Clinical features and diagnosis of supraventricular tachycardia (SVT) in children

INTRODUCTION — Supraventricular tachycardia (SVT) can be defined as an abnormally rapid heart rhythm originating above the ventricles, often (but not always) with a narrow QRS complex [1].

The clinical features and diagnosis of SVT will be reviewed here. The management of SVT in children is discussed separately. (See "Management of supraventricular tachycardia (SVT) in children".)

Specific types of SVT and atrial tachycardias are discussed in greater detail in separate topic reviews:

●(See "Atrioventricular reentrant tachycardia (AVRT) associated with an accessory pathway".)

●(See "Wolff-Parkinson-White syndrome: Anatomy, epidemiology, clinical manifestations, and diagnosis".)

●(See "Atrioventricular nodal reentrant tachycardia".)

●(See "Atrial tachyarrhythmias in children".)

TERMINOLOGY — Supraventricular tachycardia (SVT) can be defined as an abnormally rapid heart rhythm originating above the ventricles, often (but not always) with a narrow QRS complex [1]. The two most common forms of SVT in children are:

●Atrioventricular reentrant tachycardia (AVRT, including the Wolff-Parkinson-White [WPW] syndrome) (see 'AV reentrant tachycardia' below), and

●Atrioventricular nodal reentrant tachycardia (AVNRT) (see 'AV nodal reentrant tachycardia' below)

Other forms of SVT include ectopic atrial tachycardia, junctional tachycardia, atrial flutter, and atrial fibrillation. For the purpose of this topic review, we will use the term "SVT" to refer only to atrioventricular (AV) reciprocating mechanisms (AVRT and AVNRT). Other narrow complex tachyarrhythmias, including primary atrial tachycardias, atrial flutter, and atrial fibrillation, are summarized in the table (table 1) and discussed in detail separately. (See "Atrial tachyarrhythmias in children".)

EPIDEMIOLOGY — SVT is the most common rhythm disturbance in children, with an estimated prevalence of 0.1 to 0.4 percent in the general pediatric population [2]. Among children with congenital heart disease (CHD), the prevalence of SVT is approximately 7 percent [3]. However, the majority of patients presenting with SVT have structurally normal hearts.

●Frequency of AVRT and AVNRT – The two most common forms of SVT in children are:

•Atrioventricular reentrant tachycardia (AVRT), including the Wolff-Parkinson-White (WPW) syndrome (see 'AV reentrant tachycardia' below)

•Atrioventricular nodal reentrant tachycardia (AVNRT) (see 'AV nodal reentrant tachycardia' below)

In a report of 137 pediatric patients who presented with SVT and underwent electrophysiologic testing, 73 percent were found to have AVRT as the mechanism, 13 percent had AVNRT, and 14 percent had primary atrial tachycardias [4]. A similar distribution of causes was noted in another report of 346 patients (mean age 14 years) who underwent radiofrequency catheter ablation for recurrent SVT or ventricular tachycardia [5]. AVRT and AVNRT accounted for 72 and 9 percent, respectively, with various other arrhythmias comprising the remaining 19 percent.

The relative frequencies of AVRT and AVNRT vary somewhat according to age. AVRT (including WPW) accounts for the great majority of cases in infancy (>80 percent). It also is the most common category in older children, but the relative frequency is less than in infancy (50 to 60 percent) [4,6]. In contrast, AVNRT is rare before the age of two years and accounts for 20 to 35 percent of SVTs in older children [4].

●Prevalence of preexcitation – Preexcitation refers to early activation of the ventricles due to impulses bypassing the AV node via an accessory pathway. The main electrocardiogram (ECG) findings of preexcitation include shortening of the PR interval and a delta wave (waveform 1). This is termed the WPW pattern. (See "Wolff-Parkinson-White syndrome: Anatomy, epidemiology, clinical manifestations, and diagnosis", section on 'WPW pattern on ECG'.)

