Guyton and Hall Physiology Chapter 23 - Heart Valves and Heart Sounds.PDF

CHAPTER 23 Heart Valves and Heart Sounds; Valvular and UNIT IV Congenital Heart Defects Function of the heart valves was discussed in...

CHAPTER 23 Heart Valves and Heart Sounds; Valvular and UNIT IV Congenital Heart Defects Function of the heart valves was discussed in Chapter 9, The Second Heart Sound Is Associated With Closure where we pointed out that closing of the valves causes of the Aortic and Pulmonary Valves. The second heart audible sounds. Ordinarily, no audible sounds occur when sound results from sudden closure of the semilunar valves the valves open. In this chapter, we first discuss the fac- (aortic and pulmonary valves) at the end of systole. When tors that cause the sounds in the heart under normal and the semilunar valves close, they bulge backward toward abnormal conditions. Then we discuss the overall circula- the ventricles, and their elastic stretch recoils the blood tory changes that occur when valvular or congenital heart back into the arteries, which causes a short period of re- defects are present. verberation of blood back and forth between the walls of the arteries and the semilunar valves, as well as between these valves and the ventricular walls. The vibrations oc- HEART SOUNDS curring in the arterial walls are then transmitted mainly along the arteries. When the vibrations of the vessels or NORMAL HEART SOUNDS ventricles come into contact with a sounding board, such When listening to a normal heart with a stethoscope, one as the chest wall, they create sound that can be heard us- hears a sound usually described as “lub, dub, lub, dub.” ing a stethoscope. The “lub” is associated with closure of the atrioventricular (A-­V ) valves at the beginning of systole, and the “dub” is Duration and Pitch of First and Second Heart Sounds. associated with closure of the semilunar (aortic and pul- The duration of each of the heart sounds is slightly more monary) valves at the end of systole. The “lub” sound is than 0.10 second, with the first sound about 0.14 second called the first heart sound, and the “dub” is called the sec- and the second about 0.11 second. The reason for the ond heart sound, because the normal pumping cycle of shorter second sound is that the semilunar valves are the heart is considered to start when the A-­V valves close tauter than the A-­V valves, so they vibrate for a shorter at the onset of ventricular systole (Audio 23-­1). time than do the A-­V valves. The audible range of frequency (pitch) in the first and The First Heart Sound Is Associated With Closure of second heart sounds, as shown in Figure 23-­1, begins at A-V. The main cause of the first heart sound is vibra- the lowest frequency the ear can detect, about 40 cycles/ tion of the taut valves immediately after closure, along sec, and goes up above 500 cycles/sec. When a special with vibration of the adjacent walls of the heart and electronic apparatus is used to record these sounds, a major vessels around the heart. That is, in generating larger proportion of the recorded sound is at frequencies the first heart sound, contraction of the ventricles first and sound levels below the audible range, going down causes sudden backflow of blood against the A-­V valves to 3 to 4 cycles/sec and peaking at about 20 cycles/sec, (tricuspid and mitral valves), causing them to close as illustrated by the lower shaded area in Figure 23-­1. and bulge toward the atria until the chordae tendine- For this reason, major portions of the heart sounds can ae abruptly stop the back bulging. The elastic tautness be recorded electronically by phonocardiography, even of the chordae tendineae and valves then causes the though they cannot be heard with a stethoscope. back-­surging blood to bounce forward again into each The second heart sound normally has a higher fre- respective ventricle. This mechanism causes the blood quency than the first heart sound for two reasons: (1) and the ventricular walls, as well as the taut valves, to the tautness of the semilunar valves in comparison with vibrate and causes vibrating turbulence in the blood. the much less taut A-­V valves; and (2) the greater elas- The vibrations travel through the adjacent tissues to the tic coefficient of the taut arterial walls, which provides chest wall, where they can be heard as sound by using the principal vibrating chambers for the second sound, in the stethoscope. comparison with the much looser, less elastic ventricular 283 UNIT IV The Circulation Heart sounds Inaudible and murmurs Aortic area Pulmonic area 100 10 Speech Th area 1 Dynes/cm2 res ho ld 0.1 of au Heart sounds dib 0.01 ility and murmurs 0.001 0.0001 0 8 32 64 128 256 512 1024 2048 4096 Frequency in cycles per second Figure 23-­1 Amplitude of different frequency vibrations in the heart sounds and heart murmurs in relationship to the threshold of audibil- ity, showing that the range of sounds that can be heard is between 40 and 520 cycles/sec. (Modified from Butterworth JS, Chassin JL, McGrath JJ: Cardiac Auscultation, 2nd ed. New York: Grune & Strat- ton, 1960.) Tricuspid area Mitral area Figure 23-­2 Chest areas from which sounds from each valve are heard best. chambers, which provides the vibrating system for the first heart sound. The clinician uses these differences to distin- guish special characteristics of the two respective sounds. Chest Surface Areas for Auscultation of Normal Heart Sounds. Listening to the sounds of the body, usually with The Third Heart Sound Occurs at the Beginning of the the aid of a stethoscope, is called auscultation. Figure 23-­2 Middle Third of Diastole. Occasionally, a weak, rum- shows the areas of the chest wall from which the