Supraventricular tachycardia: Difference between revisions
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==Diagnosis== | ==Diagnosis== | ||
==Acute Treatment== | ==Acute Treatment== | ||
Revision as of 15:56, 10 September 2012
| Supraventricular tachycardia | |
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| ICD-10 | I47.1 |
| ICD-9 | 427.89 |
| MeSH | D013617 |
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Supraventricular tachycardia Microchapters |
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Differentiating Among the Different Types of Supraventricular Tachycardia |
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Differentiating Supraventricular Tachycardia from Ventricular Tachycardia |
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Diagnosis |
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Treatment |
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2015 ACC/AHA Guideline Recommendations |
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Case Studies |
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Supraventricular tachycardia On the Web |
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American Roentgen Ray Society Images of Supraventricular tachycardia |
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Directions to Hospitals Treating Supraventricular tachycardia |
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Risk calculators and risk factors for Supraventricular tachycardia |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Synonyms and keywords: SVT, paroxysmal supraventricular tachycardia, PSVT, paroxysmal atrial tachycardia; PAT; PAT with block
Overview
A supraventricular tachycardia (SVT) is a tachycardia or rapid rhythm of the heart in which the origin of the electrical signal is either the atria or the AV node. These rhythms, by definition, are either initiated or maintained by the atria or the AV node. This is in contrast to ventricular tachycardias, which are rapid rhythms that originate from the ventricles of the heart, that is, below the atria or AV node. The term SVT encompasses a large number of arrhythmias arising from the atria and AV node, and the term SVT is often incorrectly applied only to the subgroup of AV nodal re-entrant tachycardias.
Classification
Differentiating SVT from VT
Most supraventricular tachycardias have a narrow QRS complex on the EKG. It is not infrequent, however, for aberrant conduction to be be present, sometimes as a result of the more rapid rate of conduction. This widening of the QRS complex yields supraventricular tachycardia with aberrant conduction (SVTAC) which produces 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.[1]
In general, a history of structural heart disease, ischemic heart disease or congestive heart failure increases the likelihood that the tachycardia is ventricular in origin.
Differentiating Among the Different Types of Supraventricular Tachycardia
The individual subtypes of SVT can be distinguished from each other by certain physiological and electrical characteristics, many of which present in the patient's EKG.
Supraventricular tachycardias must be differentiated from each other because the management strategies may vary:
Atrial Fibrillation
- Rate: 110 to 180 bpm
- Rhythm: Irregularly irregular
- P waves: Absent, fibrillatory waves
- PR interval: Absent
- QRS complex: Less than 0.12 seconds, consistent, and normal in morphology in the absence of abberant conduction
- Response to Maneuvers: Does not break with adenosine or vagal maneuvers
- Epidemiology and Demographics: More common in the elderly, following bypass surgery, in mitral valve disease, hyperthyroidism
Atrial Flutter
- Rate: 75 (4:1 block), 100 (3:1 block) and 150 (2:1 block) bpm, but 150 is most common
- Rhythm: Regular
- P waves: Sawtooth pattern of P waves at 250 to 350 beats per minute
- PR interval: Varies depending upon the magnitude of the block, but is short
- QRS complex: Less than 0.12 seconds, consistent, and normal in morphology
- Response to Maneuvers: Conduction may vary in response to drugs and maneuvers dropping the rate from 150 to 100 or to 75 bpm
- Epidemiology and Demographics: More common in the elderly, after alcohol
- Pathophysiology:
AV Nodal Reentry Tachycardia
- Rate: In adults the range is 140-250 bpm, but in children the rate can exceed 250 bpm.
- Rhythm: Regular
- P waves: The p wave is usually superimposed on or buried within the QRS complex
- PR interval: The PR interval cannot be calculated as the p wave is generally obscured by the QRS complex. In uncommon AVNRT, the p wave can appear after the QRS complex and before the T wave, and in atypical AVNRT, the p wave can appear just before the QRS complex.
