Interpretation:
Rate: 114/minute
Rhythm: the overall rhythm is irregularly irregular – either atrial fibrillation…or, the other irregularly irregular rhythm. Multifocal Atrial Tachycardia (MAT).
Intervals: PR seems to vary where it can be easily measured
Chamber enlargement: none
Ischemia and infarct patterns: none

The rhythm is multifocal atrial tachycardia (MAT) as there are definite P waves discernible in front of some QRS complexes, of varying morphology and PR interval.

The wide-complex beat seen slightly after the middle of this tracing is most likely an aberrantly conducted supraventricular beat based on Ashman’s prediction. Notice the long R-R interval followed by a short R-R interval resulting in a RBBB morphology wide-complex (notice the tall R-wave in V1).

See also: EKG of the Week #42, and
EKG Discussion of Ashman beats

This EKG is common in the ED and worth being comfortable with so that young healthy patients are not inadvertently thrombolysed or referred to interventional cardiology. While there is noticeable ST-segment elevation in lead V_3-5 this pattern is consistent with Benign Early Repolarization.

Notice that the ST-segment elevation occurs in association with large amplitude QRS complexes in the chest leads, and often has a notched, or “fishhook”, appearance at the J point (apparent here in V_4-5).

Another corroborating find in early repolarization is an early R/S transition. Usually, the R/S ratio progresses across the chest leads (V₁ – V₆) with the transition, or R/S closest to 1, occurring in V_3-4. In early repolarization the R/S transition often occurs before V₃ as in this example.

Finally notice that there are no reciprocal changes noted in other leads as would typically be present with ST-segment elevation associated with an acute MI.

Each of these findings, particularly in young healthy men with an appropriately atypical chest pain complaint, suggests benign early repolarization.