differ- bling third heart sound is heard at the beginning of the ent heart valvular sounds can best be distinguished. Al- middle third of diastole. A logical but unproved explana- though the sounds from all the valves can be heard from tion of this sound is oscillation of blood back and forth all these areas, the cardiologist distinguishes the sounds between the walls of the ventricles initiated by inrushing from the different valves by a process of elimination. That blood from the atria. This is analogous to running water is, he or she moves the stethoscope from one area to an- from a faucet into a paper sack, with the inrushing water other, noting the loudness of the sounds in different areas reverberating back and forth between the walls of the sack and gradually picking out the sound components from to cause vibrations in its walls. The reason the third heart each valve. sound does not occur until the middle third of diastole is The areas for listening to the different heart sounds are believed to be that in the early part of diastole, the ven- not directly over the valves themselves. The aortic area tricles are not filled sufficiently to create even the small is upward along the aorta because of sound transmission amount of elastic tension necessary for reverberation. The up the aorta, and the pulmonic area is upward along the frequency of this sound is usually so low that the ear can- pulmonary artery. The tricuspid area is over the right ven- not hear it, yet it can often be recorded in the phonocar- tricle, and the mitral area is over the apex of the left ven- diogram. The third heart sound may be normally present tricle, which is the portion of the heart nearest the surface in children, adolescents, and young adults but generally of the chest; the heart is rotated so that the remainder of indicates systolic heart failure in older adults. the left ventricle lies more posteriorly. Atrial Contraction—Fourth Heart Sound. An atrial Phonocardiogram. If a microphone specially designed heart sound can sometimes be recorded in the phonocar- to detect low-­frequency sound is placed on the chest, diogram, but it can almost never be heard with a stetho- the heart sounds can be amplified and recorded by scope because of its weakness and very low frequency— a high-­speed recording apparatus. The recording is usually 20 cycles/sec or less. This sound occurs when called a phonocardiogram, and the heart sounds ap- the atria contract, and presumably, it is caused by the pear as waves, as shown schematically in Figure 23-­ inrush of blood into the ventricles, which initiates vibra- 3. Recording A is an example of normal heart sounds, tions similar to those of the third heart sound. A fourth showing the vibrations of the first, second, and third heart sound is common in persons who derive benefit heart sounds and even the very weak atrial sound. Note from atrial contraction for ventricular filling as a result of specifically that the third and atrial heart sounds are decreased ventricular wall compliance and increased re- each a very low rumble. The third heart sound can sistance to ventricular filling. For example, a fourth heart be recorded in only one-third to one-half of people, sound is often heard in older patients with left ventricular and the atrial heart sound can be recorded in perhaps hypertrophy. one-fourth of people. 284  Chapter 23 Heart Valves and Heart Sounds; Valvular and Congenital Heart Defects 1st 2nd 3rd Atrial The lesions of acute rheumatic fever frequently occur A on adjacent valve leaflets simultaneously, so the edges of Normal the leaflets become stuck together. Then, weeks, months, or years later, the lesions become scar tissue, permanently B fusing portions of adjacent valve leaflets. Also, the free Aortic stenosis UNIT IV edges of the leaflets, which are normally filmy and free-­ C flapping, often become solid scarred masses. Mitral regurgitation A valve in which the leaflets adhere to one another so extensively that blood cannot flow through it normally D is said to be stenosed. Conversely, when the valve edges Aortic regurgitation are so destroyed by scar tissue that they cannot close as E the ventricles contract, regurgitation (backflow) of blood Mitral stenosis occurs when the valve should be closed. Stenosis usually does not occur without the coexistence of at least some F degree of regurgitation, and vice versa. Patent ductus arteriosus Aging and Aortic Valve Stenosis Diastole Systole Diastole Systole With aging, the aortic valve often thickens, becomes cal- cified and stiffer, and may partially obstruct outflow from Figure 23-­3 A—F, Phonocardiograms from normal and abnormal the left ventricle. With increased life expectancy and hearts. aging of the population, aortic valve stenosis has become the most common heart valve disease. VALVULAR LESIONS Stenosis of a previously normal aortic valve, often called senile calcific aortic valve stenosis, is characterized Rheumatic Valvular Lesions by valve calcium deposition and ossification, which lead Rheumatic fever is an autoimmune disease in which the to narrowing of the aortic valve orifice. As a compensa- heart valves are likely to be damaged or destroyed. The tory response to the increased workload imposed on the disease is usually initiated by a streptococcal toxin. heart by the stenotic aortic valve, the left ventricle under- The sequence of events almost always begins with a goes concentric hypertrophy. This type of hypertrophy preliminary streptococcal infection caused specifically by is associated with increased left ventricular wall thick- group A hemolytic streptococci. These bacteria initially ness, which permits the heart to pump with greater vigor cause a sore throat, scarlet