Acute coronary syndrome
Definition
A set of symptoms and signs compatible with ischaemic heart disease.
Important terms
- Infarction - death of tissue due to a lack of oxygen.
- Myocardial - pertaining (big word) to heart muscle. Thus a myocardial infarction is death of heart muscle due to lack of oxygen.
- Ischaemia - lack of blood supply causing dysfunction of tissue
- Angina (full term is angina pectoris) - chest pain caused by ischaemia
Why don't we just call it a heart attack?
The problem is that the features that are typical of a myocardial infarction (MI) - colloquially known as a heart attack - aren't necessarily an MI. Essentially it's classified as the following:
- Unstable angina - angina which lasts longer that 10 minutes; severe and new onset; or distinctly more severe/prolonged that previous angina. Diagnosed by symptoms with no rise in cardiac markers.
- Myocardial infarction is diagnosed by a rise in cardiac markers. It is further split into two types based on ECG changes.
- NSTEMI (non-ST elevation MI) - myocardial infarction where the ST segment of the ECG is not elevated
- STEMI (ST elevation MI) - MI where the ST segment is elevated. Please tell me you figured that out for yourself. If you didn't, give up medicine. Now.
Everyone of these conditions can potentially present with similar clinical features. They are only differentiated through further testing.
Epidemiology
Coronary heart disease is responsible for 15% of deaths in the UK. It's a big killer which is why it's important to know about. It's basically as important as cancer.
Pathophysiology
Over time, everybody builds up atherosclerosis in their veins. The atherosclerotic plaques rupture forming clots. These occlude the coronary arteries, stopping blood flow causing ischaemia and, if blocked for long enough, infarction. In angina only ischaemia occurs. In NSTEMIs, the vessel is not completely blocked but some heart muscle still dies.
Risk Factors
Take a look at ischaemic heart disease.
Clinical Features
- Chest pain - probably the defining one. Typically central, left-sided, crushing.
- radiating to left arm and neck
- Shortness of breath
- Nausea/vomiting
- Sweating
- Tachycardic, cold
- Sense of impending doom - did they feel like they were going to die?
30% of MIs are "silent" i.e. they are asymptomatic. These are more common in diabetes and elderly patients.
Investigations
There are two things you need to do with acute coronary syndrome:
- ECG - this can be immediately diagnostic
- Cardiac markers - these can be diagnostic. There are two type:
- Troponin T (aka trop T) - is released by myocardium after infarction. Should be done 12 hours after the onset of symptoms. If done sooner, it probably will not have risen significantly.
- Creatinine Kinase (CK) - this is found in all muscle tissue so is less specific. However, it can be done immediately but is rarely done.
ECG changes
Acutely:
- The first changes seen are ST elevation and tall T waves. These occur in the first few hours.
- Within 24 hours the T waves invert and the ST elevation resolves.
- Q wave changes can occure within 24 hours or acutely. They are either wide (<0.04s) or to deep (<25% of the corresponding R wave).
Long-term: