JIENY M. HAN, MD
overview
Definitions
■ Atherosclerosis: a process of damage to the vessels supplying the heart. Damage can include flow-limiting obstructive deposits or plaques, which can rupture & lead to thrombosis
■ Infarction: death of myocardial cells
■ Ischemia: myocardial oxygen demand exceeds supply
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Can lead to angina, arrhythmias, myocardial infarction (MI)➣
Thrombosis of coronary artery limits myocardial oxygen supply & may cause infarction■ Predisposing factors
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Increased age➣
Male sex (menopause increases risk in women)➣
Hypertension➣
Cigarette smoking➣
Hyperlipidemia➣
Genetics➣
Obesity➣
Diabetes mellitus■ CAD affects 11 million people in U.S.
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1.5 million of these will have MI, & 1/3 of those will die➣
Single largest cause of death in men & women■ Perioperative cardiac events, including MI, unstable angina, con- gestive heart failure, & serious dysrhythmias, are the leading cause of perioperative deaths (25–50% of deaths following noncardiac surgery).
Usual Rx: Treatment usually fivefold:
■ Correction of risk factors (smoking cessation, cholesterol-lowering agents)
■ Lifestyle modification: diet, weight loss, exercise
Coronary Artery Disease (CAD) 77
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Hypertension➣
Anemia➣
Hypoxemia➣
Thyrotoxicosis➣
Fever➣
Infection➣
Adverse drug effects■ Pharmacologic manipulation of the myocardial oxygen sup- ply/demand relationship. The most commonly used pharmacologic agents are:
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Beta-adrenergic blocking agents: Decrease myocardial oxygen demand by decreasing heart rate & contractility. Optimal block- ade results in a resting HR 50–60 bpm. Care should be exercised in pts w/ significant ventricular dysfunction, conduction abnor- malities, or bronchospastic disease.➣
Angiotensin-converting enzyme inhibitors: Reduce afterload & improve survival in pts w/ MI or CHF. May reduce or reverse ventricular remodeling.➣
Lipid modifiers: Improve long-term survival by modifying coro- nary plaque.➣
Nitrates: Vasodilator (venous> arterial) that dilates all vessels. Lowering of blood pressure reduces myocardial oxygen demand while maintaining coronary blood flow constant. Improves demand/supply balance. May improve symptoms in CHF. No negative inotropic effect.➣
Calcium channel blockers: Reduction of myocardial oxygen demand by decreasing cardiac afterload & increasing blood flow to the heart (coronary vasodilation). Verapamil & diltiazem also reduce demand by slowing HR. All agents potentiate the circu- latory effects of volatile agents. No improvement in long-term survival.➣
Antiplatelet agents: Aspirin & super-aspirins. May prevent thrombosis. May cause profound bleeding after surgery.➣
Diuretics: Lower total blood volume to reduce myocardial demand. May affect electrolyte balance.■ PTCA
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Catheter-based intervention for correction of coronary lesions➣
Technique & indications for use constantly evolving➣
Stent & treated stent placement reduces re-stenosis rate.➣
PTCA in last 3 months increases risk of myocardial events.78 Coronary Artery Disease (CAD)
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Indicated in significant 3-vessel disease, significant left main lesion, or in pts w/ significant disease & CHF➣
Can be performed w/ or w/o extracorporeal circulatory support➣
Risk is high: mortality 3.2%, stroke 3%, global encephalopathy 3%.preop
Preop risk factors of cardiac morbidity:
■ Primary risk factors
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CHFr Risk of perioperative cardiac complications is increased in pts w/ CHF.
r Many die suddenly, presumably of dysrhythmias. r CHF progresses w/ time.
r Beta blockers, ACE inhibitors, & implantable cardioverter/ defibrillator (ICD) improve survival.
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Previous MIr Along with CHF, one of two most important preoperative risk factors is a history of recent MI (within 6 mo).
r RiskofperioperativeMIinthesurgicalpopulationis0.7%;with CAD, risk is 3%; prior MI (6 mo) risk is 6–37%.