fever, or middle ear infection. against the partially obstructed outflow. An increasing However, the streptococci also release several different pressure gradient then develops across the calcified valve, proteins against which the person’s reticuloendothelial reaching 75 to 100 mm Hg in severe cases of aortic valve system produces antibodies. The antibodies react not only stenosis. with the streptococcal protein but also with other pro- The hypertrophied left ventricle also becomes more tein tissues of the body, often causing severe immunologic fibrotic and tends to be ischemic because of impaired damage. These reactions continue to take place as long as microcirculatory perfusion, although some patients may the antibodies persist in the blood—1 year or more. also have atherosclerosis of the coronary arteries. The Rheumatic fever particularly causes damage in certain ejection fraction may be normal, and the patient may be susceptible areas, such as the heart valves. The degree of able to maintain adequate cardiac output under resting heart valve damage is directly correlated with the concen- conditions, but with even moderate exercise, symptoms tration and persistence of the antibodies. The principles of of heart failure may appear. As the stenosis progressively immunity that relate to this type of reaction are discussed in worsens, there are reductions in systolic heart function Chapter 35, and it is noted in Chapter 32 that acute glomeru- and inability of the left ventricle to develop enough pres- lar nephritis of the kidneys has a similar immunologic basis. sure to pump effectively against the load imposed by the In persons with rheumatic fever, large hemorrhagic, partially obstructed aortic valve. Consequently, symp- fibrinous, bulbous lesions grow along the inflamed edges toms of congestive heart failure appear, with reductions of the heart valves. Because the mitral valve undergoes in stroke volume and cardiac output. more trauma during valvular action than any of the other Calcific aortic valve stenosis usually does not become valves, it is the one most often seriously damaged, and the severe enough to draw clinical attention until after age aortic valve is the second most frequently damaged. The 70. Important symptoms of aortic valve stenosis are right heart valves—that is, the tricuspid and pulmonary exertion-­related angina, reduced exercise tolerance, and valves—are usually affected much less severely, probably congestive heart failure. Shortness of breath (dyspnea) is because the low-­pressure stresses that act on these valves due to increased left ventricular filling pressure or inabil- are slight compared with the high-­pressure stresses that ity to increase cardiac output adequately with exercise. act on the left heart valves. Early recognition and management of aortic stenosis are 285 UNIT IV The Circulation important because untreated symptomatic aortic valve Diastolic Murmur of Mitral Stenosis. In persons with stenosis is progressive and will ultimately be fatal. mitral stenosis, blood passes with difficulty through the The development of transcatheter aortic valve replace- stenosed mitral valve from the left atrium into the left ventri- ment technologies has provided new therapeutic oppor- cle, and because the pressure in the left atrium seldom rises tunities, especially for older patients, in whom traditional above 30 mm Hg, a large pressure differential forcing blood surgical procedures cannot be performed or are associ- from the left atrium into the left ventricle does not develop. ated with high risk. Consequently, the abnormal sounds heard in mitral stenosis (see recording E, Figure 23-­3; Audio 23-5) are usually weak Heart Murmurs Caused by Valvular Lesions and of very low frequency, so most of the sound spectrum is below the low-­frequency end of human hearing. As shown by the phonocardiograms in Figure 23-­3, many During the early part of diastole, a left ventricle with a abnormal heart sounds, known as heart murmurs, occur stenotic mitral valve has so little blood in it, and its walls when abnormalities of the valves are present, as discussed are so flabby, that blood does not reverberate back and here. forth between the walls of the ventricle. For this reason, even in persons with severe mitral stenosis, no murmur Systolic Murmur of Aortic Stenosis. In persons with may be heard during the first third of diastole. Then, after aortic stenosis, blood is ejected from the left ventricle partial filling, the ventricle has stretched enough for blood through only a small fibrous opening of the aortic valve. to reverberate, and a low rumbling murmur begins. Because of the resistance to ejection, the blood pressure in the left ventricle sometimes rises as high as 300 mm Hg; Phonocardiograms of Valvular Murmurs. Phonocar- the pressure in the aorta is still normal. Thus, a nozzle ef- diograms B, C, D, and E of Figure 23-­3 show, respectively, fect is created during systole, with blood jetting at tremen- idealized records obtained from patients with aortic ste- dous velocity through the small opening of the valve. This nosis, mitral regurgitation, aortic regurgitation, and mi- phenomenon causes severe turbulence of the blood in the tral stenosis. It is obvious from these phonocardiograms root of the aorta. The turbulent blood impinging against that the aortic stenotic lesion causes the loudest murmur, the aortic walls causes intense vibration, and a loud mur- and the mitral stenotic lesion causes the weakest murmur. mur occurs during systole (see recording B, Figure 23-­3; The phonocardiograms show how the intensity of the Audio 23-­2) and is transmitted throughout the superior murmurs varies during different portions of systole and