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DOI: 10.1542/pir.31-9-3752010;31;375Pediatrics in Review

Eric A. BiondiFocus on Diagnosis : Cardiac Arrhythmias in Children

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Cardiac Arrhythmias in ChildrenEric A. Biondi, MD*

IntroductionAlthough most childhood arrhyth-mias are benign, prompt and correctdiagnosis of a serious rhythm distur-bance in a child can be lifesaving.Such rhythm disturbances may ariseat any age and have a wide variety ofpresentations. This article discussesvarious pediatric arrhythmias thatmay be encountered by the commu-nity pediatrician, highlighting theirpresentation, findings on electrocar-diography (ECG), and when to referfor additional evaluation.

The Sinoatrial NodeSinus Rhythm and SinusArrhythmia

Some rhythm disturbances originatewithin the sinoatrial (SA) node. Thiscardiac pacemaker is located in theupper wall of the right atrium andinitiates electrical conduction throughthe cardiac muscle. The term sinusrhythm designates normal heartrhythm controlled by this node.ECG shows a P wave with a leftwardand inferior axis before each QRScomplex and a normal PR interval(120 to 200 msec).

Sinus arrhythmia occurs inhealthy children and is described asa decrease in SA node firing subse-quent to activation of the vagus nerveby exhalation. The heart rate, thus,varies with respiration, and ECGshows sinus rhythm with a prolonga-tion of the R-R interval during ex-halation. Such prolongation may besuppressed with exercise or othercauses of sinus tachycardia. This find-ing is normal and is not a reason forreferral.

Sick Sinus SyndromeAlthough most significant arrhyth-mias occur below the SA node, oneemanating from the SA node, sicksinus syndrome (SSS), is worthmentioning briefly. This rhythm isa result of SA nodal dysfunctionand is seen most often in patientswho had prior cardiac (especiallyextensive atrial) surgery or cardio-myopathy. Although many forms ofSSS are asymptomatic, common clini-cal manifestations include shortnessof breath, chest pain, and syncope.The rhythm is characterized bybrady- and tachyarrhythmias. ECGmay show SA block, atrial fibrillation(AF), or supraventricular tachycardia(SVT). Patients suspected of havingSSS should be referred to a cardiolo-gist for additional evaluation.

The AtriaSeveral common rhythm distur-bances can arise within the atria.ECG findings associated with atrialrhythms generally involve changes tothe P wave or P-R interval.

Premature Atrial ContractionsPremature atrial contractions (PACs)are very common in asymptomaticpediatric patients and are benign.They arise when an ectopic focusstimulates the atria without inputfrom the SA node. Although theymay be caused by drug use, caffeine,or electrolyte imbalances, the incit-ing factor usually is unknown. Pa-tients infrequently report feeling a“skipped beat” or “pause,” often fol-lowed by a strong beat, which is theresult of prolonged filling time be-fore resumption of sinus rhythm. Ifhistory, physical findings, and ECGare diagnostic, the patient can be re-assured, and no additional evaluationis necessary. If the patient is bothered

*Resident in Pediatrics, University of RochesterMedical Center, Rochester, NY.

Abbreviations

AET: atrial ectopic tachycardiaAF: atrial fibrillationAP: accessory pathwayAV: atrioventricularAVNRT: atrioventricular nodal

tachycardiaECG: electrocardiographyLQTS: long QT syndromePAC: premature atrial

contractionPVC: premature ventricular

contractionQTc: corrected QT intervalSA: sinoatrialSSS: sick sinus syndromeSVT: suptraventricular

tachycardiaVF: ventricular fibrillationVT: ventricular tachycardia

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by PACs, known inciting eventsshould be avoided.

Common ECG findings of PACsinclude premature, inverted, or oddlyshaped P waves, indicative of an ec-topic atrial focus, and sharp inflec-tions, often within the T waves (Fig.1). If the premature beat occurswhile both bundle branches are po-larized, it is conducted to both ven-tricles simultaneously, resulting in anormal QRS complex. If one of thebranches is refractory, the beat con-ducts along the opposite bundlebranch, resulting in a wide QRScomplex. Finally, if both ventriclesare refractory, the beat is not con-ducted and no QRS complex isformed. This is known as a blockedPAC. In older patients, such episodesare commonly but not invariablysuppressed during exercise as a resultof the sinus tachycardia. Referral to apediatric cardiologist is unnecessary.

It is important to remember thatalthough most PACs are benign,they may occur rarely in infants in abigeminal, blocked fashion, causingfeeding intolerance and decreasedcardiac output because of the slowheart rate. These unusual patientsshould be referred to a pediatric car-diologist.

