Pediatric Annals

Evaluating Cardiovascular Presentations: What Does an Electrocardiogram Have to Offer?

David M Bush, MD, PhD

Abstract

SCREENING TRENDS

Screening for uncommon disorders is one of the cornerstones of general pediatric practice and forms the basis of newbom evaluations, state metabolic screening, and health supervision assessments. Examples of these endeavors include universal newborn hearing assessment27 and screening for congenital hypothyroidism.28 In both instances, several criteria required of a successful screening program are said to be met: the condition of interest is both sufficiently frequent and important; early detection can alter the natural history of the disease positively; a sufficiently sensitive and specific screening test exists; a reliable gold standard exists to confirm the diagnosis; and testing is of sufficiently low cost and low resource use so as to be generally applicable to a large population.

While all health supervision can be considered a form of screening, the use of routine ancillary cardiac studies for the purpose of cardiovascular risk assessment in otherwise asymptomatic patients remains controversial, regardless of the age of the patient.10,29-30 In discussions of the role of routine pulse oximetry in the newborn nursery to detect asymptomatic complex congenital heart disease, or of electrocardiogram or echocardiogram studies as an adjunct to the standard sports pre-participation examination, arguments against their use return to the lack of fulfillment of the above screening criteria. To be clear, no test available can be guaranteed to provide perfect disease detection; even those accepted noncardiac screening programs mentioned above have both false positive and false negative results. Thus, the issue devolves into a consideration of the economics of screening - the cost per case identified, and the savings derived from early disease recognition.

Present published recommendations have not supported the use of ancillary screening studies in the United States, although they are employed in various settings internationally30 and have even suggested a reduction in the incidence of sudden death in selected circumstances.31 As a consequence, community practice may vary widely, potentially including pulse oximetry, electrocardiogram, and echocardiogram at various times in a child's life in an effort to identify latent cardiac disease. In no area is this truer than in sports pre-participation screening, where often grass-roots efforts are the start of community-wide programs employing electrocardiograms, echocardiograms, or both.

For the general practitioner confused about his or her role, the key is to be aware of the controversy and to recognize the limitations of the screening tool in the particular population to which it is being applied. The practitioner should remember that screening tools are just that - for screening purposes - and should not take the place of clinical regarding the need for additional ancillary testing in the proper clinical scenario. At the same time, it is imperative that the general practitioner advocate for (and, if possible, participate in) population-based studies to address the utility of these screening programs.

SUMMARY

The general pediatrician remains the key to the timely recognition and treatment of cardiovascular disorders, particularly those that present acutely and may require immediate attention. In the evaluation of these cardiovascular urgencies, ancillary studies such as the electrocardiogram continue to be important, readily available tools that can aide in the diagnostic process. It is thus incumbent on the general practitioner to foster the skill necessary to employ such tools reliably, particularly in the setting of urgent evaluations. At the same time, recognition of the limitations of such testing will help both in the acute setting and in the understanding of their application in population settings.

1. Wellens HJ, Gorgels AP. The electrocardiogram 102 years after Einthoven. Circulation. 2004;109(5):562-564.

2. Pediatric and Internal Medicine Program Requirements, Accreditation Council for Graduate Medical Education (ACGME). June 2005. Available at: http://www.acgme.org. Accessed October 18, 2005.…

Office-based cardiovascular urgencies can comprise a wide array of conditions, from arrhythmias to structural heart disease. The pediatric electrocardiogram can play a significant role in establishing a diagnosis in many of them. This article reviews four common pediatric cardiovascular presentations in routine practice - murmurs, chest pain, palpitations/arrhythmia, and syncope - with special focus on urgent diagnoses. Emphasis is placed on both the role and limitations of pediatric electrocardiograms in the evaluation of these presentations. Concluding comments are made regarding the special situation of cardiovascular screening in light of recent policy statements.

CARDIOVASCULAR PRESENTATIONS

Evaluation of cardiovascular conditions in routine practice occurs during most visits, whether in the care of acute patient concerns or as part of screening during health maintenance examinations. While presentation of true cardiovascular emergencies in this setting is rare, the occurrence of cardiovascular urgencies - conditions that warrant timely treatment or referral to reduce morbidity or mortality - is more common and necessitates an understanding of a broad spectrum of cardiac dis-or ders and therapies.