The WPW pattern is estimated to occur in 0.1 to 0.25 percent of the general population [7], though it may be less frequent in young children [8]. Most asymptomatic patients with the WPW pattern on ECG remain asymptomatic. However, there is a risk of symptomatic arrhythmia, including sudden death. This is discussed in greater detail separately. (See "Wolff-Parkinson-White syndrome: Anatomy, epidemiology, clinical manifestations, and diagnosis", section on 'Risk stratification of asymptomatic patients with WPW pattern'.)

●Congenital heart disease – Although the majority of children with SVT have normally structured hearts, children with CHD have an increased risk of SVT. In one study, the reported prevalence of SVT in children with CHD was 6.5 percent [3]. CHD is more common in children with WPW syndrome than in those with AVNRT (20 to 32 versus 7 percent) [5,9,10].

A particular association between Ebstein anomaly and AVRT has been noted; 10 to 15 percent of children with WPW have Ebstein anomaly [11], while 5 to 25 percent of children with Ebstein anomaly have WPW [12]. Ebstein anomaly is also associated with the presence of multiple accessory pathways in AVRT [2,12]. (See 'AV reentrant tachycardia' below and "Ebstein anomaly: Clinical manifestations and diagnosis".)

MECHANISMS — Most SVTs in children are reentrant rhythms. This includes atrioventricular reentrant tachycardia (AVRT, including Wolff-Parkinson-White [WPW] syndrome) and atrioventricular nodal reentrant tachycardia (AVNRT) [4,5]. A reentrant rhythm involves two distinct pathways for conduction with unidirectional block in one of the two pathways. This creates a circuit through which an electrical impulse can cycle repetitively in one direction (antegrade or retrograde), with consequent rapid, regular ventricular contractions (figure 1). (See "Reentry and the development of cardiac arrhythmias".)

AV reentrant tachycardia — AVRT requires an extranodal accessory pathway connecting the atrium and ventricle. This allows direct electrical communication between the two chambers.

Accessory pathways can be located anywhere along the right and left AV groove. The most common sites are the left lateral AV groove and posteroseptal region. Right-sided pathways are less common (figure 2) [13]. The classic accessory pathway connects atrial and ventricular myocardium directly. Rarely, connections can also be made with the conducting system (figure 3 and table 2).

Antegrade versus retrograde — The terms "antegrade" and "retrograde" refer to the direction of electrical conduction relative to the atrium and ventricle. Accessory pathways may conduct electrical signals solely in the antegrade direction (from atrium to ventricle), solely in the retrograde direction (from ventricle to atrium), or may be capable of both antegrade and retrograde conduction.

●When the accessory pathway conducts impulses in the antegrade direction, the impulse arrives at the ventricle rapidly, without the delay imposed by the AV node, a phenomenon called "preexcitation." The result is a characteristic ECG pattern during sinus rhythm consisting of a short PR interval, a "delta wave" (both of which reflect preexcitation), and a widened QRS complex due to the delta wave (figure 4). This ECG pattern is referred to as the WPW pattern. (See "Wolff-Parkinson-White syndrome: Anatomy, epidemiology, clinical manifestations, and diagnosis", section on 'Electrocardiographic findings'.)

●When the accessory pathway conducts impulses in only the retrograde direction, it is referred to as a "concealed pathway" because the ECG during sinus rhythm appears normal. (See "Wolff-Parkinson-White syndrome: Anatomy, epidemiology, clinical manifestations, and diagnosis", section on 'Prevalence of concealed accessory pathways'.)

Orthodromic versus antidromic — The terms "orthodromic" and "antidromic" refer to the direction of electrical conduction through the AV node:

●The most common type of SVT is orthodromic AVRT, in which the reentrant circuit conducts impulses antegrade down the AV node through the His-Purkinje system to the ventricles and then retrograde up the accessory pathway. This results in a narrow complex tachycardia (waveform 2 and figure 5).

●In contrast, antidromic AVRT is uncommon (<5 percent of patients).The reentrant circuit conducts impulses antegrade down an accessory pathway (which does not involve the ventricular conducting system) and retrograde up the AV node. This causes a wide complex tachycardia because conduction through the ventricular myocardium is slower than through the conducting system (figure 6 and waveform 3).

