Residency · Residency · Cardiothoracic Surgery

On-Pump CABG: Technique and Conduct of Operation

Overview

On-pump coronary artery bypass grafting remains the most commonly performed cardiac surgical procedure worldwide. Mastery of the stepwise conduct of operation — from sternotomy through chest closure — is foundational for every cardiothoracic surgery resident. This chapter covers the technical details and decision-making at each phase of the procedure.

Preoperative Planning

Review of Coronary Angiography

The surgeon must systematically identify target vessels, assessing caliber, quality, location, and severity of stenoses. Dominance pattern (right, left, or codominant) is noted and incorporated into planning. Diffusely diseased or calcified targets that may require endarterectomy or alternative strategies are flagged. The quality of the distal vessel bed is evaluated, as it is critical for graft patency.

Conduit Selection Planning

The LIMA to LAD is the cornerstone graft (Class I recommendation). Additional conduits are planned based on the remaining targets: right IMA, radial artery, or saphenous vein graft (SVG). Bilateral IMA should be considered in appropriate patients (non-diabetic, non-obese, with adequate collateral sternal blood supply). The Allen test is performed preoperatively to assess radial artery candidacy.

Operative Strategy

The number and sequence of distal anastomoses are determined. The proximal anastomosis strategy is chosen — aortic punch with partial clamp, or an aortic no-touch technique. The cardioplegia plan (antegrade, retrograde, or combined) is established.

Sternotomy and Exposure

Median Sternotomy

The skin incision extends from the sternal notch to below the xiphoid. Electrocautery is used through the subcutaneous tissue and periosteum. The sternum is divided with an oscillating saw, and sternal bleeding is controlled with bone wax and electrocautery. A sternal retractor is inserted, and the pericardium is opened longitudinally in the midline with stay sutures creating a pericardial cradle.

Assessment of the Heart

The surgeon palpates coronary arteries to confirm angiographic findings, visually assesses ventricular function and wall motion, and evaluates the ascending aorta for calcification using manual palpation and/or epiaortic ultrasound. In redo cases, adhesions must be identified and managed.

Conduit Harvest

Left Internal Mammary Artery (LIMA)

The LIMA is harvested as a pedicled graft (with accompanying veins, fascia, and pleural flap) or skeletonized. The skeletonized technique increases length and may preserve sternal blood supply. Low electrocautery settings or a harmonic scalpel are used to avoid thermal injury, and branches are divided with clips. Harvest extends from the subclavian origin to the bifurcation. After heparinization, the distal end is divided, flow is assessed, and the artery is topically vasodilated with papaverine.

Saphenous Vein Graft (SVG)

The vein is harvested either open or endoscopically (endoscopic is standard at most centers). Harvest from the thigh (above the knee) yields larger caliber and better patency. Gentle handling is essential — distension pressure should not exceed 300 mmHg. Branches are checked and ligated, and the graft is stored in heparinized blood or a balanced solution (not saline alone). The "no-touch" technique, which harvests the vein with surrounding tissue, may improve long-term patency.

Radial Artery

After confirming ulnar artery adequacy with the Allen test, the radial artery is harvested from the non-dominant arm. It can be skeletonized or taken as a pedicle. Because it is prone to spasm, it is treated with calcium channel blockers (verapamil/diltiazem) and topical papaverine or nitroglycerin. It should be used for severe stenoses (above 70-90%) to avoid competitive flow.

Cannulation and Initiation of Bypass

Heparinization

Systemic heparin (300-400 units/kg IV) is administered, and adequate anticoagulation is confirmed with a target ACT above 480 seconds. Additional heparin boluses are given as needed during CPB.

Aortic Cannulation

A site on the distal ascending aorta free of calcification or atheroma is selected, ideally guided by epiaortic ultrasound. Two concentric purse-string sutures with pledgets are placed. Systolic blood pressure is lowered to 90-100 mmHg before cannulation to reduce dissection risk. Position is confirmed with back-bleeding and transduction of the aortic line pressure.

Venous Cannulation

A single two-stage cannula is placed via the right atrial appendage (the most common approach for CABG). Alternatively, bicaval cannulation is used if access to the right heart is needed. The cannula is secured with a tourniquet or snare.

Initiation of CPB

After confirming ACT, circuit readiness, and communication with the perfusionist, bypass is commenced. Venous drainage occurs by gravity (or vacuum-assisted), and arterial inflow is provided via the pump. Target flow is 2.2 to 2.5 L/min/m2, with target MAP of 50 to 80 mmHg. Cooling to 32-34 degrees Celsius is begun if hypothermia is planned.

<image>Step-by-step illustration of aortic and venous cannulation for cardiopulmonary bypass during CABG. Panel A shows the ascending aorta with concentric purse-string sutures and arterial cannula insertion site in the distal ascending aorta. Panel B shows the two-stage venous cannula inserted through the right atrial appendage with the tip in the IVC. Panel C shows the completed cannulation with tubing connections to the CPB circuit, including the aortic cross-clamp positioned proximal to the arterial cannula.</image>

Myocardial Protection

Cardioplegia Delivery

Antegrade cardioplegia is delivered via a needle or cannula in the ascending aorta proximal to the cross-clamp. Retrograde cardioplegia is delivered via a balloon-tipped cannula in the coronary sinus. The combined approach (antegrade induction dose followed by retrograde supplemental doses) is most common for CABG.

