Acute Coronary Syndrome: Myocardial Infarction

[Section Outline]

Signs and Symptoms
Essential Workup
Diagnostic Tests & Interpretation
Differential Diagnosis

Signs and Symptoms

Chest pain:
- Most common presentation of MI
- Substernal pressure
- Heaviness
- Squeezing
- Burning sensation
- Tightness
Anginal equivalents (MI without chest pain):
- Abdominal pain
- Syncope
- Diaphoresis
- Nausea or vomiting
- Weakness
May localize or radiate to arms, shoulders, back, neck, or jaw
Associated symptoms:
- Dyspnea
- Syncope
- Fatigue
- Diaphoresis
- Nausea
- Vomiting
Symptoms are usually reproduced by exertion, eating, exposure to cold, or emotional stress
Symptoms commonly last 30 min or more
Symptoms may occur with rest or exertion
Often preceded by crescendo angina
May be improved/relieved with rest or nitroglycerin
Symptoms generally unchanged with position or inspiration
Positive Levine sign or clenched fist over chest is suggestive of angina
BP is usually elevated during symptoms

Physical Exam

Physical exam is usually unrevealing
Occasional physical findings include:
- S3 or S4 due to left ventricular systolic or diastolic symptoms
- Mitral regurgitation due to papillary muscle dysfunction
- Diminished peripheral pulses
- Physical findings of decompensated CHF

Essential Workup

History is critical in differentiating MI from noncardiac etiologies.

Diagnostic Tests & Interpretation

Lab

Electrolytes
Calcium, magnesium
Cardiac enzymes
Digoxin level

Imaging

CXR:
- May identify cardiomyopathy or CHF
- Often abnormal in aortic dissection

Diagnostic Procedures/Surgery

ECG:
- Differentiate from nonischemic causes of ST elevation:
  - Pericarditis
  - Benign early repolarization
  - Left ventricular hypertrophy with strain
  - Prior MI with left ventricular aneurysm
  - Hyperkalemia
ECG criteria for STEMI:
- New ST elevation at J point in at least 2 contiguous leads of 2 mm (0.2 mV) in men or 1.5 mm (0.15 mV) in women in leads V2-V3 and /or of 1 mm (0.1 mV) in other contiguous chest leads or the limb leads
- ST depression in leads V1-V2 may indicate posterior injury
- New or presumably new left bundle branch block (LBBB) has been considered a STEMI equivalent. Most cases of LBBB at time of presentation are not old but prior ECG is unavailable
- Modified Sgarbossa criteria for MI in LBBB or paced rhythm are diagnostic:
  - Concordant ST elevation >1 mm in leads with a positive QRS complex
  - Concordant ST depression >1 mm V1-V3 in leads with a negative QRS complex
  - Discordance of the ST segment (measured at the J point relative to the PR) with the R or S wave (whichever is larger, measured relative to the PR) in a ratio <−0.25
Echo:
- May identify regional wall motion abnormalities or valvular dysfunction

Differential Diagnosis

Aortic dissection
Anxiety
Biliary colic
Costochondritis
Esophageal spasm
Esophageal reflux
Herpes zoster
Hiatal hernia
Mitral valve prolapse
Peptic ulcer disease
Psychogenic symptoms
Panic disorder
Pericarditis
Pneumonia
Pulmonary embolus

Treatment ⬆ ⬇

[Section Outline]

Prehospital
Initial Stabilization/Therapy
ED Treatment/Procedures
Medication

Prehospital

IV access
Aspirin
Oxygen
Cardiac monitoring
Sublingual nitroglycerin for symptom relief
12-lead ECG, if possible, with transmission or results relayed to receiving hospital

Initial Stabilization/Therapy

IV access
Oxygen
Cardiac monitoring
Oxygen saturation
Continuous BP monitoring and pulse oximetry

