This Evaluation Is a Heart-stopper

ANSWER

The correct interpretation includes normal sinus rhythm with left-axis deviation, a right bundle branch block (RBBB), and a left anterior fascicular block (LAFB).

Normal sinus rhythm is evidenced by a P for every QRS and a QRS for every P, with a consistent PR interval and a rate between 60 and 100 beats/min.

A left-axis deviation is indicated by an R-wave axis of –48°, which is less than the upper limit of normal (–30°).

Criteria for an RBBB include a QRS duration ≥ 120 ms with an RSR’ complex in lead V₁. A terminal broad S wave in lead I, often seen with RBBB, is not evident in this ECG.

Finally, the criteria for LAFB include S waves > R waves in leads I, II, and aVF, which are well illustrated in this ECG. The combination of an RBBB and an LAFB is consistent with bifascicular block and places the patient at increased risk for complete heart block.