Terminology 317 - Pacemaker Rhythms

Part 1

• Oversensing occurs when the device interprets non-cardiac sources of energy as being cardiac. This results in the device not turning on when it should.
• Undersensing results in a device that doesn’t know when to turn off. This may result in pacemaker competition, a potentially dangerous situation (as discussed earlier).
• Capture refers to when the device delivers an electrical impulse of sufficient strength to result in depolarization. The waveform immediately follows the pacing spike.
• Loss or Failure to Capture may occur for a number of reasons, but commonly occurs when the generator is unable to deliver a sufficient amount of energy to cause depolarization. This may be due to the age of the batteries. This will result in a spike with no corresponding depolarization or a delayed depolarization of unusual morphology.

Part 2

Capture – notice the waveform immediately following the pacing spike.

Loss of Capture – notice the 4th and 7th complex morphology is different and the waveform does not immediately follow the pacing spike.