Figure 1. Electrocardiogram from a 4-week-old boy with hypoplastic left heart syndrome. Note the presence of right atrial enlargement (tall P waves in Lead II) and right ventricular hypertrophy with strain (tall Rwavesin Lead V1 - qR pattern - with downward sloping T waves). While these findings areabnormal and should warrant further investigation, they are not diagnostic and could equally be the result of right-sided cardiac obstruction.

Figure 1. Electrocardiogram from a 4-week-old boy with hypoplastic left heart syndrome. Note the presence of right atrial enlargement (tall P waves in Lead II) and right ventricular hypertrophy with strain (tall Rwavesin Lead V1 - qR pattern - with downward sloping T waves). While these findings areabnormal and should warrant further investigation, they are not diagnostic and could equally be the result of right-sided cardiac obstruction.

In the typical office setting, however, availability of ancillary testing and treatments may be severely limited, particularly in practices that are separated geographically from pediatric hospital or emergency faculties. As a result recognizing key historical concerns and worrisome physical findings is vital to timely triage and treatment. Equally important, however, is the knowledge of what can be gained from "additional testing," given the time and effort often needed to obtain it.

The electrocardiogram is one of the tests that has played a significant role in the diagnosis of cardiovascular disorders for more than 100 years.1 While initial emphasis was placed on the use of the routine electrocardiogram in the diagnosis of ischemic and arrhythmic diseases, pediatricians recognized early the value of this unique tool in the diagnosis of various forms of congenital and acquired heart diseases of childhood. The advent of additional diagnostic modalities such as echocardiography, however, has resulted in a shift in the emphasis placed on electrocardiogram interpretation in routine practice. This change is reflected in recent pediatric residency training guidelines that no longer mandate teaching of electrocardiogram interpretation This stands in contradistinction to internal medicine training guidelines, which continue to stress, "All residents must develop competency in interpretation of electrocardiograms."2 The change in guidelines has occurred despite the continued suggestion of contemporary literature that inexpensive tests such as an electrocardiogram may add to diagnostic accuracy in a cost-beneficial manner in selected cases.3

Cardiovascular urgencies presenting in the pediatric office setting typically fall into one of four groups: murmurs (suggesting significant heart disease), chest pain, palpitations (or arrhythmias), and syncope. These categories often are not mutually exclusive, with disease entities potentially fitting into more than one. Regardless of the group, however, understanding possible situations that may require urgent attention begins with an appreciation of the differential diagnosis. This is influenced significantly not only by the age of the patient but also by the historical context of the presentation.

A full review of each of these areas is thus beyond the scope of this article. What follows is a collection of "ones not to miss" - important diagnoses that, when delayed, can have significant effects on patient survival and well-being. In this context, emphasis is placed on the key points from history, physical examination, and ancillary studies (including electrocardiogram) that can help the primary physician arrive at a timely diagnosis.

MURMUR

The majority of pediatric heart murmurs are innocent, regardless of the age at presentation.4 Of the pathologic heart murmurs, those with critical disease (warranting immediate intervention) usually are associated with symptoms, particularly if the diagnosis is arrived upon after neonatal transitioning. Although the majority of critical forms of congenital and acquired heart disease will be evident prior to discharge from the nursery, two in particular deserve further discussion.

Left-Sided Obstructive Lesions

LeftHsided obstructive lesions (LSOLs) represent a spectrum of congenital heart diseases that, in their critical form, are characterized by inadequate blood flow to the body. With a frequency of nearly 0.5 per 1,000 live births, they are encountered routinely in standard pediatric practice.5 The practical implication of this physiology if untreated typically includes hypotension, acidosis, end-organ dysfunction, and, in the absence of intervention, death. The classic form of this disease is hypoplastic left heart syndrome, although many other diseases, including mitral stenosis, aortic stenosis, and coarctation of the aorta, may mimic the same physiology if sufficiently severe.

Presentation of LSOLs vary based on several factors, the most important of which are the presence and size of a patent ductus arteriosus. When ductal patency persists, the presentation may be delayed by as long as 3 to 4 weeks after delivery. During that interval, however, symptoms invariably will occur and may include poor feeding, early satiety, tachypnea, dyspnea, pallor, or lethargy. Infants with delayed presentations (outside the first 72 hours of life) usually gain weight poorly and present to the primary care physician with any combination of the above symptoms. Most often, a diagnosis of neonatal sepsis is entertained before suspected heart disease; the presence of a heart murmur (typically from atrioventricular valve insufficiency due to cardiac dysfunction) and the absence of lower extremity pulses help to differentiate from infectious causes.

