Pacemakers Flashcards
a pacemaker consists of a ___ generator and pacing ___ that deliver electrical current to the heart
Pulse generator and pacing leads
Position 1 pacemaker
chamber paced
position 2 pacemaker
chamber sensed
position 3 pacemaker
response to sensed native cardiac activity
position 4 pacemaker
programability options
position 5 pacemaker
indicates the pacemaker can pace multiple sites
circuit board (“hybrid”)
The pulse generator processes electrical info from the heart, and it responds to these signals based on the programmed settings
Where is the atrial lead positioned?
lodges in the right atrial appendage
Where is the ventricular lead positioned?
lodges in the apex of the right ventricle
What are the indications for pacemaker insertion?
SA node disease
AV node disease
Long QT syndrome
Dilated cardiomyopathy
Hypertrophic obstructive cardiomyopathy
What is the mnemonic that can be memorized to remember the 5 letter code of pacemakers?
PaSeR
Pa= chamber PAced
Se= chamber SEnsed
R= Response
pacemaker position 1 codes
O= none
A= atrium
V= ventricle
D= dual (A+V)
Chamber that is paced
pacemaker position 2 codes
O= none
A= Atrium
V= ventricle
D= dual (A+V)
chamber that is sensed
pacemaker position 3 codes
O= none
T= triggered (sensed activity tells the pacemaker TO fire
I= inhibited (sensed activity tells the pacemaker NOT to fire)
D= dual (T+I) (if native activity is sensed, then pacing is inhibited, if native activity is not sensed, then the pacemaker fires)
- Example: a sensed intrinsic atrial beat will inhibit atrial pacing output and will trigger ventricular pacing
pacemaker position 4 codes
O= none
R= rate modulation
This indicates the programmability of the pacemaker. This describes the ability to adjust heart rate in response to physiologic needs. Sensors can measure respiration, acid-base status vibration ect.
(will increase the pacer’s lower heart rate limit in response to activity that may require an increased myocardial oxygen demand)
pacemaker position 5 codes
O= none
A= atrium
V= ventricle
D= dual (A+V)
This indicates that the pacemaker can pace multiple sites
(pacer may pace BOTH atria and/or BOTH ventricles)
What will you see ok the EKG with atrial pacing?
A pacing spike preceded the P wave, QRS is normal
What will you see ok the EKG with ventricular pacing?
A pacing spike precedes the QRS complex. The QRS is wide
What will you see on the EKG with atrial + ventricular pacing?
There’s a pacing spike that stimulates the atria and another that stimulates the ventricles.
Examples of Asynchronous pacing
AOO
VOO
DOO
examples of single-chamber demand pacing
AAI
VVI
examples of dual-chamber AV sequential demand pacing
DDD
What does the pacer do in asynchronous pacing?
The pacemaker delivers a constant rate
There is no sense or inhibition
There can be a competitive underlying rhythm
A pacer spike delivered during ventricular Repolarization can result on R on T
What does the pacer do in Single-chamber demand pacing?
Think of this as a backup mode- it only fires when the native heart rate falls below a predetermined rate
What does the pacer do in a dual chamber AV sequential demand pacing?
The most flexible and most common
Makes sure the atrium contracts first, followed by the ventricle
This improves AV synchrony
Failure to capture:
when the pacemaker’s electrical output fails to cause myocardial depolarization
On the EKG you’ll see pacing spikes but they aren’t followed by a QRS complex (ventricular depolarization)
Failure to sense:
the pacemaker fails to recognize intrinsic cardiac electrical activity
Pacing spikes where they shouldn’t be
Indications for ICD
Ventricular tachycardia
Ventricular fibrillation
Post MI with an EF <30%
Cardiomyopathy with an EF <35%
Hypertrophic
cardiomyopathy
Awaiting a heart transplant
Long QT syndrome
A patient undergoing bunionectomy has a VOO pacemaker with a rate of 80 bpm. During the procedure, there is failure to capture and the heart rate decreases to 50 bpm. Which of the following best explains why this complication occurred
A.) the EtCO2 was 20 mmHg
B.) an ultrasonic harmonic scalpel was used
C.) the patient was hyperthermic
D.) the electrocautery setting was changed from coagulation to cutting
A.) the EtCO2 was 20 mmHg
The pacemaker failed to capture bc hypocarbia (which caused hypokalemia) made the myocardium more resistant to depolarization. The same electrical stimulus from the pacemaker was no longer sufficient to depolarize the heart. You’ll see pacer spikes but will not see capture.
can try fixing it by turning up the mV on the pacer
What does placing a magnet over a pacemaker do?
