Supraventricular tachycardia
From Wikipedia, the free encyclopedia
| ICD-10 | I47.1 |
|---|---|
| ICD-9 | 427.0 |
A supraventricular tachycardia (SVT) is a rapid rhythm of the heart in which the origin of the electrical signal is either the atria or the AV node. These rhythms require the atria or the AV node for either initiation or maintenance. This is in contrast to ventricular tachycardias, which are tachycardias that are not dependent on the atria or AV node.
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[edit] Symptoms
Symptoms can come on suddenly and may go away without treatment. They can last a few minutes or as long as 1-2 days. The rapid beating of the heart during SVT can make the heart a less effective pump so that the body's organs do not receive enough blood to work normally. The following symptoms are typical with a rapid pulse of 140-250 beats per minute:
- Palpitations - The sensation of the heart racing, fluttering or pounding strongly in the chest or the carotid arteries
- Dizziness, or light-headedness (near-faint), or fainting
- Shortness of breath
- Anxiety
- Chest pain or sensation of tightness
- Weakness in legs
[edit] Types of SVTs
Supraventricular tachycardia is a general term that describes a number of different arrhythmias of the heart, each with a different mechanism of impulse maintenance. While some treatment modalities can be applied to all SVTs with impunity, there are specific therapies available that can cure many of the arrhythmias that require intimate knowledge of how the arrhythmia is propagated.
The SVTs can be separated into two groups, based on whether they involve the AV node for impulse maintenance or not. Those that involve the AV node can be terminated by maneuvers that decrease conduction through the AV node, whereas those that do not involve the AV node may be unmasked by the transient AV block caused by the decreased conduction through the AV node.
SVTs from a SINOATRIAL source:
- Sinus Tachycardia
- Inappropriate sinus tachycardia
- Sinoatrial node reentrant tachycardia (SANRT)
SVTs from an ATRIAL source:
- (Unifocal) Atrial tachycardia (AT)
- Multifocal atrial tachycardia (MAT)
- Atrial Fibrillation with a rapid ventricular response
- Atrial Flutter with a rapid ventricular response
SVTs from an ATRIOVENTRICULAR source:
- AV nodal reentrant tachycardia (AVNRT)
- AV reentrant tachycardia (AVRT)
- Junctional tachycardia
- Permanent junctional reciprocating tachycardia (PJRT)
[edit] Diagnosis
In the clinical setting, it is important to determine whether a wide-complex tachycardia is an SVT or a ventricular tachycardia, since they are treated differently. Ventricular tachycardia has to be treated appropriately, since it can quickly degenerate to ventricular fibrillation and death. A number of different algorithms have been devised to determine whether a wide complex tachycardia is supraventricular or ventricular in origin.1 In general, a history of structural heart disease dramatically increases the likelihood that the tachycardia is ventricular in origin.
On a more complex level, SVTs can be distinguished by certain physiological and electrical characteristics, many of which present in a patient's [EKG].
Sinus Tachycardia is considered "appropriate" when a reasonable stimulus, such as the catecholamine surge associated with fright, stress, or physical activity, provokes the tachycardia. It is distinguished by a presentation identical to a normal sinus rhythm except for its fast rate (>100 beats per minute in adults). Sinoatrial node reentrant tachycardia (SANRT)is distinguished by a reentry circuit involving the SA node directly, resulting in a normal-morphology p-wave that falls before a regular, narrow QRS complex.
