Interpreting Pediatric Rhythms

The correct interpretation and treatment of pediatric rhythms requires an understanding of the normal cardiac developmental variation that occurs as the child moves from fetal to neonatal life and then progresses toward adulthood. The current electrocardiogram (ECG) standards used in the United States were developed by Davignon in 1979¹ and only reflect differences by age. Rijnbeek et al.^2,3 published normal standards for Dutch children, but they do not reflect racially and ethnically diverse populations. Appropriate assessment and management of arrhythmias in pediatric patients requires an understanding of the clinical presentation and the distinctive responses of children to the variety of available therapies.

Common Symptoms Associated With Pediatric Arrhythmias

The symptoms of an arrhythmia will vary with the age of the child. The infant may present with signs of congestive heart failure such as tachypnea, diaphoresis, poor feeding, irritability, or lethargy. A child younger than 4 or 5 years can rarely localize or verbalize symptoms of a rapid heart rate; they often complain of abdominal pain rather than chest pain. An older child may complain of palpitations, noting rapid or pounding heartbeats, fatigue, chest pain, difficulty breathing, or dizziness or syncope.

Normal or Noncritical Rhythms in Pediatrics

The most commonly misunderstood rhythms in pediatrics are sinus arrhythmia, sinus bradycardia, and sinus tachycardia. Sinus arrhythmia in pediatrics results in a 100- to 160-msec difference from one P-P interval to another, depending on the child’s age. Respiratory sinus arrhythmia is very common in children and is considered an indication of a normal heart. It is more often seen at slow rates and disappears during exercise. Conversely, nonrespiratory sinus arrhythmia is most commonly seen in children with sinus node dysfunction after various surgical procedures for repair of congenital heart defects, especially the atrial baffle procedures for d-transposition of the great arteries and the Fontan procedure for congenital heart defects with single ventricle physiology. Sinus arrhythmia must be distinguished from sinus pause, sinoatrial block, and premature atrial complex.

Continuous ambulatory monitoring techniques have demonstrated that low rates showing sinus bradycardia are normal during sleep and rest in children. Even marked sinus bradycardia in children with mild to moderate sinus node dysfunction is not a cause for alarm if the heart rate increases appropriately to meet the body’s metabolic needs to provide adequate cardiac output, such as during exercise or fever and illness. The normal increased vagal tone seen in well-trained athletes often results in resting sinus bradycardia. Abnormal sinus bradycardia is seen in pediatrics in association with increased intracranial pressure, hypothyroidism, hypothermia, and hypokalemia. Similarly, sinus tachycardia that is appropriate for the external stressors is a normal phenomenon in children and is defined by rates higher than expected for age. With illness and fever in very young children, a sinus rate may reach 240 beats/min.

Benign Common Pediatric Arrhythmias

Children may have premature atrial contractions (PACs), which are usually benign and present in low numbers. They are an uncommon cause of bradycardia in neonates when they are blocked and slow the heart rate. In addition, they can trigger episodes of supraventricular tachycardia (SVT) or atrial flutter in susceptible individuals and are more commonly seen in children with underlying ectopic atrial tachycardia or in patients with postoperative congenital heart disease. When they occur very early, PACs may be aberrantly conducted and present some confusion regarding the origin of the complex—atrial versus ventricular. The PR interval should be consistently prolonged with PACs.

Premature ventricular contractions (PVCs) are relatively common in children, occurring in 1% to 2% of those with normal hearts and in as many as 50% to 60% of adolescents.4,5 PVCs may be seen in 15% of normal newborns and two thirds of adolescents and adults with repaired congenital heart disease.⁶ There is a marked difference in prognosis between PVCs in children with normal and abnormal hearts, thus investigation for associated conditions should be undertaken. Isolated PVCs are generally benign when there is no structural or functional heart disease, and they usually do not require treatment. Both of these arrhythmias can be seen in association with intake of stimulants including coffee, tea, and decongestants. Other associations include intercurrent illness and systemic illness such as hyperthyroidism, adrenal tumors (pheochromocytoma), or myocarditis, including that associated with Lyme disease. More complex ventricular arrhythmias including couplets, triplets, and nonsustained ventricular tachycardia (VT) may require further evaluation and treatment in some instances.

