An interesting rhythm strip. What is this rhythm?

By Magnus Nossen, from NorwayI was shown this print out of a rhythm strip from a patient on telemetry. I was asked what ' s going on? There are four leads shown (II, dV2, V1 and V5). The three images beneath one and other are consecutive rhythm strips each 10 seconds long. The patient was on telemetry due to acute MI. Can you correctly describe what ' s going on in this interesting rhythm strip?The tracing begins with sinus rhythm with a right bundle branch block pattern. P-waves are not easily discerned in the first beats, but they are present superimposed on the T wave of the preceding QRS. The P wave superimposed on top of the third visible T wave does not conduct (therefore, a pause follows that P-wave). The following QRS can clearly be seen with a preceding sinus P-wave, and the next beats shows clear second degree AV block type I (Wenckebach) with a gradual prolongation of the PR interval. The P-waves can be seen " moving " closer and closer to and encroaching on the T-wave making the T waves look more pointy.Then after three sinus beats conducted fully over the AV node a beat with a different QRS morphology compared to both the preceding and following beats takes place. This beat is a fusion beat from the supraventricular sinus beat and an emerging AIVR. The AIVR then gradually takes over and the sinus P-waves again becomes more apparent as theisorhythmic AV dissociation is ongoing. Eventually sinus P waves are not visible. (buried in the QRS). This cont...
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