One of the main challenges in diagnosing heart conditions is the differentiation between stable and unstable angina.
Although unstable angina eventually occurs on top of stable angina -and rarely the patient starts with unstable angina-, the symptoms, signs, prognosis, and even the treatment are different between the two types. The main hallmark of angina is pain or discomfort.
The differentiation between the two types based on the character and duration of pain remains the focus of history taking from patients.
With that said, in this article, we will sort out the main differences between the two types according to their main points of comparison
Cause and pathophysiology
The cause of stable angina is the gradual accumulation of fatty plaques in the arteries’ walls, which is called atherosclerosis.
It results from many factors, including obesity, diabetes, smoking, hypertension, and physical inactivity.
On the other hand, unstable angina results from a sudden drop in the heart’s blood supply either due to severe vasoconstriction of the blood vessels or the formation of a blood clot within the vessel due to the rupture of a plaque, or a combination of both.
Course of the disease
Stable angina is a slowly progressive disease that results from a gradual mechanical obstruction of the coronary blood vessel by fat plaques.
The progression of obstruction takes years to become symptomatic and years to become disabling for the patient.
On the other hand, although it can develop on top of stable, unstable angina usually starts acutely and becomes severe from the start, necessitating intervention. This means that the patient can predict anginal attacks in stable angina, while they are incapable of predicting the onset of unstable angina.
Chest pain
While both stable and unstable angina cause chest pain, the character, duration, and precipitating factors differ. Stable anginal pain is characterized by being:
- Of a short duration with a maximum of 10 minutes.
- Precipitated by effort, emotional excitement, cold weather, or heavy meals.
- Relieved by rest or sublingual nitrates.
- Usually not severe and predictable.
On the other hand, unstable anginal pain is characterized by being:
- Of a duration of more than 10 minutes but usually less than 30 minutes.
- Not related to effort and may occur at rest.
- Not relieved by rest, and the effect of nitrates is not as pronounced as in stable angina.
- Usually severe and unpredictable.
The best way to understand how chest pain differs between the two is to imagine stable angina as a mountain where there is an ascent till it reaches a maximum, then the descent with rest until the pain is relieved. In unstable angina, however, the situation is like a flight of stairs, where the pain keeps getting worse with no apparent relief.
Diagnosis
In the case of stable angina, the mainstay of diagnosis is stress ECG. However, such a test is contraindicated in unstable angina as it can lead to a fatal outcome -owing to the fact that in unstable angina, the demand of the heart is greatly exceeding the supply at rest-. In most cases, the mainline of diagnosis is coronary angiography, where imaging of the coronaries either by MRI or echocardiography can provide enough information regarding the condition of the arteries and the presence of a thrombus or an infarction.
Regarding ECG, the main difference between stable and unstable angina is that while the stable type shows a characteristic ST-segment depression on stress ECG or rest ECG during the attack, unstable angina shows multiple changes, which include ST-segment depression, elevation, or T-wave changes. It is crucial to differentiate between the ST elevation of unstable angina and that of myocardial infarction (heart attack). The main difference is the duration, where the elevation is transient in unstable angina and fixed in myocardial infarction.
Treatment
Treatment of stable and unstable angina is quite similar in some aspects as lifestyle modifications and physical exercise.
Still, they differ in that while medical therapy can be definitive in stable angina. Most cases are well controlled on medical treatment with lifestyle changes, surgical treatment or percutaneous intervention are a must in unstable angina, where medical therapy only acts as a relief for the symptoms and a bridging therapy preserving the heart muscle for as long as possible as well as preventing the progression to myocardial infarction.
Prognosis
The prognosis of a disease is the likely outcome. It can be improved by treatment and worsened by additional risk factors.
The main prognostic markers in both stable and unstable angina include the number of vessels affected, location of affection, and whether it affected the heart’s contractile force -also known as left ventricular function.
Generally speaking, unstable angina has a much worse prognosis than stable angina and a higher risk of myocardial infarction progression. One of the important prognostic indicators besides treatment, is smoking.
It was observed that patients who continue to smoke after their diagnosis have an increased risk of about 50% of developing myocardial infarction than those who cease smoking—appropriate early interventions, whether medically or surgically, have a significant impact on patients’ survival as well.