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In addition, many patients also need
treatments that control or prevent abnormal heart rhythms
that may trigger ventricular fibrillation and SCD.
These treatments include:
Implantable cardioverter defibrillators
(ICDs).
In clinical trials, these devices have been the most successful
therapy to prevent sudden cardiac death in certain high-risk
patients. ICDs are 99 percent effective in stopping life-threatening
heart rhythms. The devices continuously monitor the heart
rhythm, automatically function as pacemakers
for heart rates that are too slow, and deliver life-saving
shocks if a dangerous fast heart rhythm is detected.
Medications, including ACE
inhibitors, beta blockers, calcium channel blockers and others
are prescribed to control abnormal heart rhythms or treat
other conditions that may contribute to heart disease or SCD.
There have been many clinical trials and other studies of
medications currently available to prevent cardiac arrest.
In some cases, medications have actually increased patients'
risk of SCD. Medications often are helpful in treating other
symptoms of cardiovascular disease. Sometimes, more than one
medication is prescribed at the same time. These medications
also often are prescribed for patients who have an ICD
to reduce the frequency of device firing. (more on ICDs below)
Catheter ablation (CA). In
this technique, radiofrequency energy is used to destroy small
areas of heart muscle that give rise to the abnormal electrical
signals that cause rapid or irregular heart rhythms. RFA often
is used in conjunction with ICD therapy to decrease the frequency
of abnormal heart rhythms in the ventricles. It is not usually a substitute
for an ICD.
How Do ICDs Work to Prevent SCD?
ICDs are implanted under the skin, like a pacemaker. Special
wires, or "leads" connected to the ICD are placed in the heart
to record its electrical activity. The system automatically
monitors the heart rate to detect and correct abnormal rhythms.
The device can act as a pacemaker when it detects a too-slow
heart beat (bradycardia). When a life-threatening ventricular
tachycardia or fibrillation is detected, the ICD delivers
a controlled electrical shock to restore the heart's normal
rhythm and prevent sudden cardiac death.
Modern ICD devices have an electronic
memory that records the electrical patterns of the heart whenever
an arrhythmia occurs. This record is available for review
by the physician, who can monitor the frequency and severity
of problems in the electrical conduction system of the heart.
Clinical Trials with ICDs
A number of clinical trials - some still in progress - have
studied whether ICDs are more successful than drug treatments
in preventing sudden cardiac death in certain groups of high
risk patients.
Below is a summary of the major clinical trials testing the
effectiveness of ICDs in preventing sudden cardiac death:
Primary Prevention Trials
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- Multicenter Automatic Defibrillator Implantation
(MADIT) Trial. Patients
in the study had coronary artery disease, an ejection
fraction of less than 35 percent and documented episodes
of ventricular tachycardia that were self-correcting
and caused no adverse symptoms. The patients
underwent electrophysiology study. If they had an
inducible arrhythmia, they were divided into two groups:
one received conventional drug therapy, and one received
ICD therapy.
Results: The death rate from any cause among
patients who did not have an ICD was as high as 39
percent, but much lower (16 percent) in the group
of patients with ICDs.
RECENTLY, THIS STUDY WAS STOPPED
EARLY BECAUSE PATIENTS WITH ICDS HAD SIGNIFICANTLY BETTER
SURVIAL THAN PATIENTS WITHOUT THE DEVICES.
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- Multicenter Unsustained Tachycardia Trial (MUSTT).
The study included more than 2,000 patients
who had coronary artery disease, an ejection fraction of
40 percent or less and had experienced episodes of ventricular
tachycardia that were self-correcting and caused
no adverse symptoms. Treatment decisions were based on whether
sustained VT could be induced during an electrophysiology
(EP) study.
Results: A significant reduction in the rate of sudden
cardiac death (approximately 75 percent) was seen in patients
with inducible VT who were treated with ICDs. No improvement
in survival was seen in patients who did not receive ICDs,
even when decisions to treat with drugs were based on an
EP study.
Secondary Prevention Trials
- Antiarrhythmics vs. Implantable
Defibrillators (AVID) Trial. ICDs were compared
with medications in patients with a history of documented
life-threatening arrhythmias.
Results: Of more than 1,000 patients studied, nearly
one-quarter who were taking anti-arrhythmic drugs died,
compared with only 16 percent who had an ICD. Overall, The
ICD group experienced a 39 percent reduction in deaths in
the first year, with a 27 percent and 31 percent reduction
in years two and three.
The benefit of ICDs in this group
of patients was so significant that the AVID study was terminated
early so that all patients would have the option of ICD therapy.
In two similar studies (the Canadian Implantable Defibrillator
Study (CIDs) and the Cardiac Arrest Study Hamburg (CASH),
ICD therapy significantly reduced sudden cardiac deaths
compared with conventional drug therapy in patients who
had survived a prior episode of cardiac arrest.
Who is a Candidate for ICD?
The American College of Cardiology and the American Heart
Association, along with representatives of the Heart Rhythm
Society, have developed
guidelines
to help physicians
and patients decide whether an ICD is the best treatment for
an individual at risk for SCD. For example, it is agreed that
ICD therapy will benefit:
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Individuals who have suffered a prior
cardiac arrest or who experience spontaneous, sustained
episodes of ventricular
tachycardia (VT that is not self-correcting),
especially if they also have episodes of unexplained
fainting
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Certain patients with an ejection
fraction of less than 35-40 percent and documented
episodes of ventricular tachycardia that are self-correcting
and cause no adverse symptoms. |
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People with an ejection
fraction of 35 or below with or without episodes
of ventricular tachycardia (rapid heartbeat) |
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People with
significant heart disease, syncope,
and no other explanation
for their symptoms despite thorough investigation. |
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People with inherited disorders associated with a high risk of sudden death. |
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