Valvular Heart Disease
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[edit] Valvular Heart Disease
Edgar C. SchickJr.
Significant valvular heart disease is likely to be found in only a small proportion of patients in the average primary care practice. The primary physician, however, has much to contribute to the detection of valvular disease and the initial management of these patients. Despite the growth of noninvasive diagnostic technology, the answers to many important questions about possible valvular pathology remain the prerogative of the bedside physician. Diligent auscultatory characterization of heart murmurs and pursuit of cogent ancillary physical findings often provide adequate basis for a diagnosis and obviate the need for additional, more expensive studies. Evaluation of the patient with valvular disease offers the physician a gratifying opportunity to exercise cardiovascular diagnostic skills but also poses challenging questions related to such matters as drug therapy, referral for a cardiologist's opinion, cardiac catheterization, anticoagulation, and prophylactic antibiotic use. This chapter focuses specifically on these aspects and attempts to provide the busy physician with a capsular overview of management for the valvular heart disease patient.
[edit] AORTIC STENOSIS
Aortic stenosis is the most common acquired valvular disease. After adolescence but before the seventh decade, stenosis of the aortic orifice develops as a consequence of congenital bicuspid valvular anatomy in two of every three cases. Idiopathic sclerocalcific degeneration of a normal tricuspid aortic valve predominates among older patients. Rheumatic fever may also cause aortic stenosis but seldom without evidence of mitral valvular involvement.
[edit] Pathophysiology
When the stenotic process has contracted the aortic orifice, normally between 2 and 4 cm2, by about half (Fig. 66-1), the left ventricle is presented with a progressively increasing pressure burden. This challenge is adaptively matched by ventricular hypertrophy, which maintains the systolic stress on the myocardium within the normal range. Significant ventricular dilation is not a feature of uncomplicated aortic stenosis; when present it indicates failure of the primary compensatory mechanism or superimposition of a new problem, such as coronary artery disease. Systolic wall stress increases as a result, and the ejection fraction declines. In the majority of patients these abnormalities reverse after surgery; a depressed ejection fraction improves, but may not fully normalize.
[edit] History and Physical Examination
Patients with evolving aortic stenosis may remain free of symptoms for extended periods. The cardinal symptoms are dyspnea, angina, and exertional syncope. Dyspnea initially reflects the development of abnormal diastolic function in the hypertrophied ventricle. Despite maintenance of normal diastolic volumes and ejection fraction, resting diastolic pressures become elevated and may rise dramatically during exercise. Systolic dysfunction may also develop. Exertional angina occurs in the absence of coronary artery disease. Ischemic symptoms result from insufficiency of coronary flow reserve to meet markedly increased demand. Significant coronary lesions are seldom present in patients with aortic stenosis who do not report angina and occur in about 50% of patients with angina. The traditional teaching that syncope in aortic stenosis develops as a consequence of exertional muscular vasodilation in the presence of a cardiac output response that is limited by the stenosis seems at best only a partial explanation. Abnormal vasodepressor responses to exercise or transient dysrhythmias are other likely possibilities.
[edit] Innocent Murmur.
Aortic flow murmurs are very common among adolescents and young adults. These murmurs are usually harsh in quality, crescendo-decrescendo in profile, and best appreciated along the middle to lower left sternal border. Uncertainty about the significance of murmurs with these features presents a common clinical problem. How can the so-called innocent, functional, or normal flow murmur be distinguished from that which either connotes the presence or portends the development of important valvular pathology?
Although a completely satisfactory distinction cannot always be made, several features of the examination may be helpful. Typically, aortic murmurs radiate to the upper right parasternal area and the neck in contrast to the innocent pulmonic flow murmur, which, although often prominent along the lower sternal margin, radiates to the upper left parasternal region. Pulmonic flow murmurs are characteristically associated with high-output states (e.g., pregnancy, fever, or anemia), although similar conditions may induce or augment aortic murmurs as well. Innocent flow murmurs are generally grade II/VI or less in intensity, reach their peak amplitude during early systole, are relatively brief, and diminish greatly in prominence or disappear altogether during the strain phase of Valsalva's maneuver.
