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Overview of Acute Coronary Syndromes (ACS)

(Unstable Angina; Acute MI; Myocardial Infarction)

By

Ranya N. Sweis

, MD, MS, Northwestern University Feinberg School of Medicine;


Arif Jivan

, MD, PhD, Northwestern University Feinberg School of Medicine

Last full review/revision Jul 2020| Content last modified Jul 2020
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Acute coronary syndromes result from acute obstruction of a coronary artery. Consequences depend on degree and location of obstruction and range from unstable angina to non–ST-segment elevation myocardial infarction (NSTEMI), ST-segment elevation myocardial infarction (STEMI), and sudden cardiac death. Symptoms are similar in each of these syndromes (except sudden death) and include chest discomfort with or without dyspnea, nausea, and diaphoresis. Diagnosis is by ECG and the presence or absence of serologic markers. Treatment is antiplatelet drugs, anticoagulants, nitrates, beta-blockers, and, for STEMI, emergency reperfusion via fibrinolytic drugs, percutaneous intervention, or, occasionally, coronary artery bypass graft surgery.

Classification of Acute Coronary Syndromes

Acute coronary syndromes include

  • Unstable angina

  • Non–ST-segment elevation myocardial infarction (NSTEMI)

  • ST-segment elevation myocardial infarction (STEMI)

These syndromes all involve acute coronary ischemia and are distinguished based on symptoms, ECG findings, and cardiac marker levels. It is helpful to distinguish the syndromes because prognosis and treatment vary.

Unstable angina Unstable Angina Unstable angina results from acute obstruction of a coronary artery without myocardial infarction. Symptoms include chest discomfort with or without dyspnea, nausea, and diaphoresis. Diagnosis... read more (acute coronary insufficiency, preinfarction angina, intermediate syndrome) is defined as one or more of the following in patients whose cardiac biomarkers do not meet criteria for myocardial infarction (MI):

ECG changes such as ST-segment depression, ST-segment elevation, or T-wave inversion may occur during unstable angina but they are transient. Of cardiac markers, CK is not elevated but cardiac troponin, particularly when measured using high-sensitivity troponin tests (hs-cTn), may be slightly increased. Unstable angina is clinically unstable and often a prelude to myocardial infarction or arrhythmias or, less commonly, to sudden death.

Non–ST-segment elevation MI Acute myocardial infarction is myocardial necrosis resulting from acute obstruction of a coronary artery. Symptoms include chest discomfort with or without dyspnea, nausea, and diaphoresis.... read more (NSTEMI, subendocardial MI) is myocardial necrosis (evidenced by cardiac markers in blood; troponin I or troponin T and CK will be elevated) without acute ST-segment elevation. ECG changes such as ST-segment depression, T-wave inversion, or both may be present.

ST-segment elevation MI Acute myocardial infarction is myocardial necrosis resulting from acute obstruction of a coronary artery. Symptoms include chest discomfort with or without dyspnea, nausea, and diaphoresis.... read more (STEMI, transmural MI) is myocardial necrosis with ECG changes showing ST-segment elevation that is not quickly reversed by nitroglycerin or showing new left bundle branch block. Troponin I or troponin T and creatine kinase (CK) are elevated.

Both types of MI may or may not produce Q waves on the ECG (Q wave MI, non-Q wave MI).

Etiology of Acute Coronary Syndromes

The most common cause of acute coronary syndromes is

Atheromatous plaque sometimes becomes unstable or inflamed, causing it to rupture or split, exposing thrombogenic material, which activates platelets and the coagulation cascade and produces an acute thrombus. Platelet activation involves a conformational change in membrane glycoprotein (GP) IIb/IIIa receptors, allowing cross-linking (and thus aggregation) of platelets. Even atheromas causing minimal obstruction can rupture and result in thrombosis; in > 50% of cases, pre-event stenosis is < 40%. Thus, although the severity of stenosis helps predict symptoms, it does not always predict acute thrombotic events. The resultant thrombus abruptly interferes with blood flow to parts of the myocardium. Spontaneous thrombolysis occurs in about two thirds of patients; 24 hours later, thrombotic obstruction is found in only about 30%. However, in virtually all cases, obstruction lasts long enough to cause varying degrees of tissue necrosis.

Rarer causes of acute coronary syndromes are

  • Coronary artery embolism

  • Coronary spasm

  • Coronary artery dissection

Coronary artery dissection is a non-traumatic tear in the coronary intima with creation of a false lumen. Blood flowing through the false lumen expands it, which restricts blood flow through the true lumen sometimes causing coronary ischemia or infarction. Dissection may occur in atherosclerotic or non-atherosclerotic coronary arteries. Non-atherosclerotic dissection is more likely in pregnant or postpartum women and/or patients with fibromuscular dysplasia or other connective tissue disorders.

