Grand Rounds: Girl, 6, With Rapid Heart Rate

A 6-year-old girl was brought by her parents to the emergency department (ED) with an elevated heart rate. According to the parents, the girl was carrying her younger sister when they both fell, landing on their buttocks. The child told them that her heart was beating fast, and the parents said she appeared to be on the verge of fainting.

They stated that their daughter was healthy and active; they denied previous episodes of shortness of breath, headache, weakness, tachycardia, syncope, or fatigue with exercise. Her caffeine intake, they claimed, was limited to one small cup of soda they allowed her each week.

Initial evaluation in the ED revealed an anxious child with tachycardia and shortness of breath. She presented with a temperature of 98.3°F (36.8°C); pulse, 210 beats/min; respirations, 33 breaths/min; blood pressure, 100/72 mm Hg; weight, 78 lb; height, 45 in; and BMI, 27.1. ECG revealed a heart rate exceeding 210 beats/min, and a pediatric cardiologist made a diagnosis of supraventricular tachycardia (SVT).

The pediatric cardiologist prescribed an adenosine IV drip, which successfully stabilized the child’s heart to sinus rhythm. After three hours in the ED, the patient was discharged with a stable heart rate of 100 beats/min. (It is well known that heart rate regulation changes significantly during development; this is most obvious in higher basal rates in infants and children, compared with adults.¹)

The parents were advised to administer atenolol 12.5 mg (one tablet) twice daily and to make a follow-up appointment with a pediatric electrophysiologist. (Although atenolol is not currently FDA approved for this use, a multicenter prospective randomized controlled trial comparing digoxin with beta-blockers for the treatment of SVT in children is presently under way.²)

At that appointment, the pediatric electrophysiologist provided information to the parents regarding the therapeutic options for SVT. The parents continued to administer atenolol to the child, as was deemed necessary until any accessory electrical pathway could be identified and, if so, an ablation procedure could be performed. They were uncertain how to proceed so long as their daughter experienced no recurrent episodes of SVT while receiving pharmacologic therapy.

However, six months after the initial episode, the child (then age 7) presented to the ED once again with recurrent SVT. The pediatric cardiologist ordered an adenosine IV drip, which resulted in successful conversion to sinus rhythm. The parents were instructed to increase the child’s atenolol dosage to 25 mg twice a day.

Six months later, after extensive research and consultation, the parents agreed to an ablation procedure in order to prevent further episodes of SVT. Upon their informed consent, the child was sent to a cardiac catheterization laboratory for an electrophysiology study (EPS), which confirmed the presence of an accessory pathway, as well as the diagnosis of atrioventricular reciprocating tachycardia (AVRT). The procedure was followed by radiofrequency catheter ablation to correct the 7-year-old patient’s accessory pathway–mediated reentry tachycardia.

Discussion
SVT, also known as paroxysmal supraventricular tachycardia (PSVT), is one of the most common symptomatic pediatric arrhythmias, affecting between one in 25,000 and one in 250 children.³ It is defined as rapid heart rhythm (140 to 240 beats/min) that is caused by the presence of additional electrical connections and/or congenital muscle fibers between the atrium and the ventricle or within the atrioventricular (AV) node that did not, for unknown reasons, separate completely during development.⁴ SVT can be triggered by physical or psychological stress automaticity.³

Approximately 50% of children with SVT present with a first episode before age 1. SVT usually occurs in early childhood, between ages 6 and 9.⁴ Almost 90% of pediatric patients with SVT are diagnosed with a reentry mechanism.³ The symptoms experienced may be resolved pharmacologically or by means of an invasive therapy. Serious sequelae associated with SVT include heart failure and cardiac arrest.

For children with rare and mildly symptomatic episodes in whom SVT is easily terminated, the SVT may not warrant treatment. However, it may be advisable to offer medical therapy or transcatheter ablation as therapeutic options for children with episodes that are difficult to terminate, occur frequently, or occur during participation in athletics.⁴

Pathophysiology
SVT generally presents as one of three types: AVRT, which is also known as Wolff-Parkinson-White syndrome; atrioventricular nodal reentry tachycardia (AVNRT); and automatic tachycardia (AT).

