CRM9,10: Device clinic, Troubleshooting Flashcards
What class and level of evidence for permanent pacemaker implant in complete AV block post acute MI
Class 3, Level C
-Reversible cause so don’t implant
-Use temporary pacing instead
Why do you look at lead impedance?
To check lead integrity:
-Conduction
-Insulation
-Fixation
What would indicate that CRT device is not working?
-BBB
-Heart failure symptoms:
-ankle swelling, coughing, SOB
Systematic approach to troubleshooting
-Does problem involve atrium or ventricle?
-Sensing malfunction? undersensing or oversensing?
-Pacing malfunction? loss/failure to capture, loss/failure to output pacing spike?
-Pseudo-malfunction? poor programming, reset, battery depletion, pseudo-fusion/fusion?
What is undersensing?
-When intrinsic P or R wave is not sensed
-Red arrows = R waves not sensed
-First 2 pacing spikes don’t capture because they fall in refractory periods
Causes of undersensing
-Poorly programmed sensitivity
-Change in intrinsic electrogram (sinus rhythm P waves to atrial fibrillation F waves)
-Lead failure (conduction or insulation) - reduction or loss of sensed electrogram
How to manage undersensing?
-Review patient history/ECG/drugs/ electrograms
-Measure intrinsic signals, thresholds and impedance
-Check that programming of sensing is appropriate
-Chest x ray if impedance and other lead integrity tests indicate a lead/connector issue
-Re-intervention if system failure
What is oversensing?
-Sensing of inappropriate signal causing ‘loss’ of output
-Something other P wave or R wave is sensed
-Pacemaker does not emit pacing output to atrium or ventricle
-Oversensing leads to underpacing
Causes of oversensing
-Oversensing of myopotentials, intracardiac signals (T waves and farfield P/R waves), or electromagnetic interference
Lead failure:
-insulation break (myopotentials sensed near the break)
-conductor fracture (causing electrical artefact)
-Connector/connector block issues causing electrical artefact
What can cause lead voltage to change?
-Movement of lead
-Fibrosis due to MI
What causes impedance to increase and decrease?
-Fracture of conductor causes increase
-Fracture of insulation causes decrease
How to assess oversensing?
-Does oversensing occur during activity?
-Provocative manoeuvres - arm moving, stretching, pushing
-Have telemetry while patient uses equipment that might cause oversensing
-Measure pacing threshold and lead impedance
How to manage oversensing?
If oversensing is due to programming of sensitivity:
-Reprogram sensitivity, PVARP, polarity
If oversensing is due to lead/connector issue:
-Chest x ray to inspect leads
-Consider re-intervention
Why do ICDs have sensing that degrades?
-Helps to pick up VF
-Picks up big and small complexes
What is failure to capture?
-Output pulse is not enough to capture the myocardium
-Threshold has not been programmed high enough
-No evidence of depolarisation after pacing artefact
What can fix failure to capture?
-Autocapture
Causes of failure to capture
-Battery depletion
-Low output caused by incorrect programming
-Poor connection to connector block/connector issues
-Lead dislodgement
-Lead maturation causing threshold rise
-Effects of drug causing threshold rise
-Rare causes - electrolyte imbalance/MI
How to manage loss of capture?
-Measure intrinsic signals, impedance and thresholds
-Increase pacing output if you can - consider battery life and stimulation of diaphragm/phrenic nerve
-Chest x ray if needed
-Consider re-intervention
What is failure to output?
-Impulses are generated but not transferred to myocardium
-Impulses are not generated
-Pacemaker artefacts not seen on ECG
-No spike and no depolarisation
Causes of failure to output?
-Battery depletion
-Poor connector at connector block
-Lead failure
-Pacemaker malfunction - rare
How to manage failure to output?
-Interrogate to show battery life - magnet rate
-Measure impedance
-Measure stimulation threshold
-Failure to output - verify all lead connections
-Chest x ray may help
-Consider re-intervention to look at connections/to replace lead or device
What does this image show?
Failure to output
What does this image show?
Loss of capture
What is pseudo-malfunction?
-When something looks abnormal but isn’t
-Normal pacemaker function
What is pseudo-fusion?
-Pacemaker output falls on an intrinsic event
-Refractory so no depolarisation due to paced output
-All depolarisation is intrinsic
What is true fusion?
-Pacemaker output falls at the start of intrinsic event
-Myocardial depolarisation wave from paced chamber combines and fuses with intrinsic beat
What does this image show?
Normal upper rate behaviour
-Wenckebach upper rate behaviour sensed AV delay extends until TARP is reached
-Then sensed P wave falls into TARP and is counted as ‘retrograde P wave’
-Not tracked so no V pacing spike generated
What can cause electrical reset? (device reverts to back up or factory settings)
-Electromagnetic interference
-Cold
-Electrocautery
-Defibrillation
What is battery depletion?
-When battery reverts to an end of life mode (e.g. VVI unipolar)
Symptoms due to malfunctions
-Dyspnoea
-Fatigue
-Dizziness
-Syncope
-Palpitations
What causes symptoms in device malfunction?
-Lack of AV synchrony
-Loss of capture/sensing
-Absence of rate modulation
-Biventricular pacing fails - patient can go back into heart failure
-Inappropriate shocks/withheld therapy
What is this an example of?
-Lead has moved and causes diaphragmatic stimulation
What does this image show?
Functional undersensing
-Atrial flutter
-Classing A waves as retrograde as they are falling in the TARP
-If falls in post-ventricular blanking period, wouldn’t see them at all
Patient history to consider in CRM
-Surgery, sport, traumatic injury
-New hobby/employment (deep sea diving, arc welding)
-New medication (flecainide)
High ventricular ectopic burden without ventricular ectopics?
-Device not sensing P waves
-2 R waves with no P wave in between - labelled as ectopic
What does this image show?
Hysteresis
-after sensed beat, pacing interval is increased
What does this image show?
Device is working fine
-Normal upper rate behaviour