thoracic aorta and even into the large arteries of the neck. diastole, and the relative timing of each murmur is also This sound is harsh, and in persons with severe stenosis evident. Note especially that the murmurs of aortic ste- it may be so loud that it can be heard several feet away nosis and mitral regurgitation occur only during systole, from the patient. Also, the sound vibrations can often be whereas the murmurs of aortic regurgitation and mitral felt with the hand on the upper chest and lower neck, a stenosis occur only during diastole. phenomenon known as a thrill. Diastolic Murmur of Aortic Regurgitation. In aortic ABNORMAL CIRCULATORY DYNAMICS regurgitation, no abnormal sound is heard during systole, IN VALVULAR HEART DISEASE but during diastole, blood flows backward from the high-­ pressure aorta into the left ventricle, causing a “blowing” CIRCULATORY DYNAMICS IN AORTIC murmur of relatively high pitch, with a swishing quality ­STENOSIS AND AORTIC REGURGITATION heard maximally over the left ventricle (see recording D, Figure 23-­3; Audio 23-­3). This murmur results from the In aortic stenosis, the contracting left ventricle fails to turbulence of blood jetting backward into the blood al- empty adequately, whereas in aortic regurgitation, blood ready in the low-­pressure diastolic left ventricle. flows backward into the ventricle from the aorta after the ventricle has just pumped the blood into the aorta. There- Systolic Murmur of Mitral Regurgitation. In persons fore, in both cases, the net stroke volume output of the with mitral regurgitation, blood flows backward through heart is reduced. the mitral valve into the left atrium during systole. This Several important compensations take place that can backward flow also causes a high-­ frequency blowing, ameliorate the severity of the circulatory defects. Some of swishing sound (see recording C, Figure 23-­3; Audio these compensations are described in the following sections. 23-­4) similar to that of aortic regurgitation but occurring during systole rather than diastole. It is transmitted most Hypertrophy of Left Ventricle. In both aortic stenosis strongly into the left atrium. However, the left atrium is so and aortic regurgitation, the left ventricular muscula- deep within the chest that it is difficult to hear this sound ture hypertrophies because of the increased ventricular directly over the atrium. As a result, the sound of mi- workload. In regurgitation, the left ventricular chamber tral regurgitation is transmitted to the chest wall mainly also enlarges to hold all the regurgitant blood from the through the left ventricle to the apex of the heart. aorta. This type of hypertrophy, with enlargement of the 286  Chapter 23 Heart Valves and Heart Sounds; Valvular and Congenital Heart Defects Normal Eccentric LVH Concentric LVH Right Left UNIT IV atrium atrium Figure 23-­4 Comparison of the left ventricle in a normal heart, a heart with eccentric left ventricular hypertrophy (LVH), and a heart with Right Left Dilated Hypertrophied concentric LVH. Left ventricular ventricle ventricle left ventricle left ventricle mass increases in eccentric and con- centric LVH but there is an increase Aortic/mitral valve regurgitation Aortic valve stenosis in left ventricular cavity size in ec- Ventricular septal defect Chronic hypertension centric LVH, whereas wall thickness Systolic dysfunction increases in concentric LVH. ventricular chamber, is often referred to as eccentric hy- action increases the workload and oxygen consumption of pertrophy (Figure 23-­4). Sometimes, the left ventricular the ventricle, necessitating increased coronary blood flow muscle mass increases fourfold to fivefold, creating a tre- to deliver this oxygen. The high wall tension of the ventricle, mendously large left side of the heart. however, causes marked decreases in coronary flow during When the aortic valve is seriously stenosed, the hyper- systole, particularly in the subendocardial vessels. Intraven- trophied muscle may allow the left ventricle to develop tricular diastolic pressure is also increased when there is as much as 400 mm Hg of intraventricular pressure at aortic valve stenosis, and this increased pressure may cause systolic peak. This type of concentric hypertrophy is asso- compression of the inner layers of the heart muscle and re- ciated with thickened ventricular walls and a smaller duced coronary blood flow. Thus, severe aortic valve steno- ventricular chamber (see Figure 23-­4) and also occurs sis often causes ischemia of the heart muscle. in other circumstances where afterload of the heart is With aortic regurgitation, the intraventricular diastolic increased, such as in chronic hypertension. pressure also increases, compressing the inner layer of the In persons with severe aortic regurgitation, sometimes heart muscle and decreasing coronary blood flow. Aortic the enlarged left ventricle can pump a stroke volume out- diastolic pressure decreases during aortic regurgitation, put as great as 250 milliliters, although as much as 75% which can also decrease coronary blood flow and cause of this blood returns to the ventricle during diastole, and ischemia of the heart muscle. only 25% flows through the aorta to the body. Eventual Failure of Left Ventricle and Development Increase in Blood Volume. Another effect that helps of Pulmonary Edema. In the early stages of aortic steno- compensate for the diminished net pumping by the left sis or aortic regurgitation, the intrinsic ability of the left ventricle is increased blood volume. This increased volume ventricle to adapt to increasing loads prevents significant results from the following: (1) an initial slight decrease in abnormalities in circulatory function in the person dur- arterial pressure; (2) nervous reflexes and hormonal chang- ing rest, other than the increased work output required es induced by the decrease in pressure. These mechanisms of the left ventricle. Therefore, considerable degrees of together diminish renal output of urine, causing blood aortic stenosis or aortic regurgitation often occur before ­volume to increase and the mean arterial pressure to r­ eturn the person knows that he or she has serious heart disease to normal. Also, red blood cell mass eventually increases (e.g., a resting left ventricular systolic pressure as high as because of a slight degree of tissue hypoxia. 