AVRT, the most common type of SVT, comprises about 90% of pediatric cases. It is defined by the presence of one or more accessory conduction pathways that are anatomically separated from the normal cardiac conduction system.5 AVRT may be orthodromic (that is, the arrhythmia circuit proceeds down the AV node and retrograde up the accessory conduction pathway) or antedromic (ie, proceeding down the accessory pathway and up the AV node⁵; see figure.^6,7)

AVNRT, considered the second most common type of SVT in children, accounts for about 10% of pediatric cases. AVNRT is caused by an interaction between the two types of pathways within the AV node—one with a fast conduction time and a short refractory period, and the other with a slow conduction time and a long refractory period. AVNRT occurs when the antegrade conduction block in the fast pathway results in conduction over the slow pathway and back up the fast pathway, forming a microreentrant circuit.⁵

AT is the result of rapid depolarization from an automatic focus originating within the atria but outside the sinus node.³

Patient Presentation and History
The typical presentation of AVRT in children of school age includes palpitations, chest pain or tightness, dizziness, anxiety, decrease in exercise tolerance, easy fatigability, and/or shortness of breath.³ Onset is described as abrupt, while termination of SVT is described as slower because the catecholamine levels are typically elevated.⁴

The frequency and duration of SVT can vary greatly, from a few minutes to a few hours; it can occur as regularly as daily or as uncommonly as once or twice per year.⁴ Additionally, SVT symptoms can go unrecognized until a cardiac dysfunction develops. As for the patient in the case study, no apparent factor in her history was identified that may have induced SVT.

The differential diagnosis for SVT is broad, including sinus tachycardia, multifocal atrial tachycardia, and SVT with aberrancy.⁸ Additional considerations include stress, anxiety, hyperthyroidism, electrolyte abnormalities, and dehydration—any of which can present with a tachycardia response.⁴ Furthermore, clinicians are often unlikely to diagnose a child with any cardiac problem because chest pain is more commonly a presenting symptom of a pulmonary or musculoskeletal condition than a cardiac problem.³

Physical Examination
SVT can be diagnosed based on medical history and physical examination. During the physical examination, providers will assess the patient’s blood pressure and pulse, auscultate heart and lung sounds, assess the veins in the patient’s neck for different types of pulsations, and conduct cardiac maneuvers, including the Valsalva maneuver and carotid sinus massage.^9,10

Laboratory Work-up and Diagnosis
Three specific tests help clinicians monitor and evaluate a patient’s conduction system. ECG is important to assess the heart rhythm both at baseline and when symptoms are occurring, if possible.³ Ambulatory ECG (ie, Holter monitoring, event recorders) record the patient’s heart rhythm on a continuous basis.

An EPS, which is performed to classify the mechanism of SVT, is conducted by inserting one or more electrocatheters into the heart by way of the femoral vein or other peripheral vessel.³ Pacing and sensing electrodes at the ends of the catheters record local intracardiac electrical activity and timing information, providing a detailed analysis of the heart’s electrical activity. The EPS is critical to determine the presence of one or more extra electrical pathways within the heart and to localize it by region.^3,11 An ablation procedure may follow.

Management Options
SVT can be treated pharmacologically or nonpharmacologically. First-line pharmacologic options include certain beta-blockers (including atenolol and propranolol), digoxin, and calcium channel blockers. Second-line pharmacologic treatments include amiodarone, flecainide, and sotalol,⁴ all of which are contraindicated in children younger than 1 year because of these patients’ hemodynamic dependency on the heart and inability to generate stroke volume.³ Pharmacologic treatment of SVT is associated with a 68% success rate in children⁴ (see Table 1⁴).

