Heart Block

A diagram of a heart with an ECG indicator; di...Image via Wikipedia

Definition:
A heart block is a disease in the electrical system of the heart. This is opposed to coronary artery disease, which is disease of the blood vessels of the heart. While coronary artery disease can cause angina (chest pain) or myocardial infarction (heart attack), heart block can cause lightheadedness, syncope (fainting), and palpitations.

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The heart has four chambeacemaker is called the sinoatrial (SA) node or sinus node. It’s a small mass of specialized crs. The top two are called the atria. The bottom two are called the ventricles.
The heart’s “natural” pells in the heart’s right atrium. It produces electrical impulses that make your heart beat. For your heart to beat properly, the signal must travel from the SA node down a specific path to reach the ventricles. As the signal goes from the atria to the ventricles, it passes through specialized conducting tissue called the atrioventricular (A’tre-o-ven-TRIK’u-ler) (AV) node.

On an electrocardiogram (e-lek”tro-KAR’de-o-gram) (ECG), a portion of the graph called the P wave shows the impulse passing through the atria. Another portion of the graph, the QRS wave, shows the impulse passing through the ventricles. As long as the impulse is transmitted normally, the heart pumps and beats at a regular pace.

Sometimes the signal from the heart’s upper to lower chambers is impaired or doesn’t transmit. This is “heart block” or “AV block.” This does not mean that the blood flow or blood vessels are blocked.

Heart block is classified according to the level of impairment — first-degree heart block, second-degree heart block or third-degree (complete) heart block.

Types of heart block
A heart block can be a blockage at any level of the electrical conduction system of the heart.

1.Blocks that occur within the sinoatrial node (SA node) are described as SA nodal blocks.
2.Blocks that occur within the atrioventricular node (AV node) are described as AV nodal blocks.
3.Blocks that occur below the AV node are known as infra-Hisian blocks (named after the bundle of His).
4.Blocks that occur within the left or right bundle branches are known as bundle branch blocks.
5.Blocks that occur within the fascicles of the left bundle branch are known as hemiblocks.

Clinically speaking, most of the important heart blocks are AV nodal blocks and infra-Hisian blocks.

Types of SA nodal blocks
The SA nodal blocks rarely give symptoms. This is because if an individual had complete block at this level of the conduction system (which is uncommon), the secondary pacemaker of the heart would be at the AV node, which would fire at 40 to 60 beats a minute, which is enough to retain consciousness in the resting state.

Types of SA nodal blocks include:

SA node Wenckebach (Mobitz I)
SA node Mobitz II
SA node exit block
In addition to the above blocks, the SA node can be suppressed by any other arrhythmia that reaches it. This includes retrograde conduction from the ventricles, ectopic atrial beats, atrial fibrillation, and atrial flutter.

The difference between SA node block and SA node suppression is that in SA node block an electrical impulse is generated by the SA node that doesn’t make the atria contract. In SA node suppression, on the other hand, the SA node doesn’t generate an electrical impulse because it is reset by the electrical impulse that enters the SA node.

Types of AV nodal blocks
There are four basic types of AV nodal block:

First degree AV block
Second degree AV block
Type 1 second degree AV block (Mobitz I) (also known as Wenckebach phenomenon)
Third degree AV block (Complete heart block)

Types of infra-Hisian block
Infrahisian block describes block of the distal conduction system. Types of infrahisian block include:

Type 2 second degree heart block (Mobitz II)
Left bundle branch block
Left anterior fascicular block
Left posterior fascicular block
Right bundle branch block
Of these types of infrahisian block, Mobitz II heart block is considered most important because of the possible progression to complete heart block.

Symptoms:
The symptoms and severity of heart block depend on which type you have. First-degree heart block rarely causes severe symptoms.

Second-degree heart block may result in the heart skipping a beat or beats. This type of heart block also can make you feel dizzy or faint.

Third-degree heart block limits the heart’s ability to pump blood to the rest of the body. This type of heart block may cause fatigue (tiredness), dizziness, and fainting. Third-degree heart block requires prompt treatment, because it can be fatal.

A medical device called a pacemaker is used to treat third-degree heart block and some cases of second-degree heart block.

This device uses electrical pulses to make the heart beat at a normal rate.

