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Arrhythmias (abnormal heart rhythms)

Bundle branch block
Bundle branch block (BBB) is a disruption in the normal flow of electrical pulses that drive the heart beat. 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. Bundle heart block may be caused by damage to the heart muscle resulting from a heart attack.
 
Cardiac arrhythmia
Cardiac arrhythmia is a term that denotes a disturbance of the heart rhythm. Cardiac arrhythmias can range in severity from entirely benign to immediately life-threatening. If arrhythmia is suspected, a cardiologist should be consulted for confirmation. In addition, the use of natural substances for arrhythmia should always be supervised by a doctor. A cardiac arrhythmia, also called cardiac dysrhythmia, is a disturbance in the regular rhythm of the heartbeat. Several forms of cardiac arrhythmia are life-threatening and a medical emergency.
 
Atrial fibrillation
Atrial fibrillation (AF) is an electrical rhythm disturbance of the heart affecting the atria. Abnormal electrical impulses in the atria cause the muscle to contract erratically and pump blood inefficiently. Atrial fibrillation is associated with many cardiac conditions, including cardiomyopathy, coronary artery disease, valvular heart disease, ventricular hypertrophy and other associated conditions. Atrial fibrillation has been associated with hyperthyroidism, acute alcohol intoxication, changes in the autonomic nervous system and is common after cardiac surgery.
 
Atrial flutter
Atrial flutter is a rhythmic, fast rhythm that occurs in the atria of the heart. This rhythm occurs most often in individuals with organic heart disease (ie: pericarditis, coronary artery disease, and cardiomyopathy). Atrial flutter is a regular, rhythmic tachycardia originating in the atria. The rate in the atria is over 220 beats/minute, and typically about 300 beats/minute. The morphology on the surface EKG is typically a sawtooth pattern. Atrial flutter can sometimes degenerate to atrial fibrillation.
 
Supraventricular tachycardia
Supraventricular tachycardia (SVT), also known as paroxysmal narrow complex tachycardia (PNCT), is a disturbance of heart rhythm as a result of rapid electrical activity of the upper parts of the heart. In these attacks the heart is beating very fast, usually at a rate between 140 and 240 per minute. In most cases, the heart is normal and the heart rhythm is benign although uncomfortable. Palpitation is much the commonest symptom, but there also may be dizziness or even, very occasionally, fainting.
 
Sick sinus syndrome
Sick sinus syndrome, also called Bradycardia-tachycardia syndrome is a group of abnormal heartbeats (arrhythmias) presumably caused by a malfunction of the sinus node, the heart's "natural" pacemaker. Sick sinus syndrome is a disorder of the sinus node of the heart, which regulates heartbeat. With sick sinus syndrome, the sinus node fails to signal properly, resulting in changes in the heart rate. Sick sinus syndrome is a type of bradycardia in which the sinoatrial node is not functioning as it should.
 
Ventricular arrhythmias
Ventricular arrhythmias are common and are usually benign, at least in those with a structurally normal heart. In patients with structural heart disease (usually coronary heart disease), however, ventricular arrhythmia is an adverse prognostic factor associated with cardiac arrest and cardiac mortality. Ventricular arrhythmias range from asymptomatic ventricular ectopy to sustained ventricular tachycardia and cardiac arrest. Ventricular tachycardia and ventricular fibrillation are the most life-threatening arrhythmias that require emergency treatment.
 
Ventricular tachycardia
Ventricular tachycardia (VT) is a wide complex cardiac rhythm originating in the ventricles. The rate is usually between 150 and 200 beats/minute and regular. There is dissociation between atrial and ventricular activity. The rapid rate and A-V dissociation may lead to reduced cardiac filling and low cardiac output, hypotension, and cardiac arrest. Ventricular tachycardia is a potentially lethal disruption of normal heartbeat (arrhythmia) that may cause the heart to become unable to pump adequate blood through the body.
 
Ventricular fibrillation
Ventricular fibrillation is a condition in which disordered electrical activity causes the chambers of your heart, ("ventricles"), to contract chaotically. When this occurs, little or no blood is pumped from the heart. Ventricular fibrillation (VF) is an abnormal heart rhythm that causes death. It is responsible for 75% to 85% of sudden deaths due to heart problems. Normally, heart muscle cells squeeze (contract) in rhythm at the same time to pump blood. These groups of cells are located in the bottom two pumping chambers of the heart (ventricles).
 
Heart block
Heart block is a disorder of the heartbeat. It occurs when electrical impulses can't pass from the atria (upper chambers of the heart) to the ventricles (the heart's lower chambers). This may keep the contractions of the atria from coordinating with the contractions of the ventricles , and may cause a very slow heart rate. Heart block is common in elderly people as their hearts have undergone degenerative (wear and tear) changes. Heart block has a variety of causes. It can sometimes be a result of a congenital defect.
 
Brugada syndrome
Brugada syndrome (also known by some investigators as idiopathic ventricular fibrillation, IVF), is a disease associated with an electrocardiographic abnormality of right bundle branch block with ST-elevation in the right precordial leads (Figure). It has been added to the list of possible causes of sudden death in otherwise healthy, young individuals. These patients have a propensity for life-threatening ventricular tachyarrhythmias, particularly during sleep, but no structural heart abnormalities are found. Treatment for people at high risk of sudden death is with an implantable defibrillator.
 