- QRS complex: Less than 0.12 seconds, consistent, and normal in morphology in the absence of abberant conduction, QRS alternans may be present
- Response to Maneuvers: May break with adenosine or vagal maneuvers
- Epidemiology and Demographics: Accounts for 60%-70% of all SVTs. 80% to 90% of cases are due to antegrade conduction down a slow pathway and retrograde up a fast pathway.
AV Reciprocating Tachycardia
- Rate: More rapid than AVNRT
- Rhythm:
- P waves:
- PR interval:
- QRS complex: Less than 0.12 seconds, consistent, and normal in morphology
- Response to Maneuvers: May break with adenosine or vagal maneuvers
- Epidemiology and Demographics: More common in males, whereas AVNRT is more common in females, occurs at a younger age.
- Pathophysiology:*Atrioventricular reentrant tachycardia (AVRT) also results from a reentry circuit, although one physically much larger than AVNRT. One portion of the circuit is usually the AV node, and the other, an abnormal accessory pathway from the atria to the ventricle. Wolff-Parkinson-White syndrome is a relatively common abnormality with an accessory pathway, the Bundle of Kent crossing the A-V valvular ring.
- In orthodromic AVRT, atrial impulses are conducted down through the AV node and retrogradely re-enter the atrium via the accessory pathway. A distinguishing characteristic of orthodromic AVRT can therefore be a p-wave that follows each of its regular, narrow QRS complexes, due to retrograde conduction.
- In antidromic AVRT, atrial impulses are conducted down through the accessory pathway and re-enter the atrium retrogradely via the AV node. Because the accessory pathway initiates conduction in the ventricles ouside of the bundle of His, the QRS complex in antidromic AVRT is often wider than usual, with a delta wave.
Inappropriate Sinus Tachycardia
- Rate: A resting sinus tachycardia is usually (but not always) present. The mean heart rate during 24 hrs of monitoring is > 95 beats per minute. A nocturnal reduction in heart rate is present. There is an inappropriate heart rate response on exertion.
- Rhythm: Regular
- P waves: Normal morphology and precede the QRS complex
- PR interval: Normal and < 0.20 seconds
- QRS complex: Less than 0.12 seconds, consistent, and normal in morphology
- Response to Maneuvers: Does not break with adenosine or vagal maneuvers
- Epidemiology and Demographics:
- Pathophysiology: These patients have no apparent heart disease or other causes of sinus tachycardia. IST is thought to be due to abnormal autonomic control.
Junctional Tachycardia
- Rate: > 60 beats per minute
- Rhythm: Regular
- P waves: Usually inverted, may be burried in the QRS complex
- PR interval: The p wave is usually buried in the QRS complex
- QRS complex: Less than 0.12 seconds, consistent, and normal in morphology
- Response to Maneuvers: Does not break with adenosine or vagal maneuvers
- Epidemiology and Demographics: Common after heart surgery, digoxin toxicity, as an escape rhythm in AV block
Multifocal Atrial Tachycardia
- Rate: Atrial rate is > 100 beats per minute (bpm)
- Rhythm: Irregular
- P waves: P waves of varying morphology from at least three different foci, absence of one dominant atrial pacemaker, can be mistaken for atrial fibrillation if the P waves are of low amplitude
- PR interval: Variable PR intervals, RR intervals, and PP intervals
- QRS complex: Less than 0.12 seconds, consistent, and normal in morphology
- Response to Maneuvers: Does not terminate with adenosine or vagal maneuvers
- Epidemiology and Demographics: * High incidence in the elderly and in those with COPD
Sinus Node Reentry Tachycardia
- Rate:
- Rhythm:
- P waves: Upright P waves precede each regular, narrow QRS complex
- PR interval:
- QRS complex: Less than 0.12 seconds, consistent, and normal in morphology
- Response to Maneuvers: Although it cannot be distinguished on the surface 12 lead EKG from sinus tachycardia, SA node reentry tachycardia does often terminate with vagal maneuvers unlike sinus tachycardia.
- Epidemiology and Demographics:
Sinus tachycardia
- Rate: Greater than 100.
- Rhythm: Regular.
