bundle branch block

Bundle Branch Block 

Definition

Bundle branch block (BBB) is a disruption in the normal flow of electrical pulses that drive the heart beat.

Description

Bundle branch block belongs to a group of heart problems called intraventricular conduction defects (IVCD). There are two bundle branches, right and left. The right bundle carries nerve impulses that cause contraction of the right ventricle (the lower chamber of the heart) and the left bundle carries nerve impulses that cause contraction of the left ventricle. The two bundles initially are together at a junction called the bundle of His. Nerve impulses come through the sinus node of the heart to the bundle of His and then move into the right and left bundle branches. Bundle branch block is a slowing or interruption of nerve impulses. A problem may exist in any of the three bundles.

Patients with BBB are generally without symptoms unless the disease is severe enough to cause a complete infranodal A-V block and very slow heart rate. In patients with right bundle branch block (RBBB), the nerve impulse is conducted slowly or not at all. The right ventricle finally receives the impulse through muscle-to-muscle spread, outside the regular nerve pathway. This mechanism of impulse transmission is slow and results in a delayed contraction of the right ventricle. There are several types of left bundle branch block (LBBB), each producing its own characteristic mechanism of failure. In each case, the nerve impulse is blocked or delayed. Patients with LBBB may have left ventricular disease or cardiomyopathy.

Causes and symptoms

Left bundle branch block usually happens as a consequence of other diseases such as arteriosclerosis, rheumatic fever, congenital heart disease, myocarditis, myocardial infarction, metastatic heart tumors, or other invasions of the heart tissue. Right bundle branch block happens less often from underlying heart disease.

Diagnosis

Detection of BBB usually takes place during a normal physical examination. The block shows up as a widening of the second heart sound. Confirmation of BBB is obtained by electrocardiogram (ECG). The pattern seen in the electrocardiogram indicates pulses in a heart beat and their duration. A QRS duration of greater than 110 milliseconds is a diagnostic indication of BBB. There is a unique ECG pattern for blocks in each of the three bundles.

Treatment

There is no specific therapy for BBB. Patients are usually treated for associated heart diseases.

Prognosis

The prognosis of blockage in any of the three bundle branches depends on the prognosis of the associated heart disease. The associated diseases determine the outcome of the patient's health. Occasionally, disruptions in bundle branches lead to complete infranodal A-V block, a more serious blockage of nerve impulses. Approximately 2% of patients with BBB develop infranodal A-V blockage and these patients often require artificial pacemakers.

Resources

Books

Alexander, R. W., R. C. Schlant, and V. Fuster, editors. The Heart. 9th ed. New York: McGraw-Hill, 1998.

Key terms

Electrocardiogram — The pattern of the heart's electrical impulses that indicate the order and condition of the heart's components.

QRS — A pattern seen in an electrocardiogram that indicates the pulses in a heart beat and their duration. Variations from a normal QRS pattern indicate heart disease.

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block (blok)

1. obstruction.

2. to obstruct.

3. regional anesthesia.

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ankle block  regional anesthesia of the foot by injection of anesthetic around the tibial nerves at the ankle.

atrioventricular block , AV block impairment of conduction of cardiac impulses from the atria to the ventricles, usually due to a block in the atrioventricular junctional tissue, and generally subclassified on the basis of severity as first, second, or third degree.

Bier block  regional anesthesia by intravenous injection; used for surgical procedures on the arm below the elbow or leg below the knee that are done in a bloodless field maintained by a pneumatic tourniquet.

bifascicular block  impairment of conduction in two of the three fascicles of the bundle branches.

bilateral bundle branch block  (BBBB) interruption of cardiac impulses through both bundle branches, clinically indistinguishable from third degree (complete) heart block.

brachial plexus block  regional anesthesia of the shoulder, arm, and hand by injection of anesthetic into the brachial plexus.

bundle branch block  (BBB) interruption of conduction in one of the main bundle branches, so that the impulse first reaches one ventricle, then travels to the other.

caudal block  anesthesia by injection of local anesthetic into the caudal or sacral canal.

cervical plexus block  regional anesthesia of the neck by injection of a local anesthetic into the cervical plexus.

complete heart block  see heart b.

conduction block  a blockage in a nerve that prevents impulses from being conducted across a given segment although the nerve beyond is viable.

elbow block  regional anesthesia of the forearm and hand by injection of local anesthetic around the median, radial, and ulnar nerves at the elbow.

entrance block  in cardiology, a unidirectional impasse to conduction that prevents an impulse from entering a specific region of excitable tissue; part of the mechanism underlying parasystole.

