Paroxysmal Supraventricular Tachycardia

Background

Paroxysmal supraventricular tachycardia (paroxysmal SVT) is an episodic condition with an abrupt onset and termination. (See Etiology and Presentation.)

SVT in general is any tachyarrhythmia that requires atrial and/or atrioventricular (AV) nodal tissue for its initiation and maintenance. It is usually a narrow-complex tachycardia that has a regular, rapid rhythm; exceptions include atrial fibrillation (AF) and multifocal atrial tachycardia (MAT). Aberrant conduction during SVT results in a wide-complex tachycardia. (See Etiology and Workup.)

SVT is a common clinical condition that occurs in persons of all age groups, and treatment can be challenging. Electrophysiologic studies are often needed to determine the source of the conduction abnormalities. (See Epidemiology, Prognosis, Workup, Treatment, and Medication.)

Manifestations of SVT are quite variable; patients may be asymptomatic or they may present with minor palpitations or more severe symptoms. Results from electrophysiologic studies have helped to determine that the pathophysiology of SVT involves abnormalities in impulse formation and conduction pathways. The most common mechanism identified is reentry. (See Etiology, Prognosis, Presentation, and Workup.)^{[1, 2, 3, 4]}

Rare complications of paroxysmal SVT include myocardial infarction, congestive heart failure, syncope, and sudden death. (See Prognosis and Presentation.)

Classification

The development of intracardiac electrophysiologic studies has dramatically changed the classification of SVT, with intracardiac recordings having identified the various mechanisms involved in the condition. Depending on the site of origin of the dysrhythmia, SVT may be classified as an atrial or AV tachyarrhythmia. Another way to separate the arrhythmias is to classify them into conditions having either regular or irregular rhythms.^{[5, 6]}

Atrial tachyarrhythmias include the following:

• Sinus tachycardia
• Inappropriate sinus tachycardia (IST)
• Sinus nodal reentrant tachycardia (SNRT)
• Atrial tachycardia
• Multifocal atrial tachycardia
• Atrial flutter
• Atrial fibrillation

AV tachyarrhythmias include the following:

• AV nodal reentrant tachycardia (AVNRT)
• AV reentrant tachycardia (AVRT)
• Junctional ectopic tachycardia (JET)
• Nonparoxysmal junctional tachycardia (NPJT)

Patient education

For patient education information, see the Heart Health Center, as well as Supraventricular Tachycardia (SVT, PSVT), Atrial Fibrillation (AFib ), Atrial Flutter, and Arrhythmias (Heart Rhythm Disorders).

• References

Etiology

SVT and paroxysmal SVT are triggered by a reentry mechanism. This may be induced by premature atrial or ventricular ectopic beats. Other triggers include hyperthyroidism and stimulants, including caffeine, drugs, and alcohol.

Paroxysmal SVT is observed not only in healthy individuals; it is also common in patients with previous myocardial infarction, mitral valve prolapse, rheumatic heart disease, pericarditis, pneumonia, chronic lung disease, and current alcohol intoxication.^{[7, 8, 9, 10]} Digoxin toxicity also may be associated with paroxysmal SVT.^{[9, 10, 11]}

Atrial tachyarrhythmias

Sinus tachycardia

Sinus tachycardia is the most common regular SVT. It has an accelerated sinus rate that is a physiologic response to a stressor. It is characterized by a heart rate faster than 100 beats per minute (bpm) and generally involves a regular rhythm with p waves before all QRS complexes. (See the image below.)

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Sinus tachycardia. Note that the QRS complexes are narrow and regular. The patient's heart rate is approximately 135 bpm. P waves are normal in morpho....

Underlying physiologic stresses such as hypoxia, hypovolemia, fever, anxiety, pain, hyperthyroidism, and exercise usually induce sinus tachycardia.^{[12, 13]} Certain drugs, such as stimulants (eg, nicotine, caffeine), medications (eg, atropine, salbutamol), recreational drugs (eg, cocaine, amphetamines, ecstasy), and hydralazine, can also induce the condition. Treatment involves addressing the basic underlying stressor.

Inappropriate sinus tachycardia

IST is an accelerated baseline sinus rate in the absence of a physiologic stressor. In this situation, healthy adults may have an elevated resting heart rate and an exaggerated heart rate response to even minimal exercise. This tachyarrhythmia is observed most commonly in young women without structural heart disease.^{[10, 14, 15]}

The underlying mechanism of IST may be hypersensitivity of the sinus node to autonomic input or an abnormality within the sinus node and/or its autonomic input. P wave morphology is normal on ECG and it is a diagnosis of exclusion.^{[10, 14, 15]}

Sinus nodal reentrant tachycardia

SNRT is frequently confused with IST. SNRT is due to a reentry circuit, either in or near the sinus node. Therefore, it has an abrupt onset and offset. The heart rate is usually 100-150 bpm, and electrocardiographic tracings usually demonstrate a normal sinus P wave morphology.^{[14, 15, 10]}

Atrial tachycardia

Atrial tachycardia is an arrhythmia originating in the atrial myocardium. Enhanced automaticity, triggered activity, or reentry may result in this rare tachycardia.^{[16, 17, 18, 19, 10]} The heart rate is regular and is usually 120-250 bpm. The P-wave morphology is different from the sinus P waves and is dependent on the site of origin of the tachycardia. (See the image below.)

