Most heart murmurs are normal or innocent, and must be distinguished from pathologic murmurs of congenital or acquired cardiac diseases. Whereas less than 1% of the population has structural congenital cardiac disease, as many as 85% of the population has a heart murmur sometime during childhood. The causes of cardiac murmurs are often influenced by the age of the patient at presentation ( Table 8.1 ). The causes of congenital heart disease are varied and include genetic disorders, syndrome complexes ( Table 8.2 ), metabolic disorders, and teratogenesis. The causes of acquired heart diseases in children include rheumatic fever, endocarditis, and cardiac injury caused by systemic illnesses.
| Neonate * | Infant | Older Child |
|---|---|---|
| Transient patency of the ductus arteriosus Peripheral pulmonic stenosis Cyanotic congenital heart disease Congenital valvular obstruction Arteriovenous malformation (CNS, hepatic, pulmonary) Anemia Asphyxia-related myocardial ischemia (transient TI or MI) | Congenital heart disease (L→R shunt or R→L shunt) † Ejection murmurs (normal) Anemia Arteriovenous malformation Infective endocarditis Kawasaki disease Hunter syndrome Hurler syndrome Fabry syndrome | Congenital valvular obstruction Ejection murmurs (normal) Repaired congenital heart disease Anemia Mitral valve prolapse Venous hum Bacterial endocarditis Rheumatic fever Marfan syndrome Prosthetic valves Obstructive (hypertrophic) cardiomyopathy (subaortic stenosis) Carotid or abdominal bruit Tumor (atrial myxoma) Thyrotoxicosis Systemic lupus erythematosus Pericardial friction rub |
* Common causes of congenital heart disease in low-birth-weight infants include PDA, VSD, tetralogy of Fallot, coarctation of the aorta–interrupted aortic arch, hypoplastic left heart syndrome, heterotaxy, and dextrotransposition of the great arteries, in that order. Common causes of congenital heart disease in term infants include VSD, dextrotransposition of the great arteries, tetralogy of Fallot, coarctation of the aorta, pulmonary stenosis, hypoplastic left heart syndrome, and PDA; other causes represent a smaller percentage.
† The relative percentages of congenital heart lesions are VSD (25-30%); ASD (6-8%); PDA (6-8%); coarctation of aorta (5-7%); tetralogy of Fallot (5-7%); pulmonary valve stenosis (5-7%); aortic valve stenosis (5-7%); dextrotransposition of great arteries (3-5%); and hypoplastic left ventricle, truncus arteriosus, total anomalous venous return, tricuspid atresia, single ventricle, and double-outlet right ventricle representing 1-3% each. Other and more complex lesions (forms of heterotaxy) together represent 5-10% of all lesions.
| Syndrome | Dominant Cardiac Defect |
|---|---|
| Alagille (arteriohepatic dysplasia) | Peripheral pulmonary stenosis |
| Asplenia | Complex cyanotic heart disease, anomalous veins, pulmonary atresia |
| Carpenter | Patent ductus arteriosus, ventricular septal defect |
| Cat eye | Total anomalous pulmonary venous return |
| Char | Patent ductus arteriosus |
| CHARGE | Ventricular, atrioventricular, and atrial septal defects |
| de Lange | Tetralogy of Fallot, ventricular septal defect |
| Down (Trisomy 21) | Artioventricular septal defects, ventricular septal defect, patent ductus arteriosus |
| Ellis–van Creveld | Single atrium, endocardial cushion defects |
| Fanconi | Patent ductus arteriosus, ventricular septal defect |
| Fetal alcohol | Ventricular septal defect, atrial septal defect, tetralogy of Fallot |
| Fragile X | Mitral valve prolapse, aortic root dilation |
| Goldenhar | Tetralogy of Fallot |
| Holt-Oram | Atrial or ventricular septal defect |
| Hydantoin/phenytoin embryopathy | Atrial or ventricular septal defect, coarctation of aorta |
| Infant of diabetic mother | Hypertrophic cardiomyopathy, ventricular septal defect |
| Laurence-Moon | Tetralogy of Fallot, ventricular septal defect |
| Marfan | Aortic root dissection, mitral valve prolapse |
| Mulibrey nanism | Pericardial thickening, constrictive pericarditis |
| Multiple lentigines (LEOPARD) | Pulmonary stenosis |
| Noonan | Pulmonic stenosis (dysplastic valve), atrial septal defect |
| PHACE | Coarctation of aorta, ventricular septal defect, patent ductus arteriosus |
| Pierre Robin | Coarctation of aorta |
| Polycystic kidney disease | Mitral valve prolapse |
| Polysplenia | Complex acyanotic lesions, azygos continuation |
| Rubella | Patent ductus arteriosus, peripheral pulmonary stenosis |
| Rubinstein-Taybi | Patent ductus arteriosus |
