Proper cardiac function relies on the synchronized contractions of the heart at regular intervals. When normal cardiac rhythm is initiated at the sinoatrial node, the heart is said to be in sinus rhythm. However, due to electrophysiologic disturbances caused by a disease process or from an electrical disturbance, the heart may experience irregularities in its coordinated contraction. In this situation, the heart is denoted to be arrhythmic. The resulting cardiac arrhythmia impairs cardiac efficiency and can be a potential life threatening event.
Cardiac arrhythmias occurring in the atria of the heart, for example, are called atrial tachyarrhythmias (ATs). ATs take many forms, including atrial fibrillation and atrial flutter. Both conditions are characterized by rapid, contractions of the atria. Cardiac arrhythmias occurring in the ventricular region of the heart, by way of further example, are called ventricular tachyarrhythmias. Ventricular tachyarrhythmias (VTs), are conditions denoted by a rapid heart beat, 150 to 250 beats per minute, originating from a location within the ventricular myocardium. Ventricular tachyarrhythmia can quickly degenerate into ventricular fibrillation (VF). Ventricular fibrillation is a condition denoted by extremely rapid, non synchronous contractions of the ventricles. This condition is fatal unless the heart is returned to sinus rhythm within a few minutes.
Implantable cardioverter/defibrillators (ICDs) have been used as an effective treatment for patients with serious tachyarrhythmias. ICDs are able to recognize and treat tachyarrhythmias with a variety of tiered therapies. These tiered therapies range from providing anti-tachycardia pacing pulses or cardioversion energy for treating tachyarrhythmias to high energy shocks for treating atrial and/or ventricular fibrillation. To effectively deliver these treatments, the ICD must first detect that a tachyarrhythmia is occurring, after which appropriate therapy may be provided to the heart.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading the present specification, there is a need in the art for reliably and accurately recognizing types of cardiac rhythms produced by the heart. The present invention fulfills these and other needs.