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Anginar Stable angina is induced by exercise or stress, resolves with rest, can be controlled with medication. No change in pattern, frequency, or causes.
r Unstableanginaoccursatrestorischaracterizedbyincreasing severity or number of anginal episodes. Unstable angina may be difficult to control medically & reflects severe underlying coronary disease. It frequently precedes MI. Diabetics have a relatively high incidence of silent ischemia. Women often present w/ atypical chest pain.
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Hypertensionr A risk factor for CAD & perioperative MI
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Dysrhythmiasr Ventriculardysrhythmias&supraventriculardysrhythmiasare often assoc w/ underlying myocardial disease (CAD, dilated CM) & are assoc w/ increased risk.
r Thereisnoincreaseinriskassocw/isolatedprematureventric- ular contractions w/o evidence of underlying cardiac disease.
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r Review old records to determine the nature of surgery, ade- quacy of repair, cardiac anatomy, need for anticoagulation therapy and/or antibiotic prophylaxis.
r CABG has been shown to decrease future risk, but PTCA has not been proven to have the same result.
r Graft patency after CABG varies with time & type. LIMA grafts have 95% 10-year patency. Most saphenous grafts occlude by 10 years.
■ Secondary risk factors
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Diabetes mellitusr Morbidity & mortality are greater in diabetic pts. r Duration of disease increases risk.
r Pts on oral hypoglycemic agents have equal risk to those on insulin.
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Ager The incidence of CAD & perioperative MI increases w/ age. r By age 65, the incidence of CAD is close to 37% for men, 18%
for women.
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Cigarette smokingr Smoking may double the risk of CAD.
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Hypercholesterolemia➣
Obesity➣
Geneticsr Cardiac morbidity & mortality in a first-degree relative is significant.
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Vascular diseaser Allptsundergoingvascularsurgeryorw/priorvascularsurgery should be assumed to have CAD.
r Vascular surgery pts have an increased incidence of perioper- ative MI.
r Peripheral vascular disease has higher risk than aortic disease.
■ Surgical procedures carrying the highest risk of perioperative MI:
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Major abdominal, thoracic, & emergency surgery.➣
Highest-risk procedures are vascular since all pts have CAD.Preop Evaluation
■ History
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Questions should encompass symptoms, current & past treat- ment, complications, results of previous evaluations.80 Coronary Artery Disease (CAD)
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The most important symptoms to elicit are chest pain, dyspnea, orthopnea, paroxysmal nocturnal dyspnea, poor exercise toler- ance, syncope, or near-syncope.➣
Relate symptoms to activity level.➣
Cardiac function is the best predictor of outcome in surgery.■ Physical exam: Routine PE w/ particular attention to the following:
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Evidence of jugular venous distention and/or carotid bruits.➣
Pulmonary evidence of rhonchi, rales, wheezing, or effusion.➣
Cardiac exam documenting evidence of heaves, thrills, murmurs, rubs, or gallops.➣
Abdominal exam for evidence of aortic aneurysm or cardiac dys- function (hepatomegaly).➣
Examination of extremities & peripheral pulses. Note cyanosis, clubbing, or edema.■ Routine laboratory evaluation
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Tailor to pt & specifics of surgery.➣
Pts w/ known CAD should have BUN & creatinine studies, CXR, ECG.➣
Obtain a hemoglobin level if significant blood loss is expected.➣
For pts who have a history compatible w/ recent unstable angina or MI, enzyme release (Troponin-I) will demonstrate increased risk.■ Specialized studies: No current recommendations for prophylactic testing. Tests should be obtained only if there will be a modifica- tion of technique or procedure. Indications for periop testing are identical to those for pt’s medical condition w/o regard for planned operation.
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Preop ECG: Useful for comparison to postop ECG in face of clin- ical event. Low-risk screen in pts w/ risk for CAD.➣
Preop CXR: Useful in cases of pulmonary disease or CHF■ None of the following tests are indicated prior to noncardiac surgery:
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Holter monitoring: Used to evaluate arrhythmias, anti- arrhythmic drug therapy, severity & frequency of ischemic episodes➣
Exercise stress testing: Gives estimate of functional capacity. Highly predictive when ST-segment changes are characteristic of ischemia. Usefulness of test limited in those w/ baseline ST- segment abnormalities and those who are unable to raise heart rate. 65% sensitivity, 90% sensitivity.➣
Thallium imaging: Thallium is a radioactive tracer injected IV & avidly extracted as a potassium analog by cardiac muscle. Best forCoronary Artery Disease (CAD) 81
detecting 3-vessel disease. High sensitivity but only fairly good specificity. A dipyridamole-thallium study may be useful in pts who are unable to exercise.
