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By Ken Grauer, MD, Professor, Department of Community Health and Family Medicine, University of Florida. Dr. Grauer is the sole proprietor of KG-EKG Press, and publisher of an ECG pocket brain book.
Scenario: The ECG shown above was obtained from a 47-year-old woman with atypical chest pain. Is there more going on in this tracing than just the conduction defect?
Interpretation: The rhythm is sinus tachycardia at a rate of about 110 beats/minute. The PR interval is normal, but the QRS complex is obviously widened in a pattern consistent with complete right bundle branch block (RBBB). Although ST-T wave negativity in leads V1, V2 is an expected accompaniment of complete RBBB, there may be more going on with this patient than simple RBBB. Careful inspection of the tracing reveals the presence of narrow but definite Q waves in each of the inferior leads (II, III, aVF), as well as in lateral precordial leads V4-V6. As opposed to left bundle branch block (LBBB), which typically masks development of new Q waves, it often will be possible to see Q waves with RBBB. This is because RBBB is a terminal conduction defect so that the initial phase of ventricular activation (during which Q waves are written) is relatively unaffected with RBBB. In addition to the inferolateral Q waves seen in the above tracing, there is suggestion of subtle (but possibly real) ST segment coving and early T wave inversion in lead III. Baseline artifact with beat-to-beat variability in QRS morphology makes it difficult to know if we are seeing similar changes in lead aVF. The straightened ST segment in lead II and relatively flat ST-T wave in leads V5, V6 provide no assistance for resolving the question of whether the findings in lead III are likely to represent acute injury. Once again, comparison with prior tracings and clinical correlation will provide the keys to interpretation. In addition, repeating the ECG a short time after the above tracing was obtained may provide invaluable insight as to whether acute changes are evolving in this patient with sinus tachycardia and complete RBBB.