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The correct choice is ST depression. In the context of a myocardial infarction, reciprocal changes are alterations in the ECG that occur in a lead that observes the heart from a different angle than the lead directly affected by the infarction. When one area of the heart is experiencing ST elevation due to ischemia or infarction, there are usually reciprocal changes produced in areas of the heart that are not directly involved.

Specifically, ST depression often appears in the leads that are opposite to the infarcted area. This is indicative of ischemia in those regions as well, reflecting the heart's response to the disturbance in blood flow. When a segment of the myocardium is not getting enough blood supply and sustains damage, the physiological response may cause depression of the ST segment in leads that view the heart from an opposite angle, making it a key features for diagnosing myocardial infarctions.

The other options relate to different types of ECG changes that may occur due to different conditions; however, they do not signify the reciprocal change that specifically correlates with an area opposite to an infarct. Widened QRS complexes can indicate conduction disturbances, tall pointy T waves are associated with hyperkalemia, and ST elevation itself is indicative of an acute myocardial infarction