A 67-year-old man was admitted to the primary healthcare emergency department due to dizziness. During the physical examination, an irregular heart rhythm was detected, prompting a request for a 12-lead electrocardiogram (ECG). The ECG () revealed a beat-to-beat alternating pattern of right and left bundle branch blocks (RBBB and LBBB) with Mobitz I second-degree atrioventricular (AV) block. The patient was transferred to the hospital emergency department, where two consecutive ECGs were performed. One ECG () showed persistent LBBB with first-degree […]