Coronary Hemodynamics

Sketch coronary

Coronary feeds in diastole

Measurement of coronary function

Non invasive measurement Invasive measureMR CT PET

CAGIVUSOCTFFRCFR

FFR IS GOLD STANDARD

The bottle neck of CAG

Poor correlation of physiologic ischemiaThe reason : minimal luminal dimensions and area, stenosis length,

exit and entrance angles, reference vessel diameter, and diffuse coronary narrowing

intravascular ultrasound (IVUS)

Some improvement upon the decision of removing stenosis but not satisfactory

Auto regulation limit

Maintain myocardial perfusion in systolic BP=60-180 mmHg

Auto regulation failure alarm

Angina or equivalent Myocardial hibernation Myocardial stunning Myocardial infarction

Unique metabolism in cardiac muscle• Myocardial blood flow α the balance of myocardial oxygen (MVO2)

demand and supply• Heart assimilates from instantaneous oxidation of FFA, glucose, lactate,

pyruvate, and amino acids• ATP is produced and consumed and no storage• No oxygen debt as seen in skeletal muscle• Any compromise in substrate=blood flow switch on alarm of energy

conservation of energy for the maintenance of cellular function• Mechanical work is impaired =RWMA• Myocardial sleeps in “hibernation” or death(MI)

ATP sharing areas

• Basal cellular metabolism: 20% • myocardial force generation: 80%

MVO2[/min O2 in cardiac muscle] α CBF• cardiac myocyte shortening• contractility• Relaxation• myocardial wall tension• heart rate

Sales

1st Qtr 2nd Qtr 3rd Qtr 4th Qtr

Coronary collaterals imply

• Attenuate the degree of ischemia • Degree of collaterals is variable[number,size and location] • Chronic severe stenosis • Less long term mortality

Coronary resistance

• ΣEpicardial+precapillary arteriole+ myocardial capillary resistances• Coronary blood flow is inversely related to coronary resistance• Epicardial vessels are direct conduits and no resistance• R2 is seat of coronary resistance

Resistance in series and Ohm’s law

R1:Epicardial vessel and resistance is zero in healthR2:Precapillary arteriole =Auto regulation site=the seat of Coronary resistance in healthR3:Intra myocardial capillary resistance is affected by systole And diastole

Resistance determinants1. size of individual vessels (length and diameter)2. Organization of the vascular network (series and parallel)3. Physical characteristics of the blood (viscosity, laminar flow

versus turbulent flow)4. Extravascular mechanical forces acting upon the vasculature

The seat of coronary resistance

• Precapillary arterioles[R1] connect the epicardial arteries to the myocardial capillaries and are the primary determinants of coronary resistance and flow

Microvasculature

• The myocardial capillary bed after Precapillary arterioles forms an extensive network connecting each myocyte, often referred to as the microvasculature

Coronary flow reserve (CFR)

• Ratio of maximum hyperaemic flow to resting flow• X2-5 is normal• Epicardial stenosis > 60% (diameter) limits maximal CBF in rest &work• Stenosis >80% impairs resting blood flow

TIMI FLOW GRADE

• Raw and qualitative

Grade TFG MBG/TPG

0 No antegrade flow beyond thelesion.

Minimal or no or opacification (“blush”) of themyocardium in distribution of culprit artery

1 Contrast passes beyond lesion butfails to opacify entire coronarybed.

Myocardial blush in distribution of culprit lesionthat fails to clear from microvasculature (contraststaining present on next injection (~30 seconds).

2 Contrast passes beyond lesionopacifies distal coronary bed butrate of entry and/or rate ofclearance slower than comparableareas not perfused by the culpritvessel.

There is myocardial blush in the distribution ofthe culprit lesion that is strongly persistent at theend of the washout phase (after 3 cardiac cyclesof the washout phase and either does not or onlyminimally diminishes in intensity duringwashout).

3 Antegrade flow into the bed distalto lesion occurs as promptly asinto the bed proximal to theobstruction and clearance ofcontrast material from theinvolved bed is as rapid as from anuninvolved vascular bed.

Myocardial blush in distribution of culprit lesionclears normally and is either gone or onlymildly/moderately persistent at end of washoutphase (after 3 cardiac cycles of the washout phaseand noticeably diminishes in intensity during thewashout phase) similar to that in an uninvolvedartery. Blush that is of only mild intensitythroughout the washout phase but fadesminimally is also classified as grade 3.