The key to identification of LSOLs is maintaining a high index of suspicion. This begins with consideration of the cardiovascular history and examination at each healthcare encounter in the first 6 weeks of life. Special attention should be given to vital signs (including pulse oximetry) and auscultory findings (eg, single second heart sound, possible regurgitant murmur at the left lower sternal border reflecting tricuspid insufficiency, gallop rhythm) and assessment of lower extremity perfusion, including any discrepancy in pulses compared with the upper extremities. Ancillary studies, such as electrocardiography, can offer supportive data, but rarely are diagnostic. As a result, routine use of the electrocardiogram as a sensitive means of "ruling in" or "ruling out" disease in this entity is not recommended (Figure 1, see page 860). Early case discussion with a pediatric cardiologist is essential, because the morbidity of palliative options is tied directly to pre-operative status.6

Intervening in an office setting in a definitive way usually is not possible for LSOLs. Avoiding further feeds and arranging for a timely referral to an emergency department capable of stabilizing the patient are absolutely essential. Stabilization includes prompt establishment of vascular access and initiation of prostaglandin E1 but may also include intubation, neuromuscular blockade, volume expansion, and inotropic support.

Dilated Cardiomyopathy

Dilated cardiomyopathy is a heterogeneous set of entities with a common physiology. The many etiologies result in a wide range of variability in timing of presentation, from early infancy until adulthood, yet symptom complexes are highly similar, differing most only on the basis of age. In this regard, age-dependent differences are the result of both developmental and physiologic variability.

The physiology of dilated cardiomyopathy is similar to LSOL in that inadequate blood flow to the body occurs, typically from decreased myocardial contractility. However, the presence of inadequate blood flow often is overshadowed by the congestion of the pulmonary vascular bed related a dysfunctional heart. During infancy, increased somnolence, poor feeding, early satiety, and pallor may point to inadequate systemic flow. Pulmonary vascular bed congestion may present with dyspnea with exertion (such as during feeding, resulting in early satiety), weak cry, or tachypnea. The combination of ventricular dysfunction and pulmonary venous congestion results in a precarious physiologic state, often ill-suited to weather the stresses of recurrent infectious exposures. This accounts for the frequent presentation of children with these disorders during intercurrent illnesses that "tipped them over" into dilated cardiomyopathy symptoms.

As children grow older, feeding symptoms become less obvious, although a chronic cardiomyopathy (much like in infancy) can be associated with weight loss. Symptoms of exercise intolerance and diminished stamina often are directly proportional to the degree of activity in which the child typically engaged prior to onset of the disease. With many children living increasingly sedentary lifestyles, symptoms can be delayed until activities of daily living are affected.

A danger in diagnosing and treating dilated cardiomyopathy is that clinical symptoms may seem to lag behind underlying physiologic effects. As a consequence, an office presentation of a symptomatic patient typically prompts an immediate emergency department referral, much as would be done for LSOLs. In the earlier stages, however, the office pediatrician can establish the diagnosis through careful attention to physical examination findings. These may include a barrel-chest appearance (in chronic cardiomyopathy), cardiac impulse displacement, more distanced heart sounds, gallop rhythms, regurgitant murmurs (from atrioventricular valve insufficiency), hepatomegaly, and diminished pulse pressure. Use of ancillary studies, such as an electrocardiogram or chest radiograph, often supports a diagnosis of a cardiac abnormality. While a chest radiograph typically demonstrates consistent findings (enlarged cardiothymic silhouette and increased pulmonary venous markings), an electrocardiogram can be highly variable (Figure 2). Findings may include either a marked increase or decrease in voltages, ST- and T-wave changes, and prolongation of cardiac intervals (such as AV block or QTc prolongation). No electrocardiogram finding alone is diagnostic, however.

Figure 2. Electrocardiogram from a 10-year-old girl with dilated cardiomyopathy. Findings include possible ventricular pre-excitation (short PR interval and slurred upstroke of the QRS complex),along with diffuse T-wave changes and a prolonged QTc interval (460 milliseconds). None of these, however,are diagnostic, although they are abnormal and warrant further evaluation.