Atrial Flutter and FibrillationAtrial flutter is another relativelycommon arrhythmia that is charac-terized by atrial rates of 250 to400 beats/min. Arising in newbornswho have normal hearts and older

children born with structural heartdisease, atrial flutter is caused by areentrant circuit confined to the rightatrium. Infants may present withcongestive heart failure, and olderchildren may have dizziness, syn-cope, chest pain, and shortness ofbreath. The major clinical clue is theheart rate. In children, atrial fluttercan be conducted to the ventriclesin a 1:1 fashion, resulting in ventric-ular contractions of more than300 beats/min, or in a ratio of 1:2,causing rates of 150 to 200 beats/min. In infants, the ECG often showsclassic inverted “saw-tooth” deflec-tions, best seen in leads II, III, andaVF, that usually are inverted if thepatient has the typical, counterclock-wise reentrant pathway. The patientshould be referred for urgent cardiacevaluation and treatment. Neonatalatrial flutter rarely reoccurs after si-nus rhythm is restored. It is im-portant to note that atypical atrialflutter, characterized by slower, morerounded P waves of lower voltageseparated by an isoelectric line, is apotentially lethal arrhythmia, usuallyoccurring in the setting of complexheart disease in older children.

AF is uncommon in young chil-dren, although there is evidence tosuggest that it is underreported inadolescents. The rhythm derives itsname from rapid fibrillation of theatrial muscle without coordinatedcontraction and most often is theresult of structural heart disease caus-ing stretching of the atria. AF gener-

ally is not life-threatening but cancause palpitations, chest pain, or syn-cope. Careful examination of a pa-tient’s pulse shows an irregularly irreg-ular rhythm. ECG showing absent orvery low-voltage P waves and an ir-regular R-R interval confirms the di-agnosis. If AF is suspected but theECG tracing is normal in the office,24-hour outpatient Holter monitor-ing or the use of event recorders maybe of assistance. Any patient who hasthe new diagnosis of AF should bereferred to a pediatric cardiologist. Itis very important to have the patientseen urgently because prolonged(usually �24 hour) fibrillation orflutter can result in clot developmentwithin the left atrium. With resump-tion of sinus rhythm, the clots canembolize, resulting in stroke, myo-cardial damage, or other end-organinfarctions.

The Atrioventricular Nodeand SupraventricularTachycardias

Supraventricular TachycardiaSVT is defined as a rapid tachycardiaoriginating above the bundle of His.It occurs in as many as 1 in 250children but often is misdiagnoseddue to the variety of presentationsit may cause. There are many differ-ent mechanisms for SVT, but theycan be divided into three major cate-gories: reentrant tachycardia usingan accessory pathway (AP); reentrantatrioventricular nodal tachycardia(AVNRT), typically seen in adoles-cents; and atrial ectopic tachycardia(AET).

In infants, SVT may present withheart rates of 220 to 270 beats/min.Infants who experience prolongedSVT may have a history of poor feed-ing, pallor, irritability, and lethargy.The arrhythmia often is diagnosedafter 24 or 48 hours of sustainedSVT, when hemodynamic decom-

Figure 1. There is a premature atrial complex (PAC) after the third sinus QRS. Noticethe premature, inverted P wave. The prolonged pause before the next beat suggeststhat the ectopic beat has reset the sinoatrial node. The QRS complex is normal,indicating that both bundle branches were polarized before the PAC.

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pensation arises and congestive heartfailure develops.

School-age children can verbalizesymptoms and, therefore, usually areseen before developing heart failure.They may complain of “beeping inmy chest,” heart pounding, chestpain or fullness, shortness of breath,sweating, or exercise intolerance.They almost never experience syn-cope. The tachycardia rate is slower,usually 180 to 240 beats/min ratherthan the approximately 220 to270 beats/min seen in infants.

Adolescents experience similarsigns and symptoms as seen withschool-age children, but they aremore capable of precise descriptions.It is useful to ask the patient to de-scribe the heart rate during the epi-sodes, which typically last from a fewseconds to a few hours. History of aheart rate that is “too fast to count,”a pounding sensation in the neck,or an abrupt resolution of palpita-tions, often after vagal maneuvers, ishelpful. Another clue is the descrip-tion of a “switch on-switch off”tachycardia rather than a pattern ofprogressive acceleration or decelera-tion. Occasionally, a school nurse orcoach will have counted the pulserate. Such findings help to distin-guish SVT from other commoncauses of similar symptoms in adoles-cents such as anxiety, stress, caffeineconsumption, or dehydration, all ofwhich cause sinus tachycardia.

