Tall T waves may appear within the first minute or hours after coronary occlusion, but more often isoelectric, negative or biphasic T-waves are seen at the presentation.

ST-segment elevation appears within hours after coronary arterial occlusion and lasts for approximately 2 weeks,if reciprocal ST-segment depression is also seen, the infarction is probably extensive.

Abnormal Q waves appears within hours or days after Myocardial infarction and typically persist indefinitely.

Decline in the ST-Segment elevation Occurs at the same time (or after the start) Of T waves inversion. In contrast to acute pericarditis where ST-segment becomes isoelectric before the T-wave becomes inverted.

the ST-Segment finally becomes isoelectric with symmetrical T wave inversion that may last months to years or persist indefinitely. T waves that are persistently negative for More than one Year in leads with Q waves are associated with transmural infarction with fibrosis of entry wall. In contrast, T waves that are positive in leads with Q waves correlate with non-trasmural infarction with viable myocardium within the Wall.

Name of the MIChanges of ECG
Acute Myocardial InfarctionQ waves and ST-segment elevation. Reciprocal ST-segment depression is often observed but is not necessary.
Recent MIQ waves with ischemic T-wave Changes, often inverted. The ST-Segment is typically no longer elevated
Age-indeterminate MIpersistent Q waves without ST-segment elevation or ischemic T-wave Changes.
Acute Myocardial InjuryRegional ST-segment elevation without Q waves.

Marked ST-segment elevation or depression in multiple leads usually indicates very severe ischemia. Conversely, prompt resolution of ST elevation following thrombolytic therapy or PCI is a specific marker of successful perfusion. However, these relationships are not universal, since severe ischemia or even infarction can occur with slight or even absent ST-T Changes.