Pathophysiology of Acute Coronary Syndromes

Initial consequences vary with size, location, and duration of obstruction and range from transient ischemia to infarction. Measurement of newer, more sensitive markers indicates that some cell necrosis probably occurs even in mild forms; thus, ischemic events occur on a continuum, and classification into subgroups, although useful, is somewhat arbitrary. Sequelae of the acute event depend primarily on the mass and type of cardiac tissue infarcted.

Myocardial dysfunction

Ischemic (but not infarcted) tissue has impaired contractility and relaxation, resulting in hypokinetic or akinetic segments; these segments may expand or bulge during systole (called paradoxical motion). The size of the affected area determines effects, which range from minimal to mild heart failure Heart Failure (HF) Heart failure (HF) is a syndrome of ventricular dysfunction. Left ventricular failure causes shortness of breath and fatigue, and right ventricular failure causes peripheral and abdominal fluid... read more Heart Failure (HF) to cardiogenic shock Cardiogenic and obstructive shock Shock is a state of organ hypoperfusion with resultant cellular dysfunction and death. Mechanisms may involve decreased circulating volume, decreased cardiac output, and vasodilation, sometimes... read more ; usually, large parts of myocardium must be ischemic to cause significant myocardial dysfunction. Some degree of heart failure occurs in about two thirds of hospitalized patients with acute myocardial infarction. It is termed ischemic cardiomyopathy if low cardiac output and heart failure persist. Ischemia involving the papillary muscle may lead to mitral valve regurgitation. Dysfunctional wall motion can allow mural thrombus formation.

Myocardial infarction (MI)

Myocardial infarction Acute Myocardial Infarction (MI) Acute myocardial infarction is myocardial necrosis resulting from acute obstruction of a coronary artery. Symptoms include chest discomfort with or without dyspnea, nausea, and diaphoresis.... read more Acute Myocardial Infarction (MI) is myocardial necrosis resulting from abrupt reduction in coronary blood flow to part of the myocardium. Infarcted tissue is permanently dysfunctional; however, there is a zone of potentially reversible ischemia adjacent to infarcted tissue. MI affects predominantly the left ventricle (LV), but damage may extend into the right ventricle (RV) or the atria.

Infarction may be

  • Transmural: Transmural infarcts involve the whole thickness of myocardium from epicardium to endocardium and are usually characterized by abnormal Q waves on ECG.

  • Nontransmural (subendocardial): Nontransmural infarcts do not extend through the ventricular wall and cause only ST-segment and T-wave (ST-T) abnormalities.

Because the transmural depth of necrosis cannot be precisely determined clinically, infarcts are usually classified as STEMI or NSTEMI by the presence or absence of ST-segment elevation or Q waves on the ECG.

Necrosis of a significant portion of the interventricular septum or ventricular wall may rupture, with dire consequences. A ventricular aneurysm or pseudoaneurysm may form.

Electrical dysfunction

Electrical dysfunction can be significant in any form of acute coronary syndrome. Ischemic and necrotic cells are incapable of normal electrical activity, resulting in various ECG changes (predominantly ST-T abnormalities), arrhythmias, and conduction disturbances. ST-T abnormalities of ischemia include ST-segment depression (often downsloping from the J point), T-wave inversion, ST-segment elevation (often referred to as injury current), and peaked T waves in the hyperacute phase of infarction. Conduction disturbances can reflect damage to the sinus node, the atrioventricular (AV) node, or specialized conduction tissues. Most changes are transient; some are permanent.

Symptoms and Signs of Acute Coronary Syndromes

Symptoms of acute coronary syndromes depend somewhat on the extent and location of obstruction and are quite variable. Painful stimuli from thoracic organs, including the heart, can cause discomfort described as pressure, tearing, gas with the urge to eructate, indigestion, burning, aching, stabbing, and sometimes sharp needle-like pain. Many patients deny they are having pain and insist it is merely “discomfort.” Except when infarction is massive, recognizing the amount of ischemia by symptoms alone is difficult.

Complications

Diagnosis of Acute Coronary Syndromes

  • Serial ECGs

  • Serial cardiac markers

  • Immediate coronary angiography for patients with STEMI or complications (eg, persistent chest pain, hypotension, markedly elevated cardiac markers, unstable arrhythmias)

  • Delayed angiography (24 to 48 hours) for patients with NSTEMI or unstable angina without complications noted above

