In a healthy child, the heart rate is fastest during the newborn period and decreases with age, reaching adult heart rates around adolescence. Sinus tachycardia is a common finding in a pediatric patient. In one study of cardiac rate and rhythm patterns in healthy ambulatory and hospitalized children with noncardiac conditions, a 24-hour ECG monitor identified maximal heart rates during waking periods, especially during crying and physical activity, and minimal heart rates during sleeping periods. Maximal heart rates decreased with age.⁵ Sinus arrhythmia was noted on every recording in both healthy ambulatory and hospitalized children.

Primary clinically significant cardiac arrhythmias are much less common in children than adults.⁶ The incidence of clinically significant arrhythmias is estimated at 22.5 per 100,000 pediatric patients. Tachyarrhythmias are the most common clinically significant arrhythmias in all age groups, although in Sacchetti's study of primary arrhythmias in pediatric ED patients, bradycardia was found to be more common in infants.⁶ Overall, supraventricular tachycardia is the most common clinically significant tachyarrhythmia presenting as a pediatric emergency.^{6,19, 20} Recent estimates suggest that SVT occurs in 1 in 250 to 1 in 1000 children.²⁰

Clinically significant tachyarrhythmias have a bimodal age distribution with a peak in infancy, a decline in early childhood and a steady rise in adolescence. ⁶ Most infant tachyarrhythmias resolve spontaneously within the first year with no recurrence. Riggs et al. showed that SVT recurrence occurred in 29% of patients with SVT diagnosed at greater than one year of age, and in 94% of patients with SVT diagnosed after their first year.¹⁹ Tortoriello et al demonstrated an increased risk of SVT recurrence among older infants, despite all patients being under one year of age.²¹

The prevalence of tachyarrhythmias is much higher in children and adults with congentital or acquired heart diseases. In one series of 629 patients with underlying cardiac diseases (age range, 1 day to 45.5 years, median 8.1 months) arrhythmias occurred in 29 percent.⁸ The most common arrhythmia noted in that study was nonsustained ventricular tachycardia, followed by nonsustained SVT. Ventricular tachycardia is usually observed in the setting of clearly defined underlying heart disease.^22,23 Arrhythmias are a major cause of death in children with previously diagnosed cardiovascular disorders. Ventricular fibrillation (VF) is the most common lifethreatening arrhythmia in children older than one year. The majority of patients in whom VF was the terminal event had undergone corrective surgical repair of their congenital cardiac lesions.⁷

Due to advances of pediatric cardiology and cardiac surgery, there are an increasing number of adults with congentital heart disease. These patients frequently present to pediatric EDs with a variety of cardiac and non-cardiac problems. The most frequent emergencies encountered are arrhythmias, infections, and heart failure. Arrhythmias are the primary reason for hospitalization of adults with congenital heart disease.²⁴

A cardiac arrhythmia is the manifestation of a disturbance of electric impulse formation and/or conduction. Most tachyarrhythmias are caused by aberrant or accessory conduction tissue that is responsible for the formation of reentry or reciprocating pathways.In a generally healthy child, the cause of the arrhythmia frequently remains unclear. The most common arrhythmia presenting as a pediatric emergency is a paroxysmal SVT.^6,20 About half of all cases of SVT in infants are idiopathic. One-fourth of patients with SVT have another comorbid condition, such as infection, fever, or drug exposure, at presentation. Although the vast majority of children with SVT have a structurally normal heart, 23% of patients with SVT have congenital heart disease, and 22% have Wolff-Parkinson-White (WPW) syndrome.¹⁵ Certain forms of congenital heart disease, such as Ebstein's malformation of the tricuspid valve, transposition of the great arteries, and hypertrophic cardiomyopathy, are associated with an increased prevalence of WPW. Older children presenting with SVT are more likely to have WPW.

Surgical correction of a congenital heart defect is frequently followed by the development of cardiac arrhythmias. Proposed mechanisms for postoperative dysrhythmias include direct effect of the surgical procedure on conduction tissues, the result of hemodynamic postoperative changes associated with additional pressure gradient to the repaired tissue, or the result of the natural progression of the primary heart defect. Atrial arrhythmias and sinus node dysfunction are associated with atrial-level procedures such as the Mustard or Senning procedure for transposition of the great arteries and the Fontan procedure. ⁸ Atrial tachyarrhythmias were noted in 14% of pediatric heart transplant recipients; atrial flutter and atrial fibrillation are the most frequently encountered tachyarrhythmias.²⁶ Ventricular arrhythmias are common in patients following the Fontan procedure, tetralogy of Fallot repair, the Ross procedure for left ventricular outflow tract disease, repair of ventricular septal defect.⁸ Multiple acquired heart diseases are associated with arrhythmias with the severity of symptoms frequently related to the severity of the underlying heart disease; see Table 1. Arrhythmia is a major cause of morbidity and mortality in pediatric patients with end-stage heart failure. More than half of patients with dilated cardiomyopathy and 62% of patients awaiting heart transplantation had lifethreatening arrhythmias, most commonly ventricular tachycardia.²⁷

