1. Pacemakers, Cardioverters, and Defibrillators
By: Lauryn Rametta, CRNA

2. Pacemaker Basics Pacemakers sense and pace the heart
Sense the voltage produced by the heart (mV) and respond by sending (or not) electrical current (mA) to the heart
Think of a pacemaker as a drug delivery device.
The drug it delivers is electrons.
The current it is delivering is the dose (electrons/second)

3. Pacemaker Basics Pacemakers are made up of:
A pulse generator with a computer and battery that should last 6-10 years
Leads placed in the right atrium and/or right ventricle and sometimes left ventricle
Unipolar vs bipolar leads
Unipolar leads less likely to fail but bipolar leads produce a sharper signal

4. Pacemaker Leads
Passive
Active

5. AICD Basics AICDs are made up of:
A pulse generator with a computer and battery
Battery is designed to deliver 120 shocks and usually lasts 3-6 years
A lead electrode that detects dysrhythmias, delivers defibrillating shocks, paces, telemetry, and provides diagnostic data
Many AICDs also have a 3rd lead (beyond the R atrial and ventricular leads) in the coronary sinus that can pace the left ventricular wall in synchrony with the right ventricle
These are CRT-Ds (cardiac resynchronization therapy defibrillator)
Without the defibrillation capability, these are merely bi-ventricular pacers or CRT pacemakers
AICDs programmed to recognize VF or VT.
If VF is detected, should deliver a shock within seconds (needs time to charge)
If VT is detected, it will treat with overdrive pacing

6. Why does my patient have this device?
Good question. Always determine the underlying pathology that bought your patient this expensive device.
What type of device is it?
When was it placed?
Are they pacer dependent? What is their underlying rhythm?
Have they ever been shocked? When? How often?
Has the pacer been interrogated recently?

7. Why does my patient have this device?
Sinus node dysfunction
Symptomatic bradycardia
AV node dysfunction
3rd degree or type two 2nd degree heart block, symptomatic 1st degree or type one 2nd degree heart block
Heart failure
Sustained or recurrent VT/VF
Other conditions such as alternating BBB, myotonic muscular dystrophy, neurocardiogenic syncope, cardiac transplant with persistent bradycardia, congenital heart diseases
The list goes on…

8. Why Do We Worry About Pacemakers/ICDs in the OR?
Risk of electromagnetic interference which can lead to:
Inhibition of pacemaker
Inappropriate delivery of shock by ICD
Changes in parameters
“Runaway” pacemaker
Reprogramming
Transient or permanent loss of capture
Device failure
Myocardial burns
Minimize the risk by:
Use of bipolar cautery
Placement of grounding pad so that the current does not cross the generator
Short bursts of monopolar cautery
Have magnet available

9. Low Budget Pacemaker

10. Basic Electricity Review
Voltage (measured in mV) The potential of the electrons if you cared to actually deliver them.
Think of batteries (12v, 1.5v, etc.). They just sit there holding potential power until you use them.
Current (measured in mA) The delivery of electrons.
This is your dose (electrons/sec)
Ground (earth) Basically where all the extra electrons get dumped so they don’t get dumped in you or a patient or anything else

11. Basic Electricity Review
Ohms Law
Current depends on voltage and resistance
Voltage (V) = Current (I) x Resistance (R)
V = IR
Why do we care about all this?

12. Electricity Example
Lets pretend you plug in 2 electrical wires to separate grounded outlets and then place those wires on a patient.
One ground has a voltage of 0.1v and the other has a voltage of 0.5v.
Your wires are really awesome and cutting edge. They have 0 resistance.
What does this mean for your patient??

13. Electricity Example Ohms law: ∆V = IR
We know V (0.1 and 0.5) and R (0 because of our amazing wires), so let’s rearrange our equation.
I = ∆V/R
Solve it. What does this mean?