Figure 2. Electrocardiogram from a 10-year-old girl with dilated cardiomyopathy. Findings include possible ventricular pre-excitation (short PR interval and slurred upstroke of the QRS complex),along with diffuse T-wave changes and a prolonged QTc interval (460 milliseconds). None of these, however,are diagnostic, although they are abnormal and warrant further evaluation.

Office-based therapies for the initial treatment of dilated cardiomyopathy are limited regardless of the etiology. As with LSOLs, food avoidance and arrangement of a timely referral to an emergency department will begin the therapeutic process. Depending on the patient's status, interventions vary widely. In the acute setting, significant relief of the symptoms of pulmonary venous congestion is experienced through the administration of diuretics. Additional medications aimed at improving contractility, reducing systemic afterload and modulating neurohormonal levels may also aid in treatment, though these are usually reserved for the inpatient setting.7 In rare cases, targeted metabolic therapies, such as enzyme replacement, may result in significant improvement The use of immunomodulatory agents, such as intravenous gammaglobulin for acute myocarditis, remains controversial.8

CHEST PAIN

Of all pediatric cardiovascular symptoms presenting to the general practitioner, chest pain remains the most common. Still, a cardiovascular cause to explain this presenting symptom is rare, even when the pain occurs during exertional activities.9 This creates a significant diagnostic challenge, as the clinician attempts to find conditions that may predispose to significant patient morbidity if unidentified. While some of these conditions, such as aortic valve disease, usually are identified much earlier through the recognition of a pathologic heart murmur, others, such as those listed below, may present only when the patient experiences chest pain.

Hypertrophic Cardiomyopathy

With an annual incidence of sudden cardiac death at 1% to 2% among athletes and an attributable fraction of nearly 50%, hypertrophic cardiomyopathy remains a significant focus of sports preparticipation screening.10,11 This form of cardiac muscular hypertrophy, which is associated both with a risk of left ventricular outflow obstruction and malignant ventricular dysrhythmias, most often is asymptomatic. Indeed, based on echocardiographic screening studies in the general population, the prevalence of hypertrophic cardiomyopathy has been estimated to be as high as 1 in 500 people.11 Still, the prevalence of sudden cardiac death is only 1 in 200,000, highlighting the marked disease heterogeneity.

Figure 3. Electrocardiogram from a 15-year-old with hypertrophic cardiomyopathy. Findings include right atrial enlargement (tall P waves in II), biventricular hypertrophy, and diffuse ST segment changes with - wave inversion in the inferior (leads II, III and aVF) and lateral leads (V4-V6). A reading such as this should prompt immediate referral.

Figure 3. Electrocardiogram from a 15-year-old with hypertrophic cardiomyopathy. Findings include right atrial enlargement (tall P waves in II), biventricular hypertrophy, and diffuse ST segment changes with - wave inversion in the inferior (leads II, III and aVF) and lateral leads (V4-V6). A reading such as this should prompt immediate referral.

Because of current recommendations against electrocardiogram or echocardiogram screening for hypertrophic cardiomyopathy in the general population,10 significant focus must be placed on the evaluation of clinical symptoms. These may include dyspnea, chest pain, or syncope, all most frequently occurring with exertion.

The pathophysiology of exertional symptoms is based on the effects of significant myocardial hypertrophy, which results in reduced ventricular compliance and increased myocardial oxygen demands. The outcome, in the case of exercise intolerance, may be restricted filling of the left ventricle during periods of increased cardiac demands or the initiation of subendocardial ischemia. It is the latter that can result in exertional chest pain and that has prompted the "general rule" that a cardiac cause must be ruled out in these instances. The occurrence of syncope is most commonly thought to be the result of an abrupt drop in cardiac output due to sustained arrhythmias (most commonly ventricular), although increased dynamic left ventricular outflow obstruction also may be involved in selected cases.

Establishing the diagnosis begins with aggressively pursuing the above cardiovascular symptoms when reported. Careful attention should be given to historical features as well as to the physical examination, particularly regarding auscultatory findings. In addition to delineating the nature of symptoms and other possible associated cardiovascular complaints, a review of family history is important. The latter may take some investigative work, as families often report early deaths as due to "enlarged heart" without discriminating between hypertrophy and dilation. In the case of the physical examination, it is particularly important to ensure that auscultation of the heart is accomplished in at least two positions (eg, supine and standing), as the murmur of hypertrophic cardiomyopathy often increases when fully upright as a result of decreased venous return and increased dynamic outflow obstruction.

