On-pump Coronary Artery Bypass Grafting (CABG) is a type of open-heart surgery designed to treat severe coronary artery disease. The coronary arteries, which branch off the aorta, supply the heart muscle with oxygen-rich blood. When these arteries become narrowed by the buildup of fatty material, it can lead to chest pain and heart attacks. This procedure creates new routes for blood to flow around the blockages, restoring adequate blood supply to the heart muscle.
The “on-pump” name indicates the surgery uses a cardiopulmonary bypass (CPB) machine, also known as a heart-lung machine. This device temporarily takes over the function of the heart and lungs during the operation. This allows the surgeon to work on a heart that is still and not filled with blood.
The Cardiopulmonary Bypass Machine
A cardiopulmonary bypass (CPB) machine is operated by a specialized medical professional, a perfusionist, who monitors the patient’s blood flow, oxygen levels, and temperature. The machine functions through a circuit of tubes connected to the patient’s circulatory system. Blood is drained from the heart into the machine, where an oxygenator acts as an artificial lung, infusing the blood with oxygen and removing carbon dioxide. The oxygenated blood is then pumped back into the patient’s arterial system.
To prepare the patient for bypass, the surgical team administers an anticoagulant like heparin to prevent blood from clotting in the machine’s tubing. The patient’s body temperature is often lowered to reduce metabolic rate and oxygen demand. This protects the organs during the procedure, which can last from 30 to 90 minutes while the heart is stopped.
The Surgical Procedure
The on-pump CABG procedure begins with the patient under general anesthesia. The surgical team makes an incision down the center of the chest and divides the breastbone (sternum) in a procedure called a median sternotomy. A retractor is then used to spread the two halves of the sternum, providing access to the heart. The pericardium, the protective sac surrounding the heart, is opened to expose the coronary arteries.
With the heart exposed, the surgeon places tubes into the right atrium to divert venous blood into the cardiopulmonary bypass machine. Another tube is placed into the aorta to return oxygenated blood from the machine to the body. Once the patient is fully supported by the bypass machine, the surgeon cross-clamps the aorta and infuses the heart with a cold, potassium-rich solution called cardioplegia. This solution promptly stops the heart and cools it, preserving the muscle tissue.
With the heart still and empty of blood, the surgeon performs the core task of attaching the bypass grafts. After all grafts are securely stitched into place, the clamp on the aorta is removed, allowing blood to flow into the coronary arteries and the heart itself. The surgical team then weans the patient off the bypass machine, allowing their own heart to resume its normal rhythm.
Once the heart is beating on its own and circulation is stable, the cannulas for the bypass machine are removed. The surgeon may place temporary pacing wires on the heart’s surface in case its rhythm needs to be regulated in the initial recovery period. Flexible drainage tubes are inserted into the chest cavity to remove any excess fluid. The sternum is brought back together and secured with wires or plates, and the skin incision is closed.
Graft Selection and Placement
A bypass graft is a section of a healthy blood vessel that is surgically removed from another part of the patient’s body to create the new pathway for blood flow. The selection of the graft material is a decision made by the surgical team based on the patient’s anatomy, the quality of their vessels, and the number of bypasses required. The goal is to choose a conduit that will remain open and functional for many years.
The most commonly used grafts are the internal mammary arteries, the saphenous veins, and the radial arteries. The internal mammary arteries, located inside the chest wall, are often the preferred choice because they have demonstrated excellent long-term durability. When one of these arteries is used, one end is detached and rerouted to the coronary artery just past the blockage.
Veins from the leg, specifically the great saphenous vein, are another frequent source for grafts. One end of the vein graft is sewn to the aorta, and the other end is attached to the coronary artery downstream from the narrowing. The radial artery from the arm can also be used as a graft and often provides good long-term results.
Immediate Post-Operative Period
Following an on-pump CABG procedure, the patient is transferred to a cardiovascular intensive care unit (ICU) for close monitoring. The patient will be connected to a ventilator through a breathing tube to assist with breathing until they are fully awake and strong enough to breathe independently. Monitors will be in place to track heart rate, blood pressure, and other vital signs.
Chest tubes, placed during surgery, will remain in the chest cavity for a day or two to drain any residual fluid and help the lungs re-expand completely. Pain and discomfort are expected, and pain medication is administered to keep the patient comfortable. Once vital signs are stable and the ventilator is no longer required, the patient is transferred from the ICU to a regular cardiac care floor.
The focus during this next phase of recovery is on gradually increasing activity, such as sitting in a chair and walking short distances. Nursing staff and physical therapists will assist the patient with these activities. The patient is also educated on incision care, medications, and lifestyle changes needed for long-term heart health.
Comparing On-Pump and Off-Pump Approaches
The primary alternative to on-pump CABG is the off-pump coronary artery bypass (OPCAB), a technique where the surgery is performed on a beating heart. This approach avoids the use of the cardiopulmonary bypass machine. Instead, the surgeon uses specialized stabilization devices to keep a small area of the heart still while the grafts are being attached.
The choice between on-pump and off-pump surgery is highly individualized and depends on the surgeon’s expertise and the patient’s specific clinical situation. On-pump surgery is often considered the standard approach, particularly for patients who require multiple bypasses or have blockages in difficult-to-reach arteries. The still, bloodless surgical field provided by the bypass machine can allow for more precise graft placement in these complex cases.
Off-pump surgery may be considered for certain patients to avoid the potential inflammatory effects associated with the heart-lung machine. However, on-pump CABG has been shown to result in more complete revascularization in some studies. The surgical team will evaluate the patient’s coronary anatomy, overall health, and other risk factors to determine the most appropriate surgical strategy.