MYOCARDIAL VIABILITY

For correspondence: dott. Roberto Scrofani, Department of Cardiovascular Surgery “L.Sacco” Hospital, Via GB. Grassi n.74 ,20157 Milan, Tel: 02-39042334, Fax: 02-39042652
E-mail: scrofani@robertomail.it

Introduction
The first clinical description of the left main coronary artery (left main coronary artery) disease from atherosclerosis is attributed to Henrik (1) in 1912. Although hemodynamically significant stenosis of the left main coronary artery (>50%) is not uncommon (2-4), complete occlusion is a very rare angiographic finding, and is found in approximately 0.05-1% of coronary angiographic studies (5-7). We report a case of complete occlusion of the left main coronary artery with normal left ventricular function, which represents one out of about 12.000 patients () undergoing cardiac catheterization in our institution over a 10 years .

Case Report
A 43 years-old man was admitted to our Hospital for a one year history of effort angina (CCS Class IV). His cardiac history was significant for cigarette smoking but he had no family history of coronary artery disease (CAD) or dyslipidemia.

His physical examination was normal.

His chest X-ray and electrocardiogram at rest were normal. An exercise test was positive by clinical and electrocardiographic criteria. Echocardiography showed normal left ventricular function. Laboratory results showed a normal level of A-Lipoprotein and a moderate decrease of S-protein.

Cardiac catheterization demonstrated normal ventricular function and a total occlusion of the left main coronary artery just a few millimeters after its origin. (figure 1)

The patient was referred for surgical revascularization. Because of his young age the coronary artery bypass grafting was performed with arterial grafts: the left internal mammary artery was used to graft the left anterior descending and the radial artery was used to graft the obtuse marginal branch of the circumflex artery. The postoperative course was uneventful.

Six months after surgery an exercise test was normal, without clinical or electrocardiographic findings suggestive of ischemia.

Comment
Occlusion of the ostium of a coronary artery can be associated with congenital heart anomalies such as Truncus Arteriosus or supravalvular aortic stenosis (10,11).The complete occlusion of the left main coronary artery itself is rare and complete occlusion with normal left ventricular function is even more so (8). The CASS (9) study which contains angiographic data from 25,000 patients reported the incidence of this lesion as approximately 0.05%; other reports (5) documented an incidence of less than 1%. In our experience this lesion occurred in 0.008% of about 12,000 angiographic studies.

It has not been possible to identify risk factors or clinical findings to identify patients with this rare condition and an isolated occlusion of the left main coronary artery is not considered a risk factor for developing diffuse coronary artery disease(8,9).The development of collaterals from the right coronary artery plays a basic physiopathological role to preserve left ventricular function and improve patient survival. Normal left ventricular function with occlusion of the left main coronary artery implies that the myocardium (normally supplied by the left coronary artery) receives oxygen and metabolic substrates from the right coronary artery to preserve a normal contraction pattern. The degree of blood flow from coronary collateral circulation is such that some cases of total occlusion of the left main coronary artery have been reported (12) without chest pain. In 1982 Zimmern (9) based on clinical and physiopathological studies, defined the coronary collateral flow as “substantial” or “limited” on the presence or absence of clear visualization of the left anterior descending and left circumflex artery at coronary angiography. In 1990 Topaz (13) described a complex vascular pattern with 13 specific collateral channels that originated from the right coronary artery and supplied the left coronary arteries. The relationship between coronary collateral circulation and left ventricular function seems clear. In addition it would seem logical that the degree of coronary artery disease of collateral vessels would also affect blood flow.

There are few published studies regarding medical therapy in patients with occlusion of the left main coronary artery. Watt (15) reports the case of a patient with a left main coronary artery stenosis and a nonstenotic dominant right coronary artery who refused cardiac surgery. The patient who was treated with medical therapy alone, continued for two years to have adequately controlled effort angina. A similar case was reported by Frye (16).

The long-term comparison of medical and surgical therapy in patients with stenosis of the left main coronary artery, was addressed in a randomized study (14). This study showed that although the presence of left main coronary artery stenosis alone is not a negative risk factor, the degree of stenosis is and that severe left main coronary artery stenosis significantly decreases the survival in medically treated patients. Other important variables reported by other authors are left ventricular dysfunction and the presence of right coronary lesions without an effective collateral circulation to the left coronary artery (14-16). Patient with one or both of these variables do better with surgical revascularization. Surgical revascularization has been suggested as the treatment of choice for patients with left main coronary artery disease(5).

References
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2) Cohen MV, Cohn PF, HermanMV, Gorlin R: Diagnosis and prognosis of main left coronary artery obstruction. Circ 1972; 45 (suppl. 1):57-65.
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12) Nassar H, Y Rozenman, Gotsman MS: Total occlusion of the left main coronary artery and normal left ventricular function despite critical narrowing of the right coronary artery. Eur Heart J 1992;13:850-852.
13) Topaz ON, Disciascio G, Cowley MJ, et al: Complete left main coronary artery occlusion: angiographic evaluation of collateral vassel patterns and assessement of hemodynamic correlates. Am Heart J 1991;121:450-456.
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16) Frye RL, Gura GM, Chesebro JH, Ritman EL: Complete occlusion of the left main coronary artery and the importance of coronary collateral circulation. Mayo Clin Proc 1977;52:742-5.
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