Evaluation of Pediatric Arrhythmias

The evaluation starts with a complete history, including the personal and family history and a complete physical examination, which should direct the additional testing. In addition to the resting rate noted on the ECG, evaluation of pediatric arrhythmias could include a 24-hour ambulatory monitor, and for ventricular arrhythmias or those with symptoms of palpitations with exercise, an exercise stress test and an echocardiogram to rule out structural or functional heart disease. All children with single PACs or PVCs do not need this extensive workup. Further evaluation should be predicated on the patient’s clinical symptoms and examination.

Inappropriate Sinus Tachycardia

Inappropriate sinus tachycardia is an elevated heart rate out of proportion to metabolic demand. It may be an exaggerated increase in heart rate in response to stress, physiological or psychological factors, or a change in position (e.g., from supine to standing). It is uncommon before the adolescent years and is a diagnosis of exclusion in children with high consideration given to removal of exogenous substances such as caffeine, excessive chocolate, and energy drinks, or relative dehydration, as well as ruling out conditions such as anemia, hyperthyroidism, and adrenal tumors. In disabling cases, β-blocker therapy may be considered; sinus node modification should not be a consideration in children because this condition may resolve with age and a more balanced hormonal state after adolescence.

Supraventricular Tachycardia

Supraventricular tachycardia is a rapid rhythm that involves the atria, atrioventricular (AV) node, or accessory bypass tracts. It is the most common tachycardia seen in infants and children, with an incidence of 1 in 250 to 1000, occurring most commonly before 1 year of age. The other common developmental periods with increased SVT include approximately 5 to 7 years of age and during adolescence, both periods of rapid metabolic and developmental change. Patients can exhibit tachycardia during fetal development, with diagnosis suggested by auscultation of the infant’s heart rate during a prenatal examination and confirmed by fetal ultrasonography or magnetocardiography.⁷ Neonates and infants with tachycardia often exhibit signs and symptoms of congestive heart failure, which occurs if the tachycardia is present and not interrupted for more than 48 to 72 hours. The most common mechanism of SVT in children is AV reentry through an accessory pathway between the atrium and the ventricle or within the AV node; this represents 75% to 90% of arrhythmias in children without other cardiac conditions.⁸ Two thirds of these pathways are concealed (only unidirectional retrograde conduction) and one third are manifest as Wolff-Parkinson-White (WPW) or other forms of preexcitaiton. AV nodal reentry comprises 15% of pediatric SVT, more commonly seen in adolescents, with approximately one-third of SVT seen in adolescence being the result of AV nodal reentry (AVNRT).⁸ Automatic atrial ectopic tachycardia is the mechanism in 10% to 18% of SVT in children. Atrial flutter and atrial fibrillation represent 10% of nonpostoperative SVT and 40% of postoperative SVT; junctional ectopic tachycardia represents less than 1% of overall SVT. Although the majority of SVTs will resolve at around 1 to 2 years of age, one-third will recur by adolescence.

Evaluation of SVT should include a resting ECG; capture of SVT on ECG, when possible, by 24-hour continuous monitoring or event monitoring; echocardiography to rule out structural heart disease or functional myocardial impairment; exercise stress testing (especially when WPW or symptoms are present or precipitated by exercise); and electrophysiological studies in appropriate cases. Parents and children should be educated regarding the vagal maneuvers that can be used to interrupt the tachycardia including ice or cold to the face, gagging, breath holding, Valsalva maneuver, headstand, or handstand. They should be reassured regarding the generally benign nature of these arrhythmias. Schools should develop emergency plans regarding the symptoms that should prompt a call for emergency help, such as syncope, unresponsiveness, or cardiac arrest.

Medications used to treat pediatric arrhythmias are shown in Box 109-1 and Table 109-1.

Concealed Bypass Tachycardia

Concealed bypass tachycardia, with only unidirectional retrograde accessory pathway conduction, uses the AV node for antegrade conduction. Thus the accessory pathway is not visible on a resting ECG and no delta wave is present. Location of these accessory pathways, as with WPW, is along the AV groove, either around the tricuspid or mitral valves or in the septal region.

Permanent Junctional Reciprocating Tachycardia

A specific form of AVRT using a concealed accessory pathway, called permanent junctional reciprocating tachycardia (PJRT), is generally located in the posterior septal region. These pathways have negative P waves in leads II, III, and aVF, secondary to long refractory periods with slow retrograde conduction that results in a long RP interval. PJRT usually is an incessant arrhythmia, refractory to single-drug medical therapy. It may be confused with ectopic atrial tachycardia (especially those arising from the low right atrium) secondary to the ECG findings (see Figure 109-1, C).

