MINIMALLY INVASIVE HEART SURGERY

Minimally invasive heart surgery
Definition : Minimally invasive heart surgery refers to surgery performed on the beating heart to provide coronary artery bypass grafting. This technique is often referred to suras MIDCAB, minimally invasive direct coronary artery bypass; or OPCAB, off-pump CABG.

Purpose
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.

Demographics
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 MIDCAB. With sternotomy, disease of the right and left coronary arteries can also be addressed by OPCAB. The significance and location of the coronary artery lesions may limit the success of the MIDCAB or OPCAB procedure. Most practices have at least one surgeon skilled in performing revascularizations without cardiopulmonary bypass. Of all coronary artery bypass grafting procedures, approximately 10–20% are performed in this manner.

Description
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).

MIDCAB
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.

OPCAB
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 offpump 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.

Diagnosis / Preparation
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.