Non ST-Elevation Myocardial Infarction (NSTEMI)

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Background

  • 33% with confirmed MI have no chest pain on presentation (especially older, female, DM, CHF)
  • 5% of NSTEMI will develop Cardiogenic Shock (60% mortality)
  • Age >65 with MI and anemia had 33% reduction in 30 day mort if transfused to keep HCT >30
  • Association between quantity of troponin and risk of death
  • NSTEMI includes Type 2 -Type 5 biomarker elevations

Types of Myocardial Infarction

Type 1: Ischemic myocardial necrosis due to plaque rupture ( ACS)
Type 2: Ischemic myocardial necrosis due to supply-demand mismatch, e.g. coronary spasm, embolism, low or high blood pressures, anemia, or arrhythmias.
Type 3: sudden cardiac death (no cTr values)
Type 4: procedure related, post PCI or stent thrombosis ( cTr > 5X Decision Level).
Type 5: post CABG (cTr > 10X Decision Level).

Clinical Features

Risk of ACS

Clinical factors that increase likelihood of ACS/AMI:[1][2]

Clinical factors that decrease likelihood of ACS/AMI:[3]

  • Pleuritic chest pain
  • Positional chest pain
  • Sharp, stabbing chest pain
  • Chest pain reproducible with palpation

Male and female patients typical present with similar symptoms[4]

Differential Diagnosis

Chest pain

Critical

Emergent

Nonemergent

Evaluation

  • Non-STEMI ECG + positive troponin
  • CK-MB and myoglobin are not helpful[5]
  • Angiography indicated for:
    • Recurrent angina/ischemia with or with out symptoms of CHF
    • Elevated troponins
    • New or presumably new ST-segment depression
    • High-risk findings on noninvasive stress testing
    • Depressed LV function
    • Hemodynamic instability
    • Sustained V-tach
    • PCI within previous 6 mo
    • Prior CABG

Management

  • Dual antiplatelet therapy and antithrombotic therapy is mainstay of treatment
  • Medical management vs cath determined by level of risk for future cardiovascular events

Antiplatelet

  • Aspirin
    • Recommended dose is 325mg chewed
    • Reduces death from MI by 12.5 → 6.4%
    • Should be used in all ACS unless contraindicated (eg Anaphylaxis)
    • In pts with true ASA allergies, substitute Clopidogrel[6]
  • Clopidogrel (see drug link for specific age and indication-related dosages)
    • Give in addition to ASA
    • Mortality benefit with NSTEMI (CURE trial: Decrease in cardiovascular death, MI or stroke by 9.3-11.5%)
    • Main risk and contraindication is bleeding
  • GPIIb/IIIa Inhibitors
    • Eptifibatide, abciximab, tirofiban
    • Benefit only for patients undergoing PCI
    • Administer at time of PCI, not in the ED

Antithrombotics

  • Give heparin or enoxaparin along with ASA (Class 1A evidence)
  • Enoxaparin (Lovenox)
    • 1mg/kg subq BID
    • AHA recommends for moderate & high risk Unstable angina/NSTEMI unless CABG within 24hr
    • Safer than UFH
    • ESSENCE trial showed 20% decrease in death, MI or urgent revascularization with LMWH
    • Adjust for CrCl<30ml and extremes of weight
    • No need to monitor labs
  • Unfractionated Heparin
    • Bolus 60-70u/kg (max 5000) followed by infusion of 12-15u/kg/hr (max 1000/hr), goal ptt 45-75s
    • Consider if patient likely to undergo PCI/CABG within 24hr of admission or in setting of renal failure
  • Hirudin
    • Approved only for patients with HIT

Other

  • Oxygen
    • Use only if SpO2 <90%
  • Nitrates (decrease preload)
    • Administer sublingual NTG every 5 min x3 for continuing ischemic pain and then assess need for IV NTG (AHA ACA Level I)
    • Use cautiously in inferior MI or if on sildenafil
    • Not shown to decrease MACE
  • Analgesia
    • Morphine, Fentanyl, or other opioid (AHA ACA Level IIb)
    • Do not use NSAIDs other than ASA (AHA ACA Level III: Harm)
    • Complete absence of pain is likely not feasible - aim for pain level <5
  • β-blockers
    • Start PO dose within 24 hours (Do not give IV beta blocker in ED (AHA ACA Level III: Harm))
    • Goal HR is 50-60
    • Contraindicated if HR<50 or SBP<90, acute CHF, low flow state, or PR>240ms
    • Decreases inotropic and chronotropic response to catecholamines
    • Use diltiazem if cannot use beta-blocker (nifedipine clearly harmful)
  • ACE inhibitor
    • Start short-acting (captopril) within 24 hours of admission
    • Reduces RR of 30 day mortality by 7%
    • Those with recent MI (especially anterior) and LV dysfunction benefit most
  • Transfusion
    • Transfuse to keep hemoglobin >10
  • Thrombolytics
    • Not indicated (only useful for STEMI)

Disposition

  • Admit

Prognosis

NSTEMI TIMI Score[7]

Used to estimate percent risk of all-cause mortality, new/recurrent MI, or need for revascularization at 14 days
  • Age >65 yrs (1 point)
  • Three or more risk factors for coronary artery disease: (1 point)
    • family history of coronary artery disease
    • hypertension
    • hypercholesterolaemia
    • diabetes
    • current smoker
  • Use of aspirin in the past 7 days (1 point)
  • Significant coronary stenosis (stenosis >50%) (1 point)
  • Severe angina (e.g., >2 angina events in past 24 h or persisting discomfort) (1 point)
  • ST-segment deviation of ≥0.05 mV on first ECG (1 point)
  • Increased troponin and/or creatine kinase-MB blood tests (1 point)
TIMI Risks
points % risk of mortality, MI, or need for revascularization
0 5%
1 5%
2 8%
3 13%
4 20%
5 26%
6 41%

See Also

External Links

References

  1. Body R, Carley S, Wibberley C, et al. The value of symptoms and signs in the emergent diagnosis of acute coronary syndromes. Resuscitation. 2010;81(3):281–286. PMID: 20036454
  2. Panju AA, Hemmelgarn BR, Guyatt GH, et al. The rational clinical examination. Is this patient having a myocardial infarction? JAMA. 1998;280(14):1256–1263. PMID: 9786377
  3. Swap CJ, Nagurney JT. Value and limitations of chest pain history in the evaluation of patients with suspected acute coronary syndromes. JAMA. 2005;294(20):2623–2629. PMID: 16304077
  4. Gimenez MR, et al. Sex-specific chest pain characteristics in the early diagnosis of acute myocardial infarction. JAMA Intern Med. 2014; 174(2):241-249.
  5. AHA ACA - NSTEMI ACS Guidelines 2014View Online
  6. CAPRIE Steering Committee.. A randomised, blinded, trial of clopidogrel versus aspirin in patients at risk of ischaemic events (CAPRIE). CAPRIE Steering Committee. Lancet. 1996 Nov 16;348(9038):1329-39.
  7. Antman, Elliot et al. The TIMI Risk Score for Unstable Angina/Non–ST Elevation MI A Method for Prognostication and Therapeutic Decision Making. JAMA. 2000;284(7):835-842. doi:10.1001/jama.284.7.835. PDF