SUDDEN CARDIAC DEATH
Sudden cardiac death (SCD) refers to death from a cardiac cause.
The majority of SCDs result from ventricular dysrhythmias, specifically ventricular
tachycardia or fibrillation.
Antidysrhythmia drugs may cause life-threatening dysrhythmias similar to those for which
they are administered. This concept is termed prodysrhythmia.
o The patient who has severe left ventricular dysfunction is the most susceptible to
o Digoxin and some antidysrhythmia drugs can cause a prodysrhythmic response.
Defibrillation is the most effective method of terminating VF and pulseless VT.
Defibrillation is accomplished by the passage of a DC electrical shock through the heart to
depolarize the cells of the myocardium. The intent is that subsequent repolarization of
myocardial cells will allow the SA node to resume the role of pacemaker.
Rapid defibrillation can be performed using a manual or automatic device.
o Manual defibrillators require health care providers to interpret cardiac rhythms,
determine the need for a shock, and deliver a shock.
o Automatic external defibrillators (AEDs) are defibrillators that have rhythm
detection capability and the ability to advise the operator to deliver a shock using
hands-free defibrillator pads.
Synchronized cardioversion is the therapy of choice for the patient with hemodynamically
unstable ventricular or supraventricular tachydysrhythmias.
o A synchronized circuit in the defibrillator is used to deliver a countershock that is
programmed to occur on the R wave of the QRS complex of the ECG.
o The synchronizer switch must be turned on when cardioversion is planned.
The procedure for synchronized cardioversion is the same as for defibrillation, with some
IMPLANTABLE CARDIOVERTER-DEFIBRILLATOR (ICD)
The ICD is used for patients who (1) have survived SCD, (2) have spontaneous sustained
VT, (3) have syncope with inducible ventricular tachycardia/fibrillation during EPS, and (4)
are at high risk for future life-threatening dysrhythmias (e.g., have cardiomyopathy).
The ICD consists of a lead system placed via a subclavian vein to the endocardium. A battery-powered pulse generator is implanted subcutaneously, usually over the pectoral
muscle on the patient’s nondominant side.
o The ICD sensing system monitors the HR and rhythm and identifies VT or VF.
Approximately 25 seconds after the sensing system detects a lethal
dysrhythmia, the defibrillating mechanism delivers a shock to the patient’s
If the first shock is unsuccessful, the generator recycles and can continue to
In addition to defibrillation capabilities, ICDs are equipped with antitachycardia and
Education of the patient who is receiving an ICD is of extreme importance.
The artificial cardiac pacemaker is an electronic device used to pace the heart when the
normal conduction pathway is damaged or diseased.
Pacemakers were initially indicated for symptomatic bradydysrhythmias. They now
provide antitachycardia and overdrive pacing.
A permanent pacemaker is one that is implanted totally within the body.
A specialized type of cardiac pacing has been developed for the management of HF.
o Cardiac resynchronization therapy (CRT) is a pacing technique that
resynchronizes the cardiac cycle by pacing both ventricles, thus promoting
improvement in ventricular function.
o Several devices are available that have combined CRT with an ICD for maximum
A temporary pacemaker is one that has the power source outside the body. There are
three types o