200 mm Hg in persons with aortic stenosis or a left ven- The increase in blood volume tends to increase venous tricular stroke volume output as high as twice normal in return to the heart, which, in turn, causes the left ventricle persons with aortic regurgitation). to pump with the extra power required to overcome the Beyond a critical stage in these aortic valve lesions, the abnormal pumping dynamics. left ventricle finally cannot keep up with the work demand. As a consequence, the left ventricle dilates and cardiac out- Aortic Valvular Lesions May Be Associated With put begins to fall; blood simultaneously dams up in the left ­Inadequate Coronary Blood Flow. When a person has atrium and in the lungs behind the failing left ventricle. The stenosis of the aortic valve, the ventricular muscle must de- left atrial pressure rises progressively, and at mean left atrial velop a high tension to create the high intraventricular pres- pressures above 25 to 40 mm Hg, serious edema appears in sure needed to force blood through the stenosed valve. This the lungs, as discussed in detail in Chapter 39. 287 UNIT IV The Circulation DYNAMICS OF MITRAL STENOSIS AND CIRCULATORY DYNAMICS DURING MITRAL REGURGITATION EXERCISE IN PATIENTS WITH VALVULAR LESIONS In persons with mitral stenosis, blood flow from the left atrium into the left ventricle is impeded and, in persons During exercise, increased blood flow is required to provide with mitral regurgitation, much of the blood that has additional oxygen and nutrients to the exercising muscles flowed into the left ventricle during diastole leaks back and remove waste products of increased metabolism. Con- into the left atrium during systole rather than being sequently, increased quantities of venous blood are returned pumped into the aorta. Therefore, either of these condi- to the heart from the peripheral circulation. Therefore, all the tions reduces net movement of blood from the left atrium dynamic abnormalities that occur in the different types of into the left ventricle. valvular heart disease become exacerbated. Even in persons with mild valvular heart disease, in which the symptoms may Pulmonary Edema in Mitral Valvular Disease. The be unrecognizable at rest, severe symptoms often develop buildup of blood in the left atrium causes a progressive during heavy exercise. For example, in patients with aortic increase in left atrial pressure, eventually resulting in the valvular lesions, exercise can cause acute left ventricular fail- development of serious pulmonary edema. Ordinarily, le- ure followed by acute pulmonary edema. Also, in patients thal edema does not occur until the mean left atrial pres- with mitral disease, exercise can cause so much damming sure rises above 25 mm Hg, and sometimes as high as 40 of blood in the lungs that serious or even lethal pulmonary mm Hg, because the lung lymphatic vessels enlarge many edema may ensue in as little as 10 minutes. times and can carry fluid rapidly away from the lung tis- Even in mild to moderate cases of valvular disease, the sues. patient’s cardiac reserve diminishes in proportion to the severity of the valvular dysfunction. That is, the cardiac Enlarged Left Atrium and Atrial Fibrillation. The high output does not increase as much as it should during left atrial pressure in mitral valvular disease also causes exercise. Therefore, the muscles of the body fatigue rap- progressive enlargement of the left atrium, which in- idly because of too little increase in muscle blood flow. creases the distance that the cardiac electrical excitatory impulse must travel in the atrial wall. This pathway may ABNORMAL CIRCULATORY DYNAMICS eventually become so long that it predisposes to the de- IN CONGENITAL HEART DEFECTS velopment of excitatory signal circus movements, as dis- cussed in Chapter 13. Therefore, in late stages of mitral Occasionally, the heart or its associated blood vessels are valvular disease, especially in mitral stenosis, atrial fibril- malformed during fetal life; the defect is called a congeni- lation often occurs. This development further reduces the tal anomaly. There are three major types of congenital pumping effectiveness of the heart and causes further car- anomalies of the heart and its associated vessels: (1) steno- diac debility. sis of the channel of blood flow at some point in the heart or in a closely allied major blood vessel; (2) an anomaly Compensation in Early Mitral Valvular Disease. that allows blood to flow backward from the left side of As also occurs in aortic valvular disease and in many the heart or aorta to the right side of the heart or pul- types of congenital heart disease, the blood volume monary artery, thus failing to flow through the systemic ­increases in mitral valvular disease principally because circulation, called a left-­to-­right shunt; and (3) an anomaly of diminished excretion of water and salt by the kid- that allows blood to flow directly from the right side of neys. This increased blood volume increases venous the heart into the left side of the heart, thus failing to flow return to