Permanent junctional reciprocating tachycardia — Permanent junctional reciprocating tachycardia (PJRT) is a variant of orthodromic AVRT in which the retrograde conduction in the accessory pathway is slow (waveform 4) [14]. Slow retrograde conduction through the accessory pathway coupled with the normally slow conduction antegrade through the AV node creates a stable reentrant circuit. As a result, PJRT is an incessant SVT, in contrast to the typically paroxysmal nature of most SVTs [15]. PJRT is of particular concern because its persistence can lead to tachycardia-mediated cardiomyopathy [16]. (See 'Heart failure' below.)

AV nodal reentrant tachycardia — AVNRT is mediated by the presence, within the AV node, of two conducting pathways that are designated fast and slow. The fast pathway has a short conduction time but long refractory period. The slow pathway has a long conduction time but short refractory period. These distinct pathways allow for a reentrant loop using one pathway in the antegrade direction and one in the retrograde direction. (See "Atrioventricular nodal reentrant tachycardia".)

Typical AVNRT utilizes the slow pathway in the antegrade direction and the fast pathway in the retrograde direction (figure 7 and figure 8). Atypical AVNRT employs the fast pathway in the antegrade direction and the slow pathway in the retrograde direction (figure 9).

The two pathways have distinct anatomic locations. Based upon electrophysiologic (EP) studies in adult patients, the fast pathway is found in the anterior septum, while the slow pathway is recorded in the posterior septum near the mouth of the coronary sinus [17,18].

Although it has been proposed that the ability to generate AVNRT implies the presence of dual, anatomically distinct AV nodal pathways, the two pathways may not be demonstrated with EP studies. This was illustrated in a report of 159 children with AVNRT in which 38 percent did not have clear dual AV node physiology [19]. It has been suggested that, in children without dual AV node physiology, the reentry circuit may incorporate atrial muscle tissue several millimeters outside the compact AV node [20,21].

CLINICAL FEATURES

Signs and symptoms — Signs and symptoms of SVT vary according to age:

●Infants – In infants, symptoms of SVT may include pallor, fussiness, irritability, poor feeding, and/or cyanosis. The symptoms can be subtle, and tachycardia may go unrecognized for long periods of time. Because of this, infants often present with symptoms of heart failure (eg, tachypnea, fatigue with feeding, poor weight gain) [22]. (See 'Heart failure' below.)

●Children and adolescents – Common symptoms of SVT in children and adolescents include palpitations, chest discomfort, fatigue, and lightheadedness. Syncope is less common and may be a warning sign for increased risk of sudden death [23]. (See 'Syncope and atrial fibrillation' below.)

SVT is usually paroxysmal and characterized by abrupt onset and termination. Most SVT episodes occur at rest, although exercise can be a trigger in some patients.

The average duration is 10 to 15 minutes; however, some episodes last only one to two minutes, while others persist for hours [2]. More persistent SVT can occur, most commonly due to atrial tachycardias or permanent junctional reciprocating tachycardia (PJRT). (See 'Permanent junctional reciprocating tachycardia' above.)

Most children tolerate episodes of tachycardia well. However, prolonged episodes can precipitate heart failure. (See 'Heart failure' below.)

Physical examination typically reveals tachycardia without evidence of decompensation. Some patients appear pale and diaphoretic, and the blood pressure may be reduced. Infants with sustained SVT may have signs of heart failure on examination, including tachypnea, retractions, and hepatomegaly.

Heart rate — Heart rates during SVT are age dependent. Typical ranges are as follows:

●Infants: 220 to 280 beats per minute (bpm)

●Children and adolescents: 180 to 240 bpm

Heart failure — Heart failure is not a typical feature of SVT because most episodes are paroxysmal. However, more prolonged periods of tachycardia can lead to tachycardia-induced cardiomyopathy and symptoms of heart failure. (See "Arrhythmia-induced cardiomyopathy".)