Wolff-Parkinson-White Syndrome

Wolff-Parkinson-White syndrome implies an accessory pathway between the atrium and the ventricle that usually has bidirectional conduction properties and associated episodes of SVT. The ECG reading is distinctive, with a short PR interval and a delta wave. The reported incidence is 1 to 4 per 1000 live births. Associated cardiac abnormalities include Ebstein anomaly of the tricuspid valve and l-transposition of the great arteries. In addition, WPW may be seen in association with cardiac rhabdomyoma and with hypertrophic cardiomyopathy. WPW most commonly presents in infancy with AVRT. Although many patients will have resolution of this arrhythmia after the first year of life, persistence of the WPW pattern after 5 years of life predicts continued episodes of SVT in 78% of patients.¹⁰ Antidromic tachycardia using the accessory pathway as the antegrade limb occurs in approximately 10% of children, with one half of these having multiple accessory pathways.¹⁰ The remainder use the AV node as the antegrade pathway and are termed orthodromic. If the WPW pattern persists and symptoms are present in older children, risk stratification should be performed including an exercise stress test, 24-hour ambulatory monitoring, and, possibly, an electrophysiological study. The presence of a short refractory period (<220 to 250 ms) or a shortest preexcited RR interval during atrial fibrillation (<220-250 ms) or multiple pathways increases the risk of a subsequent life-threatening event, and catheter ablation is advised.¹⁵ In addition, the presence of atrial fibrillation, present in 10% to 12% of children, can increase the risk of sudden cardiac death (SCD) because of rapid ventricular response.¹⁵

Although most children with WPW who have symptoms will have episodes of rapid heart rate or complain of palpitations, a small percentage will present with sudden cardiac death as the first manifestation.¹⁶ Asymptomatic patients may be noted to have the WPW pattern on an ECG obtained for other reasons. Concerning studies by Pappone and Santinelli show an increased risk for sudden death in WPW syndrome in association with short accessory pathway–effective refractory periods and with multiple pathways, and they recommend that catheter ablation be performed.^15,17 A recent Pediatric and Congenital Electrophysiology Society/Heart Rhythm Society consensus statement on the management of asymptomatic WPW ECG patterns has been published.¹⁸ The recommendations for ablation are largely based on finding the shortest preexcited RR interval during atrial fibrillation (<220 to 250 ms).

Treatment for patients with WPW syndrome varies based on the patient’s age and symptoms. Antiarrhythmic medications are used predominantly in infants and young children with WPW. Infrequently, an infant who presents with a narrow complex tachycardia will develop evidence of preexcitation after treatment with a medication such as digoxin that slows AV nodal conduction. β-Blockers are generally used as a first-line therapy unless there is a contraindication, such as severe reactive airway disease. When β-blocker therapy fails to control the tachycardia, other medications such as flecainide, amiodarone, or sotalol can be used. Digoxin or calcium-channel blockers should not be used in patients with WPW because of the potential for enhancement of conduction down the accessory pathway, along with block of the conduction through the AV node.¹⁹ This can lead to an increased risk of rapid conduction of atrial fibrillation or PACs through the accessory pathway. If a neonate with WPW syndrome presents with significant signs of cardiac decompensation with cardiogenic shock, digoxin can be used while the patient is still in the hospital to improve ventricular function, as well as to suppress the tachycardia. Transition to another antiarrhythmic medication other than digoxin should occur before discharge from the hospital.

Atrioventricular Nodal Reentrant Tachycardia

The AV nodal region comprises the reentry circuit in AVNRT. It occurs more commonly in young adults and adolescents than in younger children and is infrequently seen in patients during the neonatal period because dual AV nodal pathways become increasingly manifest as the child ages.²¹ The ECG usually reveals tachycardia in which there is a very short R-P interval on the ECG or no visible P wave representing typical AVNRT because the retrograde limb of the pathway conducts very rapidly from the ventricle to the atrium. Atypical AVNRT with a long R-P indicating a slow-slow circuit is less commonly seen. Treatment is aimed at the AV node with the most commonly used drugs being digoxin or β-blockers, with calcium-channel blockers only used in older children and generally if the other drugs are ineffective. Slow pathway modification is a reasonable approach in the school-age child, but the potential for AV block and the subsequent need for a pacemaker require skill and availability of all modern techniques and technology, as well as recognition of the position of AV nodal structures in the smaller heart. Newer cryoablation techniques may decrease the incidence of AV block but have a somewhat increased recurrence rate of 6.5% within 1 to 2 years after ablation.²²

