Dilemma of vein graft disease

MUCH has happened since the coronary artery bypass grafting began to manage coronary artery disease (disease of the arteries that supply blood to the heart) over three decades ago. It is now one of the most frequently performed surgical procedures, providing a marked relief of symptoms besides improving long-term survival in certain subsects of patients suffering from coronary artery disease.

In this surgery, a segment of the patient's leg vein (the "saphenous vein") is removed and used to create an artificial conduit to bypass narrowing known as blockages) in the patient's coronary arteries (also called native coronary arteries).

Of late, total arterial revascularisation has become the aim, where instead of leg veins, arteries from the patient's chest wall, forearm and, less commonly, from the upper alimentary tract are harvested for use as bypass conduits. Unlike vein grafts, arterial grafts are less prone to development of disease and thus remain functional for a longer period. However, the saphenous vein still remains as an important source for bypass conduits.

Vein graft disease

This term refers to the narrowing, either localised or diffuse, of the segment of the vein that has been used as a bypass graft. Serial follow-up studies of patients who have undergone bypass surgery have shown that up to 10 per cent of vein grafts are occluded by the time of hospital discharge, which increases to 20 per cent by the end of the first year after surgery. With time, there is continued development of disease and progression, so that by the end of 10 years only one-third of the vein grafts that were not occluded at one year are free of significant disease. Not all patients with vein graft disease need to have surgery again for replacement of diseased grafts. A re-operation becomes necessary in about 20 per cent of patients by 10 years.

Disease in a vein graft forms in different phases following surgery. In the first month following surgery, occlusion of graft is due to thrombus (blood clot) formation. This may occur due to poor flow in the graft, unrecognised disease at the site where the bypass graft is attached to the native coronary artery, or due to technical reasons. Late vein graft narrowing occurs because of thickening of the wall of the vein due to excessive proliferation of cells and accumulation of connective tissue. This is followed by deposition of fatty and thrombus-containing material.

Awareness of the consequences of vein graft disease is of importance, as it is the most important cause of recurrence of chest pain following surgery. Because of its unique pathology, presentation with severe chest pain or myocardial infarction (heart attack) are also seen as manifestations. Various options are available for the management of vein graft disease, as outlined below.

Medical therapy

The primary role of medical therapy is in the prevention of development and progression of vein graft disease. The addition of aspirin early after surgery helps decrease the incidence of vein graft occlusion. High blood cholesterol levels have been identified as an important risk factor. A landmark study, published in 1997, has demonstrated that aggressive drug therapy of high cholesterol substantially reduces the progression of vein graft disease. Mild chest pain due to graft disease may be managed with standard medications used for the treatment of angina. Recurrent or severe chest pain indicates the need for an angiogram to assess the state of the diseased vein grafts and to plan appropriate therapy.

Angioplasty

The dramatic growth of angioplasty to treat coronary artery disease, as well as other catheter-based procedures over the last two decades has resulted in the creation of interventional cardiology as a new discipline. Besides disease of native coronary arteries, angioplasty is also being increasingly used to treat vein graft disease. A successful result can be achieved in over 90 per cent of patients undergoing the procedure. However, by five years, nearly half of these patients require a repeat revascularisation procedure. An important advance in the technique of vein graft angioplasty is the deployment of "stents", which are hollow metallic tubular structures placed at the site of angioplasty. Their use has resulted in a significantly better clinical outcome and a lesser need to repeat revascularisation procedures.

In some patients, angioplasty of vein grafts could lead to breakage of small debris from the disease site. These particles, which may be as small as 10 um or as large as 3,000 um, may lead to complications if trapped downstream in the smaller blood vessels supplying the heart. New "protection devices" in the form of balloons or filters to collect and retrieve these dislodged material before they are washed downstream are under clinical evaluation, and preliminary results appear encouraging.

Recent research by this writer (in Canada and scheduled for publication in a forthcoming issue of the American Heart Journal) has revealed that the risk of an adverse outcome after angioplasty of vein grafts is greater in patients with high blood cholesterol levels. Fortunately, the risk appears to be reduced significantly by drug therapy for high blood cholesterol levels.

Re-operation

Patients with diffuse disease of vein grafts or with disease of multiple vein grafts are better managed by a repeat coronary artery bypass surgery. Re-operation carries a higher risk than the initial operation, with a mortality rate thrice that of the initial operation. Also, by five years, approximately half of patients undergoing a re-operation experience a recurrence of symptoms. Nonetheless, for the moment, re-operation remains the better option with excellent long-term survival in such patients.

The widespread utilisation of coronary artery bypass surgery is testimony to its efficacy, but the problem of vein graft disease exists. The best treatment for any disease lies in the prevention of development of the disease, which also holds true for vein graft disease. Meticulous attention to diet, and medications such as aspirin along with aggressive control of elevated blood cholesterol levels can help decrease its development and progression.

Angioplasty can provide significant relief in selected patients with vein graft disease, in whom it may delay or even preclude the need for a reoperation. For patients with extensive or multiple vein graft disease, reoperation is an option, although results are not as good as that of initial surgery.

DR. B. CHANDRASEKAR

The writer is Consultant Interventional Cardiologist, Vijaya Heart Foundation, Vijaya Hospitals, Chennai.

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