Heart failure most commonly occurs in the following settings:

●Infants – As previously mentioned, infants with SVT often present with signs and symptoms of heart failure because the tachycardia may go unrecognized for long periods of time. Heart failure is particularly likely when SVT persists for >48 hours, whereas SVT lasting <24 hours is unlikely to cause heart failure [2]. Neonates and young infants are at increased risk for heart failure due to SVT compared with older infants and children. In a study of 217 children with SVT, heart failure occurred at the first presentation in 38 percent of patients ≤4 months old compared with 19 percent of patients >4 months old [24]. In another series of 109 neonates (<30 days old) with SVT, 48 percent presented with clinical evidence of heart failure [22].

●Permanent junctional reciprocating tachycardia – In contrast to the typically paroxysmal nature of most SVTs, PJRT is associated with incessant SVT, and thus affected patients are at risk of tachycardia-induced cardiomyopathy [16].

In many patients, tachycardia-induced cardiomyopathy is reversible when the arrhythmia is terminated [16]. (See "Arrhythmia-induced cardiomyopathy", section on 'Prognosis'.)

Syncope and atrial fibrillation — Syncope is an uncommon presentation of SVT. Syncope associated with Wolff-Parkinson-White (WPW) syndrome is a serious warning sign and may signal atrial fibrillation (AF) with rapid atrioventricular (AV) conduction along the accessory pathway (waveform 5). It has been suggested that children with this presentation are at increased risk of sudden cardiac death (SCD).

In a report of 74 patients with WPW <25 years old, 19 percent had a history of syncope [25]. At electrophysiologic (EP) study, nine of these patients had sustained AF compared with none of the 60 patients without syncope [25]. The patients with AF and syncope had rapid conduction down the accessory pathway as evidenced by the shortest RR interval between two consecutive preexcited QRS complexes being ≤220 msec, which, if persistent, represents a ventricular rate above 270 bpm.

In another retrospective study of children without a history of AF who had been referred for EP study and accessory pathway ablation, spontaneous degeneration to AF occurred in 27 of 53 patients in whom AV reentrant tachycardia (AVRT) was induced [26]. Rapid ventricular response was observed in 18 of these 27 patients (34 percent). (See "Wolff-Parkinson-White syndrome: Anatomy, epidemiology, clinical manifestations, and diagnosis", section on 'Atrial fibrillation'.)

Ventricular fibrillation and sudden death — SCD is uncommon in patients with SVT who have structurally normal hearts. [27]. For patients who have ventricular preexcitation (ie, WPW pattern on ECG), the estimated rate of SCD is 1.1 to 1.9 per 1000 person-years [23,28]. The rate is considerably higher in children with associated heart disease (27 per 1000 person-years) [23].

Ventricular fibrillation (VF) can be the first manifestation of WPW syndrome, though this is uncommon [23,29]. VF occurring in WPW syndrome most often results from the rapid ventricular response during AF [30]. Risk factors for VF include history of AF, rapid accessory pathway conduction during AF, and multiple accessory pathways [29-31]. Studies are inconsistent as to whether the presence of symptoms correlates with increased risk of VF [29,32,33]. These risk factors for VF and SCD have been identified from case series and cohorts comprised mostly of adults with WPW. It is unclear if they are applicable to children with WPW [29,34]. (See "Wolff-Parkinson-White syndrome: Anatomy, epidemiology, clinical manifestations, and diagnosis", section on 'Ventricular fibrillation and sudden death'.)

EP testing to evaluate accessory pathway conduction properties may help determine which children with WPW are at high risk of SCD. (See 'Electrophysiologic evaluation' below.)

In a report of 60 children who underwent EP testing prior to planned surgery for WPW, a short preexcited RR interval (<220 msec) was found in all patients who were considered "high risk" (on the basis of a history of VF or resuscitated cardiac arrest) compared with 74 percent of "intermediate risk" patients (those with prior history of AF or syncope) and 35 percent of "low risk" patients (those with no history of VF, cardiac arrest, AF, or syncope) [29]. Other factors such as age, duration of symptoms, presence of congenital heart disease, presence of multiple accessory pathways, and location of accessory pathway did not differ between the three groups.