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2-D echocardiography: Provides information about both regional & global ventricular function. Transesophageal views provide better visualization of valvular function, mural or atrial thrombi, aortic atheroma, aortic aneurysms. Dobutamine stress echocardiography indicates presence of reversible ischemia.➣
Radionuclide angiography: Evaluates left ventricular ejection fraction both at rest & following exercise. Failure of ejection frac- tion to rise w/ exercise AND evidence of new wall motion abnor- malities has a 90% specificity & sensitivity for CAD.➣
Coronary angiography: Gold standard in evaluating CAD. Should be performed only to determine if pt would benefit from CABG or PTCA. Presence of left main disease w/ high degree of stenosis is life-threatening. Ventriculography & measurement of intrac- ardiac pressures can also be performed.Preop Management
■ Periop beta blockade
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All pts w/ known coronary artery disease, peripheral vascular dis- ease, or two risk factors for coronary artery disease (age>=65, hypertension, diabetes, smoking, cholesterol>=240 mg/dL) should be on a beta blocker unless absolute contraindications exist.➣
In cases of beta blocker intolerance alpha-2 agonist therapy (clonidine #2 TTS Patch+ 0.2 mg PO tablet) reduces risk of mor- tality.■ Maintain all cardiac medications throughout the periop period. Stopping beta blockers, nitrates, calcium channel blockers, alpha- 2 agonists, or ACE inhibitors increases risk of death & significant morbidity (stroke, renal failure, CHF).
■ Supportive preop interview may reduce fears, anxiety, pain. Anxi- olytic premedication may blunt rises in sympathetic tone. Pain mgt is critical to reduce stress of surgery.
■ Supplemental oxygen preop to all w/ significant ischemia.
intraop
■ Regional vs. general anesthesia: There are no outcome data showing the superiority of a form of anesthesia
82 Coronary Artery Disease (CAD)
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Use standard monitoring in all cases➣
Intra-arterial pressure monitoringr Usefulinptsw/knowncoronaryarterydisease,CHF,orcardiac risk factors
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Transesophageal echocardiographyr Useful in cardiac surgery to evaluate aortic atherosclerosis, valve function, ventricular function, volume status, ventricular dysfunction
r No benefit in routine use in noncardiac surgery
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CVP/PA catheterr No proven benefit to CVP or PA catheter monitoring
r Controversial: PA catheter monitoring may increase risk of death in pts w/ acute MI or in ICU pts.
■ Induction
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Avoid precipitous changes in perfusion pressure. Initiation of vasoactive therapy prior to induction may stabilize pt.■ Maintenance
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No demonstrated benefits to a particular anesthetic agent r Desflurane can increase the risk of myocardial ischemia, MI,& pulmonary hypertension. Consider another agent or use w/ caution in pts w/ known CAD.
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Hemodynamic management r Avoid tachycardia.r Maintain diastolic blood pressure. r Transient hypertension is well tolerated.
r Prolonged periods of hypotension, tachycardia, & anemia are not well tolerated.
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Drug therapyr Beta blockers by bolus or infusion decrease HR & can be used to treat ischemia & prevent MI infarction & death.
r Nitroglycerin by continuous infusion (0.5–4.0 mcg/kg/min) can be used to treat ischemia.
postop
■ Decide postop disposition (ward, ICU, telemetry) based on severity of CAD, stress of surgery, intraop course.
■ In immediate postop period, pt should receive supplemental oxygen until adequate oxygenation established.
■ Maintain good analgesia to blunt stress response.
■ If there is a suspicion of fluid overload, or if pt has history of poor ventricular function, obtain postop CXR. Important: Maintain all
Coronary Artery Disease (CAD) Cushing’s Syndrome 83
cardiac medications, including beta blockers, calcium channel blockers, nitrates, ACE inhibitors, alpha-2 agonists.
■ Issues related to postop MI