Figure 4. Electrocardiogram from a 4-week-old presenting in cardiogenic shock with a diagnosis of an anomalous left coronary artery from the pulmonary artery (ALCAPA). Note the findings of anterolateral infarction (wide, deep Q waves in Lead I and aVL) that are diagnostic for the condition (arrows). Note the absence of significant ST segment changes, which one often expects with acute coromary syndromes.

Figure 4. Electrocardiogram from a 4-week-old presenting in cardiogenic shock with a diagnosis of an anomalous left coronary artery from the pulmonary artery (ALCAPA). Note the findings of anterolateral infarction (wide, deep Q waves in Lead I and aVL) that are diagnostic for the condition (arrows). Note the absence of significant ST segment changes, which one often expects with acute coromary syndromes.

Although the role of routine screening electrocardiograms or echocardiograms remains controversial, the utility of these diagnostic tools in clinical practice is great. The electrocardiogram lacks perfect positive predictive value but has nonetheless been shown to be efficacious both in identifying patients in whom clinical suspicion exists and in screening family members of index cases.12 As such, it represents an important tool for the general practitioner, as it is more often readily available than an echocardiogram.

Features of the resting electrocardiogram that may be consistent with hypertrophic cardiomyopathy include increased voltages consistent with left ventricular hypertrophy, deep Q waves in the inferior or lateral leads, and diffuse ST- and T-wave changes (particularly inversions; Figure 3, see page 863).

The echocardiogram represents the easiest and most reliable method of diagnosing hypertrophic cardiomyopathy, by documenting left ventricular wall thicknesses greater than those expected after adjusting for body surface area, after excluding normal chamber size, associated structural heart disease (eg, aortic stenosis, coarctation of the aorta) or other systemic causes (eg, systemic hypertension). Yet even this tool lacks perfect sensitivity, owing to the frequent age-dependent delay in phenotypic expression of cardiac hypertrophy. Thus, negative testing must be placed in the context of the clinical circumstances prompting its performance. Genetic testing, while advancing rapidly, remains outside the realm of standard clinical practice.13

Triage and treatment of the patient with suspected hypertrophic cardiomyopathy begins with reviewing the diagnostic concerns with both the patient and family. This is particularly true once the diagnosis has been established. At present, medical therapy appears to play only a small role in reducing the risk of sudden death, although it can be effective in treating symptoms of heart failure when present.12 Automatic internal cardiac defibrillators have been shown to be effective in recognizing and terminating ventricular tachycardia and fibrillation in children (and presumably preventing sudden cardiac death) but come at significant financial and psychological cost.14 The mainstay of therapy for the general practitioner thus is limitation of sports participation, which has been shown to reduce mortality and has therefore formed the basis of recent recommendations.15 The importance of the primary care physician in supporting activity restrictions cannot be underestimated, both as a means to aid the patient in the grieving process associated with the diagnosis and to prevent confusion and possible engagement in high-risk competitive activities.

Coronary Anomalies

Congenital coronary artery anomalies (CAAs) often are considered one of the "silent killers," typically listed as the second most common cardiac cause of sudden death in young athletes. In fact, in populations who have undergone previous standardized screening, such as military recruits, CAAs are far more common than hypertrophic cardiomyopathy and myocarditis combined.16 Among CAAs, the most common cause of sudden cardiac death is an anomalous origin of the left main coronary artery from the right sinus of Valsalva. This coronary orientation places the left main coronary artery between the great arteries, where it may be compressed dynamically during exertional activities, resulting in myocardial ischemia.17

Figure 5. Electrocardiograms from a 12-month-old during (first tracing) and after (second tracing) an episode of supraventricular tachycardia. Note the absence of P waves in the first tracing, along with the rapid rate (280 beats per minute). The patient was hemodynamically stable throughout. In the second tracing, P waves are clearly visible, along with signs of ventricular preexcitation (short PR interval, delta wave, and QRS widening).