In a retrospective multicenter study of 912 children with WPW syndrome, those who experienced a life-ending or life-threatening event (sudden death [n = 6], aborted sudden death [n = 43], or AF [n = 47]) were older and less likely to have documented tachycardia compared with patients who did not (n = 816) [35]. Independent risk factors for experiencing a life-threatening event included male sex, Ebstein malformation, rapid anterograde conduction, multiple pathways, and inducible AF. However, approximately one-third of patients who experienced life-threatening events did not have prior symptoms or high-risk markers on EP testing.

The approach to risk stratification in asymptomatic patients with WPW pattern on ECG is discussed separately. (See "Wolff-Parkinson-White syndrome: Anatomy, epidemiology, clinical manifestations, and diagnosis", section on 'Risk stratification of asymptomatic patients with WPW pattern'.)

NATURAL HISTORY — The natural history of SVT in childhood is related in part to the age at initial presentation and the type of rhythm disturbance.

●Infants with AVRT – Atrioventricular reentrant tachycardia (AVRT, including Wolff-Parkinson-White [WPW] syndrome) is by far the most common mechanism of SVT in infancy, particularly during the neonatal period. For patients who present with SVT in early infancy, symptoms often resolve by one year of age, and long-term therapy may not be needed. Studies vary as to how commonly this occurs, ranging from 30 to >90 percent [9,10,36,37]. Some patients who have apparent resolution of symptoms can have recurrence later in childhood [9,36,37].

It is speculated that changes in autonomic tone during infancy and childhood may lead to this pattern of disappearance and recurrence by altering accessory pathway and AV nodal conduction and refractoriness [2].

●Children and adolescents with AVRT – SVT tends to persist in children who present with AVRT (including WPW) after the age of five years [9].

●Children and adolescents with AVNRT – Atrioventricular nodal reentrant tachycardia (AVNRT) is uncommon in early childhood. The development of AVNRT in older children may be due to maturational changes in the electrophysiologic (EP) properties of the AV node. Based on observations from EP studies, it appears that the substrate for AVNRT (dual AV node pathways, with inducible antegrade block in one limb at moderately rapid rates) is likely to be present in adolescents but not in children or infants [38].

DIAGNOSIS

Rapid hemodynamic assessment and initial management — An infant or child who presents with a tachyarrhythmia should have an immediate hemodynamic assessment and a 15-lead ECG (12 standard leads plus leads V3R and V4R [right-sided leads analogous to V3 and V4 on the left] and V7 [left posterior axillary line at V4 level]). Continuous ECG monitoring during therapeutic maneuvers provides insight into the cause of tachycardia and helps in the planning of chronic therapy.

The most important initial clinical determination to make in children presenting with a tachyarrhythmia is whether there are signs of hemodynamic instability, including hypotension, heart failure, shock, or decreased level of consciousness. Unstable patients require immediate intervention to terminate the rhythm (table 3 and algorithm 1). (See "Management of supraventricular tachycardia (SVT) in children", section on 'Acute management'.)

Referral — Infants and children with preexcitation on ECG or documented SVT should be referred to a pediatric cardiologist/electrophysiologist to guide the diagnostic evaluation and to discuss risk assessment and management options.

Urgent referral is warranted for children who present with SVT associated with any of the following:

●Syncope

●Heart failure

●Incessant tachycardia

●Other concerning cardiac finding (eg, depressed ventricular function on echocardiogram)

For children without any of these concerning findings, initial management should optimally include discussion with a pediatric cardiologist. However, the referral can be done electively on an outpatient basis if there are no urgent concerns.

