What is the classification of an ECG tracing showing an irregular rhythm with QRS duration greater than 0.12 seconds?

The classification of an ECG tracing displaying an irregular rhythm with a QRS duration greater than 0.12 seconds is indicative of a scenario that typically points toward ventricular ectopy. A QRS duration exceeding 0.12 seconds suggests the action potential is being conducted through the ventricles in an abnormal manner, often seen with conditions like premature ventricular contractions (PVCs).

PVCs are characterized by arise early in the heart cycle, producing a wider and atypical QRS complex compared to the normal ventricular conduction pathway. This results in irregularities within the rhythm, given that the PVC interrupts the typical pattern due to its earlier onset in the cardiac cycle. The QRS complex is broader because the ventricles are depolarized in a manner that differs from the usual conduction pathways.

While atrial fibrillation shows an irregular rhythm, it typically has a narrow QRS, and normal sinus rhythm doesn’t align with the criteria since it would have your typical narrow QRS duration and a regular pattern. Ventricular tachycardia also features wide QRS complexes but typically presents with a more regular rhythm compared to what is described in the question. Thus, the description aligns best with a premature ventricular contraction.