CardioNerds ECG Challenge #1

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You see this 58 year old man with ischemic cardiomyopathy in clinic.

What’s the rhythm❓


  1. Atrial Tachycardia with VPCs
  2. A-sense V-pace
  3. 3:2 AV Wenckebach

What’s Mode Switching?

The rhythm is atrial tachycardia at 143/min with VPCs, atrial sensing and ventricular pacing with 3:2 AV Wenckebach periodicity.  The mean V rate is 101/min.  The hallmark of Wenckebach is grouped beating.​

With the exception of the 2 VPCs there is grouped beating displayed as 2 paced beats and a pause, repetitively.  Since the P wave axis is abnormal (equivocal in lead II) and every P wave is equidistant and the P wave to ventricular paced interval prolongs until the 3rd P wave does not have a ventricular paced beat following it, this atrial rate exceeds the upper rate of the pacemaker as it is programmed.  The pacemaker is programmed to have Wenckebach A sensing and V pacing until the atrial rate slows.  This is different from mode switching that can be enabled to activate when atrial fibrillation or atrial flutter is encountered.  During mode switching atrial sensing is turned off and the pacing mode is VVI.  It is best not to allow the V pacing rate to be so high when the patient has ischemic cardiomyopathy.

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