59. Pacemakers Flashcards
Have a look at this ECG page 175
The ECG shows paced rhythm from a ventricular pacemaker with a rate of
approximately 100 bpm.
The QRS complexes are broad and bizarre looking in keeping with the abnormal pathway through slower conducting ventricular tissue.
How are pacemakers classified?
There is a five-letter code that describes the characteristics of each permanent pacemaker.
The first three letters are the most important.
The North American Society of Pacing and Electrophysiology (NASPE) and the British Pacing and
Electrophysiology Group (BPEG) produced a pacemaker code (NBG) in 1987 revised in 01
I
II
III
I
Chamber paced
O = No action
A = Atrium
V = Ventricle
D = Dual
II Chamber sensed
O = No action
A = Atrium
V = Ventricle
D = Dual
III
Response to sensed information
O = No action
T = Pacemaker triggered
I = Pacemaker inhibited
D = Dual
(ventricular sensed events lead to inhibition
but atrial sensed events trigger ventricular output)
IV
IV
Programmability, rate modulation
The ability of the pacemaker to alter the pacing rate in response to physiological
variables such as increased activity, respiration or blood temperature. Generally,
the sensors respond to increased movement or increased minute ventilation.
O = No action
R = Rate modulation
V
v
Multisite Pacing
O = No action
A = Atrium
V = Ventricle
D = Dual
The commonest pacemaker modes
The commonest pacemaker modes are:
VVI (16.9%), VVIR (24.8%), DDD
(27.3%) and DDDR (25.4%)
CRT
CRT (Cardiac resynchronisation therapy), or biventricular pacing, is used to
improve cardiac performance in patients with heart failure.
ICD
ICDs (Implantable cardioverter defibrillators) can be complex and tailored
to individual patients. They, too, have NASPE/BPEG codes to describe their
function.
Chamber shocked (I)
Anti-tachycardia pacing chamber (II)
Anti-tachycardia detection (III)
Pacing chamber (IV)
I + II + IV
O = No action
A = Atrium
V = Ventricle
D = Dual
III
Electrogram
Haemodynamic
Ventricle
What is the anaesthetic management of a patient who is fitted with a
pacemaker and requires surgery?
The main peri-operative problems in a patient with a permanent pacemaker
are due to the effects of anaesthetic agents, altered physiology and surgical
diathermy.
Pre-operative assessment
Usual anaesthetic assessment plus:
Establish the original indication for inserting the pacemaker, what type it is,
when it was last checked and information about any programmed functions
it may have. If it’s an ICD, has it shocked them?
Look for symptoms that may suggest problems with pacing, e.g. syncope or
palpitations
Pacemakers with rate-responsive or anti-tachycardia modes should probably
have them deactivated pre-operatively
Check pacemaker function:
ECG
If the intrinsic rate is higher than that set on
the pacemaker, then a Valsalva manoeuvre
may be employed to check function. CXR will
identify number and integrity of leads
Intra-operative management
Appropriate monitoring based on pre-op assessment.
An alternative means of pacing must be immediately available: external,
transvenous or oesophageal.
Care at induction – may result in stimulation or inhibition of the pacemaker
due to alterations in myocardial conduction or sensed muscular contractions
(e.g. etomidate or suxamethonium) depending on the pacemaker
programme.
Volatile agents do not significantly alter the pacing threshold
Etomidate and ketamine may be best avoided due to the possibility of
myoclonic movements.
Avoid hypoxaemia and hypercarbia – ectopics and arrhythmias.
Rate-responsive pacemakers may induce a tachycardia in response to a high
respiratory rate set on the ventilator (trans-thoracic impedance).
Diathermy
The use of diathermy may reprogramme the pacemaker, cause
microshock or induce VF. Bipolar should be used if possible or, if
unipolar is essential, the plate should be placed as far away
from the heart as possible. Short bursts followed by long pauses
should be used.
Magnets
Magnets In general should not be used. If placed over a programmable
pacemaker in the presence of electromagnetic interference (e.g.
diathermy), there may be unpredictable reprogramming. The
magnet may also initiate a ‘threshold test’ whereby the output
current gradually decreases until failure of capture occurs!
Although the ‘magnet rate’ is usually written on the packaging
for each pacemaker, most anaesthetic references now
recommend that magnets are not used.
DCCV
If DC cardioversion is required, the paddles should be placed perpendicular
to the direction of the pacing wire (i.e. in anterior and posterior positions).
The box is designed to protect itself by diverting current away from the
internal circuitry, which may then pass down a damaged lead resulting in
burns.
Temp emergency measure?
Isoprenaline may be required as a holding measure, while emergency
pacing is achieved in the event of pacemaker failure
