Coronary Artery Disease

1

What is angina, and what causes it?

Angina pectoris reflects myocardial ischemia. Patients often describe the sensation as pressure, choking, or tightness. Angina typically worsens with exertion or stress and is relieved by rest. Angina is typically produced by an imbalance between myocardial oxygen supply and myocardial oxygen demand. The classic presentation is a man (male/female ratio of 4:1) out shoveling snow on a cold night after a big meal. Alternatively, sometimes (particularly in patients with diabetes mellitus), dyspnea on exertion may also reflect myocardial ischemia. For unclear reasons, patients with diabetes may not complain of chest pain/pressure, but rather dyspnea as their presenting symptom of myocardial ischemia.

2

How is angina treated?

The treatment options for angina include medical therapy or medical therapy with myocardial revascularization with either percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG). Medical treatment is directed toward decreasing myocardial oxygen demand. Strategies include nitrates (nitroglycerin, isosorbide), which dilate coronary arteries minimally but also decrease blood pressure (afterload) and therefore myocardial oxygen demand; β-receptor antagonists, which decrease heart rate, contractility, and afterload; and calcium channel antagonists, which decrease afterload and may prevent coronary vasoconstriction. Antiplatelet therapy (e.g., aspirin, Plavix, prasugrel) is also important. Newer antiplatelet agents such as clopidogrel (Plavix) and eptifibatide (Integrilin) are promoted in the management of acute coronary syndromes. Plavix, however, is a potent, efficacious agent, and operation (i.e., CABG) within 5 days of Plavix exposure increases the risk of postoperative bleeding threefold.

Once patients are on guideline-directed medical therapy, then revascularization with either PCI or CABG is undertaken if symptoms persist.

• a.

  What is a heart team? A heart team is composed of an interventional cardiologist and a cardiac surgeon. The heart team endorses a multidisciplinary approach to coronary revascularization and seeks to inform patients about the most appropriate therapy to treat their cardiovascular disease. The use of a heart team is endorsed as a Class I indication by the American Heart Association/American College of Cardiology 2012 Stable Ischemic Heart Disease Guidelines.

• b.

  What is a syntax score? The SYNTAX trial randomized 1800 patients to receive either a drug-eluting stent (PCI) or CABG for multivessel CAD. In SYNTAX, the degree of CAD was calculated based on a score that was based on the extent, location, and severity of CAD from the coronary angiogram. The cutoff points for syntax scores are as follows: low <22, intermediate 23–32, and high >33. Patients with high syntax scores (>33) and multivessel CAD had improved survival and lower rates of death, myocardial infarction (MI), and repeat reintervention. Thus, this score can aid the heart team in counseling patients regarding revascularization options.

3

What are the indications for coronary artery bypass graft?

• a.

  Left main coronary artery stenosis: Stenosis >50% involving the left main coronary artery is a robust predictor of poor long-term outcome in patients who are medically treated. A substantial portion of the myocardium is supplied by this artery. Even if the patient is asymptomatic, survival is markedly improved with CABG. Left main coronary disease is a Class I indication for CABG according to the American Heart Association/American College of Cardiology guidelines for CABG surgery.

• b.

  Three-vessel coronary artery disease (70% stenosis) with depressed left ventricular (LV) function (i.e., <0.50) or two-vessel coronary artery disease (CAD) with proximal left anterior descending (LAD) involvement: In randomized trials, patients with three-vessel disease and depressed LV function showed a survival benefit with CABG compared with medical therapy.

• c.

  CABG also confers survival benefit in patients with two-vessel CAD with a tight proximal LAD stenosis and an ejection fraction (EF) <0.50 or demonstrable ischemia on noninvasive testing . An important caveat, however, in managing patients with depressed LV function is that operative mortality increases when the EF falls below 30%.

• d.

  Angina despite aggressive medical therapy: Patients who have lifestyle limitations because of CAD are appropriate candidates for CABG, provided surgery can be performed with acceptable risk. Data from the Coronary Artery Surgery Study suggest that patients treated with surgery have less angina, fewer activity limitations, and an objective increase in exercise tolerance compared with medically treated patients.

4

What is done during a traditional CABG procedure?

CABG is an arterial bypass procedure that can be done both on bypass and off bypass. The left internal mammary artery (LIMA) is harvested as a pedicled graft, with other conduits including the greater saphenous vein or radial artery procured as well. Cardiopulmonary bypass (CPB) is established by cannulating the ascending aorta and the right atrium, and the heart is arrested with cold blood cardioplegia. Segments of the greater saphenous vein are then reversed and sewn with the proximal (inflow) portion of the bypass graft originating from the ascending aorta and the distal (outflow) portion of the bypass graft anastomosed to the coronary artery distal to the obstructing lesion. The LIMA is typically sewn to the LAD. When the anastomoses are finished, the patient is weaned from CPB, and the chest is closed. Typically, one to six bypass grafts are constructed (hence the terms triple or quadruple bypass).

5

What is an off-pump CABG (OPCAB)?

CABG can be performed without CPB and arrest of the heart. When done with the heart beating through a median sternotomy, CABG is then called an OPCAB. The heart is positioned with commercially available stabilization devices, and the vessel to be bypassed is immobilized and snared to provide temporary occlusion. The venous or arterial conduit is then sewn to the immobilized coronary artery, and the occlusion of the vessel is released.

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