Electrocardiogram — The ECG can help determine the mechanism of tachycardia:

●ECG during SVT – During SVT, the ECG exhibits a regular rhythm (ie, no variation in the RR interval) with a rate that is usually 220 to 280 beats per minute (bpm) in infants and 180 to 240 bpm in older children (waveform 2). In most cases, the QRS complex is narrow (<80 msec) [2]. An exception is antidromic atrioventricular reentrant tachycardia (AVRT), which is associated with a wide complex tachycardia (figure 6 and waveform 3). Antidromic AVRT accounts for <5 percent of cases of pediatric SVT. (See 'Orthodromic versus antidromic' above.)

•Narrow QRS complex tachycardia – Orthodromic AVRT and AV nodal reentrant tachycardia (AVNRT) together account for >80 percent of SVTs in childhood. Distinguishing between these two entities can be challenging since both typically have a narrow QRS complex. The following criteria are useful in making this distinction (algorithm 2) [39]:

-When P waves can be discerned, the distance from the R wave of one QRS complex to the P wave following it (RP interval) has diagnostic utility. An RP interval ≥100 msec is more characteristic of AVRT than AVNRT (73 versus 6 percent of cases).

-Incessant or nearly incessant SVT with an extremely long RP interval and a P wave axis that is directed superior (negative in leads II, III, and aVF) is seen in permanent junctional reciprocating tachycardia.

-When P waves cannot be discerned, they are usually buried in the QRS complex, which is typical of AVNRT. A P wave that falls just at the end of the QRS complex may distort that complex in such a way as to create a small "pseudo r' wave" in lead V1 or a "pseudo S wave" in the inferior leads. If such terminal r' or S waves are not present during sinus rhythm, their appearance during SVT can be assumed to be diagnostic of AVNRT (figure 10).

•Wide QRS complex tachycardia – Wide QRS complex tachycardia should generally prompt consideration of ventricular tachycardia (VT). However, in children, most wide QRS complex tachycardia that occurs with a regular rate represents SVT, not VT. SVT can have a wide QRS complex if the mechanism is antidromic AVRT (figure 6 and waveform 3) or if there is aberrant conduction (eg, functional bundle branch block or "bundle branch aberration") [2,40]. Some patients with orthodromic AVRT begin with wide QRS complexes secondary to bundle branch aberration, which then resolves to a narrow QRS complex tachycardia. (See 'Antegrade versus retrograde' above.)

In a report of 32 children with wide QRS tachycardia, 7 had orthodromic AVRT with bundle branch aberration, 11 had antidromic AVRT, 8 had atrial flutter with an accessory pathway, and 6 had VT [40].

The ECG can be helpful in differentiating between VT and SVT. However, making the distinction can be challenging, especially for clinicians unfamiliar with interpreting pediatric ECGs. Consultation with a pediatric cardiologist is generally warranted. The approach to evaluating children with wide QRS complex tachycardia is discussed in greater detail separately. (See "Management and evaluation of wide QRS complex tachycardia in children", section on 'Electrocardiography'.)

●ECG in sinus rhythm – In sinus rhythm, patients with Wolff-Parkinson-White (WPW) syndrome exhibit preexcitation with a characteristic delta wave, widening of the QRS, and short PR interval (waveform 1 and waveform 6). The ECG in sinus rhythm is normal in patients with concealed accessory pathways or AVNRT. (See "Wolff-Parkinson-White syndrome: Anatomy, epidemiology, clinical manifestations, and diagnosis", section on 'Electrocardiographic findings'.)

The delta wave is due to slow spread of ventricular activation from the accessory pathway, which precedes normal activation of the ventricle via the AV nodal His-Purkinje system. The accessory pathway can often be localized based on the vector forces of the delta wave. (See "Anatomy, pathophysiology, and localization of accessory pathways in the preexcitation syndrome", section on 'Localizing the accessory AV connection site based upon the ECG'.)

Ambulatory monitoring — The majority of children with SVT have sporadic brief episodes of tachycardia. Thus, it may be difficult to capture an episode on a standard ECG. Noncontinuous or continuous ECG monitoring may be useful to record episodes of SVT that occur while the child is at home, school, or participating in sports. Ambulatory monitoring helps to establish the frequency and duration of SVT; however, it is less useful in making a diagnosis, since only a few ECG leads are used [39]. (See "Ambulatory ECG monitoring".)

