Implantable Cardiac Defibrillator (cont.)
What are the causes of ventricular
tachycardia and ventricular fibrillation?
Ventricular tachycardia and ventricular fibrillation
are most commonly caused by heart attacks (acute myocardial
infarctions) or scarring of the heart muscle from previous
heart attacks. Less common causes of ventricular
tachycardia and ventricular fibrillation include severe
weakening of the heart muscles (cardiomyopathy), medication
toxicity (such as digoxin toxicity), medication side
effects, and blood electrolyte disturbances (such as a low
potassium level). Ironically, some medications used in
treating heart rhythm abnormalities can cause ventricular
tachycardias.
How can ventricular tachycardia and
fibrillation be treated and prevented?
Medications have traditionally been used in
preventing ventricular tachycardia and fibrillation.
Examples of these medications include Pronestyl and
Cordarone and beta-blockers such as Tenormin and Inderal.
Medicines, however, are not always successful in preventing
tachycardias or in terminating tachycardias once they
occur.
Once a life threatening tachycardia occurs, the most
effective treatment is to administer mild electric shock(s)
to the heart to terminate the tachycardia and reset the
heart rhythm to normal.
If a patient is in cardiac arrest due to ventricular
fibrillation, the treatment is the delivery of a strong
electrical shock to the fibrillating heart without delay.
Irreversible brain and other organ damages can occur within
minutes if the normal heart rhythm is not restored. Most
patients can potentially be saved if shocks are delivered
quickly to convert the fibrillation to normal rhythm before
irreversible brain damages occur.
The electrical shocks (mild and strong) that terminate
ventricular tachycardia and fibrillation can be delivered
by an external defibrillator (a portable unit with pads
that deliver electrical shocks to the heart), or by an
implantable cardiac defibrillator (ICD). External
defibrillators, however, may not be readily available, and
rescuers may not be able to administer effective CPR for
long periods before paramedics arrive. Therefore, in
patients known to be at risk of developing life-threatening
tachycardias, ICDs can be implanted in their chests as a
preventive measure to terminate tachycardias and
fibrillation and avert cardiac arrest.
Next: Who should receive an ICD? »
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