ED Treatment/Procedures

STEMI requires reperfusion therapy as soon as possible:
- Percutaneous coronary intervention (PCI) is preferred diagnostic and therapeutic modality if available.
Goal is primary PCI within 90 min of first medical contact:
- Thrombolytics should be given if PCI is not available within 120 min of first medical contact (see “Reperfusion Therapy, Cardiac”).
- Patients arriving at a hospital without PCI should be transferred to a PCI-capable hospital within a door-in-door-out time under 30 min.
- Patients who are resuscitated during out-of-hospital cardiac arrest whose initial ECG shows STEMI should receive immediate PCI.
Aspirin should be administered first to all patients with suspected MI unless known allergy
Glycoprotein IIb/IIIa inhibitors (e.g., abciximab) may be started at time of PCI
Prasugrel or clopidogrel should be started at the time of PCI
Prasugrel should not be given to patients with history of prior stroke or transient ischemic attack (TIA)
Clopidogrel is the recommended ADP receptor inhibitor for patients given fibrinolytics:
- Dose is reduced (age <75 yr: 300 mg, >75 yr: 75 mg)
If BP is >90-100 mm Hg systolic, administer sublingual nitroglycerin, nitropaste, or IV nitroglycerin assuming no ECG criteria or clinical evidence of right ventricular infarct:
- Symptoms that persist after 3 sublingual nitroglycerin tablets are strongly suggestive of AMI or noncardiac etiology.
β-Blockers should be initiated within first 24 hr if not contraindicated (e.g., if heart block, heart rate <60, signs of heart failure, hypotension, or obstructive pulmonary disease is present):
- No benefit of administration prior to PCI or in ED
Morphine should be avoided unless pain does not respond to nitrates because it may delay the effects of antiplatelet agents
Fentanyl may be given as an alternative
Heparin (UFH) or bivalirudin should be used in patients undergoing primary PCI. Bivalirudin is indicated in patients at high risk for bleeding
In patients undergoing thrombolysis, heparin (UFH), enoxaparin, or fondaparinux is appropriate
If patient is in cardiogenic shock, patient should be transported to a cardiac catheterization laboratory for angioplasty and intra-aortic balloon pump as soon as possible (see “Congestive Heart Failure”)
Ventricular dysrhythmias:
- See “Ventricular Tachycardia”
Bradydysrhythmia associated with hypotension should be treated with atropine or external pacing
Conduction disturbances:
- First-degree atrioventricular (AV) block and Mobitz I (Wenckebach) are often self-limited and do not require treatment.
- Mobitz II, complete heart block, new right bundle branch block (RBBB) in anterior MI, RBBB plus left anterior branch block or left posterior fascicular block, LBBB plus first-degree AV block may require a temporary transvenous pacemaker.
Accelerated idioventricular rhythm (AIVR) may present after reperfusion, appearing as a ventricular rhythm with rate below 120 bpm:
- Only if sustained treat with electrical cardioversion or sodium bicarbonate
- Lidocaine and other antidysrhythmics may cause asystole

Medication

Aspirin: 162-325 mg PO
ADP receptor inhibitors:
- Clopidogrel (Plavix): 600 mg PO
- Prasugrel (Effient): 60 mg PO
- Ticagrelor (Brilinta): 180 mg PO
Bivalirudin: 0.75-mg/kg IV bolus, then 1.75 mg/kg/hr infusion
Enoxaparin (Lovenox): 1 mg/kg SC q12h
- Fondaparinux: 2.5 mg SC
Glycoprotein IIb/IIIa inhibitors:
- Abciximab (ReoPro) for use prior to PCI only: 0.25-mg/kg IV bolus
- Eptifibatide (Integrilin): 180 mcg/kg IV over 1-2 min, then 2 mcg/kg/min up to 72 hr
- Tirofiban (Aggrastat): 0.4 mcg/kg/min for 30 min, then 0.1 mcg/kg/min for 48-108 hr
Heparin: 60-U/kg IV bolus (max. 4,000 units), then 12 U/kg/hr (max. 1,000 U/hr)
Metoprolol: 5 mg IV q5-15min followed by 25-50 mg PO starting dose as tolerated (Note:β-blockers contraindicated in cocaine chest pain)
Morphine: 2 mg IV, may titrate upward in 2-mg increments for relief of pain assuming no respiratory deterioration and SBP >90 mm Hg
Fentanyl: 25-50 mcg IV, may titrate upward in 25-mcg doses given respiratory and hemodynamic response
Nitroglycerin: 0.4 mg sublingual q5min for max. 3 doses
Nitroglycerin: IV drip at 5-10 mcg/min, USE NON-PVD tubing
Nitropaste: 1-2 in transdermal, less favored due to inconsistent absorption
Thrombolytics: See “Reperfusion Therapy, Cardiac,” for dosing

Follow-Up ⬆ ⬇

Disposition

Admission Criteria

Patients with an AMI require hospital admission.
If the diagnosis is unclear, admission to the hospital or an ED observation unit may be useful for serial cardiac enzymes, ECGs, and exercise stress testing and /or cardiac catheterization if needed.

Discharge Criteria

No patient with an AMI should be discharged from the ED.

Issues for Referral

If PCI is unavailable at the treating institution, particularly if the patient is in cardiogenic shock, he should be transported to another hospital if PCI can be initiated within 120 min of first medical contact.
Patients with failed reperfusion should be transported urgently to a PCI-capable facility.
Patients undergoing reperfusion therapy may benefit from transfer to a PCI-capable facility within 3-24 hr as part of an invasive strategy.

Pearls and Pitfalls ⬆ ⬇

Goal of thrombolytic therapy is a 30-min door to needle time if PCI not possible.
New or presumably new LBBB at presentation occurs infrequently, and should not be considered diagnostic of AMI in isolation.

