Murmurs

The Thorax

Knowing the location of the heart chambers and valves within the thorax helps in the interpretation of the heart sounds ( Fig. 9.1 ). The left atrium is located posteriorly, close to the spine. The right atrium and right ventricle are located anteriorly, immediately beneath the sternum. The outflow tract of the right ventricle, which contains the pulmonary valve, rises to the left of the sternum. The parts of the left side of the heart that are close to the chest wall include the left ventricular apex and the ascending aorta as it passes up to the right of the sternum. In other areas, lung tissue lies between the heart and chest wall, which may diminish or distort the intensity of heart sounds.

Origins of the Heart Sounds

Normal heart sounds originate from the vibration of heart valves when they close and from heart chambers when they fill rapidly. The amount of pressure that forces valve closure influences the intensity of a heart sound. Other mechanical factors such as valve stiffness, thickness, and excursion have lesser effects on sound intensity.

Cardiac murmurs are the direct result of blood flow turbulence. The amount of turbulence and consequently the intensity of a cardiac murmur are directly proportional to both the pressure difference or gradient across a narrowing or defect and the blood flow or volume moving across the site. In contrast to intensity, the frequency or pitch of a cardiac murmur is proportional to pressure difference or gradient alone.

As sound radiates from its source, sound intensity diminishes with the square of the distance. Consequently, heart sounds should be loudest near the point of origin. However, factors other than distance may influence this relationship. Sound passage through the body is affected by the transmission characteristics of the tissues through which the sound is being transmitted. Fat has a more pronounced dampening effect on higher frequencies than does more dense tissue such as bone. If the difference in tissue density is significant—for example, between the heart and lungs—more sound energy is lost. Only the loudest sounds may be heard when lung tissue is positioned between the heart and chest wall.

The Cardiac Cycle

The timing of events in the cardiac cycle allows for a more thorough understanding of heart sounds and murmurs. The relationship between the normal heart cycle and that of the heart sounds is noted in Figure 9.2 .

The cardiac cycle begins with atrial systole , the sequential activation and contraction of the two thin-walled upper chambers. Atrial systole is followed by the delayed contraction of the more powerful lower chambers, termed ventricular systole . Ventricular systole has three phases:

• 1.

  Isovolumic contraction: the short period of early contraction when the pressure builds within the ventricle but has yet to rise sufficiently to permit ejection

• 2.

  Ventricular ejection: when the ventricles eject blood to the body (via the aorta) and to the lungs (via the pulmonary artery)

• 3.

  Isovolumic relaxation: the period of ventricular relaxation when ejection ceases and pressure falls within the ventricles

During ventricular contraction, the atria relax ( atrial diastole ) and receive venous return from both the body and the lungs. Then, in ventricular diastole , the lower chambers relax, allowing initial passive filling of the thick-walled ventricles and emptying of the atria. Later, during the terminal period of ventricular relaxation, the atria contract. This atrial systole augments ventricular filling just before the onset of the next ventricular contraction.

The sequence of contractions generates pressure and blood flow through the heart. The relationship of blood volume, pressure, and flow determines opening and closing of heart valves and generates characteristic heart sounds and murmurs.

Changes in the Circulation at Birth

The majority of significant structural congenital heart disease is recognizable in the first few weeks of life. The age at recognition or presentation often correlates with the nature of the cardiac anomaly and the urgency with which assessment and treatment are necessary.

In the fetus, oxygen is acquired from the placenta and returns via the umbilical vein and through the ductus venosus to enter the inferior vena cava and right atrium ( Fig. 9.3 ). Preferentially, flow is directed across the foramen ovale to enter the left atrium and, subsequently, the left ventricle. Deoxygenated blood returning from the superior vena cava and upper body segment is preferentially directed by the flap of the eustachian valve to enter the right ventricle and then, via the ductus arteriosus, to enter the descending aorta to return via the umbilical arteries to the placenta. The pressures within both ventricles are essentially equal, inasmuch as both chambers pump to the systemic circulation. However, in utero, the right ventricle does the majority of the work, pumping 66% of the combined cardiac output. At transition (see Fig. 9.3 ), with the first breath, pulmonary arterial resistance begins to fall as the lungs begin the process of respiration. Pulmonary venous return to the left atrium closes the flap of the foramen ovale. Through mechanical and chemical mechanisms, the ductus arteriosus begins to close. In the normal full-term infant, this is accomplished by 10–15 hours after birth. Intermittent right-to-left atrial level shunting through the foramen ovale may occur, particularly if pulmonary vascular resistance fails to drop.

