A patient in their late 80s presents to the urgent care with 2 episodes of near syncope each day for the past 3 days. The episodes are not triggered by activity, standing, or anything else he can identify. He denies palpitations, chest pain, SOB, leg swelling or pain, fever, cough, or other complaints.


Vital signs are normal. The physical exam is also normal.

An ECG is done:

Credit: Brady Pregerson, MD

What is the most likely cause of the ECG findings in this patient?