JFICM and FANZCA Examinations Book Pages 176-178

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 modulationor 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

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

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. anticipated amount of EMI

2. type of device (pacemaker, ICD or CRT)

3. pacemaker dependency

4. 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)

- 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 non-reprogrammable 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)