Lyme carditis: Where is the site of the atrioventricular block?

A 23-year-old man presented to an outside hospital with the chief complaint of fatigue and dizzy spells. He was diagnosed with Lyme disease based on the history of a tick bite, the presence of erythema migrans (2 months after the tick bite), and Borrelia IgG and IgM antibodies demonstrated by enzyme-linked immunosorbent assay and western blot findings. The patient specifically denied any history of syncope; however, the conduction system pacing was recommended due to recurrent dizzy spells. After the first electrocardiography (ECG) was taken at admission (Figure 1A and 1B), we decided to perform atropine testing (Figure 1C and 1D). Where do you locate the site of the block in the ECG?