Arrhythmias

In this section, we provide a general overview of normal conduction and arrhythmias, diagnostic tools for arrhythmia evaluation in children, and common arrhythmias seen in children.

Normal Conduction and Arrhythmias

Normal Conduction

In a normal heart, the impulse for a heartbeat is initiated in the sinoatrial (SA) node, which is located in the superior wall of the right atrium. The impulse then travels throughout the right atrium (and left atrium) before reaching the atrioventricular (AV) node, located at the base of the right atrium. The AV node acts as a gatekeeper to the ventricles and sufficiently slows the signal so that the atrial contraction can fill the ventricles with blood. From the AV node, the signal travels down the bundle of His, located in the interventricular septum. This bundle splits into left and right branches, sending the impulse across both ventricles and leading to ventricular contraction. The SA node then signals the next heartbeat.

(Source: Biventricular Pacing. N Engl J Med 2006.)

Arrhythmias

Arrhythmias are abnormal heart rhythms that deviate from the normal conduction sequence. Arrhythmias are classified in several ways, including anatomic origin and mechanism of arrhythmia (e.g., reentrant, increased automaticity). The following chart lists examples of arrhythmias seen in children based on anatomic origin.

Diagnostic Tools for Arrhythmia Evaluation

Pediatric Electrocardiogram

A full discussion of electrocardiogram (ECG) interpretation in pediatric patients is beyond the scope of this guide. Please refer to textbooks of pediatric cardiology for a more extensive discussion. The University of Texas Department of Pediatrics also provides an online overview of pediatric ECG interpretation.

Electrophysiology Study

An electrophysiology study is a minimally invasive examination that involves using special catheters to map and assess the electrical activity of the heart and identify the source and foci of abnormal rhythms. In supraventricular tachycardia (SVT), for instance, if an accessory pathway is identified during an electrophysiology study, radiofrequency (RF) ablation or cryoablation may be undertaken. RF ablation is typically used when the pathway is remote from the AV node and utilizes heat to ablate the pathway. Cryoablation is typically used when the pathway is close to the AV node and involves freezing the lesion.

Common Pediatric Arrhythmias

In this section, we briefly review the more common arrhythmias in children and other concerning components: supraventricular tachycardia (SVT), ventricular tachycardias, heart block, arrhythmias in congenital heart disease, inherited arrhythmias, and the guidelines for placement of implantable cardioverter-defibrillators (ICDs) and pacemakers in children. A full discussion of all arrhythmias seen in children is beyond the scope of this review. Please refer to textbooks of pediatric cardiology and electrophysiology for a thorough discussion of pediatric arrhythmias.

Supraventricular Tachycardia

Supraventricular tachycardia (SVT) is the most common tachyarrhythmia in children. It originates above the bundle of His and is classified into one of three major categories:

• reentrant tachycardia using an accessory pathway (atrioventricular reentrant tachycardia, AVRT)

• atrioventricular nodal reentrant tachycardia (AVNRT)

• atrial ectopic tachycardia

Presentation: SVT can present at any time from the neonatal period to adulthood. Clinical presentation often includes palpitations (usually a sudden onset of a fast heart rate) and can also include dizziness, chest pain, shortness of breath, and syncope in older children and adults. Neonates and infants may present with irritability, lethargy, and poor feeding from persistent SVT. The heart rate can be as high as 220-320 beats per minute in infants and toddlers.

Diagnosis: Relevant studies may include an ECG, Holter monitor, or exercise stress test.

Treatment: Immediate treatment may include vagal maneuvers, adenosine, or synchronized cardioversion. Some patients may then be started on a daily medication (e.g., propranolol, digoxin, or flecainide) to prevent recurrent episodes. Patients in whom medication does not control SVT may ultimately need to undergo ablation of the abnormal circuit in the electrophysiology lab. Although SVT is not usually dangerous, it can affect the heart’s function if left untreated.