SVT in infants may be difficult todifferentiate from sinus tachycardiaby ECG. SVT usually manifests as anarrow complex (�80 msec) tachy-cardia with a nonvariable heart rategreater than 220 beats/min. P wavesoften are difficult to see but may beseen as sharp deflections within the Twaves.

In older children, ECG findingsvary, based on the mechanism ofthe SVT. In patients who have AP-mediated reentry tachycardia, ECG

characteristics differ based onwhether the antegrade current iscarried by the atrioventricular (AV)node or the accessory pathway. If theAP carries such a current, as in Wolff-Parkinson-White syndrome (a condi-tion in which an aberrant AP causespre-excitation of the ventricles), theclassic findings are a shortened PRinterval and “delta waves,” a gradualsloping of the R wave caused by thepre-excitation (Fig. 2). If the AVnode carries the antegrade current,ECG shows a narrow complex tachy-cardia and typically lacks obvious Pwaves. In this case, sharp upward de-flections in the T waves, representingretrograde conduction through theAP, may be seen.

In AVNRT, which occurs morecommonly in older children, heartrates often are slower without visibleP waves, which are buried within theQRS complexes, and an initiatingevent such as a PAC may be identi-fied. Lastly, the ECG in AET mayshow a variable heart rate of up to330 beats/min with abnormal Pwaves. This form of SVT is importantto identify because rates this fast arepoorly tolerated and affected patientscan develop a cardiomyopathy.

When a patient is suspected ofhaving any form of SVT, cardiac re-ferral is indicated. Ambulatory ECGmonitoring devices (Holter monitorsor event recorders) are useful for di-agnosing SVT in patients who havesporadic episodes. Compared withHolter monitors that capture events

in only a 24- or 48-hour period,event recorders can operate for upto 1 month and are activated by thepatient when symptoms occur. Therecorded ECG is sent via telephoneto a cardiologist for analysis. Electro-physiologic study is the definitivemethod of diagnosing the mecha-nism underlying the SVT and is usedfor identification of the AP, whichcan be treated with radiofrequencyablation.

The VentriclesThe ventricles comprise the final car-diac area in which arrhythmias candevelop, and although several dan-gerous arrhythmias can develop here,this discussion focuses on the ven-tricular disturbances most likely topresent to an outpatient office. Twouncommon but potentially lethal ar-rhythmias also are mentioned.

Premature VentricularContractions

Premature ventricular contractions(PVCs) are caused by ectopic firingswithin the ventricle and, althoughless common than PACs, may occurin as many as 25% of healthy children.Patients usually are asymptomaticbut may report chest fullness, dizzi-ness, or a feeling that the “heartskips” and then resumes with astrong beat.

Twelve-lead ECG always shouldbe obtained in a patient suspectedof having PVCs to allow the clinicianto assess PVC morphology. Holter

Figure 2. Wolff-Parkinson-White (WPW) syndrome. Delta waves, a wide QRS complex,and a short P-R interval (here it is 40 msec) are classic ECG findings in WPW syndrome.

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or event monitoring may be usefulin documenting infrequent episodes.The PVC itself appears as a prema-ture, bizarre, wide QRS complex notpreceded by a P wave and often fol-lowed by a compensatory pause (Fig.3). The pause is associated with in-creased ventricular filling and in-creased stroke volume of the nextbeat that may be noticed by the pa-tient as a pause followed by a strongbeat. If the PVC occurs close enoughto the next sinus beat, a fusion beatmay occur that has characteristics ofboth a PVC and a normal QRS com-plex. If they are frequent, PVCs mayoccur with every other beat (bigem-iny) or every third beat (trigeminy).

PVCs are benign if they are single,uniform in appearance, and sup-pressed or at least not aggravated byexercise and there is no evidence ofunderlying heart disease or familyhistory of sudden, early death. Forpatients who have abnormal familyhistories, the clinician should bemore suspicious of the potential fordangerous ventricular arrhythmias,and those patients should be referredto a pediatric cardiologist for addi-tional evaluation.

