Minimally Invasive Direct CABG - MIDCAB

Dateline: 02/01/98

Over the past month, we have discussed the concept of minimally invasive heart surgery, and the use of this novel technique in treating coronary artery disease , heart valve disease and birth defects of the heart. This week, we will discuss one of the types of coronary bypass - Minimally Invasive Direct CABG.

For more information on minimally invasive surgery, including coronary bypass operations, you can visit the MICAS website.

What is a MIDCAB ?

This quintessential minimally invasive operation is simple, yet elegant in concept. Not only does it do away with the need for the heart-lung machine to support the circulation during surgery, it also utilizes a tiny key-hole incision and avoids splitting the breast-bone as in the conventional CABG operation. Through this small access incision, the surgeon connects a graft to diseased coronary arteries on a beating heart without any artificial support to the circulation. It is truly MINIMALLY invasive.

How is a MIDCAB done ?

After the patient is under anesthesia, the surgeon makes a small transverse 2 inch long incision on the front of the chest, towards the left side. This incision is then deepened, dividing the pectoral muscles. When the rib cage is reached, a small portion of the front of the rib - called the "costal cartilage" - is removed.

Just beneath this cartilage lies the Internal Thoracic Artery (ITA). With great care, the surgeon dissects out this artery for a short length, making sure that all tiny branches are clipped to prevent bleeding later on. When an adequate length has been prepared, the ITA is divided and occluded with a clamp.

The surgeon makes an opening in the sheath covering the heart (called the pericardium). On the surface of the heart, directly under the incision, lies the Left Anterior Descending (LAD) coronary artery to which a graft will be placed.

Sewing together the ITA and LAD coronary artery, both of which measure around 1.5 millimeters, is difficult in the best of circumstances. With the heart still beating during a MIDCAB, the procedure becomes infinitely more difficult. Great manual dexterity and skill are required to create such a connection. Using a variety of techniques to stabilize the heart and reduce its movement, the two arteries are connected with hair-thin sutures. When the graft has been sutured, the clamp on the ITA is released, and blood can be seen to flow through the distal LAD coronary artery. Simple, isn't it ?

Other grafts that have been placed using MIDCAB are

• Right ITA to the Right Coronary Artery (RCA)
• Right Gastro-epiploic artery (in the abdomen) to RCA branches
• Recently some surgeons have been able to graft the Left Circumflex Coronary Artery branches

Techniques used to immobilize the heart during MIDCAB

One of the drawbacks of the MIDCAB operation is the constant movement of the heart. The fine anastomosis between graft and artery cannot be made with the comfort and precision that is available in conventional CABG. To make the surgeon's life easier, many innovations have been tried out to immobilize the heart surface during the surgery.

Loop Sutures

The surgeon passes a suture around the coronary artery - above and below the site of the graft - creating a loop around it. This loop is then held in clamps, serving two functions

• it immobilizes the area of the graft anastomosis
• it occludes the coronary artery above and below the anastomosis, and provides a clear operative field that is not flooded with blood

One theoretic objection to this method is that it strangles the coronary artery and may injure its wall.

Special Clamps

Different specially-designed occlusion clamps that can be fixed to the chest wall have been tried out to immobilize the heart, with varying degrees of success.

Utrecht Octopus Device

A very innovative device, this has multiple small suction cups that are applied on to the heart surface. When suction is turned on, the cups stick to the surface, and hold the heart steady, with movement being less than 1 mm. for each heart beat.

Drug therapy

Two drugs - Esmolol (a short acting beta-receptor antagonist) and Adenosine (a natural metabolite used in arrhythmia treatment) - have been found effective in slowing, and even temporarily stopping the heart beat for short periods (around 20 seconds).

For more information on minimally invasive surgery, including coronary bypass operations, you can visit the MICAS website.