(Source: Supraventricular Tachycardia. N Engl J Med 2006.)

Note that there are no discernable P waves prior to the QRS complexes. (Source: ECG courtesy of Dr. Cheyenne Beach, Yale New Haven Children’s Hospital.)

The Wolff-Parkinson-White (WPW) syndrome: In the WPW syndrome, an accessory pathway is present that predisposes to SVT. WPW can be identified in patients at any age. As many as two-thirds of affected infants will outgrow WPW by age 1 year, although they carry a risk for recurrence later in childhood. Infants are generally treated with a beta-blocker for the first year of life to prevent SVT. Digoxin is contraindicated in WPW because it can decrease conduction down the AV node, leading to preferential conduction down the accessory pathway. Older children and adults can undergo an exercise stress test to risk-stratify the pathway and determine the need for an electrophysiology study and ablation.

In sinus rhythm, the atrial impulse reaches the ventricles via both the AV node and the accessory pathway. This causes the appearance of a delta wave on ECG (see figure below). When SVT is triggered, the atrial impulses most commonly travel down the AV node and back up the accessory pathway, leading to a narrow-complex tachycardia. Occasionally, the reentry impulse passes down the accessory pathway and up the AV node, leading to a wide-complex tachycardia. Patients who have WPW are at particular risk if they develop atrial fibrillation. Atrial fibrillation, by way of the accessory pathway, can lead to a rapid ventricular response and ventricular fibrillation. On ECG, a wide-complex, irregularly irregular tachycardia will be seen. Patients with such high-risk pathways should undergo an electrophysiology study and ablation.

(Source: A Molecular Basis for Wolff-Parkinson-White Syndrome. N Engl J Med 2001.)

(Source: A Molecular Basis for Wolff-Parkinson-White Syndrome. N Engl J Med 2001.)

(Source: ECG courtesy of Dr. Cheyenne Beach, Yale New Haven Children’s Hospital.)

Ventricular Tachycardia

Ventricular tachycardia (VT) is an arrhythmia that causes the ventricles to beat too fast and is relatively uncommon in children. As a result of VT, the heart cannot fill completely with blood between each beat, which in turn can lead to fainting or cardiac arrest. Ventricular tachycardia may occur in children with normal hearts and those with heart disease. In addition to an ECG, an echocardiogram may be performed to look for any structural cardiac abnormalities. Treatment options may include lifestyle changes, medications, ablation, or ICD implantation.

(Source: ECG courtesy of Dr. Cheyenne Beach, Yale New Haven Children’s Hospital.)

Heart Block

When the heart is in normal sinus rhythm without heart block, there is a P wave before every QRS complex and a QRS after every P wave and normal intervals. In heart block, this pattern is disrupted. There are four general categories of heart block:

• First-degree atrioventricular (AV) block: In first-degree block, all the signals that originate from the sinus node travel down to the ventricles, but the time for these beats to go across the AV node is consistently longer than accepted normal ranges. The PR interval will look prolonged on ECG.

• Second-degree AV block Mobitz type I (Wenckebach block): If a patient has Wenckebach heart block, the time it takes to conduct consecutive sinus beats to the ventricles becomes longer and longer, until eventually a beat is “dropped,” or does not conduct down to the ventricles. The ECG will show progressively longer PR intervals until there is a nonconducted P wave representing the dropped beat.

• Second-degree AV block Mobitz type II: Mobitz type II occurs when every now and again one sinus beat is blocked and fails to reach the ventricles. There can be a pattern to the block (e.g., every other beat is blocked from the ventricles), or it can be sporadic, with random beats dropping.

• Third-degree AV block (complete heart block): When a patient has complete heart block, the electrical activity of the top and bottom of the heart is not coordinated in any way. The ventricular heart rate may not raise appropriately, even when the body needs the ventricles to pump more blood, such as during exercise or while playing sports. On ECG, the P waves will occur at a different rate than the QRS complexes.

