The atria refill. The electrical activity of the heart can be detected by electrodes placed at the surface of the body. The ventricles can maintain a beat even without a functioning A-V node, although the beat is slower. There is, however, a danger that impulses arising in the ventricles may become disorganized and random. If this happens, they begin to twitch spasmodically, a condition called ventricular fibrillation .
Blood flow ceases and unless the heart rhythm is restarted, death follows swiftly.
These are devices that generate rhythmic impulses that are transmitted to the heart by fine wires. Thanks to miniaturization and long-lived batteries, pacemakers can be implanted just under the skin and reached through a small incision when maintenance is needed. Although the A-V node sets the basic rhythm of the heart, the rate and strength of its beating can be modified by two auxiliary control centers located in the medulla oblongata of the brain. One sends nerve impulses down accelerator nerves . They increase the rate and strength of the heartbeat and thus increase the flow of blood.