Transcript Pacemakers and Implantable Defibrillators

Pacemakers and Implantable
Defibrillators
By Michael Dayton
What are they?

ICD (or Implantable
Cardioverter Defibrillator):
– a small battery powered
device implanted into a
patient
– detects an arrhythmia it
delivers a shock to “restart”
the heart, and hopefully
restore a sinus rhythm

Pacemaker:
– A small battery powered
device, implanted into a
patient
– Paces the heart when normal
rhythm is slow, when there is
a heart block not allowing the
ventricles to contract when the
SA node fires, or any
arrhythmia causing a slow
rate.
Some devices can pace and defibrillate the heart.
Pacemaker and ICD Types

Asynchronous

Synchronous
– Impulse is a fixed rate
– Demand mode
– No relation to patients
– Sensing circuit
intrinsic cardiac
activity
– Susceptible to Torsades
if impulse lands on the
T-wave
searches for intrinsic
depolarization potential
– If absent, a pacing
response is generated
– Can mimic intrinsic
electrical activity
pattern of the heart
Pacemaker and ICD Types
Cont…
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Single Chamber: only one wire (pacing lead) is placed into a
chamber of the heart. Sometimes it is the upper chamber,
or atrium. Other times it is the lower chamber, or ventricle.
Dual Chamber:wires are placed in two chambers of the heart.
One lead paces the atrium and one paces the ventricle.
This approach more closely matches the natural pacing of t
he heart. This type of pacemaker can coordinate function
between the atria and ventricles.
Rate-Responsive Pacemakers – These have sensors that
automatically adjust to changes in a person's physical
activity
Other devices – Some devices, such as implantable
cardioverter defibrillators (ICDs), designed primarily for
other purposes, can function as pacemakers in certain
situations.
Determining Pacemaker Types
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The following can
help determine the
type of pacemaker:
– 1st letter – chamber
paced
– 2nd letter – chamber
sensed
– 3rd letter – Response to
chamber sensed
A= atria
 V= ventricle
 D= dual (atria and ventricle)
 O= none
 I= Pacing Inhibited
 T=Pacing Triggered

Examples:
– AAT= atria paced, atria
sensed, triggered
– VVI= ventricle paced,
ventricle sensed, pacing
inhibited
Candidates for ICD or Pacemaker

Pacemaker:
– Symptomatic sinus
–
–
–
–
bradycardia
Afib with slow
ventricular response
Heart block, especially
3rd Degree
Prolonged QT
Chronotropic
incompetence

Implantable Cardioverter
Defibrillator:
– Generally used in Pt. that
has had previous cardiac
arrest
– Pt. that has VT or VF with
unknown orgin or even with
medical treatment
– Sometimes used as
precaution, to prevent
Sudden Cardiac Death
Trivial Facts
“At the end of five years of study,
researchers determined that the
group of patients with implantable
defibrillators had nearly a 50
percent reduction in their death
rate.” Heart Rhythm Society
 Dr. Mirowski had a hand in
developing all three of the major
ICD companies (all in Minnesota).
Medtronic, St. Jude, and CPI
 Vise President Dick Cheney had
an ICD implanted after having a
heart attack as a precautionary
measure.
 Cost of a pacemaker or ICD
averages around $20,000-70,000

Implanting the Devices

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Most devices are
implanted in the upper
chest area, however
sometimes they are in
other locations on the
abdomen.
The operation is often
done under a local
anesthetic.
A 2-3in incision is made
just below the collarbone
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The leads are then placed
in a large vein
Leads are then positioned
in the heart muscle using a
special x-ray called
fluoroscopy
Another incision is made
to form a “pocket” for the
pulse generator. (at this
point some doctors will
put the people under
general anesthetic)
Implanting the Devices Cont…

After the pulse
generator is inserted
the leads are
connected to the
generator
 Next the incision is
closed up and the
procedure is finished
 This entire operation
often takes somewhere
around 1 hour
ICD and Pacemaker
Complications

These are electronic
devices that can encounter
problems, these problems
include (but are not
limited to):
– Sensing problems:
 Over-sensing
 Under-sensing
– Device deactivation
– Damage to device- lead
damage or dislodgement
– Batteries will wear out, average life
6-8 years, generally this causes
gradual drop in voltage, thus
sudden complete failure is not as
likely.
– Electrical output to low to
effectively capture or defibrillate
– May defibrillate inappropriately,
causing pain and anxiety. Consider
A-fib, T-wave oversensing, lead
fracture, insulation breakage, MRI.
– Interference by outside factors
Interference May Occur Around:


Electromagnets or other
powerful magnets;
ex.MRI’s (magnetic
resonance imaging)
Engines of cars, boats, etc
may temporarily confuse
the device. (Turn engine
off when working around
engine)

Avoid certain high-voltage or
radar machinery such as:
–
–
–
–
–
–
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electric arc welders
high-tension power wires
radar installations
smelting furnaces
electric steel furnaces
other high-current industrial
equipment
Newer devices have more
shielding around the pulse
generator to prevent
interference; thus these models
are not affected as often as
previous models.
Changes in EMS Treatment?

If needed one with a
ICD or pacemaker can
still be transcutaneously
paced.
 One with a ICD or
pacemaker can still be
defibrillated
References
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“Implantable cardioverter-defibrillator.”
2007. 11-03-07 to 11-20-07.
http://en.wikipedia.org/wiki/Implantable_cardioverter-defibrillator
“Artificial Pacemaker.” 2007. 11-01-07 to 11-20-07.
http://en.wikipedia.org/wiki/Artificial_pace
maker#Biventricular_Pacing_.28BVP.29
“Implantable Pacemaker.” 2007. 11-01-07 to 11-20-07.
http://ww2.heartandstroke.ca/Page.asp?P
ageID=1613&ContentID=25677&ContentTypeID=1
“Medtronics.” 2007. 11-01-07-11-20-07. http://www.medtronic.com/patients/heart.html
“Johns Hopkins' Welch Center for Prevention, Epidemiology and Clinical Research”
11-01-07-11-20-07. http://www.hopkinsmedicine.org/welchcenter/
“Healthy Hearts” 11-01-07-11-20-07 http://www. healthyhearts.com/ pacemaker.htm
“Heart Rhythm Society” 11-01-07-11-20-07.
http://www.hrspatients.org/patients/treatments/cardiac_defibrillators/vp.asp
“Pacemakers”. 11-01-07-11-20-07.
http://www.nlm.nih.gov/medlineplus/tutorials/pacemakers/htm/_no_50_no_0.htm