Clinical Editor's Corner: Kern

Planning Counts for Best Results in the CABG Patient

Morton J. Kern, MD

Morton J. Kern, MD

How amazed would Dr. Gruentzig be to see what has happened to his plain old balloon angioplasty (POBA)? Almost nothing from that era is the same in today’s cath lab. I was reminded of this fact again on reading a state-of-the-art paper by Xenogiannis et al1, who updated the readers on cardiac catheterization in patients with prior bypass graft surgery. In 2011, I had written an editor’s page on this subject2 but now, 9 years later, it seems a good time for a recap of how we now work with coronary artery bypass graft (CABG) patients needing angiography and percutaneous coronary intervention (PCI).

Indications for Angiography

Saphenous vein grafts (SVG) in CABG patients are said to last, on average, about 10 years, with arterial in-situ conduits (left interior mammary artery [LIMA] or right [RIMA]) remaining patent more 15 to 25 years in some patients. A majority of CABG patients may present with an acute coronary syndrome, most often due to either 1) progression of coronary artery disease (CAD) in the native arteries or 2) new disease occurring in the bypass grafts. Internal thoracic (or mammary) artery grafts rarely have intrinsic atherosclerosis, whereas free radial artery grafts are subject to degeneration at rates similar to SVG patency.

CABG patients can present to the cath lab because of ACS, increasing dyspnea with presumed silent progression of CAD or new ischemia, or because of abnormal ischemic testing prior to a major surgical procedure. CABG patients are always more complicated than routine CAD patients, frequently due to additional comorbidities like diabetes, peripheral vascular disease, chronic renal failure, and chronic obstructive pulmonary disease (COPD). The cath team should carefully review the patient’s prior illnesses, medication use, and renal failure.   

CABG Surgery and Old Records?

Depending on the demographics of your area, CABG patients returning with ACS or stable angina may account for as many as 20-25% of your patient population. Some patients have had surgery over a decade or more ago; others within the last several years. Many do not have records of the surgery or do not recall the details. Lack of prior information on the number and origin of grafts increases procedure time, contrast use, complexity, and risk to patients. The CABG conduits (SVGs, in-situ internal thoracic [mammary] or free radial artery grafts) are often, but not always, located in predictable sites. However, most graft ostia are unmarked, requiring operator experience and intuition to locate them efficiently.

A thorough review of old surgical or catheterization records (and of course, old angiograms, if available) is critical, especially focusing on the question of “How many grafts and where do they go?” Unfortunately, getting old records is often a 50/50 proposition. Working without knowledge of exactly how many grafts exist and their anastomotic touchdowns is the biggest challenge for the operator, contributing to increased contrast media use and more radiation exposure, regardless of vascular access. For routine angiography, it is always a good idea to establish a standard approach as we would do for any patient with CAD, even without knowledge of the grafts.

Access for CABG Patients in the Radial Era

Most operators still prefer a femoral over a radial vascular access approach, but in practice, either can be used with equal success. Our lab prefers left radial access when possible, since left radial access permits an easy cannulation of the LIMA and avoids the bleeding risk of the femoral approach. One recent change we’ve made is to use the distal left radial access3, which improves patient and operator comfort when working from the right side of the table with the patient’s left arm positioned over the abdomen.

Despite the highly favorable radial experience, Xenogiannis et al1 points out the downside, namely more contrast media used (about 30 mL on average), and slightly more radiation exposure (about 0.20 air kerma more) for radial procedures compared to the femoral approach. Nonetheless, complications were less and patient satisfaction was greater with radial compared to the femoral approach in these patients.4 We should remember that there are still a substantial number of patients (e.g., patients with dialysis shunts, carotid disease, prior radial artery, subclavian or other vascular problems) in whom a femoral approach is required for better results in CABG patients.

Approach to Coronary Angiographic Imaging

Although there are several ways to approach collecting the angiographic information for the CABG patient, we recommend native vessel angiography first, SVGs and LIMA angiography next, and lastly, if needed, an aortogram (with or without left ventriculography) when we are still uncertain about complete graft visualization. In 2019, it seems that the left ventriculogram has been replaced by the echocardiogram, but left ventricular end diastolic pressure (LVEDP) measurement still has some clinical value. By seeing the native coronary arteries first, we get some idea of what territories are missing their arterial perfusion vessels, areas that presumably should be supplied by a visible coronary artery or collateral. Long fluoroscopy or cine exposures may be needed to detect the contrast washout or competitive flow that might suggest a functioning graft.

After native coronary arteriography, proceed to image the SVGs. Look for the SVG markers (if any). It has always been a mystery to me as to why some surgeons use markers and others don’t. They (markers as well as surgeons) are helpful to the angiographer to some degree by 1) confirming there is a graft anastomosis, and 2) identifying an approximate location where one can cannulate the graft ostia. It is good to remember that markers do not always pinpoint the opening to the graft. By convention, SVGs to the right coronary artery (RCA) typically lie laterally and directly above the RCA ostium in the left anterior oblique (LAO) projection. Pulling up on the catheter after seating in the RCA will result in the catheter jumping into the ostium of the SVG-RCA. SVGs to the left anterior descending (LAD) coronary artery and circumflex (CFX) and their branches are placed on the anterior aortic wall above the left main in the right anterior oblique (RAO) projection. Obtuse marginal grafts are usually the highest and farthest left (Figure 1A).