 

 

Recently described Brugada syndrome is a familiar disorder of repolarization associated with right ventricular conduction delays. It is associated with spontaneous and inducible VT, recurrent syncope, and risk of sudden death in patients with structurally normal hearts. ^28,29 ECG findings include right bundle branch block, and ST elevation in leads V1-V3. The sudden onset of arrhythmia in a previously healthy child should raise the suspicion of a recreational drug overdose or toxic substance ingestion.^30-32

Two clinically significant mechanisms are responsible for the formation of arrhythmias: abnormal formation of the electric impulse (e.g. abnormal automaticity) or a change in conduction or reentry. The reentrant mechanism is responsible for the vast majority of pediatric supraventricular and ventricular tachyarrhythmias. Reentrant tachyarrhythmias can be further subdivided based on the site of the reentrant circuit origin. Reentrant circuits within the atrial muscle cause atrial flutter and atrial fibrillation. Most forms of VT are due to reentry within the ventricular muscle, usually involving a reentrant circuit in a region of scar caused by infarction, inflammation, or prior cardiac surgery.³³ Supraventricular tachycardia (SVT) is a broad term used to describe a group of arrhythmias that originate at or above the atrioventricular (AV) junction. These arrhythmias have similar ECG features but different mechanisms. Several SVT mechanisms have been identified, with the majority of SVT rhythms being caused by a reentrant circuit, with or without an accessory pathway. A reentrant rhythm involves the existence of a circuit through which the electrical impulse can cycle repetitively in one direction. This direction could be an antegrade (forward) direction from atrium to ventricle, or a retrograde (backward) direction from ventricle to atrium. The term SVT is often interchangeably used with atrioventricular reciprocating tachycardia (AVRT) and AV nodal reentrant tachycardia (AVNRT). Since most cases of pediatric tachyarrhythmias are associated with reentry mechanisms, the term SVT will include AVRT and AVNRT throughout the rest of this article.

AVRT is a common type of SVT in which the accessory pathway connects the atrial and ventricular myocardium directly without the involvement of the regular conducting system. The most common type of AVRT is orthodromic reciprocating tachycardia in which the impulses are conducted in an antegrade direction down the AV node through the His- Purkinje system to the ventricles, and then retrograde up the accessory pathway and back down the AV node.³⁴ This results in a narrow complex tachycardia; see Figure 1. Approximately one-third of patients with AVRT have pre-excitation.

 

 

When the electric impulse arrives at the ventricle through the accessory pathway in an antegrade direction, it does not slow down because it does not experience the delay imposed by the AV node. Thus, "pre-excitation" of the ventricle occurs. Characteristic ECG findings accompanying this phenomenon consist of a short PR interval (less than 0.12 seconds), a prolonged QRS duration (greater than 0.12 seconds), and a "delta" wave or a gradual upslope leading into and creating a widened QRS complex (see Figure 2), a key feature of the Wolff-Parkinson-White (WPW) pattern. Pre-excitation can be intermittent, making it difficult to assess true prevalence in the population.

 

 

Many patients with WPW do not develop SVT;³⁴ when episodes of SVT do occur, the patient is said to have WPW syndrome. The degree of pre-excitation depends on the conduction times between the AV node and the accessory pathway. The accessory pathway may start playing a leading role when the conduction through the AV node slows down or is completely blocked; for example, as a result of adenosine therapy or vagal maneuvers.

In antidromic AVRT, which is seen in less than 5% of patients, the reentrant circuit conducts impulses antegrade down an accessory pathway (not the AV node) and back up the AV node. Conduction through the ventricular myocardium is slower than through the conducting system, resulting in a widecomplex supraventricular tachycardia, which could be confused with a wide-complex ventricular tachycardia.

AV nodal reentrant tachycardia (AVNRT) is different from AVRT in that, instead of an accessory pathway, two conducting pathways are present within the AV node. Typically, conduction proceeds down a slow pathway and retrograde up a fast pathway creating a reentrant circuit. AVNRT accounts for approximately 15 to 30% of SVT in the pediatric population, 35 and is age-dependent, occuring more frequently in older patients and children less than two years of age.

