Case Based Pediatrics For Medical Students and Residents
Department of Pediatrics, University of Hawaii John A. Burns School of Medicine
Chapter VII.6. Arrhythmias
Lance K. Shirai, MD
April 2002

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This is a 1 month old male who presents to the emergency room with a chief complaint of fever, lethargy, and poor feeding for the past 36 hours. He was well until he developed a tactile fever. His parents began noticing increasing lethargy and tiring with feeding and decreased oral intake for about 12 hours prior to presentation.

He is the product of a G2P1, full term, uncomplicated pregnancy. Delivery and stay in the nursery was uneventful.

Exam: VS T 38.0, HR 240, RR 72, BP 87/64, oxygen saturation 98% in room air. He is well developed, well nourished, but pale, lethargic and tachypneic, with mild subcostal retractions. HEENT exam is normal. Neck is supple without adenopathy. Lungs are clear to auscultation with good aeration. His heart is tachycardic with a regular rhythm. No murmur, rub, or valve clicks are heard. There is a soft S3 gallop that can be head from the lower left sternal border to the cardiac apex. His abdomen is soft, non-distended, non-tender, and without masses. His liver is 2 to 3 cm below right costal margin. His feet and hands are cool. His peripheral pulses are 1+ to 2+ (out of 4+) throughout. Capillary refill time is 3 to 4 seconds. He has no rashes or other significant lesions.

A chest x-ray shows mild cardiomegaly and mild pulmonary edema. A 12 lead electrocardiogram shows a narrow complex tachycardia (rate of 240 bpm) with no visible P-waves. Mild ST segment depression in the inferior-lateral leads is present.

The patient is felt to be in supraventricular tachycardia and mild congestive heart failure. A peripheral IV is started and he is given a rapid IV bolus dose of adenosine. The patient immediately becomes briefly bradycardic followed by resumption of a normal sinus rhythm at a rate of 140 beats per minute. He is admitted for overnight observation and initiation of an anti-arrhythmic medication. A 12 lead electrocardiogram following conversion shows no evidence of a delta-wave, so a loading dose of digoxin is administered.


An irregular heart rhythm is not an unusual finding in children with or without known cardiac disease. Some irregular rhythms are normal findings in healthy children. If the heart rate is not too slow or too fast, as to limit the cardiac output, then an arrhythmia may be well tolerated. Most children can be satisfactorily evaluated with a 12 lead electrocardiogram and rhythm strip, with possible supplementation by a chest x-ray, echocardiogram, Holter or event monitor, or an exercise study. There are several important determinants of arrhythmias, which should be considered. These include the arrhythmogenic substrate (e.g., accessory conduction pathway, automatic ectopic focus), modulating factors, and triggers of the arrhythmia.

Changes in sinus rhythm (P-wave preceding each QRS complex, with a normal P-wave axis) are most commonly seen with a sinus arrhythmia, sinus bradycardia, or sinus tachycardia. In pediatrics, a sinus arrhythmia is usually secondary to a variation in vagal tone during the normal respiratory cycle. This causes an increase in heart rate during inspiration and a decrease in heart rate during exhalation. It is most pronounced when the heart rate is slower and resolves with an increase in heart rate. Sinus bradycardia is a sinus rhythm with a rate below the lower normal limits for age and activity level. It is most often encountered in well conditioned athletes. Pathologic states in which sinus bradycardia may occur include increased intracranial, intrathoracic, or intraabdominal pressure, and systemic hypertension. Sinus tachycardia is a sinus rhythm with a rate greater than the higher limits for age and activity level. If the child is not active then the tachycardia usually has a secondary cause such as fever, heart failure, pain, anxiety, hypovolemia, anemia, myocarditis, or thyrotoxicosis.

