Graft Angiography: Definition, Indications, Procedure, and Alternatives
What is Graft Angiography?
Graft angiography is the invasive radiographic visualization of coronary artery bypass grafts using contrast injection to assess patency, flow characteristics, and identify stenoses or occlusions. 1 This procedure evaluates vascular conduits including saphenous vein grafts, internal mammary artery grafts, and other arterial conduits from their origin through the body of the graft to the distal anastomotic site. 1
The technique involves selective catheterization of each graft and injection of radiopaque contrast material while obtaining fluoroscopic images in multiple projections. 1 The angiographic report must document the origin of each bypass conduit (saphenous vein or arterial grafts from the aorta, internal mammary arteries from the subclavian artery), the exact aortic attachment site, and the distal target vessel with specification of whether the anastomosis is proximal, mid, or distal. 2
Primary Indications for Graft Angiography
Early Post-Operative Period (< 30 days)
Urgent coronary angiography is indicated when recurrent ischemia occurs within 30 days postoperatively, as this usually reflects acute graft failure from thrombosis. 1 Emergency PCI of focal graft stenosis or recanalization of acute graft thrombosis may successfully relieve ischemia in the majority of these patients. 1 Balloon dilatation across suture lines can be accomplished safely within days of surgery. 1
Intermediate Period (1-3 years)
PCI is reasonable in patients with ischemia occurring 1 to 3 years after CABG who have preserved left ventricular function with discrete lesions in graft conduits. 1 During this timeframe, perianastomotic graft stenosis is the usual cause, and distal anastomotic stenoses respond well to balloon dilation with favorable long-term prognosis. 1
Late Period (> 3 years)
PCI is reasonable in patients with diseased vein grafts more than 3 years after CABG. 1 At 10 years, only 50-60% of saphenous vein grafts remain patent, and approximately half of those demonstrate atherosclerotic disease. 2 Friable atherosclerotic plaques are present in approximately 44% of saphenous vein grafts. 2
Specific Clinical Scenarios
Recurrent angina after CABG: Angiography is indicated for patients with disabling angina secondary to new disease in native coronary circulation after CABG, though objective evidence of ischemia should be obtained if angina is not typical. 1
Postrevascularization ischemia: Angiography is appropriate when ischemia develops related to prior revascularization procedures. 1
Preoperative evaluation: Angiography before valve surgery or other cardiac procedures in patients with prior CABG. 1
Angiographic Procedure and Technical Considerations
Graft-Specific Catheterization Approach
Saphenous vein grafts originate from the ascending aorta and require selective engagement with appropriately shaped catheters (typically right or left Judkins, multipurpose, or internal mammary catheters). 1 Multiple projections are essential—do not rely on a single angiographic view, as this risks missing subtle anastomotic narrowing that can precipitate early graft failure. 2
Internal mammary artery grafts arise from the subclavian artery and require internal mammary catheters for selective engagement. 1 These grafts demonstrate excellent long-term patency (>90% at 10-15 years) due to resistance to atherosclerosis attributed to a continuous internal elastic lamina and favorable endothelial factors. 2
Critical Assessment Components
Patency determination is the most critical component—every graft must be classified as patent, stenotic, or occluded. 2 In patent grafts, evaluate the uniformity of contrast opacification from proximal to distal anastomosis to ensure uninterrupted flow. 2
Anastomotic site evaluation requires systematic inspection of both proximal (aortic) and distal (coronary) anastomoses for narrowing, stenosis, or technical defects, as anastomotic complications are a leading cause of early graft failure. 2
Flow characteristics assessment includes evaluating distal runoff into the native coronary artery beyond the graft anastomosis to verify adequate perfusion. 2 Arterial grafts to vessels with <70% stenosis on the left side or <90% stenosis in the right coronary artery are prone to failure due to competitive flow. 2
Intraoperative Angiography
A newer approach involves intraoperative graft angiography during off-pump CABG, which identified angiographic defects in 15.9% of all grafts (including 2% graft defects, 10.6% anastomotic defects, and 1.8% target artery errors), leading to re-intervention in 43.4% of detected defects. 3 When utilizing the left radial artery as a free graft, the proximal radial artery stump can be cannulated with a femoral introducer sheath for transradial completion angiography. 4
Non-Invasive Alternatives
Multidetector Computed Tomography Angiography (MDCT)
MDCT is the preferred non-invasive alternative for graft patency assessment, with temporal resolution of 19-75 ms depending on heart rate. 1 Modern 16-slice and 64-slice scanners provide excellent visualization of bypass grafts with sensitivity and specificity exceeding 90% for patency determination. 5
MDCT assessment is easier for venous grafts due to their larger diameter and lack of surrounding clips. 5 However, limitations include artifacts from metallic objects (hemostatic clips, ostial stainless steel graft markers, sternal wires, prosthetic valves). 1 The mean radiation dose is approximately 1.8 mSv per examination. 3
Magnetic Resonance Angiography (MRA)
Coronary MRA using 3D contrast-enhanced techniques demonstrates 93% sensitivity and 97% specificity for detecting graft patency. 6 Both 2D spin-echo and gradient-echo MRA in the transverse plane reliably assess bypass graft patency with sensitivities ranging from 86-98% and specificities from 59-100%. 1
ECG-gated steady-state free precession (SSFP) sequences show similar accuracy to spin-echo approaches. 1 The HASTE (half-Fourier acquisition single-shot turbo spin echo) sequence recognized 95% of patent grafts with 93% specificity. 7
Critical limitation: MRA cannot reliably detect degrees of luminal narrowing in diseased yet patent grafts, and local signal loss from nearby metallic objects significantly impairs image quality. 1 Detection of graft stenosis remains unreliable with current MRA techniques—only 2 of 8 hemodynamically significant stenoses were detected with HASTE imaging and 4 of 8 with MR angiography. 7
Duplex Ultrasonography
Duplex ultrasound is the standard surveillance modality for infrainguinal vein bypass grafts in peripheral arterial disease, performed at 3,6,12,18, and 24 months postoperatively and annually thereafter. 1 However, this modality has limited applicability for coronary bypass grafts due to anatomic constraints.
Surveillance Strategy
Patients undergoing vein bypass graft placement should enter a surveillance program consisting of interval history, vascular examination with pulse palpation, periodic resting and postexercise ankle-brachial index measurements, and duplex scanning of the entire graft length. 1 The benefit of surveillance with duplex ultrasound is less established for prosthetic grafts, which fail more frequently from impaired native vessel outflow or poor arterial inflow rather than mid-graft stenosis. 1
Detection of flow-limiting lesions permits improved maintenance of long-term patency, with benefits of early intervention particularly well-established for autogenous vein grafts. 1 Prompt evaluation with invasive angiography is indicated when noninvasive methods suggest hemodynamically significant lesions (>50% stenosis). 1
Key Clinical Pitfalls
Do not overlook competitive flow as a cause of arterial graft failure when grafting vessels without critical stenosis. 2
Avoid missing subtle anastomotic narrowing by obtaining multiple angiographic projections rather than relying on single views. 2
Recognize that total occlusion occurs in 10-25% of saphenous vein grafts within the first postoperative year, with vein grafts showing higher early occlusion rates than arterial conduits. 2
Do not use distal embolic protection devices routinely—they should be used when technically feasible in patients undergoing PCI to saphenous vein grafts. 1
PCI is not recommended for chronic total vein graft occlusions in patients with prior CABG. 1