Ventricular-Paced Rhythms

Pacing with Capture

A ventricularly-paced rhythm will have a ventricular QRS (i.e. wide) following each pacer spike. In the emergency setting, ventricularly-paced rhythms will be the typical rhythm seen with both transcutaneous and transvenous pacing.

Failure to Capture

Failure to Capture occurs when a pacemaker is on but a paced-QRS does not follow the pacer spike. This is usually because the amplitude generated by the pulse generator is too low. For both transcutaneous and transvenous pacing, increase the output. If that doesn't work, the pads or pacemaker leads need to be replaced, especially if pacing has been on for awhile.

Failure to Sense: Oversensing

Failure to Sense occurs when the pacemaker is not sensing the heart's electrical activity properly. When it is oversensing, the pacemaker is not delivering a spike because it's confusing other electrical activity in the body with cardiac activity. This will put the patient in a state of bradycardia if left unchecked.

  • You cannot adjust the sensitivty of transcutaneous pacemakers. Putting the pacemaker in asynchronous mode (i.e. to deliver a pacing spike regardless of the underlying electrical activity) may help.
  • For transvenous pacemakers, decrease the sensitivity (by increasing the mV). Consider replacing the pacemaker unit and cables if the device has been on for a long period of time.

Failure to Sense: Undersensing

When it is undersensing, the pacemaker is delivering a spike despite there being appropriate electrical activity. This could potentially be dangerous and an inapprorpiately fired pacing spike could put the patient into lethal ventricular arrhythmias.

  • You cannot adjust the sensitivty of transcutaneous pacemakers. Check that the pacemaker is not in asynchronous mode.
  • For transvenous pacemakers, increase the sensitivity (by decreasing the mV). Consider replacing the pacemaker unit and cables if the device has been on for a long period of time.
  • In both cases, consider turning off the pacemaker if the patient is in an appropriate rhythm.