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Minimally Invasive Heart Surgery

Minimally Invasive Heart Surgery

Definition
Purpose
Demographics
Description
Diagnosis/Preparation
Aftercare
Risks
Normal results
Morbidity and mortality rates
Alternatives

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 as 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. In addition, smaller incisions can be used instead of the standard sternotomy (incision through the sternum, or breastbone) 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

KEY TERMS

Anastomosis— Connection of the bypassing blood vessel to the blocked blood vessel by surgical suture. The stitches may be made in continuous manner or individual, with continuous being more common. The disadvantage of continuous suture can be purse-stringing or cinching of the graft opening during knotting of the suture.

Angiography— Injecting dye into blood vessels so they can be seen on an x ray.

Arrhythmia— Cardiac electrical signaling that generates an ECG rhythm other than normal sinus rhythm.

Balloon angioplasty— A procedure used to open an obstructed blood vessel. A small, balloon-tipped catheter is inserted into the vessel and the balloon is inflated to widen the vessel and push the obstructing material against the vessel’s walls. The result is improved blood flow through the vessel.

Cannula— A small, flexible tube.

Cardioplegic arrest— Halting the electrical activity of the heart by delivery of a high potassium solution to the coronary arteries. The arrested heart provides a superior surgical field for operation.

Cardiopulmonary bypass— Use of the heart-lung machine to provide systemic circulation cardiac output and ventilation of the blood.

Coronary occlusion— Obstruction of an artery that supplies the heart. When the artery is completely blocked, a myocardial infarction (heart attack) results; an incomplete blockage may result in angina.

Coronary stent— An artificial support device used to keep a coronary vessel open.

Electrocardiography— A testing technique used to measure electrical impulses from the heart in order to gain information about its structure or function.

Myocardial infarction— Heart attack.

Stabilizer— A device used to depress the movement of the area around the coronary artery where the anastomosis is made. The stabilizer is used to provide a still, motionless field for suturing.

Sternotomy— A surgical opening into the thoracic cavity through the sternum (breastbone).

Thoracotomy— A surgical opening into the thoracic cavity.

(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 MID-CAB 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 in 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.

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.

Aftercare

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 postoperatively. 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. Home care 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.

Risks

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

WHO PERFORMS THE PROCEDURE AND WHERE IS IT PERFORMED?

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.

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.

Normal results

Patency (openness) 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.

Morbidity and mortality rates

MIDCAB

Conversion to a full sternotomy or sternotomy with cardiopulmonary bypass is expected in 1-2% of

QUESTIONS TO ASK THE DOCTOR

  • Is there a surgeon associated with this practice skilled with OPCAB or MIDCAB procedures?
  • Can the surgeon skilled in these procedures evaluate the patient for an OPCAB or MIDCAB procedure?
  • How many procedures has the surgeon performed in the last year? In the last five years?
  • What is the surgeon’s reoperation rate in regards to length of graft patency?

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.

OPCAB

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.

Alternatives

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.

Resources

BOOKS

Libby, P. et al. Braunwald’s Heart Disease. 8th ed. Philadelphia: Saunders, 2007.

Townsend, CM et al. Sabiston Textbook of Surgery. 17th ed. Philadelphia: Saunders, 2004.

Allison Joan Spiwak, MSBME

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