Figure 5. Electrocardiograms from a 12-month-old during (first tracing) and after (second tracing) an episode of supraventricular tachycardia. Note the absence of P waves in the first tracing, along with the rapid rate (280 beats per minute). The patient was hemodynamically stable throughout. In the second tracing, P waves are clearly visible, along with signs of ventricular preexcitation (short PR interval, delta wave, and QRS widening).

Diagnosis of coronary artery anomalies by the general practitioner is dependant on a high index of suspicion. If symptoms are present prior to a mortal event, they are typically the result of transient myocardial ischemia. As with hypertrophic cardiomyopathy, these may include exertional chest pain or dyspnea. In this instance, dyspnea with increased work likely is related to a fall in both ventricular systolic and diastolic function with progressive ischemia. Physical examination, however, frequently is normal, as is the resting electrocardiogram. Diagnosis is thus dependent on either direct visualization (through echocardiography or angiography) or documented ischemia (during exercise stress or perfusion testing). Treatment consists of limitation of exertional activities and surgical coronary artery reimplantation.18 The role of the general practitioner is again similar to that for hypertrophic cardiomyopathy.

A rare but important coronary artery anomaly that often presents during infancy or early childhood is an anomalous left main coronary artery from the pulmonary artery (ALC APA). In this condition, myocardial ischemia occurs as left coronary perfusion pressure falls. This typically occurs in the first weeks of life, as pulmonary vascular resistance falls. Because coronary flow occurs during diastole, a drop in diastolic pressure (due to falling pulmonary vascular resistance) results in poor blood flow to the heart muscle, particularly during exertion. For infants with this condition, periods of myocardial ischemia are manifested by infantile surrogates of chest pain. These include poor feeding, irritability with feeding (including colicky behavior during or immediately following feeds), diaphoresis, pallor, and lethargy.

The diagnosis of ALCAPA, when the above symptoms are present, should be suspected by physical examination, especially when signs of inadequate cardiac output are present. Auscultatory findings may include a gallop rhythm and a holosystolic regurgitant apical murmur (due to mitral insufficiency which results from papillary muscle ischemia). In the case of ALCAPA, the resting electrocardiogram can be diagnostic (Figure 4, see page 864), especially when wide Q waves are present in the anterolateral leads. Echocardiography and coronary angiography can confirm the anatomy, while providing additional data regarding cardiac and valvular function. For the general practitioner, however, the most important concern should be the immediate referral of the patient to a center capable of performing definitive surgery. Any medical therapies are temporizing measures, aimed at attempting to stabilize the patient for surgical intervention.

Figure 6. Electrocardiogram from a 12-year-old with Wolf-Parkinson-White syndrome. Note the three classic features present in ventricular pre-excitation, which include a short PR interval, delta wave (slurring of the upstroke of the QRS complex),and widened QRS duration. As in this tracing, abnormal T-wave patterns (such as the inversions in the lateral leads (V4-V6) are a consequence of the abnormal depolarization pattern.

Figure 6. Electrocardiogram from a 12-year-old with Wolf-Parkinson-White syndrome. Note the three classic features present in ventricular pre-excitation, which include a short PR interval, delta wave (slurring of the upstroke of the QRS complex),and widened QRS duration. As in this tracing, abnormal T-wave patterns (such as the inversions in the lateral leads (V4-V6) are a consequence of the abnormal depolarization pattern.

ARRHYTHMIAS AND PALPITATIONS

Palpitations, the sensation of an abnormal beating of the heart, frequently are encountered in the pediatric age group, although significant variability in presentation occurs. During infancy, symptomatic patients usually are identified because of the adverse hemodynamic effects of either tachyarrhythmias or bradyarrhythmias, primarily due to inadequate cardiac output. In younger children, palpitations often are confused with chest pain and should prompt consideration for a possible arrhythmia. In older children, as with adults, palpitations frequently are reported in association with other cardiovascular symptoms, including chest pain, near syncope, and syncope. In the majority of instances, they are the result of an adrenergically induced increase in the sinus rate, rather than a clinically significant rachyarrhythmia, with supraventricular tachycardia (SVT) occurring far less frequently.19

In those instances when SVT presents in the primary care setting, timely triage and intervention is essential to minimizing morbidity. Clinical recognition of a rachyarrhythmia through pulse determination should be confirmed by electrocardiogram, particularly in infants, when sinus tachycardia due to agitation can approach rates of common forms of SVT (Figure 5, see page 865). Any evidence of hemodynamic instability (eg, abnormal mentation, poor perfusion, hypotension) should warrant immediate action, using accepted algorithms for emergency intervention.20 These often are beyond the capability of most office settings and require immediate transfer to an emergency care facility.