| Scimitar | Hypoplasia of the right lung, anomalous pulmonary drainage |
| Smith-Lemli-Opitz | Ventricular septal defect, patent ductus arteriosus |
| Thrombocytopenia–absent radius (TAR) | Atrial septal defect, tetralogy of Fallot, ventricular septal defect |
| Trisomy D | Ventricular septal defect, patent ductus arteriosus, atrial septal defect |
| Trisomy E | Ventricular septal defect, patent ductus arteriosus, atrial septal defect |
| Turner | Coarctation of aorta, bicuspid aortic valve |
| VACTERL (VATER) | Ventricular septal defect, tetralogy of Fallot |
| Valproate | Coarctation of aorta, hypoplastic left heart syndrome |
| Velocardiofacial | Ventricular septal defect, right aortic arch |
| Williams (7q11.23 deletion) | Supravalvular aortic stenosis, peripheral pulmonary stenosis |
| Wolf-Hirschhorn | Atrial septal defect, ventricular septal defect |
| 22q11.2 deletion syndrome | Tetralogy of Fallot, interrupted aortic arch, ventricular septal defect, truncus arteriosus |
Thorax
Knowing the location of the heart chambers and valves within the thorax helps in the interpretation of heart sounds ( Fig. 8.1 ). 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. This may diminish or distort the intensity of heart sounds.
Origins of the Heart Sounds
Normal heart sounds originate from vibrations of heart valves when they close and from heart chambers when they fill or contract rapidly. The amount of pressure that forces the valve closure influences the intensity of a heart sound. Other mechanical factors such as valve stiffness, thickness, and excursion have less effect 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 is directly proportional to both the pressure difference or gradient across a narrowing or defect and the blood flow or volume moving across the site.
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, other factors influence this relationship. Sound passage through the body is affected by the transmission characteristics of the tissues. 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.
In contrast to intensity, the frequency of a cardiac murmur is proportional to pressure difference or gradient across a narrowing alone.
Cardiac Cycle
Cardiac sounds and murmurs that arise from turbulence or vibrations within the heart and vascular system may be innocent or pathologic. It is important to understand the timing of events in the cardiac cycle as a prerequisite to understanding heart murmurs. The relationship between the normal heart cycle and that of the heart sounds is noted in Fig. 8.2 .
The cardiac cycle begins with atrial systole , the sequential activation and contraction of the 2 thin-walled upper chambers. Atrial systole is followed by the delayed contraction of the more powerful lower chambers, termed ventricular systole . Ventricular systole has 3 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
An understanding of the fetal, transitional, and neonatal adaptations of the circulation is important in the evaluation of the pediatric cardiovascular system, because many organic heart diseases are evident in association with the circulatory changes occurring at birth. The majority of significant structural congenital heart disease is recognized in the first few weeks of life. The age at recognition or referral often dictates the nature of the cardiac anomaly and the urgency with which assessment is necessary.
In the fetus ( Fig. 8.3 ), oxygen is derived from the placenta and returns via the umbilical vein and through the ductus venosus to enter the inferior vena cava and right atrium. 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. 8.3 ), 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. In addition, structural cardiac abnormalities necessitating patency of the ductus arteriosus for maintenance of either pulmonary blood flow (pulmonary atresia) or systemic blood flow (hypoplastic left heart syndrome) most often manifest within the first few days of life. Thus, the time when a pediatric patient presents for evaluation is influenced by the spectrum of heart diseases. Ductus-dependent abnormalities, such as pulmonary atresia, transposition of the great arteries, coarctation of the aorta, hypoplastic left heart syndrome, or significant outflow obstructions (e.g., critical aortic valve stenosis) manifest in the first few days after birth. In the absence of an associated anomaly, hemodynamically significant ventricular septal defects (VSDs) seldom manifest before 2-4 weeks after birth. Atrial septal defects (ASDs) are seldom symptomatic in infancy.
