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Can we diagnose unstable angina in a patient with normal ECG ?

Posted Feb 15 2010 9:34am

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 againyou will realise ECG or enzymes never come into the  diagnostic picture .UA can be diagnosed even before one has a look at  the ECG ! Soit 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 ECGfollowing 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

Final message

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 !

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