A 68-year-old man from Delhi presents to the emergency department with acute-onset chest pain radiating to the left arm for the past 2 hours. Blood pressure is 145/92 mmHg, heart rate 102/min, and respiratory rate 20/min. His 12-lead ECG shows ST elevation of 3 mm in leads II, III, and aVF, with reciprocal ST depression in leads I and aVL. The PR interval measures 0.18 seconds, QRS duration 0.08 seconds, and QT interval 0.38 seconds. Which of the following ECG intervals or segments is most significantly abnormal and indicates acute myocardial injury?