ECG Review-LBBB—and What Else Unusual?

Clinical Scenario: The ECG shown in the Figure was obtained from a 92-year-old man with known left bundle branch block (LBBB), coronary disease, and renal failure. Can you identify at least three unusual features about this ECG and the LBBB pattern it represents? What clinical conditions do these atypical features suggest?

Interpretation: The ventricular rhythm is regular at a rate of 80/minute. The QRS complex is obviously widened, and generally resembles the pattern of LBBB. However, sinus P waves are nowhere to be found on this tracing. In view of the history (LBBB pattern on previous ECGs plus known coronary disease and renal failure), the cardiac rhythm is uncertain.

Features about the ECG pattern shown in the Figure that are distinctly atypical for LBBB include the following: 1) lack of a monophasic, upright complex in lead I; 2) the presence of a Q wave and ever-so-subtle ST elevation, and T wave inversion in lead aVL; and 3) the appearance of T wave peaking (albeit with admittedly small T wave amplitude) in each of the inferior leads and in lead V4. Several possibilities may account for these unusual findings, all of which require clinical correlation, comparison with prior ECGs, and laboratory assessment for confirmation. Unfortunately, old tracings were not available on this patient. Serum creatinine was elevated, and serum potassium was 7.6 mEq/L at the time this tracing was recorded.

Hyperkalemia could be accounting for all of the findings described for this tracing, which in this case would mean a junctional or sinoventricular rhythm that occurs in association with QRS widening and T wave peaking. Alternatively, the Q wave and subtle ST-T wave findings in lead aVL could reflect infarction of uncertain age that occurs in the setting of a junctional rhythm and LBBB pattern. A final possibility is that this rhythm could represent accelerated idioventricular rhythm (AIVR), as determined by the presence of QRS widening, a rate of 80/minute, and lack of atrial activity.