A 77-year-old white woman presents with multiple episodes of chest discomfort. She describes the discomfort as sharp and occurring in the left breast area, with each episode lasting a few seconds. On previous days she has had a sensation of being weak, accompanied by a hollow feeling in her anterior chest. Her medical history includes atrial fibrillation, hypertension, type 2 diabetes with diabetic neuropathy, and deep venous thrombosis in her left leg. A demand pacemaker was placed in 2001 because of sick sinus syndrome. Physical examination shows: weight, 225 lb; blood pressure, 156/94 mm Hg; respiratory rate, 21 breaths/min; heart rate, 65 beats/min. The heart rhythm is irregular, and there is no murmur or gallop. The abdominal examination is normal. She has trace lower extremity edema. An electrocardiogram (ECG) is obtained (Figure).

How Would You Interpret This ECG?