User:Jonram27/Ventricular escape beat



A ventricular escape beat is a term used in cardiology to describe an automated electrical discharge and resulting contraction of the ventricles. The ventricular escape beat occurs when the rate of discharge from both the SA node and AV node falls below the basal rate determined by the ventricular pacemaker cells. An escape beat usually occurs 2-3 seconds after the SA node has failed to initiate a beat, or the conductivity from the SA node is affected. This can be stimulated in response to Third degree AV block whereby atrial and ventricular contractions are completely imdependant.

The escape beat forms a part of cardiac arrhythmia, in this case known as an ectopic beat. As a result of the escape beat, ventricular contraction rate is reduced to between 15-40 beats per minute.

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.

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.

Diagnosis
An electrocardiogram can be used to identify a ventricular escape beat. The QRS portion of the electrocardiogram represents the ventricular depolarisation; in normal circumstances the QRS complex forms a sharp sudden peak. For a patient with a ventricular escape beat, the shape of the QRS complex is broader as the His bundle produces a slower heart rate

The first 2.5 seconds show a normal cardiac cycle. This is followed by a period of delayed sinus activity which initiates a takeover response by the ventricular pacemaker cells resulting in a ventricular escape beat. Two escape beats are shown between 5-8 seconds.

See also: Junctional escape beat

Cilostazol
Third degree AV block can be treated with Cilostazol which acts to increase Ventricular escape rate

Ouabain
Ouabain infusion decreases ventricular escape time and increases ventricular escape rhythm. However, a high dose of Ouabain can lead to ventricular tachycardia