Eric Griffiths, MD, and Gorav Ailawadi, MD
Concept
- Indications for redo coronary artery bypass grafting (CABG)
- Preoperative considerations
- Conduit choices
- Critical steps of redo CABG
- Pitfalls and alternative solutions
Chief complaint
“A 73-year-old man with history of CABG 12 years prior now has recurrent chest pain for 3 months and multivessel disease of both native arteries and vein grafts on repeat catheterization. He is referred to you for possible repeat surgical revascularization.”
Differential
Recurrent CAD versus other non coronary etiologies. Reoperation is indicated in symptomatic patients with ischemia who have evidence of myocardial viability or who demonstrate large areas of myocardium at risk from progression of their disease.
History and physical
Confirm presence of symptoms, evaluate functional status. Identify comorbidities that may affect surgical risk: chronic obstructive pulmonary disease, end stage renal disease, peripheral vascular disease, stroke, or arrhythmias. On exam, evaluate carotid artery/bruits, quality of potential conduits such as vein and radial arteries, and signs of congestive heart failure. Obtain prior operative report.
Tests
- EKG: evaluate for arrhythmias, prior MI (Q waves), Bundle branch blocks indicating damage to conduction system.
- Echo: evaluate LV function, wall motion abnormalities, valvular function.
- Cardiac catheterization: review prior angiograms if possible.
- Identifies location and degree of stenosis in native coronary, saphenous vein graft (SVG) and arterial conduits.
- Injection of internal mammary arteries bilaterally should be performed to eval patency or for use as possible conduits.
- Myocardial viability studies: restored perfusion to ischemic or underperfused myocardium may lead to improved contractility. Revascularized scar tissue will not provide improvement.
- Thallium scintigraphy.
- Dobutamine stress echo.
- Positron emission tomography (PET): evaluates uptake of FDG as marker of cardiac metabolic activity.
- Cardiac MRI.
- CT chest: evaluate relationship of sternum and underlying mediastinal structures including bypass graft locations, degree of aortic calcification.
- CT abd/pelv to evaluate femoral vessels for possible peripheral bypass.
- Potential conduit studies. Venous duplex and mapping for presence and adequacy of saphenous vein, Allen’s test/arterial Doppler for radial conduit, cardiac catheterization to inject the mammary arteries and chest wall mammary duplex studies.
Index scenario (additional information)
“The patient has hypertension, moderate COPD. ECHO shows EF of 45% with inferior and lateral wall motion abnormalities, and no valvular disease. Cardiac catheterization shows occlusion of SVG to PDA, 80% stenosis of SVG to OM, and patent LIMA to LAD, and 80% stenosis of proximal circumflex. Cardiac MRI shows viable myocardium in the inferior and lateral walls. How would you proceed?”
Treatment/management
The patient appears to be a candidate for surgical revascularization. Percutaneous coronary intervention (PCI) is an option for patients with discrete, focal disease with minimal myocardial areas at risk. This patient has an occluded SVG to an area with viable myocardium. This lesion is typically not accessible via PCI making it necessary for him to undergo redo CABG. Additionally, he has large areas of myocardium at risk and is a functional/active patient. Redo CABG has higher risk than primary revascularization with operative mortality rates ranging from 6.9-11% mostly due to increased risk of perioperative myocardial infarction (MI). Causes include incomplete revascularization, atheromatous emboli from diseased SVGs or aorta, damaged grafts, hypoperfusion through new grafts, or early graft occlusion.
Operative steps
- Redo sternotomy: increase risk due to adhesions to underlying structures including right ventricle, innominate vein, right atrium, aorta, lung and patent coronary bypass grafts.
- Evaluate need for possible peripheral cardiopulmonary bypass: closely adherent right ventricle, pulmonary artery or aorta (refer to Redo AVR chapter for alternative cannulation strategies).
- If so, place femoral arterial and venous lines.
- Axillary artery cannulation with end to side tube graft if warranted.
- Proceed with division of the anterior table of the sternum using oscillating saw, posterior table divided using Mayo scissors.
- Avoid excessive traction on underlying structures.
- Separate mediastinal structures from chest wall.
- Harvest the internal mammary artery (left, right, or both), if not previously used, may be performed after sternotomy, cannulation, or once on bypass depending on the stability of the patient.
- Intra-pericardial dissection.
- Avoid excessive manipulation of venous bypass grafts “no touch technique.” Avoids embolization of debri.
- Cannulation.
- Once aorta dissected out, palpate or use epiaortic U/S for safe cannulation site as well as sites for proximal grafts.
- Consider axillary or femoral bypass for excessive atherosclerotic disease.
- Venous cannulation through right atrium using multistage cannula. If unable to clear safe site on atrium due to prior vein grafts or if adhesions to the right atrium are extensive, consider femoral venous cannulation or bicaval cannulation.
- Initiate CPB, dissect out the aorta to make sufficient room for antegrade and cross clamp.
- Myocardial protection strategy: combination of antegrade and retrograde cardioplegia. Antegrade cardioplegia alone may not protect areas supplied by patent pedicled internal mammary artery grafts and may dislodge debri in SVGs. Retrograde allows possible washout of coronary debri as well as access to myocardial areas of occluded arterial grafts. Protection of the right ventricle may not be complete with retrograde only cardioplegia. Clamping of patent arterial grafts ensures uniform cooling. If safe, the LIMA can be clamped in tissue between left side of the aorta and medial surface of the left lung (check its trajectory on the CT scan). If this area is difficult to dissect, consider leaving LIMA patent. Do not risk injuring a patent LIMA. If intend to keep LIMA patent, use frequent antegrade and retrograde cardioplegia and consider cooling the patient to 28-30° C.
