A Child With Heart Murmur

By: Banani Poddar & Srikant Basu

Pediatricians often encounter children with heart murmurs, either as a part of ′well-baby′ examination or during assessment of intercurrent illnesses. The dilemma faced at such a time is to decide which child requires further evaluation and which child has an `innocent′ murmur. In this article, clinical differentiation between pathologic and innocent murmurs has been outlined so that parents of children with the latter can be re-assured and saved from further investigations and /or referral.

What is a Murmur?

Audible sound waves in the range of 20-2000 Hz emanating from the heart and vascular system constitute a cardiac murmur. It can also be said to be the auditory (auscultatory) consequence of turbulent blood flow from within the cardiovascular system.

How Important Are Murmurs?

A large number of children (including neonates) are detected to have a cardiac murmur, especially prior to school age.[1] Some murmurs in neonates, many in infants and most in childhood are ′benign′ or ′innocent′. However, a cardiac murmur may be the first sign of a serious structural cardiac disease, especially in the neonate. The latter not only carry a high morbidity (and if untreated, mortality) but also have enormous financial and psychological implications for the child and parents. Hence differentiation of one from the other is mandatory.

INNOCENT MURMURS

Those murmurs that occur in the absence of structural cardiac disease are said to be ′innocent′. They have been variously described as functional, benign, innocuous or physiologic murmurs.

Innocent Murmurs of Childhood

• Systolic murmurs
• Vibratory Still′s murmur
• Pulmonary flow murmur
• Peripheral pulmonary arterial stenosis murmur
• Supraclavicular or brachiocephalic systolic murmur
• Aortic systolic murmur
• Continuous murmurs
• Venous hum
• Mammary arterial soufflé

The Vibratory Still′s Murmur

This is the most common innocent murmur in children. First described by George F. Still in 1909 it presents most often between the ages of 2 and 6 years, though it may be present at extremes of age (adolescence and infancy). It is an early systolic, grade 1 to 3 (usually grade 2), low to medium pitched murmur, best heard at the lower left sternal edge and extending to the apex and loudest in the supine position. It changes on sitting or standing. It has a distinctive vibratory quality or a twanging sound, which gives it a musical character.

The origin of the murmur is not clear. This has been attributed to various causes including vibration of the pulmonary valves during systolic ejection, physiologic narrowing of the left ventricular outflow tract[8] and presence of ventricular false tendons.

The Pulmonary Flow Murmur

This may be heard in children, adolescents and young adults. It is an ejection systolic murmur, crescendo - decrescendo in character, of low intensity (Grade 2-3) and is heard at the left sternal border in the 2nd and 3rd intercostal spaces. It is rough in character and is thus distinct from the musical Still′s murmur. Best heard in the supine position, it is also exaggerated by a pectus excavatum, a straight back or kyphoscoliosis that results in compression or brings the right ventricular outflow tract closer to the chest wall. The murmur increases in intensity in expiration while inspiration and upright position decrease it.
The innocent pulmonary flow murmur should be distinguished from murmurs due to increased flow in an atrial septal defect and also from pulmonary valvar stenosis. The presence of a hyperdynamic right ventricular impulse; wide, fixed splitting of the S2 and a mid-diastolic flow murmur help in the distinction of the former, while in the latter, the presence of a systolic thrill, a longer and more harsh murmur and an ejection click would aid in the diagnosis.

Peripheral Pulmonary Arterial Stenosis Murmur

This is commonly heard in infants and neonates. It is of ejection systolic character, grade 1 to 2, low pitched and extends till or just beyond S2. These murmurs become more prominent with viral upper respiratory tract infections, especially in the recovery phase, and reactive airway disease. They are often best heard in the axillae or on the back.

The relative disparity in size between the main pulmonary artery trunk and its small branches at birth is thought to be the cause for this murmur. Further, the branches of the pulmonary artery arise at sharp angles, again resulting in turbulence. In older infants with respiratory tract infections, regional vascular reactivity and redistribution of blood flow may cause reappearance of the murmur. Differentiation from the murmur due to an anatomic narrowing of the pulmonary arterial branches is by the longer duration of the latter, the higher pitch and the older age group in whom the latter is heard.

