Pediatric Dysrhythmias
Pediatric Dysrhythmias
Author: Stephanie J. Doniger, MD, FAAP RDMS, Pediatric Emergency Medicine Attending Physician, Associate Director of Pediatric Emergency Ultrasound, Division of Emergency Medicine, Department of Surgery, Stanford University School of Medicine, Lucile Packard Children's Hospital, Palo Alto, CA.
Peer review: James E. Colletti, MD, FAAP, FAAEM, FACEP, Associate Residency Director, Emergency Medicine, Mayo Clinic College of Medicine, Rochester, MN.
Arrhythmia or dysrhythmia may be used to refer to a disturbance in the cardiac electrical conducting system that leads to an abnormal rate or rhythm. The successful repair of congenital heart diseases has led to an increase in the incidence of pediatric dysrhythmias. The presentation of dysrhythmias can be a diagnostic challenge to clinicians, and is especially difficult since most children present with vague and nonspecific symptoms such as "fussiness" or "difficulty feeding."
The dysrhythmias can be divided into two broad categories: the bradycardias and the tachycardias. Pediatric bradycardia is defined as a heart rate slower than the lower limit of normal for the patient's age (see Table 1), while in adults it is defined as a heart rate of less than 60 beats/min. Tachycardia is defined as a heart rate beyond the upper limit of normal for the patient's age. In adults, the heart rate is greater than 100 beats per minute (BPM). Despite their infrequency, it is crucial to expeditiously identify and treat certain rhythm abnormalities to avoid decompensation.
The Editor
Epidemiology
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The overall incidence of arrhythmias is 13.9 per 100,000 emergency department (ED) visits and 55.1 per 100,000 pediatric ED visits (children younger than age 18 years). Among those children with arrhythmias, the most common are sinus tachycardia (50%), supraventricular tachycardia (13%), bradycardia (6%), and atrial fibrillation (4.6%).1
Clinical Features
Children presenting with first degree heart block are largely asymptomatic but have the potential to progress to further heart block, including second and third degree heart blocks. Those with second degree Type I (Wenckebach) rarely progress to complete heart block, while Type II 2nd degree block frequently progress to complete heart block.2 Those children with complete heart block, most notably in infancy, may present with signs of congestive heart failure. Older children may present with syncopal attacks, otherwise known as Stokes-Adams attacks, with heart rates of less than 40-45 BPM, or even sudden death.
Those patients presenting with complete heart block may present with symptoms related to hypoperfusion, including fatigue, dizziness, impaired exercise tolerance, syncope, confusion, and even sudden death.3 Acquired or surgically induced heart block generally has a slower ventricular rate, with rates between 40-50 beats/min slower than those seen in congenital heart block, which is generally 50-80 beats/minute.4
Patients with LQTS commonly present between the ages of 9 and 15 years with recurrent episodes of near or frank syncope.5 They also may present with milder symptoms such as diaphoresis, palpitations, or lightheadedness. Of the patients with acquired LQTS, 60% of affected individuals are symptomatic at diagnosis.6 Syncopal episodes often are precipitated by intense emotion, vigorous physical activity, or loud noises. Syncopal episodes may be mistaken for seizures as they can result in loss of consciousness, tonic-clonic movements, and temporary residual disorientation following the event. Spontaneous return of consciousness usually follows a syncopal episode, but the dysrhythmia has the potential to degenerate into ventricular fibrillation and sudden death. Approximately 10% of children with LQTS present with sudden death, with the youngest children being more likely to die suddenly.7 LQTS may present in infancy as SIDS, or later in life as near-drownings. The most ominous warning sign of sudden death is syncope that occurs with exertion, while the strongest risk factor for sudden death is a prior history of syncope.
Diagnostic Studies
It is crucial to expeditiously identify and treat dysrhythmias. Further, it is important to determine whether the heart has underlying pathology. This initially can be accomplished with a thorough history and physical examination and a 12-lead electrocardiogram (ECG).
In addition to suspected dysrhythmias, common indications to consider an ECG include chest pain, seizures, syncope, drug exposure, electrical burns, and electrolyte abnormalities. Of these, the most life threatening are those caused by electrolyte disturbances, drug exposure, and burns.8 Physical examination findings including abnormal vital signs, critically ill patients, and an abnormal cardiac examination (heart murmur, gallop, tachycardia, or bradycardia) also warrant an ECG.
