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By Ken Grauer, MD
Figure. ECG obtained from a 55-year-old man with heart failure and emphysema. Do you agree with the computerized interpretation?
Clinical Scenario: The computerized interpretation for the ECG in the Figure read, "Atrial fibrillation with PVCs (premature ventricular contractions)." Do you agree?
Interpretation/Answer: The rhythm is rapid and irregularly irregular. However, it is not atrial fibrillation. Although not readily apparent in many leads, P waves are indeed present. The rhythm strip at the bottom of this tracing emphasizes the importance of assessing an adequate number of beats before deciding on the true nature of the rhythm. Even in a lead II monitoring lead (as shown here), P waves are not always apparent in all parts of the tracing.
Instead, overview of the entire rhythm strip is needed to confirm the presence of multiple P-wave shapes throughout the tracing. The rhythm is therefore multifocal atrial tachycardia (MAT), supported by the information that this patient has emphysema. The two widened complexes in lead V1 (beats X, X’-corresponding to beats Y, Y’ in the rhythm strip) almost certainly are not PVCs. Instead, these beats appear to be early occurring supraventricular impulses that are conducted with aberration. The rSR’ pattern with a taller right rabbit ear’ in lead V1 is consistent with a right bundle-branch block (RBBB) morphology that is the most common form of aberrant conduction.
In further support of our impression that these beats are conducted aberrantly, supraventricular impulses rather than PVCs is the apparent finding of a premature P wave preceding beat X in lead V1—despite the artifact present in this lead, the preceding T wave looks especially peaked and pointed—and the underlying rhythm itself. The rapid ventricular response of the MAT rhythm seen here predisposes to the occurrence of multiple early beats, some of which are likely to occur during the relative refractory period.
Dr. Grauer, Professor and Associate Director, Family Practice Residency Program, Department of Community Health and Family Medicine, College of Medicine, University of Florida, Gainesville, is on the Editorial Board of Emergency Medicine Alert.