Supraventricular tachycardia (SVT), also known as paroxysmal supraventricular tachycardia (PSVT) is a tachyarrhythmia manifesting with a narrow complex QRS duration (<0.08 sec). Many definitions of SVT exist, some of, which include all abnormal tachycardias originating in or around the atria (which would include PSVT, atrial fibrillation and atrial flutter). For the sake of this discussion, SVT will be defined as those narrow complex tachycardias involving the SA node and an accessory electrical pathway anywhere along the atrioventricular junction or very near the AV node itself (this definition excludes atrial fibrillation and atrial flutter). These are considered reciprocating tachycardias, as two discrete pathways are present, one with antegrade conduction and the other with retrograde conduction. One pathway is considered a "fast" pathway, with rapid conduction, and the other a "slow" pathway, with slower conduction. This creates the reentrant circuit. With orthodromic (conventional pathway) SVT, the antegrade conduction is down the "slow" pathway, usually the AV node, and the retrograde conduction is up the "fast" pathway, usually the accessory conduction tissue. Antidromic SVT is characterized by antegrade conduction down the "fast" pathway, and retrograde conduction up the "slow" pathway.

Supraventricular tachycardia is the most common abnormal tachycardia in the pediatric age group. The most common types of SVT in children include atrioventricular reentrant tachycardia (AVRT), which includes Wolff-Parkinson-White syndrome (WPW), and AV nodal reentrant tachycardia (AVNRT formerly called Lown-Ganong-Levine or LGL syndrome).

Supraventricular tachycardia usually has its onset at rest but may initiate during exercise. The precipitating factor(s) is often difficult to identify, but occasionally a febrile illness may precipitate an episode. The heart rate is usually in the 160 to 300 beat/min range. In general, the younger the patient the more rapid the SVT heart rate, but the longer the tachycardia is tolerated before symptoms (usually congestive heart failure) become obvious. As a rule, episodes of SVT onset and terminate abruptly, and may last anywhere from a few minutes to many hours, which is why it is called paroxysmal.

In infants, symptoms of SVT may not become apparent until the patient has been in SVT for 24 hours, or longer. They will often present with symptoms of congestive heart failure such as tachypnea, pallor, poor feeding, fussiness or lethargy.

In children and adolescents, symptoms may include palpitations, chest pain, shortness of breath, dizziness, syncope or near syncope, pallor, and diaphoresis. It is unusual for older patients to present in heart failure, as they will usually become symptomatic soon after the onset of SVT. They will often complain of intermittent episodes of palpitations, with mild associated symptoms.

Supraventricular tachycardia may present as syncope or near syncope. This may occur in patients with WPW who develop atrial fibrillation and rapid conduction down the accessory pathway to the ventricles. The onset of SVT can also cause a decrease in cardiac output with resultant hypotension, decreased cerebral perfusion pressure, and syncope. In the pediatric age group, the most common cause of syncope is neurocardiogenic syncope (also called a vasovagal faint). Syncopal episodes associated with palpitations should raise the suspicion of a possible tachyarrhythmia contributing to the patients symptoms. Nearly any type of cardiac arrhythmia can cause syncope if a sudden fall in cardiac output occurs. Cardiac dysrhythmias to consider should include SVT, ventricular tachycardia (in particular, long QT syndrome), advance degree AV block, sick sinus syndrome in patients with previous cardiac surgery, and pacemaker malfunction in those patients who are pacer dependent. Other cardiac related disease to consider in patients presenting with syncope include outflow tract obstruction (hypertrophic cardiomyopathy, aortic stenosis, pulmonic stenosis, pulmonary hypertension), coronary artery anomalies, cardiomyopathies, and mitral valve prolapse. The diagnosis can often be made with a thorough history and physical examination performed as close to the time of the syncopal episode as possible. Cases, which should arouse increased concern, include those not consistent with neurocardiogenic syncope, syncope with exercise, a family history of sudden death, and those patients with known structural cardiac disease. All patients who present with syncope should, at the minimum, have an EKG performed. In most cases of neurocardiogenic syncope, symptoms will improve or resolve with increased fluid and salt intake. Treatment for other causes of syncope should address the underlying etiology.

The differential diagnosis of a pediatric patient who presents in a narrow complex tachycardia includes SVT, sinus tachycardia, atrial flutter, atrial fibrillation, junctional ectopic tachycardia, ectopic atrial tachycardia, and chaotic atrial rhythm. Some patients with SVT and a bundle branch block or antidromic WPW, may present with a wide complex tachycardia, which if often difficult to distinguish from ventricular tachycardia (VT).

