Temporary Epicardial Cardiac Pacing

OVERVIEW

• the usual means of cardiac pacing following cardiac surgery

USES/INDICATIONS

Post cardiac surgery

• conduction abnormality (bradyarrhythmia)
• tachycardia (AV junctional tachycardia, SVT, VT, atrial flutter)
• other: restoration of AV synchrony, HOCM to prevent SAM

Indications are controversial – some centers have at least ventricular leads in almost all cardiac surgery patients, others only in those who have rhythm disturbance intraoperatively

DESCRIPTION

• produce electrical current with subsequent depolarisation + sensing function

Unipolar

• negative wire attached to the epicardium
• positive wire attached to subcutaneous tissues

Bipolar

• a single wire with two conductors insulated from one another which both run to the epicardial surface
• smaller distance for current to run -> threshold less
• more suitable for dual chamber applications
• require less energy to begin with and may have greater longevity compared to unipolar system

METHOD OF INSERTION AND/OR USE

Typical settings

• atrial and ventricular output 10mA
• lower rate 80/min
• atria and ventricular sensitivity 2-5mV
• PR interval 150ms or ‘auto’ (determined by rate)
• PVARP 250ms or ‘auto’ (determined by rate) = post ventricular (pacing spike) atrial refractory period

Daily Checks

• assess underlying rhythm
  -> turn pacemaker rate down and assess native rhythm
  (do not turn down the output energy – there may be no underlying rhythm!)
• determine sensitivity (minimum current that the pacemaker is able to sense)
  -> place in VVI, AAI or DDD, increase sensitivity until the sense indicator stops flashing
  -> asynchronous pacing should take place, then turn sensitivity down until sense indicator flashes which each endogenous depolarisation
  -> this equals the pacing threshold
  -> set pacing generator at half the pacing threshold
• determine capture threshold (minimum output required to stimulate an action potential in the myocardium)
  -> set rate above native rate
  -> then reduce output until QRS no longer follows pacing spike = capture threshold
  -> leave output at twice the threshold

Removal of wire

• gentle traction allowing cardiac motion to help dislodgement
• if they get cut, cut close to skin so they will retract

OTHER INFORMATION

Duration of use

• Epicardial wires usually fail to sense and capture after a few days
• Increases in stimulation threshold typically occur after 4 days in both atrial and ventricular wires
• failure to pace is observed in > 60% right and > 80% left atrial wires after 5 days

How to extend longevity of pacing wires

• minimise output energy
• optimise wire position (may be at odds with what is optimal for hemodynamics)
• consider steroids (reuces inflammatory reaction to wire)

MRI

• not compatible with MRI due to the amount of ferrous material in pacing box
• controversial regarding in situ epicardial wires

IABP

• if IABP is timed according to ECG with high frequency filter disabled (allowing pacing spikes to become visible) -> pacing spikes can be misinterpreted by the IABP as QRS complexes
• IABP should be timed according the arterial pulse or the high frequency filter applied
• less problematic with bipolar leads

Atrial ECG

• can be performed using atrial wires
• useful for differentiating atrial and junctional arrhythmias, and in defining the nature of an AV block

Safety

• Patients must be nursed in a cardiac-protected electrical environment
• wires should only be handled with non-conductive gloves
• a large metal object (e.g. the bed) should be touched first to discharge static potential prior to touching the wires
• wires should be protected in a non-conductive container e.g. a plastic syringe barrel) when not in use
• continuous ECG monitoring
•  immediate access to a cardiac defibrillator with transcutaneous pacing capacity

COMPLICATIONS

Cardiac complications

• infection
• myocardial damage
• perforation
• tamponade
• disruption of coronary anastomoses
• microshock induced arrhythmia (electric shock conducted down epicardial wire)

Pacing complications

• undersensing
• oversensing
• failure to capture
• output failure
• unstable lead position
• pacemaker-mediated tachycardia

References and Links

LITFL

• ECG Library — Pacemaker Rhythms — Normal Patterns
• ECG Library — Pacemaker malfunction
• Medmastery — Pacemaker Essentials: The basics

Journal articles

• Reade MC. Temporary epicardial pacing after cardiac surgery: a practical review: part 1: general considerations in the management of epicardial pacing. Anaesthesia. 2007 Mar;62(3):264-71. PMID: 17300304.
• 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. PMID: 17381573.