By Ken Grauer, MD
Figure. 12-lead ECG and lead II rhythm strip obtained
from a 67-year-old man with pulmonary disease.
Clinical Scenario: The 12-lead ECG and rhythm strip shown in the Figure was obtained from a 67-year-old man with longstanding pulmonary disease who was admitted to the hospital for an exacerbation of this underlying condition. Computerized interpretation of the ECG seen here described the rhythm as "atrial fibrillation with a rapid ventricular response with a number of aberrantly conducted beats." Do you agree with this computerized interpretation?
Interpretation: Computerized ECG interpretations must always be overread by a physician. The purpose of such overreading is to ensure accuracy of the ECG interpretation. As a rule, computerized ECG interpretation systems are exceedingly accurate in measuring intervals, calculating heart rate and axis, and assessment of normal tracings. They are much less accurate in interpretation of the cardiac rhythm when the mechanism is not sinus.
The tracing in the Figure is replete with baseline artifact. This most likely is a result of altered respiration from acute exacerbation of the patient’s underlying pulmonary disease. Unfortunately, little definitive information can be derived from the Lead II rhythm strip other than recognition that the rhythm is not regular, especially toward the latter part of the tracing. Nevertheless, near regularity of the rhythm at the beginning of this rhythm strip (at a rate just over 100/minute) and consistent presence of an upright deflection preceding most QRS complexes suggests that the computerized interpretation is wrong, and that the underlying rhythm is not atrial fibrillation. The most helpful clues leading to the etiology of the rhythm lie with the history (longstanding pulmonary disease) and with focusing attention to other parts of this 12-lead tracing, particularly to simultaneously recorded leads V4, V5, and V6. Baseline artifact is much less apparent in these 3 leads. This allows more accurate assessment of the rhythm, and suggests that the underlying irregularity is due either to the presence of multiple premature atrial contractions (PACs), or more likely multifocal atrial tachycardia (MAT) in view of this patient’s longstanding pulmonary disease (dots in the Figure between leads V4-V5 highlight the timing of several different looking P waves). Occasional QRS widening is most probably the result of aberrantly conducted PACs (the T waves are peaked immediately preceding the wide QRS in leads V3 and V6), although occasional ventricular ectopy cannot be excluded. A repeat ECG on this patient was of much better quality and confirmed MAT as the rhythm diagnosis.
Dr. Grauer, Professor and Assistant Director, Family Practice Residency Program, University of Florida, Gainesville, is on the Editorial Board of Emergency Medicine Alert.