(Unifocal) Atrial tachycardia is tachycardia resultant from one ectopic foci within the atria, distinguished by a consistent p-wave of abnormal morphology that falls before a narrow, regular QRS complex. Multifocal atrial tachycardia (MAT) is tachycardia resultant from at least three ectopic foci within the atria, distinguished by p-waves of at least three different morphologies that all fall before regular, narrow QRS complexes. Atrial Fibrillation is not, in itself, a tachycardia, but when it is associated with a rapid ventricular response greater than 100 beats per minute, it becomes a tachycardia. A-Fib is characteristically an "irregularly irregular rhythm" both in its atrial and ventricular depolarizations. It is distinguished by fibrillatory p-waves that, at some point in their chaos, stimulate a response from the ventricles in the form of irregular, narrow QRS complexes. Atrial Flutter is also not necessarily a tachycardia until the atrial kick produces a ventricular response greater than 100 beats per minute. Atrial Flutter involves a pattern of conduction where each of its regular, narrow QRS complexes is preceded by a certain number of characteristically "sawtooth" p-waves. The P:QRS pattern is consistent and most often involves either 1:1, 2:1, or 4:1 conduction, although other ratios do exist. Because of the P:QRS pattern's consistency, A-flutter is often regular versus its irregular counterpart, A-fib.
AV nodal reentrant tachycardia (AVNRT) involves an additional, accessory pathway through the AV node that becomes a reentry "circuit," causing the tachycardia. This type of SVT is often distinguished from others by having a p-wave that is buried within regular, narrow QRS complexes because atrial kick becomes insignificant due to the reentry circuit. AV reentrant tachycardia (AVRT) also results from a reentry circuit and is conducted through an accessory pathway (commonly the AV valvular ring) and the AV node. In orthodromic AVRT, atrial impulses are conducted through the AV node and retrogradely re-enter via the accessory pathway. In antidromic AVRT, atrial impulses are conducted through the accessory pathway and retrogradely re-enter via the AV node. Because the accessory pathway conducts atrial impulses slower than the AV node, the QRS complex in antidromic AVRT is often wide. A distinguishing characteristic of orthodromic AVRT is a p-wave that follows each of its regular, narrow QRS complexes, due to retrograde conduction. Finally, Junctional tachycardia usually does not involve an accessory pathway but instead results from the AV node itself initiating an impulse. This AV-initiated impulse may produce a slow ventricular response and it is not until this response becomes greater than 100 beats per minute that the junctional impulse is called "tachycardia." On an EKG, Junctional Tachycardia often presents with abnormal morphology p-waves that may fall anywhere in relation to a regular, narrow QRS complex. When these QRS complexes become irregular and wide, one should rule out the av-node as the maintenance of the impulse and consider Third degree heart block.
[edit] Treatment
In general, SVT is not life threatening, but episodes should be treated or prevented. SVT can be treated through several modalities, the simplest of which is the vagal or valsalva maneuver, wherein a patient is asked to bear down as if having a bowel movement. In doing so, the patient exhales against a closed glottis, increasing intrathoracic pressure and shunting blood toward the head. This causes the carotid baroreceptors to sense a substantial increase in blood pressure, prompting reflex bradycardia by stimulating the parasympathetic nervous system. Another modality involves treatment with medications. Prehospital care providers and hospital clinicians might administer Adenosine, Diltiazem, Metoprolol, or Verapamil. If none of the above works, or if the patient is extremely unstable, synchronized cardioversion may also be used.
Another form of treatment is Radiofrequency ablation, a low risk and usually curative surgical procedure that uses radiofrequency energy to destroy abnormal electrical pathways in heart tissue. Ablation has shown great promise in eliminating SVT.
[edit] References
Note 1: Lau EW, Ng GA. Comparison of the performance of three diagnostic algorithms for regular broad complex tachycardia in practical application. Pacing Clin Electrophysiol. 2002 May;25(5):822-7. (Medline abstract)
[edit] See also
- Tachycardia
- AV nodal reentrant tachycardia (AVNRT)
- AV reentrant tachycardia (AVRT)
- Inappropriate Sinus Tachycardia
- Ashman phenomenon
[edit] External links
- Supraventricular Tachycardia information from Seattle Children's Hospital Heart Center
- An athelete's experience with Re-entrant Supraventricular Tachycardia After being successfully diagnosed and treated, Bobby Julich went on to place 3rd in the 1998 Tour de France and win a Bronze Medal in the 2004 Summer Olympics.
- Supraventricular Tachycardia Patient Information at Arrhythmia Alliance - The Heart Rhythm Charity