The time when congenital heart disease becomes symptomatic is influenced by the specific lesion. Some structural cardiac abnormalities require patency of the ductus arteriosus for maintenance of either pulmonary blood flow (e.g., pulmonary atresia) or systemic blood flow (e.g., hypoplastic left heart syndrome). These and other ductus-dependent abnormalities, such as transposition of the great arteries, coarctation of the aorta, or significant outflow obstruction (e.g., critical aortic valve stenosis), manifest in the first few hours or days after birth when the ductus arteriosus begins to close. In the absence of an associated anomaly, hemodynamically significant ventricular septal defects (VSDs) do not manifest before 2–4 weeks after birth. Atrial septal defects (ASDs) are seldom symptomatic in infancy.

Normal Intracardiac Pressures

In the neonate, after birth and successful transition, resistance to flow in the pulmonary circuit is much lower than in the systemic circuit. As such, the pressures in the right-sided chambers are lower than those in the left-sided chambers. The higher values within the ventricles reflect the pressure during the period of ventricular systole in a normal heart (see Fig. 9.3 ). Pressure in the great vessels during systole is identical to that in the corresponding ventricles, though this relationship changes if there is outflow obstruction. In ventricular diastole, the semilunar valves (aortic and pulmonary) close. Resistance to blood flow in the vascular bed determines the diastolic pressures in the great arteries. The thin-walled atria generate much lower pressures than do the ventricles, both during the phase of passive atrial filling ( v wave ) and during atrial contraction ( a wave ). Only the mean (m) or average atrial pressure is shown in Figure 9.3 . During ventricular relaxation, the diastolic pressures are lower than those in the atria, enabling filling.

Pediatric Cardiovascular Evaluation

Symptoms and Signs of Heart Disease

The general health of a child with a suspected cardiac malformation is important to assess. Particularly relevant are the rate of growth and history of past illnesses. Although symptoms of failure to thrive are nonspecific, patterns of growth reflect the severity of the disease and effectiveness of treatment (see Chapter 12 ). In an infant, feeding difficulties are often the first evidence of congestive heart failure. Feeding problems are common manifestations of cardiac disease and may be evidenced as disinterest, excessive fatigue, long feeding duration, diaphoresis, tachypnea, dyspnea, or a change in the pattern of respiration. It is important to obtain an objective measure of caloric intake by quantitating the number and/or volume of feedings. Some index of exertional tolerance should be sought in all children as an index of cardiovascular fitness and a sign of functional capability. This index should be age relevant and, in an infant, might include assessment of the vigor and duration of feeding and the time period of interactive play. In a toddler, the index might include the ability to keep up with peers, climb stairs, or walk for extended periods. In an older child, a comparison with peer sporting interactions, level of function in physical education, and an index of aerobic ability should be sought.

Tachypnea may occur as a consequence of increased pulmonary blood flow. With increasing pulmonary congestion, particularly obstruction to pulmonary venous drainage, dyspnea is manifested as an anxious look with grunting, flaring of the alae nasi, head bobbing, and intercostal, suprasternal, and subcostal retractions. Respiratory rates and the pattern of breathing should be assessed for a full minute in the quiet infant because rates may vary considerably with activity and feeding ( Table 9.3 ), or even over shorter time periods in a quiet infant. Cardiac asthma or exercise-inducible reactive airway disease may occur as a consequence of passive or active pulmonary congestion (see Chapter 4 ). Compression of airways by plethoric vessels may contribute to the stasis of secretions and atelectasis, which predisposes to respiratory tract infections.