Although an aortic murmur with these characteristics may bespeak a completely normal valve in the adolescent and young adult, it may also represent developing but hemodynamically inconsequential aortic sclerosis in the middle-aged adult. Findings that may be dismissed as innocuous in the young assume a different significance if discovered for the first time in an adult, particularly during the fifth and sixth decades. Several studies have demonstrated that, once established, the stenotic process may progress from insignificant to severe over spans as brief as 2 years, but the majority of patients show little or no progression over a span of several years.
[edit] Physical Findings.
The peripheral manifestations of critical aortic stenosis are a reduced pulse volume and delayed upstroke, usually best appreciated on carotid artery palpation, which may also reveal systolic vibration or shudder, palpable evidence of stenotic jet-related turbulence (Fig. 66-2). The cardiac apex impulse is not displaced in uncomplicated aortic stenosis but is forceful and sustained. An exaggerated presystolic excursion somewhat medial to the apex may represent exaggerated atrial kick. A systolic thrill is often palpable at the base. A normal first sound is followed, usually after a brief gap, by a harsh, but occasionally musical murmur that radiates to the right base and neck, as mentioned above. The second heart sound is most often single in older adults, as a result of prolongation of ejection time and attenuation of A2 by the immobility of the rigid aortic cusps.
Milder degrees of aortic stenosis are indicated by an earlier peak of the systolic murmur and preservation of the aortic closure sound in the adult. A murmur that peaks in mid to late systole usually corresponds with moderate or severe stenosis. A systolic ejection click is the hallmark of the bicuspid aortic valve, but this may be absent with advanced scarring and calcification of the leaflets. Aortic ejection sounds may indicate bicuspid valvular anatomy even in the absence of a systolic murmur.
[edit] Diagnosis
Further evaluation of a basal ejection murmur is obligatory whenever aortic valve pathology is suggested. This applies to all adults with ejection murmurs of grade III/VI or greater intensity, particularly when accompanied by any additional signs of significant stenosis. Adolescents or adults with less prominent murmurs are referred for noninvasive study if an early systolic sound compatible with an aortic ejection click is detected. Although confirmation of an abnormal aortic valve may not lead to immediate corrective therapy, the noninvasive studies may prove very useful in reassuring patients in whom valvular disease can be excluded, identifying individuals who are at risk and require closer follow-up, and establishing the diagnosis of bicuspid valvular anatomy, which has other therapeutic implications. Noninvasive studies also help to identify the muscular and discrete subvalvular membranous variants of left ventricular outflow obstruction, which are the most common entities to be differentiated from valvular stenosis in the adult.
Echocardiography with Doppler provides accurate assessment of the severity of stenosis, approximation of aortic valve area, and recognition of complicating features. Exercise testing may provide useful information about functional limitation in patients with mild or vague symptoms, but should be performed with extreme caution under close supervision.
[edit] Management
Once the diagnosis of aortic stenosis has been established, management has been aptly characterized as “masterly inactivity but cat-like observation.” Morbidity and mortality risk is negligible during the asymptomatic phase, and serial noninvasive studies are unnecessary. Although the individual symptoms carry slightly different prognostic implications, it is the presence of any cardiac symptom in conjunction with physical evidence of aortic stenosis that is of paramount importance. Coincident with the advent of symptoms is a sharp downward turn in life expectancy, with an average survival thereafter of approximately 3 years. Thus the occurrence of angina, syncope, or congestive heart failure in the presence of a reasonable suspicion of aortic stenosis should always prompt referral for specialized evaluation.
Surgical replacement of the aortic valve is the only effective remedy currently available. Because of discouraging clinical results, balloon valvuloplasty has been relegated to a palliative role. Except for antibiotic prophylaxis, there is no medical treatment for aortic stenosis.
Only recently has the natural course of the bicuspid aortic valve become susceptible to prospective study. Older pathology studies suggested that about two thirds of these patients develop clinical evidence of some degree of aortic stenosis or insufficiency beyond age 40. A recent prospective echocardiographic study found that within 15 years of the diagnosis one quarter of the patients required aortic valve replacement. Because of the risk of endocarditis in these patients, antibiotic prophylaxis is a foremost consideration. For this reason, all young patients with suspected aortic ejection sounds (even if a murmur is not heard) should undergo echocardiography (Fig. 66-3) to elucidate aortic valve anatomy.
[edit] AORTIC REGURGITATION
Aortic regurgitation is encountered in clinical practice in acute, severe, and chronic forms. The hemodynamic differences are summarized in Fig. 66-4.
