Beyond CAG- IVUS and FFR Dr Frijo Jose A

CAG – Extensively used – Entire cor anatomy, including small & distal vessels – Helpful in clinical decision making 1.Eccentricity 2.Vascular remodelling 3.Relative % stenosis 4.Reference segment assessment 5.Limited correlation with physiology 6.Post PTCA/dissec

1. Eccentricity of lesions

In coronaries with atherosclerosis, the lumen is often irregular and non-circular

Topol, E. J. et al. Circulation 1995;92: Schematic representation of an important limitation of projection imaging

Pitfall: lesion eccentricity

Topol, E. J. et al. Circulation 1995;92: Angiographically unrecognized left main coronary artery disease

2. Vascular Remodelling (Glagov’s phenomenon)

Topol, E. J. et al. Circulation 1995;92: Effect of coronary remodeling

These plaques are particularly prone to rupture. Missed by angiography.

3. Reference seg assessment & Relative % stenosis

Topol, E. J. et al. Circulation 1995;92: Concealment of severe coronary disease by diffuse concentric involvement

IVUS Imaging 2D Cross-Sectional Imaging

4.Limited correlation with physiology and pre-stenting

Chest pain with normal coronaries 50 % have plaques on IVUS, which might have ruptured to cause the chest pain

IVUS before PCI Baseline plaque composition Vessel size Confirm CAG severity

Lesions of uncertain severity- IVUS can solve- (changed original provisional decision in 20%) Intermediate severity (40-75%)- FFR can provide further information (>0.75- favorable outcome with medical Rx) LMCA obstruction- – Contrast in cusps can obscure the ostium – Streaming of contrast can falsely suggest narrowing – There may not be a normal reference segment – Branch vessels overlap distal part- stenosis is masked In ostial lesions, IVUS provides information about whether there is a lesion at all and whether the lesion is truly ostial or not

Quantitation of atheroma (slight overestimation)

Intimal thickness ≥0.5 mm - abnormal and indicative of atherosclerosis Total atheroma volume- motorized device pulls back transducer at 0.5 mm/sec. From the slices so obtained, TAV is found by the Simpson’s rule Most plaques are eccentric- max thickness is more than twice the minimum thickness

Fatty streaks are not clearly identified. Atheroma- fibrosis and calcification are clearly identified, but hypoechoic part may be lipid, thrombus or necrotic degeneration. Radiofrequency analysis superimposed on IVUS helps to clarify the situation. More sensitive than fluoroscopy to detect calcification. Positive remodeling- landmark study by Glagov- initially there is increase in plaque area without decrease in luminal area- due to increase in EEM (enclosed) area.

large, soft, lipid-laden atheroma with a thin fibrous cap is seen (arrows). It is eccentric, involving only approximately 50 percent of the vessel wall shows a circumferential atheroma with an area of focal calcification is evident (arrow).

ACS- – Less obstructive plaques are much more common – More lipid pool – Thin fibrous cap – Ruptured cap – Superimposed thrombus – Multiple sites of rupture

Potentially unstable coronary lesion Echolucent

5. post-stenting and dissection

Initial procedural results Quantifying late intimal hyperplasia

Topol, E. J. et al. Circulation 1995;92: Overestimation of lumen gain by angiography after balloon angioplasty

IVUS – mechanisms of lumen gain by balloon dilation- – Fracture of the plaque – Plaque is redistributed axially – Arterial wall stretching

IVUS and stenting- – Pioneering report by Colombo – High chance of incomplete stent apposition with usual dilation- not seen by check CAG - contrast flows outside the porous stent - fills space provided by the vessel which has been passively dilated by the balloon dilation. Higher pressure dilation or larger balloon size solves problem – Even aft high pressure dilation, when IVUS was done, additional procedures done in %

– STARS study- decreased restenosis in IVUS guided stenting. TULIP study- decreased restenosis only in long and diffuse lesions. – Stent to reference area ratio does not predict TVR. Stent area of 9 mm2 or more predicts freedom from restenosis. – Very useful in suspected dissection after stenting- to know the full length of the dissection. – Useful to discern the cause of “persistent haziness” after stenting. – Restenosis mech- usually neo-intimal proliferation. Also, restenosis at the margins. No decrease in the stent area- stents can withstand remodeling.

Late stent malapposition

IVUS – Tomographic views – Vessel wall + lumen visualization – Validated quantitative software – Plaque characterization – Need to instrument vessels – Limited to proximal segments – Bifurcation lesions – Cost – Not as well validated for clinical decision making – Limited correlation with physiology – Not always perpendicular to vessel axis

IVUS Pitfall : Imaging plane not perpendicular to vessel axis

ACC/AHA Recommendations for Coronary IVUS Class II A 1. Evaluation of lesion severity at a location difficult to image by angiography in patients with a positive functional study and a suspected flow-limiting stenosis 2. Assessment of a suboptimal angiographic result after coronary intervention 3. Diagnostic and management of coronary disease after cardiac transplantation

Absolute flow reserve – Drugs- intracoronary papaverine, intracoronary adenosine, intravenous dipyridamole – Ratio of maximum to resting flow rate – Below 2- causes stress induced ischemia – Reduction may be due to ↑resting flow also – ↓ in severe stenosis and microcirculatory abn

Relative flow reserve – Maximum exercise/pharmacological dilation – Minimum threshold of 0.8 – Inaccurate in multivessel disease – Inaccurate in microcirculatory disease

Fractional flow reserve – During maximum vasodilation – Mean cor pressure/mean Ao pressure – Unaffected by alteration in resting flow – Can immediately assess importance of a lesion for guiding intervention – Considerable prognostic information – FFR more than excellent outcome with deferred rather than prophylactic intervention – Affected by microcirculatory disease – Most direct way to assess physiological significance of a lesion

Simultaneous measurement of pressure in aorta and distal LAD at rest

Simultaneous measurement of pressure in aorta and distal LAD following intracoronary adenosine

Clinical uses of FFR 1. Determining the hemodynamic significance of CAG intermediate lesions: Pijls et al - cutoff 0.75 detected ischemia – sensitivity- 88%, specificity- 100%, diagnostic accuracy- 93% DEFER - moderate CAD + FFR> PCI v/s medical – PCI event rate > medical event rate

Clinical uses of FFR 2. Determining success of PCI: Multicenter registry - FFR determined immediately after stenting – most signi independent variable related to future events

Clinical uses of FFR 3. Determining significance of LMCA lesions: Bech et al- 54pts (29/12)- equivocal LMCA Medical - 24 pts with FFRs >0.75 CABG - 30 pts with FFR <0.75 Survival – medical- 100%, CABG- 97%

Clinical uses of FFR 4. Determining the significance of multiple stenoses in the same coronary artery: FFR can be used to “map” the hemodynamic effects of multiple stenoses in the same vessel FAME (1005pts)- clinical outcomes after PCI on CAG v/s CAG+ FFR in multivessel disease FFR gp- 37% of PCI indented lesns- FFR > yr- composite event rate -18.3% CAG-guided gp V/S 13.2% CAG+FFR-guided group

Recommendations for Use of Fractional Flow Reserve Class IIa Can be useful to determine whether PCI of a specific cor lesion is warranted Can be useful as an alternative to performing noninvasive functional testing (eg, when the functional study is absent or ambiguous) to determine whether an intervention is warranted In the assessment of the effects of intermediate cor stenoses (30% to 70% luminal narrowing) in pts with anginal symptoms

Case study