Angiographic Flow Estimation

TIMI Frame Count: Epicardial coronary Number of cine frames required for radiographic contrast to reach a

standardized distal coronary landmark in the culprit vessel in a single scene

CTFC is normalized to the TFC to the LAD Better than TIMI flow grades Normal CTFC is less than 20 CTFC of up to 40 is seen in TIMI 3 flow implies vessel is diseased High CTFC despite an open epicardial artery in the setting of AMI is

thought to represent microvascular obstruction or dysfunction

TIMI myocardial perfusion grade (TMPG) TMPG is a semi quantitative Zwolle Myocardial Infarction Study Group in the Netherlands Blood flow in capillary Best angiographic projection to visualizes subtends myocardium of interest Images are obtained with adequate injection allowing reflux of contrast into

the aortic root Injection is stopped after opacification of the coronary sinus Cineangiography is continued until three cardiac cycles after myocardial

blush begins to Poor TMPG is poor outcome despite TIMI III epicardial flow

Andreas Gruentzig in 1978

First to directly measure PdDegree stenosis First coronary balloon catheters with side holesThis old gold tech was the forerunner of FFR

Sensing using a Intra coronary wire

Senses pressure/ Doppler/temperature 0.014” sensory angioplasty guide wire Intravenous heparin (40-60 IU/Kg) Intracoronary NTG Measure pressure and flow Quantify stenosis, assess the microvascular circulation, and gauge the

physiologic response to mechanical or pharmacologic interventions

FFR

Couples hemodynamic and anatomy Direct Coronary Pressure MeasurementDetects pressure loss distal to obstruction Ratio of the maximal flow to the myocardium in the presence of a

coronary stenosis normalized to the theoretical maximal flow in the same artery without a Stenosis

Normal FFR is 1.0<0.75 is intervention0.75-0.80 is grey zone

Types of FFR

FFR myocardium FFR coronary FFR collateral:CFI RELATION

(Pd –Pv) / (Pa – Pv) (Pd – Pw) / (Pa – Pw) (Pocc – CVP)/Pa – CVP) FFRcor + FFRcollateral

Pd, Pa, Pv, Pw and Pocc are the mean distal, aortic, venous,wedge pressures and coronary pressure distal to occlusion

Coronary Flow Reserve

Known as coronary vasodilatory reserve (CVR) Ratio of maximal to basal coronary flow in same artery No longer routinely used because of several limitations Doppler or thermodilution methods CFR=epicardial+ microvascular resistance Normal CFR > 3.0 CFR of <2.0 =ischemia

FFR vs. CFR

FFR CFR Wide clinical application Limitations

1.Assumes microvascular resistance is nil but it is never so2.Assumes pressure α flow but really it is relation is curvilinear

Measure for microvascular resistance Limitations: affected by in BP,HR and other factor

affecting microvascular function

Microvascular Resistance Measurements• Newer concept• Called index of microvascular resistance (IMR)• Method: combination pressure and thermo dilution• Principle: Ohm’s law like FFR• Epicardial vessel is almost normal/opened spontaneously or by PCI• Reproducible• Less hemodynamic dependence

Applied

• Intermediated stenois• Bifurcation • LMCA• Multivessel disease• Serial stenosis• Microvascular disease• Heart Failure

Intermediated stenosis

• Defer PCI if trans-stenotic gradient (<25 mmHg) or Doppler-derived CFR >1.7 after IV adenosine• DEFER trial: Defer PCI if FFR>0.75• COURAGE(using SPECT) and FAME-2(FFR) agree upon deferring PCI if

FFR>0.8

LMCA:R1 disease

A FFR cut off >0.8 do equally well on medical management or CABG

Multivessel disease and FFR

Reduces number of stents[FAME ] No survival benefit revascularising FFR<0.75 of single stenosis MACE are more with intervention Revascularisation approach PCI vs. CABG is modified Functional SYNTAX score improves the management style

Bifurcation Stenting

Provisional stenting ruled in/out Intervening on the “jailed” side branch only if FFR < 0.75: kissing

balloon/stenting

Serial stenosis or diffuse disease 2 lesions in series impair maximal flow Pd/Pa of each one interdependence Pullback and first Rx largest step-up if both have FFR <0.8 Equal step up,Rx distal first Check FFR of residual before conclusion

Heart failure:R3 is affected

Extent of functional myocardium and related vessel Heterogeneous microvascular bed Few capillary beds to dilate FFR=1 regardless of the severity of the lesion If artery supplies a large Δ of myocardium outside of the normal

distribution via collateral circulation, FFR may reach ischemic thresholds

↑ LVEDP may lead to underestimation of true FFR