Myocardial Infarction: NSTEMI Flashcards
What is non-ST-elevation myocardial infarction (NSTEMI)?
Non-ST-elevation myocardial infarction (NSTEMI) is an acute ischaemic event causing myocyte necrosis.
NSTEMI is a result of an acute imbalance between myocardial oxygen demand and supply, most commonly due to a reduction in myocardial perfusion.
How does the pathology of NSTEMI and STEMI differ?
STEMI is complete occlusion (typically thrombosis or embolism) of a coronary artery.
NSTEMI is usually a result of a transient or near-complete occlusion of a coronary artery or acute factor that deprives myocardium of oxygen.
Briefly describe the pathophysiology of NSTEMI
Unstable plaques have soft, lipid-laden contents, with thin, often sclerotic fibrous caps infiltrated by macrophages (foam cells). Release of the lipid-rich atherogenic core causes adhesion, activation, and aggregation of platelets. This initiates the coagulation cascade. A superimposed thrombus forms, occluding the coronary blood flow and resulting in myocardial ischaemia
What are the risk factors for NSTEMI?
- Diabetes
- Hyperlipidaemia
- Hypertension
- Metabolic syndrome
- Renal impairment
- Peripheral arterial disease
- A history of ischaemic heart disease and any previous treatment
- Obesity
- Advanced age
- Smoking
- Cocaine use
- Physical inactivity
- Family history of premature coronary artery disease (<60 years)
What are the signs of NSTEMI?
- A new murmur
What are the symptoms of NSTEMI?
- Chest pain (which may radiate to other areas such as the arms, back or jaw)
- Nausea and vomiting
- Marked sweating
- Breathlessness
- Palpitations
What investigations should be ordered for NSTEMI?
- ECG
- Troponin
- CXR
- FBC
- U&Es and creatinine
- LFTs
- Blood glucose
- CRP
- Echocardiogram
Why investigate using ECG?
Record and interpret a resting 12-lead ECG within 10 minutes of the point of first medical contact in any patient with suspected cardiac chest pain.
Abnormal findings that suggest NSTEMI include:
- ST depression; this indicates a worse prognosis
- Transient ST elevation
- T-wave changes
Why investigate troponins?
Troponins are proteins found in cardiac muscle. The specific type of troponin, the normal range and diagnostic criteria vary based on different laboratories (so check your policy). Diagnosis of ACS typically requires serial troponins (e.g. at baseline and 6 or 12 hours after onset of symptoms). A rise in troponin is consistent with myocardial ischaemia as the proteins are released from the ischaemic muscle. They are non-specific, meaning that a raised troponin does not automatically mean ACS.
In NSTEMI there is a dynamic elevation.
What are the other causes of a rise in troponins?
- Chronic renal failure
- Sepsis
- Myocarditis
- Aortic dissection
- Pulmonary embolism
Which troponins are specific to cardiac muscle?
Troponin I and T.
Why investigate using CXR?
The National Institute for Health and Care Excellence (NICE) recommends ordering a chest x-ray only if you suspect other diagnoses or to rule out complications of ACS.
Other causes of acute chest pain, such as pneumothorax or a widened mediastinum in aortic dissection, or complications of ACS such as pulmonary oedema due to heart failure.
Why investigate FBC?
Check full blood count to evaluate:
- Thrombocytopenia to estimate risk of bleeding; NSTEMI treatment increases the risk of bleeding
- Possible secondary causes of NSTEMI (i.e., secondary blood loss, anaemia)
Why investigate U&Es and creatinine?
Determine serum creatinine and estimated glomerular filtration rate (eGFR); these are key elements in assessing the Global Registry of Acute Coronary Events (GRACE) risk score.
Determine the choice and dose of anticoagulant.
Prevent contrast-induced nephropathy if an invasive strategy is planned in a patient with renal impairment.
Why investigate LFTs?
Measure liver function to include in the assessment of bleeding risk before starting anticoagulation.
