The correct interpretation is an atrial tachycardia with 2:1 ventricular conduction. The ventricular rate is 87 beats/min (690 ms), and the atrial rate is 174 beats/min (345 ms). Two P waves are present for each QRS, which excludes a first-degree atrioventricular block. The less obvious P wave is found in the terminal portion of the QRS complex. (You may convince yourself of this by using calipers to measure the R-R interval, dividing that measurement in half, and then applying it to the ECG. You will see the P waves march through without changing the ventricular response.)
A nonspecific intraventricular conduction delay is also present. The QRS duration is > 100 ms; however, the criteria for right or left bundle branch block are absent.
A thorough investigation revealed that the clerk formulating the herbs for the tea was using, among other things, dried foxglove. Foxglove has been used as a remedy for lethargy in the elderly, presumably because it inadvertently treats symptoms of congestive heart failure. It was the tea consumption that accounted for the presence of digoxin in the patient’s blood. (Recall that there is a substantial overlap between therapeutic and toxic serum concentrations of digoxin.) When the patient stopped consuming the tea, his atrial tachycardia resolved, as did his symptoms.