Cyanosis in association with a cardiac murmur suggests a structural lesion with restriction to pulmonary blood flow ( Table 9.4 ). Cyanosis, or a blue discoloration of the skin and mucous membranes, is a consequence of reduced hemoglobin being present in >5 g/dL of hemoglobin and is evident in one third of infants with potentially lethal congenital heart disease. Central cyanosis is distinguished from acrocyanosis (peripheral cyanosis) by involvement of the warm mucous membranes, including the tongue and buccal mucosa. Acrocyanosis or peripheral cyanosis is generally confined to the perioral and perinasal regions, extremities, or nail beds and occurs in the child who is cold, vasoconstricted, or at rest. A distinctive feature is that central cyanosis generally worsens with activity and increasing cardiac output, whereas acrocyanosis generally improves or resolves with increased activity.

General Physical Examination

Overall Appearance

Height and weight should be measured and plotted on a growth chart. An assessment of the child’s overall growth, appearance, and state of distress serves as a guide to the urgency of further investigation and management. The sick infant often appears anxious, fretful, diaphoretic, pale, or breathless and is seldom consolable. Cyanosis, pallor, digital clubbing, an abnormal pattern of respiration, and possible dysmorphic features may suggest specific structural cardiac anomalies.

Vital Signs

Normal resting heart rates and respiratory rate values for age are presented in Table 9.3 . Blood pressure should be measured using an appropriately sized cuff. Every child should have a comparison of upper and lower blood pressures on at least one occasion. The lower limb systolic blood pressure is normally 10 mm Hg higher than the upper limb pressure in older children. On occasion, the subclavian arteries may arise aberrantly beyond the site of ductal ligament insertion. Therefore, both upper limb pressures should be measured and compared with the lower limb pressure. Normal values for blood pressure in children are presented in Figure 9.4 .

Respiratory Assessment

Respiratory distress may suggest cardiac disease. In addition to noting the rate, depth, and effort of respiration, the inspection should include observation for evidence of air trapping, increased chest diameter, or the presence of Harrison sulci (horizontal grooves in the anterior chest at the diaphragm insertion site along the sixth and seventh costal cartilages) as an indication of chronic upper airway obstruction. Midfacial hypoplasia with chronic mouth breathing may also suggest upper airway obstructive disease with predisposition to hypercapnia and pulmonary hypertension. Although crackles in the lungs in infants and even young children usually indicate infection, pulmonary edema should also be a consideration.

Cardiovascular Assessment

Auscultation

Thorough auscultation in the cooperative patient may take as long as 5–10 minutes and should include listening in the principal areas of the precordial auscultation (tricuspid, pulmonary, mitral, and aortic) with both the bell and diaphragm of the stethoscope, with the patient in the supine, sitting, and standing positions. These four areas serve as a guide to auscultation of the heart ( Fig. 9.5 ). These are the optimal sites for listening to sounds that arise within the chambers and great vessels:

• 1.

  The tricuspid area is represented by the fourth and fifth intercostal spaces along the left sternal edge but extends to the right of the sternum as well as downward to the subxiphisternal area.

• 2.

  The pulmonary area is the second intercostal space along the left sternal border. Murmurs that are best heard in this area may also extend to the left infraclavicular area and often lower, along the left sternal edge to the third intercostal space.

• 3.

  The mitral area involves the region of the cardiac apex and generally is at the fifth intercostal space in the midclavicular line. This area may also extend medially to the left sternal edge and laterally to the region of the axilla.

• 4.

  The aortic area , although centered at the second right intercostal space, may extend to the suprasternal area, to the neck, and inferiorly to the third left intercostal space.

The margins of these areas are ill defined, and auscultation should not be limited to these sites and may extend to the axillae, neck, back, or infraclavicular areas.