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Atrial tachycardia. The patient's heart rate is 151 bpm. P waves are upright in lead V1.

Because the arrhythmia does not involve the AV node, nodal blocking agents, such as adenosine and verapamil, are usually unsuccessful in terminating this arrhythmia. Atrial tachycardia has also been associated with digoxin toxicity via the triggered mechanism.^{[16, 17, 18, 19, 10]}

Multifocal atrial tachycardia

Multifocal atrial tachycardia is a tachyarrhythmia that arises within the atrial tissue; it is composed of 3 or more P-wave morphologies and heart rates. This arrhythmia is fairly uncommon; it is typically observed in elderly patients with pulmonary disease. The heart rate is greater than 100 bpm, and electrocardiographic findings typically include an irregular rhythm, which may be misinterpreted as atrial fibrillation (see the image below). Treatment involves correcting the underlying disease process.^{[20, 21, 22]} Magnesium and verapamil may sometimes be effective.

View Image

Multifocal atrial tachycardia. Note the different P-wave morphologies and irregularly irregular ventricular response.

Atrial flutter

Atrial flutter is a tachyarrhythmia arising above the AV node with an atrial rate of 250-350 bpm. The mechanism behind atrial flutter is generally reentrant in nature. Typically, counterclockwise atrial flutter is due to a macroreentrant right atrial circuit. It is commonly observed in patients with any of the following conditions:

• Ischemic heart disease
• Myocardial infarction
• Cardiomyopathy
• Myocarditis
• Pulmonary embolus
• Toxic ingestion (eg, alcohol)
• Chest trauma

Atrial flutter may be a transitional rhythm and can progress to atrial fibrillation. Electrocardiographic findings of typical atrial flutter include negative sawtooth flutter waves in leads II, III, and aVF. AV conduction is most commonly 2:1, which yields a ventricular rate of approximately 150 bpm. (See the image below.)^{[12, 23, 11]}

View Image

Atrial flutter. The patient's heart rate is approximately 135 bpm with 2:1 conduction. Note the sawtooth pattern formed by the flutter waves.

Atrial fibrillation

Atrial fibrillation is an extremely common arrhythmia arising from chaotic atrial depolarization. The atrial rate is usually 300-600 bpm, while the ventricular rate may be 170 bpm or more. Electrocardiographic findings characteristically include an irregular rhythm with fibrillatory atrial activity. (See the image below.)

View Image

Atrial fibrillation. The patient's ventricular rate varies from 130-168 bpm. The rhythm is irregularly irregular. P waves are not discernible.

This arrhythmia is associated with the following conditions^{[12, 23, 11]} :

• Rheumatic heart disease
• Hypertension
• Ischemic heart disease
• Pericarditis
• Thyrotoxicosis
• Alcohol intoxication
• Mitral valve prolapse and other disorders of the mitral valve
• Digitalis toxicity

When atrial fibrillation occurs in young or middle-aged patients in the absence of structural heart disease or any other apparent cause, it is called lone or idiopathic atrial fibrillation.

AV tachyarrhythmias

AV nodal reentrant tachycardia

One of the common causes of paroxysmal SVT is AVNRT. AVNRT is diagnosed in 50-60% of patients who present with regular narrow QRS tachyarrhythmia and is often in people older than 20 years.^{[3, 23, 24, 25]} The heart rate is 120-250 bpm and is typically quite regular. (See the images below.)

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Atrioventricular nodal reentrant tachycardia. The patient's heart rate is approximately 146 bpm with a normal axis. Note the pseudo S waves in leads I....

View Image

Same patient as in the previous image. The patient is in sinus rhythm following atrioventricular nodal reentrant tachycardia.

AVNRT may occur in healthy, young individuals, and it occurs most commonly in women.^[25] Most patients do not have structural heart disease. However, occasionally these individuals may have an underlying heart condition such as rheumatic heart disease, pericarditis, myocardial infarction, mitral valve prolapse, or preexcitation syndrome.^{[3, 24, 25]}

An understanding of the electrophysiology of AV nodal tissue is very important in comprehending the mechanism of AVNRT. In most people, the AV node has a single conducting pathway that conducts impulses in an anterograde manner to depolarize the bundle of His. In certain cases, AV nodal tissue may have 2 conducting pathways with different electrophysiologic properties. One pathway (alpha) is a relatively slow conducting pathway with a short refractory period, while the second pathway (beta) is a rapid conducting pathway with a long refractory period.

The coexistence of these functionally different pathways serves as the substrate for reentrant tachycardia.^{[3, 23, 24, 9]} Electrophysiologic studies have demonstrated dual AV nodal pathways in 40% of patients.

The onset of AVNRT is triggered by a premature atrial impulse. A premature atrial impulse may reach the AV node when the fast pathway (beta) is still refractory from the previous impulse but the slow pathway (alpha) may be able to conduct. The premature impulse then conducts through the slow pathway (alpha) in an anterograde manner; the fast pathway (beta) continues to recover because of its longer refractory period.