The automatic tachycardias can be divided by site of origin, beginning with the condition of rapid discharge from the sinoatrial node known as sinus tachycardia (ST). In ST, the AV node will conduct rapidly with a normal PR interval and 1:1 AV ratio. Atrial ectopic tachycardia (AET) is a primary atrial tachycardia that arises from an automatic focus in the atria but outside the sinus node. On ECG the morphology of distinct P-waves is different from the normal sinus P-wave. Multifocal atrial tachycardia is caused by several foci of atrial automaticity present at the same time; discussion of these rare forms of SVT is beyond the scope of this review.

Atrial flutter (AF) is a type of reentrant tachyarrhythmia confined to the atria. It is very rare in children with structurally normal hearts, but is a common source of morbidity in young patients with significant structural or functional heart disease, especially due to congenital heart disease. Atrial flutter consists of rapid, regular atrial contractions at a rate of 280 to 480 beats per minute; see Figure 3. The ventricular response depends on AV node conduction and ranges from 2:1 to 4:1.

 

 

Ventricular tachycardia (VT) is an uncommon arrhythmia in the pediatric age group. It is defined as three or more consecutive premature ventricular complexes (PVCs), with a resulting rate between 120 and 250 beats per minute. VT may be nonsustained (lasting less than 10 seconds) or sustained (10 seconds or longer). VT in infants and children without structural heart disease is a rare event.^22,23 Mechanisms of VT are multiple and depend on the underlying problem. Rapid ventricular rate can result in a compromised stroke volume and cardiac output, potentially leading to pulse-less ventricular tachycardia or ventricular fibrillation.

Infrequent non-sustained VT is present in about 2 to 3% of adolescents and young adults. In the absence of other complicating disease or a specific cardiac diagnosis, the prognosis for these patients is excellent. More than 90% of younger patients and 50 to 70% of older patients appear to have resolution of their VT during two to ten years of follow-up.^29,36

Congenital long QT syndrome (LQTS) is an inherited disorder that affects the ion channels in the heart, resulting in abnormal ventricular repolarization which prolongs the action potential and results in a tendency to develop ventricular tachycardia and sudden cardiac death. LQTS is associated with an increased risk of a life-threatening polymorphic ventricular tachycardia, torsades de pointes, which often progresses to ventricular fibrillation.

SVT is frequently defined as a narrow rhythm tachycardia with a heart rate ranging from 220 to 280 beats per minute in a younger child age, and 150 to 250 beats per minute in an older age child. The majority of pediatric patients who present to the ED with a significantly elevated heart rate do not have SVT. At times, it can be challenging for the ED physician to differentiate between sinus tachycardia and reentrant tachycardia with narrow QRS complex in a younger age child.

Hanna and Greenes have shown that, in infants 2 to 12 months of age, pulse rate increases linearly with body temperature, with a mean increase of 10 beats per minute for each 1°C increase in body temperature. In a typical febrile infant, the range of expected heart rate should be less than the SVT heart rate range.³⁷ An inappropriately elevated heart rate in an otherwise calm or sleeping child is SVT until proven otherwise.³⁸ Table 2 reflects the differential diagnostic points between sinus tachycardia and SVT in a younger patient.

 

 

In a younger age patient with a new-onset tachyarrhythmia, symptoms may be nonspecific, as opposed to the older age patient who is more likely to have palpitations, dizziness, or chest pain as a chief complaint. Obtaining a complete set of vital signs is essential for Emergency Medical Services (EMS) personnel, who would likely be the first to identify an abnormally high heart rate in a patient after checking a pulse or placing the patient on a cardiac monitor.

Symptom severity in a pediatric patient with tachyarrhythmia depends on the presence of structural heart disease and on the hemodynamic compensatory abilities of the patient. Once an abnormally high heart rate is noticed by the EMS crew, supplemental oxygen should be provided based on pulse oximetry measurements or the level of distress.

The next question for the EMS provider is "Is the patient stable?" The patient with hemodynamic compromise may be tachypneic, have signs of decreased peripheral perfusion, and mental status changes consistent with shock.

Cardiac monitoring and intravenous (IV) access are essential. Every attempt should be made to obtain a 12-lead ECG, especially when an EMS provider plans to treat the patient's tachyarrhythmia in the field. For patients whose tachyarrhythmia resolves or is successfully treated prior to hospital arrival, the pre-treatment 12-lead ECG could be the only clue to the nature of their arrhythmia.⁴⁰ EMS providers who are trained and licensed to perform cardioversion should be ready to perform immediate synchronized electrical cardioversion for the pediatric patient with SVT who is in shock. It is appropriate to proceed with IV medications if the process will not take more than several minutes and preparations for cardioversion are being made at the same time.

