Non-invasive Ischaemia Testing in Patients With Prior Coronary Artery Bypass Graft Surgery: Technical Challenges, Limitations, and Future Directions

Abstract

Coronary artery bypass graft (CABG) surgery effectively relieves symptoms and improves outcomes. However, patients undergoing CABG surgery typically have advanced coronary atherosclerotic disease and remain at high risk for symptom recurrence and adverse events. Functional non-invasive testing for ischaemia is commonly used as a gatekeeper for invasive coronary and graft angiography, and for guiding subsequent revascularisation decisions. However, performing and interpreting non-invasive ischaemia testing in patients post CABG is challenging, irrespective of the imaging modality used. Multiple factors including advanced multi-vessel native vessel disease, variability in coronary hemodynamics post-surgery, differences in graft lengths and vasomotor properties, and complex myocardial scar morphology are only some of the pathophysiological mechanisms that complicate ischaemia evaluation in this patient population. Systematic assessment of the impact of these challenges in relation to each imaging modality may help optimize diagnostic test selection by incorporating clinical information and individual patient characteristics. At the same time, recent technological advances in cardiac imaging including improvements in image quality, wider availability of quantitative techniques for measuring myocardial blood flow and the introduction of artificial intelligence-based approaches for image analysis offer the opportunity to re-evaluate the value of ischaemia testing, providing new insights into the pathophysiological processes that determine outcomes in this patient population.

Keywords: CABG; ischaemia detection; myocardial perfusion; stress imaging; surgical revascularisation.

Figure 1

Panel of nine cases of coronary anatomy post coronary artery bypass graft surgery. All cases show a left internal mammary artery anastomosed to the to the left anterior descending artery (LAD), demonstrating significant variations in anastomosis position along the length of the vessel, as well as significant variations in the post-operative anatomy of the remaining vessels.

Figure 2

Rubidium-82 PET-CT with adenosine stress in an 86-year-old male with previous coronary artery bypass grafting. PET-CT images (A,B) obtained at stress and rest demonstrate a reversible perfusion defect in the mid to apical anterior segments extending into the apex. Cardiac hybrid imaging with three-dimensional fusion of PET-CT with CT coronary angiography enables localization of ischaemia to a coronary artery territory (C). CT coronary angiography reveals a patent LIMA to LAD graft with good distal opacification, and obstructive plaques in the proximal and mid segments of an intermediate artery (white arrow), responsible for the reversible perfusion defect demonstrated.

Figure 3

Patient with angiographically confirmed patent LIMA to LAD and evidence of inducible perfusion defect in LIMA—native LAD subtended territories. Images shown are short axis views from base to apex (left to right). (A) First pass perfusion imaging with adenosine stress, demonstrating a perfusion defect in the basal to mid antero-septum, basal to mid anterolateral and inferolateral and apical lateral walls. (B) Stress myocardial blood flow (MBF) evaluation using perfusion CMR showing reduced MBF in multiple territories, including those supplied by the LIMA—native LAD (e.g., MBF in mid antero-septum is 0.85 ml/g/min, MBF in apical septum is 1.65 ml/g/min). (C) Bullseye plot demonstrating stress MBF in each myocardial territory based on American Heart Association (AHA) segmentation. (D) Late gadolinium images showing no evidence of previous infarction in the LIMA—native LAD territories. (E,F) Coronary angiography demonstrating patent LIMA graft (E) and anastomosis site (F) with good distal run off. From Seraphim et al. (51). Reproduced under the Creative Commons Attribution 4.0 International License.

Figure 4

Peri-infarct ischaemia and scar. Basal (top) and Mid (Bottom) short axis views of a CMR perfusion in patient scheduled to undergo coronary artery bypass graft surgery, demonstrating a previous infarct within the left anterior descending (LAD) territory and a large superimposed perfusion defect extending beyond the area of previous infarction (^*). (A) First pass perfusion CMR during adenosine stress; (B) Perfusion mapping of the same myocardial segment as shown in (A). (C) Dark blood LGE demonstrating a previous infarction within the LAD territory.

Figure 5

Contrast echocardiography post coronary artery bypass graft surgery. Sixty-three-year-old patient with previous CABG and atypical chest pain. (A–D) Apical 3 Chamber view. Baseline, low dose, peak dose, and recovery stages, respectively. Contrast Enhanced Images. Akinetic mid and apical antero-septal wall segments (arrow). No improvement in contractility of these segments during low dose stage confirms non-viable segments. Improvement in contractility of all other segments during low dose and peak dose suggests the presence of viable myocardium and no inducible ischaemia.

Figure 6

Factors impacting non-invasive ischaemia assessment in patients with prior surgical revascularization.