Heart Disease - Heart block
Sometimes the scars resulting from rheumatic fever, heart attack, or surgical repair of the heart may damage the electrical network in a way that blocks normal transmission of the signal between the upper and lower chambers. The disruption, called atrioventricular block , manifests in three degrees of intensity. First degree heart block is only detectable by an EKG and is merely a short delay in the normal transmission. Second degree heart block shows up as an irregular pulse—some of the beats are blocked. In third degree heart block, none of the beats reach the lower chambers; they begin beating on their own, but at a much slower rate, meaning that blood flow is seriously affected, especially to the brain. Blackouts and convulsions may ensue.
For first degree heart block and many forms of second degree, there are nervous system stimulants to keep the heart from lagging. For third degree heart block and some forms of second degree, however, drugs are not enough. An artificial electronic pacemaker, implanted in the body and connected to the heart by wires, has been successfully applied to many thousands of people throughout the world. This pacemaker fires electrical shocks into the ventricle wall to make it beat at the proper rate. Most devices are powered by tiny lithium batteries that last up to 10 years.