A step-by-step auscultation—first for heart sounds, subsequently for systolic murmurs, and then separately for diastolic murmurs—is essential. The ability to clearly characterize the S ₂ is perhaps more crucial than for any other sound; the effects of respiration are important. The components of the S ₂ in childhood are normally split with inspiration and become single on expiration. A loud pulmonary closure sound should suggest the possibility of pulmonary artery hypertension. The S ₂ may be widely split and/or fixed in association with right ventricular volume overload or delayed right ventricular conduction. Normal inspiratory splitting of the S ₂ should be sought and established in all patients. As timing may be difficult in the infant with a rapid respiratory rate, the presence of splitting at any time during the respiratory cycle may be accepted as normal.

The right ventricle is normally just beneath the sternum. This proximity generally makes sounds emanating from the right heart louder and less diffuse. In addition, right heart sounds and murmurs are more influenced by the effects of respiration.

Classification of Cardiac Murmurs

Heart murmurs are the consequence of turbulent blood flow. Turbulence may arise as a result of

• high flow through abnormal or normal valves

• normal flow through narrow or stenotic valves or vessels

• backward or regurgitant flow through incompetent leaky valves

• flow through congenital or surgical communications

• anemia with high flows and decreased blood viscosity

Not all cardiac murmurs indicate heart problems.

The clinician should be able to determine and describe the following seven characteristics of heart murmurs:

• 1.

  Timing: the relative position within the cardiac cycle relative to S ₁ and S ₂

• 2.

  Intensity or loudness: murmurs are graded as

  • grade I: heard only with intense concentration

  • grade II: faint but heard immediately

  • grade III: easily heard, of intermediate intensity

  • grade IV: easily heard and associated with a thrill (a palpable vibration on the chest wall)

  • grade V: very loud, with a thrill present, and audible with only the edge of the stethoscope on the chest wall

  • grade VI: audible with the stethoscope off the chest wall

• 3.

  Location: on the chest wall with regard to

  • area where the sound is loudest (point of maximal intensity)

  • area over which the sound is audible (extent of radiation)

• 4.

  Shape: to include the duration (the length of the murmur from beginning to end) and configuration (the dynamic changing nature of the murmur)

• 5.

  Pitch: the frequency range of the murmur, generally described as low, medium, or high pitched

• 6.

  Quality: aspect that relates to the presence of harmonics and overtones

• 7.

  Physiologic effects: of different positions, manipulations, or maneuvers

Pediatric Murmur Evaluation

After the neonatal period, an innocent murmur may be detected at some time in the majority of children before school age. The clinical diagnosis of a normal ejection or innocent murmur should only occur in the setting of an otherwise normal history, physical examination, and appearance ( Table 9.5 and Fig. 9.6 ).

Thorough auscultation in the cooperative patient should include listening in the principal areas (tricuspid, pulmonary, mitral, and aortic) of the precordium with both the bell and diaphragm of the stethoscope and with the patient in the supine, sitting, and standing positions.

Systolic Murmurs

Systolic murmurs begin with or follow the S ₁ and end before the S ₂ ( Fig. 9.7 ).

• Holosystolic murmurs , beginning abruptly with S ₁ and continuing at the same intensity to S ₂ , are graphically shown as a rectangle. This murmur begins during the period of isovolumic contraction and thus occurs when there is a regurgitant atrioventricular valve (tricuspid or mitral) or in association with a VSD.

• Ejection murmurs are crescendo-decrescendo or diamond-shaped murmurs that may arise from narrowing of the semilunar valves or outflow tracts. The rising-and-falling nature of the murmur reflects the periods of lower flow at the beginning and near the end of ventricular systole.

• Innocent murmurs are almost exclusively ejection systolic in nature (see Table 9.5 ). They are generally soft, are never associated with a palpable thrill, and are subject to considerable variation with positioning changes.

• Early systolic murmurs start abruptly with S ₁ but taper and disappear before the S ₂ and are exclusively associated with small muscular VSDs.

• Mid-systolic to late systolic murmurs begin midway through systole and are often heard in association with the mid-systolic clicks and insufficiency of mitral valve prolapse.