It is said every clinical diagnosis needs to be substantiated with documented objective evidence .
Probably, the commonest cardiac emergency , that can be diagnosed purely by history is UA.
Yes , unstable angina is a symptom not a disease entity !
By definition UA is
- Any new onset angina of severe grade
- Progressive crescendo angina
- Angina with radiation to new site
- Angina not controlled by nitroglycerine
- Any angina after a PCI /CABG
If you read the definition again, you will realise ECG or enzymes never come into the diagnostic picture .UA can be diagnosed even before one has a look at the ECG ! So, it is too obvious one can diagnose UA irrespective of whatever is recorded in the ECG. Normal ECG is one such possibility.
When a patient is having severe compromise in the blood supply to his / her heart , how on earth , it is possible to have a normal ECG ?
It only tells us, ECG is not a fool proof method to exclude ongoing ischemia . When we know , ECG can miss even a STEMI it is not a big deal it misses a UA.
Apart from the electrical blind spots of conventional 12 lead ECG, following are the other explanations offered for a normal ECG in UA.We know UA occurs with ST depression(Classical ) , T inversion, rarely ST eelvation
So UA can occur with
- Pseudonormalised t waves
- Pseudo normalised ST depression
- Cancellation effect of two opposing subendocadrial ST segment vectors ( As in multiple active plaques PDA and LAD lesion )
- Even Ischemic cascade
Even though UA CAN occur with normal ECG , we are uncomfortable to diagnose UA without documenting ECG changes . We should realise this fact , as missing a diagnosis of UA , just beause the ECG is normal could have very costly consequence !