Transtelephonic electrocardiographic devices are capable of direct transmission of an ECG as an audio signal by telephone. These devices usually provide limited, noncontinuous sample ECG data for the duration of an event that can be downloaded to the clinician's office for interpretation [41,42].

Ambulatory (Holter) ECG monitoring allows continuous examination of the patient's rhythm over an extended period of time during ambulatory activity and with physical and psychologic changes. Monitoring is typically recorded from two to three ECG leads and performed for 24 to 48 hours; therefore, it is useful only in patients who have frequent runs of SVT.

Ambulatory ECG monitoring using an adhesive patch monitor is an alternative to Holter monitoring that allows recordings up to two weeks. In a national registry study of >3000 children who received a 14-day patch monitor, 44 percent of first-detected arrhythmias occurred after 48 hours [43].

Smartphone applications that can record single-lead ECGs are widely available. Two prospective studies have investigated the utility of these monitors in children and found they can successfully record tracings of diagnostic quality and can differentiate SVT mechanisms in up to 70 percent of patients [44,45].

Exercise testing — In children whose symptoms are triggered by exercise, cardiopulmonary exercise testing is sometimes used as a diagnostic modality. Increased adrenergic tone resulting from exertion can sometimes elicit SVT. (See "Exercise testing in children and adolescents: Principles and clinical application".)

Exercise testing is also used to assess the risk of developing potentially fatal arrhythmias in WPW. In adults, loss of preexcitation at higher heart rates is associated with a decreased risk of sudden death as determined by electrophysiologic (EP) testing. The relationship between loss of preexcitation during exercise and risk of sudden death in children is less certain. (See "Wolff-Parkinson-White syndrome: Anatomy, epidemiology, clinical manifestations, and diagnosis", section on 'Approach to risk stratification'.)

Studies in adult patients found that persistence of preexcitation during exercise was found to have a sensitivity of 96 percent for predicting a high-risk EP test and a sensitivity of 80 percent for identifying patients with a history of ventricular fibrillation [31,46].

Loss of preexcitation in children can be difficult to assess because of the rapidity of AV nodal conduction at young age. A prospective study of 37 children with WPW who underwent exercise testing followed by EP study found a poor correlation between loss of preexcitation and high-risk parameters on EP study, with a sensitivity and specificity of 30 and 71 percent, respectively [47]. In a retrospective study that examined EP data from 208 children with WPW, suppression of the delta wave on exercise testing occurred in 24 patients (12 percent), of whom only 3 were subsequently noted to have a high-risk pathway on EP study [48].

Electrophysiologic evaluation — An EP study is often performed as part of the diagnostic evaluation of clinically significant SVT in children. This is especially true if catheter ablation is planned to treat the arrhythmia, although in some cases a diagnostic procedure only may be performed (eg, to evaluate the effect of drug therapy). Indications for EP study for the evaluation of AVRT and AVNRT in children include the following [2]:

●Mapping the location of an accessory pathway in a patient with AVRT and determining the refractory periods (antegrade and retrograde) of the pathway. This evaluation is often performed before or in conjunction with radiofrequency catheter ablation.

●Inducing and mapping AVNRT before or in conjunction with catheter ablation.

●Determining the mechanism of an unknown type of SVT for the purpose of determining optimum antiarrhythmic drug therapy or performing catheter ablation.

●Determining the mechanism of a wide QRS tachycardia.

●Determining the inducibility and mechanism of an unknown tachycardia in a patient with a congenital heart defect before catheter ablation or surgical intervention.

●Evaluating cardiac rhythm during electrical cardioversion or intracardiac overdrive termination of a tachyarrhythmia.

●Determining the presence of arrhythmia in a patient with syncope.

