A 65-year-old man with a history of atrial fibrillation and normal renal function is prescribed digoxin 0.25 mg daily for rate control after inadequate response to metoprolol. His serum digoxin level three days ago was 1.5 ng/mL (therapeutic range 0.5-2.0 ng/mL) and serum potassium was 3.8 mEq/L. Hydrochlorothiazide 25 mg daily is then initiated for newly diagnosed hypertension. He presents three days later with nausea, vomiting, and yellow-green visual disturbances. Vital signs show blood pressure 138/86 mmHg, heart rate 140 bpm with regular rhythm, and respiratory rate 16/min. Physical examination is otherwise unremarkable. An ECG demonstrates a regular ventricular rate of 140 bpm with AV dissociation and no P waves visible. Laboratory studies reveal serum potassium 2.9 mEq/L, serum creatinine 0.9 mg/dL, and serum magnesium 1.6 mg/dL (normal 1.8-2.4 mg/dL). Which of the following best explains his clinical presentation?

1. A)Acute coronary syndrome with secondary arrhythmia and demand ischemia from tachycardia
2. B)Progression of atrial fibrillation to atrial flutter with 1:1 atrioventricular conduction
3. C)Digoxin toxicity secondary to thiazide-induced hypokalemia and hypomagnesemia increasing myocardial sensitivityGABARITO
4. D)Digoxin-induced second-degree atrioventricular block with accelerated junctional escape rhythm
5. E)Thiazide diuretic-induced hypokalemia causing increased automaticity without digoxin toxicity