the pattern of flow was also related
to right atrial pressure with two distinct systolic
and diastolic waves, considering that systolic
CABG related coronary reserve flow www.icrj.ir
91 Iranian Cardiovascular Research Journal Vol. 1, No. 2, 2007
wave was dominant in the healthy subjects11.
Therefore, simple CFR assessment by dia-
stolic velocity ratio in the coronary artery could
be used with reasonable accuracy (6), but this
is not true with respect to CS, as there was
a significant difference between CFR and dia-
stolic velocity ratio in our study.
Another variable of the coronary blood flow
was heart rate. In our study measurement of
CFR was done in two ways:
CFR/min=HR ×D² /4 × (S+D) VTI
CFR/beat=D² /4 × (S+D) VTI
In our study, a close relationship between
above equations led to CFR/min to be higher
than CFR/beat in all cases. Therefore, con-
sidering these technical points, coronary flow
reserve measurement by transthoracic echo-
cardiography can be used as a feasible and
reproducible method to monitor the changes in
cardiac perfusion after revascularization.
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