If the patient is hemodynamically stable, age-appropriate attempts at vagal maneuvers may be employed. Regardless of the method of cardioversion, every effort should be made to monitor (and record) the rhythm before, during, and immediately following an intervention. These recordings often provide clues about the mechanism of the tachyatrhythmia and help guide a discussion of prognosis and treatment. Both of these should occur in conjunction with a pediatric cardiologist or pediatric heart rhythm specialist.

Wolf-Parkinson-White Syndrome

The special case of Wolf-Parkinson-White Syndrome (WPW) warrants additional discussion, largely because of its frequency and implications for sports participation. WPW is said to be present when SVT is identified in association with ventricular pre-excitation on a resting electrocardiogram (Figure 6, see page 866). The latter is the unique change that occurs because of electrical conduction of atrial impulses to the ventricle through cardiac tissue other than the atrioventricular node.

While clinical symptoms and acute treatment of patients experiencing SVT are similar to those without ventricular pre-excitation in the pediatric population, management differs. Special attention must be given to avoidance of medications known to preferentially slow atrioventricular node conduction (eg, digoxin, verapamil), which might otherwise be used in selected SVT cases. Furthermore, patients with WPW syndrome appear to be at increased risk of sudden cardiac death (0.15% per year) due to rapid conduction of atrial fibrillation down the accessory pathway.21 It is for this reason that pediatric WPW patients should be excluded from moderate- to high-intensity competitive sporting activity unless an electrophysiology study is performed.22

SYNCOPE

As with chest pain and palpitations, syncope is a common event among pediatric patients, occurring in nearly 50% of adolescents in some series.23 In the overwhelming majority of circumstances, syncope represents a neurocardiogenic phenomenon - an interaction of neurological and cardiac reflexes in response to either external or internal stimuli, resulting in a sudden fall in heart rate, blood pressure or both. This entity, while distressing to patients, family, friends, and onlookers, is considered benign.

However, syncope can also be the first presenting symptom of far more life-tlnreatening conditions, both cardiac and noncardiac (Sidebar). Cardiac causes may be further subdivided into mechanical (resulting from pump dysfunction or outflow obstruction) and electrical causes. The former largely have been covered in other sections, as they may be associated with heart murmurs and chest pain. While some electrical causes of syncope, such as WPW, also have been discussed, it is the family of conditions predisposing to malignant ventricular atrhytiunias that deserves special attention as a primary care urgency.

Long QT Syndrome

Long QT syndrome (LQTS) is a disorder characterized by a pathologic lengthening of the time needed to repolarize cardiac muscle cells, which results in a form of "electrical instability" that can lead to ventricular tachycardia, torsades de pointe (a type of rapid ventricular tachycardia), or even sudden death. The condition can be either congenital or acquired, the latter occurring in such situations as electrolyte abnormalities, side effects of certain medications, or elevated intracranial pressure.11

Congenital LQTS is the result of either a sodium or potassium cardiac ion channel abnormality that delays cardiac repolarization. Although great strides have been made in our understanding of the genetics of congenital LQTS24 and genotype-phenotype correlations have been made,25 establishment of the diagnosis continues be clinical, largely because of the cost-prohibitive and labor-intensive nature of genotype screening. Furthermore, commercially available testing lacks specificity, presently identifying only 50% to 75% of LQTS cases.26 In this way, the resting electrocardiogram remains the cornerstone of the diagnosis (Figure 7), with more than 94% of people with congenital LQTS having a corrected QT interval greater than 440 milliseconds.11 Additional electrocardiogram findings may include T-wave abnormalities, resting bradycardia, prominent U waves, and ventricular arrhythmias. It is for this reason that a resting ECG should be a part of the initial work-up of all cases of pediatric syncope.

Figure 7. Electrocardiogram from an 8-year-old giri with congenital long QT syndrome. Note the markedly prolonged QTc interval (600 milliseconds) and bizarre T waves (including biphasic T waves in V4 and V5). The resting bradycardia for age also is a common feature in patients with congenital long QT syndrome.

