A 77-year-old woman with longstanding paroxysmal atrial fibrillation (PAF), hypertension, hyperlipidemia, and coronary artery disease presents to your office for follow-up one month after undergoing coronary artery bypass grafting (CABG) with concomitant left atrial maze ablation. She feels well without angina but describes persistent dyspnea on exertion and fatigue since the operation. She denies any palpitations or dizziness consistent with her prior episodes of PAF. She was discharged home on post-operative day 7 on metoprolol succinate 50 mg daily for presumed persistent sinus tachycardia. Her pre- and post-operative ECGs are shown in Figure 1 below (ECGs 1 and 2, respectively):
ECG 2. Post-operative 12-lead ECG, below
Question 1: Does the post-operative ECG represent sinus tachycardia as thought or an arrhythmic process?