Acute coronary syndromes should be considered in men > 30 years and women > 40 years (younger in patients with diabetes) whose main symptom is chest pain or discomfort. Pain must be differentiated from the pain of pneumonia Overview of Pneumonia Pneumonia is acute inflammation of the lungs caused by infection. Initial diagnosis is usually based on chest x-ray and clinical findings. Causes, symptoms, treatment, preventive measures, and... read more , pulmonary embolism Pulmonary Embolism (PE) Pulmonary embolism (PE) is the occlusion of pulmonary arteries by thrombi that originate elsewhere, typically in the large veins of the legs or pelvis. Risk factors for pulmonary embolism are... read more Pulmonary Embolism (PE) , pericarditis Pericarditis Pericarditis is inflammation of the pericardium, often with fluid accumulation. Pericarditis may be caused by many disorders (eg, infection, myocardial infarction, trauma, tumors, metabolic... read more Pericarditis , rib fracture Rib Fracture One or more ribs can be fractured due to blunt chest injury. (See also Overview of Thoracic Trauma.) This x-ray of the chest shows multiple fractures to the right ribs (seen on left). Typically... read more Rib Fracture , costochondral separation, esophageal spasm Diffuse Esophageal Spasm Symptomatic diffuse esophageal spasm is part of a spectrum of motility disorders characterized variously by nonpropulsive contractions and hyperdynamic contractions, sometimes in conjunction... read more , acute aortic dissection Aortic Dissection Aortic dissection is the surging of blood through a tear in the aortic intima with separation of the intima and media and creation of a false lumen (channel). The intimal tear may be a primary... read more Aortic Dissection , renal calculus Urinary Calculi Urinary calculi are solid particles in the urinary system. They may cause pain, nausea, vomiting, hematuria, and, possibly, chills and fever due to secondary infection. Diagnosis is based on... read more , splenic infarction, or various abdominal disorders. In patients with previously diagnosed hiatus hernia, peptic ulcer, or a gallbladder disorder, the clinician must be wary of attributing new symptoms to these disorders. (For approach to diagnosis, see also Chest Pain Chest Pain Chest pain is a very common complaint. Many patients are well aware that it is a warning of potential life-threatening disorders and seek evaluation for minimal symptoms. Other patients, including... read more .)

The approach is the same when any ACS is suspected: initial and serial ECG and serial cardiac marker measurements, which distinguish among unstable angina, NSTEMI, and STEMI. Every emergency department should have a triage system to immediately identify patients with chest pain for rapid assessment and ECG. Pulse oximetry and chest x-ray (particularly to look for mediastinal widening, which suggests aortic dissection) is also done.

ECG

ECG is the most important test and should be done within 10 min of presentation. It is the center of the decision pathway because fibrinolytics benefit patients with STEMI but may increase risk for those with NSTEMI. Also, urgent cardiac catheterization is indicated for patients with acute STEMI but not for those with NSTEMI.

Acute lateral left ventricular infarction (tracing obtained within a few hours of onset of illness)

There is striking hyperacute ST-segment elevation in leads I, aVL, V4, and V6 and reciprocal depression in other leads.

Acute lateral left ventricular infarction (tracing obtained within a few hours of onset of illness)

Pathologic Q waves are not necessary for the diagnosis. The ECG must be read carefully because ST-segment elevation may be subtle, particularly in the inferior leads (II, III, aVF); sometimes the reader’s attention is mistakenly focused on leads with ST-segment depression. If symptoms are characteristic, ST-segment elevation on ECG has a specificity of 90% and a sensitivity of 45% for diagnosing MI. Serial tracings (obtained every 8 hours for 1 day, then daily) showing a gradual evolution toward a stable, more normal pattern or development of abnormal Q waves over a few days (see figure Inferior (diaphragmatic) left ventricular infarction Inferior (diaphragmatic) left ventricular infarction (after the first 24 hours) Acute coronary syndromes result from acute obstruction of a coronary artery. Consequences depend on degree and location of obstruction and range from unstable angina to non–ST-segment elevation... read more ) tends to confirm the diagnosis.

Inferior (diaphragmatic) left ventricular infarction (after the first 24 hours)

Significant Q waves develop with decreasing ST-segment elevation in leads II, III, and aVF.

Inferior (diaphragmatic) left ventricular infarction (after the first 24 hours)

Because nontransmural (non–Q wave) infarcts are usually in the subendocardial or midmyocardial layers, they do not produce diagnostic Q waves or distinct ST-segment elevation on the ECG. Instead, they commonly produce only varying degrees of ST-T abnormalities that are less striking, variable, or nonspecific and sometimes difficult to interpret (NSTEMI). If such abnormalities resolve (or worsen) on repeat ECGs, ischemia is very likely. However, when repeat ECGs are unchanged, acute MI is unlikely and, if still suspected clinically, requires other evidence to make the diagnosis. A normal ECG taken when a patient is pain free does not rule out unstable angina; a normal ECG taken during pain, although it does not rule out angina, suggests that the pain is not ischemic.

If right ventricular (RV) infarction is suspected, a 15-lead ECG is usually recorded; additional leads are placed at V4R, and, to detect posterior infarction, V8 and V9.

ECG diagnosis of myocardial infarction is more difficult when a left bundle branch block configuration is present because the ECG changes resemble changes due to STEMI (see figure Left bundle branch block Left bundle branch block Acute coronary syndromes result from acute obstruction of a coronary artery. Consequences depend on degree and location of obstruction and range from unstable angina to non–ST-segment elevation... read more ). ST-segment elevation concordant with the QRS complex strongly suggests MI as does > 5-mm ST-segment elevation in at least 2 precordial leads. But generally, any patient with suggestive symptoms and new-onset (or not known to be old) left bundle branch block is treated as for STEMI.

