Reviewed and revised 18 August 2014

OVERVIEW

Problems with pacing

• output failure
• failure to capture

Problems with sensing

• oversensing
• undersensing

Pacemaker syndromes

• Cross-talk
• Pacemaker syndrome
• Pacemaker-mediated tachycardia
• Sensor-induced tachycardia
• Runaway pacemaker
• Lead displacement dysrhythmia
• Twiddler’s syndrome

GENERAL MANAGEMENT

Systematic approach is essential

• review rhythm strip and 12 lead ECG
• check integrity of circuit (start at patient -> pacing box): lead placement, polarity, integrity, tightly connected to correct port of pacing box (atrial/ventricular), battery, settings
• check mode
• check rate
• check capture threshold (find threshold and double it for safety)
• check sensitivity (normal = 2-5mV) – changes with position
• fixes: change patient position, reverse bipolar pacing leads, convert to unipolar pacing, replace pacing equipment, return to OT for reinsertion of epicardial wires
• back up plan in emergency: transcutaneous or tranvenous pacing, atropine, adrenaline, isoprenaline, ephedrine, electrolyte correction

FAILURE TO PACE DUE TO OUTPUT FAILURE

• no electrical output at the pacing wire tips (pacing spikes absent on ECG)
• causes: lead malfunction, unstable connection, insufficient power, cross-talk inhibition, oversensing (see below), apparent failure to pace
  ⇒ check power, battery and connections
  ⇒ increase output to maximum (20mA atrial and 25mA ventricular)
  ⇒ switch to an asynchronous mode to prevent oversensing (AOO, VOO)
  ⇒ connect the pacemaker directly to the pacing lead (occasionally the connecting wires may be faulty)
  ⇒ prepare for transcutaneous pacing
  ⇒ prepare for CPR and chronotropic drugs

FAILURE TO CAPTURE

• visible pacing spikes are seen on ECG but no electrical capture on ECG or cardiac contraction seen in arterial line or SpO2 waveform
• usually due to some specific mechanical problem (wires no longer connected to heart, wires not tightly connected to cable, cable not connected to correct port, output setting to low)
• other causes: fibrosis at wire-myocardium interface, MI, electrolyte imbalance, post-defibrillation, drugs (flecanide, sotalol, betablockers, lignocaine, verapamil)
• approach:
  ⇒ correct exacerbating causes
  ⇒ tight and confirm all external connections
  ⇒ increase output if possible
  ⇒ bipolar leads may be tried in reverse positions or can try convert to unipolar pacing
  ⇒ in bipolar leads, the negative electrodes develop fibrosis first -> use other electrode and plug into negative terminal and insert return electrode in the subcutaneous tissue (create unipolar circuit)
  ⇒ may need temporary transvenous wire

FAILURE TO SENSE

• produces atrial pacing when not appropriate
• due to specific setting of sensitivity (including AOO mode)
  ⇒ same mechanisms as failure to capture and pace
  ⇒ decrease absolute value of sensitivity (making it easier to inhibit)

OVERSENSING

• Oversensing occurs when electrical signal are inappropriately recognised as native cardiac activity and pacing is inhibited
• produces inappropriate/excessive inhibition of atrial pacing -> confuses pacemaker into thinking that there has been a return to spontaneous atrial activity
• These inappropriate signals may be large P or T waves, skeletal muscle activity or lead contact problems
• Abnormal signals may not be evident on ECG
• Reduced pacemaker output / output failure may be seen on ECG monitoring if the patient contracts their rectus or pectoral muscles (due to oversensing of muscle activity)
• usually due to settings on the pacemaker
  ⇒ increase absolute value of sensitivity (making it harder to inhibit)
• in DDD external electrical impulses can also be misinterpreted as atrial activity causing pacemaker mediated tachycardia
  ⇒ increase sensitivity threshold or switch to an asynchronous mode (AOO, VOO)

CROSS TALK

• in dual chamber pacing it is possible that the atrial pacemaker spike will be sensed by the ventricular wire and is misinterpreted as a ventricular depolarisation
  -> inhibits ventricular pacemaker output (ventricular standstill)
• the opposite can happen as well
  ⇒ reduce sensitivity in atrial or ventricular channel
  ⇒ reduce mA delivered to the ventricular or pacing wire

