Tachyarrhythmia

'Cardiac arrhythmia (also dysrhythmia) is a term for any of a large and heterogeneous group of conditions in which there is abnormal [[Electrical conduction system of the heart|electrical activity]] in the heart. The heart beat may be too fast or too slow, and may be regular or irregular. Some arrhythmias are life-threatening medical emergencies that can result in cardiac arrest and sudden death. Others cause aggravating symptoms such as an abnormal awareness of heart beat, and may be merely annoying. Others may not be associated with any symptoms at all, but pre-dispose toward potentially life threatening stroke or embolus. Some arrhythmias are very minor and can be regarded as variants of normal. In fact, most people will sometimes feel their heart skip a beat, or give an occasional extra strong beat - neither of which is usually a cause for alarmhttp://familydoctor.org/online/famdocen/home/articles/286.html familydoctor.org]. The term sinus arrhythmia refers to a normal phenomenon of mild acceleration and slowing of the heart rate that occurs with breathing in and out. It is usually quite pronounced in children, and steadily lessens with age.

Classification of common cardiac arrhythmias

Arrhythmia may be classified by rate (normal, tachycardia, bradycardia), or mechanism (automaticity, reentry, fibrillation). It is also appropriate to classify by site of origin:

=Atrial= *Premature Atrial Contractions (PACs) *Wandering Atrial Pacemaker *Multifocal atrial tachycardia *Atrial flutter *Atrial fibrillation (Afib)

=Junctional arrhythmias= *Supraventricular tachycardia (SVT) *AV nodal reentrant tachycardia is the most common cause of Paroxysmal Supra-ventricular Tachycardia (PSVT) *Junctional rhythm *Junctional tachycardia *Premature junctional complex

=Atrio-ventricular= *AV reentrant tachycardia occurs when a re-entry circuit crosses between the atria and ventricles somewhere other than the AV node: **Wolff-Parkinson-White syndrome **Lown-Ganong-Levine syndrome

=Ventricular= *Premature Ventricular Contractions (PVC) sometimes called Ventricular Extra Beats (VEBs) **Premature Ventricular beats occurring after every normal beat are termed ventricular bigeminy **Two premature ventricular beats for each normal beat is termed ventricular trigeminy *Accelerated idioventricular rhythm *Monomorphic Ventricular tachycardia *Polymorphic ventricular tachycardia *Ventricular fibrillation

=Heart blocks= These are also known as AV blocks, because the vast majority of them arise from pathology at the atrioventricular node. They are the commonest cause of bradycardia: *First degree heart block, which manifests as PR prolongation *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

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. 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 include viral myocarditis, long QT syndrome, Brugada syndrome, Catecholaminergic polymorphic ventricular tachycardia and hypertrophic cardiomyopathy and arrhythmogenic right ventricular dysplasia.

Treatment

Because arrhythmias are such a heterogeneous group of conditions, treatment needs to be carefully selected by a patient with their physician. Some arrhythmias require no treatment at all. Others require immediate emergency treatment if death is to be avoided. Treatments include physical maneuvers, antiarrhythmic drugs, other drugs, electricity, and electro or cryo cautery.

=Physical maneuvers= A number of physical acts can increase parasympathetic nervous supply to the heart, resulting in blocking of electrical conduction through the AV node. This can slow down or stop a number of arrhytmias that originate above or at the AV node (see main article: supraventricular tachycardias). Parasympathetic nervous supply to the heart is via the vagus nerve, and these maneuvers are collectively known as vagal maneuvers.

=Antiarrhythmic drugs= See main article on [[antiarrhythmic agents]]. There are many classes of antiarrhythmic medications, with different mechanisms of action and many different individual drugs within these classes. Although the goal of drug therapy is to prevent arrhythmia, nearly every antiarrhythmic drug has the potential to act as a pro-arrhythmic, and so must be carefully selected and used under medical supervision.

===Other drugs

 A number of other drugs can be useful in cardiac arrhythmias. Several groups of drugs slow conduction through the heart, without actually preventing an arrhythmia. These drugs can be used to "rate control" a fast rhythm and make it physically tolerable for a patient. Some arrhythmias promote blood clotting within the heart, and increase risk of embolus and stroke. [[Anticoagulant]] medications such as warfarin and heparins, and anti-platelet drugs such as aspirin can reduce the risk of clotting.

=Electricity= Dysrhythmias may also be treated electrically, by applying a shock across the heart - either externally to the chest wall, or internally to the heart via implanted electrodes. Cardioversion is the application of a shock synchronised to the underlying heartbeat. It is used for treatment of supraventricular tachycardias. In elective cardioversion, the recipient is usually sedated or lightly anesthetized for the procedure. Defibrillation differs in that the shock is not synchronised. It is needed for the chaotic rhythm of ventricular fibrillation and is also used for pulseless ventricular tachycardia. Often, more electricity is required for defibrillation than for cardioversion. In most defibrillation, the recipient has lost consciousness so there is no need for sedation. Defibrillation or cardioversion may be accomplished by an implantable cardioverter-defibrillator (ICD). Electrical treatment of dysrhythmia also includes cardiac pacing. Temporary pacing may be necessary for reversible causes of very slow heartbeats, or bradycardia, (for example, from drug overdose or myocardial infarction). A permanent pacemaker may be placed in situations where the bradycardia is not expected to recover.

=Electrical cautery= Some cardiologists further sub-specialise into electrophysiology. In specialised catheter laboratories, they use fine probes inserted through the blood vessels to map electrical activity from within the heart. This allows abnormal areas of conduction to be located very accurately, and subsequently destroyed with heat, cold, electrical or laser probes. This may be completely curative for some forms of arrhythmia, but for others, the success rate remains disappointing. AV nodal reentrant tachycardia is often curable. Atrial fibrillation can also be treated with this technique (e.g. pulmonary vein isolation), but the results are less reliable.