Left bundle branch block

Left bundle branch block

Cardiac markers

Cardiac markers (serum markers of myocardial cell injury) are

  • Cardiac enzymes (eg, CK-MB [creatine kinase MB isoenzyme])

  • Cell contents (eg, troponin I, troponin T, myoglobin)

These markers are released into the bloodstream after myocardial cell necrosis. The markers appear at different times after injury, and levels decrease at different rates. Sensitivity and specificity for myocardial cell injury vary significantly among these markers, but the troponins (cTn) are the most sensitive and specific and are now the markers of choice. Recently, several new, highly sensitive assays of cardiac troponin (hs-cTn) that are also very precise have become available. These assays can reliably measure troponin levels (T or I) as low as 0.003 to 0.006 ng/mL (3 to 6 pg/mL); some research assays go as low as 0.001 ng/mL (1 pg/mL).

Previous, less sensitive cTn tests were unlikely to detect cTn except in patients who had an acute cardiac disorder. Thus, a "positive" cTn test (ie, above the limit of detection) was very specific. However, the newer hs-cTn tests can detect small amounts of cTn in many healthy people. Thus, troponin levels detected with hs-cTn tests need to be referenced to the normal range, and are defined as "elevated" only when higher than 99% of the reference population. Furthermore, although an elevated troponin level indicates myocardial cell injury, it does not indicate the cause of the damage (although any troponin elevation increases the risk of adverse outcomes in many disorders). In addition to acute coronary syndromes, many other cardiac and non-cardiac disorders can elevate cTn levels (see table Causes of Elevated Troponin Levels Causes of Elevated Troponin Levels Acute coronary syndromes result from acute obstruction of a coronary artery. Consequences depend on degree and location of obstruction and range from unstable angina to non–ST-segment elevation... read more ); not all elevated levels detected with hs-cTn represent myocardial infarction, and not all myocardial necrosis results from an acute coronary syndrome event even when the etiology is ischemic. However, by detecting lower levels of troponin, hs-cTn assays enable earlier identification of MI than other assays, and have replaced other cardiac marker tests in many centers.

Patients suspected of having an ACS should have an hs-cTn assay done on presentation and again 3 hours later. Troponin should be measured at 0 and 6 hours if a standard cTn assay is used.

An hs-cTn level must be interpreted based on the patient's pre-test probability of disease, which is estimated clinically based on

  • Risk factors for ACS

  • Symptoms

  • ECG findings

A high pre-test probability plus an elevated level detected with an hs-cTn assay is highly suggestive of ACS, whereas a low pre-test probability plus a normal hs-cTn assay result is unlikely to represent ACS. Diagnosis is more challenging when test results are discordant with pre-test probability, in which case serial hs-cTn assays often help. A patient with low pre-test probability and an initially slightly elevated troponin level detected with hs-cTn that remains stable on repeat testing probably has non-ACS cardiac disease (eg, heart failure Heart Failure (HF) Heart failure (HF) is a syndrome of ventricular dysfunction. Left ventricular failure causes shortness of breath and fatigue, and right ventricular failure causes peripheral and abdominal fluid... read more Heart Failure (HF) , stable coronary artery disease). However, if the repeat level rises significantly (ie, > 20 to 50%) the likelihood of ACS becomes much higher. If a patient with high pre-test probability has a normal troponin level detected with hs-cTn and that rises > 50% on repeat testing, ACS is likely; continued normal levels (often including at 6 hours and beyond when suspicion is high) suggest need to pursue an alternate diagnosis.

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Coronary angiography

Coronary angiography Angiography Angiography is sometimes called conventional angiography to distinguish it from CT angiography (CTA) and magnetic resonance angiography (MRA). Angiography provides detailed images of blood vessels... read more Angiography most often combines diagnosis with percutaneous coronary intervention (PCI—ie, angioplasty, stent placement). When possible, emergency coronary angiography and PCI are done as soon as possible after the onset of acute myocardial infarction (primary PCI). In many tertiary centers, this approach has significantly lowered morbidity and mortality and improved long-term outcomes. Frequently, the infarction is actually aborted when the time from pain to PCI is short (< 3 to 4 hours).

After initial evaluation and therapy, coronary angiography may be used in patients with evidence of ongoing ischemia (ECG findings or symptoms), hemodynamic instability, recurrent ventricular tachyarrhythmias, and other abnormalities that suggest recurrence of ischemic events. Some experts also recommend that angiography be done before hospital discharge in patients with STEMI who have not yet had angiography who have inducible ischemia on stress imaging or an ejection fraction < 40%.

Other tests

Routine laboratory tests are nondiagnostic but, if obtained, show nonspecific abnormalities compatible with tissue necrosis (eg, increased erythrocyte sedimentation rate, moderately elevated white blood cell count with a shift to the left). A fasting lipid profile should be obtained within the first 24 hours for all patients hospitalized with ACS.

