Pacemakers
Saturday, March 14, 2009
OHOA
JFICM and FANZCA Examinations Book – pages 176-178
Allen, M (2006) “Pacemakers and Implantable Cardioverter Defibrillators – Review Article”
Anaesthesia 61, pages 883-890
- work by delivering a very short (<1ms), low voltage (<3V) electrical current via an
insulated pacing lead to the heart muscle @ a preprogrammed rate.
- also have the ability to detect the heart’s native electrical impulses and respond accordingly.
- single or dual chamber device
- radiofrequency reprogramming
HISTORY
- reason for pacemaker (bradyarrhythmias, severe heart failure – biventricular pacemaker, AV
synchrony -> shown to reduce the risk of heart failure and AF)
- how long patient has had it
- whether functioning adequately
- last interrogation (ideally within last 3 months)
- battery life
- base line rate
- review device ‘passport’
Pacemaker Code = 5 letters
- first 3 = anti-bradycardia functions (always stated)
- last 2 = related to additional functions
1. Paced chamber (0 = none, V = ventricle, A = atrium, D = dual (A+V))
2. Sensing chamber (0, V, A, D (A+V))
3. Response to sensing (0 = none, T = triggered, I = inhibited, D = dual (T+I))
4. Rate modulation or Programmability (0 = none, P = single programmable, M =
multiprogrammable, R = rate modulation in response to minute ventilation or movement)
5. Anti-tachycardia functions (0 = none, P = pacing, S = shock, D = dual (P+S) or
Multi-site pacing
Acronym = PS RRA
COMMON MODES
VVI
-
ventricular pacing and sensing
if no electrical impulse sensed then pacemaker will pace @ a pre-programmed rate
if electrical impulse sensed then pacing inhibited
asynchronous pacing
VVIR
- same as above but there is a rate-adaptive mechanism installed to match physiological
needs of patient
Jeremy Fernando (2011)
DDD
- both atrium and ventricle both sensed and paced
- if both SA and AV node functioning then pacemaker will just sense
- if either atrium or ventricle not conveyed -> pacemaker will take over
DDDR
- same as above except has a rate-adaptive mechanism
VOO
-
mode that pacemaker should be set to for surgery (asynchronous pacing)
ventricle paced at a pre-programmed rate
sensing not interfered with by diathermy and other forms of electromagnetic interference
monitor for R on T with diathermy ->
- recent visit to cardiology clinic should confirm; adequate battery life and normal function of
pacemaker system
- pacemakers work but inducing a current between anode and cathode above the threshold
of the myocardial cell -> depolarization
- symptoms – chest pain, palpitations, black outs, collapses, orthopnoea, PND, SOBE, ankle
swelling
- exercise capacity
- co-morbidities: IHD, HT, CVA, COPD, hyperlipidaemia, cardiomyopathy, valve dysfunction,
HOCM, congenital QT syndromes
- medications: relevant anti-arrhythmics and treatments for above conditions
- recent cardioversions
EXAMINATION
- thorough CVS examination
- pacemaker site – integrity, signs of infection, relation to operative site and diathermy.
- signs of heart failure – tachycardia, hyper/hypotension, atrial fibrillation, JVP, HS and
murmurs, RVH and apex displacement, crackles or pleural effusions in chest, enlarged liver,
pitting oedema.
INVESTIGATIONS
- U+E – electrolytes balanced including Mg2+ (abnormalities can result in loss of capture)
- relevant drug levels – digoxin
- 12 Lead ECG – underlying rhythm and rate, pacing spikes, electrical activity followed by
pacing spike, AV synchronicity
- ECHO – LV function and valve function, signs of PHT
- CXR: cardiac failure, position of pacemaker, leads position
- Angiogram – coronary artery integrity
- Recent interrogation
- EPS studies
Jeremy Fernando (2011)
MANAGEMENT
Pre-procedure
- surgery – approach, duration, position of patient required (supine or beach chair), location of diathermy pad and type of diathermy
- whether a device is to be altered prior to surgery is dependent on 4 things:
1.
2.
3.
4.
anticipated amount of EMI
type of device (pacemaker, ICD or CRT)
pacemaker dependency
rate adaptive features
- if surgery is not around the pacemaker and use if diathermy minimal -> don’t have to alter
- if rate modulated pacemaker -> deactivate prior to theatre
Intraoperative
- standard monitoring
- turn paced mode on the ECG
ELECTROMAGNETIC INTERFERENCE (EMI)
Causes
-
diathermy (monopolar & bipolar)
mobile phones (don’t place over pacemaker)
MRI
shivering
faciculations
alterations in heart size
positive pressure ventilation
peripheral nerve stimulators
TENS machine
defibrillation
Possible Results
-
inappropriate triggering or inhibition of output
asynchronous pacing
reprogramming
damage to device circuitry
pacing wires may acts as aerials and cause heating of endocardium
Prevention
- use bipolar diathermy
- if conventional diathermy required  position plate so that most of current passes away
from the pacemaker, use short, sharp bursts and watch SpO2 or art line.
- ensure all devices are not in the same vector as the pacemaker current (between
pacemaker and heart)
Jeremy Fernando (2011)
- if reason for pacemaker severe heart failure where loss of AV synchrony may precipitate
haemodynamic compromise -> have a telemetric programmer and cardiac technician close @
hand
- keep lithotripter atleast 6 inches away from pacemaker (should be timed with ECG and rate
modulation deactivated)
- if have to defibrillate keep pads as far from pace maker as possible
- avoid sux c/o faciculations (if used in a patient with a sensing mode activated -> use
defaciculating dose of NDNMBD)
- avoid using defibrillation if at all possible (high level of EMI) -> if required use AP pad
configuration and keep pad’s 10cm away from pacemaker.
Magnets and Pacemakers
- no longer recommended to place magnet over pacemakers -> only applicable to older nonreprogrammable pacemakers.
- placement of a magnet would default mode to an asynchronous mode or a fixed rate
- all modern pacemakers are reprogrammable.
Management of Pacemaker Malfunction
-
have cardio-technician in OT
praecordial thumps (percussive pacing)
isoprenaline
adrenaline
transthoracic external pacing (capture around 80mA)
trans-venous pacing
trans-oesophageal pacing
Post-procedure Management
- cardiac technician should interrogate pacemaker and reprogram rate modulation or other
specific modes
PROBLEMS
- pacemaker syndrome: single chamber pacing -> retrograde conduction from ventricular
systole -> flows to atria and produces decreased Q, SOB, palpitations, syncope
- pacemaker tachycardia: dual chamber pacing -> short circuit between the two electrodes.
Jeremy Fernando (2011)