After the impulse conducts in an anterograde manner through the slow pathway (alpha), it may find the fast pathway (beta) recovered. The impulse then conducts in a retrograde manner via the fast (beta) pathway. If the slow pathway (alpha) has repolarized by the time the impulse completes the retrograde conduction, the impulse can reenter the slow pathway (alpha) and initiate AVNRT. (See the image below.)

View Image

Image A displays the slow pathway and the fast pathway, with a regular impulse being conducted through the atrioventricular node. Image B displays a p....

Importantly, note that AVNRT does not involve the ventricles as part of the reentry circuit; the necessity of perinodal atrial tissue to the circuit is controversial. Because the impulse typically conducts in an anterograde manner through the slow pathway and in a retrograde manner through the fast pathway, the PR interval is longer than the RP interval. Thus, in patients with typical AVNRT, the P wave is usually located at the terminal portion of the QRS complex.^{[3, 23, 11, 24, 9]}

In patients with atypical AVNRT, anterograde conduction is via the fast pathway, while retrograde conduction is via the slow pathway. For these atypical patients, the RP interval is longer than the PR interval.^{[24, 26, 23, 25, 3, 9, 27, 11]}

AV reentrant tachycardia

AVRT is another common form of paroxysmal SVT. The incidence rate of AVRT in the general population is 0.1-0.3%. AVRT is more common in males than in females (male-to-female ratio of 2:1), and patients with AVRT commonly present at a younger age than do patients with AVNRT. AVRT is associated with the Ebstein anomaly, although most patients with AVRT do not have evidence of structural heart disease.

AVRT results from the presence of 2 or more conducting pathways; specifically, the AV node and 1 or more bypass tracts. In a normal heart, only a single route of conduction is present. Conduction begins at the sinus node, progresses to the AV node, and then to the bundle of His and the bundle branches. However, in AVRT, 1 or more accessory pathways connect the atria and the ventricles. The accessory pathways may conduct impulses in an anterograde manner, a retrograde manner, or both.^{[28, 29, 24, 30, 31, 32, 9, 10]}

When impulses travel down the accessory pathway in an anterograde manner, ventricular preexcitation results. This produces a short PR interval and a delta wave, as is observed in persons with Wolff-Parkinson-White (WPW) syndrome. A delta wave is the initial deflection of the QRS complex, owing to depolarization of the ventricles. (See the image below.)^[28]

View Image

Wolff-Parkinson-White pattern. Note the short PR interval and slurred upstroke (delta wave) to the QRS complexes.

Importantly, note that not all accessory pathways conduct in an anterograde manner. Concealed accessory pathways are not evident during sinus rhythm, and they are only capable of retrograde conduction.

A reentry circuit is most commonly established by impulses traveling in an anterograde manner through the AV node and in a retrograde manner through the accessory pathway; this is called orthodromic AVRT. (See the image below.)

View Image

Orthodromic atrioventricular reentrant tachycardia. This patient has Wolff-Parkinson-White syndrome.

A reentry circuit may also be established by a premature impulse traveling in an anterograde manner through a manifest accessory pathway and in a retrograde manner through the AV node; this is called antidromic AVRT. While the orthodromic AVRT is typically a narrow-complex tachycardia, antidromic AVRT inscribes a bizarre, wide-complex tachycardia. (See the images below.)^{[33, 34, 35]}

View Image

The left image displays the atrioventricular node with the accessory pathway. The impulse is conducted in an anterograde manner in the atrioventricula....

View Image

The left panel depicts antidromic atrioventricular reentrant tachycardia. The right panel depicts sinus rhythm in a patient with antidromic atrioventr....

Patients with WPW syndrome can develop atrial fibrillation and atrial flutter (see the image below). The rapid conduction via the accessory pathways can result in extremely rapid rates, which can degenerate to ventricular fibrillation and cause sudden death. Patients with preexcitation syndromes with atrial fibrillation must not be administered an AV nodal blocking agent; these agents can further increase conduction via the accessory pathway, which increases the risk of ventricular fibrillation and death.^{[36, 37, 7, 33, 38, 8, 39]}

View Image

Atrial fibrillation in a patient with Wolff-Parkinson-White syndrome. Note the extremely rapid ventricular rate and variability in QRS morphology. Sev....

Junctional ectopic tachycardia and nonparoxysmal junctional tachycardia

JET and NPJT are rare; they presumably arise because of increased automaticity, triggered activity, or both. They are usually observed following valvular surgery, after myocardial infarction, during active rheumatic carditis, or with digoxin toxicity. These tachycardias are also observed in children following congenital heart surgery. Electrocardiographic findings include a regular narrow QRS complex, although P waves may not be visible. Patients with AV dissociation have also been described.^{[9, 40, 41]}

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Epidemiology

Occurrence in the United States

The incidence of paroxysmal SVT is approximately 1-3 cases per 1000 persons, with a prevalence of 0.2%. Atrial fibrillation is the most common, affecting 3 million people in the United States alone, with prevalence of 0.4-1% in the population. It is estimated that atrial fibrillation will affect more than 7.5 million people by 2050.^{[7, 8, 9, 10, 42, 43, 44]}