Normal Intracardiac Pressures
In the child after birth and successful transition, resistance to flow in the pulmonary circuit is much lower than in the systemic circuit. Therefore, the pressures in the right-sided chambers are lower than those in the left-sided chambers. The higher values (see Fig. 8.3 ) reflect pressures during ventricular systole in a normal heart. Pressure in the great vessels during systole is identical to that in the corresponding ventricles. This 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 Fig. 8.3 . During ventricular relaxation, the diastolic pressures are lower than those in the atria, enabling filling. Knowledge of the cardiac cycle is important in understanding the more complicated hemodynamics and flow patterns of specific cardiac abnormalities.
Pediatric Cardiovascular Evaluation
History
Historical assessment of the pediatric patient referred for evaluation of a cardiac murmur should include questions about the family history, the pregnancy, and perinatal course, in addition to questions about symptoms of cardiovascular disease. An index of exercise or play capacity should be sought, as should an assessment of growth and development. The presence of congenital abnormalities of other major organ systems is associated with structural cardiac problems in as many as 25% of patients.
Structural heart disease is frequently seen in association with recognizable syndromes (see Table 8.2 ). Children with clearly definable chromosomal disorders known to have a significant incidence of structural cardiac abnormalities, such as Down or Turner syndromes, are usually referred for further diagnostic evaluation. Family history of sudden unexplained death, rheumatic fever, sudden infant death syndrome, or a structural cardiac abnormality in a first-degree relative may be relevant. Hypertrophic cardiomyopathy in a first-degree relative is associated with a high incidence of inheritance, and this condition is sufficiently subtle that echocardiographic screening is mandatory.
A maternal history of gestational diabetes mellitus may be associated with a transient hypertrophic cardiomyopathy in as many as 30% of infants of these mothers, as well as with definable congenital structural abnormalities. Additional relevant pregnancy history may include the presence of chronic or acute maternal illness, congenital infections, or medication use, any of which may be associated with significant structural heart disease. Unexplained fever, lethargy, a history of intravenous drug use, or additional symptoms arising after recent dental work should arouse suspicion of possible endocarditis.
Symptoms and Signs of Heart Disease
(See Nelson Textbook of Pediatrics, p. 2261.)
The general health of a child with a suspected cardiac malformation is important. Particularly relevant are the rate of growth, development, and history of past illnesses. Although symptoms of failure to thrive are nonspecific, patterns of growth reflect duration and severity of the disease and effectiveness of treatment (see Chapter 9 ). 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 a 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 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.
Respiratory rates should be assessed in the quiet infant ( Table 8.3 ). The rate and pattern of breathing should be assessed for a full minute, because rates may vary considerably with activity and feeding. 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, and intercostal, suprasternal, and subcostal retractions. Cardiac asthma or exercise-inducible reactive airway disease may occur as a consequence of passive or active pulmonary congestion (see Chapter 3 ). Compression of airways by plethoric vessels may contribute to the stasis of secretions and atelectasis, which predisposes to respiratory tract infections.
| AGE | |||||
|---|---|---|---|---|---|
| Birth-6 Weeks | 6 Weeks-2 Years | 2-6 Years | 6-10 Years | Older Than 10 Years | |
| Respiratory rate | 45-60/min | 40/min | 30/min | 25/min | 20/min |
| Heart rate | 125 ± 30/min | 115 ± 25/min | 100 ± 20/min | 90 ± 15/min | 85 ± 15/min |
Cyanosis in association with a cardiac murmur suggests a structural lesion with restriction to pulmonary blood flow ( Table 8.4 ). Cyanosis, or a blue discoloration of the skin and mucous membranes, is a consequence of reduced hemoglobin (>5 g/dL), and is evident in one third of infants with potentially lethal congenital heart disease. Central cyanosis is distinguished from acrocyanosis or 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.
| Group | Heart Size | Pulmonary Blood Flow | Low Cardiac Output | Respiratory Distress | Examples |
|---|---|---|---|---|---|
| I | Small | Reduced | No | None | Hypoplastic RV with pulmonary atresia |
| Hypoplastic RV with tricuspid atresia | |||||
| Tetralogy of Fallot (severe) | |||||
| II | Small or slight cardiomegaly | Increased | No | Moderate | Transposition of great arteries with intact ventricular septum |
| III | Large | Increased | Yes | Yes | Complicated coarctation of aorta with VSD, hypoplastic LV |
| IV | Small | Pulmonary venous congestion | Yes | Yes | Obstructed total anomalous pulmonary veins |
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. Observe for cyanosis, pallor, digital clubbing, an abnormal pattern of respiration, and possible dysmorphic features, which may suggest specific structural cardiac anomalies.