For children in whom pharmacologic treatment is ineffective, an ablation procedure may be performed. Radiofrequency catheter ablation is currently considered first-line therapy for AVRT and AVNRT.¹² In this invasive procedure, intracardiac electrical mapping is performed and the initiating focus of the arrhythmia or the accessory electrical pathway that has been identified within the heart is destroyed by radiofrequency energy, delivered by electrocatheter. Ablations performed during the acute phase of SVT have a 95% success rate.^3,13

Cryoablation is a relatively new treatment in which liquid nitrous oxide is used to cool the catheter to subfreezing temperatures, enabling it to destroy the myocardial tissue by freezing.^3,14 The advantage of cryoablation is the option of reversible cooling, which allows the electrophysiologist to test the area first, confirming the accuracy of the apparent location accessory pathway.¹⁵

Noninvasive, nonpharmacologic interventions that increase the refractoriness of the AV node may be successful in terminating the tachyarrhythmia during episodes of SVT (see Table 2^3,9,13,16). They are used to terminate and diagnose tachydysrhythmias, increase parasympathetic tone, and slow conduction through the AV node.³

Patient Education
It is very important for health care providers to relieve parents’ and caregivers’ stress, anxiety, and uncertainty by educating them about the child’s cardiac condition of SVT. Information to convey include an understanding of what SVT is, what may cause it, what triggers the patient should avoid, what treatments are available and appropriate (including the maneuvers shown in Table 2), and what outcomes may be expected. An excellent patient/family education handout from the Children’s Hospitals and Clinics of Minnesota¹⁷ is available at www.childrensmn.org/Manuals/PFS/Condill/018303.pdf.

Follow-Up
Primary care providers must emphasize the importance of monitoring the patient’s progress, based on the severity of his or her SVT symptoms. The provider may choose to monitor the patient for a few weeks or a few months, assessing the frequency of arrhythmia recurrence and the heart rate, to adjust or substitute medications based on repeat ECG or Holter evaluations, and to plan further therapy, should the condition worsen.⁵

The Case Patient
One month after undergoing radiofrequency catheter ablation, the child presented to the pediatric cardiologist for follow-up. Since the procedure, she had been without any symptoms referable to the cardiovascular system. She denied experiencing any fast heart rate, palpitations, chest pain, shortness of breath, or dizziness. ECG demonstrated normal sinus rhythm.

Two years after undergoing radiofrequency ablation, the child is functioning at a normal activity level with no recurrence of SVT episodes.

Conclusion
The purpose of this case study is to improve primary care providers’ understanding of SVT in children and to convey the importance of identifying the condition in a timely manner and referring patients to a pediatric cardiologist or electrophysiologist. For most children affected by SVT, a regimen of pharmacologic and/or nonpharmacologic treatment—supported by detailed education for their parents and caregivers—can allow them to live a healthy, normal life.

A 6-year-old girl was brought by her parents to the emergency department (ED) with an elevated heart rate. According to the parents, the girl was carrying her younger sister when they both fell, landing on their buttocks. The child told them that her heart was beating fast, and the parents said she appeared to be on the verge of fainting.

They stated that their daughter was healthy and active; they denied previous episodes of shortness of breath, headache, weakness, tachycardia, syncope, or fatigue with exercise. Her caffeine intake, they claimed, was limited to one small cup of soda they allowed her each week.

Initial evaluation in the ED revealed an anxious child with tachycardia and shortness of breath. She presented with a temperature of 98.3°F (36.8°C); pulse, 210 beats/min; respirations, 33 breaths/min; blood pressure, 100/72 mm Hg; weight, 78 lb; height, 45 in; and BMI, 27.1. ECG revealed a heart rate exceeding 210 beats/min, and a pediatric cardiologist made a diagnosis of supraventricular tachycardia (SVT).

