Coronary heart disease is the term used to describe those heart conditions that are caused by disease of the coronary arteries.
The coronary arteries are blood vessels that arise from the aorta and run over the surface of the heart branching into smaller vessels as they progress and eventually penetrating the muscle of the heart to carry the blood to the muscle thus supplying it with the oxygen and nutients that it requires to maintain its continuous pumping action.
Most of the oxygen and nutrients that the heart muscle receives are delivered in this way, although some are derived directly from the blood in the cavity of the heart chambers.
When the blood supply is insufficient to the muscle it may cause pain through a reversible reduction in supply and this is called angina due to myocardial ischaemia.
If the flow down the artery is completely lost this may cause the muscle that the artery was supplying to die in which case it is called a myocardial infarction - the technical term for a heart attack.
Over the past few years the way that we have classified angina and heart attacks has changed somewhat. This is principally for two reasons. First there has been a lot of research looking at the outcome in patients presenting with chest pains characterised by different ECG changes and different patterns of release of chemicals from the damaged muscle. Second, our ability to measure chemicals released from heart muscle has become much more sophisticated over the past few years.
Historically we use to divide patients with coronary disease into those with stable angina (those with typical symptoms of chest pain coming on with exertion or emotion but not spontaneously or at rest), those with unstable angina (typically anginal symptoms but getting progressively worse and coming on with minimal exertion or spontaneously) and heart attacks. The decision as to whether we would classify people with new onset chest pains of an unstable nature as unstable angina or heart attacks was principally made on the basis of ECG changes, the duration of their chest pain and as to whether or not they had a significant rise in a chemical called creatine kinase (CK; an enzyme which is contained within muscle cells). A rise of this chemical within the blood stream would be suggestive of significant damage to the heart muscle during their symptoms. Hence if there was no CK rise, their attack would be diagnosed as angina and if there was a CK rise then they would be diagnosed as having a heart attack. The heart attacks (i.e. those with a CK rise) were subdivided into two groups depending on the changes on the electrocardiogram (ECG). Those which showed significant elevation of the part of the ECG known as the ST segment were classified as full thickness myocardial infarctions and those showing a variety of other changes including depression of this segment or T wave inversion where classified as having a sub-endocardial myocardial infarction.
We now have new biochemical markers which we can measure in the blood stream which are much more sensitive to loss or reduction of the blood supply to the heart muscle. These chemicals are called troponins.
It is recognised that troponins are not released into the blood stream in patients with stable angina and are released in patients having heart attacks as defined above. However, we also see troponins released into the blood stream in a proportion of patients who we would previously have classified as having unstable angina. This means that we are now more likely to diagnose patients who previously would have been called unstable angina as having had a heart attack.
It is important to recognise that troponin levels may be elevated in the blood of patients for reasons other than heart attacks. For instance they can be elevated where there is reduced kidney function, in severe infections, with pulmonary embolism (clots in the lung) and in response to fast heart rhythm disturbances (as well as in other conditions).
Where we are confident that someone is having a heart attack we divide these patients into two groups depending on the their ECG changes. Those heart attacks with significant ST segment elevation on the ECG are called an ST segment elevation myocardial infarction (STEMI) and those without these changes are called a non-ST segment elevation myocardial infarction (NSTEMI). There is a more in-depth discussion of this in the section on heart attacks. What is clear however is that all patients who have unstable coronary syndromes are at the significant risk of having heart attacks in the future and merit careful clinical evaluation to determine their immediate management and future investigations.
The old and new classifications of angina and heart attacks are summarised in the table below.
| OLD | NEW | ||
|---|---|---|---|
| ANGINA | Angina | Angina | STABLE ANGINA |
| Unstable angina | Unstable angina | ACUTE CORONARY SYNDROME | |
| HEART ATTACK | Subendocardial myocardial infarction | NSTEMI | |
| Full thickness myocardial infarction | STEMI | ||
The change in classification of the acute coronary syndromes which has led to more patients being diagnosed with heart attack rather than unstable angina has led to some difficulties for some patients claiming insurance benefits where the companies are more likely to use the old criteria for diagnosing a heart attack. Similarly there may also be issues where the patient maybe being evaluated in terms of capacity for continued employment in certain jobs where employing bodies may use the old criteria whereas doctors are likely to have used the new criteria.
The pages that can be accessed by following the links below give fuller descriptions of angina and heart attacks, their treatments and possible complications. There are also sections on operative interventions such as angioplasty (and possible adjunctive stenting) and coronary artery by-pass grafting.