PACEMAKER MEDIATED TACHYCARDIA

• Also known as endless-loop tachycardia or pacemaker circus movement tachycardia
• VDD or DDD pacing problem
• can switch to VVI or DVI (but may lose AV synchrony)
• Mechanisms:

(1) atrial sensing of a ventricular spike -> interpreted as an endogenous atrial depolarisation -> another ventricular impulse
⇒ use an atrial blanking period (now preset into box)

(2) retrograde conduction between ventricle and atrium through AV node or accessory pathway -> retrograde p waves being sensed as native atrial activity with subsequent ventricular pacing -> paced ventricular complex results in further retrograde conduction with retrograde p wave generation ->  ‘endless’ loop of periodicity -> re-entry tachycardia
⇒ adjustable post ventricular (pacing spike) atrial refractory period (PVARP) or slowing AV conduction e.g. adenosine or activation of magnet mode.

• Results in a paced tachycardia with the maximum rate limited by the pacemaker programming
• Newer pacemakers contain programmed algorithms designed to terminate PMT
• May result in rate-related ischaemia in the presence of IHD

PACEMAKER SYNDROME

• Caused by improper timing of atrial and ventricular contractions resulting in AV dyssynchrony and loss of atrial “kick”
• Variety of clinical symptoms including fatigue, dizziness, palpations, pre-syncope
• Associated decrease in systolic blood pressure > 20 mmHg during change from native rhythm to paced rhythm

TWIDDLER’S SYNDROME

• Patient manipulation of the pulse generator (accidentally or deliberately)
• The pacemaker rotates on its long axis, resulting in dislodgement of pacing leads
• Can result in diaphragmatic or brachial plexus pacing (e.g. arm twitching) depending on extent of lead migration

LEAD DISPLACEMENT DYSRHYTHMIA

• A dislodged pacing wire may float around inside the right ventricle intermittently “tickling” the myocardium and causing ventricular ectopics or runs of VT alternating with failure of capture.
• If the paced QRS morphology changes from a LBBB pattern (indicating RV placement) to a RBBB pattern (indicating LV placement), this suggests that the electrode has eroded through the interventricular septum.
• A chest x-ray will usually help to confirm the diagnosis.

RUNAWAY PACEMAKER

• This potentially life-threatening malfunction of older-generation pacemakers is related to low battery voltage (e.g. overdue pacemaker replacement)
• The pacemaker delivers paroxysms of pacing spikes at 2000 bpm, which may provoke ventricular fibrillation
• Paradoxically, there may be failure to capture — causing bradycardia — because the pacing spikes are very low in amplitude (due to the depleted battery voltage) and because at very high rates the ventricle may become refractory to stimulation
• Application of a magnet can be life saving but definitive treatment requires replacement of the pacemaker

SENSOR INDUCED TACHYCARDIA

• Modern pacemakers are programmed to allow increased heart rates in response to physiological stimuli such as exercise, tachypnoea, hypercapnia or acidaemia
• Sensors may “misfire” in the presence of distracting stimuli such as vibrations, loud noises, fever, limb movement, hyperventilation or electrocautery (e.g. during surgery)
• This misfiring leads to pacing at an inappropriately fast rate
• The ventricular rate cannot exceed the pacemaker’s upper rate limit (usually 160-180 bpm)
• These will also usually terminate with application of a magnet

References and Links

LITFL

• CCC — Pacemakers
• ECG Library — Pacemaker malfunction
• ECG Library — Pacemaker Rhythms – Normal Patterns

Medmastery

• Types of pacemakers
• Common pacemaker issues: Failure to capture
• Common pacemaker issues: Undersensing
• Common pacemaker issues: Oversensing
• Troubleshooting with vectors
• Course: Pacemaker Essentials

Journal articles

• Reade MC. Temporary epicardial pacing after cardiac surgery: a practical review. Part 2: Selection of epicardial pacing modes and troubleshooting. Anaesthesia. 2007 Apr;62(4):364-73. Review. PubMed PMID: 17381573. [Free Full Text]