PACEMAKERS AND DEFIBRILLATORS

Pacemakers produce small electrical impulses that stimulate the heart to beat. They are used when the natural heartbeat is too slow. Depending on the type of pacemaker, the impulses are carried by wires (leads) threaded through a vein into the right ventricle, the right atrium, or, as illustrated here, both chambers. Occasionally, wires can be placed surgically on the outer surface of the heart instead. Inserting a pacemaker with wires through the vein is a minor procedure that can be done with local anesthesia. The X-ray shows the appearance of a pacemaker system.

Internal defibrillators produce larger stimuli that are capable of shocking a heart with ventricular fibrillation o ventricular tachycardia back to a more normal rhythm. These devices are larger and must be implanted under the muscle of the abdomen. Different types of defibrillators use different systems of leads. The one shown here has a wire in the right ventricle and a "patch" or "mesh" electrode under the skin of the chest, near the heart. The win inside the heart monitors the rhythm. A computer in the device determines whether the rhythm is satisfactory o requires a shock. The shock is produced by an electrical current passed between the patch electrode and the wire in the heart.

*17\252\8*

Cardio & Blood-holesterol