Intraventricular conduction delay overview

# Overview
The term intraventricular conduction delay or intraventricular conduction disturbances (IVCDs) refers to disturbances in the intraventricular propagation of supraventricular impulses resulting in changes in the QRS complex  either in morphology or duration, or both.  The QRS complex represents electrical activation of the ventricle and normally the entire process of ventricular depolarization in adults is completed within about 0.1 sec (100 msec).  An IVCD is the result of abnormal activation of the ventricles caused by conduction delay or block in one or more parts of the specialized conduction system (bundle of His, bundle branch or purkinje conduction system) resulting in widening of QRS complex.  Abnormalities of local myocardial activation can further alter the specific pattern of venticular activation.

# Anatomy and Physiology
Intraventricular conduction delay are due to abnormalities in the specialized conduction system in the ventricles that transmit impulses arising from the SA node transmitted through the AV node to the ventricles.  The normal intraventricular system starts at the AV node as bundle of His that divides into right and left bundle branches which after giving of the fascicular branches ends in the complex Purkinje system.

# Classification
Intraventricular conduction delay can be caused by structural abnormalities in the bundle of His or Purkinje system or ventricular myocardium, functional refractoriness in a portion of the conduction system (i.e., aberrant ventricular conduction) or ventricular preexcitation over a bypass tract.  Intraventricular conduction disturbances can be broadly classified based upon the underlying physiology or based upon the site of block (anatomical classification).   However, the anatomic description of conduction abnormalities are not intended to localize sites of impaired function precisely because the electrocardiographic changes may be caused by abnormalities in various sites within the ventricles.

# Pathophysiology
Intraventricular conduction delay involves a variety of disturbances of the His-Purkinje/ventricular conduction system that affects the electrocardiogram (ECG) in distinctive ways and may or may not lead to a wide QRS complex and/or axis deviation.

# Causes
Intraventricular conduction delays(IVCDs) refers to abnormalities in the intraventricular propagation of supraventricular impulses.  These abnormalities can be due to pathology in either the left bundle of His or its fascicular branches or the right bundle of His or its combination resulting in changes to the QRS complex.  Causes can be classified based upon the site of pathology in the ventricular conduction system as well as the associated medical condition.

# Differentiating Intraventricular Conduction Delay from other Disorders
Intraventricular conduction delay's need to be differentiated from other conditions resulting in wide QRS complex such as LVH, pacemaker rhythms and accessory pathway arrythmias.

# Epidemiology and Demographics
Intraventricular condution delay ECG patterns can be seen commonly in general population and their prevalence increases with age.  Bifascicular block (especially RBBB and LAF block) is the most common IVCD.

# Natural History, Complications and Prognosis
Intraventricular conduction delay usually has no prognostic significance in patients without underlying heart disease but may progress to complete heart block or ventricular arrhythmia with worse prognosis in underlying heart disease.

# Diagnosis

## History and Symptoms
Intraventricular conduction delays (IVCD) are abnormal ECG pattern, which may or may not be associated with symptoms.  Complete history to find out underlying cardiac condition would be the best approach in asymptomatic patients.

## Physical Examination
Physical examination should consist of a thorough cardiac exam, lung exam, and close monitoring of vital signs.  Jugular pulsation may be noted in the neck exam.

## Laboratory Findings
Electrophysiological testing help localize the site of conduction delay or block within the conduction system of the ventricles.

## Electocardiogram
Intraventricular conduction delay is a common clinical abnormality detected on the electrocardiogram (ECG).  Right and left bundle branch blocks usually reflect intrinsic impairment of conduction in either the right or left bundle system (intraventricular conduction disturbances) which can be either chronic or intermittent.  Transient rate-related bundle branch blocks occurs when the heart rate increases (tachycardia or acceleration-dependent) or when heart rate decreases (bradycardia or deceleration-dependent) which are relatively rare.

# Treatment
Asymptomatic patients with isolated IVCD and no underlying heart disease require no treatment.  In symptomatic patients, with syncope and AV block may have a rhythm disturbance that requires a pacemaker.  Given the dys-ynchrony that occurs with left ventricular contractility, cardiac resynchronization therapy in heart failure patients may be of benefit.