The pediatric cardiologist prescribed an adenosine IV drip, which successfully stabilized the child’s heart to sinus rhythm. After three hours in the ED, the patient was discharged with a stable heart rate of 100 beats/min. (It is well known that heart rate regulation changes significantly during development; this is most obvious in higher basal rates in infants and children, compared with adults.¹)

The parents were advised to administer atenolol 12.5 mg (one tablet) twice daily and to make a follow-up appointment with a pediatric electrophysiologist. (Although atenolol is not currently FDA approved for this use, a multicenter prospective randomized controlled trial comparing digoxin with beta-blockers for the treatment of SVT in children is presently under way.²)

At that appointment, the pediatric electrophysiologist provided information to the parents regarding the therapeutic options for SVT. The parents continued to administer atenolol to the child, as was deemed necessary until any accessory electrical pathway could be identified and, if so, an ablation procedure could be performed. They were uncertain how to proceed so long as their daughter experienced no recurrent episodes of SVT while receiving pharmacologic therapy.

However, six months after the initial episode, the child (then age 7) presented to the ED once again with recurrent SVT. The pediatric cardiologist ordered an adenosine IV drip, which resulted in successful conversion to sinus rhythm. The parents were instructed to increase the child’s atenolol dosage to 25 mg twice a day.

Six months later, after extensive research and consultation, the parents agreed to an ablation procedure in order to prevent further episodes of SVT. Upon their informed consent, the child was sent to a cardiac catheterization laboratory for an electrophysiology study (EPS), which confirmed the presence of an accessory pathway, as well as the diagnosis of atrioventricular reciprocating tachycardia (AVRT). The procedure was followed by radiofrequency catheter ablation to correct the 7-year-old patient’s accessory pathway–mediated reentry tachycardia.

Discussion
SVT, also known as paroxysmal supraventricular tachycardia (PSVT), is one of the most common symptomatic pediatric arrhythmias, affecting between one in 25,000 and one in 250 children.³ It is defined as rapid heart rhythm (140 to 240 beats/min) that is caused by the presence of additional electrical connections and/or congenital muscle fibers between the atrium and the ventricle or within the atrioventricular (AV) node that did not, for unknown reasons, separate completely during development.⁴ SVT can be triggered by physical or psychological stress automaticity.³

Approximately 50% of children with SVT present with a first episode before age 1. SVT usually occurs in early childhood, between ages 6 and 9.⁴ Almost 90% of pediatric patients with SVT are diagnosed with a reentry mechanism.³ The symptoms experienced may be resolved pharmacologically or by means of an invasive therapy. Serious sequelae associated with SVT include heart failure and cardiac arrest.

For children with rare and mildly symptomatic episodes in whom SVT is easily terminated, the SVT may not warrant treatment. However, it may be advisable to offer medical therapy or transcatheter ablation as therapeutic options for children with episodes that are difficult to terminate, occur frequently, or occur during participation in athletics.⁴

Pathophysiology
SVT generally presents as one of three types: AVRT, which is also known as Wolff-Parkinson-White syndrome; atrioventricular nodal reentry tachycardia (AVNRT); and automatic tachycardia (AT).

AVRT, the most common type of SVT, comprises about 90% of pediatric cases. It is defined by the presence of one or more accessory conduction pathways that are anatomically separated from the normal cardiac conduction system.5 AVRT may be orthodromic (that is, the arrhythmia circuit proceeds down the AV node and retrograde up the accessory conduction pathway) or antedromic (ie, proceeding down the accessory pathway and up the AV node⁵; see figure.^6,7)

AVNRT, considered the second most common type of SVT in children, accounts for about 10% of pediatric cases. AVNRT is caused by an interaction between the two types of pathways within the AV node—one with a fast conduction time and a short refractory period, and the other with a slow conduction time and a long refractory period. AVNRT occurs when the antegrade conduction block in the fast pathway results in conduction over the slow pathway and back up the fast pathway, forming a microreentrant circuit.⁵

AT is the result of rapid depolarization from an automatic focus originating within the atria but outside the sinus node.³

Patient Presentation and History
The typical presentation of AVRT in children of school age includes palpitations, chest pain or tightness, dizziness, anxiety, decrease in exercise tolerance, easy fatigability, and/or shortness of breath.³ Onset is described as abrupt, while termination of SVT is described as slower because the catecholamine levels are typically elevated.⁴

The frequency and duration of SVT can vary greatly, from a few minutes to a few hours; it can occur as regularly as daily or as uncommonly as once or twice per year.⁴ Additionally, SVT symptoms can go unrecognized until a cardiac dysfunction develops. As for the patient in the case study, no apparent factor in her history was identified that may have induced SVT.

