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  1. What is a pacemaker and how does it work?
  2. Are there different kinds of pacemakers ?
  3. How is a pacemaker checked ?
  4. How long do pacemakers last ?
  5. Who manufactures most pacemakers and how can I contact them ?
  6. Are there any restrictions once a pacemaker has been implanted ?

What is a pacemaker and how does it work?

 

A pacemaker is any device which prevents the heart from going too slow by delivering an electrical impulse to the heart.  Different types of pacemakers include temporary pacemakers inserted with a catheter through the skin and external pacing pads applied to the chest wall.  The pacers we commonly use however are the permanent Implantable cardiac pacemakers such as the one illustrated above.  This device, about the size of a silver dollar, goes under the skin usually in the chest area.  Wires ("pacing leads") are attached to the pacemaker at the header (the clear plastic part on the top of the pacemaker).These wires are run through a vein into the heart and deliver electrical energy to the heart to keep the heart from going too slow.  A pacemaker will sense the heart beat through these wires and only delivery energy if the patients heart is beating slower then the rate the pacemaker is programmed to keep the heart at.  Many patients are not "pacer dependent" and there pacer only will deliver pacing when the heart slows.  Other patients are pacer dependant and require continuous pacing without which the heart would stop (a condition termed asystole - and one which we generally wish to avoid)

 

An excellent description of how the heart works and why a pacemaker is at times needed can be found in a section of Guidant's web site here.

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Are there different kinds of pacemakers ?

There are numerous different types of pacemakers and a variety or different pacemaker manufacturers.  At Florida Electrophysiology Associates, we utilize pacemakers from the industry leaders Medtronic and Guidant.  Although many other companies manufacture pacemakers (and we are continually approached by them to use their products), reliability and the ability to have the unit serviced once implanted are critical in our view.  Pacers we implant can generally be checked anywhere in the free world and throughout the United States.  Many of our patients are "snow-birds" and an off-brand pacemaker would require checking only in specific metropolitan locations.  True, second tier company pacemakers are generally less costly; but we believe it's Ok to put regular unleaded in your car -  but exclusively use premium in our patients  hearts.  

Aside from the different manufacturers, there are multiple different models and types of pacemakers.  Pacers can be made to pace only a single chamber of the heart or designed to sequentially pace both the upper chambers (i.e. the atria) and then the lower chambers of the heart (i.e. the ventricles).  Which type of pacer we implant in a patient is a medical decision individualized to the specific patient.  In addition, modern pacemakers have the ability to sense when a person is exercising and even sleeping.  Pacers do this by using an accelerometer to sense body movement or a breathing sensor to sense respiratory rate.  A pacer can thus mimic the actions of the hearts natural physiology, and will increase it's rate when the person is exercising or decrease it's rate when the person is resting of sleeping.  This type of pacer is termed a rate responsive pacer.  Approximately 95% of the pacers we implant are rate responsive.   In addition to these features, modern pacemakers have all types of automatic diagnostics such as the ability to automatically record in memory any abnormal heart rates or any out or range electrical activity in the pacing wires.  Modern pacemakers are essentially battery powered small computers in their ability to process information and treat a patient.

For more specific information on your particular pacemaker we suggest browsing the websites of some of the major manufactures

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How is a pacemaker checked ?

 

A pacemaker is checked in our office with a device called a programmer.  A pacemaker programmer is a computer which can communicate with the pacemaker using radio waves.  Using a programmer we can "interrogate" the pacemaker and determine how efficiently it's pacing the different chambers of the heart, the remaining life of the pacemakers battery and if there have been any unusual events such as a life-threatening arrhythmia that the pacemaker picked up (even if the patient was unaware that they may have occurred).  In addition, aside from just checking a pacemaker, we can reprogram the unit to behave more ideally for the individual patients problem.  This periodic fine tuning of the pacemaker will help maximize the benefit that the patient gets from cardiac pacing and also help maximize the pacers battery life because we will adjust the pacemakers energy delivery to more finely match the amount required for that particular patient.  Many patients ask us if we perform trans-telephonic (i.e. over the telephone) pacemaker checks.  We do not.  A transtelephonic pacer check will only tell the doctor very rudimentary information (i.e. that the pacers still working) but not provide any critical diagnostic information or allow us to change any pacing parameters.  You don't invest in a $10,000 piano and never fine tune it after the first use and you definitely want to keep your heart in tune.  Generally, we like to check pacemakers quarterly (i.e. every three months) but occasionally will want to check a unit more frequently if we detect the battery is running out or find another potential problem we want to monitor more closely.  We check pacemakers in our pacer clinic.

