85 yo M with PMHx of CHF, paroxysmal atrial fibrillation and dual chamber PPM placed for sick sinus syndrome, who presents with lightheadedness, confusion and progressive lethargy x 1 day. At arrival to the ED patient hypotensive 70/30, bradycardic 46 x min, febrile 102 F.
EKG is obtained
Initial labs are remarkable for pH 7,10 HCO3 10 and Lactate of 5, with normal electrolytes
Patient’s pacemaker is set at a rate of 60 and recent interrogation showed no abnormalities.
What is the diagnosis and most likely explanation for this problem?
Dx: Failure to capture
EKG shows low voltage pacing spikes (circles) which are not associated with ventricular activity.
Following initial standard resuscitation measures (fluids, abx, etc.) in the setting of suspected severe sepsis, pacemaker dysfunction was addressed.
CXR showed no evidence of lead displacement or fractures and further pacemaker interrogation showed no problems with output failure or pacemaker sensing.
Problem was thought to be pacemaker’s failure to capture in the setting of metabolic acidemia due to sepsis from urinary source. Patient was temporarily supported with noreepineprhine and IV fluids and pacemaker function normalized once metabolic disturbances were corrected.
Main causes to consider for a malfunctioning pacemaker can be classified as:
1. Problems with sensing
- Undersensing: pacemaker fails to sense native cardiac activity
- Oversensing: artifact signals such as skeletal muscle contractions or lead contact problems are inappropriately recognized as native cardiac activity and pacing is inhibited
2. Problems with pacing:
- Output failure: paced stimulus is not generated (common causes include wire fracture and lead displacement)
- Failure to capture: when pacemaker stimulus does not result in myocardial depolarisation
In a patient who presents with pacemaker malfunction in the setting of sepsis, metabolic acidemia should be considered as a potential underlying factor causing failure of the device to capture. Additional attempts of pacing such as placement of a intravenous pacing wire will likely not be effective until correction this problem.