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ARTICLES IN THE BOOK

  1. Acute abdomen
  2. Acute coronary syndrome
  3. Acute pancreatitis
  4. Acute renal failure
  5. Agonal respiration
  6. Air embolism
  7. Ambulance
  8. Amnesic shellfish poisoning
  9. Anaphylaxis
  10. Angioedema
  11. Aortic dissection
  12. Appendicitis
  13. Artificial respiration
  14. Asphyxia
  15. Asystole
  16. Autonomic dysreflexia
  17. Bacterial meningitis
  18. Barotrauma
  19. Blast injury
  20. Bleeding
  21. Bowel obstruction
  22. Burn
  23. Carbon monoxide poisoning
  24. Cardiac arrest
  25. Cardiac arrhythmia
  26. Cardiac tamponade
  27. Cardiogenic shock
  28. Cardiopulmonary arrest
  29. Cardiopulmonary resuscitation
  30. Catamenial pneumothorax
  31. Cerebral hemorrhage
  32. Chemical burn
  33. Choking
  34. Chronic pancreatitis
  35. Cincinnati Stroke Scale
  36. Clinical depression
  37. Cord prolapse
  38. Decompression sickness
  39. Dental emergency
  40. Diabetic coma
  41. Diabetic ketoacidosis
  42. Distributive shock
  43. Drowning
  44. Drug overdose
  45. Eclampsia
  46. Ectopic pregnancy
  47. Electric shock
  48. Emergency medical services
  49. Emergency medical technician
  50. Emergency medicine
  51. Emergency room
  52. Emergency telephone number
  53. Epiglottitis
  54. Epilepsia partialis continua
  55. Frostbite
  56. Gastrointestinal perforation
  57. Gynecologic hemorrhage
  58. Heat syncope
  59. HELLP syndrome
  60. Hereditary pancreatitis
  61. Hospital
  62. Hydrocephalus
  63. Hypercapnia
  64. Hyperemesis gravidarum
  65. Hyperkalemia
  66. Hypertensive emergency
  67. Hyperthermia
  68. Hypoglycemia
  69. Hypothermia
  70. Hypovolemia
  71. Internal bleeding
  72. Ketoacidosis
  73. Lactic acidosis
  74. Lethal dose
  75. List of medical emergencies
  76. Malaria
  77. Malignant hypertension
  78. Medical emergency
  79. Meningitis
  80. Neuroglycopenia
  81. Neuroleptic malignant syndrome
  82. Nonketotic hyperosmolar coma
  83. Obstetrical hemorrhage
  84. Outdoor Emergency Care
  85. Overwhelming post-splenectomy infection
  86. Paralytic shellfish poisoning
  87. Paramedic
  88. Paraphimosis
  89. Peritonitis
  90. Physical trauma
  91. Placenta accreta
  92. Pneumothorax
  93. Positional asphyxia
  94. Pre-eclampsia
  95. Priapism
  96. Psychotic depression
  97. Respiratory arrest
  98. Respiratory failure
  99. Retinal detachment
  100. Revised Trauma Score
  101. Sepsis
  102. Septic arthritis
  103. Septic shock
  104. Sexual assault
  105. Shock
  106. Simple triage and rapid treatment
  107. Soy allergy
  108. Spinal cord compression
  109. Status epilepticus
  110. Stroke
  111. Temporal arteritis
  112. Testicular torsion
  113. Toxic epidermal necrolysis
  114. Toxidrome
  115. Triage
  116. Triage tag
  117. Upper gastrointestinal bleeding
  118. Uterine rupture
  119. Ventricular fibrillation
  120. Walking wounded
  121. Watershed stroke
  122. Wilderness first aid
  123. Wound
 



THE BOOK OF MEDICAL EMERGENCIES
This article is from:
http://en.wikipedia.org/wiki/Cardiac_arrhythmia

All text is available under the terms of the GNU Free Documentation License: http://en.wikipedia.org/wiki/Wikipedia:Text_of_the_GNU_Free_Documentation_License 

Cardiac arrhythmia

From Wikipedia, the free encyclopedia

 

Cardiac arrhythmia is a group of conditions in which the muscle contraction of the heart is irregular or is faster or slower than normal. Cardiac dysrhythmia is technically more correct, as arrhythmia would imply that there is "no rhythm," but this term is not used frequently.

Some arrhythmias are life-threatening medical emergencies that can cause cardiac arrest and sudden death. Others cause aggravating symptoms, such as an awareness of a different heart beat, or palpitation, which can be annoying. Some are quite benign and normal. Sinus arrhythmia is the mild acceleration followed by slowing of the normal rhythm that occurs with breathing. In adults the normal heart rate ranges from 60 beats per minute to 100 beats per minute. The normal heart beat is controlled by a small area in the upper chamber of the heart called the sinoatrial node or sinus node. The sinus node contains specialized cells that have spontaneous electrical activity that starts each normal heart beat.

