coronary physiology
DESCRIPTION
Various coronary physiological measurements can be made in the cardiac catheterization laboratory using sensor-tipped guidewires; they include the measurement of poststenotic absolute coronary flow reserve, the relative coronary flow reserve, and the pressure-derived fractional flow reserve of the myocardium. Ambiguity regarding abnormal microcirculation has been reduced or eliminated with measurements of relative coronary flow reserve and fractional flow reserve. The role of microvascular flow impairment can be separately determined with coronary flow velocity reserve measurements. In addition to lesion assessment before and after intervention, emerging applications of coronary physiology include the determination of physiological responses to new pharmacological agents, such as glycoprotein IIb/IIIa blockers, in patients with acute myocardial infarction. Measurements of coronary physiology in the catheterization laboratory provide objective data that complement angiography for clinical decision-makingTRANSCRIPT
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