the heart, thereby helping overcome the through the lungs, called a right-­to-­left shunt. ­effect of the ­c ardiac debility. Therefore, after compen- The effects of the different stenotic lesions are easily sation, cardiac output may fall only minimally until the understood. For instance, congenital aortic valve stenosis late stages of mitral valvular disease, even though the results in the same dynamic effects as aortic valve stenosis left atrial pressure is rising. caused by other valvular lesions, namely, cardiac hyper- As the left atrial pressure rises, blood begins to dam up trophy, heart muscle ischemia, reduced cardiac output, in the lungs, eventually all the way back to the pulmonary and a tendency to develop serious pulmonary edema. artery. In addition, incipient edema of the lungs causes Another type of congenital stenosis is coarctation of the pulmonary arteriolar constriction. These two effects aorta, often occurring above the level of the diaphragm. This together increase systolic pulmonary arterial pressure stenosis causes the arterial pressure in the upper part of the and also right ventricular pressure, sometimes to as high body (above the level of the coarctation) to be much greater as 60 mm Hg, which is more than double normal. This than the pressure in the lower body because of the great increased pressure, in turn, causes hypertrophy of the resistance to blood flow through the coarctation to the lower right side of the heart, which partially compensates for its body; part of the blood must go around the coarctation increased workload. through small collateral arteries, as discussed in Chapter 19. 288  Chapter 23 Heart Valves and Heart Sounds; Valvular and Congenital Heart Defects Aorta through the ductus arteriosus ceases suddenly at birth and, in fact, blood begins to flow backward through the ductus, Ductus arteriosus from the aorta into the pulmonary artery. This new state of backward blood flow causes the ductus arteriosus to be- come occluded within a few hours to a few days in most UNIT IV Head and upper babies, so blood flow through the ductus does not persist. extremities The ductus is believed to close because the oxygen concen- tration of the aortic blood now flowing through it is about Pulmonary Left twice as high as that of the blood flowing from the pulmo- artery pulmonary nary artery into the ductus during fetal life. The oxygen artery presumably constricts the muscle in the ductus wall. This Right phenomenon is discussed further in Chapter 84. Left lung lung Unfortunately, in about 1 of every 5500 babies, the ductus does not close, causing the condition known as patent ductus arteriosus, which is shown in Figure 23-­5. Dynamics of the Circulation With a Persistent Patent Ductus During the early months of an infant’s life, a patent ductus usually does not cause severely abnormal function. How- Trunk and lower ever, as the child grows older, the differential between extremities the high pressure in the aorta and the lower pressure in Figure 23-­5 Patent ductus arteriosus, showing by the blue color that the pulmonary artery progressively increases, with a cor- venous blood changes into oxygenated blood at different points in responding increase in the backward flow of blood from the circulation. Inset, Backflow of blood from the aorta into the pul- the aorta into the pulmonary artery. Also, the high aortic monary artery and then through the lungs for a second time. blood pressure usually causes the diameter of the partially open ductus to increase with time, making the condition even worse. PATENT DUCTUS ARTERIOSUS—A LEFT-­ TO-­RIGHT SHUNT Recirculation Through the Lungs. In an older child with During fetal life, the lungs are collapsed, and the elastic com- a patent ductus, one-half to two-thirds of the aortic blood pression of the lungs that keeps the alveoli collapsed keeps flows backward through the ductus into the pulmonary most of the lung blood vessels collapsed as well. Therefore, artery, then through the lungs, and finally back into the resistance to blood flow through the lungs is so great that left ventricle and aorta, passing through the lungs and left the pulmonary arterial pressure is high in the fetus. Also, side of the heart two or more times for every one time because of low resistance to blood flow from the aorta that it passes through the systemic circulation. People through the large vessels of the placenta, the pressure in the with this condition do not show cyanosis until later in life, aorta of the fetus is lower than normal—in fact, lower than when the heart fails or the lungs become congested. Indeed, in the pulmonary artery. This phenomenon causes almost early in life, the arterial blood is often better oxygenat- all the pulmonary arterial blood to flow through a special ed than normal because of the extra times that it passes artery present in the fetus that connects the pulmonary through the lungs. artery with the aorta (Figure 23-­5), the ductus arteriosus, thus bypassing the lungs. This mechanism allows immedi- Diminished Cardiac and Respiratory Reserve. The ma- ate recirculation of the blood through the systemic arteries jor effects of patent ductus arteriosus on the patient are de- of the fetus without the blood going through the lungs. This creased cardiac and respiratory reserve. The left ventricle is lack of blood flow through the lungs is not detrimental to pumping about two or more times the normal cardiac out- the fetus because the blood is oxygenated by the placenta. put, and the maximum that it can pump after hypertrophy of the heart has occurred is about four to seven times nor- Closure of Ductus Arteriosus After Birth. As soon as a mal. Therefore, during exercise, the net blood