Further diagnostic evaluation includes searching for the underlying cause of the rhythm abnormality. Additional laboratory studies may include electrolytes (especially potassium, calcium, magnesium, and glucose), complete blood count, toxicology screen, blood gas, and thyroid function tests. Additionally, CK (creatine kinase), and troponins may be added if myocarditis is suspected. Imaging studies can include a chest radiograph and echocardiogram.
While a complete ECG interpretation is beyond the scope of this article, it is advisable to use a systematic approach, paying special attention to rate, rhythm, axis, ventricular and atrial hypertrophy, and the presence of any ischemia or repolarization abnormalities. More specifically, it is essential to interpret pediatric ECGs based on age-specific rates and intervals (see Table 1).2,9,10 The ECG can be further evaluated for rhythm, chamber size, and T wave morphology. Interpretation of the ECG guides which specific management path the physician must pursue.
The Bradycardias
Bradycardia in children may be attributable to vagal stimulation, hypoxemia, acidosis, or an acute elevation of intracranial pressure. Other serious etiologies can include first, second, and third degree heart block. Overall, the most common cause of bradycardia in the pediatric population is hypoxemia.
Sinus Bradycardia. Sinus bradycardia includes a heart rate less than the lower limit of normal for the patient's age (see Table 1), with P waves preceding each QRS on ECG. Usually, the heart rate is less than 80 BPM in infants and less than 60 BPM in older children.11 Sinus bradycardia is predominantly a benign entity, most often seen in athletes and during sleep.
Sinus bradycardia also may be associated with underlying causes. An important cause of bradycardia is respiratory compromise; therefore, the adequacy of the patient's oxygenation and ventilation should be rapidly assessed. Bradycardia also can be associated with hyperkalemia, hypercalcemia, hypoxia, hypothermia, hypothyroidism, and medications (digitalis, beta-blockers).
An important distinction must be made between sinus bradycardia and junctional (nodal) bradycardia. On electrocardiogram, junctional bradycardia has either no P waves or inverted P waves after QRS complexes. QRS complexes have normal configuration, and generally have rates between 40 BPM and 60 BPM. Junctional bradycardia may occur in an otherwise normal heart, post-operatively, with digitalis toxicity, or with increased vagal tone. If the patient is asymptomatic, no treatment is indicated. However, if the patient has signs of decreased cardiac output, atropine or pacing may be indicated.2
Conduction Abnormalities
First Degree Atrioventricular (AV) Block. First degree AV block is an abnormal delay in conduction through the AV node that manifests as a prolonged PR interval on electrocardiogram. Meanwhile, the heart is maintained in sinus rhythm, with a normal QRS configuration and no dropped beats.
First-degree heart block may even be an incidental finding on an otherwise normal ECG. Common causes include otherwise healthy children with an infectious disease, myocarditis (e.g., rheumatic fever, Lyme disease), cardiomyopathies, and congenital heart disease (ASD [atrial septal defect], Ebstein's anomaly).
Second Degree AV Block: Mobitz Type I (Wenckebach). In Mobitz Type I, otherwise known as the Wenckebach phenomena, the PR interval progressively lengthens until a QRS is dropped. This usually occurs over 3-6 cardiac cycles, followed by a long diastolic pause, and then resuming the cycle. There are occasional and frequent P waves that conduct, and the QRS configuration is normal. The block is due to an increased refractory period at the level of the AV node. Though this can be seen in otherwise healthy individuals, it also can be seen in patients with myocarditis, myocardial infarctions, cardiomyopathies, congenital heart disease, digoxin toxicity, and post-operative cardiac repairs.
Second Degree AV Block: Mobitz Type II. This type of 2nd degree heart block also is known as the "all or none" phenomenon. There is either a normal AV conduction with a normal PR interval, or a completely blocked conduction. The failure of conduction is at the level of the bundle of His, with a prolongation of the refractory period in the His-Purkinje system. Since some of the atrial impulses are not conducted to the ventricle, the ventricular rate depends on the number of conducted atrial impulses.
Third Degree (Complete) Heart Block. Complete heart block occurs when none of the atrial impulses are conducted to the ventricles. On electrocardiogram, the P waves are completely dissociated from the QRS waves; both the atrial and ventricular rhythms are regular, maintaining regular PP intervals and RR intervals, respectively. The QRS duration is usually normal if the block is proximal to the bundle of His, while a wide QRS indicates that the block is most likely in the bundle branches (e.g., surgically induced complete heart block). Oftentimes, the ventricular rhythm is slower than normal. (See Figure 1.)