Frequency too high or too low

A heart rate faster than 100 beats/minute is considered a tachycardia. This number varies with age, as the heartbeat of a younger person is naturally faster than that of an older person's. With exercise the sinus node increases its rate of electrical activity to accelerate the heart rate. The normal fast rate that develops is called sinus tachycardia. Arrhythmias that are due to fast, abnormal electrical activity can cause tachycardias that are dangerous. If the ventricles of the heart experience one of these tachycardias for a long period of time, there can be deleterious effects. Individuals may sense a tachycardia as a pounding sensation of the heart, known as palpitations. If a tachycardia lowers blood pressure it may cause lightheadedness or dizziness, or even fainting (syncope). If the tachycardia is too fast, the pump function of the heart is impeded, which may lead to a sudden death.

Most tachycardias are not dangerous. Anything that increases adrenaline or its effects on the heart will increase the heart rate and potentially cause palpitations or tachycardias. Causes include stress, ingested or injected substances (ie: caffeine, alcohol--see Holiday heart syndrome), and an overactive thyroid gland (hyperthyroidism). Individuals who have a tachycardia are often advised to limit or remove exposure to any causative agent.

A slow rhythm, known as bradycardia (less than 60 beats/min), is usually not life threatening, but may cause symptoms. When it causes symptoms implantation of a permanent pacemaker may be needed.

Either dysrhythmia requires medical attention to evaluate the risks associated with the arrhythmia.

Fibrillation

A serious variety of arrhythmia is known as fibrillation. The muscle cells of the heart normally function together, creating a single contraction when stimulated. Fibrillation occurs when the heart muscle begins a quivering motion due to a disunity in contractile cell function. Fibrillation can affect the atrium (atrial fibrillation) or the ventricle (ventricular fibrillation); ventricular fibrillation is imminently life-threatening.

Atrial fibrillation is the quivering, chaotic motion in the upper chambers of the heart, known as the atria. Atrial fibrillation is often due to serious underlying medical conditions, and should be evaluated by a physician. It is not typically a medical emergency.

Ventricular fibrillation occurs in the ventricles (lower chambers) of the heart; it is always a medical emergency. If left untreated, ventricular fibrillation (VF, or V-fib) can lead to death within minutes. When a heart goes into V-fib, effective pumping of the blood stops. V-fib is considered a form of cardiac arrest, and an individual suffering from it will not survive unless cardiopulmonary resuscitation (CPR) and defibrillation are provided immediately.

CPR can prolong the survival of the brain in the lack of a normal pulse, but defibrillation is the intervention which is most likely to restore a more healthy heart rhythm. It does this by applying an electric shock to the heart, after which sometimes the heart will revert to a rhythm that can once again pump blood.

Almost every person goes into ventricular fibrillation in the last few minutes of life as the heart muscle reacts to diminished oxygen or general blood flow, trauma, irritants, or depression of electrical impulses themselves from the brain.

Origin of impulse

When an electrical impulse begins in any part of the heart, it will spread throughout the myocardium and cause a contraction; see Electrical conduction system of the heart. Abnormal impulses can begin by one of two mechanisms: automaticity or reentry.

Automaticity

Automaticity refers to a cardiac muscle cell firing off an impulse on its own. Every cardiac cell has this potential: if it does not receive any impulses from elsewhere, its internal "pacemaker" will fire off an impulse after a certain amount of time. A single specialized location in the atrium, the sinoatrial node, has a higher automaticity (a faster pacemaker) than the rest of the heart, and therefore is usually the one to start the heartbeat.

Any part of the heart that initiates an impulse without waiting for the sinoatrial node is called an ectopic focus, and is by definition a pathological phenomenon. This may cause a single premature beat now and then, or, if the ectopic focus fires more often than the sinoatrial node, it can produce a sustained abnormal rhythm. Rhythms produced by an ectopic focus in the atria, or by the atrioventricular node, are the least dangerous dysrhythmias; but they can still produce a decrease in the heart's pumping efficiency, because the signal reaches the various parts of the heart muscle with slightly different timing than usual and causes a poorly coordinated contraction.

Conditions that increase automaticity include sympathetic nervous system stimulation and hypoxia. The resulting heart rhythm depends on where the first signal begins: if it is the sinoatrial node, the rhythm remains normal but rapid; if it is an ectopic focus, many types of dysrhythmia can result.

Reentry

Reentrant dysrhythmias occur when an electrical impulse travels in a circle within the heart, rather than moving outward and then stopping. Every cardiac cell is able to transmit impulses in every direction, but will only do so once within a short period of time. Normally the impulse spreads through the heart quickly enough that each cell will only respond once, but if conduction is abnormally slow in some areas, part of the impulse will arrive late and will be treated as a new impulse, which can then spread backward. Depending on the timing, this can produce a sustained abnormal rhythm, such as atrial flutter, a self-limiting burst of supraventricular tachycardia, or the dangerous ventricular tachycardia.