Vital Signs
Normal resting heart rates and respiratory rate values for age are presented in Table 8.3 . Blood pressure should be measured manually 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 Fig. 8.4 .
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 subcostal Harrison sulci as an indication of chronic upper airway obstruction. An allergic malar facies 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
Arterial Examination
Pulses should be assessed for rate, rhythm, volume, and character. The dynamic character of the pulse may provide information about the cardiac output. A clinical index of cardiac output includes the warmth of the digits and measured capillary refill time. This is obtained by blanching the nail beds or digits and estimating the time to full reperfusion, which is normally less than 2 seconds. Initially, the radial and brachial pulses should be assessed simultaneously in the upper limb. By palpating the pulse at 2 sites and altering the pressure applied by the palpating fingers, a more accurate assessment of the rate of rise, volume, and contour may be obtained. Assessment of the femoral pulse requires that the infant be quiet. Palpating parallel to the inguinal crease and allowing the leg to continue to flex is generally more effective than extending the leg. Blood pressures in the arm and leg should be assessed, and the radial and femoral pulses should be palpated simultaneously. Whenever possible, the radial pulse should be brought in close apposition to the femoral pulse to compare for any delay. This enables a more accurate appreciation of any temporal delay and enables more accurate detection of the presence of coarctation of the aorta . The presence of a palpable femoral pulse is by itself an inadequate screen for coarctation because a widely patent ductus arteriosus (PDA) or collateral vessels (particularly in the older patient) may provide delayed perfusion. Previous arterial instrumentation, injury, or congenital variability may account for reduction in palpable peripheral pulses.
Venous Examination
In infants and young children, the liver character and size offer more reliable indicators of right atrial pressure and systemic congestion than does the jugular venous pressure. The position, size, and consistency of the liver should be assessed. The character of the normal liver margin is generally likened to that of the cartilage of the external pinna, and the margin should be sharp and angulated. In the newborn, the liver may be normally palpable at 1.5-2.5 cm below the right costal margin in the midclavicular line. This distance decreases to approximately 1-2 cm by 1 year of age and remains just palpable until school-entrance age. In the presence of congestive heart failure, the liver enlarges and distends downward. The congested liver margin becomes rounded and firm and is often more difficult to feel. An enlarged liver may be tender, and aggressive palpation may cause discomfort and tensing of the abdominal musculature, making accurate assessment difficult. A transverse liver is suggestive of a heterotaxy syndrome with abnormal abdominal organ location (situs abnormalities) and complex congenital heart lesions. The spleen should always be sought; enlargement suggests endocarditis in the patient with a heart murmur. Splenic enlargement in association with congestive heart failure is unusual (see Chapter 17 ).
Precordial Examination
Inspection of the chest may suggest the presence of a precordial bulge of long-standing right ventricular volume overload. The examiner’s entire palm and hand should be warmed and then fully applied to the patient’s chest wall to maximize ability to detect thrills or heaves. Whereas the examiner’s fingertips are best utilized to localize an abnormality, the palmar surface of the metacarpals and first phalanges are more sensitive for the detection of low-frequency events. The fingertips should be used to localize the most lateral displacement of the apical impulse. In patients of all ages, the apical impulse should be confined to one intercostal interspace and would be described as localized; however, if the apical impulse is equally dynamic in 2 or more interspaces then it is best described as diffuse. In the neonate, a right ventricular impulse may be felt close to the sternum. Later in life, the same degree of parasternal activity is likely to suggest pulmonary hypertension, right-sided heart volume overload, or right ventricular outflow obstruction. The lateral displacement of the apex, normally located in the midclavicular line, should be compared to existing landmarks. A dynamic or thrusting character to an apical impulse may be detected in association with an elevated cardiac output or various forms of obstruction to left ventricular outflow. On occasion, an apical filling impulse, coinciding with an audible S 3 , may be normally palpable, particularly in the adolescent or athlete with a relative bradycardia and increased stroke volume.
A thrill is a palpable murmur and should be sought in the precordial and suprasternal areas. The palmar surface of the examiner’s hand is most sensitive in detection of a thrill; however, only the tips of the digits fit in the patient’s suprasternal notch. A palpable second heart sound (S 2 ), indicative of a significant level of pulmonary hypertension, may be detected as a sharp or distinctive impulse in the pulmonary outflow.
