Minimally invasive cardiac surgery

Advances in Cardiovascular Surgery - Minimally invasive Cardiac Surgery

Wilson Ko, M.D.
(presented at the 1997 CAMS Semiannual Scientific meeting)
A Historical Perspective

The concept of endoscopic surgery was first applied widely in the clinical arena by gynecologists who applied laparoscopic procedures for lysis of adhesion and for diagnosis of various pelvic ailments. This innovative approach was not accepted in main stream general surgery. In the late 1980's, the standard techniques for laparoscopic cholecystectomy were developed primarily by young, non-academic general surgeons. This important advance was made possible primarily by the tremendous industrial investments for the development of technologically advanced electronic, video, optical and endoscopic instrumentation. The financial incentive for industrial research and development were the disposable instruments specifically designed for this operation. Initially, there was strong reluctance to accept this new surgical technique by the academic surgeon. However, public demand for the popularized "minimally invasive" surgery increased due to an aggressive marketing campaign launched by medical industries. Laparoscopic cholecystectomy was rapidly developed into a safe and effective procedure and has become the standard of care. The tiny incisions, the marked reduction in postoperative pain, and the absence of ileus have led to patient satisfaction. Perhaps the most important impact was the windfall created for hospitals from the shortened length of hospital stays and for corporations who benefitted from the expeditious return of their employee to the workplace. These were notable savings during the time of corporate restructuring and hospital down-sizing.

Following the boom in laparoscopic cholecyctectomy, general surgeons extended the laparoscopic techniques into other areas of abdominal surgery with varying degrees of success. Although the concept of thoracoscopy was originated during the beginning of this century, it had very limited utility because of mini-mal access and exposure. The application of the same technologically advanced instrumentation from newly developed laparoscopic surgery allowed the thoracic surgeon access to all areas of the intrathoracic cavity via "video assisted thoracoscopy or VAT". These new endoscopic instruments have allowed many minor thoracic procedures such as diagnostic thoracoscopy, pleural or lung biopsy, resection of mediastinal tumors to be performed without a formal thoracotomy. Indeed, video-assisted thoracoscopic procedures are now the standard of care.

As in the historical development of surgery, cardiac surgery is the last frontier for endoscopic surgery. In light of over 300,000 cases of coronary artery bypass surgery and over 100,000 valvular surgeries done in this country alone, cardiac surgery has become the next and largest industrial target.

What is Minimally Invasive Cardiac Surgery?

The development of minimally invasive cardiac surgery is currently in its infancy. Therefore, it means very dif-ferent things to different cardiac surgeons, cardiologists, internists, and the lay public. The exact definition is being worked out by the Society of Thoracic Surgeons, and the American Association of Thoracic Surgery. Unlike any other field of surgery, the conduct of cardiac surgery is much more than anesthesia, bodily surface wound, invasion of a body cavity, excision, replacement or manipulation of organs. In order to appreciate what is truly "minimally invasive", one needs to understand the complexity and different components of cardiac surgery.

Fundamentally, cardiac surgery involves a sternotomy wound where the sternum is divided. This allows access to the heart and the great vessels. For coronary surgery, other wounds are created for the harvest of bypass conduits. These wound may be in the legs, arms or the surface of the abdomen, to harvest the saphenous vein, the cephalic vein, the radial artery, or the inferior epigastric artery. A full laporaotomy is required for the gastroepiploic artery. Only the internal mammary artery does not require a separate wound. All wounds have the potential to develop postoperative pain and infection. In coronary surgery, leg wounds are the most common source of patient problems and complaints. Deep sternal wound infection, albeit uncommon, carries a 10% risk of mortality despite aggressive treatment and it is the cause of prolonged and costly recovery. The use of cardiopulmonary bypass diverts the blood away from the heart and lung; the blood then goes through a pump-oxygenator for gas exchange and is mechanically pumped back into the aorta. In conjunction, cardioplegia is used to stop the heart. This provides the cardiac surgeon with an uncompromising bloodless quiet field, and a non-beating heart. Yet, the use of cardiopulmonary bypass is by far a major cause of morbidity, including strokes, embolic complications, pulmonary insufficiency, renal insufficiency, and coagulopathy causing significant postoperative bleeding. One must keep this in mind when evaluating any new minimally invasive approach.