(Usually) converts the pacemaker to asynchronous mode
“magnet rate” is typically 85-100 bpm
What does placing a magnet over a ICD do?
Suspends the ICD and prevents shock delivered
What does placing a magnet over a pacemaker + ICD do?
Suspends the ICD and prevents shock delivery. It has no effects on the pacemaker function.
Pacemaker function will be subject to EMI. If EMI is likely, then the pacemaker should be reprogrammed by the manufacturer before the surgical procedure
What conditions can impair pacemaker performance?
EMI (electromagnetic interference)
conditions that make the myocardium more resistant to depolarization:
hyper/hypokalemia
Hypocapnia
hypothermia
If surgical electrocautery is used, the best option for the surgeon to use a ______ device
bipolar device
T/F: MRI is typically contraindicated for a pt with a pacemaker or ICD
TRUE (some newer devices may be compatible)
The most critical information to have preoperatively about a pt with a pacemaker:
The pt’s underlying rhythm - so you know how to prepare for device failure
How is pacemaker failure treated?
Isoproterenol
Epinephrine
Atropine
(all depending on underlying rhythm)
When does failure to sense (undersensing) happen?
When the pacemaker does not sense the underlying (native cardiac rhythm)
you will see pacing spikes in areas you would not expect to see them
can cause R on T if pacer fires during ventricular repolarization
V.fib can happen with ventricular spike lands on T wave
Causes of failure to capture:
electrode displacement
Wire fracture
Conditions that make the myocardium more resistant to depolarization:
-hyper/hyperkalemia
-hypocapnia (intracellular K+ shift)
-Hypothermia
-myocardial infarction
-Fibrotic tissue buildup around the pacing leads
-antiarrhythmic medications
Failure to output
Occurs when a pacing stimulus is not produced in a situation when it should be.
can be caused by oversensing, pulse generator failure or lead failure
What can cause failure to output?
oversensing
pulse generation failure
lead failure
When is the risk of EMI greatest?
use of electrocautery and radio frequency ablation
Does the coagulation or cutting setting on electrocautery cause more EMI?
Coagulation setting causes more
use cutting
What causes more EMI?
A.) monopolar
B.) Bipolar
C.) ultrasonic harmonic scalpel
Monopolar causes more
If the surgeon insists on monopolar cautery, then you insist that they use short bursts
<0.5 seconds
The risk of EMI is highest when the electrocautery tip is used within:
a 15 cm radius of the pulse generator
Place the electrocautery return pad _____ away from the pulse generator and in a location that prevents a ______ line of current through the pulse generator
Far away
direct line
Select the interventions that are NOT contraindications with a pacemaker or ICD
A. MRI
B. Lithotripsy
C. electroconvulsive therapy
NOT contraindicated:
B. Lithotripsy
C. electroconvulsive therapy
Contraindicated:
A. MRI
ICD position 1 codes
SHOCK CHAMBERS
O= none
A= Atrium
V= ventricle
D= dual
ICD position 2 codes:
ANTI-TACHYCARDIA PACING CHAMBERS:
O= none
A= atrium
V= ventricle
D= dual
ICD position 3 codes:
TACHYCARDIA DETECTION
E= electrocardiogram
H= hemodynamic
ICD position 4 codes:
ANTI-BRADYCARDIA PACING CHAMBERS
O= none
A= atrium
V= ventricle
D= dual
An ICD cardioverts V tach with:
1-30 joules
and ICD defibs V.fib with
10-30 joules
If an ICD acknowledges that a shock is needed, it will deliver how many shocks?
