Cardiac ischemia means that blood flow to the cardiac muscle tissue has decreased, which can lead to poor oxygen supply or hypoxia. Myocardial infarction means that the blood flow is completely cut off, resulting in cellular death or necrosis of the affected part of the heart muscle.
ECG changes associated with myocardial infarction and ischemia can be difficult to differentiate. Generally, ischemia will present with inverted T waves and flat or downsloping ST-segment depression, whereas myocardial infarction will show ST-segment elevation, T wave inversion, and Q waves.
The best way to differentiate acute myocardial infarction (AMI) from ischemia is to look at the changes in multiple leads. AMI will typically cause ST elevation in two or more contiguous leads, while ischemia may only cause ST elevation in one lead. In addition, AMI will usually cause Q waves, while ischemia typically does not.
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