ECG Rounds Challenging ECG's with explanations.

DIAGNOSIS: Sinus rhythm, left bundle branch block, acute infero-lateral myocardial infarction.

EXPLANATION: P waves with a normal PR interval are evident at a rate of 75. Monophasic complexes with a duration of at least 120 msec are present with the V1 morphology typical of LBBB; a slick downstroke to an early intrinsicoid deflection which has a duration of <60 msec as we have seen in prior examples.
More important from an emergency medicine viewpoint are the marked ST segment elevations noted in leads II, III, aVF, V5, and V6 of 3-5 mm! Note the upward convexity of the ST segments in many of these leads; classic for acute injury. In addition, the T wave axes in leads II, aVF, V5, and V6 are about the same as the QRS axes; these then are primary T wave changes. [The T wave changes secondary to the BBB are expected to be opposite in direction to the QRS]. Note also the clear reciprocal changes in leads I and aVL; essential to confirm the diagnosis of acute infarction.
As I mentioned in a prior example of acute infarction with concomitant RBBB, although BBB in general is traditionally reputed to mask ischemia, most emergency physicians had little trouble making the diagnosis of infarction in this case. LBBB may hide the Q waves but the current of injury is evident in the majority of cases. [Thanks for staying tuned.]
In this patient, a 58 year old female with chest pain, based on the ECG changes, thrombolytics were clearly indicated and were given with a favorable outcome for her.

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