Use of Indocyanine Green (ICG) to Assess Myocardial Perfusion and Territorial Distribution of Vein Grafts Implanted on Coronary Arteries in an Ex-vivo Porcine Model. A Potential Adjunct to Assist Revascularization Strategies and Training in Coronary Artery Bypass Grafting

Abstract

Background: The fluorescent dye indocyanine green (ICG) has been used to identify anatomical structures intraoperatively in coronary artery bypass grafting (CABG). This study aimed to evaluate the feasibility of using ICG to assess graft patency and territorial distribution of myocardial reperfusion during CABG.

Methods: Porcine arrested hearts (n = 18) were used to evaluate territorial distribution of native coronary arteries and of a coronary bypass constructed with porcine saphenous vein graft (SVG) using ICG. Coronary ostia were dissected and selectively cannulated for ICG injection. Sequential fluorescence was assessed in the epicardial coronary arteries, myocardium and coronary veins using an infrared-sensitive charge-coupled device (CCD) camera system. In a separate set of experiments, SVG was used for anastomosis in end-to-side fashion to a terminal obtuse marginal (OM) branch. This approach was used to avoid bias in the assessment of territorial distribution. The anastomosis was injected with ICG; graft patency and territorial distribution was assessed using an infrared-sensitive CCD camera system from 30 cm above the field, as previously described. Native circulation and SVG grafts were assessed using real-time video recording and fluorescence intensity mapping that was averaged into a graded scoring system. The heart was divided into functional regions: anterior wall, lateral wall, inferior wall and right ventricle. All experiments were performed in triplicates.

Results: After ICG injection into the individual coronary ostia, perfusion of the native coronary artery was visible. Portions of the vessels embedded into the epicardial fat could be easily visualized on the surface of the heart and the dissection facilitated via fluorescence guidance. The territorial distribution reflected the expected regional perfusion. The SVG graft was anastomosed to an OM branch. ICG visualization allowed for assessment of graft patency excluding potential technical anastomosis problems or graft twisting or dissection. The myocardial perfusion observed in real-time confirmed regional distribution to the entire lateral wall and minimally to the inferior wall. These findings were confirmed in all the specimens used in the study.

Conclusions: Besides assisting the identification of intramyocardial vessels, ICG can provide information on the native coronary circulation status and the territorial distribution of the perfusion before and after grafting. It enables visualization of collaterals and the territory of distribution subtended by a graft offering real-time assessment and guidance on the grafting strategy.

Keywords: arteriogenesis; coronary artery bypass grafting; fluorescent imaging; fractional flow reserve; graft patency; incomplete revascularization; indocyanine green; neoangiogenesis.

Fig. 1.

Karl Storz Rubina® lens system and IMAGE1 S™ technology. During the injection of ICG into the bypass graft, the light emitted by the laser device at 806 nm and 2.0 W excites the fluorophore and the fluorescent emitted light is captured by an infrared-sensitive charge-coupled device (CCD) camera system. The image is clearly displayed in a 4K monitor with the opportunity to obtain information about the intensity of the fluorescent signal (intensity map) and a pure modality of near infrared (monochromatic) to distinguish the contour of the anatomical structure. The possibility to register the fluorescent signal assures the quantification of parameters which are helpful for the stenosis measurement and the control of quality of graft-coronary anastomosis. ICG, indocyanine green. The persons approved the use of this photograph for publication.

Fig. 2.

Visualization of coronary arteries after ICG injection. The injection of ICG into coronary ostia via direct cannulation shows coronary stenosis or occlusion and, when there is a thick layer of epicardial fat, the fluorescence of the dye may guide the dissection of fat tissue to show the coronary arteries (red arrows). Therefore, it is possible to visualize in real time the perfusion of intramural coronary arteries to facilitate dissection (A, B: lateral wall; C, D: inferior wall). This technique allows an initial assessment of the course and the occlusions of coronary arteries. ICG, indocyanine green.

Fig. 3.

Visualization of the native coronary arteries with ICG injection. Anatomic visualization (A) and fluoroscopic signal (B). Red arrow: native coronary artery. ICG, indocyanine green.

Fig. 4.

Identification of target coronary artery, removal of epicardial tissue and end-to-side anastomosis with the aid of ICG injection. Vessel identification (A), opening (B,C) and anastomosis (D). ICG, indocyanine green.

Fig. 5.

Visualization of the saphenous graft to obtuse marginal perfusion with ICG injection. Anatomic visualization (A) and fluoroscopic signal (B). Red arrow: graft anastomosis. ICG, indocyanine green.

Fig. 6.

Fluorescence and territorial distribution at baseline and after graft injection. Box-and-Whisker plot is formatted according to Tukey.