E

Ectopic focus. Source of a stimulating impulse for the heart other than the normal one, that is, other than the SA node. Typical ectopic foci are the atria, the AV junction and the ventricles, each of which has a characteristic, inherent rate. The rhythm originating from an ectopic focus is either an escape rhythm or an accelerated ectopic rhythm.

EGM. Abbreviation for electrogram. Also known as intracardiac electrogram gram, abbreviated IEGM.

Ejection fraction. A measure of myocardial contractility reflecting the effectiveness of ventricular ejection. It is calculated by dividing the stroke volume by the end diastolic volume, and it is reported as a percentage. A normal ejection fraction is greater than 55 percent.

Elective replacement time. See recommended replacement time.

Elective Replacement Time (ERT) — The point at which a pacemaker indicates that it should be replaced because its battery is near depletion.

Electrical interference. Extracardiac signals which can potentially disturb normal pacemaker operation by inappropriately suppressing or triggering pulse generator output (depending on the mode and sensing design). Informally, electrical interference is called noise.

Electrocardiogram. A graphic depiction of the electrical signal emitted by active cardiac tissue and recorded through electrodes placed on the body pacemaker. Typical causes of exit block are elevated thresholds during lead maturation, in association with myocardial infarction or tissue damage from defibrillation. Exit block may also be induced by an electrolyte abnormality (an elevated potassium level) or various drugs (such as flecainide).

External pacemaker. A nonimplantable pacemaker used temporarily outside the body to stimulate the heart and sense intrinsic cardiac activity. Also known as temporary pacemaker.