the preferred initial diagnostic testing is the ecg, which may demonstrate a 12-lead electrocardiogram with diffuse, non-specific, concave ("saddle-shaped"), st-segment elevations in all leads except avr and v1 and pr-segment depression possible in any lead "except avr"; sinus tachycardia, and low-voltage qrs complexes can also be seen if there is subsymptomatic levels of pericardial effusion. the pr depression is often seen early in the process as the thin atria are affected more easily than the ventricles by the inflammatory process of the pericardium.