In cardiology, a ventricular escape beat is a self-generated electrical discharge initiated by, and causing contraction of the ventricles of the

heart The heart is a muscular organ found in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon diox ...

; normally the heart rhythm is begun in the atria of the heart and is subsequently transmitted to the ventricles. The ventricular escape beat follows a long pause in ventricular rhythm and acts to prevent

cardiac arrest Cardiac arrest is when the heart suddenly and unexpectedly stops beating. It is a medical emergency that, without immediate medical intervention, will result in sudden cardiac death within minutes. Cardiopulmonary resuscitation (CPR) and possib ...

. It indicates a failure of the

electrical conduction system of the heart The cardiac conduction system (CCS) (also called the electrical conduction system of the heart) transmits the signals generated by the sinoatrial node – the heart's pacemaker, to cause the heart muscle to contract, and pump blood through the ...

to stimulate the ventricles (which would lead to the absence of heartbeats, unless ventricular escape beats occur).

Causes

Ventricular escape beats occur when the rate of electrical discharge reaching the ventricles (normally initiated by the heart's

sinoatrial node The sinoatrial node (also known as the sinuatrial node, SA node or sinus node) is an oval shaped region of special cardiac muscle in the upper back wall of the right atrium made up of cells known as pacemaker cells. The sinus node is approxi ...

(SA node), transmitted to the

atrioventricular node The atrioventricular node or AV node electrically connects the heart's atria and ventricles to coordinate beating in the top of the heart; it is part of the electrical conduction system of the heart. The AV node lies at the lower back section of t ...

(AV node), and then further transmitted to the ventricles) falls below the base rate determined by the rate of Phase 4 spontaneous depolarisation of ventricular 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

(SA node) failing to initiate a beat, by a failure of the conductivity from the SA node to the

(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 ventricular pacemaker cells, a ventricular escape beat ensues. An escape beat is a form of cardiac

arrhythmia Arrhythmias, also known as cardiac arrhythmias, heart arrhythmias, or dysrhythmias, are irregularities in the heartbeat, including when it is too fast or too slow. A resting heart rate that is too fast – above 100 beats per minute in adults ...

, 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. Ventricular 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

(AV node) is usually only capable of generating a rhythm at 40-60 BPM or less. Ventricular contraction rate is thus reduced by 15-40 beats per minute.D.D. Costa, W.J. Brady, J. Edhouse (March 2002), BMJ Publishing Group Ltd., ABC of clinical electrocardiography, British Medical Journal: 324:535-538. 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

is a compensatory mechanism that indicates a serious underlying problem with the SA node or conduction system (commonly due to

heart attack A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops to the coronary artery of the heart, causing damage to the heart muscle. The most common symptom is chest pain or discomfort which m ...

or medication

side effect In medicine, a side effect is an effect, whether therapeutic or adverse, that is secondary to the one intended; although the term is predominantly employed to describe adverse effects, it can also apply to beneficial, but unintended, consequence ...

), and because of its low rate, it can cause a drop in

blood pressure Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressur ...

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 impulse can not travel quickly via the normal electrical conduction system. Ventricular escape beats differ from ventricular extrasystoles (or premature ventricular contractions), which are spontaneous electrical discharges of the ventricles. These are not preceded by a pause; on the contrary they are often followed by a compensatory pause.

Management

Cilostazol

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

Ouabain

Ouabain Ouabain or (from Somali ''waabaayo'', "arrow poison" through French ''ouabaïo'') also known as g-strophanthin, is a plant derived toxic substance that was traditionally used as an arrow poison in eastern Africa for both hunting and warfare. O ...

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

ventricular tachycardia Ventricular tachycardia (V-tach or VT) is a fast heart rate arising from the lower chambers of the heart. Although a few seconds of VT may not result in permanent problems, longer periods are dangerous; and multiple episodes over a short perio ...

References

{{reflist Cardiac arrhythmia