Long QT syndrome
The long QT syndrome (LQTS) is a heart condition in which there is an abnormally long delay between the electrical excitation (or depolarization) and relaxation (repolarization) of the ventricles of the heart. It is associated with syncope (loss of consciousness) and with sudden death due to ventricular arrhythmias. Arrhythmias in individuals with LQTS are often associated with exercise or excitement. The cause of sudden cardiac death in individuals with LQTS is ventricular fibrillation.
 
Short QT syndrome
Short QT syndrome is a genetic disease of the electrical system of the heart. It is made up of a constellation of signs and symptoms, made up of a short QT interval interval on EKG (≤ 300 ms) that doesn't significantly change with heart rate, tall and peaked T waves, and a structurally normal heart. Short QT syndrome appears to be inherited in an autosomal dominant pattern, and a few affected families have been identified. Individuals with short QT syndrome frequently complain of palpitations and may have syncope (loss of consciousness) that is unexplained.
 
Wolff-Parkinson-White syndrome (WPW syndrome)
Wolff-Parkinson-White syndrome (WPW) is a syndrome of pre-excitation of the ventricles due to an accessory pathway known as the bundle of Kent. This accessory pathway is an abnormal electrical communication from the atria to the ventricles. Wolff-Parkinson-White syndrome is characterised by attacks of rapid heart rate (tachycardia). The heartbeat is regulated by electrical impulses that travel through the atria (upper chambers of the heart) to a knot of tissue known as the atrioventricular node, and then to the ventricles.
Arrhythmias (abnormal heart rhythms or dysrhythmias) are problems that affect the electrical system of the heart muscle, producing abnormal heart rhythms. They can cause the heart to pump less effectively. Arrhythmias are disturbances in the normal rhythm of the heartbeat. An occasional palpitation or fluttering is usually not serious, but a persistent arrhythmia may be life-threatening.

The heart is a muscular organ with four chambers designed to work efficiently, reliably, and continuously over a lifetime. The muscular walls of each chamber contract in a regulated sequence, pumping blood as required by the body while expending as little energy as possible during each heartbeat. Contraction of the muscle fibers in the heart is controlled by electricity that flows through the heart in a precise manner along distinct pathways and at a controlled speed. The electrical current that begins each heartbeat originates in the heart's pacemaker (sinus or sinoatrial node), located in the top of the upper right heart chamber (right atrium). The rate at which the pacemaker discharges the electrical current determines the heart rate. This rate is influenced by nerve impulses and by levels of certain hormones in the bloodstream.

The heart rate is regulated automatically by the autonomic nervous system (see Biology of the Nervous System: Nerves), which consists of the sympathetic and parasympathetic divisions. The sympathetic division increases the heart rate through a network of nerves called the sympathetic plexus. The parasympathetic division decreases the heart rate through a single nerve, the vagus nerve. Heart rate is also influenced by hormones released into the bloodstream by the sympathetic division: epinephrine (adrenaline) and norepinephrine (noradrenaline), which increase the heart rate. Thyroid hormone, which is released into the bloodstream by the thyroid gland, also increases the heart rate.

In an adult at rest, the normal heart rate is usually between 60 and 100 beats per minute. However, lower rates may be normal in young adults, particularly those who are physically fit. A person's heart rate varies normally in response to exercise and such stimuli as pain and anger. Heart rhythm is considered abnormal only when the heart rate is inappropriately fast (called tachycardia) or slow (called bradycardia), or is irregular or when electrical impulses travel along abnormal pathways.

There are many different types of arrhythmias. The heart may beat too rapidly (tachycardia) or too slowly (bradycardia), or it may beat irregularly. Atrial fibrillation and atrial flutter are common arrhythmias, which lead to an irregular and sometimes rapid heart rate. These atrial arrhythmias may interfere with the heart’s ability to pump blood properly from its upper chambers (atria). The atria may not always empty completely, and blood remaining there too long may stagnate and clot. Such clots may travel to other parts of the body, where they may cause blockages in the blood vessels that lead to the limbs, brain, or heart. In ventricular fibrillation, the lower chambers of the heart (ventricles) quiver feebly instead of contracting powerfully. This is the most severe type of arrhythmia, causing death in minutes unless medical assistance is obtained immediately.

Arrhythmias can develop from either altered impulse formation or altered impulse conduction. The former concerns changes in rhythm that are caused by changes in the automaticity of pacemaker cells or by abnormal generation of action potentials by sites other than the SA node (termed ectopic foci). Altered impulse conduction is usually associated with complete or partial block of electrical conduction within the heart. Altered impulse conduction commonly results in reentry, which can lead to tachyarrhythmias.

Topics in heart disease and cardiovascular disorders

Coronary circulation disorders
Myocardium disorders
Heart valve disorders
Arrhythmias (abnormal heart rhythms)
Heart inflammation and infection
Congenital heart disease
Valvular disease (blood vessels disorders)
Procedures done for coronary artery disease
Devices used in cardiology
Diagnostic tests and procedures for heart diseases
Heart transplant
 

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