14. Oops. You just killed your patient
Infinity is a lot of electricity to send through a person. Probably try not to do that.
This is called a “ground loop.” This is why all of the electricity in the OR is isolated.
Ground 0.5 V
Ground 0.1 V

15. I thought this lecture was about pacemakers?
That example was on a macro scale but pacemakers, defibrillators, etc. follow these same laws and principles but from within the body and directly connected to the heart.
This principle of grounded vs ungrounded has an impact on pacemaker interference as well

16. Pacemaker Vocab
When talking about pacemakers in the most basic sense – whether they function or not – we focus on sensitivity, threshold, and inhibition.
Sensitivity is the lowest voltage that must be achieved for a pacemaker to sense an R wave or P wave
Threshold is the minimum current needed to pace the ventricle/atrium
Inhibition refers to whether or not the pacemaker delivers a current. Basically whether it paces or just sits there doing nothing. Inhibition is determined by the pacemaker sensing electrical activity (from the heart or other sources such as cautery)
Remember the inhibiting is done to the pacer, not by it. Pacemakers can only make the heart beat faster, they cannot slow it down!

17. Sensitivity
Sensitivity is the lowest voltage that must be achieved for a pacemaker to sense an R wave or P wave
You control the sensitivity. What happens if your sensitivity is too high/too low?

18. Sensitivity
In order to make a pacemaker more sensitive you have to lower the sensitivity voltage.

19. A note on Atrial Sensing
P wave sensing works on the same principle as we’ve described for R wave sensing
You set an atrial sensitivity level that must be crossed in order to sense a P wave
One exception
Atrial sensitivity might also be set off by the T wave and that would be bad.
So, for atrial sensing, the pacemaker senses an R wave and then waits.
It waits for a refractory period and then assumes the next thing after that refractory period that crosses the atrial sensitivity level is a P wave.
Sensitivity Level

20. Pacemaker/ICD Codes
VOO, DOO, AOO, DDD, AAI, VVI, DVI – what does it all mean?
ICDs have a 4 letter code and pacemakers have a 5 letters code. In this lecture, we will focus on the first 3 letters of the pacemaker code
Pacemakers
I: Chamber(s) paced
II: Chamber(s) sensed
III: Response to sensed event
IV: Programmability, rate responsive
V: Multisite pacing
ICDs
I: Chamber(s) shocked
II: Antitachycardia Pacing Chamber(s)
III: Tachycardia Detection
E: Electrogram
H: Hemodynamic
IV: Antibradycardia Pacing Chamber(s)

21. A A I Pacemaker Codes O: None A: Atrium V: Ventricle
D: Dual (A + V) or (Trigger + Inhibit)
I: Inhibition
Chamber Paced
Chamber Sensed
Response to Sensed Event

22. Pacemaker Code Practice
Here are some common pacemaker codes you may encounter. Make sure you know what they each mean.
DDD
VVI
VOO
AOO
DVI
AAI

23. What Happens if a Pacemaker Senses Something Besides a Heartbeat?
If you have a pacemaker that is programmed to inhibit (VVI, for example) it will sense this interference and inhibit its pacing
Inhibition = no pacing = no heartbeat in a pacemaker dependent patient = Bad news

24. Pacemakers in the OR
So, your patient has a pacemaker and is coming in for surgery. No big deal right?
You’ve read their chart, and the cardiologist has made them low risk for surgery.
You’re in a hurry so you haven’t had time to ask a lot of questions about the pacemaker but your attending tells you to put a magnet on the pacemaker when you get in the room and everything will be fine.
Which brings us to our next topic…

25. Magnets!

26. Magnets Rule number one: MAGNETS ARE NOT MAGIC!
They do NOT fix everything.
They do NOT magically make your pacemaker or ICD lovely and compatible with any situation.
You do NOT always have to put a magnet on every implantable device just because the patient is going to surgery.
You DO always want a magnet available

27. Magnets – What do they do?
Generally will put a pacemaker into asynchronous mode
Not always the same response, even for the same company
May be high rate asynchronous (80-100), asynchronous with programmed rate or asynchronous low rate (60-100)
Generally will suspend the arrhythmia detection on an ICD
Will NOT switch the pacemaker function to asynchronous
If you’re expecting electrical interference for a patient with an ICD-pacemaker you should have the rep reprogram the device to turn off arrhythmia detection and put the pacemaker into asynchronous mode

28. Caution
Asynchronous modes are for the OR – only when you expect or see interference with the pacemaker/ICD
In asynchronous modes YOU are the sensor
Never leave a patient in asynchronous mode
Risk of R-on-T → VT/VF
If you turn off arrhythmia detection in an ICD, you must have an external defibrillator immediately available