AVNRT and AVRT

In a population-based study, the incidence of paroxysmal SVT was 35 cases per 100,000 person-years and peak incidence was in the middle age people.^[45] AVNRT is more common in patients who are middle-aged or older, while adolescents are more likely to have SVT mediated by an accessory pathway like AVRT.^{[43, 46]} The incidence rate of the WPW pattern on ECG tracings is 0.1-0.3% in the general population, although not all patients develop SVT.^{[7, 8, 9, 43]}

Paroxysmal SVT is observed not only in healthy individuals; it is also common in patients with previous myocardial infarction, mitral valve prolapse, rheumatic heart disease, pericarditis, pneumonia, chronic lung disease, and current alcohol intoxication.^{[7, 8, 9, 10]} Digoxin toxicity also may be associated with paroxysmal supraventricular tachycardia.^{[9, 10, 11]}

Sex- and age-related demographics

Most series of catheter ablation reflect a higher proportion of female patients with AVNRT than male patients. This may reflect a true higher incidence in women, or it may reflect the sample of patients who are referred (or choose) to undergo extensive evaluation and/or catheter ablation. In a population-based study, the risk of developing paroxysmal SVT was twice as high in women as it was in men.^[45] However, the prevalence of atrial fibrillation is the same in men and women.^[47]

The prevalence of paroxysmal SVT increases with age. AVNRT is seen more commonly in persons who are middle aged or older, while adolescents usually have SVT from an accessory pathway.^[45] The relative frequency of tachycardia mediated by an accessory pathway decreases with age.

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Prognosis

Patients with symptomatic Wolff-Parkinson-White Syndrome (WPW) syndrome have a small risk of sudden death. Otherwise, prognosis in paroxysmal SVT is dependent on any underlying structural heart disease; patients with a structurally normal heart have an excellent prognosis.

Morbidity and mortality

Paroxysmal SVT may start suddenly and last anywhere from seconds to days. Patients may or may not be symptomatic, depending on their hemodynamic reserve, heart rate, the duration of the paroxysmal SVT, and coexisting diseases.

Paroxysmal SVT can result in heart failure, pulmonary edema, myocardial ischemia, and/or myocardial infarction secondary to an increased heart rate in patients with poor left ventricular function.^{[9, 10, 11]} In fact, one study found that one third of patients with SVT experienced syncope or required cardioversion.^[48] Incessant SVT can cause tachycardia-induced cardiomyopathy.

Patients with WPW syndrome may be at risk for cardiac arrest if they develop atrial fibrillation or atrial flutter in the presence of a rapidly conducting accessory pathway (ie, a pathway with a short anterograde refractory period).

Extremely rapid ventricular rates during atrial fibrillation or atrial flutter can cause deterioration to ventricular fibrillation. This complication is unusual and occurs primarily in patients who have had prior symptoms due to WPW syndrome. Sudden death may be the initial presentation of WPW syndrome, but how often this occurs is unclear.

In the absence of manifest preexcitation (ie, WPW syndrome), the risk of sudden death with paroxysmal SVT is extremely small.

A study by Bánhidy et al of 252 pregnant women indicated that the presence of paroxysmal SVT in the second and/or third gestational month of pregnancy increases the risk that the resulting child will have a secundum atrial septal defect.^[49]

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History and Physical Examination

History

Because symptom severity depends on the presence of structural heart disease and on the hemodynamic reserve of the patient, individuals with paroxysmal supraventricular tachycardia (paroxysmal SVT) may present with mild symptoms or severe cardiopulmonary complaints. Common presenting symptoms of paroxysmal SVT and their frequency rates are as follows^{[42, 48]} :

• Palpitations - Greater than 96%
• Dizziness - 75%
• Shortness of breath - 47%
• Syncope - 20%
• Chest pain - 35%
• Fatigue - 23%
• Diaphoresis - 17%
• Nausea - 13%

Palpitations and dizziness are the most common symptoms reported by patients with SVT. Chest discomfort may be secondary to a rapid heart rate, and it frequently subsides with the termination of the tachycardia. Persistent SVT may lead to tachycardia-induced cardiomyopathy.

History should include time of onset, any triggers, any previous episodes or arrhythmia, and previous treatment. A detailed past medical and cardiac history and a complete list of all medications should be obtained.

Patients who are hemodynamically unstable should be resuscitated immediately with cardioversion. An electrocardiogram (ECG) should be performed as soon as possible.

Many patients with frequent episodes of paroxysmal supraventricular tachycardia tend to avoid activities such as exercising and driving due to past episodes of syncope or near-syncope.

Physical examination

Pertinent findings are generally limited to the patient’s cardiovascular and respiratory systems. Patients often appear quite distressed. Tachycardia may be the only finding in persons who are otherwise healthy and have significant hemodynamic reserve.

Patients who have limited hemodynamic reserve may be tachypneic and hypotensive. Crackles may be auscultated secondary to heart failure. An S₃ may be present, and large jugular venous pulsations may also be visualized.^{[9, 48, 10]}

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Approach Considerations

Laboratory studies

A cardiac enzyme evaluation should be ordered for patients with chest pain, patients with risk factors for myocardial infarction, and patients who are otherwise unstable and present with heart failure, hypotension, or pulmonary edema. Young patients with no structural heart defects have a very low risk of myocardial infarction.

