A 68-year-old man with severe COPD on home oxygen is admitted with acute exacerbation presenting with dyspnea, productive cough, and irregular palpitations. His ECG shows heart rate 88 bpm with irregular R-R intervals. The feature marked **A** in the diagram—at least three distinct P wave morphologies within a single lead reflecting shifting pacemaker origins between the sinoatrial node and multiple ectopic atrial foci—is the critical diagnostic finding. Which of the following best describes the pathophysiologic mechanism underlying this ECG pattern in the context of COPD exacerbation?