Glossary of Terms

Amiodarone-A medication used for the treatment of heart rhythm disturbances originating both in the upper chambers of the heart (the atria), and the lower chambers of the heart (the ventricles). Amiodarone works by prolonging the electrical conduction time of various tissues within the heart; it increases the amount of time between cycles of electrical excitation of these tissues, with a net damping down of electrical activity.

Antitachycardia Pacing (ATP)-An ICD therapy option often used to treat ventricular tachycardia (VT). ATP consists of small, rapid pacing pulses that are designed to interrupt and stop a heart rhythm that is starting to accelerate.

Arrhythmia-An abnormal or absent heart rhythm.

Atrioventricular (AV) Node-A group of cells located in the middle of the heart. When electrical signals leave the sinoatrial (SA) node, they travel through the AV node before moving on to the rest of the heart. The AV node helps keep the heart beating in a normal rhythm.

Atrium-One of the two upper chambers of the heart. The right atrium pumps blood into the right ventricle, and the left atrium pumps blood into the left ventricle.

Bradycardia-A heart rhythm disorder characterized by an abnormally slow heart rhythm. Bradycardia may also result after an ICD delivers a defibrillation shock. If this occurs, a Medtronic ICD can deliver bradycardia pacing therapy until the heart begins to beat normally on its own again.

Cardiac Arrest-A medical situation characterized by the stopping of normal heart function. During cardiac arrest, the heart is not pumping blood to the body. If left untreated, it is dangerous and life-threatening.

Cardioversion-An ICD therapy option used to treat rapid heart rhythms. Cardioversion consists of shock impulses that may progress from low-energy to high-energy levels, depending on what is needed to stop the rapid rhythm.

Defibrillation-An ICD therapy option used to treat ventricular fibrillation. Defibrillation consists of high-energy shock impulses.

Defibrillator-See ICD.

Electrocardiogram (ECG)-A printout from an electrocardiography machine which is used to measure and record the electrical activity of the heart.

Electromagnetic Interference (EMI)-A disruption caused by energy fields. An ICD can be affected by these fields if they are very strong, causing the ICD to either pause its normal operation or deliver an inappropriate therapy. If you move away from the source of EMI, your Medtronic ICD will return to its normal operation.

Electrophysiologist-A cardiologist with a specialization in the diagnosis and treatment of arrhythmias. Electrophysiologists are experts in the electrical function of the heart.

External defibrillators-Portable devices used to electrically stimulate a fibrillating heart. Using an external defibrillator, strong electric shocks are passed between paddles electrodes placed on a patient's chest.

ICD-An abbreviation for Implantable Cardioverter-Defibrillator. An ICD is used to treat abnormally rapid heart rhythms. It can deliver several types of therapies, including cardioversion, defibrillation, and antitachycardia pacing. An ICD is usually implanted in the upper chest or in the abdominal area.

Myocardial Infarction-Damage or death of myocardial tissue (middle muscle layer of the heart), caused by an interruption of blood flow to the area.

Sinoatrial (SA) Node-A group of cells located in the right atrium that sends out electrical signals which make the heart pump. These signals travel from the SA node, through the atrioventricular (AV) node, and then to the rest of the heart. This causes the heart to pump uniformly.

Sotalol-An oral medication for hypertension, angina, and arrhythmias. Sotalol works by prolonging the electrical conduction time of various tissues within the heart; it increases the amount of time between cycles of electrical excitation of these tissues, with a net damping down of electrical activity.

Sudden cardiac death (SCD)-natural death due to cardiac causes, noted by abrupt loss of consciousness within an hour of the onset of acute symptoms. Preexisting heart disease may or may not have been known to be present, but the time and mode of death are unexpected.

Supraventricular tachyarrhythmias-Arrhythmias that originate in the upper chambers of the heart (atria): supraventricular tachycardia (SVT), atrial flutter, atrial fibrillation.

Tachyarrhythmia-A category of heart rhythm disorders characterized by an abnormally rapid heart rhythm. Known causes of tachyarrhythmias include coronary artery disease, heart attack, and heart muscle disease (cardiomyopathy).

Ventricle-One of the two lower chambers of the heart. The right ventricle pumps blood to the lungs. The left ventricle pumps blood to the body's organs.

Ventricular Fibrillation (VF)-A heart rhythm disorder that originates in the ventricles. It is characterized by an abnormally rapid heart rhythm that is also highly unstable and irregular. During VF, electrical signals are moving chaotically through the heart, preventing it from beating properly. This often results in fainting. If left untreated, it may result in cardiac arrest.

Ventricular Tachycardia (VT)-A heart rhythm disorder that originates in the lower chambers. VT is characterized by a rapid heart rhythm during which patients may feel faint or dizzy, or even pass out. During VT, the heart does not pump blood as efficiently as it does during a normal rhythm, and rapid contractions prevent it from filling adequately with blood between beats. VT can be dangerous, even life-threatening, if not properly treated.