Minimally Invasive Coronary surgery

There are two new approaches to coronary bypass surgery. One involves performing bypass surgery through a mini chest incision without the use of cardiopulmonary bypass. The second has been designed to be totally endoscopic with the use of cardiopulmonary bypass.

1. Minimally Invasive Direct Coronary Artery Bypass (MID-CAB) The MID-CAB approach involves a small left anterior thoracotomy, through which the fourth and part of the third costal cartilages are removed to provide exposure. Alternatively, a lower sternotomy (the bottom two third) incision is made. The left internal mammary artery (LIMA) is taken down from the chest wall through these mini incisions. The pericardium is then opened, which usually exposes the middle territory of the left anterior descending (LAD) coronary artery as the target site for bypass. Techniques similar to peripheral vascular surgery are then applied. The LAD is occluded proximally and distally with sutures and an open-ing is made in it. The end of the LIMA is then anastomosed to the opening of the LAD. The salient features are the absence of a full sternotomy incision, and that cardiopulmonry bypass and cardioplegia are not used.

It is interesting to point out that this technique was first attempted in a few patients and reported by a Russian surgeon in the 1967 meeting of the American Association of Thoracic Surgery. At that time, it was viewed as an inferior technique to the conventional approach and was not accepted in this country. Over the last three years, this approach has been re-popularized by a handful of cardiac surgeons in this country and Europe. Using much finer sutures, delicate operating instruments, operating glasses, and sophisticated intraoperative hemodynamic monitoring with a pulmonary catheter and a transesophageal echocardiogram, this old Russian approach appears to be operable with reasonable safety. This less invasive approach has several obvious advantages. First, it obviates the possibility of the dreaded sternal wound infection. Second, by not using the pump-oxygenator and cardiopulmonary bypass, many of the associated complications mentioned earlier are obviated. Based on the initial experience of centers across the country, the length of hospital stay and the duration of out patient recovery are significantly shortened. The disadvantages of MID-CAB are (1) the lack of myocardial protection by the use of cardioplegia during the anastomosis; (2) the circumflex and the distal right coronary arteries cannot be reliably accessed; and (3) the anastomosis is done on a moving target. The lack of myocardial protection implies that multi-vessel disease, left main disease and poor ventricular function are relative contra-indications to this approach. This operation is really designed for bypass lesions in the LAD. For patients with multi-vessel disease, it is fraud with problems of incomplete revascularization. The most important concern is the sub-optimal condition of performing a delicate anastomosis on a beating heart. A perfect anastomosis and durability of the bypass graft patency are critical to the benefit of coronary artery bypass surgery. The efficacy of this approach can only be judged against other well known modalities. The 10 year patency rate of the LIMA-LAD bypass is greater than 90%, which should be used as the gold standard for all other procedures aimed to achieve long term efficacy. For the short term evaluation of this new procedure, it should be pointed out that one year re-stenosis rates of LAD angioplasty, LAD angioplasty with stent, and conventional LIMA-LAD bypass are 40, 20 and <20%, respectively. Most cardiac surgeons do not expect the results of MID-CAB to be as good as the conventional approach.. The hope is that it will be significantly better than PTCA with or without a stent. With the minimal post-operative morbidity and rapid recovery, MID-CAB may become an attractive alternative to patients with isolated LAD disease.
The current indications for MID-CAB used by the Cornell Cardiothoracic Surgical Group are (1) patients with sig-nificant potential problems with cardiopulmonary bypass, i.e., significant cerebrovascular disease, calcified and atheromatous aorta, severe renal insufficiency, and (2) patients with failed PTCA or recurrent LAD disease after PTCA, or with complex LAD lesions not amenable to angioplasty. the choice of MID-CAB rather than PTCA as the primary procedure for most patients with isolated LAD lesions will certainly be of major debate pending the long term data. In order to achieve results close to conventional CABG, we have adopted a policy that we will not accept a less than perfect technical result. In the face of a technical problem with the anastomosis, we will convert the MID-CAB procedure to the conventional approach.

