Complete Heart Block in a Diabetic Patient with a Preexisting LBBB and Normal Coronaries, Paradoxically Responding to Atropine

We present a case of a complete atrioventricular block (AV block) with different aberrancy patterns during sinus rhythm and escape rhythm. A 66-year-old woman visited our emergency department complaining of sudden onset dizziness and fatigue over the past thirty minutes. Her medical history was remarkable for arterial hypertension, type 2 diabetes mellitus, and hypothyroidism. The patient had a known Left Bundle Branch Block (LBBB) on past ECGs. Upon palpation of peripheral pulse, a measurement of 32 beats per minute was obtained. No other sign of hemodynamic instability was present. A 12-Lead ECG revealed a complete heart block with sparse QRS complexes with a Right Bundle Branch Block (RBBB) morphology. Before the insertion of a temporary transvenous pacemaker, atropine was administered intravenously. Shortly after the administration, the patient's heart rhythm was restored to sinus rhythm (SR) with LBBB. The patient remained hemodynamically stable and in sinus rhythm at the cardiac ICU and was scheduled for implantation of a permanent pacemaker at a specialized tertiary center. Before successful implantation, a coronary angiography revealed normal coronary anatomy with no atherosclerotic lesions.