6 shocks
EMI:
Any external non-physiologic signal that interferes with pacemaker function
o Degree of EMI interference is variable
o Inhibition of pacemaker function, inappropriate triggering, electrical reset, damage at tissue -lead interference, tracking of electrical noises are all possible responses
What is the most prevalent source of electromagnetic interference in the OR?
electrocautery
monopolar cautery produces more energy than bipolar and requires a:
grounding pad
Distance between the electrocautery tip and grounding pad will determine:
The area in which a stray current can be sensed and misinterpreted
grounding pad should be placed near:
the site of surgery/ away from heart/pacemaker
Why is bipolar cautery safer?
has the anode and cathode at the tip of the device, this proximity gives less area for a stray interface to be misinterpreted
o does not require grounding pad, gives off less energy, not generally a surgeon’s preference
Effects of EMI
-Interpreted as serious dysrhythmia
-viewed as “noise” and initiate asynchronous pacing, leading to R on T
-Current conducted down lead and damage myocardium
-Decrease battery life
-Reset device to alternate rate
-Be interpreted as P wave causing device to only pace the ventricle, possibly losing atrial kick
-Reprogram and alter device setting
-Alter thresholds
“Magnet rate”
- typically 85-100 beats per minute
If a magnet was used intraoperatively, what must be done post-operatively?
a device interrogation must occur postoperatively
How much is each horizontal small box?
.04 seconds
how much is each horizontal large box?
.20 secs
how much is one small box vertically?
1mm (0.1mV)
what is the J-point?
end of QRS and beginning of ST segment
what is the J-point used to identify/measure?
use the J point with the ST segment to identify myocardial ischemia
threshold values for ST segment depression in males and females of all ages in leads V2-V3
-0.5mm (-0.05mV)
threshold values for ST segment depression in males and females of all ages in all other leads
-1.0 mm (-0.1 mV)
best leads for continuous monitoring of ST segment changes:
V3
V4
V5
III
avF
best leads for continuous monitoring of ST segment changes:
V3
V4
V5
III
avF
what is the best lead to assess narrow QRS complex rhythms?
Lead II
Which lead is best to assess ST segment changes?
V5 and V3
H’s
Hypovolemia
Hypoxia
Hydrogen ion excess (acidosis)
Hypoglycemia
Hypokalemia
Hyperkalemia
Hypothermia
T’s
Tension pneumothorax
Tamponade – Cardiac
Toxins
Thrombosis (pulmonary embolus)
Thrombosis (myocardial infarction)
V.fib/pulseless Vtach ACLS intervention
CPR 2 mins
shock
CPR 2 mins
Epi 1mg Q3-5 mins
shock
CPR 2 mins
Amiodarone 1st dose: 300mg
Amiodarone 2nd dose: 150mg
Asystole/PEA ACLS
CPR 2 mins
Epi 1mg every 3-5 mins
Bradycardia ACLS
Atropine first dose: 1mg (repeat 3-5 mins)
max: 3mg
transcutaneous pacing
dopamine infusion (5-20mcg/kg/min)
Epi infusion (2-10mcg/per)
when will you see torsades?
Seen with hypokalemia, hypocalcemia, hypomagnesemia
May be worsened with lidocaine administration
whats the rate of torsades?
150-250bpm
if the pt has a pulse and v.tach how would you treat it?
synchronized cardioversion
When is a. fib considered “controlled”?
Rate less than 100
T/F: you can measure the PR interval in a.flutter
FALSE
How long is the PR interval in first degree heart block?
> .20 secs
What are the characteristics of second degree block-mobitz 1 (wenkeback)?
Atrial rhythm is regular, but the ventricular rhythm is irregular
PR progressively lengths until QRS complex is dropped
what are the characteristics of second degree AV block- mobitz II?
p-waves are normal, but some are not followed by QRS
PR intervals are constant- the dropped QRS occurs w/o warning
What is the rate in 3rd degree?
Less than 45
Pacer is needed
What is the rate in Sinus tach?
100-160
Males > 40 years of age J-point elevation in all leads
1 mm (0.1mV)
Males > 40 V2, V3 J-point elevation
2 mm (0.2mV)
females in all leads J-point elevation
> 1mm (0.1mV)
females V2, V3 J-point elevation
1.5 mm (0.15mV)
Causes of failure to capture:
-electrode displacement, wire fracture, and conditions that make the myocardium more resistant to depolarization:
-Hyper/hypokalemia
-Hypocapnia
-MI
-fibrotic tissue buildup around the pacing leads
-anti-arrhythmic medications