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It is important to note that not all atrioventricular dissociation is complete heart block. Third-degree atrioventricular block is present if the ventricular rate is slower than the atrial rate.
Complete heart block may be an isolated anomaly, congenital, or associated with structural lesions like L-transposition of the great arteries and maternal connective tissue disorders such as Lupus. Any infant presenting with third degree heart block should have an investigation for neonatal lupus that includes testing for transplacentally acquired antibodies anti-Ro and anti-La. Acquired heart block may result from cardiac surgery, especially when there is suturing in the atrium. This effect can either be transient, resolving within 8 days post-operatively, or permanent. Other etiologies include infectious causes such as myocarditis, Lyme disease, rheumatic fever, and diphtheria; and inflammatory disorders such as Kawasaki disease and lupus. Complete heart block also is associated with myocardial infarction, cardiac tumors, muscular dystrophies, hypocalcemia, and drug overdoses.12
Prolonged QT Syndrome
Prolonged QT syndrome, otherwise referred to as long QT syndrome (LQTS), is a disorder of delayed ventricular repolarization, characterized by prolongation of the QT interval on electrocardiogram. Prolongation of the QT interval may be either hereditary or acquired. Jervell and Lange-Nielsen syndrome is an autosomal recessive form of prolonged QT syndrome that is associated with congenital deafness, whereas Romano-Ward syndrome is an autosomal dominant form not associated with deafness. Congenital LQTS, which often presents in childhood, has an estimated incidence of 1/10,000 to 1/15,000 and is responsible for 3-4,000 cases of sudden death each year in the United States. Patients with the acquired type of LQTS usually present in the fifth or sixth decades of life.13 Causes include medications, most common (see Table 2), and electrolyte abnormalities, such as hypokalemia, hypocalcemia, and hypomagnesemia.
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The hallmark dysrhythmia of LQTS, is a polymorphic ventricular tachycardia known as torsades de pointes ("twisting of the points") (see Figure 2).14 Although many of these events are self-limiting and the patient has spontaneous return of consciousness, the dysrhythmia has the potential to degenerate into ventricular fibrillation and sudden death. With the potential for fatal consequences in undiagnosed affected individuals, the recognition of LQTS is of paramount importance.
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LQTS should be considered and an ECG obtained for any patient who presents with a suggestive history, including: first-degree relatives of a known LQTS carrier; family history of syncope, seizures, or sudden death; a sibling with sudden infant death syndrome (SIDS); seizure of unknown etiology; or unexplained near-drowning. Other risk factors include congenital deafness and bradycardia in infants. The QT interval should be manually measured, with Lead II generally accepted as being the most accurate. To account for the normal physiologic shortening of the QT interval that occurs with increasing heart rate, the corrected QT interval (QTc) is calculated using the Bazett formula:15 QTc = QT / Ö RR. For greatest accuracy, the QT and preceding RR intervals should be measured for three consecutive beats and averaged. The current practice identifies a QTc > 460 ms as prolonged. (See Figure 3.) A QTc value between 420-460 ms is borderline and warrants additional assessment.16,17 Although ECGs automatically calculate the QT and QTc, a manual calculation of the QTc should be performed as the computer calculation often is inaccurate.18 If the diagnosis of LQTS is suspected but the screening ECG is not diagnostic, increasing sympathetic activity may trigger abnormalities on electrocardiogram.
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Management and Disposition
The management of the bradycardias primarily includes identifying and treating the underlying causative factor. It is important to note that hypoxemia should be corrected. In patients presenting with a heart rate of less than 60 beats per minute, providers must support oxygenation and ventilation and perform CPR with effective chest compressions as indicated.19 If symptomatic bradycardia persists despite initial resuscitative measures, pharmacologic therapy should be initiated. Epinephrine is the initial drug of choice in children with symptomatic bradycardia. It is important to note that the updated 2005 American Heart Association guidelines no longer recommend high-dose epinephrine, as it is associated with a worse outcome, especially in cases of asphyxia.20 Moreover, high-dose epinephrine has been associated with post-resuscitative tachycardia, systemic hypertension, and a higher mortality rate when compared with standard-dose epinephrine.21 Alternatively, atropine may be given19
No treatment is indicated for a first degree heart block. However, if suspicious features are present, patients may require evaluation for underlying disease (i.e., Lyme disease, rheumatic fever). For second degree heart blocks, treatment is directed at the underlying cause. In those patients with Mobitz Type II second degree heart block, a prophylactic pacemaker may be warranted since there is a risk of progressing to complete heart block. For those with complete heart block, the mainstay of therapy is a pacemaker. While awaiting pacemaker insertion, it may be necessary to administer atropine or isoproterenol, which temporarily increases the heart rate.