Most of the narrow complex tachyarrhythmias may be distinguished from their electrocardiogram findings. Supraventricular tachycardia ranges in heart rate from 160 to 300 beats per minute. The diagnosis of AVRT or AVNRT requires the presence of 1:1 A-V conduction. The heart rate usually remains in a very narrow range regardless of the patient's physiologic state. P-waves, which are oftentimes retrograde, are visible only in 50% or less of cases. Upon conversion to a sinus rhythm, patients with WPW or Mahaim fibers (an accessory pathway able to conduct only antegrade, with slow conduction, connecting the atrium directly to a portion of the right bundle branch) will demonstrate the classical delta waves as evidenced by an upsloping or slurring of the initial portion of the QRS complex. Delta waves are secondary to rapid antegrade conduction from the atrium to the ventricles through the accessory pathway, thus causing ventricular pre-excitation. With WPW the PR interval is short, but with the presence of Mahaim fibers the PR interval is normal. Forms of SVT with concealed accessory pathways (i.e., those capable of only retrograde conduction), will not show evidence of a delta wave, and therefore most will have normal PR intervals. An exception is those patients with James fibers (a form of AVNRT), who have a short PR interval. Most patients with SVT have normal cardiac anatomy. Congenital heart defects in which SVT is most commonly encountered are Ebstein's anomaly and L-transposition of the great arteries.

Atrial flutter may present with a regular or regularly irregular tachycardia with an atrial rate in the range of 250 to 400 beats per minutes. The classic sawtooth flutter waves may be seen, or revealed following a dose of adenosine. The ventricular rate will depend on the degree of A-V conduction (e.g. 2:1, 3:1, etc.). Atrial flutter will most often be encountered in the setting of congenital heart disease, presence of significant mitral or tricuspid valve regurgitation with atrial dilatation, fetuses or newborns with normal hearts (i.e., it sometimes occurs in normal fetuses and newborns), or in patients with myocarditis.

Atrial fibrillation demonstrates a rapid atrial rate (300-500 beats per minute) with a very chaotic pattern, and an irregularly irregular ventricular rhythm. Atrial fibrillation is most often seen in older children following palliative surgery for congenital heart defects, especially those involving intra-atrial surgery (e.g., Fontan, Mustard, or Senning procedures), and those children with significant atrioventricular valve disease.

Ectopic atrial tachycardia and chaotic atrial rhythm are rare tachyarrhythmias in the pediatric age group. On EKG, ectopic atrial tachycardia will show the presence of a variable atrial rate with an abnormal P-wave axis indicating a single atrial focus. Chaotic atrial rhythm, also referred to as multifocal atrial tachycardia, typically demonstrates at least 3 non-sinus P-wave morphologies, an irregular ventricular response, and variable PR, PP, and RR intervals. Both types of dysrhythmias occur most often in patients with structurally normal hearts, at times with concomitant myocarditis.

Junctional ectopic tachycardia is most commonly encountered in children less than 2 years of age, in the immediate post-operative period following corrective surgery for a congenital heart defect involving the region around the AV node (e.g., a VSD or tetralogy of Fallot repair). This is one of the most common post-operative arrhythmias encountered. The EKG typically demonstrates a narrow complex tachycardia with a regular atrial and ventricular rhythm, and a ventricular rate, which is more rapid than the atrial rate. This dysrhythmia originates from a focus of enhanced automaticity in the peri-AV nodal region. The heart rate typically rises and decreases gradually (warms up and cools down). This feature helps differentiate it from a reentrant type of tachyarrhythmia.

