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Less discussed issues in coronary care : Preinfarction angina vs Acute MI – problems in estimating Time window in STEMI

Posted Dec 29 2009 11:58pm

Acute MI is a major medical emergency encountered in ER . Prompt adminstration of thrombolytic agents or rapid   triaging for a  primary PCI   may be required . The whole concept of management of STEMI  revolves around time as a therapeutic   target .Every minute counts . The beneficial effects of  reperfusion   and the resultant  myocardial salvage  rapidly declines over time . Hence ,  the symptom to door time  remains the ultimate determinant of  outcome in most situations.

So , estimating the  time window of  ”Symptom to door time “ becomes an all important parameter. This is often done by paramedics .

The apparently  simple  job  measurement of time window  can be  misleading at times especially in elderly, diabetic and alcohol abusers .

When  a patient  says he has chest pain since yesterday straightaway he is excluded from reperfusion strategies as 12 hours  would have elapsed

When a patient  describes  chest  pain since two days , but  more intense  only since today morning what does it imply ?

  • The first episode of pain could  either  preinfarction angina or infarct
  • The second episode of pain could again be the continuation of same  angina or conversion of that angina into infarct

So ,  calculating the time window  when a  patient has recurrent episodes of angina prior to an MI is a real difficult issue.For the benefit of doubt, we have to take the last episode of chest pain  which was continuous and more severe as the infarct pain.

How does ECG help to time STEMI ?

When it is difficult  , to differentiate pre infarction angina from infarct pain, the ECG may give  useful clues to time the STEMI.

  • Degree  ST elevation
  • T wave inversion
  • Q waves

Among the  above three ,T wave inversion is most useful to time an infarct. If T wave begins to invert, it can generally assumed the acute  infarct process is  almost complete . Q waves are less reliable  to time a acute MI as ischemic stunning can in the  very early phase of STEMI   inscribe a q wave over the infarct territory.

How will you time a STEMI in silent MI ?

There is no symptom to door time in patients with silent MI . Many do not even reach the door , for the simple reason there is no symptom that drives them to hospital. Those who are refered  have vague non cardiac symptoms and incidental ECG  which shows STEMI like changes. Here , the decision to thrombolyse is taken entirely on the basis of ECG *finding .

Note : Cardiac enzymes are used only to diagnose a STEMI.The enzyme levels are not iseful to estimate the time window .

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