2. The HeartportTM Approach

The approach, developed by the Standford group, was originally designed to perform endoscopic coronary artery bypass surgery without an open chest incision. All basic techniques of conventional coronary artery bypass surgery are applied. Without the access provided by the sternotomy incision, the Heartport approach used femoral arterial and venous cannulation through a groin incision to institute cardiopulmonary bypass. Additional catheters are placed percutaneously through the internal jugular vein for ventricular decompression and the administration of retrograde cardioplegia. Fluoroscopy is required for the very important and accurate placement of the catheters. These maneuvers require additional time and multiple small incisions (about six) to place the thoracoscope and endoscopic instruments. The procedure was used on two patients at Stanford with disastrous clinical outcome. Currently, this totally endoscopic approach was changed to a semi-open approach similar to that of MID-CAB. Unlike the MID-CAB where the surgery is done on a beating heart, the current Heartport approach uses femoral-femoral cardiopulmonary bypass. an intra-aortic ballon is used to occlude the ascending aorta and to administer cardioplegia. Through a left mini-thoracotomy as in MID-CAB, the left internal mammary artery is anastomosed to the LAD. Saphenous vein grafts are anastomosed to other arteries of the left heart. Proximal anastomosis are all made with the left internal mammary artery since the aorta is not accessible from the mini-incision.
There are several criticisms of the Heartport approach. the foremost is that it utilizes cardiopulmonary bypass like the conventional approach which carries major morbidities and mortalities. The only less invasive feature is the left mini-thoracotomy rather than a full stenotomy. The groin wound and cannulation of the femoral vessels create morbidities that are unique to this approach. Aortic dissection is also a well known complication of femoral cannulation, and was seen in more than 20 cases among the first 700 Heartport cases, an unacceptable rate. The current approach relies on using the left internal mammary artery as the sole inflow to all bypass grafts, like "putting all eggs in one basket". The Heartport approach represents a substantial added cost (longer operating time, etc.) that is difficult to justify in the current climate of managed care. The most obvious benefits of this approach are a more cosmetically pleasing wound and more expeditious outpatient rehabilitation. This may be important to younger patients, and allow them to return to work earlier than the usual 4 to 8 weeks of convalescence. These potential benefits will need to be documented. At the moment, the patient will need to be well informed of all the pros and cons of this new approach.

Minimally Invasive Valve Surgery

The main objective of the new "minimally invasive" approach is for valvular surgery is to avoid the sternotomy incision. Currently, aortic valve replacement, mitral valve replacement or repairs can be performed through a 8 centimeter right parasternal incision, through which the third and fourth cartilages are removed. This usually provides adequate albeit very limited exposure to the aortic and mitral valves. The Heartport system uses femoral vessel cannulations through a separate groin wound. However, there are several companies which have developed specialized instrumentation allowing the surgeon to cannulate the great vessels through a small incision. This is not an endoscopic approach, all surgery is done under direct vision. Other than a smaller incision, at a slightly different location, the conduct of the operation is unchanged. The main question is whether avoiding sternotomy is worth giving up the exposure which allows the safe conduct of traditional cardiac surgery.

Conclusion

Minimally invasive cardiac surgery does not offer any new treatment of cardiac diseases, but rather a different approach for the same operation. MID-CAB is an attractive approach for patients with isolated LAD coronary artery disease, and has gained national acceptance. Minimally invasive valve surgery may be preferred by younger patients for cosmetic reasons, and its potential for shorter convalescence still remains to be seen.