Other laboratory tests include the following:

• Electrolyte levels - Should be checked because electrolyte abnormalities can contribute to paroxysmal supraventricular tachycardia (paroxysmal SVT)
• Complete blood count (CBC) - Helps to assess whether anemia is contributing to the tachycardia or ischemia
• Thyroid studies - The results are rarely diagnostic of hyperthyroidism
• Digoxin level - Obtain for patients on digoxin, because paroxysmal SVT is one of the many dysrhythmias that can be caused by supratherapeutic levels of this drug

Electrophysiology

Electrophysiologic studies have dramatically changed the diagnosis of SVT. Intracardiac recordings have helped to map accessory pathways and reentry circuits in patients, and they have also assisted cardiologists and electrophysiologists in understanding the mechanisms behind these tachyarrhythmias.

In a prospective registry, Lauschke et al compared the prevalence of inducible arrhythmias and the clinical outcome in 525 patients with and without ECG documentation. Results showed that a substantial proportion of patients with suspected paroxysmal tachycardia, but without ECG documentation, had inducible supraventricular tachycardias (SVTs) and clinically benefited from an electrophysiological study (EPS).^[69]

At present, electrophysiologic studies are generally performed in combination with radiofrequency catheter ablation.

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Imaging Studies

Chest radiography

Obtain a chest radiograph to assess for the presence of pulmonary edema and cardiomegaly. In certain cases, infections such as pneumonia are also associated with paroxysmal SVT and can be confirmed with chest radiography.^{[9, 10, 11, 40, 41]}

Transthoracic echocardiography

A transthoracic echocardiogram may be helpful if structural or congenital heart disease is suggested.

Magnetic resonance imaging

Cardiac magnetic resonance imaging (MRI) can be useful, especially if a congenital heart disease is being considered.

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Electrocardiography

Electrocardiographic findings permit classification of the tachyarrhythmia, and they may allow a precise diagnosis. P waves may not be visible; when present, they may be normal or abnormal, depending on the mechanism of atrial depolarization.^{[9, 10, 35]}

Electrocardiographic characteristics of the various SVTs are as follows:

• Sinus tachycardia - Heart rate greater than 100 bpm; P waves similar to sinus rhythm
• Inappropriate sinus tachycardia (IST) - Findings similar to sinus tachycardia; P waves similar to sinus rhythm
• Sinus nodal reentrant tachycardia (SNRT) - P waves similar to sinus rhythm; abrupt onset and offset
• Atrial tachycardia - Heart rate 120-250 bpm; P-wave morphology different from sinus rhythm; long RP interval (in general); AV block does not terminate tachycardia
• Multifocal atrial tachycardia - Heart rate 100-200 bpm; 3 or more different P-wave morphologies
• Atrial flutter- Atrial rate of 200-300 bpm; flutter waves; AV conduction of 2:1 or 4:1
• Atrial fibrillation - Irregularly irregular rhythm; lack of discernible P waves
• AV nodal reentrant tachycardia (AVNRT) - Heart rate of 150-200 bpm; P wave located either within the QRS complex or shortly after the QRS complex; short RP interval in typical AVNRT and long RP interval in atypical AVNRT
• AV reentrant tachycardia (AVRT) - Heart rate of 150-250 bpm; narrow QRS complex in orthodromic conduction and wide QRS in antidromic conduction; diagnosis excluded by AV block during SVT; P wave after QRS complex

Following the termination of the tachycardia, an ECG should be performed during the sinus rhythm to screen for WPW syndrome. Holter monitoring also may be useful as it can help to assess the frequency and duration of SVT episodes, although they have a low yield. Echocardiography may be helpful in screening for structural or congenital heart disease.

Characterizing a patient’s SVT by comparing the RP interval to the PR interval is helpful. Long RP tachycardias result when atrial activity precedes the QRS complex. In short RP tachycardias, atrial activity occurs with or shortly after ventricle excitation, and the P wave is found within the QRS complex or shortly after the QRS complex.^{[9, 10, 40, 41]} The classifications of SVTs based on the RP interval are as follows:

• Short RP tachycardias – Typical AVNRT, AVRT, junctional ectopic tachycardia (JET), and nonparoxysmal junctional tachycardia (NPJT)
• Long RP tachycardias – Sinus tachycardia, SNRT, atrial tachycardia, atrial flutter, atypical AVNRT, and a permanent form of junctional reciprocating tachycardia

Two consecutive P waves without an intervening QRS complex may be due to atrial tachycardias, in some cases, AVNRT, but they are unlikely to be due to AVRT. Vagal maneuvers and nodal blocking agents like adenosine work in AVNRT in some cases, but not in atrial tachycardias. Blocking the tachycardia with adenosine or vagal maneuvers may assist in diagnosing the rhythm as well as treating it.

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Approach Considerations

Acute management of paroxysmal supraventricular tachycardia (PSVT) includes controlling the rate and preventing hemodynamic collapse. If the patient is hypotensive or unstable, immediate cardioversion with sedation must be performed. If the patient is stable, vagal maneuvers can be used to slow the heart rate and to convert to sinus rhythm. If vagal maneuvers are not successful, adenosine can be used in increasing doses. If adenosine does not work, atrioventricular (AV) nodal blocking agents like calcium channel blockers or beta-blockers should be used, as most patients who present with PSVT have AV nodal reentrant tachycardia (AVNRT) or AV reentrant tachycardia (AVRT). These arrhythmias depend on AV nodal conduction and therefore can be terminated by transiently blocking this conduction.

