ICD Info
Home Up Pacemaker info


Search Contents





Table of Contents

  1. What is an ICD and what does it do ?
  2. How long does an ICD last ?
  3. What's the difference between a pacer and an ICD ?
  4. Who manufactures ICDs ?
  5. How are ICDs followed ?
  6. Special precautions with ICDs

What does an ICD do?

A Guidant ICD

Ventricular fibrillation is an immediately life-threatening rhythm disorder involving the lower chambers of the heart (i.e. the ventricles).  When the heart enters ventricular fibrillation, the ventricles stop beating in a coordinated fashion.  Rather they twitch uncontrollably at rates exceeding 500 beats a minute.  At this rate the heart isn't really moving and unless reversed within 4 minutes the patient dies.  This is the rhythm problem people receive CPR for and it's also the one where doctors take a set of paddles, yell "clear" and shock the patient.  Ventricular fibrillation is the most common cause of death in the developed world.  When most patients die of heart disease, it is usually the result of the heart entering this rhythm;  true, some heart disease deaths are due to the heart simply being unable to pump blood and others are due to the heart stopping completely.  However, the majority of heart disease deaths, especially the sudden deaths in people with a history of heart disease are due to ventricular fibrillation.  Ventricular fibrillation is also commonly called "V. Fib."

 ICD stands for "Implantable Cardioverter Defibrillator".  A defibrillator is any device which will get a person out of ventricular fibrillation.  External manual defibrillators are commonly seen on  television shows such as "E.R"  where  paddles are use to shock a patients heart back to normal.  These external defibrillators have saved thousands of lives but need to be activated by a team of trained medical personnel.  An Implantable defibrillator or ICD will automatically reset the heart when the heart enters a potentially life-threatening arrhythmia.  An ICD can deliver a shock to the heart through electrodes placed near the heart at the time of implant.  These devices are almost 100% effective at preventing death from a life-threatening arrhythmia.  Often times the ICD will get the patient out of the abnormal rhythm by pacing the heart rapidly.  Although a shock can be felt by the patient, pacing to terminate an abnormal rhythm occurs usually without the patient being aware.

ICD's are also commonly, albeit mistakenly, called "AICDs" which stands for automatic Internal cardiac defibrillator.  This acronym was copyrighted by Guidant corporation in the early days of ICDs and only really applies to the units made by Guidant. 

An excellent description of how an ICD works and why it is needed can be found in a section of Guidant's web site by clicking here.

Back to Top

How long does an ICD last?

This depends on a number of factors including the size of the ICD (larger units are less comfortable but last longer), the type of defibrillator needed by a patient, the amount of pacing an ICD is doing and the number of shocks a patient is receiving.  A typical shock takes about two weeks of energy from the ICD battery.  ICD batteries are made of lithium vanadium oxide and are different then pacemaker batteries.  ICD batteries are called upon at times to deliver very high current flows.  Unfortunately, the type of battery chemistry needed for this feature makes ICD batteries last a shorter amount of time then pacemaker batteries.  ICD's generally will last between three and 8 years, again depending on a number of individual variables.   When an ICD starts to run low, we get nearly a year of warning so that an exchange can be scheduled.  Many ICDs also have a feature in which they will start to beep or produce steady tones (yes like an alarm clock) when the battery had reached elective replacement time (i.e. when about six months of battery life remains).  These ICDs will also start to produce tones to alert the patient is any of a number of other technical self checks that the ICD routinely performs results in an abnormal reading.  Should you hear your ICD beep or produce a tone, please contact us so that we can interrogate the ICD to determine the cause of the fault.  You can contact the ICD device manufacturers listed below for more specific answers to your questions. 

Back to Top

What's the difference between a pacer and an ICD?

A pacemaker will prevent the heart from going too slow but will do nothing if the heart enters a potentially life-threatening fast heart rhythm such as ventricular tachycardia or ventricular fibrillation.  These fast heart rhythms are very common causes of death in people with previously damaged hearts.  An ICD can treat these rhythms either with rapid pacing or by delivering a shock.  All modern ICDs also have pacemakers in them and can thus also prevent the heart from going too slow.  ICDs because of their added complexity are larger then pacemakers and have different types of batteries in them and therefore generally have a shorter life span.  The combination pacemaker/ICD devices are relatively new and many patients from several years back have both a separate  pacemaker and ICD in place.  

Back to Top

Who manufactures ICDs?

As with pacemakers, there are basically two major manufactures of these devices.  Although about a half dozen companies currently manufacture defibrillators on a worldwide basis, the two technology leaders are Medtronic and Guidant.  The devices made by these companies are more advanced then those made by their competitors and are the only manufactures ICDs we routinely implant in this practice.  ICD technology is much more complex then pacer technology and it really benefits the patient when a state of the art unit is implanted.  For example, second tier ICDs from other companies are much larger then the current ICDs available from Medtronic or Guidant - so much so that many times these need to be implanted in the abdomen and not in the chest.  In addition, Medtronic and Guidant ICDs both have built in dual chamber state of the art pacing systems in their ICDs.  Other competing ICDs only have rudimentary single chamber pacing ability.  True, ICDs from other manufactures are cheaper but we believe regular unleaded gas is OK for the car but only premium products should go in our patients hearts.  Both of these companies have extensive web sites were many of your questions can be answered.

Back to Top

How are ICDs followed ?

An ICD Programmer

ICDs are followed in our ICD clinic.  We generally like to check ICDs every three months.  the ICD is checked with a machine (essentially a computer) called a programmer.  This communicates with the ICD through radio waves and allows us to change the way the ICD functions.  Hundreds of different setting can be programmed into an ICD and each patient's defibrillator is individually adjusted to suite a particular set of problems.  The ICD if it treats a rhythm problem will memorize the patients EKG at the time the problem occurred. This information too can be extracted from the ICD during a routine check and additional decisions made.  At the time of the ICD check a number of other parameters are also checked such as the pacing threshold of the patient's heart and the resistance (i.e. lead impedance) of the ICDs electrodes..  Modern ICDs also perform some self diagnostics.  Should your ICD start to beep, this indicates a problem which requires further investigation and you should contact our office.  Should your ICD discharge (i.e. you receive a shock), please give one of our doctors a call.

Back to Top

Special precautions with ICDs ?

patients can live full and normal lives with an ICD in place.  Most all forms of exercise can be engaged in (including golf and tennis) and for the most part patients can ignore the fact that an ICD has been implanted.  Microwave ovens are safe to be around as are the vast majority of electrical products.  We ask our patients with ICDs to avoid high energy electrical and magnetic fields.  Thus, if a patient is an arc welder or works on high energy power lines then we would suggest a lifestyle change.  Magnetic field need to be high as well such as what might be encountered if a stereo speaker magnet was held within 6 inches of the ICD or if a patient worked around an MRI machine or large generator.  These are unusual circumstances and for the vast majority of ICD patients no special lifestyle precautions need be observed.  Please join us at our ICD support group meeting should you have specific questions about your ICD 

Back to Top


Home Up Search Contents