CRACKCast E080 – Implantable Cardiac Devices

In CRACKCast, Podcast by Adam ThomasLeave a Comment

This episode of CRACKCast covers Rosen’s Chapter 80, Implantable Cardiac Devices. These devices are becoming more and more prevalent in our aging population, and an understanding of some of the nuances with these devices is a must. Maybe you will be shocked by what you didn’t know!

Shownotes – PDF Here


Rosen’s in Perspective

It is important to understand how these devices work, and how they can go wrong in our patients presenting to the ED

Transvenous pacemakers have been around since the 1960s! ICDs are increasingly showing mortality benefit in those patients requiring long term anti-dysrhythmics.

LVADs aren’t just unicorns anymore, you will see these in your ED!

Pacemaker essentially has 2 core functions: stimulate myocardium electrically and sense intrinsic cardiac electrical activity

3 basic components:

  • Pulse generator (with power source)
  • Electronic circuitry
  • Lead system (connecting pulse generator to endocardium)

Typically leads placed in endocardium of Right Ventricle and Right Atrium, via cephalic or subclavian vein approach. Also can see epicardial leads into left ventricle as in with Cardiac resynchronisation therapy (eg biventricular failure)

Battery type is important – all new systems are lithium batteries. Tend to last 4-10 years depending on function and abilities of unit.

  • Lithium batteries tend to gradually lose power,
  • versus Mercury-Zinc batteries used to have abrupt and catastrophic unit failure due to sudden power loss.

Most common cause of failure is with electrical circuitry eg.

  1. a) lead disruption or breakage resulting in failure to pace or sense; or
  2. B) partial fracture resulting in a “make or break” contact with intermittent failure to sense or pace

Leads can be unipolar versus Bipolar

  • Bipolar leads: has negative (distal) and positive (proximal) electrodes, separated by approximately 1 cm, within the heart
    • Compatible with ICD, but more prone to lead fracture. Over-sensing rarely a problem
  • Unipolar lead has negative electrode contacting endocardium & positive pole is the metallic casing of the pulse generator.
    • Smaller diameter and less prone to lead fracture. Not compatible with ICD as prone to over-sensing

Pacemakers can be confusing… but remember it is programmed to do a set amount of things.  Think of it as the pacemaker is always listening to the atria and ventricles. If it does not hear / sense an intrinsic P wave or QRS complex after a set amount of time, it will fire either the atria, ventricle or both depending on its function. If it does sense a P wave or QRS, then it will inhibit its preprogrammed stimulation of the atria, ventricle, or both (ie it will reset its output to prevent competition with intrinsic electrical activity).

ICDs are similar in construction and function, just add a defib function that is done via a coil in the right ventricle and the pulse generator.


1) List 5 Indications for permanent pacing


2) Pacemaker nomenclature – what do the 5 letters mean

-What are common Pacemakers? PSRPA (Poor Second Rate Pacers Atrophy)


3) Causes of pacemaker malfunction (main categories with 2 examples each)

Big shout out to LITF –

Essentially 3 things:

(1) failure to capture (no pacemaker spikes or spikes not followed by an atrial or ventricular complex)

(2) inappropriate sensing (oversensing or undersensing spikes occur prematurely or do not occur even though the programmed interval is exceeded)

(3) inappropriate pacemaker rate.

Failure to Capture -” occurs when paced stimulus does not result in myocardial depolarisation. Multiple causes including electrode displacement, wire fracture, electrolyte disturbance, MI or exit block.

Undersensing – “occurs when the pacemaker fails to sense native cardiac activity. Results in asynchronous pacing. Causes include increased stimulation threshold at electrode site (exit block), poor lead contact, new bundle branch block or programming problems. ECG findings may be minimal, although presence of pacing spikes within QRS complexes is suggestive of undersensing.”

Oversensing – “occurs when electrical signal are inappropriately recognised as native cardiac activity and pacing is inhibited. These inappropriate signals may be large P or T waves, skeletal muscle activity or lead contact problems. Abnormal signals may not be evident on ECG. Reduced pacemaker output / output failure may be seen on ECG monitoring if the patient stimulates their rectus or pectoral muscles (due to oversensing of muscle activity).”

Inappropriate rate –    when in doubt: put a magnet on it!!!

  • Low rate – think battery depletion and does not occur abruptly with lithium-iodine batteries.
  • Extreme rate (“runaway pacemaker,” rare.  If seen usually when limits set high (typically 140 beats/minCan cause VF or brady. Need pacemaker change
  • An “endless loop” tachycardia may develop during dual-chamber pacing when ventriculoatrial conduction occurs, and the resulting retrograde atrial depolarization results in a stimulated or paced ventricular depolarization. Tx with magnet to terminate loop.

