American Journal of Critical Care. 2002;11: 487-488
A regular feature of the American Journal of Critical Care, the ECG Puzzler addresses ECG interpretation for clinical practice. We welcome letters to the Editors regarding this feature.
Intermittent Conduction Disturbances
By
Mary G. Adams, RN, PhD and
Michele M. Pelter, RN, PhD.
From the School of Nursing, the State University of New York at Buffalo (MGA) and Department of Physiological Nursing, University of California, San Francisco, Calif (MMP).
Scenario: This is a dual lead (leads V1 and V6) ECG strip of a 52-year-old man hospitalized on the cardiac telemetry unit for management of acute coronary syndromes. Upon comparison, the nurse concludes that this ECG strip is similar to the 12-lead ECG obtained after the patient’s admission to the emergency department. The patient denies having pain or symptoms, and his vital signs are stable.
Interpretation: Atrial fibrillation with developing right bundle branch block (RBBB).
Rationale
Atrial fibrillation is one of the most common arrhythmias seen in clinical practice. It is characterized by disorganized electrical activity of the atrium and is recognized by irregular undulations of the baseline. In this strip, there are barely recognizable deflections in the baseline (fine fibrillation); however, atrial fibrillation may be inferred from the irregularly irregular ventricular response rate.
In the first 4 seconds of this strip, the QRS complexes are 0.11 to 0.13 seconds, suggesting incomplete left bundle branch block. Then the QRS complexes become wide and bizarre due to an RBBB. In RBBB, the ventricles are activated successively, in this case from left to right, instead of simultaneously. Although the QRS morphology in V1 is not the typical rSR configuration usually seen in RBBB, ventricular tachycardia is ruled out because the heart rate is too slow and the rhythm remains irregular. Intermittent bundle branch block usually denotes a transition stage before a permanent block develops. The ST-segment deviation seen throughout this strip is the result of abnormal depolarization and, in this case, is not an indication of ischemia. Given that atrial fibrillation and RBBB are chronic, persistent conduction abnormalities in this patient, the goals of therapy are focused on control of the ventricular response rate. In this case, a heart rate of 70 beats per minute requires no specific intervention at this time.
