Minimally invasive heart surgery refers to surgery performed on the beating heart to provide coronary artery bypass grafting. This technique is often referred to as MIDCAB, minimally invasive direct coronary artery bypass; or OPCAB, off-pump CABG.
Minimally invasive heart surgery is performed on the diseased heart to reroute blood around clogged arteries and improve the blood and oxygen supply to the heart. This approach provides patients some benefit in that cardiopulmonary bypass (use of a heart-lung machine) may be avoided, and smaller incisions can be used instead of the standard sternotomy (incision through the sternum, or breast bone) approach. Faster recovery time, decreased procedure costs, and reduced morbidity and mortality are the goals of this technique.
Minimally invasive technique is not new to the field of cardiac surgery. It was performed as early as the 1950s, although the technology associated with stabilizing the cardiac structure during the procedure has become more sophisticated. Also, the anesthesiologist and perfusionist (person monitoring blood flow) have developed better techniques to preserve cardiac function during the procedure to help the surgeon achieve the desired outcome. During the 1990s these new techniques were named: off-pump CABG (OPCAB) and minimally invasive direct coronary artery bypass (MIDCAB). The MIDCAB procedure includes procedures done both with and without cardiopulmonary bypass, the later being referred to as off-pump MIDCAB. Unless otherwise specified, MIDCAB refers to both types of procedures.
Minimally invasive valve surgery has been an outgrowth of the success with minimally invasive coronary artery bypass grafting. Incisions other then the traditional sternotomy allow access to the heart. Minimally invasive valve surgery still requires cardiopulmonary bypass, since this is a true open-heart procedure, (i.e. this is not surgery that is done while the heart is beating). New tools in managing cardioplegic cardiac arrest allow for the smaller incision unobstructed by the required instrumentation. Cannulation of the femoral vessels instead of the larger vessels of the heart also improves visualization.
Patients under the age of 70, but not limited by age, with a history of coronary artery disease can be evaluated for this procedure. High risk patients with advanced age, at risk for stroke, or suffering peripheral vascular disease, renal disease, or with poor lung function may benefit from OPCAB and MIDCAB.
Typically disease of the left anterior descending coronary artery is treated with the technique called off-pump
The patient receives cardiac monitoring during general anesthesia. Systemic anticoagulation is given to avoid clot formation from foreign surfaces and any periods of artery blockage (occlusion).
If cardiopulmonary bypass is not employed, the procedure is called an off-pump MIDCAB. The surgeon performs an alternative incision (rather than a midline sternotomy), typically a left anterior thoracotomy . The left internal mammary artery is dissected from the left chest wall. A stabilizer device is placed on the heart to provide support of the left anterior descending artery as the heart continues to beat. This device applies gentle pressure or suction, mildly limiting cardiac function. The left internal mammary artery is sutured to the left anterior descending artery to bypass the blockage (anastomosis).
If cardiopulmonary bypass is indicated, the surgeon inserts cannulae (small, flexible tubes) into the femoral vessels. Aortic occlusion and cardioplegia are administered through a catheter advanced through the contralateral femoral artery into the aortic root (ascending aorta). This catheter has a balloon tip that stops blood flow to the coronary arteries when inflated, but allows selective administration of cardioplegia (a solution that stops the heart) to the coronary arteries. Angiography is performed to provide visualization of catheter placement.
The surgeon performs an alternative incision (rather than a midline sternotomy), typically a left anterior thoracotomy. The left internal mammary artery is dissected from the left chest wall. Cardiopulmonary bypass can be instituted with or without cardioplegic arrest. Cardioplegic arrest requires cardiopulmonary bypass. The use of cardioplegic arrest makes this a non-beating heart procedure, but it is still considered MIDCAB. Cardioplegic arrest of the heart occurs as the balloon tip of the catheter is inflated. The left internal mammary artery is sutured to the left anterior descending artery to bypass the blockage (anastomosis). Once the anastomosis is complete the balloon is deflated, allowing the heart to begin to beat. Cardiopulmonary bypass is discontinued once cardiac function is stabilized. The cannulae and catheter are removed, and the groin wounds are closed with sutures.
The OPCAB procedure does not use cardiopulmonary bypass. The incision of choice can be a midline sternotomy or a left anterior thoracotomy (incision into the side). The midline sternotomy allows access to both the right and left internal mammary arteries. Additional vascular bypass conduits may be acquired by harvesting the saphenous vein (in the leg), gastroepiploic artery (near the stomach), or radial artery (in the arm). A stabilizing device is used to secure the coronary artery of choice. This device applies gentle pressure or suction, mildly limiting cardiac function, but providing better access to posterior and inferior vessels of the heart. The surgeon makes the necessary anastomosis to the targeted coronary arteries. If conduits other then the mammary arteries are used they are connected to the ascending aorta to provide systemic blood flow.
