ECG Challenge

ECG Section Editors

Authors: Justin Phan, MD, Callum Cherrett, MD, Rajesh Subbiah, MD

ECG Challenge: A curious device-detected arrhythmia 

Case Presentation


Figure 1. Interval plot of tachycardia episode 


This remote monitoring transmission was received from an 83 year old man with a dual chamber Medtronic (Minneapolis, Minnesota) Azure XT pacemaker. The episode was asymptomatic and the patient had a history of complete atrioventricular block. What does this tracing show?


Multiple choice:

  1. Supraventricular tachycardia and ventricular safety pacing
  2. Ventricular tachycardia and ventricular safety pacing
  3. Supraventricular tachycardia with frequent ventricular ectopic beats
  4. Ventricular tachycardia with frequent ventricular ectopic beats
  5. Sinus tachycardia  

Interval Plot Interpretation

At the beginning of the recording, the atrial events are regular at just below 900ms, suggestive of an atrial-paced rhythm. The ventricular events are irregular, with an alternating pattern of very short-coupled events (<100ms), suggestive of ventricular safety pacing. Frequent ventricular ectopic beats are possible although the short coupling interval makes this unlikely. Prior to the -5s marker, there is an increase in ventricular rate (approximately 320ms) and a slower atrial cycle length is noted (1200-1500ms). Given the greater number of ventricular events compared to atrial events during tachycardia, the most likely diagnosis is ventricular tachycardia (VT).

 Intracardiac Electrogram Interpretation


Figure 2. Intracardiac electrograms of tachycardia. The first row shows the atrial channel, the second row shows the ventricular channel and the third row shows the device marker channel.


At the beginning of the recording, there is an atrial paced rhythm with a cycle length of 860ms. The second and fourth beats show a ventricular sensed event occurring shortly after the atrial paced event, followed by a ventricular paced beat with a short atrio-ventricular interval. This is consistent with ventricular safety pacing.


Subsequently, there is an acceleration in the ventricular cycle length to 320-330ms. There is ventriculoatrial dissociation, with more ventricular events (Vs) than atrial events (Ar / Ab). Intermittent undersensing of atrial events is also noted, however, the overall appearances are consistent with VT. Careful observation of the complexes during VT, shows a sharp spike preceding most of the ventricular signals, which are not generated by the pacemaker (which would have a Vp marker). These spikes are suspicious for pacing spikes from a second device. Termination of the tachycardia occurs spontaneously to an atrial and ventricular paced rhythm.



Clinical history was obtained from the patient after this remote monitoring transmission was received. At this time, the patient was undergoing transcatheter aortic valve implantation. Review of the medical record showed that rapid pacing was performed using a temporary transvenous pacing wire. The possibilities for ventricular safety pacing include premature ventricular complexes or pacing from the temporary pacemaker at a rate of 40 beats per minute, with undersensing by the temporary pacemaker. No further intervention was required and the patient resumed their usual device follow-up schedule.



Remote monitoring is increasingly used in the follow-up of patients with cardiac implantable electronic devices (CIEDs), and has been associated with increased patient satisfaction (1). However, an overly burdensome volume of transmissions has been raised as a significant problem (2), and may lead to diagnostic or management errors. This is particularly true in patients with more than one CIED (3).


This case highlights a scenario where the diagnosis of ventricular tachycardia is relatively simple to recognise, but there are only subtle clues as to the underlying cause. Depending on the structure of the device clinic, it is foreseeable that an incorrect diagnosis could have been made, and triggered inappropriate follow up management (such as a recommendation for medical therapy or upgrade to implantable cardioverter-defibrillator).



In the era of increasing utilization of remote monitoring, this case highlights the importance of careful scrutiny of arrhythmia electrograms to avoid pitfalls in diagnosis. Clinical correlation of recorded events is critical in ensuring appropriate follow up and management.



  1. Lappegård KT, Moe F. Remote Monitoring of CIEDsFor Both Safety, Economy and Convenience?

Int J Environ Res Pu. 2021;19(1):312.

  1. O’Shea CJ, Middeldorp ME, Hendriks JM, Brooks AG, Lau DH, Emami M, et al. Remote Monitoring Alert Burden An Analysis of Transmission in >26,000 Patients. JACC Clin Electrophysiol.


  1. Mendez Zurita F, Alonso Martin C, Diego IR de, Rodriguez Font E, Campos Garcia B, Guerra

Ramos JM, et al. Remote monitoring in a patient with multiple leadless pacemakers. J Arrhythmia.