Patients presenting with LQTS and an episode of polymorphic ventricular tachycardia or torsades de pointes of unknown etiology should receive IV magnesium (25-50 mg/kg maximum 2 grams). Serum electrolytes and a toxicology screen should be obtained. Beta-blockers may be useful in suppressing catecholamine surges and further dysrhythmic activity. Patients with torsades due to prolonged QT may worsen acutely, while those with normal QT improve. Patients with recurrent ventricular tachycardia may require temporary transcutaneous ventricular pacing.
Any patient with a compatible history and prolonged or borderline prolongation of the QT interval should have a cardiology consultation. Therapy is aimed at reducing sympathetic activity of the heart, either pharmacologically or surgically. Beta-blockers generally are recommended as the initial therapy of choice, which has been shown to effectively eradicate dysrhythmias in 60% of patients, and to decrease mortality from 71% in untreated patients to 6% in those who are treated.13,22 The most commonly used beta-blockers are propranolol and nadolol. Patients with severe asthma in whom beta-blockers are contraindicated may be candidates for pacer therapy.
Anticipatory guidance to patients diagnosed with LQTS is important. All affected individuals, regardless of age, should be restricted from competitive sports and educated to avoid triggering factors, such as certain medications, loud noises, emotionally stressful situations, and dehydration. Because of the high risk of unexpected cardiac events, family members and close friends should be instructed in CPR and even consider purchasing a home AED. Also, due to the inherited patterns of LQTS, it is suggested that other family members receive a screening ECG.
The Tachycardias
The tachycardias can be classified broadly into those that originate from loci above the AV node (i.e., supraventricular), those that originate from the AV node (AV node re-entrant tachycardias), and those that originate from the ventricle. The vast majority of tachycardias are supraventricular in origin. Those that are ventricular in origin are typically associated with hemodynamic compromise.2 Of the tachycardias, sinus tachycardia is the most common tachycardia overall, while paroxysmal supraventricular tachycardia (SVT) is the most common symptomatic pediatric tachyarrhythmia. Atrial flutter and atrial fibrillation in children are largely attributed to structural heart disease.
Clinical Features. The majority of children with tachycardia are asymptomatic, with the minority of patients presenting with an unstable rhythm (such as pulseless ventricular tachycardia and ventricular fibrillation), in heart failure, or in frank cardiac arrest. Those patients presenting with sinus tachycardia usually present with a cause such as fever, dehydration, fluid, blood loss, anxiety, or pain.
Patients who present with SVT often are reported from triage to have a heart rate that is "too fast to count." In newborns and infants with SVT, the heart rate often is between 220 BPM and 280 BPM.23 Most patients do not have an underlying cause to account for the extremely fast tachycardia. Infants in particular often present with nonspecific complaints, such as "fussiness," lethargy, poor feeding, pallor, sweating with feeds, or simply "not acting right." If congestive heart failure is present, caretakers may describe pallor, cough, and respiratory distress. Though many infants may tolerate SVT well for 24 hours, within 48 hours, 50% develop congestive heart failure (CHF) and may deteriorate rapidly.23 In contrast, CHF rarely occurs in older children who are usually able to describe palpitations, chest pain, dizziness, or shortness of breath. Important historical factors include a relationship to exercise, meals, or stress, color changes, neurological changes, or syncope. A past medical history significant for cardiac problems, current medications, allergies, or a family history of sudden death or cardiac disease should be investigated.