Atrial Tachycardia

Junctional Ectopic Tachycardia

Two distinct types of junctional ectopic tachycardia (JET), an automatic tachycardia that arises from the AV junction, are seen in childhood. One is a familial form occurring early in infancy. The second occurs in the early postoperative period after congenital heart repair. In familial JET, heart rates range from 180 to 240 bpm, with a faster ventricular rate than the atrial rate and a narrow QRS complex (see Figure 109-1, G). Rarely, a rate-related aberrancy is seen, leading to a wide-complex tachycardia. If the QRS complex is wide, the diagnosis of VT must be considered.

Postoperative Junctional Ectopic Tachycardia

Postoperative JET is a common arrhythmia after more complex congenital heart surgery, particularly after long pump runs or if the function of the heart is compromised. It generally occurs in the first 24 hours after surgery and is self-limited in surviving patients within 48 hours to a week. It can be treated by decreasing pressors as tolerated, treating fevers, and, pharmacologically, by intravenous administration of digoxin or amiodarone. Cardiac output is improved by atrial pacing when possible.

JET is characterized by a narrow QRS tachycardia at a rate of 170 to 300 bpm, with the atrial rate slower than the ventricular rate. Sudden death has been reported in this patient population.34,35 Treatment for the familial form of JET includes digoxin to slow the rhythm and improve ventricular function or amiodarone to slow the rate and/or convert the rhythm. Patients with JET have been treated with cathether ablation, with a 80% to 85% success rate, but with a risk of AV block, leading to recommendations for the use of cryothermal energy.³⁶ In some patients, more commonly males, the junctional rate will slow over time and the patient may be weaned from taking long-term medications.

Ventricular Tachycardia

Ventricular arrhythmias are less common than supraventricular arrhythmias in children. Because postoperative survival after complex surgery has increased, an increase in VT has been noted in these patients.³⁷ The most common etiologies of VT in children include congenital heart disease, preoperatively and postoperatively; acquired heart disease such as myocarditis, cardiomyopathies including hypertrophic and dilated cardiomyopathies, ARVC, and left ventricular noncompaction (LVNC); coronary anomalies or disease resulting in myocardial ischemia; channelopathies such as congenital LQTS and catecholaminergic polymorphic ventricular tachycardia (CPVT); abnormal foci or circuits in structurally normal hearts; tumors or infiltrates; or idiopathic etiologies. Although the failure to identify a specific cause is not unusual in children, persistence in evaluations often identifies pathology in patients initially thought to have an unidentifiable etiology.

Although the presence of a wide QRS tachycardia with AV dissociation suggests VT, many children have excellent ventriculoatrial (VA) conduction, and AV dissociation may not be seen. Causes of wide complex tachycardia in children include SVT with bundle branch aberrancy; antidromic SVT using an accessory AV connection; SVT using a nodoventricular, nodofascicular, or atriofascicular connection; or AF with aberrant conduction from which VT must be differentiated. Until proven otherwise, a wide QRS tachycardia in a child should be considered to be VT. The normal QRS duration in infants and young children is 40 to 80 ms, so widening is relative to the initial QRS complex duration. The rates of VT in children vary from 120 to 300 bpm. Left bundle branch block (LBBB) is the most common morphology, but right bundle branch block (RBBB) or alternating RBBB and LBBB may occur.

Polymorphic VT includes torsades de pointes and bidirectional VT. Torsades de pointes is associated with LQTS. Bidirectional VT has been associated with familial hyperkalemic paralysis, CPVT, or digoxin toxicity. The mechanisms of VT in children include abnormal automaticity in 40% and reentry in 60%.³⁸ Reentry is most often the mechanism in postoperative congenital heart patients, with reentry circuits that develop around suture lines, ventriculotomy scars, and anatomic obstacles.

Symptoms appear to be rate related, most frequently seen with VT rates over 150 bpm. Patients with VT and heart disease often have symptoms, whereas only one-third of patients with normal hearts and VT have symptoms. Sudden death occurs most commonly in the presence of an abnormal heart but has been reported in patients with normal hearts.³⁹ Evaluation of VT should include ECG, 24-hour ambulatory monitoring, echocardiography, and exercise stress testing in patients older than 5 years of age who can cooperate during the procedures.

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