Overview of Acute Coronary Syndromes (ACS)

Myocardial infarction in the absence of obstructive coronary artery disease (MINOCA) is found in about 5% to 6% of patients with acute MI who undergo coronary angiography (1 Etiology 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 ). Patients with MINOCA tend to be younger, women, and without dyslipidemia, and they have myocardial necrosis without significant coronary atherosclerosis. Plaque disruption and coronary vasospasm are common in MINOCA. Coronary thrombosis or embolism and spontaneous coronary artery dissection are causes of MINOCA.

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 (LV) failure causes shortness of breath and fatigue, and right ventricular (RV) failure causes peripheral and abdominal... read more 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 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/or diaphoresis... read more 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

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 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.

After the acute event, many 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 can occur. They usually involve

Electrical dysfunction can be significant in any form of ACS, but usually, large parts of myocardium must be ischemic to cause significant myocardial dysfunction. Other complications of ACS include recurrent ischemia and pericarditis. Pericarditis Pericarditis Pericarditis is inflammation of the pericardium, often with fluid accumulation in the pericardial space. Pericarditis may be caused by many disorders (eg, infection, myocardial infarction, trauma... read more that occurs 2 to 10 weeks after an MI is known as post-MI syndrome Post-MI Syndrome (Dressler Syndrome) 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 , or Dressler syndrome.

ECG is the most important test and should be done as soon as possible (eg, within 10 minutes 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.

For STEMI, initial ECG is usually diagnostic, showing ST-segment elevation ≥ 1 mm in 2 or more contiguous leads subtending the damaged area (see figure Acute lateral left ventricular infarction 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) ) tends to confirm the diagnosis.

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 ). 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.

Cardiac markers (serum markers of myocardial cell injury) are

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 ); 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 2 to 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

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 (LV) failure causes shortness of breath and fatigue, and right ventricular (RV) failure causes peripheral and abdominal... read more , 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.

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 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).

Angiography is obtained urgently for patients with STEMI, patients with persistent chest pain despite maximal medical therapy, and patients with complications (eg, markedly elevated cardiac markers, presence of 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 , acute mitral regurgitation Mitral Regurgitation Mitral regurgitation (MR) is incompetency of the mitral valve causing flow from the left ventricle (LV) into the left atrium during ventricular systole. MR can be primary (common causes are... read more , ventricular septal defect Ventricular Septal Defect (VSD) A ventricular septal defect (VSD) is an opening in the interventricular septum, causing a shunt between ventricles. Large defects result in a significant left-to-right shunt and cause dyspnea... read more , unstable arrhythmias). Patients with uncomplicated NSTEMI or 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 whose symptoms have resolved typically undergo angiography within the first 24 to 48 hours of hospitalization to detect lesions that may require treatment.

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%.

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 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 with 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.

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* ), 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, 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 ).

Early diagnostic data and response to treatment can help determine the need for and timing of revascularization Revascularization for Acute Coronary Syndromes Revascularization is the restoration of blood supply to ischemic myocardium in an effort to limit ongoing damage, reduce ventricular irritability, and improve short-term and long-term outcomes... read more when primary percutaneous coronary intervention is not possible.

On arrival to the emergency room, the patient's diagnosis is confirmed. Drug therapy and choice of revascularization depend on the type of acute coronary syndrome as well as the clinical picture (see figure Approach to acute coronary syndromes Approach to acute coronary syndromes ). Choice of drug therapy is discussed in Drugs for Acute Coronary Syndrome 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 , and choice of reperfusion strategy is further discussed in Revascularization for Acute Coronary Syndromes Revascularization for Acute Coronary Syndromes Revascularization is the restoration of blood supply to ischemic myocardium in an effort to limit ongoing damage, reduce ventricular irritability, and improve short-term and long-term outcomes... read more .

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 critical 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).

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 older 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... 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 . 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 older 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 (LV) failure causes shortness of breath and fatigue, and right ventricular (RV) failure causes peripheral and abdominal... read more . 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.

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 of some sort before or shortly after discharge (see table Functional Evaluation After Myocardial Infarction Functional Evaluation After Myocardial Infarction ).

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 post-discharge 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 ).

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.

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

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. Dual antiplatelet therapy with aspirin and a P2Y12 receptor blockers (eg, ticagrelor, clopidogrel) for up to 1 year is recommended (2, 3 Rehabilitation and post-discharge 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 ).

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.