EMS providers who are not very familiar with the use of adenosine should proceed with transporting a reasonably stable patient to the nearest appropriate facility. In a study of adult patients with paroxysmal SVT treated by paramedics, inappropriate use of adenosine occurred in 20% of cases.⁴¹ Agreement between paramedic and physician rhythm strip interpretations was fair to moderate in a similar patient population study.⁴² Scene times were about seven minutes longer in patients receiving adenosine. Although there is no pediatric data to support this, one could assume that the same concerns would apply to EMS providers treating children with SVT.

Recent data suggests that VF is not a rare rhythm in pediatric arrest victims.⁴³ The automatic external defibrillators (AED) are becoming widely available, and may be the first device available for defibrillation in the prehospital setting. The probability of successful defibrillation declines significantly for each minute of cardiac arrest, and early defibrillation is a major determinant of successful resuscitation.⁴⁴ Current evidence suggests that AEDs are both safe and effective for defibrillation of children one to eight years of age. (Please see the September 2005 issue of Pediatric Emergency Medicine Practice titled "Pediatric Out-of-Hospital Cardiopulmonary Arrest And Public Access Defibrillation Programs For Children" for a comprehensive review of this topic). Attenuated pediatric electrode pads were shown to perform appropriately and are recommended for use in children.⁴⁵

Obtaining a complete history is an essential step in the evaluation of a child with a tachyarrhythmia. Younger children are limited in the ability to describe symptoms and answer questions reliably. Information regarding change in behavior (irritability, lethargy) and feeding pattern (decreased appetite, vomiting) in a previously healthy child could lead the physician towards suspecting arrhythmia. A thorough history of recent illnesses (fever, vomitingand/or diarrhea), and medications used (recent Albuterol nebulizations) helps the ED physician to differentiate between sinus tachyarrhythmia and SVT in a previously healthy child.

Young patients with undiagnosed congenital heart disease usually present to the ED with symptoms other than arrhythmia. The majority of these patients exhibit cyanosis, signs of left-sided outflow obstruction with shock-like picture, or signs of congestive heart failure. Some congenital heart diseases, such as Ebstein's anomaly, transposition of great vessels, or hypertrophic cardiomyopathy, are more commonly associated with arrhythmias than others. Children with a history of surgery for congenital heart disease are at an increased risk of developing cardiac arrhythmias and sudden death.

Chest pain is the most common complaint noted in older children with tachyarrhythmias, followed by symptoms of palpitations, syncope, and respiratory distress.⁶ Chest pain is a distressing symptom, which raises a concern regarding heart disease. Patients with chest pain are frequently referred to the ED for further evaluation. Although several studies have shown that chest pain is often benign, up to 6% of patients have underlying cardiac problems.^9,46 One study identified SVT in 7% of patients with recurrent chest pain referred to the cardiologist.9 Older children with tachyarrhythmia frequently describe palpitations or a fluttering sensation in the chest, although sustained ventricular tachycardia has been occasionally noted in asymptomatic patients by routine ECG.³⁶

Syncope is a relatively frequent pediatric symptom encountered in the ED. Malignant causes of syncope are more likely to be present with exertional syncope. Diagnostic evidence for congenital LQTS was present in less than 1% of all patients with syncope and 16.7% of patients with exertional syncope.⁴⁷

Patients with LQTS typically present between the ages of 9 and 15 years with recurrent episodes of pre-syncope or syncope. Syncopal episodes are frequently precipitated by vigorous physical activity, emotional stress, and noxious stimuli.⁴⁷ Seizures and breath-holding-like conditions occasionally are manifestations of underlying LQTS.⁴⁸ Approximately 10% of children with LQTS present with sudden death. Wide QT dispersion was found in infants presenting with acute life-threatening events in comparison to normal infants.⁴⁹ More than half of patients have a family member with LQTS or a history of a sudden premature death. Once a diagnosis of LQTS is made, all first-degree family members should be referred for a 12-lead ECG and training in CPR.⁵⁰ Implantable cardioverter defibrillators are part of first-line therapy for adults with long QT syndrome and have been occasionally used as preventative treatment in children with LQTS.⁵¹

In a child who presents to the ED with tachyarrhythmia, the initial goal is to assess the patient's hemodynamic stability. Obtaining a complete set of vital signs cannot be overemphasized. An abnormally fast heart rate obtained at triage is frequently the first clue to the presence of SVT in a previously healthy child with nonspecific symptoms.