Patients with symptomatic Wolff-Parkinson-White (WPW) syndrome should not be treated with calcium channel blockers or digoxin unless the pathway is known to be of low risk (long anterograde refractory period). This is because of the potential for rapid ventricular rates should atrial fibrillation or atrial flutter occur, which can result in cardiac arrest.

Patients with preexcited atrial fibrillation should not be treated with intravenous AV nodal blocking agents, such as adenosine, beta-blockers, calcium channel blockers, and digoxin. Rather, if the patient is hemodynamically stable, intravenous procainamide should be administered. If the patient is unstable, direct current cardioversion should be performed.

Electrical cardioversion

Electrical cardioversion is the most effective method for restoring sinus rhythm. Synchronized cardioversion starting at 50J can be used immediately in patients who are hypotensive, have pulmonary edema, have chest pain with ischemia, or are otherwise unstable.

If atrial fibrillation has been present for longer than 24-48 hours, defer cardioversion until the patient has been adequately anticoagulated to prevent thromboembolic complications.^{[40, 36, 50, 51, 52, 53, 54, 41]}

Inpatient care

Patients who require cardioversion, are unstable, and have comorbid illnesses should be admitted to the hospital. Patients who are young, healthy, and asymptomatic may be discharged and advised to have a follow-up examination with their primary physician or cardiologist. If the patient is having more frequent episodes of paroxysmal SVT and medical therapy is not successful or desired, then radiofrequency catheter ablation should be proposed.

Diet and activity

Dietary changes depend on underlying medical problems. Changes in physical activity depend on underlying cardiac problems and other comorbidities.

Consultations

A cardiologist should be consulted for patients with frequent episodes of paroxysmal SVT, syncope, and/or preexcitation syndromes. Consultation with a cardiologist should also be obtained for patients in whom medical management has failed.

An electrophysiologist should be consulted for patients considered for radiofrequency catheter ablation. Pediatric patients should be referred to a pediatric electrophysiologist.

Transfer

Patient transfer to a center with radiofrequency catheter ablation is reasonable if this therapy is planned. Alternatively, patients can be discharged home and scheduled for outpatient procedures. Exceptions include patients with syncope, profound symptoms, or preexcited atrial fibrillation or atrial flutter.

Monitoring

Patients treated medically should be monitored regularly. Patients cured with radiofrequency catheter ablation are typically seen once in a follow-up examination following the procedure, then as needed for recurrent symptoms.

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Vagal Maneuvers

The first-line treatment in hemodynamically stable patients, vagal maneuvers, such as breath-holding and the Valsalva maneuver (ie, having the patient bear down as though having a bowel movement), slow conduction in the AV node and can potentially interrupt the reentrant circuit.

Carotid massage is another vagal maneuver that can slow AV nodal conduction. Massage the carotid sinus for several seconds on the nondominant cerebral hemisphere side. This maneuver is usually reserved for young patients. Due to the risk of stroke from emboli, auscultate for bruits before attempting this maneuver. Do not perform carotid massage on both sides. A Valsalva maneuver, if performed properly by the patient, can frequently avert an attack.

• References

Short-Term Pharmacologic Management

When SVT is not terminated by vagal maneuvers, short-term management involves intravenous adenosine or calcium channel blockers. Adenosine is a short-acting drug that blocks AV node conduction; it terminates 90% of tachycardias due to AVNRT or AVRT. Adenosine does not usually terminate atrial tachycardia, although it is effective for terminating SNRT.^{[40, 36, 50, 55, 53, 41]}

Typical adverse effects of adenosine include flushing, chest pain, and dizziness. These effects are temporary because adenosine has a very short half-life of 10-20 seconds.^[54]

Other alternatives for the acute treatment of SVT include calcium channel blockers, such as verapamil and diltiazem, as well as beta-blockers, such as metoprolol or esmolol. Verapamil is a calcium channel blocker that also has AV blocking properties. It has a longer half-life than adenosine and may help to maintain sinus rhythm following the termination of SVT. It is also advantageous for controlling the ventricular rate in patients with atrial tachyarrhythmia.^{[9, 56, 50, 51, 10, 53, 54, 11]}

In a randomized clinical trial of 92 patients with paroxysmal supraventricular tachycardia, Shaker et al found evidence that oral verapamil can decrease recurrence of paroxysmal supraventricular tachycardia after successful control with intravenous adenosine. Patients in the adenosine-only group received adenosine; patients in the adenosine/verapamil group received adenosine and then received oral verapamil immediately after conversion of the rhythm to sinus rhythm. The adenosine/verapamil group had a significantly lower recurrence rate than the adenosine-only group between 30 and 120 minutes post-treatment and thereafter.^[70]

Wide-complex tachycardia

Acute management of a wide-complex tachycardia in a hemodynamically unstable patient requires immediate cardioversion, whereas in a stable patient, intravenous procainamide, propafenone, or flecainide is acceptable. Amiodarone is preferred in patients with impaired left ventricular function or in patients with heart failure or structural heart disease.^[57]

