What kind of changes might be seen in reciprocal leads during a STEMI?

During a STEMI (ST-Elevation Myocardial Infarction), reciprocal leads provide essential information regarding the areas of the heart affected by ischemia. In leads that are positioned opposite to the area of acute injury or ischemia, one would typically observe ST segment depression. This occurs because the electrical activity of the heart becomes imbalanced due to the injury in the affected region, resulting in the downward displacement of the ST segment in the reciprocal leads.

For example, if there is ST elevation in the anterior leads due to an anterior wall infarction, corresponding leads in the inferior part of the heart may show ST segment depression, signifying that the electrical activity is being altered due to the ischemic process in the anterior wall. This ST segment depression in reciprocal leads is a crucial diagnostic feature and helps confirm the diagnosis of a STEMI by providing insight into the extent of myocardial damage and the involvement of different coronary territories.