[edit] Chronic Aortic Regurgitation
Although the etiologic list is long, the most likely basis for chronic aortic regurgitation is a congenitally bicuspid aortic valve. Other causes include endocarditis, connective tissue disorders (e.g., Marfan syndrome), aortic aneurysm, myxomatous valvular degeneration, rheumatic fever, syphilis, and aortic involvement by rheumatoid arthritis or one of its variants.
[edit] History and Physical Examination.
Most often, patients with chronic aortic regurgitation are asymptomatic at the time of diagnosis. The essential features of the physical examination are the bounding, collapsing (water-hammer) peripheral pulses with a widened pulse pressure; a downward, laterally displaced, hyperdynamic apex impulse; and the characteristic murmur. The high-pitched, blowing diastolic murmur is usually best heard along the left sternal margin; audibility to the right of the sternum suggests an aortic aneurysm. Of the plethora of eponymic designations assigned to the many peripheral manifestations of dynamic ejection of an abnormally large stroke volume, none contribute significantly to assessment of severity or management.
[edit] Diagnosis and Management.
Echocardiography is indicated in all patients with aortic regurgitation and is used to establish the etiology, assess the severity of regurgitation, evaluate left ventricular size and function, and provide a basis for serial comparison.
Although severe aortic regurgitation can be tolerated for many years without symptoms, the adaptive reserve of the left ventricle is eventually exhausted. Ventricular function then declines, and symptoms of congestive heart failure or, rarely, angina appear. The latter symptom has been attributed to the increased left ventricular muscle mass and low diastolic (coronary perfusion) pressure.
Contemporary management is predicated on the repeatedly confirmed observation that replacement of the aortic valve prior to the onset of left ventricular dysfunction, even in asymptomatic patients, achieves better outcomes.[1][2] The most recent recommendations for management of chronic aorticregurgitation are summarized in Table 66-1. Vasodilator therapy theoretically reduces regurgitant volume; slows, stabilizes, or reverses left ventricular dilation; and preserves left ventricular function. Salutary effects have been demonstrated with hydralazine and nifedipine in the short term (1 to 2 years) and with sustained-release nifedipine in the longer term (up to 6 years). Results with converting enzyme inhibition have been less compelling. Vasodilator therapy is indicated in all patients with severe aortic regurgitation accompanied by hypertension.
Table 66-1 Guidelines for Management of Chronic Aortic Regurgitation
| Severity | Left ventricular size and function | Symptoms | Management |
|---|---|---|---|
| Mild-Moderate | Normal | No | Annual clinical evaluation, antibiotic prophylaxis |
| Echocardiogram every 2-3 years | |||
| Moderate-Severe | Enlarged (>60 mm) | ||
| Normal Function | No | Clinical evaluation every 6 months | |
| Echocardiogram every 6-12 months depending on severity and stability✢ | |||
| Vasodilator therapy | |||
| Yes | Referral for consideration of aortic valve replacement | ||
| Vasodilator therapy | |||
| Abnormal (LVEF <0.50)† | Yes or No | Referral for aortic valve replacement | |
| Vasodilator therapy |
✢Serial echocardiography is recommended at 4-6 month intervals in those with advanced LV dilation (end-diastolic dimension >70, end-systolic >50).
†Valve replacement is recommended for all patients with severe LV dilation (end-diastolic dimension >75 mm, or end-systolic dimension >55 mm).
[edit] Acute Aortic Regurgitation
[edit] Pathophysiology.
Most commonly, infective endocarditis causes acute aortic regurgitation. Less often, aortic trauma, prolapse, or rupture of a myxomatous valve, aortic dissection, or rupture of one of the sinuses of Valsalva, which may result in regurgitation into the right heart, is responsible. In contrast to the slowly progressive regurgitation dealt with above, sudden, massive aortic valvular incompetence precludes effective adaptive compensation. In the chronic situation, the left ventricle gradually dilates to accommodate the necessarily larger end-diastolic volume while maintaining a normal end-diastolic pressure (i.e., improved compliance). Following the Frank-Starling relationship, total stroke volume increases. The abrupt increase in diastolic volume with acute regurgitation into a nondilated ventricle produces a sharp increase in end-diastolic pressure. The contractile response is overwhelmed, and stroke volume decreases; increases in left atrial pressure and pulmonary arterial pressure ensue, aggravated by tachycardia and premature closure of the mitral valve.
[edit] Physical Examination.