The physical examination in patients with SVT typically reveals tachycardia without evidence of decompensation, as most children tolerate tachycardia well. Heart failure is not an uncommon presentation of SVT in infants, however, because the tachyarrhythmia may go unrecognized for long periods of time.³⁴ Infants with sustained SVT may present with typical signs of CHF, including tachypnea, retractions, cardiomegaly, and hepatosplenomegaly.

In a stable child, a complete physical examination may be helpful in diagnosing underlying cardiac diseases (e.g., congenital heart disease, hypertrophic cardiomyopathy) and other medical conditions potentially associated with tachyarrhythmia (e.g., anemia, hyperthyroidism, etc.). Poor perfusion, altered mental status, and respiratory distress are signs of hemodynamic instability in a patient with tachyarrhythmia and require immediate intervention.

The initial assessment of the ECG should clarify whether the QRS complex is "narrow" or "wide." This is the first step to discriminate between SVT and VT. The normal QRS duration in infants ranges from 0.04 to 0.06 seconds and is up to 0.08 seconds in older children. If a wide QRS is observed, the immediate consideration should be ventricular tachycardia, which increases the urgency of evaluation and appropriate management. The ECG during sinus rhythm may be helpful in determining the mechanism of tachyarrhythmia. Patients with WPW show ECG evidence of preexcitation with a typical delta wave, widening of the QRS, and short PR interval; see Figure 2 . Patients with LQTS typically have prolongation of the QT interval in ECG, measuring greater than 440 to 460 msec. Patients with LQTS may develop Torsades de pointes (twisting of the points), which is a polymorphic ventricular tachycardia characterized by rapid, wide QRS complexes spiraling around an axis.

 

 

During SVT, the ECG exhibits a regular rhythm, without beat-to-beat variability, and a heart rate greater than 220 beats per minute in infants and greater than 180 beats per minute in older children. P waves may be visible, but generally are not; see Figure 1. In most cases, the QRS complex is narrow (less than 80 msec) with the exception of antidromic AVRT, which is seen in less than 5% of patients with SVT and is associated with a wide complex tachycardia.³⁴ In this type of SVT, conduction of an electric impulse down the accessory pathway is much slower than through the conducting system, which results in a wide QRS tachycardia.

 

 

Patients with atrial flutter exhibit a typical ECG pattern of saw-toothed flutter waves of atrial contractions with a 2:1 to 4:1 ventricular response. Patients with ventricular tachycardia typically have a wide QRS complex tachycardia with a regular rhythm. HR typically ranges between 120 bpm and 250 bpm. P waves may not be visible or may be seen behind each QRS complex.

Other diagnostic studies should be aimed at discovering the underlying causes of the arrhythmia. The routine use of echocardiography in infants with SVT in the first two years of life has been helpful in identifying cardiac structural defects not detected by clinical examination, ECG, or chest radiography.⁵³ Chest radiography is warranted if the patient has respiratory symptoms or chest pain, especially if accompanied by fever. In patients with VT, check electrolytes. Potassium and calcium abnormalities are most commonly associated with arrhythmias. Obtain serum and urine drug screens in patients with possible drug ingestion.

Consider cardiology consultation early in the management of a tachyarrhythmia.

In a review of conditions leading to pediatric cardiology consultation in a tertiary academic hospital, evaluation of an arrhythmia accounted for 12.7% of consultations. The majority of cases originated in the emergency department, with atrial arrhythmias representing 63% of consultations for arrhythmia. SVT was the most common arrhythmia requiring consultation.⁵⁴

All patients presenting to the ED with tachyarrhythmias should have an immediate hemodynamic assessment, a 12-lead ECG, and continuous cardiac monitoring initiated. The initial treatment strategy depends on the patient's presentation and clinical status (hemodynamically stable or unstable).

Altered mental status or signs of shock and severe heart failure may be present. Perform immediate synchronized cardioversion with 0.5 to 1 J/kg. Cardioversion in a synchronous mode will not allow a shock to be delivered during a vulnerable repolarization period. Perform cardioversion in children over 10 kg using adult electrode paddles, which results in lower thransthoracic impedance and higher current flow.⁵⁵ If time permits, give the patient adequate sedation before the procedure. Sedation for cardioversion may be provided by 0.1 mg/kg midazolam and/or 1 to 2 mg/kgpropofolintravenous.⁵⁶

In children with mild symptoms, vagal maneuvers may be attempted initially while preparations are made for medication therapy. The Valsalva maneuver or a carotid sinus massage may be effective in terminating SVT and is considered to be safe in older children.⁵⁷ Applying a bag of ice water to the center of the face for 15 to 30 seconds to elicit the diving reflex may be successful in terminating SVT in infants.⁵⁸ This maneuver is successful in 30 to 60% of cases.^59,60 Rectal stimulation with a thermometer has been used in young children. All attempts should be performed with continuous ECG monitoring. Avoid ocular pressure because of the theoretical possibility of producing retinal detachment.⁶¹

If vagal stimulation is not successful in SVT termination, and the patient remains hemodynamically stable, place an intravenous line for medication therapy. Adenosine is considered the drug of choice for acute management of SVT.