If an anticoagulant was administered, drugs are given to reverse the anticoagulant. Upon completion of the off-pump MIDCAB, MIDCAB, or OPCAB procedure, the chest is closed. If a midline sternotomy was performed, stainless steel wires are implanted to hold the sternal bone together. Sutures are used to close the skin wound, and sterile bandages are applied as a wound dressing.
An electrocardiogram detects the presence of acute coronary blockage (occlusion). A history of myocardial infarction can also be detected by electrocardiogram. Patients with a history of angina also are evaluated for coronary artery disease. Coronary angiography provides the best diagnostic information about the extent and location of the coronary artery disease.
The patient receives continued cardiac monitoring in the intensive care unit . Once the patient is able to breathe on his/her own, the breathing tube is removed (extubation), if it is not removed immediately post-operatively. Any medications to treat poor cardiac function or manage blood pressure are discontinued as cardiac function improves and blood pressure stabilizes. Blood drainage tubes protruding from the chest cavity are removed once internal bleeding decreases. The patient also may be equipped with external cardiac pacing to maintain heart rate. The pacing is terminated once the heart is beating at an adequate rate free of arrhythmia. A warming blanket may be used to warm the patient's core temperature that was decreased by the surgical exposure.
The duration of the post-operative hospital stay is reduced by one to two days in these procedures. Pain also should be reduced. Homecare for the wound is described prior to discharge, and instructions for responding to adverse events after discharge also are given. Patients who have undergone these procedures should expect to return to normal activities sooner than those who have undergone traditional coronary artery bypass grafting.
MIDCAB can result in a higher rate of restenosis (recurrence of narrowing of the arteries) then traditional coronary artery bypass grafting, but these numbers continue to decrease as experience with the procedure improves. Some patients may have to have the procedure converted to a standard sternotomy with cardiopulmonary bypass, if the anastomosis can not be completed from the MIDCAB approach. Rib fracture is the most common adverse event. Pericarditis also is a possible complication. Supraventricular arrhythmias and ST segment elevation also may develop.
In the event of systemic blood pressure abnormalities, arrhythmia, poor surgical anastomosis, or poor exposure of the coronary blood vessels, OPCAB patients may require conversion to cardiopulmonary bypass for completion of the anastomosis. Post-operatively some patients may need additional surgery to control bleeding or to address poor sternal healing. This is related to the increased use of both internal mammary arteries for these procedures. Cerebral complications and atrial fibrillation also may be experienced. These post-operative complications are comparable to those seen in patients who have undergone traditional coronary artery bypass grafting.
Patency (openess) of the grafted vessels is expected to be the same as what is seen in traditional coronary artery bypass grafting. When compared to traditional coronary artery bypass grafting, minimally invasive heart surgery also is expected to result in a shorter hospital stay, less pain, fewer blood transfusions, and quicker return to normal activity.
Conversion to a full sternotomy or sternotomy with cardiopulmonary bypass is expected in 1–2% of patients. Redo procedures and reoperation can occur in over 5% of patients, which is still lower than the risk of a second procedure associated with balloon angioplasty and stent placement. Over 90% of all patients are expected to be free of adverse events. Complications most frequently involve rib fracture (over 10% of patients). Mortality associated with MICAB is low and is not seen during the surgical procedure in most instances, but is associated with post-operative complications.
Conversion to cardiopulmonary bypass may be required in patients if anastomosis cannot be completed due to unstable blood pressure, arrhythmia, ischemia, poor anastomosis, or poor surgical access. The same operative mortality is expected when compared to cardiopulmonary bypass patients. The expected decrease in neurological events, renal dysfunction, pulmonary complications, or arrhythmias has not yet been shown to be a consistent benefit, therefore all of these complications can still occur.
Percutaneous balloon angioplasty and coronary stenting of the left anterior descending artery are successful alternative procedures. MIDCAB may be a preferred treatment when compared to balloon angioplasty and stenting because fewer repeat interventions are required. An additional alternative is traditional on-pump, cardiopulmonary bypass; coronary artery bypass grafting is a powerful technique with a long record of safety and effectiveness since the 1960s.
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Allison Joan Spiwak, MSBME
Medical centers performing cardiac surgical procedures are equipped to perform this procedure. A cardiothoracic, cardiovascular, or cardiac surgeon receives additional training to successfully complete this procedure. Special technology in stabilizer design is purchased by the institution and made available for the surgeon to master. Within most clinical practices one surgeon becomes skilled in the technique. This one surgeon completes most procedures off-pump with MIDCAB or OPCAB techniques as necessary to revascularize the patient.