Sudden cardiac (SCD) refers to the situation when a person
collapses due to the sudden occurrence of a lethal rhythm
disturbance. As noted above, invariably ventricular tachycardia
is the cause. In contrast to syncope due to the more benign
causes outlined above, patients generally require resuscitation
because of their unconscious, pulseless and apneic (not breathing)
state. Without adequate CPR and prompt defibrillation, death is
fairly certain. In fact, over 80% of patients experiencing ventricular
tachycardia/fibrillation die before reaching the hospital. The
arrhythmia occurrence is dramatic and is often later referred
to as a 'massive heart attack.' Rarely is this the case. Most
episodes of SCD are not associated with heart attack.
It would be most desirable to be able to predict which patients
will experience SCD. However, this is currently not possible.
Obviously, patients at greatest risk include survivors of SCD
and specific subgroups of patients with significantly impaired
heart function. These patients usually require a diagnostic
electrophysiology study to document the presence of
ventricular tachycardia.
The problem of SCD is significant, affecting one in every
100,000 persons yearly. Among patients with prior heart
attacks, nearly one half will experience SCD. The survival
rate is poor, ranging between 5% in large metropolitan areas
such as New York City to 10-15% in Sangamon County, Illinois.
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