Myocardial imaging Cardiac Imaging Tests Cardiac imaging tests can delineate cardiac structure and function. Standard imaging tests include Echocardiography Chest x-ray CT MRI read more Cardiac Imaging Tests is not needed to make the diagnosis if cardiac markers or ECG is positive. However, in patients with myocardial infarction, bedside echocardiography is invaluable for detecting mechanical complications. Before or shortly after discharge, patients with symptoms suggesting an ACS but nondiagnostic ECGs and normal cardiac markers should have a stress imaging test (radionuclide or echocardiographic imaging with pharmacologic or exercise stress). Imaging abnormalities in such patients indicate increased risk of complications in the next 3 to 6 months and suggest need for angiography, which should be done before discharge or soon thereafter, with PCI or CABG done as necessary.

Right heart catheterization using a balloon-tipped pulmonary artery catheter Pulmonary Artery Catheter (PAC) Monitoring Some monitoring of critical care patients depends on direct observation and physical examination and is intermittent, with the frequency depending on the patient’s illness. Other monitoring... read more can be used to measure right heart, pulmonary artery, and pulmonary artery occlusion pressures and cardiac output. This test is not routinely recommended and should be done only if patients have significant complications (eg, severe heart failure, hypoxia, hypotension) and by doctors experienced with catheter placement and management protocols.

Prognosis for Acute Coronary Syndromes

Global risk should be estimated via formal clinical risk scores (Thrombosis in Myocardial Infarction [TIMI], Global Registry of Acute Coronary Events [GRACE], Platelet Glycoprotein IIb/IIIa in Unstable Angina: Receptor Suppression Using Integrilin Therapy [PURSUIT]—1 Prognosis reference Acute coronary syndromes result from acute obstruction of a coronary artery. Consequences depend on degree and location of obstruction and range from unstable angina to non–ST-segment elevation... read more ) or a combination of the following high-risk features:

  • Recurrent angina/ischemia at rest or during low-level activity

  • Heart failure

  • Worsening mitral regurgitation

  • High-risk stress test result (test stopped in ≤ 5 minutes due to symptoms, marked ECG abnormalities, hypotension, or complex ventricular arrhythmias)

  • Hemodynamic instability

  • Sustained ventricular tachycardia

  • Diabetes mellitus

  • PCI within past 6 months

  • Prior CABG

  • LV ejection fraction < 0.40

Prognosis reference

  • 1. Boersma E, Pieper KS, Steyerberg EW, et al: Predictors of outcome in patients with acute coronary syndromes without persistent ST-segment elevation. Results from an international trial of 9461 patients. The PURSUIT Investigators. Circulation 101(22): 2557–2567, 2000.

Treatment of Acute Coronary Syndromes

  • Prehospital care: Oxygen, aspirin, and nitrates and triage to an appropriate medical center

  • Drug treatment: Antiplatelet drugs, antianginal drugs, anticoagulants, and in some cases other drugs

  • Often, angiography to assess coronary artery anatomy

  • Often, reperfusion therapy: Fibrinolytics, percutaneous coronary intervention or coronary artery bypass surgery

  • Supportive care

  • Post discharge cardiac rehabilitation and chronic management of coronary artery disease

Treatment, including drug treatment Drugs for Acute Coronary Syndromes Treatment of acute coronary syndromes (ACS) is designed to relieve distress, interrupt thrombosis, reverse ischemia, limit infarct size, reduce cardiac workload, and prevent and treat complications... read more , is designed to relieve distress, interrupt thrombosis, reverse ischemia, limit infarct size, reduce cardiac workload, and prevent and treat complications. An acute coronary syndrome is a medical emergency; outcome is greatly influenced by rapid diagnosis and treatment.

Treatment occurs simultaneously with diagnosis.

Contributing disorders (eg, anemia, heart failure) are aggressively treated.

Because the chest pain of myocardial infarction usually subsides within 12 to 24 hours, any chest pain that remains or recurs later is investigated. It may indicate such complications Complications of Acute Coronary Syndromes Numerous complications can occur as a result of an acute coronary syndrome and increase morbidity and mortality. Complications can be roughly categorized as Electrical dysfunction (conduction... read more Complications of Acute Coronary Syndromes as recurrent ischemia, pericarditis Pericarditis Pericarditis is inflammation of the pericardium, often with fluid accumulation. Pericarditis may be caused by many disorders (eg, infection, myocardial infarction, trauma, tumors, metabolic... read more Pericarditis , pulmonary embolism Pulmonary Embolism (PE) Pulmonary embolism (PE) is the occlusion of pulmonary arteries by thrombi that originate elsewhere, typically in the large veins of the legs or pelvis. Risk factors for pulmonary embolism are... read more Pulmonary Embolism (PE) , pneumonia Overview of Pneumonia Pneumonia is acute inflammation of the lungs caused by infection. Initial diagnosis is usually based on chest x-ray and clinical findings. Causes, symptoms, treatment, preventive measures, and... read more , gastritis Overview of Gastritis Gastritis is inflammation of the gastric mucosa caused by any of several conditions, including infection (Helicobacter pylori), drugs (nonsteroidal anti-inflammatory drugs, alcohol), stress... read more Overview of Gastritis , or ulcer Peptic Ulcer Disease A peptic ulcer is an erosion in a segment of the gastrointestinal mucosa, typically in the stomach (gastric ulcer) or the first few centimeters of the duodenum (duodenal ulcer), that penetrates... read more Peptic Ulcer Disease .