A complete EP evaluation requires transvenous catheter electrode insertion and manipulation for pacing and recording. A more limited evaluation may also be made with the use of transesophageal electrodes for pacing and recording [49,50]. (See "Wolff-Parkinson-White syndrome: Anatomy, epidemiology, clinical manifestations, and diagnosis", section on 'Electrophysiology studies (EPS)'.)

The details of EP testing are discussed separately. (See "Invasive diagnostic cardiac electrophysiology studies".)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Arrhythmias in children".)

SUMMARY AND RECOMMENDATIONS

●Terminology – Supraventricular tachycardia (SVT) SVT refers to an abnormally rapid heart rhythm originating above the ventricles, often (but not always) with a narrow QRS complex (waveform 2). (See 'Terminology' above.)

The two most common forms of SVT in children are:

•Atrioventricular reentrant tachycardia (AVRT, including the Wolff-Parkinson-White [WPW] syndrome) (see 'AV reentrant tachycardia' above)

•Atrioventricular nodal reentrant tachycardia (AVNRT) (see 'AV nodal reentrant tachycardia' above)

In this topic review, we use the term "SVT" to refer only to atrioventricular (AV) reciprocating mechanisms (AVRT and AVNRT), excluding primary atrial tachycardias, atrial flutter, and atrial fibrillation. Atrial tachycardias are discussed separately. (See "Atrial tachyarrhythmias in children".)

●Epidemiology – SVT is the most common rhythm disturbance in children. Most patients with SVT have structurally normal hearts; however, children with congenital heart disease are at the greatest risk for SVT. (See 'Epidemiology' above.)

●Mechanism – Both AVRT and AVNRT are reentrant rhythms (two distinct pathways for conduction with unidirectional block in one of the two pathways), which allows an electrical impulse to cycle repetitively, resulting in rapid and regular ventricular contractions. AVRT is particularly common during infancy, while AVNRT is more common after two years of age. (See 'Mechanisms' above.)

●Signs and symptoms – Signs and symptoms of SVT vary according to age. In infants, symptoms of SVT may include pallor, fussiness, irritability, poor feeding, and/or cyanosis. If tachycardia goes unrecognized for a long period of time, symptoms of heart failure (eg, tachypnea, fatigue with feeding, poor weight gain) can develop. Common symptoms of SVT in children and adolescents include palpitations, chest discomfort, fatigue, and lightheadedness. Syncope is less common and may be a warning sign for increased risk of sudden death. (See 'Signs and symptoms' above.)

●Diagnosis – The diagnosis of SVT is based chiefly on the ECG findings. Ambulatory monitoring can help establish the frequency and duration of SVT. Infants and children with preexcitation on ECG or documented SVT should be referred for evaluation by a pediatric cardiologist. Electrophysiologic testing is often performed as part of the diagnostic evaluation of clinically significant SVT in children, particularly if catheter ablation is planned. (See 'Diagnosis' above.)

•ECG during SVT – Episodes of SVT are usually paroxysmal and characterized by abrupt onset and termination. The average duration is 10 to 15 minutes. During SVT, the ECG exhibits a regular rhythm (ie, no variation in the RR interval) with a rate that is usually 220 to 280 beats per minute (bpm) in infants and 180 to 240 bpm in older children (waveform 2). In most cases, the QRS complex is narrow (<80 msec). Wide QRS complex tachycardia occurs in antidromic AVRT (figure 6 and waveform 3) and occasionally in other reentrant tachycardias with aberrant conduction (eg, functional bundle branch block or "bundle branch aberration"). (See 'Electrocardiogram' above.)

•ECG in sinus rhythm – In sinus rhythm, patients with WPW exhibit preexcitation with a characteristic delta wave, widening of the QRS, and short PR interval (waveform 1 and waveform 6). The ECG in sinus rhythm is normal in patients with concealed accessory pathways or AVNRT. (See 'Electrocardiogram' above.)

●Natural history – For patients who present with SVT in early infancy, symptoms often resolve by one year of age and long-term therapy may not be needed; however, some patients may have recurrence later in childhood. By contrast, SVT tends to persist in children who present after the age of five years. (See 'Natural history' above.)