| Supraventricular tachycardia | |
|---|---|
| Classification and external resources | |
Lead II electrocardiogram strip showing SVT with a heart rate of about 150. |
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| ICD-10 | I47.1 |
| ICD-9 | 427.89, 427.0 |
| MeSH | D013617 |
Supraventricular tachycardia (SVT) is a general term that refers to any rapid heart rhythm originating above the ventricular tissue. Supraventricular tachycardias can be contrasted to the potentially more dangerous ventricular tachycardias - rapid rhythms that originate within the ventricular tissue. Although technically an SVT can be due to any supraventricular cause, the term is often used by clinicians to refer to one specific cause of SVT, namely Paroxysmal supraventricular tachycardia (PSVT) which is due to AV nodal reentrant tachycardia.
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The term supraventricular tachycardia is often used differently in different settings.
The following are types of supraventricular tachycardias, each with a different mechanism of impulse maintenance. It should be noted that whilst all of the below terms are technically causes of SVT, clinicians usually use the specific term/diagnosis, when possible:
SVTs from a sinoatrial source:
SVTs from an atrial source:
SVTs from an atrioventricular source (junctional tachycardia):
Symptoms can come on suddenly and may go away without treatment. Stress, exercise, and emotion can all result in a normal or physiological increase in heart rate, but can also, though more rarely, precipitate SVT. Episodes can last a few minutes or as long as 1 or 2 days, sometimes persisting until treated. The rapid beating of the heart during SVT can make the heart a less-effective pump, decreasing cardiac output and blood pressure. The following symptoms are typical with a rapid pulse of 150–270 or more beats per minute:
The individual subtypes of SVT can be usually be distinguished from each other by the physiological and electrical characteristics that are present in the patient's electrocardiogram (ECG).
Most supraventricular tachycardias have a narrow QRS complex on ECG, but supraventricular tachycardia with aberrant conduction (SVTAC) can produce a wide-complex tachycardia that may mimic ventricular tachycardia (VT). 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.[3] In general, a history of structural heart disease dramatically increases the likelihood that the tachycardia is ventricular in origin.
In general, SVT is rarely life threatening, but episodes can be treated or prevented. While some treatment modalities can be applied to all SVTs with impunity, there are specific therapies available to cure some of the different sub-types. Cure requires intimate knowledge of how and where the arrhythmia is initiated and 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 slowing conduction through the AV node. Those that do not involve the AV node will not usually be stopped by AV nodal blocking maneuvers. These maneuvers are still useful however, as transient AV block will often unmask the underlying rhythm abnormality.
AV nodal blocking can be achieved in at least three different ways:
A number of physical maneuvers cause increased AV nodal block, principally through activation of the parasympathetic nervous system, conducted to the heart by the vagus nerve. These manipulations are therefore collectively referred to as vagal maneuvers.
The Valsalva maneuver should be the first vagal maneuver tried.[4] It works by increasing intra-thoracic pressure and affecting baro-receptors (pressure sensors) within the arch of the aorta. It is carried out by asking the patient to hold their breath and try to exhale forcibly as if straining during a bowel movement, or by getting them to hold their nose and blow out against it.[5]
There are many other vagal maneuvers including: holding ones breath for a few seconds, coughing, plunging the face into cold water,[5] (via the diving reflex[6]), drinking a glass of ice cold water, and standing on one's head. Carotid sinus massage, carried out by firmly pressing the bulb at the top of one of the carotid arteries in the neck, is effective but is often not recommended due to risks of stroke in those with plaque in the carotid arteries.
Adenosine, an ultra short acting AV nodal blocking agent, is indicated if vagal maneuvers are not effective.[7] If this works, followup therapy with diltiazem, verapamil or metoprolol may be indicated. SVT that does not involve the AV node may respond to other anti-arrhythmic drugs such as sotalol or amiodarone.
In pregnancy, adenosine is the treatment of choice as recommended by the ACC/AHA/ESC Guidelines for the Management of Patients With Supraventricular Arrhythmias.[8]
If the patient is unstable or other treatments have not been effective, cardioversion may be used, and is almost always effective.
Once the acute episode has been terminated, ongoing treatment may be indicated to prevent a recurrence of the arrhythmia. Patients who have a single isolated episode, or infrequent and minimally symptomatic episodes usually do not warrant any treatment except observation.
Patients who have more frequent or disabling symptoms from their episodes generally warrant some form of preventive therapy. A variety of drugs including simple AV nodal blocking agents like beta-blockers and verapamil, as well as anti-arrhythmics may be used, usually with good effect, although the risks of these therapies need to be weighed against the potential benefits.
A limited study has demonstrated that acupuncture can also be effective in preventing paroxysmal supraventricular tachycardia[9].
Radiofrequency ablation has revolutionized the treatment of tachycardia caused by a re-entrant pathway. This is a low risk procedure that uses a catheter inside the heart to deliver radio frequency energy to locate and destroy the abnormal electrical pathways. Ablation has been shown to be highly effective: around 90% effective in eliminating AVNRT. Similar high rates of success are achieved with radio frequency ablation in eliminating AVRT and typical Atrial Flutter.
There is a newer treatment for SVT involving the AV node directly. This treatment is called Cryoablation. SVT involving the AV node is often a contraindication for using radiofrequency ablation due to the small (1%) incidence of injuring the AV node requiring a permanent pacemaker. With Cryoablation, a supercooled catheter is used (cooled by nitrous oxide gas), and the tissue is frozen to -10 °C. This provides the same result as radiofrequency ablation but does not carry the same risk. If you freeze the tissue and then realize you are in a dangerous spot, you can halt freezing the tissue and allow the tissue to spontaneously rewarm and the tissue is the same as if you never touched it. If after freezing the tissue to -10 °C, you get the desired result, then you freeze the tissue down to a temperature of -73 °C and you permanently ablate the tissue.
This therapy has further improved the treatment options for people with AVNRT (and other SVTs with pathways close to the AV node), widening the application of curative ablation to young patients with relatively mild but still troublesome symptoms who would not have accepted the risk of requiring a pacemaker.
After being successfully diagnosed and treated, Bobby Julich went on to place third in the 1998 Tour de France and win a Bronze Medal in the 2004 Summer Olympics.[10] Women's Olympic volleyball player Tayyiba Haneef-Park underwent an ablation for SVT just two months before competing in the 2008 Summer Olympics.[11] Tony Blair, former PM of the UK, was also operated on for atrial flutter. Anastacia was diagnosed with the disease.[12] Women's Olympic gold medalist swimmer, Rebecca Soni has had SVT and has had heart surgery for it. In addition, Neville Fields had corrective surgery for SVT in early 2006.
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