Long QTc SyndromeThe long QT syndrome (LQTS) isassociated with a potentially danger-ous ventricular arrhythmia, torsadesde pointes. Although not every pa-tient who has a prolonged correctedQT interval (QTc) has LQTS, an

interval of more than 450 msec issuggestive of LQTS and more than470 msec is considered abnormal(Fig. 4). Using the QTc, calcu-lated as the QT interval divided bythe square root of the previous R-Rinterval, is important because thatvalue “corrects” the QT interval forthe patient’s heart rate. There isoften a family history of unexplainedsudden death (50% in symptom-atic patients). Patients can presentwith syncope, seizures, palpitations,and cardiac arrest. As many as 10%have episodes of sudden death. Fre-quently, a previously healthy patientreports fainting spells while swim-ming, playing sports, or exercising.Several genetic cases of LQTS havebeen identified. Specifically askingabout congenital deafness in the fam-ily can provide a clue to the diagnosisbecause deafness often is associatedwith a particularly malignant form ofhereditary LQTS. Any patient whohas symptoms and even a borderlineprolonged QTc should be referred toa pediatric cardiologist.

Ventricular TachycardiaVentricular tachycardia (VT) in chil-dren is defined as a tachycardia ofat least three successive ventricularbeats. It is referred to as nonsus-tained if the rhythm lasts less than30 seconds and terminates spontane-ously. If it lasts longer than 30 sec-onds, it is considered sustained andusually requires therapeutic interven-tion.

VT in the pediatric populationoccurs most commonly in childrenwho have abnormal hearts. Althoughmany patients are asymptomatic,symptoms such as pallor, fatigue, andchest palpitations may occur. In in-fants, VT often manifests as feedingintolerance. Among children whohave healthy hearts, VT carries agood prognosis, in contrast to VT inchildren who have abnormal heartsor a history of cardiac dysrhythmias.Causative factors include use ofdrugs, caffeine, and decongestants aswell as electrolyte imbalances andunderlying cardiac disease.

On physical examination, theremay be evidence of unsuspected con-genital or acquired cardiac disease.ECG shows a bizarre, wide QRScomplex (�120 msec) tachycardia,which usually has a regular rhythm(Fig. 5). P waves may or may not berecognizable, depending on the ven-tricular rate, and T waves typically areopposite in polarization to the QRS.The QRS complexes may vary inappearance if the ectopic input ismultifocal. Any patient identified as

Figure 3. Ventricular bigeminy with premature ventricular beats (PVCs) occurring aftereach sinus beat. The PVCs are uniform, are bizarre, demonstrate wide QRS complexeswithout a preceding P wave, and show T-wave inversion. There is also a prolongedpause after each PVC.

Figure 4. Long QT syndrome. The interval from the Q wave to the time at which theT wave returns to the isoelectric point is prolonged. This ECG also demonstrates sinusarrhythmia, a normal finding, with prolongation of the R-R interval during exhalation.To calculate the corrected QT (QTc) interval, the formula QT/� previous R-R is used.The corrected QT interval (QTc) here is 505 msec. (48/�90)

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having VT should be assessed imme-diately for hemodynamic instability.Once clinically stable, such patientsrequire a cardiac evaluation, includ-ing radiography, echocardiography,exercise stress testing, and 24-hourHolter monitoring.

Ventricular FibrillationVentricular fibrillation (VF) is a rarecardiac emergency caused by unco-ordinated activity of the cardiac mus-cle fibers, often resulting in cardiacarrest. The heart tremors rather thancontracts and, therefore, pulses arenonpalpable. The confirmatory diag-nostic test is ECG, which shows a

bizarre, random waveform withoutclearly identifiable P waves or QRScomplexes and a roaming baseline.Any patient suspected of having VFrequires advanced cardiac life sup-port intervention because circulationmay cease within seconds of onset. Inthe acute setting, such treatment in-volves the use of an electric defibril-lator.

Although many clinicians may goan entire career without seeing anepisode of VF, its rarity makes it allthe more dangerous. Because this ar-rhythmia occurs most commonly inchildren after heart surgery, and thenumber of children surviving opera-

tive congenital heart disease is in-creasing, it is important to have atleast a cursory knowledge of theacute diagnosis and management ofVF.

ACKNOWLEDGMENT. I would liketo thank Dr J. Peter Harris for hisguidance and support in the writingof this article.

Figure 5. Ventricular tachycardia. The heart rate is approximately 200 beats/min, andthe QRS complexes are wide (>120 msec). The QRS complexes vary in appearance,suggesting multifocal ectopic input. Summary

• As in many aspects of medicine,a thorough history is vital foridentification and diagnosis ofcardiac arrhythmias in childrenand can help differentiate abenign arrhythmia from apathologic one.

• In most cases, ECG issatisfactory for diagnosis.However, if the pediatricianfeels that ECG is insufficient, itis best to refer the patient to acardiologist for furtherevaluation.

focus on diagnosis




DOI: 10.1542/pir.31-9-3752010;31;375Pediatrics in Review

Eric A. BiondiFocus on Diagnosis : Cardiac Arrhythmias in Children

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