Pediatric ECG Interpretation: Normal Tracings From Children of Various Ages

Pediatric ECGs vary by age;tracings change considerablyfrom birth through adulthood.In the ECG tracing above, theT waves are inverted. Nevertheless,as we outline here, the tracingis normal in a 9-year-old child; theT waves may not revert to normaluntil he reaches puberty.Databases that contain normalreference tracings are rarely availablefor primary care providers who seepatients in the emergency departmentor office settings. Office ECGmachines produce interpretationsthat often cannot be substantiated bythe practitioner by referencing visualcopies that are normal because normaltracings are difficult to locate.Needless to say, problematic tracingsand irregularities suggest overreadingor the need for consultation withcardiologists familiar with pediatricECGs.This is the first of 2 articles inwhich we present a database of normal pediatric ECGs. The tracings arearranged according to age starting at2 days and continuing to 14 years.Each ECG is accompanied by a briefdiscussion of the pathophysiology ofthe changes that produce the varioustracing patterns.Normal ECG tracings of childrenfrom 4 years to 14 years old will appearin an upcoming issue.PATHOPHYSIOLOGYPediatric tracings show higherheart rates and narrower QRS complexes;they are often "noisier" andhave more artifacts than adult ECGs.¹Tracing patterns normally change as a child ages; however, the greatestchanges are seen in the first fewweeks of life as a result of circulatorychanges at birth.²Before birth, the right ventricle(RV) pumps blood into the aorta viathe ductus arteriosus. To shunt bloodacross the ductus, the RV must producea higher pressure than the leftventricle (LV) and must work againsta higher resistance than the LV.³ TheRV, therefore, gains more mass in thefetal period because it works harderthan the LV--making it the dominantventricle at birth by weight and tracingimage.After delivery, significant changesin the circulatory system occur.Systemic peripheral resistance increasesafter cessation of the placentalcirculation.Lung expansion results in theopening of more vascular channels onthe RV side. The open pulmonary vascularsystem lowers pulmonary resistanceand reduces the necessity forthe RV to produce enough pressureto shunt blood through the ductusarteriosus, which now begins to close.RV pressure, therefore, decreasesdramatically during the first week oflife and LV pressure increases. Thereafter,the LV gains mass quickly,becoming the dominant ventricle.⁴The LV wall continues to thickenas systemic arterial pressure risesover time. Concomitantly, the RV wallprogressively becomes relatively thinnerbecause of the decrease in pulmonaryarterial pressure.² The LV is alwayssignificantly larger than the RVby 1 month. The LV/RV ratio approachesthe adult value by 3 to 6months. However, the ECG is not thesame as an adult's at this point, sincethe chest dimension and the size ofthe infant's heart and its positionwithin the chest affect the tracing.⁴ECG FINDINGSAs a result of the RV dominancerequired to push blood through thepatent ductus, and the relative weaknessof the LV caused by the lowarterial resistance secondary to theplacental circulation, the neonate'sECG demonstrates rightward and anterioraxis deviation (Table 1).⁵ TheT waves are usually inverted in leadsV₁ through V₄. Persistence of uprightT waves after the first week of lifein leads V₁ through V₄ is abnormal.6,7After closure of the ductus arteriosus,with cessation of the placentalcirculation (which provides low resistance)and opening of the pulmonarycirculation, the pattern reverses; bythe end of year 1, the adult LV dominantleftward and posterior QRS axisbecomes the norm. The anterior precordialT waves then usually becomeprogressively positive, although negativityof lead V₁ (occasionally V₂ andV₃) may persist for some time (seeTable 1).Pediatric heart rates are normallyhigher than those of adults; therates slow as the child grows older(Table 2). Other durations and intervalsof the ECG increase from infancyonward as well.⁸ There may be differencesin tracings because of size andgender as well as age; the QRS intervalsof females are slightly shorterthan those of males.⁹ Racial differencesare also present; these are unpredictable,however, and of minorclinical importance (eg, T waves arepersistently inverted further to theleft in African American children) andare not further discussed here.^7,10The importance of such differencesawaits more definitive analysis usingdata based on newer techniques,such as signal-averaged ECGs.^10-12

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