Sinus Tachycardia. Sinus tachycardia can be differentiated from other tachycardias by a narrow QRS and a P wave that precedes every QRS. The rate is usually greater than 140 BPM in children and greater than 160 BPM in infants. Sinus tachycardia typically is benign and often seen with etiologies such as anxiety, pain, exercise, or with fevers. It is interesting to note that, the pulse rate has been shown to increase linearly with temperature in children older than than 2 months of age; for every 1 degree C (1.8 degrees F) increase, the pulse rate increases an average of 9.6 beats/min.24 Sinus tachycardia also can be associated with more serious underlying conditions such as hypoxia, anemia, hypovolemia, shock, myocardial ischemia, pulmonary edema, hyperthyroidism, medications (catecholamines), hypocalcemia, and illicit drug use. Most commonly, it is a result of dehydration and hypovolemia.1,2
Supraventricular Tachycardia (SVT). SVT is the most common symptomatic dysrhythmia in infants and children. In newborns and infants with SVT, the heart rate is greater than 220 BPM. In older children, it is defined as having a heart rate of more than 180 BPM.23
The majority of infants with SVT present at younger than 4 months of age, with a 3:2 male to female ratio; one-half have an idiopathic etiology. While 24% are associated with conditions such as fever and drug exposure, 23% are due to congenital heart disease (most commonly Ebstein's anomaly, single ventricle, L-transposition), and 10-20% are due to WPW syndrome.25 Among older children, causes are more likely to be WPW syndrome, concealed bypass tracts, or as a result of congenital heart disease. The AV reentrant type tachycardia is more common in children who present at younger than age 12 years, while the AV node tachycardia becomes more evident in adolescents.4
Other causes of SVT include hyperdynamic cardiac activity as is seen in response to catecholamine release, drug use, and post-operative cardiac repair. Toxic causes of SVT include stimulants, beta agonists, anticholinergics, salicylates, theophylline, tricyclics, and phenothiazines. Non-toxic causes include anxiety, anemia, sedative and ethanol withdrawal, dehydration, acidosis, exercise, fever, hypoglycemia, hypoxemia, and pain.23
The ECG shows a narrow complex tachycardia, either without discernible P-waves or retrograde P-waves with an abnormal axis. The QRS duration is normal, but is occasionally increased with aberrancy. It is further characterized by little or no variation in the heart rate.
The most common type of SVT is the AV reentrant tachycardia phenomenon. In addition to the normal conduction from the SA node, to the AV node, to the bundle of His, to the Purkinje fibers, there is an accessory "bypass" pathway in conjunction with the AV node. This pathway is an anatomically separate bypass tract, such as the bundle of Kent, which is seen in Wolff-Parkinson-White (WPW) syndrome. Conduction through this accessory pathway occurs more rapidly than through the normal conduction pathway, creating a cyclic pattern of reentry that is independent of the SA node. Typical ECG findings of WPW syndrome are a short PR interval, wide QRS, and a positive inflection in the upstroke of the QRS complex, known as the delta wave. (See Figure 4.) This characteristic finding is only evident after the rhythm is converted to sinus rhythm.26
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The second type of SVT is the AV nodal/ junctional tachycardia, which is a cyclical reentrant pattern from dual AV node pathways that are simultaneously depolarized. The third type of SVT, ectopic atrial tachycardia, is rare and is manifested by the rapid firing of a single ectopic focus in the atrium. The hallmark of ectopic atrial tachycardia is the presence of different P wave morphologies. Each P wave is conducted to the ventricle and since the ectopic atrial focus is faster than the SA node, it takes over rate determination.2
Premature Ventricular Contractions (PVCs). A PVC is a premature wide QRS complex that has a distinct configuration and is not preceded by a P wave. They may appear in patterns of 2 consecutive PVCs (couplet), alternating PVC with normal QRS (bigeminy), or with every third beat a PVC (trigeminy). Three or more consecutive PVCs are considered ventricular tachycardia. Further, the "R on T phenomenon" can occur when a PVC occurs on the T wave, which is considered a "vulnerable period" of stimulating abnormal rhythms. This can be seen with hypoxia or hypokalemia and may result in life threatening arrhythmias.27
For the most part, patients with PVCs are asymptomatic. When examined, 50-75% of otherwise normal children may have PVCs on Holter monitor.2 However, PVCs also can be associated with congenital heart disease, mitral valve prolapse, prolonged QT syndrome, and cardiomyopathies (dilated and hypertrophic). Malignant etiologies further include electrolyte imbalances, drug toxicities (general anesthesia, digoxin, catecholamines, amphetamines, sympathomimetics, phenothiazines), cardiac injury, cardiac tumors, myocarditis (Lyme and viral), hypoxia, and an intraventricular catheter.
