When a patient comes with angina at rest , it could mean two things .Either a STEMI or an NSTEMI .This , we can diagnose only after seeing the ECG .
Can we differentiate these two by the character of chest pain alone ?
Very tough task isn’t ? But there are some definite clues .
Infarct pain
- Is mostly sudden .
- Likely to be crescendo , lasts more than 20-30 minutes .
- Fails to get relived by rest or even Nitrites.
- Sweating due to sympathetic activation is more pronounced.
Unstable angina
- Is rarely sudden .Often has a pro-drome.
- UA is mostly precipitated by an increased demand situation or a stress.
- It has a typical waxing and waning pattern . Rarely assume a true crescendo character as myocytes does not necrose (Just threaten to die !)
- The chest pain radiation to shoulder is less conspicuous , instead it tends to reach the jaw area .(* An observation,Is it something to do with multi-vessel CAD in UA ?)
Mechanism of the difference : Epicardial vs Endocardial angina
The pain of UA is due to subtotal occlusion and endocardial ischemia , while STEMI is sudden total occlusion and the resultant transmural ischemia . In STEMI epicardial surface is always involved (Which lifts the ST segment in ECG .).We know epicardium is same as visceral layer of pericardium which is well innervated .Hence pain of STEMI acquires more of somatic character than a predominately visceral type pain that occurs with UA/NSTEMI where epicardial ischemia is absent.
Clinical importance
The demarcation between unstable angina and Infarct pain becomes vital when we calculate the time window for thrombolysing STEMI .Many of them have a phase of pre infarction angina which is a type of unstable angina. If we mistake it for Infarct pain then one may falsely calculate a prolonged time window and deny re-perfusion therapy.
Post -amble
It is tricky issue to differentiate the chest pain of STEMI and NSTEMI .A significant overlap can occur in real coronary care scenario . We know chest pain that occurs in both pre and post infarct phase is considered as unstable angina .(With infarct pain sandwiched between them!) Hence differentiating them may even be termed as futile.
Still,clinical cardiology can be made fascinating by indulging in such exercise !
Dr.S.Venkatesan MD 