The differential diagnosis for SVT is broad, including sinus tachycardia, multifocal atrial tachycardia, and SVT with aberrancy.⁸ Additional considerations include stress, anxiety, hyperthyroidism, electrolyte abnormalities, and dehydration—any of which can present with a tachycardia response.⁴ Furthermore, clinicians are often unlikely to diagnose a child with any cardiac problem because chest pain is more commonly a presenting symptom of a pulmonary or musculoskeletal condition than a cardiac problem.³

Physical Examination
SVT can be diagnosed based on medical history and physical examination. During the physical examination, providers will assess the patient’s blood pressure and pulse, auscultate heart and lung sounds, assess the veins in the patient’s neck for different types of pulsations, and conduct cardiac maneuvers, including the Valsalva maneuver and carotid sinus massage.^9,10

Laboratory Work-up and Diagnosis
Three specific tests help clinicians monitor and evaluate a patient’s conduction system. ECG is important to assess the heart rhythm both at baseline and when symptoms are occurring, if possible.³ Ambulatory ECG (ie, Holter monitoring, event recorders) record the patient’s heart rhythm on a continuous basis.

An EPS, which is performed to classify the mechanism of SVT, is conducted by inserting one or more electrocatheters into the heart by way of the femoral vein or other peripheral vessel.³ Pacing and sensing electrodes at the ends of the catheters record local intracardiac electrical activity and timing information, providing a detailed analysis of the heart’s electrical activity. The EPS is critical to determine the presence of one or more extra electrical pathways within the heart and to localize it by region.^3,11 An ablation procedure may follow.

Management Options
SVT can be treated pharmacologically or nonpharmacologically. First-line pharmacologic options include certain beta-blockers (including atenolol and propranolol), digoxin, and calcium channel blockers. Second-line pharmacologic treatments include amiodarone, flecainide, and sotalol,⁴ all of which are contraindicated in children younger than 1 year because of these patients’ hemodynamic dependency on the heart and inability to generate stroke volume.³ Pharmacologic treatment of SVT is associated with a 68% success rate in children⁴ (see Table 1⁴).

For children in whom pharmacologic treatment is ineffective, an ablation procedure may be performed. Radiofrequency catheter ablation is currently considered first-line therapy for AVRT and AVNRT.¹² In this invasive procedure, intracardiac electrical mapping is performed and the initiating focus of the arrhythmia or the accessory electrical pathway that has been identified within the heart is destroyed by radiofrequency energy, delivered by electrocatheter. Ablations performed during the acute phase of SVT have a 95% success rate.^3,13

Cryoablation is a relatively new treatment in which liquid nitrous oxide is used to cool the catheter to subfreezing temperatures, enabling it to destroy the myocardial tissue by freezing.^3,14 The advantage of cryoablation is the option of reversible cooling, which allows the electrophysiologist to test the area first, confirming the accuracy of the apparent location accessory pathway.¹⁵

Noninvasive, nonpharmacologic interventions that increase the refractoriness of the AV node may be successful in terminating the tachyarrhythmia during episodes of SVT (see Table 2^3,9,13,16). They are used to terminate and diagnose tachydysrhythmias, increase parasympathetic tone, and slow conduction through the AV node.³

Patient Education
It is very important for health care providers to relieve parents’ and caregivers’ stress, anxiety, and uncertainty by educating them about the child’s cardiac condition of SVT. Information to convey include an understanding of what SVT is, what may cause it, what triggers the patient should avoid, what treatments are available and appropriate (including the maneuvers shown in Table 2), and what outcomes may be expected. An excellent patient/family education handout from the Children’s Hospitals and Clinics of Minnesota¹⁷ is available at www.childrensmn.org/Manuals/PFS/Condill/018303.pdf.

