25.6 ICDs Flashcards
a) What are the indications for insertion of an implantable cardiac defibrillator (ICD)? (20%)
> > Patients with a history of serious ventricular arrhythmia who:
• Have survived cardiac arrest.
• Have had significant haemodynamic compromise or syncope.
• Have left ventricular ejection fraction (LVEF) less than 35% but no worse than class III New York Heart Association function.
> > Patients with familial conditions predisposing them to ventricular arrhythmia or following surgical correction of congenital heart disease.
> > In conjunction with cardiac resynchronization therapy for selected patients with LVEF less than 35%
b) How might surgical diathermy affect the ICD? (20%)
1»_space; Damage to and, therefore,
malfunction of device.
2»_space; Sensing of diathermy by ICD as arrhythmia,
resulting in inappropriate shock delivery.
3»_space; Energy induction in cardiac leads,
resulting in tip heating and tissue damage.
Scar development around the lead tips can cause changes in resistance and failure of the device to work.
c) A patient with an ICD is listed for elective surgery; what preparations are necessary preoperatively,
intra-operatively and postoperatively? (45%)
Preop
Preoperatively:
» Patient history and examination focusing on cardiac conditions and symptoms.
> > Check electrolytes – increased risk of arrhythmia if abnormal.
> > Device registration card:
• Manufacturer, model number, serial number.
• Implanting hospital, follow-up hospital.
• Date of and reason for implant.
> > ICD check within the last three months:
Extent of any heart failure.
• Battery life, leads, sensing, correct functioning.
> > Discussion with surgeon regarding need for use of diathermy or any other possible risk of interference that may be interpreted as arrhythmia by ICD.
> > Reprogramme ICD component to ‘monitor only’ mode – patient to have ECG monitoring from the time of ICD deactivation.
> > Diathermy may be interpreted as cardiac activity by pacemaker, resulting in risk of asystole in a pacemaker-dependent patient. Pacemaker can be
switched to fixed mode to avoid this.
c) A patient with an ICD is listed for elective surgery; what preparations are necessary preoperatively,
intra-operatively and postoperatively? (45%)
Intraoperatively:
+
postoperatively
Intraoperatively:
» Ensure availability of cardio-pulmonary resuscitation, temporary external/ transvenous pacing and external defibrillation equipment. Attach remote pads before surgery starts if this would be problematic to do intraoperatively. Anterior–posterior positioning recommended to minimise current passage through device.
> > Ensure availability of appropriate cardiac personnel especially cardiac physiologist.
> > ECG monitoring throughout.
> > Avoid diathermy use if possible. If diathermy needed, ideally use bipolar, keeping the cables away from the ICD as much as possible. If monopolar
essential, ensure the return electrode is anatomically positioned so that the current pathway between the diathermy electrode and return electrode is as far away from the ICD (and leads) as possible. Limit use to
short bursts.
Postoperatively:
» Patient to remain fully monitored in a high-observation area until ICD
reactivated and checked for functionality.
d) How does the management differ if this patient requires emergency surgery? (15%)
1»_space; If the emergency surgery is during normal working hours with usual staffing, aim to follow the same approach as for elective surgery.
2»_space; If out-of-hours, or time not permitting,
a clinical magnet secured over the implant site
with surgical tape will deactivate shock mode.
Any subsequent VT/VF will need to be treated
using external defibrillation
(although magnet can be removed and functionality should return within a number of seconds if problems with external defibrillation).
The pacemaker component would be put into a fixed mode.
The fundamental information about a pacemaker can be determined from its pacemaker code – what does each letter represent? (5 marks)
Letter 1: chamber paced
Letter 2: chamber sensed
Letter 3: mode of response/ response to sensing
Letter 4: programmability/rate modulation
Letter 5: multi-site function&&&(((*****
b) What is meant by the sensitivity of a pacemaker? (1 mark
The threshold electrical current at which it will respond to a stimulus
Minimum intrinsic atrial or ventricular electrical activity that is sensed by the device (measured in mV)
If incorrectly set, the device may fail to detect intrinsic
atrial or ventricular activity.
This can result in
• Over-pacing – firing
despite intrinsic activity, which risks
triggering malignant tachyarrhythmias.
• Under-sensing – which leads to a failure to pace
despite there being no intrinsic electrical
activity.
c) Aside from performing a pacemaker check, list three routine investigations you would request pre-operatively in a well patient with a cardiac implantable electronic device (CIED). (3 marks)
1 • ECG
may demonstrate pacing activity:
Atrial pacing = spike followed by a P-wave
Ventricular pacing = spike followed by a broad QRS complex.
• Chest X-ray
Chest X-ray shows the number and configuration of leads,
and
may also demonstrate lead fracture or migration.
3 •Electrolytes
Electrolyte abnormalities
(especially of potassium and
magnesium)
may precipitate arrhythmias
and/or interfere with pacemaker capture.
d) In which three scenarios should re-programming of a CIED prior to anaesthesia/surgery be considered? (3 marks)
- Any patient with significant permanent pacemaker (PPM) dependency
If there is the potential for electromagnetic
interference during the procedure, temporary reprogramming of the PPM to an asynchronous (non sensing) mode (e.g. A00, V00 or D00) may be
required.
- Any PPM with rate-responsive functions
Otherwise mechanical ventilation may stimulate
excessive pacing rates. - Any defibrillator function
Electromagnetic interference during the
procedure may trigger inappropriate defibrillation.
If deactivation is not possible (e.g. emergency
surgery), the application of a magnet may be
considered.
e) Apart from monopolar or bipolar diathermy, state four devices or procedures that may
produce electromagnetic interference of relevance to anaesthesia. (4 marks)
- Spinal cord stimulator
- TENS machine
- ECT
- External shockwave lithotripsy
Devices:
• Medical equipment incorporating wireless technology
• Mobile phones
Diathermy should be avoided where possible;
bipolar is considered safer than monopolar.
If monopolar diathermy is absolutely necessary, short
1–2 s bursts with 10 s pauses should be used, and
cutting current is safer than coagulation current.
The pathway from the diathermy to the ground
electrode should not pass near the CIED.
Procedures:
• Radiofrequency ablation
• Insertion of tissue expanders
• Electroconvulsive therapy
• Transcutaneous electric nerve stimulation
• Radiation therapy
• Extracorporeal shock-wave lithotripsy
What is the commonest response of a permanent pacemaker (PPM) and an implantable
cardioverter defibrillator (ICD) to the application of a magnet? (2 marks)
PPM: asynchronous mode/fixed rate pacing
ICD: deactivation of shock and
anti-tachycardia pacing functions
Less commonly, application of a magnet to a PPM
initiates a diagnostics function, followed by
reversion to its programmed mode of pacing.
Magnet application has no effect on bradycardia pacing of ICDs.
When applying external defibrillator pads, how far (in cm) from a CIED should the pads
be placed? (1 mark)
10–15 cm
Anterior–posterior pad
placement is usually
preferred
Aside from the risk of damage to the device itself, state one consequence of external
defibrillation when the pads are positioned too closely to a CIED. (1 mark
Damage to the myocardium as a consequence of excess
current flow
Implantable cardioverter defibrillators (ICDs) letter coding
Implantable cardioverter defibrillators (ICDs) have
a four-letter coding system:
• Letter 1 = chamber shocked
• Letter 2 = chamber paced during antitachycardia
functions
• Letter 3 = method through which tachycardia is detected
• Letter 4 = chambers paced during anti-bradycardia
functions
