Unstable angina and non-ST elevation myocardial infarction


Unstable angina (UA) and non-ST elevation myocardial infarction (NSTEMI) are two possible manifestations of acute coronary syndrome. They have substantial morbidity and mortality and non-STEMIs represents 60% of all the infarctions.

SIGNS & SYMPTOMS:

Patients may present with typical chest pain (pressure that radiates to the left arm or neck associated with diaphoresis), unspecific chest discomfort, or with other symptoms, such as mild shortness of breath, dizziness, lightheadedness or epigastric discomfort.

DIAGNOSIS:

After stabilization of Airway, Breathing and Circulation, history and physical examination should be obtained.

An ECG should be ordered. T wave inversions or ST-depression may be present. If there is significant ST elevation (2 or more contiguous leads with the cut-off points of ≥0.2 mV in leads V1, V2, or V3 and ≥0.1 mV in other leads), the patient should be treated as ST-elevation MI.

Clinically there is no difference between UA and NSTEMI. The main difference between UA and NSTEMI is the fact that NSTEMI has elevation of myocardial injury markers. Troponin is the marker of choice and should be measured on arrival as well as after 6 and 12 hours.

Other tests to be obtained include CBC with platelet count, PT and INR, aPTT, electrolytes, magnesium, BUN, creatinine, glucose and lipid profile.

RISK STRATIFICATION:

Two models can be used for risk stratification: TIMI risk, GRACE ACS risk calculator or the HEART score.

TIMI risk:               Online Calculator (MDCalc)          Online Calculator (QxMD)

GRACE ACS risk:     Online Calculator (MDCalc)          Online Calculator (QxMD)

HEART score:          Online Calculator (MDCalc)          Online Calculator (QxMD)

TREATMENT:

Airway, breathing and circulation should be assessed. Cardiac monitoring should be provided and venous access obtained.

Oxygen therapy: Oxygen should be provided for all patients with saturation lower than 90-92%.

Antiplatelet therapy: Aspirin should be used (162-325mg once immediately and 81mg/day after). The addition of a second antiplatelet agent can be beneficial (a situation called dual antiplatelet therapy – DAPT). This second agent is usually a P2Y12 receptor blocker (e.g. ticagrelor – BRILINTA – 180mg once followed by 90mg BID OR clopidogrel – PLAVIX – 300-600mg once followed by 75mg daily OR prasugrel – EFFIENT – 60mg once followed by 10mg qDaily). Ticagrelor appears to be better than the others, and prasugrel has a higher bleeding risk. If there is a concern regarding the need for CABG, it is reasonable to wait and give the P2Y12 inhibitor only after PCI since these agents may increase the risk of bleeding.

Other antiplatelet agents include the GP IIb/IIIa inhibitors (e.g. tirofiban – AGGRASTAT – 25mcg/kg loading dose in 5 minutes followed by 0.15mcg/kg/min infusion for up to 18h OR eptifibatide – INTEGRILIN – 180mcg/kg bolus followed by 2mcg/kg/minute for up to 18-24h OR abciximab – REOPRO – 0.25mg/kg bolus followed by 0.125mcg/kg/minute for 12 hours). They should generally not be used if DAPT with aspirin and a P2Y12 blocker is already used and the patient is stable. They may be used in patients with ongoing ischemia despite DAPT or those at high risk of ischemic event or complication of PCI.

Nitrates: Sublingual nitroglycerin 0.4mg q5 minutes for 3 doses may be used. However, patients with hypotension, right ventricular infarction or those already using phosphodiesterase 5 inhibitors (e.g. sildenafil) should not receive nitrates.

Beta-blockers: Should be started in all patients without contraindications within 24 hours. Cardioselective agents (metoprolol or atenolol) are preferred.

Statins: High-dose statins may be used (e.g. atorvastatin 80mg/day) regardless of LDL or cholesterol levels.

Anticoagulation: All patients with acute coronary syndrome should receive anticoagulation. Patients with early-invasive strategy may receive UFH or bivalirudin as the drugs of choice. Other patients may receive enoxaparin or fondaparinux.

Left Heart Catheterization + Percutaneous Intervention in the first 24-72h (early invasive strategy) vs Medical Therapy and Observation with a stress test later (ischemia guided therapy)

All patients should have their risk assessed (check risk stratification above) because the choice for an aggressive or conservative approach depends on that. Most of the patients will have moderate or high risk will benefit from an early invasive strategy (catheterization within 24 hours). Very feel patients will be low risk (TIMI risk 0-2 or GRACE score <=108) and may be considered for ischemia-guided approach.

The early invasive strategy consists on early left heart catheterization to identify lesions and treat them with PCI as soon as possible.

The ischemia guided approach consists on medical therapy alone and a stress test when the patient is stable. In such cases, in patients that have not received PCI or CABG, stress testing before discharge can be considered if the patient has a stable EKG and no symptoms of angina or heart failure in the past 12-24h.

SOURCES & FURTHER READING:

  1. McManus DD et al. Recent Trends in the Incidence, Treatment, and Outcomes of Patients with ST and Non-ST-Segment Acute Myocardial Infarction. Am J Med. 2011 Jan; 124(1): 40–47.
  2. Khera S et al. Non-ST-Elevation Myocardial Infarction in the United States: Contemporary Trends in Incidence, Utilization of the Early Invasive Strategy, and In-Hospital Outcomes. Journal of the American Heart Association. 2014. Vol 3. Issue 4.
  3. Amsterdam EA et al. 2014 AHA/ACC Guideline for the Management of Patients With Non-ST-Elevation Acute Coronary Syndromes. Circulation. 2014.
  4. Patel MR, Ohman EM. The Early Invasive Strategy in Acute Coronary Syndromes. Should the Guideline Recommendations Be Revisited? Journal of the American College of Cardiology. Volume 66, Issue 5, August 2015.