Follow-Up
Primary care providers must emphasize the importance of monitoring the patient’s progress, based on the severity of his or her SVT symptoms. The provider may choose to monitor the patient for a few weeks or a few months, assessing the frequency of arrhythmia recurrence and the heart rate, to adjust or substitute medications based on repeat ECG or Holter evaluations, and to plan further therapy, should the condition worsen.⁵

The Case Patient
One month after undergoing radiofrequency catheter ablation, the child presented to the pediatric cardiologist for follow-up. Since the procedure, she had been without any symptoms referable to the cardiovascular system. She denied experiencing any fast heart rate, palpitations, chest pain, shortness of breath, or dizziness. ECG demonstrated normal sinus rhythm.

Two years after undergoing radiofrequency ablation, the child is functioning at a normal activity level with no recurrence of SVT episodes.

Conclusion
The purpose of this case study is to improve primary care providers’ understanding of SVT in children and to convey the importance of identifying the condition in a timely manner and referring patients to a pediatric cardiologist or electrophysiologist. For most children affected by SVT, a regimen of pharmacologic and/or nonpharmacologic treatment—supported by detailed education for their parents and caregivers—can allow them to live a healthy, normal life.

A 6-year-old girl was brought by her parents to the emergency department (ED) with an elevated heart rate. According to the parents, the girl was carrying her younger sister when they both fell, landing on their buttocks. The child told them that her heart was beating fast, and the parents said she appeared to be on the verge of fainting.

They stated that their daughter was healthy and active; they denied previous episodes of shortness of breath, headache, weakness, tachycardia, syncope, or fatigue with exercise. Her caffeine intake, they claimed, was limited to one small cup of soda they allowed her each week.

Initial evaluation in the ED revealed an anxious child with tachycardia and shortness of breath. She presented with a temperature of 98.3°F (36.8°C); pulse, 210 beats/min; respirations, 33 breaths/min; blood pressure, 100/72 mm Hg; weight, 78 lb; height, 45 in; and BMI, 27.1. ECG revealed a heart rate exceeding 210 beats/min, and a pediatric cardiologist made a diagnosis of supraventricular tachycardia (SVT).

The pediatric cardiologist prescribed an adenosine IV drip, which successfully stabilized the child’s heart to sinus rhythm. After three hours in the ED, the patient was discharged with a stable heart rate of 100 beats/min. (It is well known that heart rate regulation changes significantly during development; this is most obvious in higher basal rates in infants and children, compared with adults.¹)

The parents were advised to administer atenolol 12.5 mg (one tablet) twice daily and to make a follow-up appointment with a pediatric electrophysiologist. (Although atenolol is not currently FDA approved for this use, a multicenter prospective randomized controlled trial comparing digoxin with beta-blockers for the treatment of SVT in children is presently under way.²)

At that appointment, the pediatric electrophysiologist provided information to the parents regarding the therapeutic options for SVT. The parents continued to administer atenolol to the child, as was deemed necessary until any accessory electrical pathway could be identified and, if so, an ablation procedure could be performed. They were uncertain how to proceed so long as their daughter experienced no recurrent episodes of SVT while receiving pharmacologic therapy.

However, six months after the initial episode, the child (then age 7) presented to the ED once again with recurrent SVT. The pediatric cardiologist ordered an adenosine IV drip, which resulted in successful conversion to sinus rhythm. The parents were instructed to increase the child’s atenolol dosage to 25 mg twice a day.

Six months later, after extensive research and consultation, the parents agreed to an ablation procedure in order to prevent further episodes of SVT. Upon their informed consent, the child was sent to a cardiac catheterization laboratory for an electrophysiology study (EPS), which confirmed the presence of an accessory pathway, as well as the diagnosis of atrioventricular reciprocating tachycardia (AVRT). The procedure was followed by radiofrequency catheter ablation to correct the 7-year-old patient’s accessory pathway–mediated reentry tachycardia.