The characteristic bounding pulse and low diastolic pressure of the chronic counterpart are absent. Furthermore, lowered aortic pressure and tachycardia conspire to obscure the diastolic murmur, which often assumes a lower-pitched, coarser quality and may evade detection. More often, however, a to-and-fro auscultatory impression is imparted along the left sternal edge (see Fig. 66-4).
[edit] Diagnosis and Management.
Echocardiography establishes the diagnosis, and transesophageal study provides superior definition of etiology (e.g., vegetations, aortic dissection).
Severe regurgitation of this type, apart from considerations pertinent to the primary cause (e.g., aortic dissection), is best managed by prompt replacement of the aortic valve. Interim support is frequently necessary, since these patients often verge on shock. Infusion of dobutamine or dopamine, with or without nitroprusside, as circumstances may allow, usually helps temporarily. When endocarditis presents in this fashion, the risk of mortality outweighs that of subsequent infection of the replacement valve, and surgery should not be deferred.
[edit] MITRAL STENOSIS
[edit] Etiology and Pathophysiology
Classic rheumatic mitral stenosis has virtually disappeared from practice in this country over the last 2 decades, and is now encountered most often in late evolution among the elderly or as a recurrent problem in patients who have previously undergone surgical or percutaneous palliation. Significant stenosis may occasionally be related to extensive calcification of the mitral annulus, and is infrequently simulated by an atrial tumor or a supravalvular membrane (cor triatriatum).
When the original mitral valve orifice has been reduced by about half, atrial pressure must increase to maintain normal diastolic flow into the left ventricle; tachycardia (reduced time for atrial emptying) or an increase in cardiac output raises atrial pressures further. Atrial pressures may reach 20 to 25 mm Hg at rest when the orifice is reduced to about 1 cm2 or during exertion with less severe stenosis. This pressure is transmitted to the pulmonary capillary bed, tipping the normal transcapillary balance and producing interstitial edema. This mechanism is counterpoised to some extent by the development of pulmonary arteriolar vasoconstriction, pulmonary hypertension, and the decline in cardiac output that is characteristic of mitral stenosis.
[edit] History and Physical Examination
The course of rheumatic mitral stenosis, as elucidated by the now classic observations of Wood, includes a prolonged asymptomatic latency, a span of 20 years or more after the episode of rheumatic fever. Typically, this phase is punctuated by symptoms during periods of cardiovascular stress, particularly pregnancy, before sustained manifestations materialize. Once established, symptoms progress to disabling proportions over roughly a decade. Wide individual variability, however, applies, and although progression of stenosis usually leads to symptoms during the fourth and fifth decades, a significant proportion of patients remain asymptomatic for much longer periods, some for a lifetime.
From the hemodynamic considerations cited above, the primacy of dyspnea as a manifestation of mitral stenosis, as well as the basis for the exacerbations of pulmonary congestion that accompany febrile conditions, anemia, and pregnancy, is readily apparent. Asymptomatic or mildly symptomatic patients may decompensate precipitously with the onset of atrial fibrillation, which occasions an abrupt rise in left atrial pressure. When querying patients with mitral stenosis, it is important to consider the dilatory pace of the symptoms, which affords the opportunity for both physiologic and psychologic adaptation.
On examination, the left ventricular apex impulse, which may elude palpation because of posterior rotation by an enlarged right ventricle, is normal in diameter, tapping, and nearly always accompanied by a systolic lift along the lower sternal edge. Emblematic of mitral stenosis are accentuation of S1; the opening snap, a high frequency sound heard during early diastole and widely transmitted across the precordium caused by an abrupt halt to opening of the pliable though tethered anterior mitral leaflet (Fig. 66-5); and the low-pitched diastolic rumble. The diastolic murmur, as underscored by Sir William Osler, “may be concealed under a quarter of a dollar.” It is thus essential to listen with the bell of the stethoscope applied immediately over the apex impulse.
[edit] Diagnosis and Management
Echocardiographic imaging and Doppler study confirm the diagnosis and accurately categorize the severity. Valuable additional information provided includes atrial dimension, the extent and severity of leaflet thickening and calcification, the presence and degree of subvalvular chordal involvement, semiquantitation of any associated mitral regurgitation, and assessment of right ventricular function and pulmonary artery pressure (Fig. 66-6). All of these factors contribute to management decisions. Doppler evaluation with exercise may be useful when symptoms seem disproportionately more or less severe than resting hemodynamics imply.
