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
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 .