flow through baby is born and begins to breathe, the lungs inflate. Not the remainder of the body can never increase to the lev- only do the alveoli fill with air, but also the resistance to els required for strenuous activity. With even moderately blood flow through the pulmonary vascular tree decreases strenuous exercise, the person is likely to become weak and tremendously, allowing the pulmonary arterial pressure to may even faint from momentary heart failure. fall. Simultaneously, the aortic pressure rises because of The high pressures in the pulmonary vessels caused sudden cessation of blood flow from the aorta through the by excess flow through the lungs may also lead to pulmo- placenta. Thus, the pressure in the pulmonary artery falls, nary congestion and pulmonary edema. As a result of the while that in the aorta rises. As a result, forward blood flow excessive load on the heart, and especially because the 289 UNIT IV The Circulation pulmonary congestion becomes progressively more severe Stenosis of Aorta with age, most patients with uncorrected patent ductus die pulmonary artery from heart disease between the ages of 20 and 40 years. Heart Sounds: Machinery Murmur Head and upper extremities In a newborn infant with patent ductus arteriosus, occa- sionally no abnormal heart sounds are heard because the quantity of reverse blood flow through the ductus may Septal be insufficient to cause a heart murmur. However, as the defect baby grows older, to 1 to 3 years of age, a harsh blowing Right murmur begins to be heard in the pulmonary artery area lung Left lung of the chest, as shown in recording F, Figure 23-­3. This sound is much more intense during systole when the aor- tic pressure is high and much less intense during diastole when the aortic pressure falls low, so that the murmur waxes and wanes with each beat of the heart, creating the so-­called machinery murmur. Surgical Treatment Trunk and lower Surgical treatment of patent ductus arteriosus (PDA) is extremities simple; one need only ligate the patent ductus or divide Figure 23-­6 Tetralogy of Fallot, showing by the blue color that most it and then close the two ends. This procedure was one of the venous blood is shunted from the right ventricle into the aorta of the first successful heart surgeries ever performed. without passing through the lungs. Catheter-­based devices often are used to close PDAs in infants or children who are large enough to have the pro- of Fallot is the shunting of blood past the lungs without cedure. A small metal coil or other occlusion device is its becoming oxygenated. As much as 75% of the venous passed up through the catheter and placed in the PDA to blood returning to the heart passes directly from the right block blood flow through the vessel. ventricle into the aorta without becoming oxygenated. This can lead to cyanosis (blue coloration) of the baby’s TETRALOGY OF FALLOT—A RIGHT-­TO-­ skin. Other signs include high right ventricular pressures, LEFT SHUNT right ventricular enlargement, and a left-­to-­right shunt through the interventricular septum, which can be visual- Tetralogy of Fallot is shown in Figure 23-­6; it is the most ized by echocardiography. common cause of blue baby. Most of the blood bypasses the lungs, so the aortic blood is mainly unoxygenated Surgical Treatment. Tetralogy of Fallot can often be venous blood. In this condition, four abnormalities of the treated successfully with surgery. The usual procedure is heart occur simultaneously: to open the pulmonary stenosis, close the septal defect, 1. The aorta originates from the right ventricle rather and reconstruct the flow pathway into the aorta. When than the left, or it overrides a hole in the septum, as surgery is successful, the average life expectancy increases shown in Figure 23-­6, receiving blood from both from only 3 to 4 years to 50 or more years. ventricles. 2. Because the pulmonary artery is stenosed, much CAUSES OF CONGENITAL ANOMALIES lower than normal amounts of blood pass from the right ventricle into the lungs; instead, most of the Congenital heart disease is not uncommon, occurring blood passes directly into the aorta, thus bypassing in about 8 of every 1000 live births. One of the most the lungs. common causes of congenital heart defects is a viral 3. Blood from the left ventricle flows through a ven- infection in the mother during the first trimester of tricular septal hole into the right ventricle and then pregnancy when the fetal heart is being formed. Defects into the aorta or directly into the aorta that over- are particularly prone to develop when the expectant rides this hole. mother contracts German measles (rubella) during the 4. Because the right side of the heart must pump large first trimester of pregnancy. Taking certain medications, quantities of blood against the high pressure in the such as angiotensin-­converting enzyme (ACE) inhibitors aorta, its musculature is highly developed, causing and acne medications (e.g., isotretinoin), and alcohol or an enlarged right ventricle. drug abuse during pregnancy also increases the risk for heart defects in the developing fetus. Abnormal Circulatory Dynamics. It is readily apparent Some congenital defects of the heart are hereditary that the major physiological difficulty caused by tetralogy because the same defect has been known to occur in 290  Chapter 23 Heart Valves and Heart Sounds; Valvular and Congenital Heart Defects identical twins, as well as in succeeding generations. for this is that the coronary vasculature typically does not Children of patients surgically treated for congenital heart increase to the same extent as the mass of cardiac muscle disease have about a 10 times greater chance of having