The Supraclavicular /Brachiocephalic Systolic Murmur
This murmur, heard in children and young adults is a crescendo - decrescendo early systolic murmur best heard above the clavicles with radiation to the neck. It is low to medium pitched and brief. The murmur does not change with supine or sitting position but diminishes with hyperextension of the shoulders.[10] This murmur is thought to originate from the brachiocephalic vessels as they arise from the aorta.

The Aortic Systolic Murmur

This murmur is an innocent systolic flow murmur arising from the left ventricular outflow tract and associated with increased systemic cardiac output. It is ejection in character, systolic and is best heard in the aortic area. Common situations in children when these murmurs are heard include fever, anemia, anxiety, hyperthyroidism etc. Similar murmurs may be heard in trained athletes with slower heart rates and greater stroke volume.

The main differentiation is from hypertrophic obstructive cardiomyopathy (HOCM) and left ventricular outflow tract obstruction. In HOCM, increased venous return (as in rapid squatting) diminishes the murmur, while the Valsalva maneuver causes it to be louder. Also, the presence of a positive family history should alert the clinician in favour of HOCM.

The Venous Hum

This is the most common continuous murmur in children. Initially described by Potain in 1867,[11] it is most audible in the neck, anteriorly, just lateral to the sternocleidomastoid muscle often extending to the infraclavicular region of the chest wall. It is usually louder on the right side, better heard sitting than lying and is best elicited with the patient sitting up and looking away from the side of examination. It is widely variable in character and intensity, from faint to grade 6. Gentle compression over the jugular vein or turning the head towards the side of the murmur diminishes the murmur.

Turbulence at the confluence of flow from the internal jugular and subclavian veins as they enter the superior vena cava, or angulation of the internal jugular vein as it courses over the transverse process of the atlas, is thought to cause this venous hum.[12]

The Mammary Artery Soufflé

This murmur, well recognised in late pregnancy and lactation, can rarely occur in adolescence. This starts in systole but may extend into diastole and is heard on the anterior chest wall over the breast. It is high pitched, has a superficial character and firm pressure with the stethoscope may sometimes abolish the murmur. Thought to be arterial in origin, it occurs due to the enlarged vessels of the chest wall. Differentiation from a murmur due to patent ductus arteriosus or arterio-venous fistula is essential.

APPROACH TO A CHILD WITH A MURMUR

Having thus described the various innocent murmurs in childhood, let us now examine the approach to a child with a heart murmur.

History
The history should elicit the presence or absence of the cardinal cardiac symptoms. The symptoms of congestive heart failure in infants are very subtle and may be missed, if not specifically asked for. Past history to suggest rheumatic fever must be excluded. Family history of hypertrophic cardiomyopathy, congenital heart disease or unexplained childhood/early adulthood death is of importance. A perinatal history of premature birth, maternal diabetes, drug or toxin ingestion and intrauterine infection is relevant.

Examination
Apart from examination of the cardiovascular system, perhaps, the most important assessment is the evaluation for dysmorphism and the presence of other congenital anomalies. Presence of anomalies of other organ systems is associated with congenital heart disease in as many as 25% of cases. The assessment of the child’s growth and development is vital and may inform us about "failure to thrive". The child’s play capacity &/or ability to exercise should be sought for. A systematic cardiovascular examination including assessment of the arterial pulses and perfusion, measurement of blood pressure, the systemic venous assessment, precordial inspection, palpation and auscultation in the four different areas, are done. Step-by-step auscultation firstly for heart sounds and subsequently for murmurs, and for additional sounds, as also clicks is required. A crucial auscultatory assessment in children is to characterize the second heart sound and its components. Auscultation should also be carried out over the back, the axillae and the neck. Variations of murmurs and heart sounds with position (supine, sitting, standing) and various manouvres (respiration, Valsalva, exercise) further characterise the nature of these.

Investigations
The chest X-ray (CXR), electrocardiogram (ECG) and echocardiogram are invaluable tools to diagnose and assess the severity of a cardiac disease. However, they add little or no information in a child clinically assessed to have an `innocent murmur′. Hence, these investigations are not routinely recommended. The pitfalls associated with such investigations have been dealt with later.

A INNOCENT MURMUR- CLINICAL DIAGNOSIS

The diagnosis of an innocent murmur requires the absence of symptoms referable to the cardiovascular system, the absence of dysmorphism or characteristic cardiovascular signs and the recognition of the characteristic features of ′innocent′ murmurs.. To aid us to this end, several ′guidelines′ have been published.

