W10 Pacemakers Flashcards
Outline the early history of implantable pacemakers (4 key dates)
- 1958: R. Elmqvist - an engineer at Siemens-Elema - develops the first implantable pacemaker in Sweden
- 1958: E. Bakken - Medtronic Founder - first ‘wearable’, battery-powered pacemaker
- 1963: G. Wickham - Telectronics Founder - first definition of the relationship between surface area of the heart electrodes and pacing pulse characteristics, first use of integrated circuits, and the first hermetic titanium encapsulation
- 1969: revolutionary research into implantable defibrillator (prevention of cardiac arrest)
Describe the “Greatbatch-Chardack” pacemaker
- consisted of a transistor oscillator and an amplifier energised by 10 mercury-zinc cells
- the 10 cells and electronic circuitry were potted in epoxy and covered by a double shell of Silastic
- the electrode used was about the size of a postage stamp
Describe 3 basic types of pacemakers
- Single-chamber pacemaker paces either the right atrium or the right ventricle (most common)
- Dual-chamber pacemaker paces both the right atrium and ventricle of the heart with two pacing leads (standard)
- Rate responsive - one or two sensors that detect changes in the heart rate needs and adjusts the heart rate accordingly (e.g. activity, respiration)
What are the Principal Elements of the Pacing System?
Describe the weight and size changes that occurred in pacemakers since 1958.
- 1958
- Weight 73.4g
- Size 35cc (cubic centimetres)
- 1981
- 55g
- 25cc
- 1995
- 14g
- 6cc
- 2009
- 23g
- 12.8cc
- 2013
- 2g
- 1cc
Name three conditions pacemakers treat.
- Bradycardia
- Tachycardia/Fibrillation
- Heart Failure
What does AICD stand for?
Automatic implantable cardioverter defibrillator
What is the main speculated weakness of the Medtronic (Sprint Fidelis) implantable pacemaker system and why?
Leads - Sprint Fidelis recall in 2007
- inappropriate shocks in patients (46%)
- inappropriate alarm alert (34%)
- routine follow up (20%)
- sudden rises in impedance and/or frequent short VV intervals prior to lead failure
- isolated decrease of R wave
“The rate of Sprint Fidelis lead failure reaches 5.7% at a mean follow-up duration of 32 months. The rate of failure does not seem to stabilise. Routine follow-up cannot predict lead failure or prevent inappropriate shocks.” –2010
No official disclosure from Medtronic of precise mechanism of lead fracture failures, but speculation that the thin design of the leads might not be durable enough to survive either the pressure of implantation or the stresses exerted on them once they’re in the body.
One description, “classic fatigue failures” - typically denotes weakening of metal exposed to repeat stresses.
Describe the St Jude Medical ICD recall in 2011.
“Riata” leads posed greater concern than the Medtronic Fidelis recall. (Similar concerns for the Durata lead, which shared many design elements with the Riata.)
Failure due to unique “inside-out” form of lead insulation abrasion - where lead cables shown to externalise (although commonly externalisation not associated with failure and vice versa; there is no single common sign of lead failure on electrical measurements).
Industry & FDA knew about Riata problems for over a year and now only collecting prospective data.
What considerations must be taken (x7) when it comes to selecting the right lead for ICDs?
- Endocardial vs. epicardial
- Unipolar vs. bipolar
- Electrodes
- Fixation mechanism
- Insulation
- Pulse generator (connection)
- Atrial vs. ventricular
Regarding Epicardial Leads, briefly list the:
i) attachment
ii) surgery
iii) mechanism
iv) main applications
v) limitations
i) fastened (sutured) to outside of heart
ii) requires open-chest procedure
iii) typically has corkscrew mechanism
iv) main applications:
- pediatric patients (vessels too small for endocardial leads)
- patients having open-chest surgery already
v) limitations:
- more difficult (and invasive) to implant
- pacing thresholds may increase over time
List the main elements of an endocardial pacing lead (see image)
Connector Pin
Suture Sleeve
Lead Body
Proximal Ring Electrode
Passive-Fixation Mechanism
Distal Tip Electrode
(see image)
Discuss Polarity with respect to biploar and unipolar ICD leads.
All electricity travels in a circuit (circle) from a positive pole (anode) to a negative pole (cathode)
A bipolar lead has both anode and cathode (two poles) on the lead itself
A unipolar lead has a negative pole (cathode) on the lead itself (tip electrode) and takes the pulse generator can as the positive pole (anode)
Compare a Unipolar/Bipolar Antenna and Configuration in terms of:
- directions of energy travel
- antenna size
- pacing spike in ECG
- electrodes
- conductor coils
see image
List the Advantages and Disadvantages between Unipolar and Bipolar leads
see image
Describe the effect of electrode variables on Performance
List the advantages and disadvantages between active and passive fixation methods.
see image
Comparing Telectronics’ Laserpor, Dish and Laserdish electrodes (image), which required the greatest and least stimulation energy?
Laserpor - greatest
Laserdish - least
(see image)
Describe the effect of steroids on electrode leads.
Many leads incorporate a small amount of steroid on the lead tip (see image) which is released in a controlled fashion
1 mg of dexamethasone sodium phosphate (St. Jude Medical):
- reduces inflammation at interface
- has been associated with lower thresholds
- dampens the acute-to-chronic threshold increase
- widely accepted in clinical community
Discuss the advantages and disadvantages of Polyurethane vs. Silicone Insulation types
see image
On Pacing Lead Connections…
see slide
Describe existing Leadless Systems for Right Ventricle Pacing
see image
