1. Pacemakers and Implantable Defibrillators
By Michael Dayton

2. 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.

3. Pacemaker and ICD Types
Asynchronous
Impulse is a fixed rate
No relation to patients intrinsic cardiac activity
Susceptible to Torsades if impulse lands on the T-wave
Synchronous
Demand mode
Sensing circuit searches for intrinsic depolarization potential
If absent, a pacing response is generated
Can mimic intrinsic electrical activity pattern of the heart

4. Pacemaker and ICD Types Cont…
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.

5. Determining Pacemaker Types
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
The following can help determine the type of pacemaker:
1st letter – chamber paced
2nd letter – chamber sensed
3rd letter – Response to chamber sensed

6. Candidates for ICD or 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

7. 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

8. Implanting the Devices
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
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)

9. 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

11. ICD and Pacemaker Complications
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
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

12. 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:
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.

13. 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

14. References
“Implantable cardioverter-defibrillator.” to
“Artificial Pacemaker.” to maker#Biventricular_Pacing_.28BVP.29
“Implantable Pacemaker.” to ageID=1613&ContentID=25677&ContentTypeID=1
“Medtronics.”
“Johns Hopkins' Welch Center for Prevention, Epidemiology and Clinical Research”
“Healthy Hearts” healthyhearts.com/ pacemaker.htm
“Heart Rhythm Society”
“Pacemakers”