Cardiomyopathy, Ischemic

• • Normal coronary blood flow: 1 mL per gram of myocardium per minute

  • Oxygen extraction from coronary bed: 75% at rest, 100% during stress

  • Coronary flow primarily during diastole

  • Mean coronary resistance is 3-6 times the totally vasodilated value, implying extreme vasodilator reserve

  • Atherosclerosis progression: Intimal incorporation of lipids → expanding plaque with fibrosis and calcification → finally rupture of plaque causing thrombosis → acute infarction

  • Subtotal occlusions important in pathogenesis of unstable angina

  • Usual pattern

  • -Short, proximal stenoses of left coronary artery

    -In right coronary artery, disease more diffuse, involving proximal and middle portions of artery

    -Patients with type 1 diabetes mellitus have diffuse disease

  • Blood flow may be adequate at rest; exercise and stress may produce ischemia

  • Acute coronary insufficiency (angina pectoris): Immediate decrease in myocardial work

  • After only 15 minutes of reversible ischemia, may take 24-48 hrs for complete recovery

Epidemiology

• • Coronary artery disease responsible for 20% of all deaths

  • Cardiovascular disease accounts for > 40% of all deaths

  • Atherosclerosis identified in up to 50% of autopsies of patients in second decade of life

  • Risk factors

  • -Smoking (secondhand increases death rate from coronary disease by 30%; smoking cessation decreases coronary risk by 50% after 1 year of abstinence)

    -Hypercholesterolemia

    -Male

    -Diabetes mellitus

    -Hypertension

    -Family history

    -Obesity

    -Inactivity

  • Coronary mortality rate directly proportional to number of vessels affected and LV function

Symptoms and Signs

• • Retrosternal chest pain

  • -Pressure

    -Choking

    -Tightness

    -Frequently radiates down left arm, left neck, occasionally right arm, mandible, ear

  • Exercise, cold exposure, eating can precipitate symptoms

  • Stable, progressive, or unstable angina

  • Pulmonary edema from ischemia (poor prognosis)

  • Some have no symptoms (silent myocardial ischemia)

Laboratory Findings

• • ECG

  • -Normal in 50% of patients

    -May have inverted T waves, ST segment abnormalities, or Q waves at rest

Imaging Findings

• • Coronary angiography: Highest sensitivity and specificity of any test available (10% of patients underestimated)

  • Screening

  • -Stress ECG

    -Stress echocardiography

    -Dobutamine echocardiography

    -Stress thallium may identify viability

• • Consider other causes of chest pain, including gastroesophageal reflux disease, aneurysms, aortic dissection

• • Screening test

  • If high suspicion, proceed to angiography

• • Risk reduction: Smoking cessation, hypertension control, lipid reduction

  • Percutaneous transluminal coronary angioplasty (> 90% successful but repeat interventions common)

  • Operative therapy: Complete revascularization associated with improved outcome

  • Evaluate carotid bruits, renal function, respiratory status, coagulation studies

Conventional Coronary Artery Bypass Grafting (CABG)

• • Internal mammary (preferred), saphenous vein, or radial artery used to bypass on average 3-4 coronary vessels

  • Graft patency affected by smoking, low-density lipoprotein

Minimally Invasive

• • Off-pump coronary artery bypass (OPCAB)

  • -Performed without cardiopulmonary bypass

    -Best for left anterior descending, ...