We are aware of the `Nadas′ criteria′ for the diagnosis of congenital heart disease. In addition, several studies have addressed this issue as to whether clinicians can accurately classify murmurs as ′innocent′ or ′pathologic′ and several characteristic attributes of each murmur were found. In a study of 222 children being evaluated for a heart murmur by pediatric cardiologists, the following clinical signs were identified, the presence of any of which negates a diagnosis of an ′innocent murmur′. These include:

• Pansystolic Murmur
• Murmur Intensity ≥ grade 3
• Maximal intensity of murmur at left sternal border.
• Harsh quality murmur
• Presence of an early/midsystolic click.
• Presence of abnormal S2

In another such study, the characteristics of pathologic murmurs were found to be

• A systolic murmur with intensity of ³ grade 3
• A diastolic murmur
• An increase in murmur intensity with the patient standing.
  

Hence, the Nadas′ criteria, in addition to these above attributes of murmurs, clearly define ′red flags′ in the diagnosis of innocent murmurs.

Important Pitfalls of Diagnostic Tests

While an enlarged thymus on a CXR causes confusion about heart size in the infant, interpretation of an ECG requires a thorough knowledge of normal age-related changes in infancy and childhood.

In a study of asymptomatic infants and children with a cardiac murmur, a low reproducibility and accuracy was found of radiologic assessment of chest radiography by pediatric radiologists with respect to presence or absence of heart disease. Similarly, in a study on 120 infants and children being evaluated for a heart murmur, the ECG was found to be of no help in discrimination between heart disease and no heart disease. In this study mentioned above,[16] revision of the diagnosis after ECG and CXR was more often misleading than helpful. However, these modalities certainly enhance the diagnostic accuracy when heart lesions are present. While the ECG enhanced detection of an atrial septal defect and to a certain extent pulmonary stenosis, the X-ray enhanced detection of a hemodynamically significant ventricular septal defect. Hence, there are limitations of diagnostic utility of routine CXR and ECG, especially where the clinical diagnosis is that of an `innocent murmur′.

The gold standard for the diagnosis of a structural cardiac disease is an echocardiographic evaluation. However, there can be problems when performed in laboratories without expertise in pediatric heart disease. Normal physiological variations such as presence of a patent foramen ovale or PDA in a neonate may be misinterpreted as presence of heart disease. It has been amply demonstrated that a routine echocardiography is not required in all cases with a heart murmur. Moreover, these babies often require conscious sedation for the procedure, which may lead to problems.

Even in today’s hi-tech world, the best way to correctly classify a murmur as ′innocent′ or ′pathological′ is by clinical evaluation with special emphasis on a careful auscultation. Recently a technique for sending a recording of heart sounds (electronic stethoscope) via e-mail to a specialist, with a high sensitivity and specificity of correctly classifying the murmur. Has been described similarly, using an electronic stethoscope, heart sounds were recorded and fed into an artificial neural network (ANN) after processing The accuracy of classification into ′innocent′ and ′pathological′ was 100% using this ANN. In the absence of such sophistication available routinely, pediatricians can play a pivotal role in correctly classifying a heart murmur as ′innocent′ or ′pathological′. Thus all further investigations and/or referral in children with ′innocent′ murmurs may be avoided and the child kept on follow-up. In case of a clinical impression of a ′pathological′ murmur or the presence of the ′red flags′ as highlighted above, the child may be referred for further evaluation. The urgency with which such an evaluation is done depends on the age of the patient. It is usually within hours in neonates, days in infants and weeks in children.[1]

Hence, to conclude the only way to make a diagnosis of an innocent murmur is by auscultation and routine echocardiography is not indicated. The decision regarding referral for echocardiography and/or to a pediatric cardiologist depends on:

(a)The clinical impression (`innocent′ or pathologic murmur),

(b) The ′comfort′ factor i.e. the anxiety level of the parents,

(c) The confidence of the examining pediatrician and

(d) The availability of the child for follow-up.

This important and useful article is inspired by a special write-up by respected BANANI PODDAR & SRIKANT BASU, from the department of pediatrics, Govt. Medical College and Hospital, Chandigarh.

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