Adenosine is an edogenous nucleoside that interacts with A1 receptors on the surface of cardiac cells: the resulting effect is a temporary blockage of conduction through the AV node, which interrupts the reentrant circuit. During the administration of adenosine the patient should be supine with continuous ECG and blood pressure monitoring. Deliver adenosine by rapid intravenous injection via peripheral or central line, and immediately follow with 5 ml normal saline flush to optimize rapid delivery to the heart. Chose a peripheral venous line site as close to the heart as possible, as the drug is rapidly metabolized into an inactive form. The starting dose of adenosine is 0.1 mg/kg. In assessing the effectiveness of the first dose, the ED physician must watch the cardiac monitor very closely. If no response is seen within two minutes after the dose is administered, double the dose. The subsequent doses of adenosine can be increased by 0.05 mg/kg increments until termination of the arrhythmia or the maximum dose of 0.25 to 0.35 mg/kg or 12 mg is given.⁵⁵

Adenosine successfully terminates 80 to 95% of episodes of AVRT, which accounts for the majority of SVT in children, and approximately 75% of episodes due to other SVT causes. Early recurrence of the SVT after termination occurs in 25 to 30% of cases.^20,62,55 Transient side effects, including flushing, nausea, chest pain, or dyspnea, are common with adenosine administration, but usually resolve rapidly. Serious side effects after adenosine administration are rare. In adult patients with SVT, adenosine may induce VT/PVC episodes, which are usually brief and selfterminating. ⁶³ Atrial fibrillation induced by adenosine is relatively uncommon and is, in most instances, self-limited and without significant clinical consequence. If the arrhythmia is persistent, it may require treatment with other antiarrhythmic agents such as procainamide or amiodarone. If the arrhythmia is not hemodynamically tolerated or is drug resistant, electrical cardioversion is required.⁶⁴

In patients with WPW associated SVT, adenosine can cause atrial fibrillation progressing into ventricular fibrillation. Caution is advised with adenosine administration if WPW is a likely mechanism, and resuscitation equipment should always be available.⁵⁵ Patients with antidromic SVT may present with a wide-complex tachycardia. If the episode is the first presentation of a regular wide-complex tachycardia, the arrhythmia should be treated as ventricular tachycardia until proven otherwise. Using adenosine in such patient requires close cardiologist involvement.

A variety of antiarrhythmic medications have been suggested for the management of SVT refractory to adenosine in an acute care setting,¹⁴ but there are few studies and no randomized clinical trials that compare one medication to another. If left ventricular function is preserved, calcium channel blockers (verapamil or diltiazem), B-blockers, or digoxin may be used.⁶⁵ A reasonable approach for the ED physician would be to obtain a cardiology consult in a stable patient with refractory SVT.

In their survey of pediatric cardiologists, Wong et al indicated that digoxin and propranolol are the most commonly chosen medications in the management of SVT refractory to adenosine in the acute setting. 14 Propranolol is the most frequently suggested medication for patients with known or suspected preexcitation. Digoxin, although infrequently used by physicians in an acute care setting because of the delay in achieving therapeutic levels and the narrow therapeutic margin, is used in patients without known preexcitation, as it may potentiate accessory pathway conduction in a patient with WPW.

Strong consideration should be given to electrical cardioversion if SVT is not terminated with these agents. When electrical cardioversion is not feasible, desirable, or successful, antiarrhythmic agents should be used, although their proarrhythmic potential makes them less desirable in the management of patients with refractory SVT.

Procainamide is one of the most frequently suggested antiarrhythmics, which acts by inhibiting sodium-dependent depolarization and slowing atrial conduction. Procainamide does not block reentry at the AV node and can be safely used in patients with WPW without the risk of provoking accessory pathway conduction. Procainamide is administered intravenously; a loading dose in patients under one year of age is 7 to 10 mg/kg, given over 30 to 45 minutes. In older children the loading dose is 15 mg/kg. Continuous infusion starting at 40 to 50 mcg/kg per minute should follow. Negative inotropic effects and prolongation of the QT interval may be observed followed the administration of procainamide.

