Heart surgery

Congenital, valvular and coronary heart disease all have a largely mechanical component and lend themselves particularly well to surgical correction. This was predicted in 1925 by Henry Souttar of the London Hospital, Whitechapel, who wrote in the British Medical Journal, in the introduction to his report of the first mitral commissurotomy, that the heart should be as amenable to surgery as any other organ and that many of the problems in heart disease were to a large extent mechanical. He saw the main problem as being maintenance of blood flow, particularly to the brain, while surgery was being performed. The first real steps in surgery in and around the heart came in the late 1940s and early 1950s, driven by surgeons who had gained confidence and experience under the pressures and opportunities provided by war. Further progress had to wait until the development of cardiopulmonary bypass in the mid 1950s. Now the number, range and technical complexity of heart operations are remarkable; with the pump restored to good working order, the well-being and lifespan of patients with congenital, valvular and degenerative heart disease can be very much improved.

In this chapter those cardiac diseases that can be helped by surgery are included. The surgical management of heart disease is particularly appropriate to illustrate some principles in the logic of surgical decision making.

The purpose of an operation should be to relieve symptoms, to improve prognosis or both. As far as symptoms are concerned the surgeon should help the patient towards an informed appraisal of the risks and benefits applicable to the particular case, as with any other operation. For prognosis, the matter is one in which the surgeon should provide the patients with advice based on the best available knowledge. Ideally, three numerical pieces of information are required:

1. the outlook if the condition remains unoperated on;

2. the risk of the operation itself, including failure to deal with the disease;

3. the outlook following successful surgery.

The approach is illustrated diagrammatically (Fig. 48.1).

Cardiopulmonary bypass

Cardiopulmonary bypass allows the surgeon to manage the circulation while operating on a still heart in a bloodless field. Valve surgery under direct vision would not have been possible had it not been for the introduction of cardiopulmonary bypass in the 1950s by Gibbon. Before this, valve surgery was performed using closed techniques (mostly

commissurotomies or valvotomies performed with dilators). There is still a role for these procedures, but now most valve procedures are performed on a still heart with the aid of cardiopulmonary bypass, which has undergone many modifications since its first development (Figs 48.2  -  48.4).

Today it is a very safe way to manage the circulation during surgery, although there are still some associated problems that cause morbidity. For most operations, the heart is approached by a median sternotomy. An incision is made from the jugular notch to the lower end of the xiphisternum. The sternum is divided and retracted to expose the pericardium. The patient is fully heparinised and the pericardium is opened, taking care nor to damage the brachiocephalic vein. The great vessels are exposed and a purse string is inserted into the adventitia of the ascending aorta proximal to the brachiocephalic artery. A second purse-string suture is inserted into the right atrium by the appendage. A 1-cm cannula is inserted into the ascending aorta and held in place by the purse-string suture. Air is excluded and the cannula is connected to the bypass circuit. Venous drainage is established from a cannula placed in the right atrium. Alternatively, the superior and inferior caval veins may be cannulated separately to gain better control over the venous return and to facilitate surgery within the right atrium. Once the circuit is connected, the cardiopulmonary bypass machine (the pump') takes over the circulation and ventilation can be discontinued. The core temperature may be lowered to reduce the metabolic demands of the tissues, and the surgeon can now isolate the heart from the rest of the circulation.

At the end of the procedure air must be meticulously excluded from the cardiac chambers. Once perfusion is restored to the coronary arteries, the heart may beat spontaneously or, if ventricular fibrillation is present, it may require a shock by a direct current (DC). Epicardial pacing wires may be placed to treat postoperative bradycardia or heart block. The patient is rewarmed, acidosis or hypokalaemia is corrected, ventilation is restarted and venous blood is allowed to fill the right atrium by clamping the venous line of the bypass machine. The heart gradually takes over the circulation while the arterial flow from the cardiopulmonary bypass machine is reduced. When the blood pressure is acceptable and the surgeon is confident that the heart function is adequate, cardiopulmonary bypass is discontinued and the venous

cannula removed. Blood from the bypass reservoir may be given through the arterial cannula while protamine is given to reverse the effects of heparinisation.

Femorofemoral bypass

This is a form of cardiopulmonary bypass that is used when it is difficult or impossible to enter the chest until bypass has been established. Venous drainage may be from the femoral vein or the right atrium. Arterial return is via the femoral artery which has to be surgically exposed.

Vascular shunts

Heparin-bonded shunts are used to bypass a section of aorta requiring resection or repair. They are particularly useful for aortic transection repair following a high-speed deceleration injury when cardiopulmonary bypass would be inadvisable. The shunt perfuses the aorta distal to the site of injury and therefore protects against paraplegia (Fig. 48.5).