<unk> s occur when the rate of electrical discharge reaching the ventricles (normally initiated by the heart's sinoatrial node (SA node), transmitted to the atrioventricular node (AV node), and then further transmitted to the ventricles) falls below the base rate determined by the rate of Phase 4 spontaneous depolarisation of<unk>  pacemaker cells. An escape beat usually occurs 2–3 seconds after an electrical impulse has failed to reach the ventricles. This phenomenon can be caused by the sinoatrial node (SA node) failing to initiate a beat, by a failure of the conductivity from the SA node to the atrioventricular node (AV node), or by atrioventricular block (especially third degree AV block). Normally, the pacemaker cells of the sinoatrial node discharge at the highest frequency and are thus dominant over other cells with pacemaker activity. The AV node normally has the second fastest discharge rate. When the sinus rate falls below the discharge rate of the AV node, this becomes the dominant pacemaker, and the result is called a junctional escape beat. If the rate from both the SA and AV node fall below the discharge rate of<unk>  pacemaker cells, a<unk>  ensues. An escape beat is a form of cardiac arrhythmia, in this case known as an ectopic beat. It can be considered a form of ectopic pacemaker activity that is unveiled by lack of other pacemakers to stimulate the ventricles.<unk>  pacemaker cells discharge at a slower rate than the SA or AV node. While the SA node typically initiates a rate of 70 beats per minute (BPM), the atrioventricular node (AV node) is usually only capable of generating a rhythm at 40-60 BPM or less.<unk>  contraction rate is thus reduced by 15-40 beats per minute. If there are only one or two ectopic beats, they are considered escape beats. If this causes a semi-normal rhythm to arise it is considered an idioventricular rhythm. The escape arrhythmia is a compensatory mechanism that indicates a serious underlying problem with the SA node or conduction system (commonly due to heart attack or medication side effect), and because of its low rate, it can cause a drop in blood pressure and syncope.
Ventricular escape beat
Junctional escape beat
Infradian rhythm
Ultradian rhythm
Sinoatrial arrest
Junctional rhythm
Electrical alternans
Junctional ectopic tachycardia