Cardioplegia Solution Comparison

Cardioplegia Solutions

Blood cardioplegia at a 4:1 blood-to-crystalloid ratio is most common in North America. Del Nido cardioplegia, originally developed for pediatric cases, is a single-dose strategy gaining popularity in adult CABG, allowing prolonged arrest up to approximately 90 minutes without redosing. Crystalloid solutions (such as Custodiol/HTK) are used in some centers as a single-dose option.

Cross-Clamp Application

The aortic cross-clamp is applied between the arterial cannula and the aortic root. Cessation of cardiac activity is confirmed after cardioplegia delivery. Cross-clamp time is a key quality metric that should be minimized.

Maintenance of Arrest

For multi-dose protocols, cardioplegia is redosed every 15 to 20 minutes. Retrograde delivery ensures protection of territories supplied by severely stenosed coronary arteries. Topical hypothermia (ice slush or cold saline pads) serves as an adjunct.

Distal Anastomoses

General Principles

The most distal anastomosis is typically performed first, which reduces cardioplegia washout from completed grafts. A typical sequence is PDA/RCA territory, followed by obtuse marginals, then the diagonal, with the LIMA to LAD often done last. The arteriotomy is 5 to 7 mm in length, made with a #15 or #11 blade and extended with Potts scissors. Target vessel caliber should ideally exceed 1.0 to 1.5 mm.

Technique of Anastomosis

Running suture technique (parachute or sew-in-place) using 7-0 or 8-0 polypropylene suture is standard. The suture begins at the heel of the anastomosis and runs along each side, completing at the toe. Adequate bites (approximately 1 mm apart, 1 mm from the edge) are essential, and catching the back wall must be avoided. Hemostasis is confirmed after completion.

LIMA-to-LAD Anastomosis

This is the most critical anastomosis and the primary determinant of long-term outcome. The distal LIMA is beveled and spatulated to match the arteriotomy length. Careful positioning avoids kinking or tension, and a pedicled LIMA must be routed without twisting.

Proximal Anastomoses

Partial Aortic Clamping

A partial-occluding (side-biting) clamp is applied to the ascending aorta, and an aortotomy is created with a 4-mm aortic punch. The SVG or radial artery is anastomosed to the aorta with 6-0 polypropylene running suture. After releasing the clamp, hemostasis is confirmed.

Alternatives to Partial Clamping

Proximal anastomoses can be performed during the cross-clamp period to avoid additional aortic manipulation. Clampless connectors (such as the Heartstring device) are available for patients with diseased ascending aorta. The aortic no-touch technique, in which all grafts arise from in-situ arterial conduits (bilateral IMA or LIMA-radial Y-graft), eliminates aortic manipulation entirely.

Considerations

Epiaortic ultrasound identifies safe aortic sites. Atheromatous or calcified regions must be avoided to reduce stroke risk. Proximal anastomoses should be spaced adequately to prevent competitive flow and kinking.

<image>Intraoperative surgeon's view of a completed distal anastomosis of a saphenous vein graft to a coronary artery. The image shows the running polypropylene suture technique, with the heel and toe of the anastomosis clearly labeled. Adjacent labels indicate the native coronary artery, the vein graft, and the surrounding epicardial fat. A second panel shows the proximal anastomosis being performed on the ascending aorta using a partial-occluding clamp with an aortic punch hole visible.</image>

Weaning from Cardiopulmonary Bypass

Preparation for Weaning

The patient is rewarmed to 36-37 degrees Celsius (core temperature). The heart is reperfused for at least one-third to one-half of the cross-clamp time (or a minimum of 15-20 minutes). The aortic cross-clamp is removed, and the heart should resume rhythm (sinus, or defibrillation may be required). The heart is de-aired via the aortic root vent, with the patient placed in Trendelenburg and the heart gently agitated. Temporary pacing wires are placed on the right ventricle and optionally the right atrium.

TEE Assessment Before Weaning

TEE is used to assess ventricular function (new regional wall motion abnormalities may indicate graft problems), evaluate for new mitral regurgitation, confirm adequate de-airing, and assess volume status.

Weaning Protocol

Venous drainage is gradually reduced while preload increases. The heart is allowed to eject against reduced CPB flow. Vasoactive support (norepinephrine, vasopressin, epinephrine, milrinone) is initiated as needed. Stable hemodynamics are required before full separation from bypass: MAP above 60 mmHg, CI above 2.0 L/min/m2, acceptable CVP and PA pressures, and adequate rhythm and rate.

Troubleshooting Difficulty Weaning

Low cardiac output calls for inotropes, assessment of graft patency, and evaluation for new regional wall motion abnormalities. Right heart failure may respond to milrinone, inhaled nitric oxide, or RVAD. Vasoplegia is treated with vasopressin, norepinephrine, or methylene blue. Persistent intracardiac air requires continued de-airing maneuvers and patience.

