Ventricular escape beat
Synonyms and keywords: Ventricular escape; ventricular escape beats; ventricular escape beat, ventricular escape rhythm

# Overview
A ventricular escape beat is a self-generated electrical discharge initiated by and causing contraction of the ventricles of the heart.  It is a heart rhythm finding discovered on EKG, that indicates the normal electrical conduction system of the heart is disrupted or performing inadequately i.e failure of the SA node and AV node to generate an impulse.  The ventricular escape beat follows a long pause in ventricular rhythm and acts to prevent cardiac arrest.

# Pathophysiology
- Ventricular escape beats occur when the rate of electrical discharge reaching the ventricles (normally initiated by the heart's sinoatrial node, transmitted to the atrioventricular node, and then further transmitted to the ventricles) falls below the base rate determined by the ventricular pacemaker cells.
- Normally, the pacemaker cells of the sinoatrial node discharge at the highest frequency (70 beats per minute) and are thus dominant over other cells with pacemaker activity.  The AV node normally has the second fastest discharge rate (40-60 beats per minute).  If the rate from both the SA and AV node fall below the discharge rate of ventricular pacemaker cells, a ventricular escape beat ensues (less than 40 beats per minute).
- An escape beat usually occurs 23 seconds after an electrical impulse has failed to reach the ventricles. 

# Causes

## Life Threatening Causes
Life-threatening causes include conditions which may result in death or permanent disability within 24 hours if left untreated.
- Acute coronary syndrome
- Carbamate poisoning
- Diabetic ketoacidosis
- NSTEMI
- Organophosphate poisoning
- Parathion poisoning
- Severe brain injury

## Common Causes
- Acetylcholine
- Acute coronary syndrome
- Acute rheumatic fever
- Amiodarone
- Beta-blockers
- Calcium channel blockers
- Cardiac catheterization
- Congestive heart failure
- Dilated cardiomyopathy
- Hyperkalemia
- Hypermagnesemia
- Hypertensive heart disease
- Myocarditis
- Renal failure

## Causes by Organ System

## Causes in Alphabetical Order

# Differentiating Ventricular Escape Beat from other Diseases
- Junctional escape beat : 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.  The AV node usually generates a rhythm at 40-60 BPM.
- Idioventricular rhythm : An escape beat is a form of cardiac arrhythmia, in this case known as an ectopic beat.  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.
- Premature ventricular contraction : An absence of P wave activity, associated with a widened QRS complex resembles a PVC, but occuring after a pause of variable duration differentiate ventricular escape beat from PVCs.
- Complete heart block : In complete or third degree heart block there is sinus node activity but failure of conduction through the AV node.  There are P waves dissociated from the ventricular complexes with a rate faster than the ventricular rate that differentiates complete heart block from ventricular escape beat where there is absence of P waves.

# Diagnosis

## History and Symptoms
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.  Some of the symptoms related to hypotension are:
- Dizziness
- Fatigue
- Presyncope
- Syncope

## Physcial Examination
- Bradycardia may be present.  The rate is below 40 beats per minute.
- Tachypnea may be present.
- Elevated JVP may be seen if heart failure is present.
- S3 gallop may be heard in the presence of heart failure.

## Laboratory Findings
The following laboratory studies should be done, depending upon the cause, while investigating a case of ventricular escape beat.
- Complete blood count
- Differential count
- Serum electrolytes - hyperkalemia (renal insufficiency)
- Blood digoxin levels should be measured in case of digoxin overdose
- Myocarditis related studies - HIV serologies, Lyme titers, Chagas titers, enterovirus PCR, adenovirus PCR

## Electrocardiogram
An electrocardiogram can be used to identify a ventricular escape beat.  The QRS portion of the electrocardiogram represents the ventricular depolarization; 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.

# Factors Affecting Ventricular Escape Beat
- Cilostazol has been used in patients with third degree AV block to increase ventricular escape rate.
- Ouabain infusion decreases ventricular escape time and increases ventricular escape rhythm.  However, a high dose of ouabain can lead to ventricular tachycardia.