Transcript Diapositiva 1

Pathophysiology of the
coronary circulation:
role of FFR
Giuseppe Biondi Zoccai
University of Modena and Reggio Emilia, Modena, Italy
[email protected]
Functional significance of coronary
stenosis
• Past, present, future
• Pathophysiology
• Definitions and basics
• Other aspects
The original balloon from Andreas
Gruentzig
The first coronary angioplasty by
Andreas Gruentzig
Functional significance of coronary
stenosis
• Past, present, future
• Pathophysiology
• Definitions and basics
• Other aspects
Basic coronary physiology
• Coronary blood flow = 3-5% of CO
• Resting myocardial O2 demand is extremely
high
(20 x skeletal O2 demand)
• Myocardium extracts maximum O2 from blood
(80% versus 30-40% skeletal muscle)
• Myocardium has high capillary density
(3000-4000/mm2 versus 500-2000/mm2 skeletal muscle)
• Therefore, only way to meet increasing
demand is to increase blood flow
Maintaining coronary flow
Maintaining coronary flow
Coronary circulation
Myocardial blood flow
=
coronary flow (Qs) + collateral flow (Qc)
Coronary circulation
Pressure derived flow measurements
Pressure (Pmean)
Blood flow (Q) =
Resistance (R)
Coronary circulation
Resistance distribution in the coronary tree
Stenosis lead to drop in pressure
Stenosis lead to drop in pressure
Coronary blood flow vs % diameter stenosis:
Autoregulation of resting flow
50%
85%
Rest CBF Ml/gm/min
1.0
0%
0
50
% Stenosis
80
Coronary reserve
Functional significance of coronary
stenosis
• Past, present, future
• Pathophysiology
• Definitions and basics
• Key aspects
Coronary circulation
What is FFR?
FFR is a ratio or % of two flows:
Maximum hyperemic flow in the presence of a stenosis
FFR =
Normal maximum flow
FFR represents the extent to wich maximal myocardial blood
flow is limited by the presence of epicardial stenosis
FFR is a segment by segment evaluation of the flow
Pressure derived flow measurements
Theoretical bases of FFR
Pressure derived flow measurements
FFRmyo=
Q
QN
( Pd – Pv )
=
R
=
(Pa - Pv)
(Pd – Pv)
=
(Pa - Pv)
Pd
Pa
R
• Because the myocardial vascular bed is maximally vasodilated
its resistance is minimal and constant.
• Because, generally, central venous pressure is close to 0
R = Myocardial resistance at maximum vasodilation
Pd = Hyperemic distal coronary pressure
Pa = Mean aortic pressure
PV = Mean central venous pressure
Relative pressure and relative flow
QS = Flow in stenotic vessel
QN = Flow in normal vessel
Pijls et al, Circulation 1993;87:1354-67
Rationale of FFR
Rationale of FFR
ΔP = 30 mm Hg in all 3 cases
but
Driving pressure over the myocardium
(wich determines myocardial perfusion
at maximum vasodilatation) varies from
25 to 70 mm Hg
Hyperemic blood flow is not determined
by ΔP but by (Pd-Pv)/(Pa-Pv)
=
FFR myo
Intermediate lesions
54-y-o. man, PTCA prox LAD 8 years ago,
stable angina, occluded distal LCx
Adenosine 40 µg IC
48-y-o. man, aborted sudden death,
no other stenosis at angio
Adenosine 40 µg IC
• Intermediate stenosis
• Mild-to-moderate stenosis
Angiographist’s glossary • Non flow limiting stenosis
• Non significant stenosis
FFR = 90 / 93 = 0.97 • Gross irregularity FFR = 50 / 92 = 0.53
• ...
Coronary circulation
Myocardial blood flow
=
coronary flow (Qs) + collateral flow (Qc)
An identical stenosis, but...
• 26 col-schema fcf (figuur)
100
50
0
Pd
Poor collaterals
low FFR = 0.50
An identical stenosis, but...
• 26 col-schema fcf (figuur)
100
75
0
Pd
Good collaterals
higher FFR = 0.75
Visible collaterals on the coronary
angiogram (Rentrop) and fractional
collateral blood flow Qc/Qn
Comparison with stress testing
Anatomic assesement of a stenosis
% diameter
stenosis
Angiographic significance of coronary lesions
0
10
20
30
40
50
60
70
Discrete nonischemic
Ambiguous
Borderline
Intermediate
Moderate
Gould, Am J Cardiol 1974;33:87-94
80
90
100
Critical
Ischemic
Severe
Significant
Physiologic lesion assessment
Threshold value of FFR to detect
significant stenosis
Gray zone
FFR
Non-signif.
1.0
0.80
Significant stenosis
0.75
Sensitivity : 90%
Specificity : 100%
Pijls et al, New Engl J Med 1996; 334:1703-1708
0
Visual angiographic assessment vs
FFR in the FAME trial
Tonino et al, J Am Coll Cardiol 2010;55:2816-21
Functional significance of coronary
stenosis
• Past, present, future
• Pathophysiology
• Definitions and basics
• Other aspects
Acute microvascular damage in
myocardial infarction
STEMI
Variable degree of
reversible microvascular
stunning
Maximum achievable
flow is less
Smaller gradient and
higher FFR across any
given stenosis
With time, the microvasculature may recover, maximum
achievable flow may increase, and a larger gradient with a
lower FFR may be measured across a given stenosis
Similar stenosis but different extent
of perfusion area
50 ml /min is too low
Normal Myocardium
50 ml /min is sufficient
Scar
Normal Myocardium
FFR = degree of stenosis and extent of perfused miocardial mass
What about serial lesions?
Hyperemic stimulants
Hyperemic stimulants
Jeremias et al, Am Heart J 2000;140:651-7
Hyperemic stimulants
Casella et al, Am Heart J 2004;148:590-5
What about coffee?
What about severe left ventricular
hypertrophy?
In severe left ventricular hypertrophy, there is an exaggerated increase of
left ventricular mass in comparison to the vascular bed, resulting in the
potential for ischemia even in normal or almost normal coronary arteries
Thus, sensitivity may be reduced (cut-off >0.80?)
However, specificity remains satisfactory
What about lesion length?
Brosh et al, Am Heart J 2005;150:338-43
What about microcirculation?
Take home messages
Take home messages
• Normal value = 1.0 for every patient and every artery
• FFR is not influenced by changing hemodynamic
conditions (heart rate, blood pressure, contractility)
• FFR specifically relates the influence of the epicardial
stenosis to viable myocardial perfusion area and blood flow
• FFR accounts for collaterals
• FFR has a circumscript threshold value (~ 0.75 – 0.80 ) to
indicate ischemia
• FFR is easy to measure (success rate 99 %) and extremely
reproducible
• Pressure measurement has un unequaled spatial resolution
(pressure pull-back curve)
• Caution in acute myocardial infarction and LV hypertrophy
Interested in more?
Thank you for your attention
For any correspondence:
[email protected]
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