Protamine and Decannulation

Protamine Administration

Protamine is administered to neutralize heparin (1 mg per 100 units of total heparin, or dose-response titrated). It is given slowly via a peripheral line, with monitoring for hypotension and pulmonary hypertension (protamine reaction). Reversal is confirmed with ACT returning to baseline.

Decannulation

The venous cannula is removed first, then the arterial cannula. Purse-string sutures are secured, and cannulation sites are inspected for hemostasis.

Chest Closure

Hemostasis

Meticulous hemostasis before closure is mandatory. All anastomoses, cannulation sites, and sternal edges are inspected. Mediastinal and/or pleural drainage tubes (typically two chest tubes) are placed. Platelet count and coagulation studies are checked, with TEG/ROTEM-guided transfusion considered as needed.

Sternal Closure

The sternum is closed with 6 to 8 stainless steel wires using figure-of-eight or simple interrupted technique. Secure approximation without excessive tension is ensured. Fascia, subcutaneous tissue, and skin are closed in layers.

Temporary Pacing Wires

Epicardial pacing wires are placed on the RV (and RA if needed) and brought out through the skin below the incision.

<image>Schematic of the completed on-pump CABG operation showing a frontal view of the heart with a LIMA-to-LAD pedicled graft in situ, a saphenous vein graft from the aorta to an obtuse marginal branch, and a saphenous vein graft from the aorta to the posterior descending artery. Each graft is labeled with conduit type and target vessel. The aortic cross-clamp position, cardioplegia cannula site, and venous cannula in the right atrium are annotated. Mediastinal chest tubes and temporary pacing wires are shown in position.</image>

Intraoperative Quality Checks

Graft Assessment

Transit-time flow measurement (TTFM) provides quantitative assessment of graft flow. Mean graft flow should exceed 15-20 mL/min for SVGs. A pulsatility index (PI) below 5 indicates acceptable flow, and diastolic filling fraction above 50% confirms that coronary flow is primarily diastolic (as expected). Visual inspection confirms there are no kinks, twists, or tension on the grafts. TEE provides wall motion assessment before and after bypass.

Documentation

Cross-clamp time, bypass time, cardioplegia strategy, graft flows, and any complications are recorded. General targets for isolated CABG are cross-clamp time below 60 minutes and CPB time below 90 minutes.

Complications and Troubleshooting

Intraoperative Complications

Aortic dissection at the cannulation site requires immediate recognition and either extended repair or a change in cannulation site. Poor target quality may necessitate endarterectomy (which increases thrombosis risk) or selection of an alternative target. If the IMA is irreparably injured, an SVG to the LAD must be used, though with inferior long-term results. Graft kinking or tension must be revised before leaving the operating room.

TTFM Quality Metrics for Graft Assessment

Early Postoperative Complications

Bleeding requiring re-exploration occurs in 2-5% of cases. Perioperative MI from graft occlusion or inadequate revascularization is a serious concern. Atrial fibrillation is common (25-40% incidence). Stroke occurs in 1-2%, and sternal wound infection in 1-3%.

Clinical Pearls

The LIMA-to-LAD anastomosis is the single most important determinant of long-term outcome in CABG and must be technically perfect. Epiaortic ultrasound should be used routinely to guide aortic cannulation and clamping — it detects atheroma missed by palpation in up to 25% of patients. Transit-time flow measurement is a cost-effective intraoperative quality check that can detect technical errors before leaving the operating room. Gentle conduit handling is paramount: overdistension of SVGs during preparation contributes to intimal injury and early graft failure. Cross-clamp and CPB times are independent predictors of morbidity — efficient operative conduct reduces myocardial ischemia, bleeding, and end-organ injury. The sequence of anastomoses should be planned to allow retrograde cardioplegia to reach all territories effectively. In patients with a calcified or "porcelain" aorta, a no-touch technique (all arterial grafts or clampless connectors) can dramatically reduce stroke risk.

References

• Aldea GS, Bakaeen FG, Pal J, et al. The Society of Thoracic Surgeons Clinical Practice Guidelines on Arterial Conduits for Coronary Artery Bypass Grafting. Ann Thorac Surg. 2016;101(2):801-809.
• Cohn LH, Adams DH. Cardiac Surgery in the Adult. 5th ed. McGraw-Hill; 2017. Chapters on CABG technique.
• Sellke FW, del Nido PJ, Swanson SJ. Sabiston and Spencer Surgery of the Chest. 9th ed. Elsevier; 2016.
• Taggart DP, Altman DG, Gray AM, et al. ART Trial Investigators. Randomized trial of bilateral versus single internal-thoracic-artery grafts. N Engl J Med. 2016;375(26):2540-2549.
• Sousa-Uva M, Neumann FJ, Ahlsson A, et al. 2018 ESC/EACTS Guidelines on myocardial revascularization. Eur J Cardiothorac Surg. 2019;55(1):4-90.

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