CHAPTER 101

Heart Murmurs

Robin Winkler Doroshow, MD, MMS, MEd, FAAP

Asymptomatic children with heart murmurs are commonly encountered by physicians. A murmur is a finding rather than a medical sign or symptom, because it is detected incidentally at an examination conducted for another purpose.

Correct assessment of the significance of a heart murmur is important to ensure appropriate treatment of children with heart disease. Complications of undiagnosed cardiac disease in children include progressive hemodynamic impairment, endocarditis, and even sudden death.

The misinterpretation of an innocent murmur as organic in nature can also be a source of stress, primarily in the form of parental anxiety. Unnecessary restriction of activities may result, which can have a negative effect on children’s school and social lives as well as self-image. As adults they may be denied health insurance, life insurance, and certain types of employment. Additionally, misdiagnosis is financially costly and uses limited resources, with unnecessary tests and doctor visits, as this “nondisease” is evaluated and followed.

Epidemiology

An estimated 50% of healthy children have heart murmurs. The overall incidence of congenital heart disease (CHD), including symptomatic cases, is just under 1%, most of which are identified prenatally (by ultrasonography) or in the newborn period (by pulse oximetry screening [see Chapter 103]). Some children with CHD have no murmur. Therefore, approximately 98 of 100 murmurs noted during childhood are “innocent” (ie, have no organic basis).

Clinical Presentation

Heart murmurs are usually detected on routine examination for well-child care or on evaluation for an unrelated problem. Innocent murmurs are not associated with signs or symptoms, because they are normal findings. Most of the symptoms sometimes associated with organic murmurs (ie, murmurs of heart disease) are related to the presence of congestive heart failure (CHF) (see Chapter 104) and usually become evident during infancy. Some children with murmurs come to medical attention with reports of exercise intolerance or chest pain. It is necessary to determine whether these problems are truly referable to the heart, which is uncommon (see Chapter 105).

The noting of a murmur in a child for the first time may be considered a “new murmur,” which in the adult can be a serious finding heralding new onset of acquired heart disease, such as mitral insufficiency resulting from poor ventricular function or aortic insufficiency resulting from infective endocarditis. In the pediatric patient, these findings are rare. Much more commonly, a murmur not previously noted may be heard for the first time for benign reasons. These murmurs are referred to as innocent murmurs and may vary by patient age or the position in which the child is examined. Previously very soft murmurs may be more pronounced under different conditions, such as fever or anxiety. Murmurs that are predominantly audible in the supine position may not have been noted when the child was examined only in the upright position, or vice versa. The lower heart rate and better level of cooperation of the child, compared with the infant, may allow the examiner to identify a murmur not heard on previous examinations.

Pathophysiology

A murmur is a sustained sound that can be detected with a stethoscope placed on the chest. This sound is produced by turbulence of blood flow in the heart or great vessels. This turbulence may be caused by structural abnormalities (eg, aortic valve stenosis), benign or normal flow patterns (discussed later in this chapter), or exaggeration of normal flow patterns (as in high-output states, such as fever, exercise, anxiety, or anemia, and sometimes termed “functional”).

Not all significant heart disease in children is heralded by a murmur. Structural heart disease may be silent and be indicated by other findings. For example, transposition of the great arteries results in cyanosis, anomalous pulmonary venous return in pulmonary edema and hypoxia, and anomalous origin of the left coronary artery from the pulmonary artery in CHF. Acquired heart disease, such as Kawasaki disease, myocarditis, or cardiomyopathy, often produces no murmur.

The common innocent murmurs are better recognized than understood. Because they occur in normal, healthy individuals, few hemodynamic or anatomical data exist to correlate with the murmur, and in some cases pathophysiology is conjectural. Still murmur, which once was thought to be the result of easily appreciated aortic valve flow, is now believed to result from vibration of normal fibrous bands (“false tendons”) that cross the left ventricle. This murmur may also be heard in children who have undergone spontaneous closure of a membranous ventricular septal defect, with a small residual aneurysm in the septum. The pulmonary flow murmur seems to be caused by normal flow across the pulmonary valve, perhaps made more apparent because of high cardiac output, close proximity to the chest wall, and, in adolescent females, mild anemia. The venous hum is attributed to turbulence at the confluence of the innominate veins, which is exacerbated in the upright position by gravity.