Ventricular Tachycardia. Though rare in children, ventricular tachycardia is an important rhythm to recognize and promptly treat. By definition, ventricular tachycardia is three or more consecutive PVCs, with heart rates ranging from 120-200 BPM. The rate may be as rapid as 400 or 500 BPM.28 Ventricular tachycardia may present with or without a pulse. Nonperfusing ventricular rhythms are seen in up to 19% of pediatric cardiac arrests when SIDS cases are excluded.29
On electrocardiogram, the QRS complexes have a wide configuration. The QRS duration is prolonged, ranging from 0.06 to 0.14 seconds. Complexes may appear monomorphic, with a uniform contour and absent or retrograde P waves. Alternatively, the QRS complexes may appear polymorphic or vary randomly as is seen in torsades de pointes. ECG findings that further support the presence of ventricular tachycardia include the presence of AV dissociation, with the ventricular rate exceeding the atrial rate. (See Figure 5.)
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Ventricular tachycardia may result from electrolyte disturbances (hyperkalemia, hypokalemia, hypocalcemia) metabolic abnormalities, congenital heart disorders, myocarditis, or drug toxicity. Other etiologies include cardiomyopathies, cardiac tumors, acquired heart disease, prolonged QT syndrome, and idiopathic causes.
With prolonged rapid ventricular rhythms, decreased cardiac output and hypotension can quickly ensue. Though the heart may be contracting and pulses palpable in some patients with ventricular tachycardia, those contractions are hemodynamically inefficient and can ultimately lead to syncope and death if left untreated. Ventricular tachycardia also can decompensate into ventricular fibrillation, which is a nonperfusing, terminal arrhythmia.
Ventricular Fibrillation. Ventricular fibrillation is an uncommon rhythm in the pediatric population, but is certainly life threatening. It is an uncommon cause of cardiac arrest in infants younger than 1 year of age, but increases with advancing age. The hallmark is chaotic, irregular ventricular contractions without circulation to the body. On electrocardiogram, the rhythm is one of bizarre QRS complexes with varying sizes and configurations. It is one of a rapid, irregular rate.
Causes of ventricular fibrillation include post-operative complications from congenital heart disease repair, severe hypoxemia, hyperkalemia, medications (digitalis, quinidine, catecholamines, anesthesia), myocarditis, and myocardial infarction.12
Atrial Flutter. Atrial flutter is an uncommon rhythm presenting in the pediatric population. Atrial rates may present in the range of 240-450 BPM2 with the ventricular response depending on the AV nodal conduction. On electrocardiogram, the hallmark pattern is "saw toothed" flutter waves, which are best viewed in leads II, III, and V1. The atrial rate is, on average, approximately 300 atrial BPM.2 Since the AV node cannot respond this quickly, there is an AV block that can present as a 2:1, 3:1, or 4:1 block. The QRS is generally normal in configuration.
Significant cardiac pathology usually accompanies atrial flutter. Causes of atrial flutter in children are largely attributed to structural heart disease, including a dilated atria, myocarditis, or acute infection. It is most notably associated with post-operative complications of congenital heart disease repairs, such as ASD repairs, Mustard procedure for D-transposition of the great arteries, or the Fontan procedure for single ventricle. Occasionally, patients who have had ventricular surgeries, such as tetralogy of Fallot repairs, may present with atrial arrhythmias. Atrial flutter also is seen in such conditions as Duchenne muscular dystrophy and central nervous system injury.
Atrial Fibrillation. Atrial fibrillation is another rare rhythm in children. It is defined as disorganized, rapid atrial activity, with atrial rates ranging from 350-600 BPM;30 the ventricular rate is variable, and is dependent upon a varying AV block. The rhythm of atrial fibrillation is described as being irregularly irregular, alternating between fast and slow rates. The hallmark ECG features are irregular atrial waves, with beat-to-beat variability of the atrial size and shape. This is best recognized in lead V1. The QRS complexes appear normal. Children at increased risk of developing atrial fibrillation include patients with an underlying structural heart defect (such as congenital mitral valve disease and those who have had an intra-atrial operative procedure) and hyperthyroidism. Atrial fibrillation also is associated with decreased cardiac output. With a significantly increased ventricular rate, incoordination between the atria and ventricles ensues, thereby decreasing cardiac output.
Management, Disposition
Upon recognition of a tachycardia, stepwise questioning can help evaluate the ECG tracing. Is it regular or irregular? Is the QRS narrow or wide? Does every P result in a single QRS? Once this is established, treatment options are considered, according to whether or not the patient has a pulse and the presenting rhythm on ECG (See Algorithm, Figure 6).19
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The treatment of sinus tachycardia is largely targeted at treating the underlying disorder rather than treating the tachycardia itself.