Significant ventricular arrhythmias, such at ventricular tachycardia (VT) and ventricular fibrillation (VF), are rarely encountered in the pediatric age group. Benign premature ventricular contractions (PVC) are not uncommon in infants, older children, and adolescents. Patients with ventricular arrhythmias may be asymptomatic or they may present with symptoms of palpitations, chest pain, dizziness, and/or syncope. Ventricular tachycardia is defined at 3 or more consecutive abnormal QRS complexes at a rate greater than 120 beats per minute. As mentioned previously, SVT may occasionally present as a wide complex tachycardia, which may be difficult to distinguish from ventricular tachycardia. In these cases, the definitive diagnosis may not be known until the patient is converted to a sinus rhythm. In these situations the patient should be presumptively treated as having ventricular tachycardia (VT) until proven otherwise. It should be remembered that VT does not always present as a wide QRS complex tachycardia, especially in infants. Ventricular fibrillation displays unidentifiable QRS complexes due to an uncoordinated state of ventricular depolarization, resulting in a state of poor cardiac output. Significant ventricular dysrhythmias in the pediatric age range are most commonly encountered in the setting of congenital heart disease, myocarditis, cardiomyopathies, myocardial trauma, hypoxia, acidosis, and electrolyte abnormalities (most notably hypokalemia and hyperkalemia).

The prolonged QT syndrome causes a distinct type of VT called Torsades de Pointes characterized by a polymorphic VT, which oftentimes causes syncope or sudden death. Recent genetic linkage analyses have isolated a number of genetic foci associated with defects in cardiac ion channels (namely sodium and potassium channels). Prior to the advent of genetic analysis, patients with long QT syndrome were classified into two groups: Jervell-Lange-Nielsen (autosomal recessive, associated with congenital deafness) and Romano-Ward (autosomal dominant, without deafness). Prolongation of the QT interval may also develop secondary to drugs (anti-arrhythmic agents, antihistamines, antidepressants, antipsychotics, some antibiotics), CNS trauma, cardiomegaly, hypokalemia, and hypocalcemia.

Various forms of heart block are usually encountered in children with congenital heart defects, heart failure, or with congenitally acquired heart block. Congenital complete heart block is most commonly seen in the setting of a maternal collagen vascular disorder, namely systemic lupus erythematosus or Sjogren's syndrome. In nearly all cases, maternal SS-A/Ro and SS-B/La autoantibodies can be isolated. Conversely, not all fetuses whose mother is positive for these antibodies will develop heart block. The most common congenital heart defect associated with complete heart block is L-transposition of the great arteries. If the ventricular rate is too slow to maintain adequate cardiac output, heart failure may develop in utero or postnatally. Treatment involves permanent pacing. The decision to treat depends on the baseline ventricular rate and the likelihood of sudden death.

The management approach for SVT depends upon the age and condition of the patient on presentation. If the patient is clinically stable, vagal maneuvers may be initially attempted to convert the tachycardia. Such vagal maneuvers may include bearing down (as though having a bowel movement, i.e., Valsalva maneuver), or inducing the diving reflex using an ice bag to the face or submerging the patient's face into a container of ice water. Other vagal maneuvers such as eyeball pressure and unilateral carotid massage are less effective and may be harmful.

If the patient appears clinically unstable, then an intravenous line should be immediately started in a centrally located peripheral vein (antecubital preferred over a hand vein) through which an IV bolus of adenosine may be given. It must be remembered that this medication has a very short half life of approximately 10 seconds, therefore it should be administered via bolus injection followed by an immediate bolus of saline utilizing either a 3 way stopcock or simultaneous needles within the same IV hub (the IV push and immediate flush technique). A 12 lead electrocardiogram should be obtained before and after conversion, if possible, and a rhythm strip should be continuously run during attempted conversion. External pacing equipment should be available since some patients go into sinus arrest following administration of adenosine. Adenosine causes a transient AV block and sinus bradycardia thus interrupting the reentrant circuit involving the AV node and accessory pathway. Potential side effects with adenosine include hypotension, bronchospasm, and flushing.

In rare cases, a patient will present in very unstable condition. Immediate electrical cardioversion may be required in such cases, especially if an IV cannot be started in an expedient manner or the patient fails to convert with IV adenosine.

Other modes of acute treatment include use of digoxin, verapamil, propranolol, transesophageal or transvenous pacing. Conversion to a sinus rhythm with these medications will usually be slower, therefore most are utilized for chronic control once the SVT has been converted by other means. If adenosine fails to convert the SVT, but the patient is hemodynamically stable, they may be started on one, or more, of these medications (with the exception of verapamil which should be avoided in infants) and monitored for conversion. It is important to remember not to use digoxin on patients with ventricular pre-excitation (e.g., WPW), as it may increase antegrade conduction down the accessory pathway. Patients with WPW are more prone to develop atrial flutter or fibrillation, and are therefore at risk for 1:1 conduction to the ventricles while on digoxin, potentially sending the patient into ventricular tachycardia or fibrillation.

