A 28-year-old medical student presents to the clinic complaining of sudden-onset, sharp chest pain of 1 day duration. The pain is retrosternal, radiates to his left trapezius ridge, worsens with deep inspiration, and is partially relieved by sitting up and leaning forward. On examination, a scratchy high-pitched sound is heard at the lower left sternal border during expiration. An electrocardiogram (ECG) is performed. Which of the following ECG findings is most characteristic of this patient's condition?