Sometimes, however, there are no symptoms at all.

It is important to note that during a period of heart block, persons may not know how to describe what they are feeling. They may have trouble keeping up with other persons, realize they are having “spells” and want to sit down and rest.

Causes:
Heart block has a variety of causes. It can sometimes be a result of a congenital defect. It can also occur after a heart attack or as a result of myocarditis (inflammation of the heart muscle), cardiomyopathy (a disorder of the heart muscle) and other types of heart disease. Although these conditions are more common in older people, young people can also be affected.

Heart block may also occur after heart surgery and in this case may be either temporary or permanent. Wenckebach block may occur as a result of taking too much digoxin, or can occur after a heart attack. Heart block may be caused by coronary artery disease, inflammation of the heart muscle, rheumatic fever, or overdose of certain heart drugs. Treatment depends on the degree of heart block experienced. Some cases need no treatment while others require medication or an artificial pacemakers.

Diagnosis

Heart block may occur spontaneously with unpredictable timing. Therefore, in some cases, the condition may require specialized tests to acquire an accurate diagnosis. If your doctor suspects that a person has heart block, he or she will order one or more of the following diagnostic tests to determine the cause of person’s symptoms.

Electrocardiogram -- An electrocardiogram (ECG or EKG) records the heart’s electrical activity. Small patches called electrodes are placed on person’s chest, arms and legs, and are connected by wires to the ECG machine. The electrical impulses of your child’s heart are translated into a graph or chart, enabling doctors to determine the pattern of electrical current flow in the heart and to diagnose arrhythmias.

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Holter Monitor — A Holter monitor is a small, portable machine that the person wears for 24 hours. It is about the size of a portable tape player and provides a continuous 24-hour recording of your child’s heartbeat onto a tape. You will be asked to keep a diary of your activities and symptoms. This monitor may detect arrhythmias that might not show up on a resting electrocardiogram, which only records a heartbeat for a few seconds at rest.

Event Monitor – This is a small monitor about the size of a pager that the person can have for up to a month. Since the arrhythmia may occur at unpredictable times, this will help to record the abnormal rhythm when he or she is experiencing symptoms. He or she can just push a button on the pager and record the heartbeat. The recording can than be transmitted by phone to the doctor.

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Exercise Stress Test -- An exercise stress or treadmill test, records the electrical activity of the person’s heart during exercise, which differs from the heart’s electrical activity at rest.

Electrophysiology Study -- In an electrophysiology (EP) study, doctors insert special electrode catheters — long, flexible wires — into veins and guide them into the heart. These catheters sense electrical impulses and also may be used to stimulate different areas of the heart. Doctors can then locate the sites that are causing arrhythmias. The EP study allows doctors to examine an arrhythmia under controlled conditions and acquire more accurate, detailed information than with any other diagnostic test.

Treatment
Heart block is a rhythm disturbance that can be treated with the implantation of a permanent pacemaker. The pacemaker helps your heart beat consistently. A pacemaker is a medical device that regulates the heart beat. It consists of two parts — the generator and the lead. The generator is a small metal container with a battery and tiny computer. The lead is an insulated wire that carries electrical impulses to the heart to ensure a stable heartbeat.

The computer in the pacemaker is constantly monitoring your heartbeat. This is called sensing. When the pacemaker senses your heartbeat, it continues to “watch” or monitor your heart and does not send a signal to stimulate the heart to beat. If no electrical impulse is sensed by the pacemaker, it sends out a signal to stimulate your childs heart to beat.

Proper Yoga exercise specially Deep Breathing and Pranayama are very helpful for all types of heart block.

Disclaimer: This information is not meant to be a substitute for professional medical advise or help. It is always best to consult with a Physician about serious health concerns. This information is in no way intended to diagnose or prescribe remedies.This is purely for educational purpose.

Resources:

http://www.americanheart.org/presenter.jhtml?identifier=4611

http://en.wikipedia.org/wiki/Heart_block

http://www.nhlbi.nih.gov/health/dci/Diseases/hb/hb_whatis.html

http://www.ucsfhealth.org/childrens/medical_services/heart_center/arrhythmia/conditions/block/diagnosis.html

http://heart-disease.health-cares.net/heart-block-causes.php

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