Mindful of the tendency for these patients to view behavioral adjustments, restrictions, and omissions as normal, symptoms that limit routine daily activities should prompt referral for evaluation and possible percutaneous or surgical intervention. Patients with evidence of NYHA class II symptoms and more than moderate stenosis (mitral valve area ≤ 1.5 cm2) should be considered for valvuloplasty if valve morphology is suitable, and all patients with more advanced symptoms should be referred for intervention. In general, the results of percutaneous balloon valvulotomy are equivalent to those achieved with open surgical commissurotomy when performed by experienced operators, establishing this technique as the initial modality of choice when valvular morphology and related considerations are favorable.[3]
Atrial fibrillation commonly develops in patients with mitral stenosis, and often marks the onset of the progressive symptomatic phase. Digitalis is used for control of the ventricular response rate. Addition of low-dose calcium channel blocker or β-blocker may be necessary in some instances. Systemic embolization, most commonly cerebral, complicates the course of mitral stenosis in about 10% to 20% of cases and is usually associated with atrial fibrillation. All patients with atrial fibrillation and any patient with a history of embolization, regardless of rhythm, should be anticoagulated with warfarin.
Subacute bacterial endocarditis is seldom encountered as a complication of pure mitral stenosis. Nevertheless, antibiotic prophylaxis is recommended for dental and other procedures in the presence of rheumatic valvular disease.
[edit] MITRAL REGURGITATION
[edit] Pathophysiology and Natural History
Competence of the mitral valve during ventricular systole requires precisely coordinated interaction of the principal components of the mitral valve complex: valve leaflets, chordae tendineae, papillary muscles, and mitral annulus. Mitral regurgitation may be caused by dysfunction of any of these components. Common causes of mitral incompetence are mitral valve prolapse (myxomatous degeneration of the mitral valve), ruptured chordae tendineae, rheumatic fever, papillary muscle ischemia or infarction, tissue erosion related to endocarditis, and calcification of the mitral annulus. The term functional mitral regurgitation applies when regurgitation develops as a consequence of left ventricular dilation.
The natural history of this disorder is highly variable and depends on the etiology, acuity, and severity of the regurgitation, as well as the ability to mount and sustain an adaptive response. As an extreme example, the severe acute mitral regurgitation occasioned by papillary muscle rupture or endocarditic valvular disruption is immediately associated with pulmonary edema and often rapidly fatal if uncorrected. On the other hand, some patients with clinically severe mitral regurgitation may maintain functional class I status for over 20 years.
The left ventricle's ability to withstand the often massive volume overload imposed by mitral incompetence apparently results from the rapid decline in systolic wall tension (related to the product of systolic pressure and radius) permitted by left atrial decompression. Ventricular radius shortens more rapidly than normal in the presence of regurgitation. Because development of tension is a much more important determinant of myocardial oxygen demand than an actual decrease in muscle length, this compensation limits the energy cost and allows prolonged stability. Ventricular compensatory reserve, however, may eventually be exhausted; elevated diastolic pressures and progressive congestive symptoms follow. The left atrium also contributes importantly to the adaptive response. In chronic mitral regurgitation the left atrium dilates and may provide a cushion for the pulmonary circuit by absorbing a large regurgitant volume with minimal increases in pressure. Massive acute regurgitation into a small, noncompliant atrium, however, often results in marked pulmonary venous hypertension and pulmonary edema (Fig. 66-7).
[edit] Physical Examination
A briskly rising and somewhat collapsing arterial pulse termed little water hammer (an allusion to similar but much more pronounced findings in aortic regurgitation) is typical of compensated chronic severe mitral regurgitation. The apical impulse is enlarged, displaced downward to the left, and is a rapidly retracted or dynamic impulse. A systolic lift appreciated along the lower left sternal edge may suggest right ventricular overload but is as likely to reflect anterior displacement of the entire heart by left atrial expansion in systole. An attenuated S1 coincides with the onset of a high-pitched, holosystolic murmur, which may radiate to the axilla and extend beyond A2. Because A2 occurs prematurely due to the inability to sustain ventricular pressure, splitting of the second sound may be noted during expiration. Rapid, early diastolic filling of the left ventricle produces a prominent S3 gallop, which may be followed by a brief flow rumble. The presence of an S4 gallop is indicative of a small, noncompliant, forcefully contracting left atrium and implies regurgitation of recent onset (within approximately 18 months) (e.g., chordal rupture).
