A cardiac arrest is the complete cessation of the heartbeat and results in death in seconds. This is almost always due to ventricular fibrillation. This is not a “heart attack” or “heart failure.”
Discussion
The heart consists of four main chambers called the left and right atria and the left and right ventricles. The heartbeat signal originates in the right atrium and travels down to the ventricles.
During rest, the heart beats about 70 times a minute in the adult male, while pumping about 5 liters of blood in that minute. The cells of the pacemaker region oscillate spontaneously about 70 times each minute. This, in turn, initiates a similar discharge of the nearby muscle fibers of the atrium. A tiny wave of current sweeps over the atria, causing them to contract.
When this current reaches the region of connective tissue between the atria and the ventricles, it is picked up by the AV (atrio-ventricular) node. This delays the signal slightly (about 1/10 second) to allow the ventricles to fill with the blood from the atria. The AV node then connects to a system of branching fibers that carries the current to all parts of the ventricles.
The contraction of the ventricles (lower chambers of the heart) in response to this electrical activity is called systole. A period of recovery follows called diastole. Here the heart muscle relaxes and the atria refill.
The electrical activity of the heart can be detected by electrodes placed at the surface of the body. Analysis of an electrocardiogram (ECG or EKG) aids in determining, for example, the existence of damage following a heart attack. This is because death of a portion of the heart muscle blocks electrical transmission through that area and alters the appearance of the ECG.
In ventricular fibrillation (VF), impulses arising in the ventricles are disorganized and random. If this happens, they begin to twitch spasmodically. In VF, blood flow ceases and — unless the heart rhythm is reset — death follows swiftly — within seconds. In fact, VF is the immediate cause of as much as 25% of all deaths.
Hospital emergency departments, ambulances, and (recently) commercial aircraft and grade schools are routinely equipped with defibrillators which, by giving the heart a jolt of direct current, may reset its rhythm and restore the victim’s life.
The coronary arteries feed blood back to the heart muscle itself. When an artery is blocked the muscle being fed by this artery will die. This is called a “heart attack.” Sometimes the heart is so weakened by the heart attack that it slowly wears out and the patient dies after a few years. This slow death is referred to as “heart failure.”
VF (the most common type of cardiac arrest) is an electrical riot of the heart cells. It results in death in seconds. It is not a heart attack; it is not heart failure.
Automobile analogies may be helpful. The heart attack is a fuel problem in that the fuel (blood) is being restricted from getting to the heart muscle itself. VF is an electrical problem. Finally, heart failure is the engine simply slowly wearing out.