Isoelectric PVC Mimicking AV Block!

The above electrocardiogram (ECG) was obtained due to pauses reported on telemetry. Figure A is lead II (simulating telemetry lead configuration) showing what seemed to be an unconducted atrial beat (red arrow), which marched with the underlying sinus P waves, concerning for Mobitz II second degree atrioventricular (AV) block, versus an unconducted premature atrial contraction (PAC), given the slightly different morphology compared to sinus P waves. Figure B, the 12-lead ECG, demonstrates that this complex was in fact an isoelctric premature ventricular contraction (PVC), as seen in other precordial leads (blue arrows). Figure C shows the limb lead pattern of the PVC (green arrows), yielding a – 30° axis, causing it to be isoelctric in lead II, mimicking an unconducted atrial activity on telemetry.