Amiodarone is another antiarrhythmic occasionally used for SVT refractory to other agents (adenosine, procainamide). It is administered intravenously, starting with a bolus infusion of 5 mg/kg over 20 to 60 minutes. If there is no response, repeat the bolus dose up to a total of 20 mg/kg. A recent study demonstrated higher dosages of amiodarone 5 mg/kg and 10 mg/kg to be effective in the management of a variety of critical supraventricular and ventricular arrhythmias in the pediatric population.¹⁵ Side effects of amiodarone, including hypotension, bradycardia, and proarrhythmic properties, were common and clinically significant.^15,66 Amiodarone and procainamide should not be administered together as they both prolong the QT interval.⁶⁵

Acute management of ventricular tachycardia requires a full evaluation of the ABCs of resuscitation. Management of VT with a pulse in an unstable patient requires immediate synchronized cardioversion at 0.5 to 1 J/kg. Medications may include amiodarone, lidocaine, or procainamide. Amiodarone and procainamide should not be used together. Treat pulseless VT or VF with defibrillation at 2 J/kg and re-start CPR immediately after defibrillation. If the defibrillation is unsuccessful, epinephrine should be given, and repeated every three to five minutes as necessary. If shockable rhythm is present after five rounds of CPR, additional defibrillation attempts with 4 J/kg are indicated (PALS 2005). Seek and treat any acute and reversible causes, such as electrolyte abnormalities, acidosis, or drug toxicity.

Intravenous administration of magnesium sulfate (MgSo4) was found to be a very effective and safe treatment for torsades de pointes in pediatric patients with LQTS.⁶⁷ Bolus injection is given at 3 to 9 mg/kg initially up to 12 mg/kg over one to two minutes until the torsades de pointes is completely abolished. A second bolus can be given under the same protocol within 5 to 15 minutes. It should be followed by a continuous infusion at a rate of 0.5 to 1.0 mg/kg/hr. When the total bolus dose of MgSo₄ exceeds 24 mg/kg in a pediatric patient and 400 mg in adults, measurement of serum Mg concentration and careful monitoring is mandatory. Optimal serum Mg concentration is 3 to 5 mg/dL.^67,68.

Management of hemodynamically stable patients with sustained ventricular tachycardia should be discussed with a cardiologist. Multiple pharmacologic options exist, including verapamil, beta-blockers, flecainide, and catheter ablation treatment.

The acute onset of a tachyarrhythmia in a previously healthy child should raise the suspicion of possible drug ingestion. Accidental ingestion of 10 to 20 mg/kg of most tricyclic antidepressants can potentially result in coma and cardiovascular symptoms, while ingestion of 35 to 50 mg/kg may result in death. In addition to measures to decrease gastrointestinal absorption, alkalinization of the blood with a sodium bicarbonate bolus of 1 to 2 mEq / kg is recommended. Continuous ECG monitoring is essential. A QRS interval greater than 0.1 second is associated with significant morbidity and mortality in these patients.

Cocaine use can acutely trigger both atrial and ventricular arrhythmias secondary to direct sympathetic effect and coronary vasoconstriction. This can occur during either acute use or withdrawal and can result in ischemic cardiomyopathy or sudden cardiac death.²⁹ Cool patients aggressively if febrile as hyperthermia is associated with an increase in toxicity. Nitroglycerine, benzodiazepines, or phentolamine are indicated for coronary vasospasm relief. Sodium bicarbonate (1-2 mEq/kg) should be considered for ventricular arrhythmias in addition to standard treatment.¹

Postoperative arrhythmias occur frequently in children with congenital heart disease. Lower body weight, longer cardiopulmonary bypass duration, and a higher surgical complexity are risk factors for arrhythmias.⁶⁹ The incidence of supraventricular tachyarrhythmias immediately after the modified Fontan procedure ranges from 20% to 37.5% (and late onset tachyarrhythmias approach 20% by five years post operation).⁷⁰ Types of tachyarrhythmias include atrial flutter, atrial ectopic tachycardia, and atrioventricular reentry tachycardia. Associated symptoms frequently include chest pain, palpitations, and signs of congestive heart failure. 12-lead ECG, cardiac monitoring, and early consultation with a pediatric cardiologist is a reasonable approach for the ED physician. Transesophageal atrial pacing has been shown to be a safe and highly successful tool for the acute termination of atrial tachycardia in the pediatric age group.⁷¹

Radiofrequency catheter ablation (RFA) has become an increasingly popular treatment modality for all types of tachycardia. The first successful catheter ablation using radiofrequency energy in a child was performed in 1991. Catheter ablation involves the application of radiofrequency energy through an electrode catheter to the arrhythmia substrate (e.g., accessory pathway), which causes tissue heating and necrosis.⁷⁷