Atrial fibrillation and atrial flutter

The treatment of atrial fibrillation and atrial flutter involves controlling the ventricular rate, restoring the sinus rhythm, and preventing embolic complications. The ventricular rate is controlled with calcium channel blockers, digoxin, amiodarone, and beta-blockers. The sinus rhythm may be restored with either pharmacologic agents or electrical cardioversion. Medications such as ibutilide, propafenone, and flecainide convert atrial fibrillation and atrial flutter of short duration to sinus rhythm. Since atrial fibrillation and atrial flutter increase risk of stroke or cerebrovascular accidents, anticoagulation is usually recommended. Drugs like warfarin, as well as novel oral anticoagulant agents like dabigatran, rivaroxaban, and apixaban, may be used for anticoagulation.^{[58, 59, 60]}

• References

Long-Term Pharmacologic Management

The choice of long-term therapy for patients with SVT depends on the type of tachyarrhythmia that is occurring and the frequency and duration of episodes, as well as the symptoms and the risks associated with the arrhythmia (eg, heart failure, sudden death). Evaluate patients on an individual basis, and tailor treatment to the best therapy for the specific tachyarrhythmia.

Patients with paroxysmal SVT may initially be treated with calcium channel blockers, digoxin, and/or beta-blockers. Class IA, IC, or III antiarrhythmic agents are used less frequently because of the success of radiofrequency catheter ablation.^{[40, 36, 50, 51, 52, 53, 54, 41, 61]}

• References

Radiofrequency Catheter Ablation

Prior to the advent of percutaneous radiofrequency catheter ablation, open cardiac surgical procedures were the only means of curing paroxysmal SVT. Currently, however, open surgical procedures are rarely performed, and catheter ablation is considered the first-line treatment of many recurrent symptomatic SVTs. It is generally performed using conscious sedation in an outpatient setting or with an overnight hospital stay for observation.

Catheter ablation involves focally ablating the crucial component of the arrhythmic mechanism. For example, in AVNRT, the slow pathway is ablated, which prevents the reentry cycle. The accessory pathway is targeted in patients with AVRT. Focal atrial tachycardia, atrial flutter, and, in some cases, atrial fibrillation can also be cured with ablation.

Consider catheter ablation for any patient with symptomatic paroxysmal SVT in whom long-term medical treatment is not effectively tolerated or desired. In addition, because of the risk of sudden cardiac death, perform catheter ablation on patients with symptomatic WPW syndrome.^{[9, 40, 10, 41, 13]} The optimal management strategy for patients with asymptomatic preexcitation syndromes remains uncertain.^{[62, 63, 19, 9, 13]}

The efficacy of catheter ablation often exceeds that of medical therapy for symptoms, recurrences requiring medical intervention, and the prevention of consequences, such as defibrillator discharges in patients with an implanted defibrillator and SVT. (A study by Mainigi et al found that SVT causes a significant number of inappropriate implantable cardioverter-defibrillator therapies and that catheter ablation is an effective strategy to avoid these inappropriate therapies.^[64] ) Catheter ablation is more than 90% effective in curing paroxysmal SVT.

Complications

Potential complications of radiofrequency catheter ablation include the following:

• Hematoma
• Bleeding
• Infection
• Pseudoaneurysm
• Myocardial infarction
• Cardiac preformation
• Heart block that requires a pacemaker
• Thromboembolic complications - Including deep venous thrombosis and systemic embolism
• Cardiac tamponade
• Stroke
• Need for emergency surgery
• Radiation burn
• Increased risk of malignancy - Lifetime risk of fatal malignancy as a result of radiation exposure is low
• Death - Risk is approximately 0.1%

Bohnen et al performed a prospective study to assess the incidence and predictors of major complications from contemporary catheter ablation procedures. Major complication rates ranged between 0.8% (SVT) and 6% (ventricular tachycardia associated with structural heart disease), depending on the ablation procedure performed. The investigators reported that renal insufficiency was the only independent predictor of a major complication.^[65]

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Medication Summary

As previously stated, short-term management of supraventricular tachycardia (SVT) involves intravenous adenosine or calcium channel blockers.

In cases of wide-complex tachycardia, hemodynamically stable patients can be treated with intravenous procainamide, propafenone, or flecainide. Amiodarone is preferred in patients with impaired left ventricular function or in patients with heart failure or structural heart disease.^[57]

Treatment for atrial fibrillation and atrial flutter includes medications that control the ventricular rate (calcium channel blockers, digoxin, amiodarone, beta-blockers), restore the sinus rhythm (such as ibutilide, flecainide, amiodarone, propafenone), and prevent embolic complications.

Long-term pharmacologic therapy for patients with SVT depends on the type of tachyarrhythmia that is occurring and the frequency and duration of episodes, as well as the symptoms and the risks associated with the arrhythmia (eg, heart failure, sudden death).

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Flecainide (Tambocor)

• Dosing, Interactions, etc.

Clinical Context:  Flecainide blocks sodium channels, producing a dose-related decrease in intracardiac conduction in all parts of heart. The drug increases electrical stimulation of threshold of ventricle, HIS-Purkinje system. Flecainide shortens phase 2 and 3 repolarization, resulting in a decreased action potential duration and effective refractory period.

