NBRC Sleep Disorders Specialty (SDS) Practice Exam 2025 - Free SDS Practice Questions and Study Guide

A multi-focal PVC (premature ventricular contraction) tracing is characterized by having different morphologies of the QRS complexes due to the ectopic foci in different locations within the ventricles. This variation can lead to negative wide QRS deflections being observed on the ECG. The presence of multiple shapes of the QRS complex indicates that the PVCs are originating from various parts of the ventricular myocardium, which is a hallmark of multi-focal PVCs. Therefore, identifying these wide QRS deflections as negative confirms their multi-focal nature.

In contrast, the other options describe characteristics that are not consistent with multi-focal PVCs. For example, a positive narrow QRS deflection typically indicates a normal conduction system and is more associated with supraventricular beats rather than the ectopic origins of PVCs. A uniform QRS complex would suggest that the PVCs are arising from the same ectopic focus, which does not reflect the multi-focal aspect. Lastly, while irregular heart rhythm can occur with PVCs, it does not specifically define the multi-focal nature nor differentiate it from unifocal PVCs. The primary feature that stands out is the negative wide QRS deflections resulting from varying ectopic foci.