Figure 7. Electrocardiogram from an 8-year-old giri with congenital long QT syndrome. Note the markedly prolonged QTc interval (600 milliseconds) and bizarre T waves (including biphasic T waves in V4 and V5). The resting bradycardia for age also is a common feature in patients with congenital long QT syndrome.

SCREENING TRENDS

Screening for uncommon disorders is one of the cornerstones of general pediatric practice and forms the basis of newbom evaluations, state metabolic screening, and health supervision assessments. Examples of these endeavors include universal newborn hearing assessment27 and screening for congenital hypothyroidism.28 In both instances, several criteria required of a successful screening program are said to be met: the condition of interest is both sufficiently frequent and important; early detection can alter the natural history of the disease positively; a sufficiently sensitive and specific screening test exists; a reliable gold standard exists to confirm the diagnosis; and testing is of sufficiently low cost and low resource use so as to be generally applicable to a large population.

While all health supervision can be considered a form of screening, the use of routine ancillary cardiac studies for the purpose of cardiovascular risk assessment in otherwise asymptomatic patients remains controversial, regardless of the age of the patient.10,29-30 In discussions of the role of routine pulse oximetry in the newborn nursery to detect asymptomatic complex congenital heart disease, or of electrocardiogram or echocardiogram studies as an adjunct to the standard sports pre-participation examination, arguments against their use return to the lack of fulfillment of the above screening criteria. To be clear, no test available can be guaranteed to provide perfect disease detection; even those accepted noncardiac screening programs mentioned above have both false positive and false negative results. Thus, the issue devolves into a consideration of the economics of screening - the cost per case identified, and the savings derived from early disease recognition.

Present published recommendations have not supported the use of ancillary screening studies in the United States, although they are employed in various settings internationally30 and have even suggested a reduction in the incidence of sudden death in selected circumstances.31 As a consequence, community practice may vary widely, potentially including pulse oximetry, electrocardiogram, and echocardiogram at various times in a child's life in an effort to identify latent cardiac disease. In no area is this truer than in sports pre-participation screening, where often grass-roots efforts are the start of community-wide programs employing electrocardiograms, echocardiograms, or both.

For the general practitioner confused about his or her role, the key is to be aware of the controversy and to recognize the limitations of the screening tool in the particular population to which it is being applied. The practitioner should remember that screening tools are just that - for screening purposes - and should not take the place of clinical regarding the need for additional ancillary testing in the proper clinical scenario. At the same time, it is imperative that the general practitioner advocate for (and, if possible, participate in) population-based studies to address the utility of these screening programs.

SUMMARY

The general pediatrician remains the key to the timely recognition and treatment of cardiovascular disorders, particularly those that present acutely and may require immediate attention. In the evaluation of these cardiovascular urgencies, ancillary studies such as the electrocardiogram continue to be important, readily available tools that can aide in the diagnostic process. It is thus incumbent on the general practitioner to foster the skill necessary to employ such tools reliably, particularly in the setting of urgent evaluations. At the same time, recognition of the limitations of such testing will help both in the acute setting and in the understanding of their application in population settings.

REFERENCES

1. Wellens HJ, Gorgels AP. The electrocardiogram 102 years after Einthoven. Circulation. 2004;109(5):562-564.

2. Pediatric and Internal Medicine Program Requirements, Accreditation Council for Graduate Medical Education (ACGME). June 2005. Available at: http://www.acgme.org. Accessed October 18, 2005.

3. Swenson JM, Fischer DR, Miller SA, et al. Are chest radiographs and electrocardiograms still valuable in evaluating new pediatric patients with heart murmurs or chest pain? Pediatrics. 1997;99(1):1-3.

4. Fogel DH. The innocent systolic murmur in children: a clinical study of its incidence and characteristics. Am Heart J. 1960 Jun;59:844-855.

5. Barber G. Hypoplastic left heart syndrome. In: Garson A Jr, Bricker JT, Fisher DJ, Neish SR, eds. The Science and Practice of Pediatric Cardiology. 2nd ed. Baltimore, MD: Lippincott Williams & Wilkins; 1998:1625-1645.

6. Mahle WT, Clancy RR, McGaurn SP, Goin JE, Clark BJ. Impact of prenatal diagnosis on survival and early neurologic morbidity in neonates with the hypoplastic left heart syndrome. Pediatrics. 2001;107(6):1277-282.

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