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 4 areas serve as a guide to auscultation of the heart ( Fig. 8.5 ). 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.
Heart Sounds
First direct the examination to the normal heart sounds in sequence. Appreciate the effects of inspiration and expiration on the heart sounds. Then address additional heart sounds and murmurs. Describe any variability that occurs with a change of body position.
First Heart Sound
The first heart sound (S 1 ) (see Fig. 8.2 ) arises from closure of the atrioventricular (mitral and tricuspid) valves in early isovolumic ventricular contraction and, consequently, is best heard in the tricuspid and mitral valve areas. Mitral valve closure occurs slightly in advance of tricuspid valve closure, and, on rare occasion, near the lower-left sternal edge 2 components (splitting) of the S 1 may be heard. There is usually a single sound. The S 1 is most easily heard when the heart rate is slow because the interval between the S 1 and S 2 is shorter than the interval between the S 2 and subsequent S 1 . The intensity of the S 1 is influenced by the position of the atrioventricular valve at the onset of ventricular contraction.
Second Heart Sound
Shortly after the onset of ventricular contraction, the semilunar valves (aortic and pulmonary) open and permit ventricular ejection. This opening does not usually generate any sound. The atrioventricular valves remain tightly closed during ventricular ejection. As ventricular ejection nears completion, the pressure begins to fall within the ventricles, and the semilunar valves snap closed. This prevents regurgitation from the aorta and pulmonary artery back into the heart. The closure of the semilunar valves generates the S 2 (see Fig. 8.2 ). The S 2 usually consists of a louder and earlier aortic valve closure sound (A 2 ), followed by a later and quieter pulmonary valve closure sound (P 2 ). Normal physiologic splitting or variability is appreciated most easily in the pulmonary area during or near the end of inspiration. During expiration, the aortic and pulmonary valves close almost synchronously and produce a single or narrowly split S 2 . Normal splitting of S 2 is caused by (1) increased right-sided heart filling during inspiration because of increased blood volume returning via the venae cavae; and (2) diminished left-sided heart filling because blood is retained within the small blood vessels of the lungs when the thorax expands. During inspiration, when the right ventricle is filled more than the left, it takes slightly longer to empty. This causes the noticeable inspiratory delay in P 2 in relation to A 2 . Splitting of the S 2 during inspiration is a normal finding and should be sought in all patients.
The aortic and pulmonary pressure in diastole closes the semilunar valves. Many forms of congenital or acquired heart disease have an impact on the pulmonary circulation and, consequently, often affect the S 2 . Thus, the higher the pulmonary artery diastolic pressure, the more intense and earlier the P 2 is. Pulmonary hypertension in children is suggested when the P 2 is palpable, loud, and narrowly split or cannot be separated from A 2 . If the P 2 is audible outside of the pulmonary area, particularly at the apex, then pulmonary hypertension is likely. A single or narrow split S 2 may also be noted in patients with severe pulmonic or aortic valve stenosis, tetralogy of Fallot, truncus arteriosus, pulmonary atresia, hypoplastic left heart syndrome, tricuspid valve atresia, or Eisenmenger syndrome with a VSD. In the presence of moderate to severe pulmonic stenosis, there is low pulmonary artery diastolic pressure. The pulmonary valve closure is therefore delayed and of decreased intensity and is occasionally inaudible.
The S 2 may be widely split and/or fixed in association with right ventricular volume overload or delayed right ventricular conduction.
Third Heart Sound
The third heart sound (S 3 ) (see Fig. 8.2 ), which is of very low frequency, occurs about a third of the way into diastole, at the time of the most rapid filling of the ventricles. It is most likely caused by sudden tension of the ventricles, enough to produce sound vibrations within the myocardial wall. Vibrations in the atrioventricular valve itself, as well as in the chordae, may also contribute to the sound. The amplitude of S 3 increases with an increased ventricular filling rate. When heard at the apex, S 3 is considered left ventricular in origin, and when heard at the lower left sternal border, S 3 is likely to be right ventricular in origin. An apical S 3 of soft to moderate intensity is readily heard in most children and young adults. An S 3 in association with tachycardia is termed a gallop and may be caused by lesions associated with left or right ventricular diastolic overload or diminished ventricular compliance.
