Paced Rhythms

This section will be entirely related to rhythms related to pacemakers, including both the normal and abnormal behaviours of these devices.

Topics to be covered:

• Indications for the implantation of pacemakers

• An overview of how pacemakers work, including discussions on:

  • Different type of pacemaker technology such as traditional transvenous pacemakers and the newer leadless pacemakers. 

  • Different lead configurations, such as: single-chamber, dual-chamber, biventricular (cardiac resynchronization therapy), and physiologic conduction system pacing.

  • An overview of pacing modes and important pacemaker intervals.

• ECG characteristics of the paced rhythm. This includes a look into the pacing spike and how it differs in unipolar versus bipolar leads. We will also cover the appearance of a paced beat (with or without physiologic pacing) as well as fusion and pseudofusion beats, as well as expected secondary ST-T changes. We will look into how to localize the origin of the paced beat, and how to identify the underlying atrial rhythm.

• We will look into ECG examples of normal pacing function, such as:

  • ECGs of various different pacing modes (asynchronous modes, inhibited modes, triggered modes, and rate adaptive modes).

  • Electronic Wenckebach.

  • Hysteresis.

  • Dynamic AV delay.

  • Ventricular safety pacing.

  • Post-PVC extension of PVARP.

• We will also cover mechanisms and ECG manifestations of abnormal pacemaker function, such as:

  • Failure to sense (i.e. oversensing or undersensing).

  • Failure to pace (i.e. output failure versus non-capture).

  • Sensor-induced tachcyardia.

  • Pacemaker-mediated tachycardia, and its risk factors.

  • Battery depletion and runaway pacemaker.

  • Lead displacement dysrhythmia.

  • Pacemaker syndrome.