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 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

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.

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

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

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 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)

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 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

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.

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 “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