Discussion
SVT, also known as paroxysmal supraventricular tachycardia (PSVT), is one of the most common symptomatic pediatric arrhythmias, affecting between one in 25,000 and one in 250 children.³ It is defined as rapid heart rhythm (140 to 240 beats/min) that is caused by the presence of additional electrical connections and/or congenital muscle fibers between the atrium and the ventricle or within the atrioventricular (AV) node that did not, for unknown reasons, separate completely during development.⁴ SVT can be triggered by physical or psychological stress automaticity.³

Approximately 50% of children with SVT present with a first episode before age 1. SVT usually occurs in early childhood, between ages 6 and 9.⁴ Almost 90% of pediatric patients with SVT are diagnosed with a reentry mechanism.³ The symptoms experienced may be resolved pharmacologically or by means of an invasive therapy. Serious sequelae associated with SVT include heart failure and cardiac arrest.

For children with rare and mildly symptomatic episodes in whom SVT is easily terminated, the SVT may not warrant treatment. However, it may be advisable to offer medical therapy or transcatheter ablation as therapeutic options for children with episodes that are difficult to terminate, occur frequently, or occur during participation in athletics.⁴

Pathophysiology
SVT generally presents as one of three types: AVRT, which is also known as Wolff-Parkinson-White syndrome; atrioventricular nodal reentry tachycardia (AVNRT); and automatic tachycardia (AT).

AVRT, the most common type of SVT, comprises about 90% of pediatric cases. It is defined by the presence of one or more accessory conduction pathways that are anatomically separated from the normal cardiac conduction system.5 AVRT may be orthodromic (that is, the arrhythmia circuit proceeds down the AV node and retrograde up the accessory conduction pathway) or antedromic (ie, proceeding down the accessory pathway and up the AV node⁵; see figure.^6,7)

AVNRT, considered the second most common type of SVT in children, accounts for about 10% of pediatric cases. AVNRT is caused by an interaction between the two types of pathways within the AV node—one with a fast conduction time and a short refractory period, and the other with a slow conduction time and a long refractory period. AVNRT occurs when the antegrade conduction block in the fast pathway results in conduction over the slow pathway and back up the fast pathway, forming a microreentrant circuit.⁵

AT is the result of rapid depolarization from an automatic focus originating within the atria but outside the sinus node.³

Patient Presentation and History
The typical presentation of AVRT in children of school age includes palpitations, chest pain or tightness, dizziness, anxiety, decrease in exercise tolerance, easy fatigability, and/or shortness of breath.³ Onset is described as abrupt, while termination of SVT is described as slower because the catecholamine levels are typically elevated.⁴

The frequency and duration of SVT can vary greatly, from a few minutes to a few hours; it can occur as regularly as daily or as uncommonly as once or twice per year.⁴ Additionally, SVT symptoms can go unrecognized until a cardiac dysfunction develops. As for the patient in the case study, no apparent factor in her history was identified that may have induced SVT.

The differential diagnosis for SVT is broad, including sinus tachycardia, multifocal atrial tachycardia, and SVT with aberrancy.⁸ Additional considerations include stress, anxiety, hyperthyroidism, electrolyte abnormalities, and dehydration—any of which can present with a tachycardia response.⁴ Furthermore, clinicians are often unlikely to diagnose a child with any cardiac problem because chest pain is more commonly a presenting symptom of a pulmonary or musculoskeletal condition than a cardiac problem.³

Physical Examination
SVT can be diagnosed based on medical history and physical examination. During the physical examination, providers will assess the patient’s blood pressure and pulse, auscultate heart and lung sounds, assess the veins in the patient’s neck for different types of pulsations, and conduct cardiac maneuvers, including the Valsalva maneuver and carotid sinus massage.^9,10

Laboratory Work-up and Diagnosis
Three specific tests help clinicians monitor and evaluate a patient’s conduction system. ECG is important to assess the heart rhythm both at baseline and when symptoms are occurring, if possible.³ Ambulatory ECG (ie, Holter monitoring, event recorders) record the patient’s heart rhythm on a continuous basis.

