DIAGNOSIS: Atrial Fibrillation with a rapid ventricular response. Left Bundle Branch Block.

EXPLANATION: This wide complex tachycardia at a rate of 180 bpm is irregularly irregular. There are no visible P waves in an undulating baseline; as we have seen before, only atrial fibrillation can look like this. What about the wide complexes? The following finding is helpful in suggesting LBBB and aberrancy: when the QRS is predominantly negative in V1, a slick downstroke to an early intrinsicoid deflection [as has been discussed previously, the major change in polarity of the QRS] with a duration of 60 msec or less, either with an rS or just a Q wave. Although the V1 morphology supports the diagnosis of atrial fibrillation in this case, the most important finding on the ECG is the irregularly irregular pattern as noted above.

In this 69 year old female who was brought to the Emergency Department because of chest pain and shortness of breath, the rhythm disturbance was felt to be the primary cause of her complaints. She was treated with adenosine without effect, then was given diltiazem with gradual slowing of her rate, improvement in her clinical condition, and eventual resolution of the LBBB.

Editor: Sol Nevins MD FACEP. Faculty, Emergency Medicine Residency, Morristown Memorial Hospital, Morristown, N.J.