A 78-Year-Old Man Is Brought to the Emergency Department Due

A 78-year-old man is brought to the emergency department due to lightheadedness that began earlier in the day.  This morning, the patient felt unsteady and almost passed out when he tried to get out of bed.  He has not had similar symptoms before and he has had no chest pain or shortness of breath.  He has a history of coronary artery disease requiring percutaneous coronary intervention.  The rhythm strip of the ECG obtained in the emergency department is shown in the exhibit. 
Which of the following is the most likely cause of this patient's current symptoms?

A) Degenerative changes involving the atrioventricular node
B) Degenerative changes involving the sinus node
C) Ectopic electrical foci in left ventricular myocardium
D) Reentrant circuit involving the cavotricuspid isthmus
E) Sporadic depolarization of atrial cardiomyocytes

Correct Answer:

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