Prehospital care

  • Oxygen

  • Aspirin

  • Nitrates

  • Triage to appropriate medical center

A reliable IV route must be established, oxygen given (typically 2 L by nasal cannula), and continuous single-lead ECG monitoring started. Prehospital interventions by emergency medical personnel—including ECG, chewed aspirin (325 mg), pain management with nitrates (see table Drugs for Coronary Artery Disease Drugs for Coronary Artery Disease* Treatment of acute coronary syndromes (ACS) is designed to relieve distress, interrupt thrombosis, reverse ischemia, limit infarct size, reduce cardiac workload, and prevent and treat complications... read more ), early thrombolysis when indicated and possible, and triage to the appropriate hospital where primary PCI is available—can reduce risk of mortality and complications.

Although opioids have long been used to treat pain in patients with acute coronary syndromes, new data suggest that morphine attenuates activity of some P2Y12 receptor inhibitors and may contribute to worse patient outcomes (1, 2 Treatment references Acute coronary syndromes result from acute obstruction of a coronary artery. Consequences depend on degree and location of obstruction and range from unstable angina to non–ST-segment elevation... read more ).

Hospital admission

  • Drug therapy with antiplatelet drugs, anticoagulants, and other drugs based on reperfusion strategy

  • Risk-stratify patient and choose a reperfusion strategy (fibrinolytics or cardiac angiography with PCI or CABG for patients with STEMI and cardiac angiography with PCI or CABG for patients with unstable angina or NSTEMI)

Approach to acute coronary syndromes

Approach to acute coronary syndromes

* Morphine should be used judiciously (eg, if nitroglycerin is contraindicated or if the patient has symptoms despite nitroglycerin therapy). New data suggest that morphine attenuates activity of some P2Y12 receptor inhibitors and may contribute to worse patient outcomes (1, 2 Treatment references Acute coronary syndromes result from acute obstruction of a coronary artery. Consequences depend on degree and location of obstruction and range from unstable angina to non–ST-segment elevation... read more ).

† Complicated means that the hospital course was complicated by recurrent angina or infarction, heart failure, or sustained recurrent ventricular arrhythmias. Absence of any of these events is termed uncomplicated.

‡ Although some recent trials raise questions, CABG is generally preferred to PCI for patients with the following:

  • Left main or left main equivalent disease

  • Left ventricular dysfunction

  • Treated diabetes

Also, lesions that are long or near bifurcation points are often not amenable to PCI.

CABG = coronary artery bypass grafting; GP = glycoprotein; LDL = low density lipoprotein; NSTEMI = non-ST-segment elevation MI; MI = myocardial infarction; PCI = percutaneous intervention; STEMI = ST-segment elevation MI.

When the diagnosis is unclear, bedside cardiac marker tests can help identify low-risk patients with a suspected ACS (eg, those with initially negative cardiac markers and nondiagnostic ECGs), who can be managed in 24-hour observation units or chest pain centers. Higher-risk patients should be admitted to a monitored inpatient unit or coronary care unit (CCU). Several validated tools can help stratify risk. Thrombolysis in MI (TIMI) risk scores may be the most widely used.

Patients with suspected NSTEMI and intermediate or high risk should be admitted to an inpatient care unit or CCU. Those with STEMI should be admitted to a CCU.

Only heart rate and rhythm recorded by single-lead ECG are consistently useful for routine, continuous monitoring. However, some clinicians recommend routine multilead monitoring with continuous ST-segment recording to identify transient, recurrent ST-segment elevations or depressions. Such findings, even in patients without symptoms, suggest ischemia and identify higher-risk patients who may require more aggressive evaluation and treatment.

Qualified nurses can interpret the ECG for arrhythmia and initiate protocols for its treatment. All staff members should know how to do CPR (cardiopulmonary resuscitation).

Supportive care

The care unit should be a quiet, calm, restful area. Single rooms are preferred; privacy consistent with monitoring should be ensured. Usually, visitors and telephone calls are restricted to family members during the first few days. A wall clock, a calendar, and an outside window help orient the patient and prevent a sense of isolation, as can access to a radio, television, newspaper and/or digital devices.

On day 1, patients without complications (eg, hemodynamic instability, ongoing ischemia), including those in whom reperfusion with fibrinolytics or PCI is successful, can sit in a chair, begin passive exercises, and use a commode. Walking to the bathroom and doing nonstressful paperwork are allowed shortly thereafter. Patients with successful, uncomplicated primary PCI for acute MI may be ambulated quickly and be safely discharged in 2 to 4 days.

