Pacemakers

OVERVIEW

• pacemakers are devices that detect the electrical activity of the heart and stimulate it to contract at a faster rate.

DESCRIPTION

1. Pulse generator
   • Power source
   • Battery
   • Control circuitry
   • Transmitter / Receiver
   • Reed Switch (Magnet activated switch)
2. Lead(s)
   • Single or multiple
   • Unipolar or bipolar

USES

• The 2002 American College of Cardiology, American Heart Association and North American Society for Pacing and Electrophysiology guidelines for implantation of cardiac pacemakers

GENERAL APPROACH TO PACEMAKER PATIENT

• work by delivering a very short (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

• NASPE/BPEG Generic (NBG) Pacemaker Code was last revised in 2002

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 PACING 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 -> torsades de pointes

HISTORY

• 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

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

References and Links

LITFL

• CCC — Temporary pacemaker trouble-shooting
• CCC — Electromagnetic interference
• ECG Library — Pacemaker malfunction
• ECG Library — Pacemaker Rhythms – Normal Patterns

FOAM and web resources

• Radiopaedia — Cardiac Pacemakers
• Pacemakers for Anesthesiologists Made Incredibly Simple by Art Wallace MD PhD

Medmastery

• Course: Pacemaker Essentials
• Types of pacemakers
• Common pacemaker issues: Failure to capture
• Common pacemaker issues: Undersensing
• Common pacemaker issues: Oversensing
• Troubleshooting with vectors