Angina pectoris , classically occur on exertion and gets relieved on rest .This is called typical chronic stable angina as described by Heberden (CSA ) . Unstable angina(UA), the term originally described by Noble O Fowler in early 1970s. ( Also being referred as intermediate coronary syndrome , preinfarction angina etc).The definition for unstable angina has evolved over the years and currently refers to .
1.All new onset angina of any degree* Some include severe angina only ! New onset angina of very mild degree on exertion could be the onset of the first episode of stable angina.
2.Rest angina of more than >30 mts not relieved by taking sublingual nitroglycerine.
3.All Post MI angina
4.Any angina in patients who have been stented by PCI.How to recognise a patient who is shifting from stable angina to UA ? UA is to be suspected when a patient develops. 5.More frequent episodes than usual 6.Angina occurring at lesser level of exertion than before 7.Angina radiating to new site ( Example : Chest pain radiating to jaw rather than to the usual left arm or vice versa)
Why the first episode of angina is given a special status and often considered critica ?Angina is the clinical expression of myocardial ischemia.The course of the first episode of angina , can not be predicted.It could be a the beginning of a chronic disease process, or it could be a progressive coronary occlusion as in unstable angina /NSTMEI , or the onset of even a STEMI. In contrast a patient with chronic stable angina has a predictable chest pain , at a particular level of exertion, radiation to same site, same character, and the patient knows for sure the pain would promptly dissappear when he takes rest or nitroglycerine tablets.
What is the underlying pathology in UA ?Generally it is very rare for a stable plaque to produce a serious episode of unstable angina .It requires an unstable plaque* to precipitate an unstable angina ! Unstable plaque refers to any plaque which is eroded, fissured, ruptured or hanging eccentrically , with an active thrombus.
What is the significance of post PCI angina?It is an irony, any angina following PCI is to be considered unstable as sudden occlusion of stent is quiet common.This is a paradox of sorts as one would wonder in a patient with CSA who undergoes PCI with stenting of left anterior descending coronary artery (LAD) all his subsequent episodes of angina will be labelled as UA even if a stable angina occur in his other coronary artery.And these patients would go for early invasive approach and potentially inappropriate interventions even if they are at low risk !
Is all angina at rest can be termed as unstable angina ?No, but many times , rather most of the times cardiologist believe all rest angina to be unstable.
What are the situations where stable angina can occur at rest?An episode of angina during mental stress, or post prandial* state are very common in patients with CSA. This gets relieved after the stress. Some times patients with CSA during episodes of fever may get angina at rest .These are considered variants of stable angina. Post prandial angina , may be considered by some as unstable
How often a diagnostic confusion occur between CSA and UA ?Generally, this issue is rarely addressed in cardiology literature , for the simple reason it is never considered an issue at all ! According to Canadian cardiovascular society grade 4 stable angina is almost similar to unstable angina , as it denotes angina occurs with minimal effort or even at rest. In fact CCSC grade 4 should be termed as UA.
Can ECG be useful to identify stable angina from unstable angina ?ECG will some times come to our rescue when one is confused between stable and unstable angina even though resting ST depression can occur in both stable and unstable angina . Statistically , if ST depression is noted during an episode of angina it is more likely to be UA rather than CSA. . Apart from ECG , Troponin T or I levels may be elevated in some of the patients with unstable angina. Rarely stable angina can also show elevated troponin.
So differentiation between, stable and unstable angina even though appear simple and straight forward, it requires a diligent appraisal of history , physical examination (Aortic stenosis /HCM may cause stable angina) and ECG, enzyme evaluation.
In patients with systemic hypertension and LVH or cardiomyopathy resting ST depression may not indicate UA
Final messageIn any coronary care unit , admissions with initial diagnosis of ACS/UA/NSTEMI , subsequently turn out to be simple stable coronary artery disese . This error happens because the chest pain or ECG changes are aggravated by non cardiac factors like a mental stress or a post operative stress or fever etc. There could be another school of thought, that is to err on the side of safety, and manage all rest angina as UA .But the hazards of unwarranted therapy might exceed the risks of leaving these patients alone. In this context ,there is a need for a new definition for unstable angina . One ideal version could be . . .
- Any angina , of any degree which is caused mainly by the supply side defect (By a acute thrombotic /disruptive plaque occluding the coronary lumen with a imminent danger of myocardial infarction is to termed as real UA.
- All post MI and post PCI angina are unstable angina
- Rest angina which occurs due to increased demand situations need not be labelled as unstable angina for the simple reason there is neither an active plaque nor a fresh thrombus likely in these patients. They rarely develop recurrent angina or MI . The mechanism of angina at rest here is most often due to a tachycardia and resultant increase in MVO2 .(myocardial oxygen consumption) .Currently they are called as secondary unstable angina.In fact , anti thrombotic drugs are misused in these situations as they satisfy the criteria of UA/NSTEMI.