If reperfusion is not successful or complications are present, patients require longer bed rest, but they (particularly elderly patients) are mobilized as soon as possible. Prolonged bed rest results in rapid physical deconditioning, with development of orthostatic hypotension Orthostatic Hypotension Orthostatic (postural) hypotension is an excessive fall in blood pressure (BP) when an upright position is assumed. The consensus definition is a drop of > 20 mm Hg systolic, 10 mm Hg diastolic... read more , decreased work capacity, increased heart rate during exertion, and increased risk of deep venous thrombosis Deep Venous Thrombosis (DVT) Deep venous thrombosis (DVT) is clotting of blood in a deep vein of an extremity (usually calf or thigh) or the pelvis. DVT is the primary cause of pulmonary embolism. DVT results from conditions... read more Deep Venous Thrombosis (DVT) . Prolonged bed rest also intensifies feelings of depression and helplessness.

Anxiety, mood changes, and denial are common. A mild tranquilizer (usually a benzodiazepine) is often given, but many experts believe such drugs are rarely needed. Reactive depression is common by the 3rd day of illness and is almost universal at some time during recovery.

After the acute phase of illness, the most important tasks are often management of depression, rehabilitation Cardiovascular Rehabilitation Rehabilitation may benefit some patients who have coronary artery disease or heart failure or who have had a recent myocardial infarction or coronary artery bypass surgery, particularly those... read more , and institution of long-term preventive programs. Overemphasis on bed rest, inactivity, and the seriousness of the disorder reinforces anxiety and depressive tendencies, so patients are encouraged to sit up, get out of bed, and engage in appropriate activities as soon as possible. The effects of the disorder, prognosis, and individualized rehabilitation program should be explained to the patient.

Maintaining normal bowel function with stool softeners (eg, docusate) to prevent straining is important. Urinary retention is common among elderly patients, especially after several days of bed rest or if atropine was given. A catheter may be required but can usually be removed when the patient can stand or sit to void.

Because smoking is prohibited, a hospital stay should be used to encourage smoking cessation Smoking Cessation Most smokers want to quit and have tried doing so with limited success. Effective interventions include cessation counseling and drug treatment, such as varenicline, bupropion, or a nicotine... read more . All caregivers should devote considerable effort to making smoking cessation permanent.

Although acutely ill patients have little appetite, tasty food in modest amounts is good for morale. Patients are usually offered a soft diet of 1500 to 1800 kcal/day with sodium reduction to 2 to 3 g. Sodium reduction is not required after the first 2 or 3 days if there is no evidence of heart failure Heart Failure (HF) Heart failure (HF) is a syndrome of ventricular dysfunction. Left ventricular failure causes shortness of breath and fatigue, and right ventricular failure causes peripheral and abdominal fluid... read more Heart Failure (HF) . Patients are given a diet low in cholesterol and saturated fats, which is used to teach healthy eating.

For patients with diabetes Diabetes Mellitus (DM) Diabetes mellitus is impaired insulin secretion and variable degrees of peripheral insulin resistance leading to hyperglycemia. Early symptoms are related to hyperglycemia and include polydipsia... read more and STEMI, intensive glucose control is no longer recommended; guidelines call for an insulin-based regimen to achieve and maintain glucose levels <180 mg/dL (9.9 mmol/L) while avoiding hypoglycemia.

Treatment references

  • 1. Meine TJ, Roe MT, Chen AY, et al: Association of intravenous morphine use and outcomes in acute coronary syndromes: results from the CRUSADE Quality Improvement Initiative. Am Heart J 149(6):1043-1049, 2005. doi: 10.1016/j.ahj.2005.02.010

  • 2. Kubica J, Adamski P, Ostrowska M, et al: Morphine delays and attenuates ticagrelor exposure and action in patients with myocardial infarction: the randomized, double-blind, placebo-controlled IMPRESSION trial. Eur Heart J 37(3): 245–252, 2016. doi: 10.1093/eurheartj/ehv547

Rehabilitation and Postdischarge Treatment

  • Functional evaluation

  • Changes in lifestyle: Regular exercise, diet modification, weight loss, smoking cessation

  • Drugs: Continuation of antiplatelet drugs, beta-blockers, ACE inhibitors, and statins

Functional evaluation

Patients who did not have coronary angiography during admission, have no high-risk features (eg, heart failure, recurrent angina, ventricular tachycardia or ventricular fibrillation after 24 hours, mechanical complications such as new murmurs, shock), and have an ejection fraction > 40% whether or not they received fibrinolytics usually should have stress testing Stress Testing In stress testing, the heart is monitored by electrocardiography (ECG) and often imaging studies during an induced episode of increased cardiac demand so that ischemic areas potentially at risk... read more Stress Testing of some sort before or shortly after discharge (see table Functional Evaluation After Myocardial Infarction Functional Evaluation After Myocardial Infarction Acute coronary syndromes result from acute obstruction of a coronary artery. Consequences depend on degree and location of obstruction and range from unstable angina to non–ST-segment elevation... read more ).