epidural block  regional anesthesia by injection into the epidural space, either between the vertebral spines, in the cervical, thoracic, or lumbar region, or into the sacral hiatus, which is also called caudal block

Production of epidural block by injection through the ligamentum flavum into the epidural space, the needle stopping just short of the dura mater.

exit block  in cardiology, delay or failure of an impulse to be conducted from a specific region to surrounding tissues.

fascicular block  any of a group of disorders of conduction localized within any combination of the three fascicles of the bundle branches or their ramifications.

femoral block  regional anesthesia of the posterior thigh and the leg below the knee by injection of a local anesthetic around the femoral nerve just below the inguinal ligament at the lateral border of the fossa ovalis.

field block  regional anesthesia by encircling the operative field with injections of a local anesthetic.

first degree heart block  see heart b.; see also atrioventricular b.

heart block  impairment of conduction of an impulse in heart excitation; it is subclassified as first degree when conduction time is prolonged, second degree (partial heart b.) when some atrial impulses are not conducted, and third degree (complete heart b.) when no atrial impulses are conducted; the term and its subcategories are often used specifically for atrioventricular block.

high grade atrioventricular block  second or third degree atrioventricular block.

incomplete heart block  first or second degree heart block.

intraspinal block  spinal anesthesia (1).

intravenous block  Bier b.

lumbar plexus block  regional anesthesia of the anterior and medial aspects of the leg by injection of a local anesthetic into the lumbar plexus.

mental block  blocking (2).

metabolic block  the blocking of a biosynthetic pathway due to a genetic enzyme defect or to inhibition of an enzyme by a drug or other substance.

Mobitz type I block  Wenckebach b.

Mobitz type II block  a type of second degree atrioventricular block in which dropped beats occur periodically without previous lengthening of the P–R interval, due to a block within or below the bundle of His.

motor point block  interruption of impulses, by anesthesia or destruction of the nerve, at a motor point in order to relieve spasticity.

nerve block  regional anesthesia by injection of anesthetics close to the appropriate nerve.

paracervical block  regional anesthesia of the inferior hypogastric plexus and ganglia produced by injection of the local anesthetic into the lateral fornices of the vagina.

parasacral block  regional anesthesia produced by injection of a local anesthetic around the sacral nerves as they emerge from the sacral foramina.

paravertebral block  infiltration of anesthetic into an area near the vertebrae.

partial heart block  see heart b.

periinfarction block  disturbance of intraventricular conduction after a myocardial infarction, due to delayed conduction in the infarct region.

presacral block  anesthesia produced by injection of the local anesthetic into the sacral nerves on the anterior aspect of the sacrum.

pudendal block  anesthesia produced by blocking the pudendal nerves, accomplished by injection of the local anesthetic into the tuberosity of the ischium.

retrobulbar block  that performed by injection of a local anesthetic into the retrobulbar space to anesthetize and immobilize the eye.

sacral block  see under anesthesia.

saddle block  regional anesthesia in an area of the buttocks, perineum, and inner aspects of the thighs, by introducing the anesthetic agent low in the dural sac.

second degree heart block  see heart b.; see also atrioventricular b.

sinoatrial block  delay or absence of the atrial beat due to partial or complete interference with the propagation of impulses from the sinoatrial node to the atria.

spinal block  see under anesthesia.

subarachnoid block  spinal anesthesia (1).

third degree heart block  see heart b.; see also atrioventricular b.

trifascicular block  impairment of conduction in all three fascicles of the bundle branches, a form of complete heart block.

unifascicular block  impairment of conduction in only one fascicle of the bundle branches.

vagal block , vagus nerve block blocking of vagal impulses by injection of a solution of local anesthetic into the vagus nerve at its exit from the skull.

Wenckebach block  a type of second degree atrioventricular block in which one or more dropped beats occur periodically after a series of steadily increasing P–R intervals.

wrist block  regional anesthesia of the hand by injection of a local anesthetic around the median, radial, and ulnar nerves of the wrist.

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bundle branch block (BBB),

an inability of cardiac impulses to be conducted down the bundle branches, causing a broad and abnormally shaped QRS complex. BBB is commonly seen in high-risk, acute, anterior wall myocardial infarction. It may be caused by ischemia or necrosis of the bundle branches, trauma (as in surgical manipulation), or mechanical compression of the branches by a tumor. A pacemaker may be inserted if further deterioration of conduction is anticipated. See also left bundle branch block, right bundle branch block.

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bundle branch block

Cardiology Abnormal conduction through one of the conduction branches which normally supplies the right and left ventricles, often resulting in delayed conduction though either the right or left bundle branches. See Left bundle branch block, Right bundle branch block.