By analogy, imagine a room full of people all given these instructions: "If you see anyone starting to stand up, then stand up for three seconds and sit back down." If the people are quick enough to respond, the first person to stand will trigger a single wave which will then die out; but if there are stragglers on one side of the room, people who have already sat down will see them and start a second wave, and so on.

Diagnosis

Cardiac dysrhythmias are often first detected by simple but nonspecific means: auscultation of the heartbeat with a stethoscope, or feeling for peripheral pulses. These cannot usually diagnose specific dysrhythmias, but can give a general indication of the heart rate and whether it is regular or irregular. Not all the electrical impulses of the heart produce audible or palpable beats; in many cardiac arrhythmias, the premature or abnormal beats do not produce an effective pumping action and are experienced as "skipped" beats.

The simplest specific diagnostic test for assessment of heart rhythm is the electrocardiogram (abbreviated ECG or EKG). A Holter monitor is an ECG recorded over a 24-hour period, to detect dysrhythmias that may happen briefly and unpredictably throughout the day.

SADS

SADS, or sudden arrhythmia death syndrome, is a term used to describe sudden death due to cardiac arrest brought on by an arrhythmia. The most common cause of sudden death in the US is coronary artery disease. Approximately 300,000 people die suddenly of this cause every year in the US. SADS can also occur from other causes. Also, there are many inherited conditions and heart diseases that can affect young people that can cause sudden death. Many of these victims have no symptoms before dying suddenly.

The most common causes of SADS in young people are long QT syndrome, Brugada syndrome, and hypertrophic cardiomyopathy and arrhythmogenic right ventricular dysplasia ("arrythmia"-causing, "right ventricle"-involving, pre-cancerous malformation(bad-growth)).

List of common cardiac dysrhythmias

  • Atrial Arrhythmias
    • Atrial fibrillation
  • Atrial Dysrhythmias
    • Premature atrial contraction
    • Atrial flutter
    • Supraventricular tachycardia
    • Sick sinus syndrome
  • Ventricular Arrhythmias
    • Ventricular fibrillation
  • Ventricular Dysrhythmias
    • Premature ventricular contraction
    • Pulseless electrical activity
    • Ventricular tachycardia
    • Asystole
  • Junctional Dysrhythmias
    • Premature junctional contraction
    • Junctional tachycardia
  • Heart Blocks
    • First degree heart block
    • Second degree heart block
      • Type 1 Second degree heart block, also known as Mobitz I or Wenckebach
      • Type 2 Second degree heart block, also known as Mobitz II
    • Third degree heart block, also known as complete heart block

Antiarrhythmic therapies

There are many classes of antiarrhythmic medications and many individual drugs within these classes. See the article on antiarrhythmic agents.

Dysrhythmias may also be treated electrically. Cardioversion is the application of electrical current across the chest wall to the heart and it is used for treatment of supraventricular or pulsed ventricular tachycardia. Defibrillation differs in that it is used for ventricular fibrillation and pulseless ventricular tachycardia, and more electricity is delivered with defibrillation than with cardioversion. In cardioversion, the recipient is either sedated or lightly anesthetized for the procedure. In defibrillation, the recipient has lost consciousness so there is no need for sedation.

Electrical treatment of dysrhythmia includes cardiac pacing. Temporay pacing may be done for very slow heartbeats, or bradycardia, from drug overdose or myocardial infarction. A pacemaker may be placed in situations where the bradycardia is not expected to recover.

Atrial fibrillation can also be treated through a procedure, e.g. pulmonary vein isolation. This is performed by a cardiologist who specializes in electrophysiology and is done percutaneously with catheters. Alternatively, a maze procedure can be performed through cardiothoracic surgery.

Transvenous catheter ablation is established as a curative treatment for many arrhythmias. Using Image Integration Guided Catheter Ablation it is possible to know the precise location of the catheter in relation to the cardiac anatomy. The CartoMergeTM mapping system from Biosense Webster integrates pre-procedural computed tomography (CT) or magnetic resonance (MR) images with electroanatomic maps has recently been approved for patient care.[1]

References

  1. ^ J. Dong & H. Calkins (2006). Image Integration Guided Catheter Ablation of Arrhythmias.

See also

  • Antiarrhythmic agents
  • Artificial pacemaker
  • Electrical conduction system of the heart
  • Implantable cardioverter-defibrillator.

External links

  • Arrhythmia information from Seattle Children's Hospital Heart Center
  • SADS Foundation
  • Cardiac Risk in the Young (UK)
Retrieved from "http://en.wikipedia.org/wiki/Cardiac_arrhythmia"

 

 

 


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