To locate arrhythmia substrate, electrophysiologic mapping is performed prior to or in conjunction with radiofrequency catheter ablation. Computerized mapping systems have become commonplace in the electrophysiology laboratory and have improved the recognition and approach to tachycardias, particularly for post-operative congenital heart disease patients.¹³

The initial success rate for RFA in children with SVT can exceed 90%, although at three years after the procedure 71 to 77% of patients remained free of SVT.⁵⁵ In asymptomatic, high-risk children with the WPW syndrome, prophylactic catheter ablation reduces the risk of life-threatening arrhythmias.⁷² Although the incidence of sudden death in children with WPW is unclear, the lifetime incidence is estimated to be about 3 to 4%.

Cryoablation utilizes a new method to ablate arrhythmogenic lesions. Liquid nitrous oxide circulates through the catheter, cools the tip to subfreezing temperatures, and results in the destruction of the tissue directly beneath the catheter tip. Cryoablation is a safe and effective alternative to RF ablation and has been used to treat tachycardias considered too risky to be treated by other means.^18,13

Most pediatric patients who have symptomatic tachyarrhythmias will require cardiac consultation and admission to the hospital for further observation and treatment and continuous ECG monitoring. The recurrence risk of pediatric SVT is related to age at onset and the presence of WPW syndrome. The recurrence rate of SVT in infants without underlying heart disease is estimated to be around 30%, but is much higher among older patients.¹⁹ The presence of WPW syndrome is associated with a 29 - fold higher odd of SVT recurrence.²¹

Children who have a history of chest pain, palpitations, or syncope, but who are asymptomatic in the ED and have reassuring workup results, can be discharged after a period of observation in the ED. Refer these patients to a cardiologist for further outpatient workup. Holter monitoring (HM), a noninvasive and relatively inexpensive procedure that can be utilized in patients of any age, enables cumulative analysis of heart rhythm variability, and is frequently used as a first line diagnostic tool in investigating known or suspected arrhythmias. However, HM has a low diagnostic yield in pediatric patients. In one study, only 5.3% of generally healthy children presenting with palpitations and/or chest pain had similar complaints during HM, and only 34.8% of the 5.3% had an arrhythmia in their Holter records.⁷³ Patient-activated transtelephonic electrocardiographic event monitors (TTMs) are often used for the evaluation of older children and adolescents with suspected arrhythmias. Vickers Saarel et al addressed the utility of TTMs for children and adolescents with symptoms of a possible cardiac rhythm disturbance and showed that TTMs are useful for the evaluation of patients with palpitations but not with isolated chest pain, syncope, or presyncope. The sensitivity of TTMs for detection of SVT was 83%, with a monitoring length of four weeks' duration proven most cost effective. ¹² When patients have worrisome, though infrequent symptoms, TTMs may not yield a symptom- rhythm correlation. Insertable loop recorders implanted subcutaneously allow continuous rhythm monitoring that is stored either when manually activated by a patient/parent or automatically when high or low rate parameters are met.⁷⁴

Tachycardia may be associated with a number of medical conditions, some of which may present a significant diagnostic challenge for the ED physician. Myocarditis is one of the common pediatric diagnoses involved in emergency department malpractice claims.⁷⁵ In a child with myocarditis, the presentation is often nonspecific. The clinical signs of congestive heart failure can be confused with bronchiolitis or viral illness, especially during the viral season. Cardiac examination usually reveals tachycardia out of proportion to the degree of fever or the patient's activity level, and signs of poor perfusion. An ECG may show sinus tachycardia, arrhythmias, or a low QRS voltage, and CXR may show cardiomegaly. The ED physician should suspect myocarditis if a child with nonspecific symptoms has an unexplained tachycardia, especially if there is no improvement in vital signs after the resolution of fever or fluid replacement. Consider echocardiography evaluation and cardiology consult. Initial ED management includes respiratory and circulatory stabilization, with appropriate transfer plans as necessary, as these patients can deteriorate rapidly.

Another challenge for the ED physician is a patient with a history of syncope or seizure-like activity. Although not a common occurrence, children with underlying LQTS can present with a history of syncope or seizures as a result of decreased cardiac output secondary to ventricular tachycardia. It is prudent to obtain an ECG in all patients presenting with a first-time afebrile seizure to rule out LQTS. Many examples of patients with missed or delayed diagnosis of LQTS have been reported in the literature.⁴⁸ Lawsuits have been filed against physicians who misdiagnosed LQTS and managed it as idiopathic epilepsy.⁷⁶ It is also very important to refer family members for evaluation once the patient is diagnosed with LQTS.