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Activity

Physical activity is gradually increased during the first 3 to 6 weeks after discharge. Resumption of sexual activity, often of great concern to the patient and partner, and other moderate physical activities may be encouraged. If good cardiac function is maintained 6 weeks after acute myocardial infarction, most patients can return to all their normal activities. A regular exercise program consistent with lifestyle, age, and cardiac status reduces risk of ischemic events and enhances general well-being. Supervised cardiac rehabilitation programs Cardiovascular Rehabilitation Rehabilitation may benefit some patients who have coronary artery disease or heart failure or who have had a recent myocardial infarction or coronary artery bypass surgery, particularly those... read more decrease mortality after revascularization (1 Rehabilitation and postdischarge treatment reference Acute coronary syndromes result from acute obstruction of a coronary artery. Consequences depend on degree and location of obstruction and range from unstable angina to non–ST-segment elevation... read more ).

Risk factor modification

The acute illness and treatment of ACS should be used to strongly motivate the patient to modify risk factors. Evaluating the patient’s physical and emotional status and discussing them with the patient, advising about lifestyle (eg, smoking, diet, work and play habits, exercise), and aggressively managing risk factors may improve prognosis.

Drugs

Several drugs clearly reduce mortality risk post-MI and are used unless contraindicated or not tolerated:

  • Aspirin and other antiplatelet drugs

  • Beta blockers

  • Angiotensin-converting enzyme (ACE) inhibitors

  • Statins

Aspirin and other antiplatelet drugs Antiplatelet Drugs Treatment of acute coronary syndromes (ACS) is designed to relieve distress, interrupt thrombosis, reverse ischemia, limit infarct size, reduce cardiac workload, and prevent and treat complications... read more reduce mortality and reinfarction rates in patients after myocardial infarction. Enteric-coated aspirin 81 mg once/day is recommended long-term. Data suggest that warfarin with or without aspirin reduces mortality and reinfarction rates.

Beta-blockers Beta-Blockers Treatment of acute coronary syndromes (ACS) is designed to relieve distress, interrupt thrombosis, reverse ischemia, limit infarct size, reduce cardiac workload, and prevent and treat complications... read more are considered standard therapy. Most available beta-blockers (eg, acebutolol, atenolol, metoprolol, propranolol, timolol) reduce post-MI mortality rate by about 25% for at least 7 years.

ACE inhibitors are also considered standard therapy and are given to all post-MI patients if possible, particularly if ejection fraction post MI is < 40%. These drugs may provide long-term cardioprotection by improving endothelial function. If an ACE inhibitor is not tolerated because of cough or rash (but not angioedema or renal dysfunction), an angiotensin II receptor blocker (ARB) may be substituted.

Statins are also standard therapy and are routinely prescribed regardless of lipid levels. Reducing cholesterol levels after MI reduces rates of recurrent ischemic events and mortality in patients with elevated or normal cholesterol levels. Statins appear to benefit post-MI patients regardless of their initial cholesterol level. Post-MI patients whose primary problem is a low HDL level or an elevated triglyceride level may benefit from a fibrate, but evidence of benefit is less clear. The statin should be continued indefinitely, unless significant adverse effects occur, and dose should be increased to the maximally tolerated dose.

Rehabilitation and postdischarge treatment reference

  • 1. Goel K, Lennon RJ, Tilbury RT, et al: Impact of Cardiac Rehabilitation on Mortality and Cardiovascular Events After Percutaneous Coronary Intervention in the Community. Circulation 123:2344–2352, 20111. doi: 10.1161/CIRCULATIONAHA.110.983536

Key Points

  • Unstable angina, NSTEMI, and STEMI represent worsening degrees of myocardial ischemia and necrosis; the distinctions help differentiate prognosis and guide treatment.

  • Diagnosis is based on serial ECG and cardiac marker levels, particularly using new, highly sensitive troponin T tests.

  • Immediate medical treatment depends on the specific syndrome and patient characteristics but typically involves antiplatelet drugs, anticoagulants, beta-blockers, and nitrates as needed (eg, for chest pain, hypertension, pulmonary edema), and a statin to improve prognosis.

  • For unstable angina and NSTEMI, do angiography within 24 to 48 h of hospitalization to identify coronary lesions requiring PCI or CABG; fibrinolysis is not helpful.

  • For STEMI, do emergency PCI when door to balloon-inflation time is < 90 min; do fibrinolysis if such timely PCI is not available.

  • Following recovery, initiate or continue aspirin and other antiplatelet drugs, beta-blockers, ACE inhibitors, and statins in most cases unless contraindicated.

Drugs Mentioned In This Article

Drug Name Select Trade
DESOXYN
NITRO-DUR
INDERAL
SECTRAL
BRILINTA
LOPRESSOR, TOPROL-XL
ATROPEN
COUMADIN
DURAMORPH PF, MS CONTIN
TENORMIN
No US brand name
TIMOPTIC
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