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 (biology), organ found in humans and other animals. This organ pumps blood through the blood vessels. The heart and blood vessels together make the circulatory system. The pumped blood carries oxygen and nutrie ...

; normally the heart rhythm is begun in the

atria Atria may refer to: Science *Atrium (heart) (plural: atria), an anatomical structure of the heart *Atria (genus), a flatworm genus in the family Dendrocoelidae * Atria (star) or Alpha Trianguli Australis, a star in the constellation Triangulum Aus ...

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 (also known as sudden cardiac arrest CA is when the heart suddenly and unexpectedly stops beating. When the heart stops beating, blood cannot properly Circulatory system, circulate around the body and the blood flow to the ...

. 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 Cardiac action potential, signals generated by the sinoatrial node – the heart's Cardiac pacemaker, pacemaker, to cause the heart musc ...

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, sinus node or Keith–Flack node) is an ellipse, oval shaped region of special cardiac muscle in the upper back wall of the right atrium made up of Cell (biology), cells known as pa ...

(SA node), transmitted to the

atrioventricular node The atrioventricular node (AV node, or Aschoff-Tawara 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 ...

(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 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 ...

). 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 heartbeat originating not from the atrium but from an ectopic focus somewhere in the atrioventricular junction. It occurs when the rate of depolarization of the sinoatrial node falls below the rate of the ...

. 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, are irregularities in the cardiac cycle, heartbeat, including when it is too fast or too slow. Essentially, this is anything but normal sinus rhythm. A resting heart rate that is too fast – ab ...

, 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 impuls ...

. 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 conducted P waves and widening of the QRS complex. In cases where the heart rate is between 50 and 110 bpm, it ...

. 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 Ischemia, blood flow decreases or stops in one of the coronary arteries of the heart, causing infarction (tissue death) to the heart muscle. The most common symptom ...

or medication

side effect In medicine, a side effect is an effect of the use of a medicinal drug or other treatment, usually adverse but sometimes beneficial, that is unintended. Herbal and traditional medicines also have side effects. A drug or procedure usually use ...

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

blood pressure Blood pressure (BP) is the pressure of Circulatory system, 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 ...

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 ...

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 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. ...

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 cardiovascular disorder in which fast heart rate occurs in the ventricles of the heart. Although a few seconds of VT may not result in permanent problems, longer periods are dangerous; and multiple ...

References

{{reflist Cardiac arrhythmia