- Revascularization strategy: determine vessels/conduits to be bypassed and conduits to be used. Consider replacing older (> 5 yr) SVG when high degree of atherosclerosis is present. Must be individualized based on degree of stenosis, availability of conduit, and patient risk.
- Avoid manipulation of SVGs to avoid embolization of atheroma.
- Stenotic SVGs can be left in place or divided and replaced with new SVG.
- When replacing stenotic SVG with arterial graft, should leave SVG in place in order to prevent hypoperfusion syndrome (worsening myocardial ischemia or infarction).
- If possible, place left internal mammary artery (LIMA) graft to left anterior descending artery (LAD) or another large vessel perfusing a large ischemic region.
- Distal sites of anastomosis: may consider reusing prior distal site when replacing SVG with another depending on degree of disease present there. Otherwise consider “landing” on native coronary distal to prior anastomosis.
- Sites for proximal anastomosis may be limited due to prior involvement on the reoperative aorta.
- Consider sequencing vein grafts to minimize number of proximal anastomoses.
- Arterial free grafts can be anastomosed to the hood of new or old SVG due to lack of atherosclerotic involvement there or can be sewn to other arterial grafts for a “Y” type anastomosis.
- Arterial grafts.
- LIMA to LAD if not previously performed.
- Right internal mammary artery (RIMA) to right coronary artery/posterior descending artery or through transverse sinus to circumflex/proximal obtuse marginal. Transverse sinus is typically adherent and requires dissection. Also consider utilizing the RIMA as a free graft.
- Radial artery free graft: affected by competitive flow, best if stenosis > 70% and used to a large vessel/large runoff territory.
- Evaluate need for possible peripheral cardiopulmonary bypass: closely adherent right ventricle, pulmonary artery or aorta (refer to Redo AVR chapter for alternative cannulation strategies).
Potential questions/alternative scenarios
“Patient fails to wean from bypass.”
Check ABG, electrolytes (K+), assess degree of inotropic support, adequate volume and heart rate. Transesophageal echo (TEE) useful for assessing for old/new wall motion abnormalities, volume status of the heart, presence of unrecognized valvular dysfunction, and possible air in the aortic root. For visible air in the bypass graft, the vein can be clamped and deaired with a small 27g needle. A balloon pump may be necessary. These are longer operations on chronically ischemic hearts and patients are prone to myocardial dysfunction postoperatively. Myocardial protection must be as optimal as possible (refer to CPB pitfalls chapter).
Assess all grafts for adequate positioning (no kinks). Doppler assessment of new constructed graphs to check for patency. If poor flow with associated regional abnormality on TEE, grafts to that area should be reconstructed immediately. Revision can be performed by clamping and arresting the heart. Alternatively, if familiar with off-pump CABG techniques, can use cardiac stabilizer while on full cardiopulmonary bypass and revise the distal anastomosis (but be cautious, it went down for a reason, so you want to have optimal conditions the second time). If low cardiac output or regional abnormalities persist, then proceed to intra-aortic balloon pump placement (IABP). If IABP and inotropes fail, then consider placing mechanical ventricular support (ECMO, Abiomed, CentriMag, Impella, or other).
“No room on the aorta for proximal anastomosis.”
Other locations for proximals include end- to- side anastomosis to patent arterial grafts, using the hood of patent old or new SVGs. Even occluded SVGs may have a patent hood that can be used. Consider using the RIMA in situ such that a proximal aortic site is not needed.
“You are doing the redo sternotomy and encounter bright red blood before sternum is open. You now see EKG changes.”
Suspect coronary/graft injury. Heparinize and emergently place the patient on femoral bypass, open the sternum and expeditiously continue your dissection. If you can identify the injured coronary you can either repair, it or place a coronary perfusion catheter in the lumen to perfuse the area with warm blood. Continue operation. Replace injured vein graft.
“You heparinize, cannulate and dissect out the ascending aorta making enough room for cross clamping and antegrade access. The ACT is 480. Unfortunately, you injure the patent mammary while attempting to dissect it near the lung. Almost immediately you notice hemodynamic changes and regional wall motion abnormalities.”
Initiate CPB, clamp and arrest the heart. Try to repair the injured mammary. If not, it will have to be replaced. Note that this illustrates the importance of being ready to clamp and arrest prior to dissecting out a patent mammary.
Pearls/pitfalls
- Review cath films, ensure myocardial viability in areas with diseased grafts.
- Thorough preoperative planning including op note, cannulation strategy and conduit assessment.
- Minimize manipulation of old SVGs.
- Make every effort to place LIMA on LAD if not done previously.
- SVGs that are bypassed by arterial conduit should be left in place.
- Be prepared to clamp and arrest when dissecting out a patent mammary.
Suggested readings
- Barreiro CJ and Bansal A. Reoperative coronary artery bypass surgery. Yuh D, Vricella LA, and Baumgartner WA (eds). Johns Hopkins Manual of Cardiothoracic Surgery 2007.
- Lytle BW. Re-do coronary artery bypass surgery. Little AG (editor). Complications in Cardiothoracic Surgery: Avoidance and Treatment. 1st ed. Blackwell Futura. 2004.
