Myocardial Ischemia

Incidence in USA: 1.5 million/y develop acute MI; about 50% are silent (without enough symptoms to cause a medical visit); decreased rate of death in the United States balanced by increased population has kept MI numbers constant since 1970 despite increased population; worldwide, the incidence of MI is 9 million/y.

Some 12 million individuals in USA have narrowing of 70% or more of one or more coronary arteries; among unselected pts over age 40 years, 1.4% have MIs; cardiac death occurs in 1.7%.

Risk is higher among those of European, Indian, and African American heritage than among Japanese, but the environment of North America equalizes risks.

Risk is highest in pts with known other atherosclerotic disease (including prior MI): smokers (3.5-fold increase); hypertensives (threefold increase); diabetics (4-fold increase); hypercoagulable or chronic inflammatory diseases (threefold increase); stressed, divorced, or unstable marriage (2.5-fold increase); with wt gain since age 20 years (1.5-fold increase for each 5-kg increase); increased LDL cholesterol in those who do not exercise (0.5% increase for each 1% increase above 100 mg/dL); who do not drink or take vitamin D or aspirin; whose parent died of CAD at <40 y of age (1.4- to 2.5-fold increase); age (threefold increase per decade over 50), family Hx (1.1-fold to 2.4-fold increase)

Periop CV complication (MI, CHF, RHF, arrhythmia requiring Rx) increases the risk ninefold.

2-y survival: Rate in high-risk pt with periop MIsch is 25% versus 85% for those without periop MIsch.

Inadequate coronary perfusion (1–6% reinfarction rate with general surgery; higher with vascular/thoracic/upper abd surgery); lower with cataract/prostate/peripheral surgery with single-limb anesthesia only.

Can lead to increased left or right ventricular compliance and CHF and dysrhythmias.

Can lead to inadequate perfusion of other organs and their insufficient function (brain, kidney, liver, gut).

Postop period if stressed by perturbations that increase demand (pain, sepsis, fever, hypervolemia and hypovolemia, and tachycardia), or limit supply (thrombosis, hyperviscosity states, diseases limiting pulm function and gas exchange [restrictive, obstructive, parenchymal], Hct <28%)

Condition of inadequate supply of O ₂ and nutrients to myocardial cells relative to need associated with the increased stress of periop period,

Treatment and prophylaxis of this and related disorders consume 10–20% of total health expenditures. Periop CV complications double with MIsch, with threefold reduction in 2-year survival and threefold increase in periop costs for major surgery.

Major foci of clinical and basic studies are to decrease incidence and risks from concern over risk-benefit ratio and cost-effectiveness, identifying high-risk pts prior to surgery and segregating them for prior therapy (smoking cessation, control of Htn, hypercholesterol states, hypercoagulable states, PTCA, CABG) or increased periop vigilance and care (PA lines, TEE, ICU care, prophylactic pain therapy).

Known atherosclerotic risks (genetic predisposition, smoking, Htn, diabetes, divorced or unstable marriage, inflammation, hypercoagulable states, increase LDL or decrease HDL cholesterol, weight gain)

Known conditions that increase periop demands on heart (tachycardia: 2-fold greater for HR >90, 11-fold greater for HR >110); or limit supply (vasospastic states; Pa CO ₂ <25; Hct <28%; hyperviscosity and hypercoagulable states; inadequate O ₂ exchange)