- P waves: Upright, consistent, and normal in morphology (if no atrial disease)
- PR interval: Between 0.12–0.20 seconds and shortens with increasing heart rate
- QRS complex: Less than 0.12 seconds, consistent, and normal in morphology
- Response to Maneuvers:
- Epidemiology and Demographics:
- Pathophysiology: *Sinus tachycardia is considered "appropriate" when a reasonable stimulus such as fever, anemia, fright, stress, or physical activity, provokes the tachycardia. This is in distinction to Inappropriate sinus tachycardia where no such stiumulus exists.
Ventricular Tachycardia
- Rate:
- Rhythm: Generally regular
- P waves: Normal morphology, upright, but dissociated from the QRS complex (i.e. "march through" the QRS complex)
- PR interval:
- QRS complex: Wide and greater than 0.12 seconds
- Response to Maneuvers: Does not terminate in response to adenosine or vagal maneuvers
- Epidemiology and Demographics:
- Risk Factors:: Occurs in the context of myocardial ischemia, myocardial infarction, congestive heart failure, drug toxicity, and inhereted channelopathies
Wolff-Parkinson-White syndrome
- Pathophysiology: Anatomically and functionally, the fast and slow pathways of AVNRT should not be confused with the accessory pathways that give rise to Wolff-Parkinson-White syndrome (WPW) syndrome or atrioventricular re-entrant tachycardia (AVRT). In AVNRT, the fast and slow pathways are located within the right atrium in close proximity to or within the AV node and exhibit electrophysiologic properties similar to AV nodal tissue. Accessory pathways that give rise to WPW syndrome and AVRT are located in the atrioventricular valvular rings, they provide a direct connection between the atria and ventricles, and have electrophysiologic properties similar to ventricular myocardium.
- Rate:
- Rhythm:
- P waves: In WPW with orthodromic conduction due to a bypass tract, the p wave generally follows the QRS complex, whereas in AVNRT, the p wave is generally buried in the QRS complex.
- PR interval:
- QRS complex: In WPW there is a delta wave and evidence of ventricular preexcitation if there is conduction to the ventrilce via antegrade conduction down an accessory pathway. It should be noted, however, that in some patients with WPW, a delta wave and pre-excitation may not be present because bypass tracts do not conduct antegrade.
- Response to Maneuvers: May break in response to procainamide, adenosine, vagal maneuvers
- Epidemiology and Demographics:
- Risk Factors: None, an inhereted disorder
Risk Factors
Natural History, Complications, Prognosis
Diagnosis
Acute Treatment
In general, SVT is not life threatening, but episodes should 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 manoevres. These manoevres 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:
Physical maneuvers
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 maneuver.
The best recognised of these is the Valsalva maneuver, which increases intra-thoracic pressure and affects baro-receptors (pressure sensors) within the arch of the aorta. This can be achieved by asking the patient to hold their breath and "bear down" as if straining to pass a bowel motion, or less embarrassingly, by getting them to hold their nose and blow out against it. Plunging the face into, or just drinking a glass of ice cold water is also often effective. Firmly pressing the bulb at the top of one of the carotid arteries in the neck (carotis sinus massage, stimulating carotid baro-receptors) is also effective, but not recommended for those without adequate medical training.
Drug Treatment
Another modality involves treatment with medications. Prehospital care providers and hospital clinicians might administer Adenosine, an ultra short acting AV nodal blocking agent. 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, Metoprolol is the treatment of choice as recommended by the American Heart Association.
Prevention & Cure
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 preventative 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.
For supraventricular tachycardia caused by a re-entrant pathway, another form of treatment is radiofrequency ablation. This is a low risk procedure that uses a catheter inside the heart to deliver radiofrequency energy to locate and destroy the abnormal electrical pathways. Ablation has been shown to be highly effective: up to 99% effective in eliminating AVNRT, and similar results in typical Atrial flutter.
Paroxysmal atrial tachycardia is a period of very rapid and regular heart beats that begins and ends abruptly. The heart rate is usually between 160 and 200 beats per minute. This condition is also known as paroxysmal supraventricular tachycardia.
See also
- Tachycardia
- AV nodal reentrant tachycardia (AVNRT)
- AV reentrant tachycardia (AVRT)
- Inappropriate Sinus Tachycardia
- Ashman phenomenon