An EPS, which is performed to classify the mechanism of SVT, is conducted by inserting one or more electrocatheters into the heart by way of the femoral vein or other peripheral vessel.³ Pacing and sensing electrodes at the ends of the catheters record local intracardiac electrical activity and timing information, providing a detailed analysis of the heart’s electrical activity. The EPS is critical to determine the presence of one or more extra electrical pathways within the heart and to localize it by region.^3,11 An ablation procedure may follow.

Management Options
SVT can be treated pharmacologically or nonpharmacologically. First-line pharmacologic options include certain beta-blockers (including atenolol and propranolol), digoxin, and calcium channel blockers. Second-line pharmacologic treatments include amiodarone, flecainide, and sotalol,⁴ all of which are contraindicated in children younger than 1 year because of these patients’ hemodynamic dependency on the heart and inability to generate stroke volume.³ Pharmacologic treatment of SVT is associated with a 68% success rate in children⁴ (see Table 1⁴).

For children in whom pharmacologic treatment is ineffective, an ablation procedure may be performed. Radiofrequency catheter ablation is currently considered first-line therapy for AVRT and AVNRT.¹² In this invasive procedure, intracardiac electrical mapping is performed and the initiating focus of the arrhythmia or the accessory electrical pathway that has been identified within the heart is destroyed by radiofrequency energy, delivered by electrocatheter. Ablations performed during the acute phase of SVT have a 95% success rate.^3,13

Cryoablation is a relatively new treatment in which liquid nitrous oxide is used to cool the catheter to subfreezing temperatures, enabling it to destroy the myocardial tissue by freezing.^3,14 The advantage of cryoablation is the option of reversible cooling, which allows the electrophysiologist to test the area first, confirming the accuracy of the apparent location accessory pathway.¹⁵

Noninvasive, nonpharmacologic interventions that increase the refractoriness of the AV node may be successful in terminating the tachyarrhythmia during episodes of SVT (see Table 2^3,9,13,16). They are used to terminate and diagnose tachydysrhythmias, increase parasympathetic tone, and slow conduction through the AV node.³

Patient Education
It is very important for health care providers to relieve parents’ and caregivers’ stress, anxiety, and uncertainty by educating them about the child’s cardiac condition of SVT. Information to convey include an understanding of what SVT is, what may cause it, what triggers the patient should avoid, what treatments are available and appropriate (including the maneuvers shown in Table 2), and what outcomes may be expected. An excellent patient/family education handout from the Children’s Hospitals and Clinics of Minnesota¹⁷ is available at www.childrensmn.org/Manuals/PFS/Condill/018303.pdf.

Follow-Up
Primary care providers must emphasize the importance of monitoring the patient’s progress, based on the severity of his or her SVT symptoms. The provider may choose to monitor the patient for a few weeks or a few months, assessing the frequency of arrhythmia recurrence and the heart rate, to adjust or substitute medications based on repeat ECG or Holter evaluations, and to plan further therapy, should the condition worsen.⁵

The Case Patient
One month after undergoing radiofrequency catheter ablation, the child presented to the pediatric cardiologist for follow-up. Since the procedure, she had been without any symptoms referable to the cardiovascular system. She denied experiencing any fast heart rate, palpitations, chest pain, shortness of breath, or dizziness. ECG demonstrated normal sinus rhythm.

Two years after undergoing radiofrequency ablation, the child is functioning at a normal activity level with no recurrence of SVT episodes.

Conclusion
The purpose of this case study is to improve primary care providers’ understanding of SVT in children and to convey the importance of identifying the condition in a timely manner and referring patients to a pediatric cardiologist or electrophysiologist. For most children affected by SVT, a regimen of pharmacologic and/or nonpharmacologic treatment—supported by detailed education for their parents and caregivers—can allow them to live a healthy, normal life.