A 14-year-old male adolescent attended his paediatrician without an appointment due to chest pain in the left anterior hemithorax radiating to the neck. The pain started the previous day, began as mild and has been increasing, and the patient has observed that the discomfort worsens in decubitus and with deep breathing, and improves when he sits up and tilts his trunk forward. He denies fever or other symptoms, and has no medical or surgical history of interest. The physical examination is completely normal; however, the paediatrician performs an electrocardiogram (ECG) and decides, in view of the test findings, to refer the patient to hospital. Before reading on, take a close look at the ECG.

Following the routine reading1, the ECG shows a sinus rhythm at 100 beats per minute. There are no abnormalities in the P wave or PR segment, and the QRS complex presents an axis within the lower left quadrant (between 0 and +90o, being positive in I and aVF) without morphological alterations. So far, we have not detected any unusual data. On analysing the repolarisation, we observed a QTc interval of normal duration, although the presence of negative T waves in leads V3-V6 is striking. We observed a marked decrease in the ST segment in V4 and slightly less in V5, without pathological Q waves or signs of ventricular hypertrophy. Given the patient's clinical and electrocardiographic findings, the paediatrician diagnosed acute pericarditis and referred the patient to hospital.