29. Program these numbers into your phone
Magnets
Notice that these slides said what magnets generally do. Magnet response depends on brand, type of device, whether magnet mode is turned on, battery level…
It’s good practice to call the manufacturer to confirm the device response to a magnet before using one.
Program these numbers into your phone
Biotronik:
Boston Scientific:
Medtronic:
St Jude:
These numbers are available 24/7, everyday

30. Asynchronous Modes AOO, DOO, and VOO are asynchronous modes
They only pace
They have no sense and no inhibitions
“The Paris Hilton of pacing modes”
It’s fun to be Paris Hilton for a little while, but no one wants to be Paris Hilton forever (as evidenced by her current irrelevance)
Also all the OO modes = 007 → License to Kill
(DOO, VOO, AOO)

31. What do you need to know Preoperatively?
Type of device
ICD - history of shock, lowest HR for shock delivery, resynchronization therapy?
Brand/model
Does the company have a rep available at your facility? Who can interrogate the device? Will someone be able to reprogram the device if a magnet is used?
Why does the patient have it?
When was it placed?
Underlying rhythm/pacemaker dependent?
When was it last interrogated?
What does the magnet do?
Confirm that battery life > 3 months
If the patient does not have a report in the chart with all of this information, call the device company!
It will only take 5 minutes and they will gladly help you and provide all this information.

32. Other Pre-op Considerations
What type of surgery is the patient having?
Do you anticipate electromagnetic interference (EMI) from cautery or any other source?
Monopolar vs bipolar cautery
Placement of grounding pad
Patient positioning
Location of the surgery
EMI is much more likely if within 15 cm of the pacemaker/ICD generator
Type of surgery
EMI is more common with certain procedures such as ECT, radiofrequency ablation, lithotripsy…

34. What do you do Post-op? Interrogate the device
If you have used the magnet or reprogrammed the device pre-op/intra-op
If the pt had significant perioperative events
i.e. cardiac arrest, anything that required temporary pacing, CPR
If the pt had hemodynamically challenging surgery
i.e. large vascular surgery, any surgery that led to or may lead to large shifts in hemodynamic status
If the pt had cardiothoracic surgery
If the patient underwent any surgery with high risk of EMI
Always make sure you pass on in report everything you know about the patient’s device

35. What if the pacemaker stops working?

36. Take Home Quick Facts
Pacemakers can only accelerate the heart. They never slow it down.
Never leave a patient in asynchronous mode.
Magnets do NOT fix everything!
Always make sure you know what a magnet will do to a device before using it.
Make sure you know everything you need to know about a device before going to the OR
Type
Brand/model
Why the patient has it
Underlying rhythm/pacemaker dependent?
What does the magnet do?
ICD history of shock
Battery life > 3 months

37. Pacemaker Code Quick Reference
What is it?
Who gets it?
AOO
Atrial pace, no sense, no inhibition
(Paris Hilton)
Sick sinus syndrome (SSS) with intact conduction in OR with Bovie interference
AAI
Atrial pace, atrial sense, inhibited by atrium
SSS with intact conduction system
VOO
Ventricular pace, no sense, no inhibition
3rd degree heart block in OR with afib
VVI
Ventricular pace, ventricular sense, inhibited by ventricle
3rd degree heart block with a fib
DOO
Dual pace, no sense, no inhibition
3rd degree heart block in OR
DVI
Dual pace, ventricular sense, inhibited by ventricle
3rd degree heart block with SVT
DDD
Dual pace, dual sense, inhibited by either atrium or ventricle
3rd degree heart block

39. References
Barash, P., Cullen B. & Stoelting R., Cahalan, M., & Stock, M., (2013) (7th ed.). Clinical anesthesia. Philadelphia: J.B. Lippincott Appendix 2
Kirk, M. (2005) Basic principles of pacing.
Nagelhout, J., & Plaus, K.,(2014). Nurse anesthesia (5th ed.). St. Louis: Elsevier Sanders.
Wallace, A. (2008). Pacemakers for anesthesiologists made incredibly simple. Obtained from