[edit] Diagnosis and Management
Echocardiographic imaging with Doppler is indicated to confirm the diagnosis, determine the etiology, and establish baseline values for left ventricular dimensions and systolic function for serial comparison.
The goal of medical therapy for acute, severe regurgitation is stabilization prior to surgery. Nitroprusside, alone or in combination with an inotropic agent, such as dobutamine, and aortic balloon counterpulsation are most commonly employed.
Management of chronic mitral regurgitation has been somewhat more controversial, particularly the indications for and timing of surgery. The most current recommendations are summarized in Table 66-2. The aim is to intervene prior to the development of left ventricular decompensation that may lead to suboptimal outcomes after valve repair or replacement. Although vasodilator therapy has some intuitive appeal, it is of no proven benefit in nonhypertensive patients with mitral regurgitation.[4]
Table 66-2 Guidelines for Management of Chronic Mitral Regurgitation
| Severity | Left ventricular size and function | Symptoms | Management |
|---|---|---|---|
| Mild-Moderate | Normal | No | Annual clinical evaluation, antibiotic prophylaxis |
| Echocardiography only with evidence of significant clinical changes | |||
| Patients instructed to report symptoms of dyspnea or palpitations immediately | |||
| Moderate-Severe | Enlarged (>60 mm) | ||
| LV ejection fraction >0.60 | |||
| End-systolic dimension <45 mm | No | Refer for cardiology evaluation and consideration of early repair (versus continued medical management) based on etiology and suitability | |
| Yes | Refer for surgery | ||
| LV ejection fraction <0.60 | Yes or No | Refer for surgery | |
| End-systolic dimension >45 mm |
[edit] MITRAL VALVE PROLAPSE
The observations of Reid and Barlow just over 3 decades ago established the relationship between systolic prolapse of the mitral valve leaflets and the auscultatory findings of midsystolic click with or without a late systolic murmur. This disorder has now emerged as the most prevalent and problematic concern of the medical practitioner, affecting approximately 5% of the general population. Prolapse is encountered at all ages, and, contrary to popular belief, involvement appears to be approximately equal in men and women.
[edit] Pathophysiology
The term primary mitral prolapse is used to distinguish inherent abnormalities in the mitral valve apparatus from prolapse secondary to other conditions. The primary abnormality is myxomatous degeneration that disrupts the normal connective tissue architecture of the valve leaflets, chordae, or annulus. Myxomatous tissue, consisting of an abundant mucopolysaccharide matrix within which collagen fibers are sparsely and haphazardly arrayed, is ultimately responsible for the characteristic redundancy or hooding of the valve leaflets on gross inspection and for the propensity to chordal rupture associated with mitral prolapse. Cohort studies indicate that primary prolapse is hereditary and transmitted as an autosomal dominant trait with variable expression. The causes of secondary mitral prolapse are numerous, but connective tissue disorders, notably Marfan syndrome, secundum atrial septal defect, coronary artery disease, and mitral valvuloplasty, are commonly cited.
[edit] History and Physical Examination
Population studies indicate that the vast majority of affected individuals are asymptomatic. Furthermore, several symptoms traditionally ascribed to prolapse (e.g., dyspnea in the absence of significant mitral regurgitation, fatigue, dizziness, and neurosis) seem to bear no direct relation to the valvular abnormality and may be only coincidentally associated.
The two most common complaints from patients with mitral prolapse are chest pain and palpitations. Chest pain usually differs from typical angina in several respects; specifically, the character is usually sharp or stabbing, the duration is often protracted, a relationship to exertion is absent, and nitroglycerin seldom affords relief. Very rarely the pain closely mimics angina.
Thoracic cage abnormalities, such as pectus excavatum or straight back, are associated with mitral prolapse. The hallmark of prolapse is the mid to late systolic click, which is the only detectable manifestation in more than half the cases. Aortic or pulmonic ejection clicks are frequently mistaken as a manifestation of prolapse but are distinguishable by their timing with the upstroke of the carotid pulse and by typical respiratory variation in the case of the pulmonic click. Rarely, a prolapsing mitral leaflet generates an early systolic click. Estimates vary, but in approximately 15% of cases the click is followed by a brief midsystolic or late systolic murmur. Occasionally the murmur is pansystolic in duration or honking in quality.
