20. Mechanisms and consequences of chronic ischemic heart disease

Chronic IHD (or ischaemic cardiomyopathy) is a progressive heart failure that occurs due to ischaemic myocardial damage. The myocardial damage is often due to a previous myocardial infarct, but in some cases can severe coronary artery disease cause myocardial ischaemia and dysfunction without infarction or symptoms.

Some consider the term “chronic ischaemic heart disease” to mean all non-acute ischaemic heart diseases (like the anginas), which appearently the pathophysiology department does too. Others consider chronic ischaemic heart disease as a clinical entity synonymous with ischaemic cardiomyopathy. This topic will use the latter definition.

Stable angina

Stable angina is a condition where angina pain occurs during physical activity. It occurs due to an atherosclerotic plaque that occludes around 70% of the lumen of a coronary artery.

During rest will there be no symptoms, as the myocardial oxygen demand is relatively low, so even with a 70% occlusion can the artery supply enough oxygen. However, when the myocardial oxygen demand increases, like during exercise, will the oxygen demand suddenly increase. Because of the occlusion is the artery unable to supply enough oxygen, so ischaemia develops, with the characteristic angina pectoris pain and ST depression signs.

The symptoms (both pain and ECG signs) go away when the patient rests after the exercise. The condition is called stable angina because it only occurs at a certain level of exercise and not at random times, like unstable angina does.

Prinzmetal’s angina

This type of angina doesn’t occur due to atherosclerosis at all. Instead, Prinzmetal’s angina is caused by spasms of subepicardial arteries. The mechanisms that cause these strong vasospasms are unknown, however recreational drugs (like cocaine) increase the risk. The spasms are only temporary, so infarction rarely occurs.

The vasospasms occur randomly, so there can be symptoms in rest as well as during exercise.

Prinzmetal’s angina is associated with the same ECG signs as an acute myocardial infarction (ST elevation), however the signs are transient and subside when the vasospasm subsides.

Silent myocardial infarction

A silent infarct is an infarct that occurs without any symptoms. It is diagnosed based on ECG and troponins. It’s more common in disorders that affect autonomic nerves, like untreated diabetes mellitus. Diabetes-induced neuropathy means that the pain is unnoticable and so these infarcts can go unnoticed by the patient.

Mixed angina and walk-through angina

What differentiates mixed angina from stable angina is that the amount of exercise that is needed to trigger the angina varies considerably (within the same patient) in mixed angina. Patients with stable angina always have symptoms around the same exercise level, however patients with mixed angina can sometimes exercise a lot before symptoms develop and sometimes the symptoms develop with just a little exercise.

Patients with walk-through angina develop angina symptoms early during exercise, however the symptoms go away when they continue to exercise. The phenomenon is paradoxical, and the pathomechanism is unknown.