Additional Reading ⬆ ⬇

FilippoC, GiovannaL. Pathogenesis of acute coronary syndromes . J Am Coll Cardiol. 2013;61:1-11.
JneidH, AddisonD, BhattDL, et al. 2017 AHA/ACC clinical performance and quality measures for adults with ST-elevation and non-ST-elevation myocardial infarction: A report of the American College of Cardiology/American Heart Association Task Force on Performance Measures . J Am Coll Cardiol. 2017;70:2048-2090.
MeyersHP, LimkakengAT, JaffaEJ, et al. Validation of the modified Sgarbossa criteria for acute coronary occlusion in the setting of left bundle branch block: A retrospective case-control study . Am Heart J. 2015;170:1255-1264.
O'GaraPT, KushnerFG, AscheimDD, et al. 2013 ACCF/AHA guideline for the management of ST-elevation myocardial infarction. A report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines . Circulation. 2013;127:e362-e425.
ParodiG, Belland iB, XanthopoulouI, et al. Morphine is associated with a delayed activity of oral antiplatelet agents in patients with ST-elevation acute myocardial infarction undergoing primary percutaneous coronary intervention . Circ Cardiovasc Interv. 2015;8:1-7.

See Also (Topic, Algorithm, Electronic Media Element)

Codes ⬆

ICD9

410.90 Acute myocardial infarction, unspecified site, episode of care unspecified
410.91 Acute myocardial infarction of unspecified site, initial episode of care
410.92 Acute myocardial infarction of unspecified site, subsequent episode of care
411.1 Intermediate coronary syndrome
410.00 Acute myocardial infarction of anterolateral wall, episode of care unspecified
410.01 Acute myocardial infarction of anterolateral wall, initial episode of care
410.02 Acute myocardial infarction of anterolateral wall, subsequent episode of care
410.0 Acute myocardial infarction of anterolateral wall
410.10 Acute myocardial infarction of other anterior wall, episode of care unspecified
410.11 Acute myocardial infarction of other anterior wall, initial episode of care
410.12 Acute myocardial infarction of other anterior wall, subsequent episode of care
410.1 Acute myocardial infarction of other anterior wall
410.20 Acute myocardial infarction of inferolateral wall, episode of care unspecified
410.21 Acute myocardial infarction of inferolateral wall, initial episode of care
410.22 Acute myocardial infarction of inferolateral wall, subsequent episode of care
410.2 Acute myocardial infarction of inferolateral wall
410.30 Acute myocardial infarction of inferoposterior wall, episode of care unspecified
410.31 Acute myocardial infarction of inferoposterior wall, initial episode of care
410.32 Acute myocardial infarction of inferoposterior wall, subsequent episode of care
410.3 Acute myocardial infarction of inferoposterior wall
410.40 Acute myocardial infarction of other inferior wall, episode of care unspecified
410.41 Acute myocardial infarction of other inferior wall, initial episode of care
410.42 Acute myocardial infarction of other inferior wall, subsequent episode of care
410.4 Acute myocardial infarction of other inferior wall
410.50 Acute myocardial infarction of other lateral wall, episode of care unspecified
410.51 Acute myocardial infarction of other lateral wall, initial episode of care
410.52 Acute myocardial infarction of other lateral wall, subsequent episode of care
410.5 Acute myocardial infarction of other lateral wall
410.60 True posterior wall infarction, episode of care unspecified
410.61 True posterior wall infarction, initial episode of care
410.62 True posterior wall infarction, subsequent episode of care
410.6 True posterior wall infarction
410.70 Subendocardial infarction, episode of care unspecified
410.71 Subendocardial infarction, initial episode of care
410.72 Subendocardial infarction, subsequent episode of care
410.7 Subendocardial infarction
410.80 Acute myocardial infarction of other specified sites, episode of care unspecified
410.81 Acute myocardial infarction of other specified sites, initial episode of care
410.82 Acute myocardial infarction of other specified sites, subsequent episode of care
410.8 Acute myocardial infarction of other specified sites
410.9 Acute myocardial infarction of unspecified site
410 Acute myocardial infarction

ICD10

I21.3 ST elevation (STEMI) myocardial infarction of unspecified site
I21.29 STEMI involving oth sites
I24.9 Acute ischemic heart disease, unspecified
I21.01 STEMI involving left main coronary artery
I21.02 STEMI involving left anterior descending coronary artery
I21.09 STEMI involving oth coronary artery of anterior wall
I21.0 ST elevation (STEMI) myocardial infarction of anterior wall
I21.11 STEMI involving right coronary artery
I21.19 STEMI involving oth coronary artery of inferior wall
I21.1 ST elevation (STEMI) myocardial infarction of inferior wall
I21.21 STEMI involving left circumflex coronary artery
I21.2 ST elevation (STEMI) myocardial infarction of other sites

SNOMED

22298006 Myocardial infarction (disorder)
57054005 Acute myocardial infarction (disorder)
401303003 Acute ST segment elevation myocardial infarction (disorder)
394659003 Acute coronary syndrome (disorder)
15990001 Acute myocardial infarction of posterolateral wall (disorder)
54329005 Acute myocardial infarction of anterior wall
65547006 Acute myocardial infarction of inferolateral wall (disorder)
70211005 Acute myocardial infarction of anterolateral wall (disorder)
73795002 acute myocardial infarction of inferior wall (disorder)

section name header

Basics ⬇

Diagnosis ⬆ ⬇