M YOCARDIAL ISCHEMIA Prepared by: Dr. Nehad Ahmed

S TUDY OBJECTIVES Understand the relationship between myocardial ischemia and angina. Distinguish among classic angina, unstable angina, variant angina and silent ischemia. Provide a rationale for pharmacologic and non- pharmacologic therapy in angina and myocardial ischemia. Explain the mechanism of action for the nitrates, β- blockers, calcium channel antagonists, aspirin and heparin in treatment of angina.

I NTRODUCTION Myocardial ischemia occurs when the blood flow demands of the heart exceed the blood supplied by the coronary arteries. The leading cause of myocardial ischemia is atherosclerosis or blockage of coronary arteries due to the accumulation of lipid plaques and/or thrombus

Under conditions of rest, myocardial oxygen supply and delivery of nutrients through the coronary arteries should match the metabolic requirements of the heart. When the metabolic needs of the heart increase, the coronary blood flow must increase accordingly.

With age and progressive occlusion of coronary arteries, smaller vessels may begin to carry a greater proportion of blood and provide an alternate means of perfusion for an area of myocardium. These collateral blood vessels may run parallel to the larger coronary arteries and be connected to other small coronary vessels by vascular connections called anastomoses.

Development of collateral circulation may reduce or delay the occurrence of symptoms from myocardial ischemia until the blockage is very progressed. The presence of extensively developed collateral circulation Might also explain why many older individuals often survive serious heart attacks when younger individuals, who have not yet developed collateral circulation, often do not.

M ANIFESTATIONS OF MYOCARDIAL ISCHEMIA Angina pectoris is the major symptom of myocardial ischemia. most commonly presents as pain, pressure or a burning sensation in the area of the sternum. Angina pectoris There are three types of angina pectoris: 1. Classic or exertional angina 2. Unstable angina 3. Variant angina

1. Classic or exertional angina - Pain is precipitated by increased workload on the heart. May be caused by exercise, emotions, stress and cold exposure. - Symptoms may remain “stable” for a number of years or progress in severity.

2. Unstable angina - Angina that occurs at rest. - Also referred to as “pre-infarct” angina since it is usually associated with extensive blockage of coronary arteries. - Coronary blood flow does not meet the needs of the heart even at rest. - Requires intensive treatment and evaluation.

3. Variant angina ( vasospastic angina, Prinzmetal’s angina) Caused by vasospasm of the coronary arteries. Usually associated with coronary artery disease but may result from excess sympathetic activity. Frequently occurs at night, at rest or during minimal exercise. May be precipitated by stress, cold exposure or smoking.

Silent ischemia is a particularly dangerous form of myocardial ischemia as there is a lack of clinical symptoms, i.e., ischemia without angina. Usually diagnosed by exercise stress testing or Holter monitoring

D IAGNOSIS OF M YOCARDIAL I SCHEMIA Electrocardiograph Holter monitoring — 24 ambulatory electrocardiograph Stress testing with electrocardiograph Nuclear imaging Cardiac catheterization

R ATIONALE FOR TREATMENT OF MYOCARDIAL ISCHEMIA Treatment of myocardial ischemia and the resulting angina can involve two strategies: 1. Increase coronary blood flow by dilating coronary arteries 2. Reduce cardiac workload by reducing heart rate and/or force of contraction

T REATMENT OF MYOCARDIAL ISCHEMIA The treatment regimen may include both nonpharmacologic and pharmacologic therapies. - Nonpharmacologic treatment physical activity Avoidance of stress (emotional, physiologic, cold) Reduction of risk factors for ischemic heart disease (hyperlipidemia, obesity, hypertension, diabetes, smoking, etc.)

P HARMACOLOGIC TREATMENT Organic nitrates Dilate coronary arteries and increase myocardial blood flow. Dilate peripheral arteries and reduce β afterload Dilate peripheral veins and reduce preload

Adrenergic blockers Block myocardial β. -adrenergic receptors. Reduce heart rate and cardiac output (reduced myocardial work- load and oxygen demand).

calcium channel blockers Block calcium channels in vascular smooth muscle. Dilate coronary arteries and increase myocardial blood flow. Dilate peripheral arteries and reduce afterload.

Aspirin, heparin Prevent platelet aggregation. Use for prophylaxis of blood clots particularly in unstable angina.

S URGICAL TREATMENT Coronary angioplasty Uses a balloon catheter to open occluded blood vessels Usually performed under local anesthetic 5% mortality, high rate of vessel re- occlusion Use of metal “stents” in opened vessel reduces rate of occlusion

Coronary artery bypass graft Revascularization procedure in which a blood vessel is taken from elsewhere in the body and surgically sutured around a blocked coronary artery May involve multiple (one to five) blood vessels Re-occlusion of transplanted vessel is possible

K EY TERMS Ischemia — Inadequate blood flow to a tissue or part of the body. Hypoxia — Deficiency of oxygen in tissues. Preload —The load on the heart at the end of diastole. Afterload —The force that the contracting heart must generate to eject blood.

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