Cardiac arrhythmia

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Cardiac arrhythmia
Ventricular Fibrillation or V-Fib, an example of cardiac arrhythmia.
ICD-10 I47 - I49
ICD-9 427
DiseasesDB 15206
MedlinePlus 001101
MeSH D001145

Template:Cardiac arrhythmia Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]

Overview

Faster and slower arrythmias

In an adult, a heart rate faster than 100 beats/minute is considered tachycardia. This number varies with age, as the heartbeat of a younger person is naturally faster than that of an older person's. During exercise the sinus node increases its rate of electrical activity to accelerate the heart rate. Such normal fast rate that develops is called sinus tachycardia. In contrast, 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, and rarely may lead to 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, amphetamines, 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. However, these causative agents are not the only contributors to tachycardias and their prevalence has not been evaluated statistically.

A slow rhythm, known as bradycardia (less than 60 beats/min), is usually not life threatening, but may cause symptoms. It may be caused by reversible causes (low oxygen, electrolyte abnormalities), or be more permanent (heart block). 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.

Differential Diagnosis

AV Reentry Tachycardia with Preexcitation Complex

  • Congenital
  • Drugs
  • Emotional excitation
  • Heavy exercise

AV Node Reentry Tachycardia Without Preexcitation

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 EKG 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.

Sudden Arrhythmia Death Syndrome (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.

Causes of SADS in young people are long QT syndrome, Brugada syndrome, Catecholaminergic polymorphic ventricular tachycardia and hypertrophic cardiomyopathy and arrhythmogenic right ventricular dysplasia ("arrythmia"-causing, "right ventricle"-involving, pre-cancerous malformation).

List of common cardiac arrhythmias

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. Temporary 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.

Fatty acids

Fatty acids play an important role in the life and death of cardiac cells because they are essential fuels for mechanical and electrical activities of the heart.[1][2] [3] [4] Retrieved on 18 January 2007

References

  1. ↑ "External blockade...by polyunsaturated fatty acids". pubmed.Retrieved on 18 January 2007
  2. ↑ "Antiarrythmic effects of omega-3 fatty acids". pubmed.Retrieved on 18 January 2007
  3. ↑ "Alpha-linolenic acid, cardiovascular disease and sudden death". pubmed.Retrieved on 18 January 2007
  4. ↑ "Omega-3 and health". pubmed.

Related Chapters

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