A 68-year-old man with mild cognitive impairment is started on donepezil 5 mg daily for suspected early Alzheimer disease. His past medical history is significant for hypertension controlled with lisinopril. Two days after initiation, he presents to the emergency department with presyncope, dizziness, and fatigue. Vital signs are: BP 88/54 mmHg, HR 46 bpm, RR 14, temperature 36.8°C, SpO2 99% on room air. Physical examination reveals no acute distress, clear lungs, and regular bradycardic heart sounds. ECG shows sinus bradycardia with a PR interval of 280 ms (baseline PR 160 ms). Troponin I is normal. Recent basic metabolic panel and magnesium are within normal limits. Which of the following mechanisms best accounts for this patient's cardiac findings?

1. A)Increased vagal tone via M2 muscarinic receptor stimulation at the sinoatrial and atrioventricular nodesGABARITO
2. B)Direct inhibition of the L-type calcium channel current in cardiac myocytes
3. C)ACE inhibitor-induced hyperkalemia prolonging the PR interval and slowing conduction
4. D)Donepezil-induced QT prolongation triggering torsades de pointes and hemodynamic compromise
5. E)Acute decompensated heart failure from increased cardiac acetylcholine load