Fourth Heart Sound
The fourth heart sound (S 4 ) (see Fig. 8.2 ) is also of low frequency and can be both left-sided and right-sided in origin. It occurs with atrial contraction against a high resistance and is therefore heard just before S 1 . It is more difficult to hear than S 3 , particularly in children, in whom the PR interval is usually shorter than that in the adult. The S 4 is thought to be caused by a forceful atrial contraction against a poorly compliant left ventricle (e.g., as in diastolic overload). The sound is readily heard in adults with significant chronic hypertension or left ventricular cardiomyopathy and, except for its timing, sounds much like an S 3 . In a young baby with total anomalous pulmonary venous return, low pulmonary vascular resistance, and significantly increased right ventricular and pulmonary blood flow, a loud right ventricular S 4 (as well as S 3 ) may be heard as part of a quadruple rhythm at the lower left sternal border. An intermittent S 4 may be heard in children with complete atrioventricular block. Whereas an S 3 may be heard in a normal adolescent and can be physiologic, the S 4 only occurs in a pathologic condition.
Ejection Click
An audible ejection click (see Fig. 8.2 ) is abnormal and is either related to the hemodynamics associated with a dilated root of the aorta ( aortic ejection click ) or a dilated root of the pulmonary artery ( pulmonary ejection click ) or the effects of a thickened and immobile semilunar valve. The sound is sharp and of very high frequency. The pulmonary ejection click is best heard at the upper-left sternal border, whereas the aortic ejection click is usually best heard at the apex. It may also be heard at the upper-right sternal border, but if so, it is always louder at the apex or the lower-left sternal border. The click arises either from sudden tension of the semilunar valve or from sudden distention with lateral pressure at the root of the aorta or pulmonary artery. The sound is present in aortic or pulmonary valve stenosis. In such cases, the rapid movement of the stenotic valve is suddenly checked. An aortic ejection click may be heard in the presence of a normal aortic valve (as in severe tetralogy of Fallot with a large aortic root); a pulmonary ejection click may be heard with a normal pulmonic valve (as in Eisenmenger syndrome with a large pulmonary root). The aortic ejection click, best heard at the apex, does not vary with respirations. However, the pulmonary ejection click, best heard at the upper-left sternal border, is better heard on expiration than inspiration.
An ejection click or a sharp sound present at the upper-left sternal border, louder with expiration or heard only on expiration, is characteristic of pulmonary valve stenosis . The ejection click follows the period of isovolumic contraction and occurs as a consequence of restricted semilunar (aortic or pulmonary) valve excursion at the onset of ventricular ejection. When the ejection sound occurs at the upper-right sternal border or at the apex, a bicuspid or stenotic aortic valve disease is suggested. In contrast to ejection clicks, right-sided cardiac murmurs are accentuated with inspiration. Left-sided heart auscultatory abnormalities vary little with the respiratory cycle.
In the case of the aortic ejection click, the sound is usually well separated from S 1 . However, the pulmonary ejection click is usually closer to S 1 than is an aortic click. In some moderate to severe cases, the pulmonary ejection click occurs at the same time as S 1 . If one perceives a split S 1 , one is most likely hearing an ejection click as the causes of a true split S 1 are very rare.
Opening Snap
The opening snap, present only in rheumatic mitral valve stenosis when the anteromedial leaflet is immobile, is heard early in diastole, usually above the apex, and is of medium frequency. Because the leaflets are fused, the downward movement of the opening valve is suddenly checked, resulting in the opening snap. This sound is often confused with an S 3 . The frequency is somewhat higher and the timing is earlier than those of an S 3 . The opening snap and the S 3 , although similar in timing, can never occur together in the same patient.
Non-Ejection Click
Non-ejection clicks are heard at the apex and occur one third to half of the way between S 1 and S 2 . Thus, they are commonly called mid-systolic clicks . The sounds are of medium to high frequency. The sound is caused by the sudden tensing of the posterior mitral valve leaflet as it prolapses into the left atrium; in rare cases, there may be multiple mid-systolic clicks. The clicks may be loud, but they may also be soft and easily missed.
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
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normal flow through narrow or stenotic valves or vessels
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backward or regurgitant flow through incompetent leaky valves
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flow through congenital or surgical communications
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anemia with high flows and discrete 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
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grade I: heard only with intense concentration
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grade II: faint but heard immediately
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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)
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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 the 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 8.5 and Fig. 8.6 ).
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