Long term management of SVT depends on the severity and frequency of episodes. In those patients with no ventricular pre-excitation and infrequent, mild episodes that can be converted with vagal maneuvers, no treatment is required. Patients with frequent episodes, or severe symptoms, and those with ventricular pre-excitation, medical management should be started with a beta-blocker, digoxin, or calcium channel blocker. Patients diagnosed in infancy often will not require continued treatment beyond 1 year of age, but may have recurrent episodes later in life. With the presence of severe symptoms, syncope, difficult to control SVT, or other situations, e.g., patient preference, an electrophysiology study and radiofrequency ablation can be performed with a high success rate for cure.

The majority of fetuses and infants who present in SVT will have no recurrences off medication after 6 to 12 months of age. Patients who present in later childhood or during adolescence will likely have recurrent episodes of SVT throughout their lifetime. Many of these patients will require medical treatment and will eventually seek curative treatment with radiofrequency ablation. Radiofrequency ablation involves mapping out accessory conduction pathways in the heart with the use of electrodes placed in the atria, coronary sinus, and ventricles through central venous access. Upon localization of the pathway a specialized ablation catheter (tip is heated using radiofrequency energy) is used to burn and cause irreversible tissue injury to the accessory conduction tissue.

With the recent advancements in pediatric electrophysiology, the prognosis for patients with SVT is very good. The success rate with radiofrequency ablation continues to improve, especially when performed at centers with experienced specialists. Death or significant morbidity is rare with the present state of medical management. Most patients can be expected to live a normal life expectancy with little or no lifestyle alteration due to this condition.


Questions

1. What are the two most common forms of SVT in the pediatric population?

2. What are the two most common types of congenital heart defects associated with SVT?

3. Name two instances in which SVT may present as a wide complex QRS tachycardia.

4. In a hemodynamically stable patient who presents with SVT, what are the two most commonly used methods for attempted conversion to a sinus rhythm?

5. True/False: Supraventricular tachycardia is the most common cause of syncope in the pediatric age group.


References

1. Fish FA, Benson W. Disorders of Cardiac Rhythm and Conduction. In: Allen HD, Gutgesell HP, Clark EB, Driscoll DJ (eds). Moss and Adam's Heart Disease in Infants, Children, and Adolescents, 6th edition. 2001, Philadelphia: Lippincott, Williams, and Wilkins, pp. 482-553.

2. Deal BJ. Supraventricular Tachycardia: Mechanisms and Natural History. In: Deal BJ, Wolff GS, Gelband H (eds). Current Concepts in Diagnosis and Management of Arrhythmias in Infants and Children. 1998, Armonk, NY: Futura Publishing Company, Inc., pp. 117-143.

3. Vane Hane GF. Supraventricular Tachycardia. In: Gillette PJ, Garson A (eds). Clinical Pediatric Arrhythmias, 2nd edition. 1999, Philadelphia: W.B. Saunders Company, pp. 97-120

4. Silka MF, Garson A. Ventricular Arrhythmias. In: Clinical Pediatric Arrhythmias, 2nd edition. 1999, Philadelphia: W.B. Saunders Co., pp. 121-145.

5. Bernstein D. Disturbances of Heart Rate and Rhythm of the Heart. In: Nelson WE, Behrman RE, Kliegman RM, Arvin AM (eds). Nelson Textbook of Pediatrics, 15th edition. 1996, Philadelphia: W.B. Saunders Company, pp. 1335-1343.

6. Tanel RE. Putting the Bite Into the Pediatric Syncope Evaluation. Pediatric Case Reviews 2001;1(1):3-18.


Answers to questions

1. Atrioventricular reentrant tachycardia (AVRT) and AV nodal reentrant tachycardia (AVNRT).

2. Ebstein anomaly and L-transposition of the great vessels.

3. With the presence of a bundle branch block or with antidromic conduction.

4. Vagal maneuvers and intravenous adenosine.

5. False.


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