ECG Review: RBBB—and Something Else?

By Ken Grauer, MD

Clinical Scenario: The ECG in the Figure was obtained from a 41-year-old woman with chest pain of suspected cardiac etiology. The tracing shows complete RBBB (right bundle branch block). How many additional ECG findings of potential concern can you identify that may be relevant in view of this patient’s clinical history?

Interpretation: As stated, the ECG in the Figure shows complete RBBB, as determined by the presence of an rSR’ pattern in lead V1 and wide terminal S waves in lateral leads I and V6. Findings of potential concern in view of the history of chest pain of suspected cardiac etiology include the following: i) sinus bradycardia and arrhythmia; ii) a deeper than anticipated Q wave in lead aVL; iii) slight ST segment coving in lead aVL; iv) flattening of the ST segment in lead V1 (instead of ST depression), and persistence of deep, symmetric T wave inversion throughout the precordial leads.

Typical bundle branch block produces a pattern of secondary ST segment and T wave changes as a direct consequence of the conduction system defect. Specifically with isolated complete RBBB, the ST segment and T wave are directed opposite to the last QRS deflection in the 3 key leads (leads I, V1, and V6). This normally results in an upright T wave in leads I and V6, and ST segment depression in lead V1. Alteration of this typical pattern is said to reflect a "primary" ST-T wave change, and may be indicative of ischemia and/or infarction superimposed on the underlying bundle branch block. Thus, the usual pattern of ST segment depression in lead V1 has been replaced in this case by a flat ST segment in this lead. While this change is admittedly subtle and non-specific, of much greater concern is the fairly deep and symmetric (ischemic looking) T wave inversion in leads V3 through V6. This is clearly much more extensive T wave inversion than should be anticipated with complete RBBB. While small septal q waves may be seen in the presence of uncomplicated RBBB, the deep Q wave in lead aVL is not anticipated. Slight coving of the ST segment in this lead could reflect a recent acute change. In summary, the combination of findings described above in this 41-year-old woman with chest pain should prompt evaluation to ensure that these changes are not acute.

Dr. Grauer is Professor and Assistant Director, Family Practice Residency Program, University of Florida.