Sudden occurrence of Q waves: missed infarction?

A 61-year-old lady was admitted to the emergency department because of atypical chest pain lasting for several days. Her ECG on admission is shown in figure 1. After cardiac troponin level was found to be normal, she was discharged. Because she was a smoker and had a positive family history for coronary artery disease, an exercise stress test (EST) was scheduled some days later. Her ECG obtained immediately before the EST is shown in figure 2. (1.) What happened in between the registration of the two ECGs, and (2.) what should be done? Explanatory answers