Catheter selection for graft angiography is a matter of operator experience. In most cases, SVG-RCA angiography can be easily performed with a right Judkins catheter. In a patient with a SVG-RCA graft with a downward takeoff, a multipurpose or right coronary bypass vein graft catheter may be needed. A right (modified) Amplatz catheter also can be used for horizontal or vertical takeoff vein grafts, and may serve a dual purpose to easily cannulate a left SVG-CFX graft, usually located above the LCA ostium (Figure 1A). One should avoid unnecessary manipulation of catheters in vein grafts, especially in old grafts or stump occlusions that may contain friable atherosclerotic material with a potential risk of embolization.

Internal Mammary Artery Grafts

The left internal mammary artery originates anteriorly from the subclavian artery just beyond the vertebral artery origin (Figure 1B). From the left radial approach, cannulation should be simple with a LIMA or right Judkins catheter. Because there are many variations in the shape of the aortic arch and subclavian artery, it may be more difficult to selectively engage the IMA from the femoral approach.  There are numerous reports of successful cannulation of the LIMA from the right radial approach, but the operators should avoid vigorous catheter manipulation, because of the risk of artery dissection or stroke.     

RIMA cannulation is less commonly needed and more difficult to cannulate than the LIMA from either the leg or the left arm. Once the right brachiocephalic truncus is entered, the sequence of cannulation is similar to that described for LIMA graft cannulation (Figure 1B). For best angiographic imaging, the C-arm angulations should be set to see the length and contours of the graft, as well as the anastomotic connection. For example, the best projection to view the IMA to LAD anastomosis is the true lateral view. A more detailed review of CABG angiography can be found in the Catheterization Handbook, 6th edition.5

Fractional Flow Reserve (FFR) in SVG Lesion Assessment

Some patients may have intermediately severe lesions in the SVG. Uncertainty as to the ischemic potential and clinical significance of such lesions requires fractional flow reserve (FFR) measurement of the SVG or native vessels, if approachable. Recall that flow to the myocardium in these patients is the net result of three sources of perfusion. Blood flow to the myocardial bed passes through the 1) SVG, 2) native artery (if not totally occluded), and 3) through the collateral flow (Figure 3). Thus, although a SVG lesion might appear to be very severe, if the native supply and collateral supply are sufficiently large, the FFR could be normal and give reassurance to the team that a risky SVG intervention is unnecessary. It should be remembered that SVGs have a different biology and natural history when compared to native CAD, and appropriate consideration to alternatives to SVG PCI should be strongly considered.

For FFR, flow to the bed from whatever sources should yield the same information that would help one decide about ischemia/no ischemia. Despite factors that complicate the SVG assessment (competing flow, collaterals, microvascular disease, scarring, and fibrosis), the theory of FFR applies just as much to a lesion in a SVG to the RCA feeding a normal myocardial bed as a lesion in the native right coronary. The technique for FFR in SVGs is described in detail elsewhere.2

Considerations for PCI Success

Over the last decades, several novel approaches, concepts, and techniques have emerged to assist us in getting better results when we must percutaneously revascularize the CABG patient. Xenogiannis et al1 expertly summarize these important considerations (Table 1).

The Bottom Line

CABG patients represent a subset of patients at high risk for events during and after angiography/PCI, as well as the highest technical challenges for angiographers. Decisions for PCI in this patient population demand our concentrated attention to avoid complications. Preprocedural review of the clinical needs and patient-specific findings will dictate the best access approach and PCI management.   

I hope this brief review has been helpful the next time your CABG patient requires catheterization and intervention. 

Disclosures: Dr. Morton Kern reports he is a consultant for Abiomed, Abbott Vascular, Philips Volcano, ACIST Medical, Opsens Inc., and Heartflow Inc.

References
  1. Xenogiannis I, Tajti, P Hall AB, et al. Update on cardiac catheterization in patients with prior coronary artery bypass graft surgery. JACC Cardiovasc Interv. 2019 Sep 9; 12(17): 1635-1649. doi: 10.1016/j.jcin.2019.04.051.
  2. Kern M. Editor’s corner: Evaluation of coronary artery bypass graft lesions in the cath lab. Cath Lab Digest. 2011 Sept; 19(9): 4-6. Available online at https://www.cathlabdigest.com/articles/Evaluation-Coronary-Artery-Bypass-Graft-Lesions-Cath-Lab. Accessed October 16, 2019.       
  3. Kern M. Editor’s corner: A light bulb goes on – my first use of the distal radial artery for the left arm approach. Cath Lab Digest. 2019 June; 6-11.
  4. Michael TT, Alomar M, Papayannis A, et al. A randomized comparison of the transradial and transfemoral approaches for coronary artery bypass graft angiography and intervention: the RADIALCABG trial (RADIAL Versus Femoral Access for Coronary Artery Bypass Graft Angiography and Intervention). JACC Cardiovasc Interv. 2013 Nov; 6(11): 1138-1144. doi: 10.1016/j.jcin.2013.08.004.
  5. Kern M, Sorajja PS, Lim MJ, eds. Chapter 3: Angiography. In: The Cardiac Catheterization Handbook. 6th ed. Philadelphia, PA: Elsevier; 2016: 1-494.