The management of SVT always begins with ensuring that the patient is maintaining his/her airway, breathing, and cardiovascular status. It is important to promptly administer oxygen and to obtain a 12-lead ECG with rhythm strip. It is of utmost importance to expeditiously differentiate those who are stable from those who are unstable. In a child presenting with unstable SVT (severe heart failure and poor perfusion), cardioversion is initiated at 0.5 J/kg and can be increased up to 1 J/kg. Adenosine may be given prior to cardioversion if intravenous access already has been established. In unstable patients, cardioversion should not be delayed for attempts at IV access or sedation.19
In children with asymptomatic SVT or with mild heart failure, vagal maneuvers such as ice to the face in an infant, or an older child blowing through a straw may be attempted.4 If vagal maneuvers are unsuccessful, adenosine is administered through an IV that is preferably close to the heart. Due to the extremely short half-life, adenosine must be pushed and flushed (with 5 mL normal saline) quickly to be effective. The initial dose of adenosine is 0.1 mg/kg (up to 6 mg), and can be increased to 0.2 mg/kg/dose (up to 12 mg) if the first dose is ineffective.31 An effective response is a brief period of asystole on ECG, with the return of a normal sinus rhythm. Failure to terminate the dysrhythmia after the second dose of adenosine in a stable patient should prompt consultation with a pediatric cardiologist. Adenosine can be therapeutic as well as diagnostic; it is not effective with nonreciprocating atrial tachycardia, atrial flutter, atrial fibrillation, or ventricular tachycardia. There are minimal hemodynamic consequences associated with adenosine administration.32 Contraindications include a denervated heart (transplant) and second or third degree heart block. Additionally, adenosine can worsen bronchospasm in asthmatics and increase heart block or precipitate ventricular arrhythmias in those taking carbamazepine, verapamil, or digoxin. Alternative medications include procainamide and amiodarone. Beta-blockers such as propranolol or esmolol may be used, but with caution, as they may cause hypotension.33 In addition, verapamil should be avoided in children younger than age 1 year, as cardiovascular collapse and death can occur.23 Amiodarone also can be associated with a "gasping syndrome" in the first month of life. This is characterized by an abrupt onset of gasping respiration, hypotension, bradycardia, and cardiovascular collapse.34,35 Further precautions should be taken in the use of digoxin, as it may act as a proarrhythmic agent in SVT associated with WPW syndrome. The long-term management of SVT may include beta-blockers, procainamide, sotalol, amiodarone, or flecainide. When pharmacologic treatments fail, radio-frequency catheter ablation has an 85-95% success rate of preventing recurrence of SVT.36 Once stabilized, the majority of patients with SVT will need hospital admission to investigate the underlying cause of SVT and the potential for long-term medical management or radiofrequency ablation.
Though PVCs are for the most part benign, when left unrecognized and untreated, there is a risk of developing ventricular tachycardia in those with a serious underlying cause. Premature ventricular contractions are considered malignant if they are associated with underlying heart disease, there is a history of syncope or family history of sudden death, precipitated or increased with activity, multiform morphology, symptomatic runs of PVCs, or if there are frequent episodes of paroxysmal ventricular tachycardia. Children presenting with premature ventricular contractions require evaluation and possibly treatment in conditions that are likely to cause cardiopulmonary compromise. For those patients with an underlying cause (e.g., electrolyte abnormality, hypoxia, severe acidosis), treatment consists of managing the underlying cause. Treatment is largely with IV lidocaine, followed by a lidocaine drip. Amiodarone, procainamide, and beta-blockers are reserved for those who are refractory to lidocaine.30 (See Table 3.)
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In those asymptomatic patients presenting with isolated PVCs and normal cardiac structure and function, no treatment is necessary. For those patients with couplets, multiform PVCs, or frequent PVCs, a referral to a pediatric cardiologist for further investigation is indicated. It is prudent to advise any patient with PVCs to avoid stimulants, such as caffeine, theophylline, and pseudoephedrine, since they may precipitate more frequent PVCs.
