How can survivors of unexpected cardiac arrest be protected from fatal recurrences?
Survivors of unexpected cardiac arrest (aborted sudden cardiac death) due to ventricular tachycardia or fibrillation are at risk for recurrent arrest. This is especially true if they have underlying heart disease. Patients with atherosclerotic heart disease are at risk of recurrent cardiac arrests when the first, aborted sudden death episode occurs in the absence of a new heart
attack, because this implies a persistent underlying tendency toward electrical instability.
To find the treatment program most likely to prevent recurrent cardiac arrest in a patient, it's critical to identify any predisposing anatomic or electrophysiologic abnormalities. This often requires cardiac catheterization (to show the heart and coronary blood vessels) and electrophysiologic testing. It's also necessary to determine the possible contribution of reversible causes; if they're identified and removed or corrected, the risk of recurrent cardiac arrest can be markedly reduced or eliminated. Such factors may include excessive doses of various cardiac drugs, the presence of antiarrhythmic agents and abnormal blood levels of various minerals, especially potassium.
The treatment program used to prevent fatal recurrences in survivors of cardiac arrest due to ventricular tachycardia or fibrillation must be chosen based upon several factors that depend on the individual. These include the underlying cardiac condition, how well the heart can pump and the demonstration of ventricular tachycardia or fibrillation during electrophysiologic testing.
For example, cardiac arrest survivors with the Wolff-Parkinson-White syndrome (who otherwise have normal hearts) may be satisfactorily treated simply with a catheter procedure that destroys the short circuit between the upper and lower heart chambers. At the other extreme, a heart transplant may be recommended for patients who've had a cardiac arrest as a result of very severe heart failure.
In cardiac arrest survivors with atherosclerotic heart disease but without a new heart attack, attention must be paid to both the degree of narrowing in the coronary arteries and the presence of ventricular tachycardia and fibrillation that can occur during electrophysiologic testing. Therapy limited to reversing or blunting the effects of reduced blood supply to the heart (through bypass surgery, angioplasty or medication) is likely to protect only a minority of these aborted sudden death patients from recurrent cardiac arrest. The reason is that such treatments alone don't stabilize the electrical abnormalities in scarred heart muscle that can lead to recurrent cardiac arrest.
A number of therapies exist for controlling potentially life-threatening ventricular tachyarrhythmias that result from diseased or scarred heart muscle. Antiarrhythmic medication may protect against subsequent sudden death in certain subsets of cardiac arrest survivors (for example, in persons whose hearts pump well who are given a drug that suppresses ventricular tachycardia induced during electrophysiologic testing). However, antiarrhythmic medication is limited by the need for life-long dosing and the potential for intolerable or lethal side effects. Consequently, there's been increasing reliance on the use of implantable cardioverterdefibrillators. They can automatically detect ventricular tachycardia or fibrillation when it occurs and, within seconds, deliver a lifesaving electrical shock to restore the normal rhythm.
Rapid heart rhythms account for the great majority of sudden cardiac deaths. Still, very slow rhythms due to conduction system failure are sometimes responsible for cardiac arrest. Persons resuscitated from this uncommon type of cardiac arrest are treated with a permanent pacemaker after acute reversible causes, such as drug toxicity, have been ruled out. |