increases. The second reason is that fibrosis often develops congenital heart disease than other children. Congenital in the muscle, especially in the subendocardial muscle where defects of the heart are also frequently associated with the coronary blood flow is poor, with fibrous tissue replacing UNIT IV other congenital defects of the baby’s body. degenerating muscle fibers. Because of the disproportion- ate increase in muscle mass relative to coronary blood flow, relative ischemia may develop as the cardiac muscle hyper- USE OF EXTRACORPOREAL trophies, and coronary blood flow insufficiency may ensue. CIRCULATION DURING CARDIAC Anginal pain is therefore a frequent accompaniment of car- SURGERY diac hypertrophy associated with valvular and congenital It is almost impossible to repair intracardiac defects sur- heart disease. Enlargement of the heart is also associated gically while the heart is still pumping. Therefore, many with a greater risk for developing arrhythmias, which in turn types of artificial heart-­lung machines have been developed can lead to further impairment of cardiac function and sud- to take the place of the heart and lungs during the course den death because of fibrillation. of an operation. Such a system is called extracorporeal cir- culation. The system consists principally of a pump and an oxygenating device. Almost any type of pump that does not Bibliography cause hemolysis of the blood seems to be suitable. Bing R, Cavalcante JL, Everett RJ, Clavel MA, Newby DE, Dweck MR: Methods used for oxygenating blood include the fol- Imaging and impact of myocardial fibrosis in aortic stenosis. JACC lowing: (1) bubbling oxygen through the blood and remov- Cardiovasc Imaging 12:283, 2019. ing the bubbles from the blood before passing it back into Bonow RO, Leon MB, Doshi D, Moat N: Management strategies and future challenges for aortic valve disease. Lancet 387:1312, 2016. the patient; (2) dripping the blood downward over the sur- Burchfield JS, Xie M, Hill JA: Pathological ventricular remodeling: faces of plastic sheets in the presence of oxygen; (3) passing mechanisms: part 1 of 2. Circulation 128:388, 2013. the blood over surfaces of rotating discs; and (4) passing Fahed AC, Gelb BD, Seidman JG, Seidman CE: Genetics of congenital the blood between thin membranes or through thin tubes heart disease: the glass half empty. Circ Res 112(4):707, 2013. that are permeable to oxygen and carbon dioxide. Clyman RI: Patent ductus arteriosus, its treatments, and the risks of pulmonary morbidity. Semin Perinatol 42:235, 2018. Gould ST, Srigunapalan S, Simmons CA, Anseth KS: Hemodynamic HYPERTROPHY OF THE HEART IN and cellular response feedback in calcific aortic valve disease. Circ Res 113:186, 2013. VALVULAR AND CONGENITAL HEART Hinton RB, Ware SM: Heart failure in pediatric patients with congeni- DISEASE tal heart disease. Circ Res 120:978, 2017 Kodali SK, Velagapudi P, Hahn RT, Abbott D, Leon MB: Valvular heart Hypertrophy of cardiac muscle is one of the most impor- disease in patients ≥80 years of age. J Am Coll Cardiol 71:2058, 2018 tant mechanisms whereby the heart adapts to increased Lindman BR, Bonow RO, Otto CM: Current management of calcific workloads whether these loads are caused by increased aortic stenosis. Circ Res 113:223, 2013. pressure against which the heart muscle must contract Manning WJ: Asymptomatic aortic stenosis in the elderly: a clinical or by increased cardiac output that must be pumped. review. JAMA 310:1490, 2013. Maron BJ: Clinical course and management of hypertrophic cardio- One can calculate approximately how much hypertrophy myopathy. N Engl J Med 379:655, 2018. will occur in each chamber of the heart by multiplying Maron BJ, Maron MS, Maron BA, Loscalzo J: Moving beyond the sar- the ventricular output by the pressure against which the comere to explain heterogeneity in hypertrophic cardiomyopathy. J ventricle must work, with an emphasis on pressure. Thus, Am Coll Cardiol 73:1978, 2019. hypertrophy occurs in most types of valvular and con- Nishimura RA, Otto CM, Bonow RO, Carabello BA, et al: 2017 AHA/ ACC Focused update of the 2014 AHA/ACC guideline for the man- genital disease, sometimes causing the heart to weigh as agement of patients with valvular heart disease: A report of the much as 800 grams instead of the normal 300 grams. American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines. Circulation 135:e1159, 2017. Detrimental Effects of Late Stages of Cardiac Hyper- Ohukainen P, Ruskoaho H, Rysa J: Cellular mechanisms of valvular trophy. Although the most common cause of cardiac thickening in early and intermediate calcific aortic valve disease. Curr Cardiol Rev 14:264, 2018. hypertrophy is hypertension, almost all forms of cardiac Remenyi B, ElGuindy A, Smith SC Jr, Yacoub M, Holmes DR Jr: Val- diseases, including valvular and congenital disease, can vular aspects of rheumatic heart disease. Lancet 387:1335, 2016. stimulate enlargement of the heart. Sommer RJ, Hijazi ZM, Rhodes JF Jr: Pathophysiology of congeni- So-­called physiological cardiac hypertrophy is generally tal heart disease in the adult: part I: shunt lesions. Circulation considered to be a compensatory response of the heart to 117:1090, 2008. Sommer RJ, Hijazi ZM, Rhodes JF: Pathophysiology of congenital increased workload and is usually beneficial for maintain- heart disease in the adult: part III: complex congenital heart dis- ing cardiac output in the presence of abnormalities that ease. Circulation 117:1340, 2008. impair the heart’s effectiveness as a pump. However, extreme Zaidi S, Brueckner M: Genetics and genomics of congenital heart dis- degrees of hypertrophy can lead to heart failure. One reason ease. Circ Res 120:923, 2017. 291