Inherited Arrhythmia Syndromes

Inherited arrhythmias include channelopathy syndromes, such as:

• Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a life-threatening ventricular tachycardia triggered by the body’s release of catecholamines (hormones such as adrenaline). Catecholamines are released at times of stress or exercise.

• Long-QT syndrome (LQTS) is due to abnormal flow of ions in the cardiac cells leading to a prolonged QT interval on ECG. This can predispose to life-threatening ventricular arrhythmias.

• Brugada syndrome is a rare genetic channelopathy, which can predispose to life-threatening ventricular arrhythmias.

Channelopathies are ion channel disorders of cardiac cells, affecting the influx or efflux of certain ions. Channelopathies increase a child’s risk for life-threatening aberrant heart rhythms and sudden cardiac death. Diagnosis may include ECG, exercise stress testing, Holter monitor, and/or genetic testing. Referral to a pediatric electrophysiologist should be made if any of these syndromes are suspected. More details of these syndromes are beyond the scope of this review. Please refer to the guidelines and reviews provided with this rotation guide.

(Source: ECG courtesy of Dr. Cheyenne Beach, Yale New Haven Children’s Hospital.)

Arrhythmias and Congenital Heart Disease

Arrhythmias can develop in patients with CHD due to thickening or weakening of the heart muscle, abnormal heart anatomy, abnormal circulation, or scarring from prior surgeries. These arrhythmias include:

• SVT

• atrial flutter/atrial fibrillation

• sinus node dysfunction

• junctional rhythm

• ventricular tachycardia

• various degrees of heart block (AV node block)

Implantable Cardioverter-Defibrillators and Pacemakers

The following recommendations reflect the 2021 PACES Expert Consensus Statement on the Indications and Management of Cardiovascular Implantable Electronic Devices in Pediatric Patients.

Pacemakers

Pacemakers in children are placed either in the abdomen or upper chest, depending on the size of the child.

Indications: Common class I indications for permanent pacemaker implantation in children include the following:

• sinus node dysfunction with symptomatic age-appropriate bradycardia

• symptomatic sinus node dysfunction secondary to chronic medical therapy for which there is no alternative treatment

• congenital complete atrioventricular block (CCAVB) with symptomatic bradycardia

• CCAVB with a wide QRS escape rhythm, complex ventricular ectopy, or ventricular dysfunction

• CCAVB with heart rate <50 bpm in asymptomatic neonates or infants

• symptomatic idiopathic advanced second- or third-degree AV block

• persistent postoperative high second- or third-degree AV block for at least 7-10 days after cardiac surgery

• late-onset second- or third-degree AV block in patients with a history of cardiac surgery and transient postoperative AV block

• CCAVB and complex congenital heart disease with bradycardia associated with hemodynamic compromise or heart rate <60-70 bpm in neonate or infants

• persistent symptomatic bradycardia after cardiac transplantation

• channelopathy with pause-dependent clinically significant ventricular tachycardia

• high-grade AV block attributable to a known potential reversible cause that does not resolve despite treatment

Implantable Cardioverter-Defibrillators

ICDs are implantable devices that can cardiovert, defibrillate, or pace the heart. These devices are typically placed for life-threatening arrhythmias.

Indications: Common class I indications for ICD placement in children include the following:

• prior cardiac arrest due to ventricular fibrillation (VF) or hemodynamically unstable ventricular tachycardia (VT) after excluding reversible causes

• long QT syndrome (LQTS) in patients who survived cardiac arrest and are on beta blockers

• catecholaminergic polymorphic ventricular tachycardia (CPVT) with cardiac arrest or arrhythmogenic syncope despite medical therapy

• Brugada syndrome, hypertrophic cardiomyopathy, or arrhythmogenic cardiomyopathies in patients who survived cardiac arrest

• sustained VT in patients with CHD regardless of hemodynamic effect

• syncope due to an arrhythmia