The physiologic peripheral pulmonic stenosis murmur, which is an innocent murmur found in newborns, is produced by turbulence at the origins of the left and right pulmonary arteries. Because less than 10% of the combined ventricular output of the fetus goes to these branches, they are small and arise at a sharp angle from the main pulmonary artery. When postnatal circulation abruptly requires the entire cardiac output to enter these vessels, a relative stenosis is encountered. This physiologic stenosis resolves gradually with remodeling of the pulmonary artery tree by 2 to 3 months of age.

Differential Diagnosis

In healthy children, the differential diagnosis of a heart murmur includes innocent murmurs and murmurs resulting from structural lesions, most of which are congenital. Although the specific features of a particular murmur usually provide many clues to the diagnosis, in the current era, the main task of the primary care physician is to correctly identify the patient who requires cardiology referral. It is therefore important to develop and maintain auscultatory skills. No written or visual material is a good substitute for practice with recordings and actual patients. A good quality stethoscope, with both diaphragm and bell correctly sized for the patient, and snugly fitting but comfortable earpieces, is essential. Conditions should be optimized: The patient should be kept comfortable and, if necessary, distracted, and extraneous environmental noise should be minimized.

Some features may alert examiners to the organic nature of a murmur. Although very loud murmurs (grades 4–6; ie, with associated precordial thrill) usually are not innocent, some innocent murmurs may be as loud as grade 3, particularly with high cardiac output (eg, fever, anxiety, anemia). Diastolic murmurs and continuous murmurs, other than the easily recognizable venous hum, are usually pathologic, as are high-pitched and harsh murmurs, which are better heard with the diaphragm of the stethoscope. Murmurs that change strikingly with body position are rarely the result of CHD.

The common innocent murmurs of childhood are recognizable on auscultatory examination. Still murmur, or the “innocent vibratory murmur,” is a low-pitched, vibratory, or musical murmur that sounds like a groan. Because of its low frequency, the murmur is better heard with the bell. It is loudest at the left lower sternal border but often is distributed widely over the precordium. This murmur often is quite loud, particularly in the supine position, and is extremely common in school-age children, although it also may be heard in the infant. The characteristics of the murmur itself are diagnostic, although the absence of other findings is supportive.

The pulmonary flow murmur, which usually is heard in older children, is a short, blowing systolic ejection (ie, crescendo-decrescendo) murmur localized to the left upper sternal border. It may be louder with the patient in the supine position.

The venous hum is a soft continuous murmur, similar to the sound heard in a seashell. Because of its constancy, it is often overlooked. This murmur is commonly heard in preschool and school-age children. Loudest in the right infraclavicular area, it may also be heard on the left. This murmur is highly variable with head and neck position and compression of the neck veins, which may increase or diminish it. It usually disappears with the patient in the supine position.

The physiologic peripheral pulmonic stenosis murmur, an innocent murmur found in newborns, is best heard at the upper left sternal border. This blowing systolic ejection murmur radiates strikingly over the lung fields into the back and both axillae. Typically, it disappears by 3 months of age, whereas the murmur of true stenosis of the pulmonary arteries persists.

Evaluation

History

The history may be helpful in assessment of the child with a murmur. If a thorough history shows that the child has no symptoms, this suggests the absence of severe heart disease and helps exclude many major or complex defects as well as CHF. The absence of symptoms does not, however, exclude several common defects that may require intervention (Table 101.1).

The most common cardiac symptom reported by children or their parents is easy fatigability (Box 101.1). This is difficult to quantitate. Determining exercise intolerance on the basis of history is quite subjective; of course, it may be the result of noncardiac causes and may be unrelated to the murmur. Easy fatigability during infancy may be reported as slow or poor feeding. Chest pain, a common symptom in adults with heart disease, is rarely cardiac in origin in children (see Chapter 105). A history of rapid breathing, excessive sweating, and other symptoms referable to CHF is suggestive of organic heart disease. Central cyanosis (ie, involving the oral mucosa rather than the perioral area or the fingers) may be reported occasionally by parents of children with cyanotic CHD but often is not recognized.

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