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Pathophysiology of the coronary circulation : role of FFR. Giuseppe Biondi Zoccai University of Modena and Reggio Emilia, Modena, Italy gbiondizoccai@gmail.com. Functional significance of coronary stenosis. Past, present, future Pathophysiology Definitions and basics Other aspects.

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pathophysiology of the coronary circulation role of ffr

Pathophysiology of the coronary circulation: role of FFR

Giuseppe Biondi Zoccai

University of Modena and Reggio Emilia, Modena, Italy

gbiondizoccai@gmail.com

functional significance of coronary stenosis
Functionalsignificance of coronary stenosis
  • Past, present, future
  • Pathophysiology
  • Definitions and basics
  • Other aspects
functional significance of coronary stenosis1
Functionalsignificance of coronary stenosis
  • Past, present, future
  • Pathophysiology
  • Definitions and basics
  • Other aspects
slide6

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

coronary circulation
Coronary circulation

Myocardial blood flow

=

coronary flow (Qs) + collateral flow (Qc)

slide10

Coronary circulation

Pressure derived flow measurements

Pressure (Pmean)

Blood flow (Q) =

Resistance (R)

coronary circulation1
Coronary circulation

Resistance distribution in the coronary tree

slide14

50%

Coronary blood flow vs % diameter stenosis:

Autoregulation of resting flow

85%

0%

1.0

Rest CBF Ml/gm/min

0

50

80

% Stenosis

functional significance of coronary stenosis2
Functionalsignificance of coronary stenosis
  • Past, present, future
  • Pathophysiology
  • Definitions and basics
  • Key aspects
what is ffr
Whatis 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
Pressurederived flow measurements

( Pd – Pv )

Pd

(Pd – Pv)

Q

R

=

=

FFR =

=

Pa

myo

(Pa - Pv)

QN

(Pa - Pv)

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

Pa = Mean aortic pressure

PV = Mean central venous pressure

Pd = Hyperemic distal coronary pressure

relative pressure and relative flow
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 ffr1
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 ΔPbut by (Pd-Pv)/(Pa-Pv)

=

FFR myo

slide25

Adenosine 40 µg IC

Adenosine 40 µg IC

  • Intermediate stenosis
  • Mild-to-moderate stenosis
  • Non flow limiting stenosis
  • Non significant stenosis
  • Gross irregularity
  • ...

Angiographist’s glossary

FFR = 90 / 93 = 0.97

FFR = 50 / 92 = 0.53

Intermediate lesions

54-y-o. man, PTCA prox LAD 8 years ago,

stable angina, occluded distal LCx

48-y-o. man, aborted sudden death,

no other stenosis at angio

coronary circulation3
Coronary circulation

Myocardial blood flow

=

coronary flow (Qs) + collateral flow (Qc)

slide27

An identical stenosis, but...

  • 26 col-schema fcf (figuur)

100

50

0

Pd

Poor collaterals low FFR = 0.50

slide28

An identical stenosis, but...

  • 26 col-schema fcf (figuur)

100

75

0

Pd

Good collaterals higher FFR = 0.75

anatomic assesement of a stenosis
Anatomicassesement of a stenosis

Angiographicsignificance of coronary lesions

% diameter

stenosis

10

20

30

40

50

60

70

80

90

100

0

Discrete non-ischemic

Critical

Ischemic

Severe

Significant

Ambiguous

Borderline

Intermediate

Moderate

Gould, Am J Cardiol 1974;33:87-94

physiologic lesion assessment
Physiologic lesion assessment

Threshold value of FFR to detect significant stenosis

Gray zone

FFR

Non-signif.

Significant stenosis

1.0

0.80

0.75

0

Sensitivity : 90%

Specificity : 100%

Pijls et al, New Engl J Med 1996; 334:1703-1708

slide33

Visualangiographicassessment vs FFR in the FAME trial

Tonino et al, J Am Coll Cardiol 2010;55:2816-21

functional significance of coronary stenosis3
Functionalsignificance of coronary stenosis
  • Past, present, future
  • Pathophysiology
  • Definitions and basics
  • Other aspects
slide35

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

slide36

Scar

Normal Myocardium

Similar stenosis but different extent of perfusion area

50 ml /min is too low

Normal Myocardium

50 ml /min is sufficient

FFR = degree of stenosis and extent of perfused miocardial mass

hyperemic stimulants1
Hyperemic stimulants

Jeremias et al, Am Heart J 2000;140:651-7

hyperemic stimulants2
Hyperemic stimulants

Casella et al, Am Heart J 2004;148:590-5

slide42

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
What about lesion length?

Brosh et al, Am Heart J 2005;150:338-43

take home messages1
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 toviable myocardial perfusion area and blood flow
  • FFR accounts for collaterals
  • FFR has a circumscriptthreshold 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
slide48

Thank you for your attentionFor any correspondence: gbiondizoccai@gmail.comFor these and further slides on these topics feel free to visit the metcardio.org website:http://www.metcardio.org/slides.html