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

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

FOAM and web resources

Medmastery


CCC 700 6

Critical Care

Compendium

Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also the Innovation Lead for the Australian Centre for Health Innovation at Alfred Health and Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of two amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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