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How long do pacemakers last ?

This depends on how often the pacemaker is used to pace the heart and the amount of energy used for each paced heartbeat.  If a pacemaker is only being used infrequently, one can expect about 10 years of battery life with at least a six month warning that the battery is running down.  We can detect a low battery warning in our office during a routine pacer check in our pacer clinic.  If a pacemaker is being used constantly then it will usually last between five and 8 years again depending on the amount of energy the pacer needs to deliver to the heart for every heartbeat.  Larger pacemakers have bigger batteries and will generally last longer then the most cosmetically appealing smaller units.  In the 1960's, a Florida company marketed a nuclear powered pacemaker.  This pacemaker used a small pile of Plutonium-236.  P-236 will naturally become warm due to neutron decay.  The friction of the neutrons passing through the metal generates heat.  A thermocouple in the pacemaker then can generate a current due to the temperature differential between the pacer and the patients skin.  These pacemakers were thus warm to the touch.  The "battery" life of this type of pacemaker is around the radioactive half life of Plutonium-238 (i.e. 14,000 years).  These pacemakers would thus generally out-last the patient who had the implant.  Plutonium-238 can very easily be made into a nuclear bomb; all you need to obtain is a critical quantity of this man made metal and when symmetrically compressed with a spherical high explosive charge the self generated neutrons of the element will reach a stage of criticality and fission will occur.  It's thus easy to make a Nagasaki type atomic bomb in your garage - all you need is plutonium, some plastic explosives and very precise timing fuses to allow for spherical symmetric compression of the Plutonium sphere(s).  Getting the Plutonium however represents a bit of a challenge for most terrorists since P-238 can only be manufactured in a nuclear reactor (a so called breeder reactor in which a common isotope of uranium is converted into Plutonium by neutron bombardment  generally for the purpose of making an atomic bomb - but occasionally also to be used as fuel to power another reactor).  This is why nuclear powered pacemakers are no longer manufactured and the few still in patients are followed closely by the government.  When a patient dies, an NRC agent comes and retrieves the pacemaker from the body to contain the P-238.  Thermocouple based plutonium fuel cells are still used in application where long lasting reliable power is needed for years at a time (i.e. a satellite traveling to a distant planet too far from the sun to allow for solar cells).  Modern pacemakers used Lithium iodide fuel cells.  This compound has a high energy density and a predictable internal resistance and voltage during depletion.  The compound also does not give off volatile gasses or liquids during depletion unlike some of the early Zinc oxide cells in the pacemakers of the 50's.  Other energy sources for pacemakers have been considered.  For example, I once tried to get a patent on a pacemaker powered by a patients body movement much like an automatic watch is powered by the users wrist movement.  This however increased the size of the pacemaker beyond adequate limits and also was not reliable enough for all patients. 

Editorial Note: Sorry about the digression into physics but it's always been one of my interests, I also thought patients might find these little facts of interest and...... after all this is my web site - RF

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Who manufactures most pacemakers and how can I contact them ?

There are over a dozen different manufacturers of pacemakers.  In the United states however 90% of all implanted units are made by three main companies: Medtronic, Guidant and St. Jude Medical.  Because of reliability and support reasons we offer our patients mostly Medtronic and Guidant pacing systems with the particular pacer selected customized to the individual patients problem.  Please feel free to browse the web site's of Medtronic and Guidant - there's a great deal of additional information available there in regards to pacers and ICDs.

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Are there any restrictions once a pacemaker has been placed ?

After a pacemaker has been implanted, we give our patients post-operative instructions.  After the initial post-operative period ends, patients can generally resume a normal lifestyle.  Many patients ask about microwave ovens.  patients can use microwave ovens with modern pacers.  A few pacemakers manufactured in the 60's and 70's were sensitive to microwave radiation.  This is no longer a problem with modern pacers.  Cellular phones can also be used but generally patients should use analog phones.  Digital cellular phones can inhibit certain pacemakers.  If you're not sure about your situation, contact your pacemakers manufacturer.  Patients should not engage in any activity using high strength electrical or magnetic fields (such as arc welding). Diagnostic MRI scanning is generally avoided once a patient has a pacemaker in place.  For over 90% of our patients however, once a pacemaker is implanted the patient can essentially ignore its presence (aside from of course coming to get it checked in pacer clinic) and resume a completely normal lifestyle.  This includes (after six weeks of healing) golf and tennis and any other physical activity a patient wishes to engage in.

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