In a patient with ventricular tachycardia, the urgency of treatment depends on the patient's clinical status. Initially, the ABCs must be maintained, and it must be determined whether the patient has a pulse and is hemodynamically stable. The American Heart Association has set forth treatment algorithms to facilitate prompt treatment for this potentially fatal rhythm (see Figure 6).19
Ventricular tachycardia with a pulse in an unstable patient warrants immediate synchronized cardioversion at 0.5-1 J/ kg. It is important to pretreat conscious patients with light sedation (i.e., midazolam 0.1 mg/kg). Pharmacologic interventions include amiodarone or procainamide. It is important to note that amiodarone and procainamide should not be administered together since this can lead to severe hypotension and prolongation of the QT interval. Lidocaine is no longer listed on the stable ventricular tachycardia algorithm.31 When using procainamide, the infusion is stopped once the arrhythmia resolves, if the QRS widens >50 % over the baseline, or if hypotension ensues. Pulseless ventricular tachycardia should be treated the same as ventricular fibrillation. The preferred drug of choice for pulseless arrest is amiodarone, since adult studies have shown that it is more effective. However, amiodarone may cause hypotension, the severity of which is related to the infusion rate. Lidocaine is only recommended when amiodarone is unavailable. When compared with lidocaine, amiodarone has been shown to have higher rates of return of spontaneous circulation and survival to hospital admission in shock resistant ventricular fibrillation.37
Since ventricular fibrillation is a non-perfusing rhythm, CPR must be immediately initiated, according to the updated AHA guidelines, focusing on effective chest compressions. Of note, the treatment pathway is the same as for ventricular tachycardia without a pulse. Defibrillation is initiated at 2 Joules/kg, increased to 2-4 J/kg, and then to 4 J/kg. If defibrillation is unsuccessful, epinephrine should be given and repeated every 3-5 minutes as necessary. If pulseless ventricular tachycardia is refractory to defibrillation, antiarrhythmics are indicated: amiodarone or lidocaine. Although the pediatric dosing of amiodarone has not been clearly established, the recommended loading dose of 5 mg/kg IV may be given over minutes to 1 hour. If rate control is not achieved, the dose may be repeated in 5 mg/kg IV increments to a maximum of 15 mg/kg/day IV.38 For polymorphic ventricular tachycardia (torsades), the mainstay of treatment is magnesium (20-50 mg/kg IV).
With regard to the treatment approach of atrial fibrillation, the clinician must first recognize whether the patient is hemodynamically stable. An unstable patient may warrant electrical cardioversion, with consideration to adding heparin to prevent embolization.9,39 In those patients receiving digoxin, it is advisable to avoid electrical cardioversion unless the condition is life threatening, since the combination is associated with malignant ventricular arrhythmias.40,41 Alternatives in those receiving digoxin are rapid atrial pacing with catheterization or lower current settings.39 For those patients who are hemodynamically stable, digoxin is administered to increase AV blockade, thereby slowing the ventricular rate. Propranolol also may be added. Recurrences are then prevented, by administering quinidine.
In treating atrial fibrillation, those who are hemodynamically unstable warrant immediate cardioversion. However, in those who are hemodynamically stable, digoxin can be administered for ventricular rate control, allowing for a 24-hour time period to assess for its efficacy. After that time period elapses, and digoxin proves to be ineffective, a second medication may be added such as propranolol, esmolol, or procainamide. In those patients who have undergone cardioversion, recurrence is common. During admission, cardioverted patients often are started on an agent to keep them in normal sinus rhythm (e.g., amiodarone, procainamide, quinidine, or a beta-blocker).42
Summary
Arrhythmias in children are less common than in adults, but are increasing due to the successful repair of congenital heart diseases. The bradycardias are defined as a heart rate less than the lower limit of normal for a child's age, with the most common cause being sinus bradycardia, which for the most part is benign. The tachycardias are defined as a heart rate greater than the upper limit of normal for a child's age. Sinus tachycardia is the most common asymptomatic tachyarrhythmia, while paroxysmal SVT is the most common symptomatic pediatric tachyarrhythmia. Atrial flutter and atrial fibrillation in children are largely attributed to structural heart disease. Despite their infrequency, it is crucial to expeditiously identify and treat certain rhythm abnormalities as they can lead to further patient decompensation.
Acknowledgements
The author would like to acknowledge Ghazala Sharieff, MD, for her collaboration and mentorship and CDR Jonathan T. Fleenor, MD, in the division of Pediatric Cardiology at the Naval Medical Center San Diego for his electrocardiogram contributions.
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The successful repair of congenital heart diseases has led to an increase in the incidence of pediatric dysrhythmias. The presentation of dysrhythmias can be a diagnostic challenge to clinicians, and is especially difficult since most children present with vague and nonspecific symptoms such as "fussiness" or "difficulty feeding."Subscribe Now for Access
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