This agent is indicated for the treatment of paroxysmal atrial fibrillation/flutter (PAF) associated with disabling symptoms. It is also indicated for paroxysmal SVTs, including atrioventricular nodal reentrant tachycardia (AVNRT), atrioventricular reentrant tachycardia (AVRT), and other SVTs of unspecified mechanism associated with disabling symptoms in patients without structural heart disease.

In addition, Flecainide is indicated for the prevention of documented, life-threatening ventricular arrhythmias, such as sustained ventricular tachycardia. It is not recommended for less severe ventricular arrhythmias, even if patients are symptomatic.

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Propafenone (Rythmol)

• Dosing, Interactions, etc.

Clinical Context:  Propafenone shortens the upstroke velocity (phase 0) of monophasic action potentials. It reduces the fast inward current carried by sodium ions in Purkinje fibers and, to a lesser extent, myocardial fibers. Propafenone may increase the diastolic excitability threshold and prolong the effective refractory period. It also reduces spontaneous automaticity and depresses triggered activity.

Propafenone is indicated for the treatment of documented, life-threatening ventricular arrhythmias, such as sustained ventricular tachycardia. It appears to be effective in the treatment of SVTs, including atrial fibrillation and flutter. The drug is not recommended for patients with less severe ventricular arrhythmias, even if the patients are symptomatic.

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Adenosine (Adenocard)

• Dosing, Interactions, etc.

Clinical Context:  Adenosine is the first-line medical treatment for the termination of paroxysmal SVT. It is a short-acting agent that alters potassium conductance into cells and results in hyperpolarization of nodal cells. This increases the threshold to trigger an action potential and results in sinus slowing and the blockage of AV conduction.

Adenosine is effective in terminating AVNRT and AVRT. More than 90% of patients convert to sinus rhythm with adenosine at 12mg. As a result of its short half-life, adenosine is best administered in an antecubital vein as an intravenous bolus, followed by rapid saline infusion.

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Digoxin (Lanoxin)

• Dosing, Interactions, etc.

Clinical Context:  Digoxin indirectly increases vagal activity, thereby decreasing conduction velocity through the AV node. This can result in termination of paroxysmal SVT.

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Class Summary

These medications are used to treat or prevent arrhythmia.

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Verapamil (Isoptin, Calan, Verelan, Covera-HS)

• Dosing, Interactions, etc.

Clinical Context:  Calcium channel blockers prevent calcium influx into the slow channels of the AV node, decrease the conduction velocity, and prolong the refractory period, which effectively terminates reentrant conduction.

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Diltiazem (Cardizem, Tiazac, Dilacor XR)

• Dosing, Interactions, etc.

Clinical Context:  Diltiazem is similar to verapamil. This agent decreases the conduction velocity in the AV node and increases the refractory period via a blockade of calcium influx. This, in turn, stops the reentrant phenomenon.

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Class Summary

Class IV calcium channel blockers decrease the conduction velocity and prolong the refractory period.

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Atenolol (Tenormin)

• Dosing, Interactions, etc.

Clinical Context:  Atenolol selectively blocks beta-1 receptors, with little or no effect on beta-2 types. Atenolol is excellent for use in patients at risk for experiencing complications from beta-blockade, particularly those with reactive airway disease, mild-to-moderate LV dysfunction, and/or peripheral vascular disease.

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Esmolol (Brevibloc)

• Dosing, Interactions, etc.

Clinical Context:  Esmolol is a short-acting beta-blocker that abolishes reentry-induced paroxysmal SVT by increasing the refractory period of the AV node.

It selectively blocks beta-1 receptors, with little or no effect on beta-2 receptor types. It is particularly useful in patients with elevated arterial pressure, especially if surgery is planned. It has been shown to reduce episodes of chest pain and clinical cardiac events compared with placebo. It can be discontinued abruptly if necessary. It is useful in patients at risk for experiencing complications from beta-blockade, particularly those with reactive airway disease, mild-to-moderate LV dysfunction, and/or peripheral vascular disease. A short half-life of 8 min allows for titration to the desired effect and quick discontinuation if needed.

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Metoprolol (Lopressor, Toprol XL)

• Dosing, Interactions, etc.

Clinical Context:  Metoprolol is a selective beta-1 adrenergic receptor blocker that decreases the automaticity of contractions. During intravenous administration, carefully monitor blood pressure, heart rate, and ECG.

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Class Summary

These agents slow the sinus rate and decrease AV nodal conduction. Beta-blockers now have more of a secondary role in AF rate control. Carefully monitor blood pressure.

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Propranolol (Inderal LA, InnoPran XL)

• Dosing, Interactions, etc.

Clinical Context:  Beta-blockers abolish reentry-induced paroxysmal SVT by increasing the refractory period of the AV node.

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Nadolol (Corgard)

• Dosing, Interactions, etc.

Clinical Context:  Nadolol is frequently prescribed because of its long-term effect. It reduces the effect of sympathetic stimulation on the heart. Nadolol decreases conduction through the AV node and has negative chronotropic and inotropic effects. Patients with asthma should use cardioselective beta-blockers.

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Class Summary

These agents increase the refractory period of the AV node. Beta-blockers that are effective in treating paroxysmal SVT include propranolol, esmolol, metoprolol, atenolol, and nadolol.

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