4) List the complications of a pacemaker insertion

  • Infection
    • ~%2 incidence
    • Usually staph aureus
    • 20-25% can be blood culture positive. So get cultures
      • May cut insulation around pulse generator
    • Thrombophlebitis
      • 30-50% incidence!!!
        • But only 1% symptomatic secondary to good collateralization
      • ⅓ of all patients can have complete venous occlusion
      • Watch out for SVC syndrome
      • Dx with Duplex U/S
    • Pacemaker syndrome (more later)
      • Loss of AV synchrony

5) What is pacemaker pseudo-malfunction?

Often confused with failure to sense, seen when pacemaker is firing at pre-determined interval, however competing with underlying intrinsic cardiac rhythm.


6) What is pacemaker syndrome, which type of pacer is most commonly involved, and what is the treatment?

Typically patients complain of worsening of sx that lead to pacemaker placement in the first place. Secondary to loss of AV synchrony

Eg: syncope or near-syncope, orthostatic dizziness, fatigue, exercise intolerance, weakness, lethargy, chest fullness or pain, cough, uncomfortable pulsations in the neck or abdomen, right upper quadrant pain, and other nonspecific symptoms.

Most commonly seen in VVI pacemakers

Tx: Consult cardiology for interrogation

  • If VVI – change pacemaker to dual chamber
  • If dual chamber already – optimise atrial and ventricular pacing
  • May need biventricular pacing

7) What does magnet application do to a pacemaker? to an ICD?

Pacemaker:    Converts pacemaker into asynchronous pacing mode. No longer inhibited by intrinsic electrical activity

ICD:     Deactivates the defibrillator (note should only be done during resuscitation efforts, comfort care or inappropriate delivery of shocks eg in SVTs)


8) List 4 Indications for ICD


9) Causes of shock delivery in patient with ICD

Specifically for shock delivery:

  • Increase VF / VT (ischemia / electrolyte disturbance / drug effect)
  • Displaced or break in ventricular lead
  • Recurrent non-sustained VT
  • Sensing and Shock of SVT
  • Oversensing T-waves
  • Sensing non-cardiac signals

 10) Causes of syncope/presyncope in patient with ICD (three)

  • Recurrent VT with slow shock strength (lead problem / change in defib threshold)
  • Hemodynamically significant SVT
  • Inadequate backup pacing for bradyarrythmias


11) Functions of an ICD

Essentially Cardioversion / defibrillation / pacemaker

  • Back-up ventricular pacemakers for bradyarrhythmias
  • Works via complex computing for rate, rhythm and morphology discrimination

Wise Cracks

1) What do you see on ECG when pacer battery dies (2)?

Intermittent failure to capture versus complete failure to capture

Look for complete absence of pacemaker spikes to spikes not followed by a stimulus-induced complex

2) What is Twiddler’s syndrome?

According to LITFL

“Patient manipulation of the pulse generator (accidentally or deliberately).

The pacemaker rotates on its long axis, resulting in dislodgement of pacing leads.

Can result in diaphragmatic or brachial plexus pacing (e.g. arm twitching) depending on extent of lead migration.”

3) Describe your Approach to LVAD complications

Big shout out to Jared Baylis

  1. Ask the patient or their family for the info card for their device as well as the contact details for their VAD specialist and contact them (In BC, the 24/7 VAD Hotline can be reached at 604-250-2658).
  2. If unable to obtain blood pressure by NIBP, use Doppler with a manual cuff. Remember that they need a narrowly normal MAP: 70-80 (If it’s higher or lower you need to be concerned!)
  3. If pulse oximetry is not reliable, then pursue cerebral oximetry, ABG, or an arterial line depending on the scenario.
  4. If hypotensive, obtain a work-up including basic CBC, electrolytes, coagulation panel, chest xray, and ECG. Consider adding hemolytic work up and performing bedside ultrasound. Administer an IV fluid bolus or PO fluids if awake and alert.
  5. If you suspect infection, draw blood cultures, cover with broad spectrum antibiotics, and resuscitate as appropriate.
  6. Sustained symptomatic ventricular tachycardias/ventricular fibrillation should be treated urgently with cardioversion. Defibrillator pads should not be placed directly over the LVAD device.
  7. If there is no “hum” on chest auscultation and/or there are no signs of perfusion, begin chest compressions and contact a cardiac surgeon if one is available on site.
    1. Risk of dislodging LVAD but.. They are dead, so CPR takes precedence.

This post was edited and uploaded by Ross Prager (@ross_prager)

Adam Thomas

CRACKCast Co-founder and newly minted FRCPC emergency physician from the University of British Columbia. Currently spending his days between a fellowship in critical care and making sure his toddler survives past age 5.

Justin Roos

Justin Roos is an emergency medicine resident at the University of British Columbia. His interests include mountain and wilderness medicine. He is a contributor to the CrackCast podcast.

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Chris Lipp is one of the founding Fathers for CrackCast. He currently divides his time as an EM Physician in Calgary (SHC/FMC) and in Sports Medicine (Innovative Sport Medicine Calgary). His interests are in paediatrics, endurance sports, exercise as medicine, and wilderness medical education. When he isn’t outdoors with his family, he's brewing a coffee or dreaming up an adventure…..