Cardiac Arrest

When the heart suddenly ceases to pump effectively it is said to be in cardiac arrest . This condition is characterized by loss of consciousness resulting from the absence of blood supply to the brain. It is similar to sudden cardiac death, except that rescue efforts initiated within a few minutes of the attack can resuscitate the heart. Delayed resuscitation may reestablish the circulation but often results in "brain death"—irreversible damage to the brain, which is more sensitive to lack of oxygen than any other organ. Loss of consciousness is abrupt, and the pulses disappear. In most cases cardiac arrest is caused by ventricular fibrillation or very rapid ventricular tachycardia.

Survival of cardiac arrest depends on initiating effective treatment as soon as the mechanism of the arrest is clarified. The simplest form of treatment—only occasionally effective but worth trying—is a blow on the chest in the region of the heart, which may terminate ventricular fibrillation or restart a heart in standstill. The definitive treatment of ventricular fibrillation is electric shock to the chest, or defibrillation. If a defibrillator is not immediately available, the circulation of blood can be artificially supported for a short time by periodic chest compression along with mouth-to-mouth breathing. Injection of drugs into the heart is rarely effective.

The success of electric-shock treatment of ventricular fibrillation depends largely on the underlying state of the heart. In most cases ventricular fibrillation develops as an electrical accident in a heart still capable of resuming good function (primary ventricular fibrillation), and its termination is usually successful and complete recovery possible. The long-term prognosis is thus also related to the underlying cardiac status. Ventricular fibrillation frequently develops in a fatally damaged heart (secondary ventricular fibrillation) in which normal rhythm cannot be restored or, if restored, cannot be maintained.

Another mechanism of cardiac arrest is ventricular standstill, or extreme bradycardia (see chap. 6). It occurs in complete heart block or abnormal function of the sinus node. Such patients can be treated with an external electronic pacemaker to restart heart action and maintain it until an intracardiac pacemaker can be inserted.