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 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 dioxide t ...

; 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 ...

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 approximat ...

(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 Phase 4, Phase IV or Phase Four may refer to: Media * Marvel Cinematic Universe: Phase Four, a group of superhero films and television series beginning in 2021 * ''Phase IV'' (1974 film), a 1974 film * ''Phase IV'' (2002 film), a 2002 film * ...

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 Atrioventricular block (AV block) is a type of heart block that occurs when the electrical signal traveling from the atria, or the upper chambers of the heart, to ventricles, or the lower chambers of the heart, is impaired. Normally, the sinoatr ...

(especially

third degree AV block Third-degree atrioventricular block (AV block) is a medical condition in which the electrical impulse generated in the sinoatrial node (SA node) in the atrium of the heart can not propagate to the ventricles. Because the impulse is blocked, an a ...

). 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 A junctional escape beat is a delayed Cardiac cycle, heartbeat originating not from the atrium (anatomy), atrium but from an Cardiac ectopy, ectopic focus somewhere in the atrioventricular node, atrioventricular junction. It occurs when the rate o ...

. 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 Ectopic beat is a disturbance of the cardiac rhythm frequently related to the electrical conduction system of the heart, in which beats arise from fibers or group of fibers outside the region in the heart muscle ordinarily responsible for impulse ...

. 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 An idioventricular rhythm is a cardiac rhythm characterized by a rate of <50 beats per minute (bpm), absence of P waves and widening of the QRS complex. In cases where the heart rate is between 50 and 110 bpm, it is known a ...

. 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 may tr ...

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 pressure" r ...

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 biology, depolarization or hypopolarization is a change within a cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell compared to the outside. Depolarization is esse ...

; 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 Third-degree atrioventricular block (AV block) is a medical condition in which the electrical impulse generated in the sinoatrial node (SA node) in the atrium of the heart can not propagate to the ventricles. Because the impulse is blocked, an a ...

can be treated with

Cilostazol Cilostazol, sold under the brand name Pletal among others, is a medication used to help the symptoms of intermittent claudication in peripheral vascular disease. If no improvement is seen after 3 months, stopping the medication is reasonable. It ...

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 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 period ...

References

{{reflist Cardiac arrhythmia