American Medical Association Family Medical Guide - American Medical Association [343]
Implantable defibrillator
An implantable defibrillator is an electronic device that is implanted just beneath the skin of the abdomen and attached with very thin wires to the heart. Whenever it is needed, the defibrillator delivers an electrical charge to the heart to slow a potentially dangerous rapid heartbeat and return the heartbeat to normal.
Diagnosis
To diagnose paroxysmal atrial tachycardia, your doctor will examine you, and may order an electrocardiogram (ECG; see page 559) to evaluate the electrical activity of your heart. If your symptoms come and go, you may need to wear a portable electronic ECG device called a Holter monitor (see page 580) to record the electrical activity of your heart over a period of 24 hours or more.
Treatment
If you have palpitations, try to slow your heart rate by holding your breath, taking a slow drink of cold water, or rinsing your face with cold water. If these measures do not help, try bearing down as if having a bowel movement. This is called the Valsalva maneuver and can sometimes correct an arrhythmia.
To help prevent further episodes, your doctor will probably recommend that you cut down on alcohol and caffeine and quit smoking (if you smoke). He or she may massage the carotid artery in your neck to try to slow your heart rate. The doctor may prescribe medication that decreases the excitability of the heart muscle and prevents the heart rate from increasing. In some cases, the doctor may inject a medication that helps slow a rapid heartbeat. In severe cases of persistent atrial tachycardia, the doctor may recommend cardioversion (see page 582), a procedure in which an electrical shock is administered to the heart while the person is under mild anesthesia.
Heart Valve Disorders
The heart has four valves. The mitral valve controls the flow of blood from the left atrium (the filling chamber on the upper left side of the heart) into the left ventricle (the pumping chamber on the lower left side of the heart). The tricuspid valve performs the same function between the right atrium and right ventricle. The pulmonary valve controls the opening from the right ventricle into the pulmonary artery, which carries blood into the lungs. The aortic valve controls the movement of blood from the left ventricle into the aorta (the main artery in the body).
How heart valves work
With each heartbeat, the left ventricle contracts and pumps fresh, oxygenated blood out of the heart. The aortic and pulmonary valves open to let blood flow out of the heart and into the arteries. Between heartbeats, the ventricles relax and the aortic and pulmonary valves close. The mitral and tricuspid valves then open to allow blood to flow into the ventricles from the atria. The constant and regular repetition of this cycle keeps blood circulating throughout the body.
When a valve does not open wide enough, the heart must work harder to pump out an adequate supply of blood to the rest of the body. When a valve does not close completely, some of the blood leaks back into the heart, which must then pump it out again. Both of these conditions increase the heart’s workload and can lead to thickening of the heart muscle and eventually to heart failure.
Inflammation of a valve or other changes such as scarring can eventually lead to stenosis or insufficiency. Stenosis is thickening of a valve, which narrows its opening. Insufficiency results when a change in a valve prevents it from closing fully, allowing blood to flow back into the chamber.
Blood flow to the heart
The veins bring oxygen-depleted blood back to the heart from body tissues for a fresh supply of oxygen. The tricuspid valve opens to allow the oxygen-poor blood into the right ventricle of the heart, which sends it to the lungs for oxygen. When the oxygen-rich blood