Coronary physiology before and after chronic total occlusion treatment: what does it tell us?

Abstract

Studies performed in the last two decades demonstrate that after successful percutaneous coronary intervention (PCI) of a chronically occluded coronary artery, the physiology of the chronic total occlusion (CTO) vessel and dependent microvasculature does not normalise immediately but improves significantly over time. Generally, there is an increase in fractional flow reserve (FFR) in the CTO artery, a decrease in collateral blood supply and an increase in FFR in the donor artery accompanied by an increase in blood flow and decrease in microvascular resistance in the myocardium supplied by the CTO vessel. Analogous to these physiological changes, positive remodelling of the distal CTO artery also occurs over time, and intravascular imaging can be helpful for analysing distal vessel parameters. Follow-up coronary angiography with physiological measurements after several weeks to months can be helpful and informative in a subset of patients in order to decide upon the necessity for treatment of residual coronary artery stenosis in the vessel distal to the CTO or in the contralateral donor artery, as well as in deciding whether stent optimisation is indicated. We suggest that such physiological guidance of CTO procedures avoids unnecessary overtreatment during the initial procedure, guides interventions at follow-up, and improves our understanding of what PCI in CTO means.

Keywords: Chronic total occlusion; Coronary flow reserve; Fractional flow reserve; Percutaneous coronary intervention; Physiology.

Fig. 1

Fractional flow reserve (FFR) in a normal vessel (a), in an intermediate stenosis (b) and a chronic coronary total occlusion (CTO) (c). Generally, when using myocardial FFR (FFR_myo), venous pressure (P_v) is neglected and FFR is defined as the distal coronary to aortic pressure ratio (P_d / P_a) at maximum hyperaemia. When there is no stenosis (a) there is no pressure loss over the coronary artery, meaning P_a and P_d are equal and FFR is 1.0. In an intermediate stenosis (b) FFR is decreased due to the loss of pressure over the stenosis and the contribution of collateral blood flow is small. In the case of CTO (c) collateral flow becomes the predominant contributor to distal myocardial perfusion. The collateral contribution can be calculated separately by FFR_coll = P_w / P_a, where P_w is wedge pressure. If there is elevated P_v, this component should be measured separately. FFR_cor coronary FFR, RCA right coronary artery, LAD left anterior descending artery, V venous pressure

Fig. 2

Collateral fractional flow reserve (FFR_coll) assessment using coronary wedge pressure (P_w). Example of how to assess P_w. In order to evaluate the contribution of collateral vessels a pressure wire can be advanced into the just opened chronic total occlusion (CTO) vessel. Then a balloon is advanced over the pressure wire and inflated at low atmospheric pressure to occlude the vessel transiently (preferably within the just placed stent) and P_w is measured. FFR is still represented by the ratio of P_d (called now P_w) and P_a. When antegrade flow is 0, FFR consists exclusively of FFR_coll. FFR_myo myocardial FFR, FFR_cor coronary FFR, RCA right coronary artery, LAD left anterior descending artery, V venous pressure

Fig. 3

Example synthesising all angiographic and physiological measurements before and after percutaneous coronary intervention (PCI) and at follow-up. All values in the images are based on measurements in one selected patient. To date, no large studies have combined all measurements. a Schematic and angiographic situation before intervention with a chronic total occlusion (CTO) of the right coronary artery (RCA) and donor arteries from the left anterior descending (LAD) artery to the distal RCA. b Situation before PCI of the CTO when assessment of only collateral and donor vessel flow is possible. c Situation immediately after opening the CTO vessel. Now both assessment of antegrade flow and fractional flow reserve (FFR) of the CTO vessel and donor/collateral supply is possible. d Assessment of all values is possible. FFR_cor fractional flow reserve of the coronary artery, FFR_coll collateral fractional flow reserve, FFR_myo myocardial fractional flow reserve (= FFR_cor + FFR_coll), Q absolute myocardial blood flow in ml/min, R microvascular resistance in Wood units (WU) (mm Hg · ml/min), V venous pressure