The timing of mitral prolapse has been demonstrated to occur reproducibly at a critical systolic volume, thereby accounting for the effects of various maneuvers in evoking characteristic responses in this condition (Fig. 66-8). Measures that decrease cardiac filling (e.g., standing, Valsalva's strain, amyl nitrite administration) reduce ventricular end-diastolic volume. As a result the critical systolic volume and the click/murmur occur earlier. Conversely, passive leg elevation or a deep knee bend increases ventricular filling, delays attainment of the prolapse volume, and either displaces the click/murmur into later systole or eradicates the findings altogether. The variability in auscultation from one examination to another may be striking. Some patients exhibit only a click on occasion, no evidence of prolapse at times, and both click and murmur in other instances.
[edit] Diagnosis
Echocardiography corroborates clinical findings and may identify the estimated 20% of patients in whom auscultatory evidence is lacking. Echocardiography also provides important prognostic information, such as the presence or absence of leaflet thickening, left atrial or ventricular enlargement, and mitral regurgitation.
Somewhat more than one third of patients display ECG repolarization abnormalities. These usually consist of T wave flattening or inversion in the inferior leads; variable ST-segment changes accompany these changes, which frequently are noted in the lateral precordial leads as well. The occurrence of falsely positive exercise ECG in patients with mitral prolapse should be recalled when exercise testing is considered.
[edit] Management
The outlook for most patients with mitral prolapse is favorable, and this aspect deserves the strongest emphasis in discussions of the diagnosis with patients. Because of selection bias, relevant literature includes a disproportion of symptomatic patients. This complicates projection of progression to chordal rupture or significant mitral regurgitation, reported at about 15%, to the asymptomatic patient seen in the office. The presence of a systolic murmur at diagnosis and the presence of significant leaflet thickening or mitral regurgitation on echocardiography confer a higher risk for subsequent complications (Fig. 66-9), and these individuals warrant more cautious observation. As a rule, annual follow-up with echocardiograms when changes are suspected suffices for those with mild regurgitation. Significant mitral regurgitation is managed as previously outlined.
Although it is widely conceded that prolapse poses a hazard for endocarditis in patients with a systolic murmur, there is no firm evidence that an isolated click imparts the same liability. Currently, it is recommended that patients with a murmur and those with features implying a higher risk for endocarditis (e.g., leaflet thickening, left atrial or ventricular enlargement) receive prophylaxis.
All varieties of dysrhythmia have been associated with mitral prolapse, but the actual prevalence is substantially less than case reports imply. It has been suggested that supraventricular premature beats and tachydysrhythmias in mitral valve prolapse may be caused by depolarization of smooth muscle cells that have been identified in excised mitral valve tissue. Alternatively, concealed atrioventricular (AV) nodal bypass tracts, so-called because they permit any retrograde conduction (ventricle to atrium), may foster reentry. Regardless of the substrate, therapy is necessary only for symptomatic and distressing dysrhythmias, and a β-blocker is a good first choice.
Sudden death occurs in a very small proportion of patients with prolapse. Reported cases occurred predominantly in women, age 40 or older, usually with evidence of advanced mitral regurgitation. Ventricular ectopy was evident in more than three fourths of those for whom relevant information was available, and more than half of those described in sufficient detail had previously experienced syncope. Patients with recurrent syncope and symptomatic ventricular dysrhythmias should be referred for electrophysiologic evaluation.
Both transient and permanent neurologic impairment have been observed in patients with mitral valve prolapse. An excessive prevalence of mitral prolapse has also been noted among patients under 40 years of age who incur a stroke. The inference that cerebral embolism explains these observations derives from the identification of macroscopic coalescence of platelets and fibrin on the atrial surface of the abnormal mitral leaflets in some patients. Attractive as this hypothesis may seem, it is far from firmly established. The role played by atrial rhythm disturbances requires further clarification, and an association of migraine headache with prolapse suggests another possible basis (i.e., vasospasm). Conclusive data notwithstanding, warfarin is usually utilized in patients with transient ischemia or stroke. Aspirin may be of benefit for patients in sinus rhythm and high-risk prolapse by echocardiography.
[edit] TRICUSPID VALVE DISEASE
[edit] Tricuspid Stenosis
Tricuspid stenosis is nearly always a consequence of rheumatic fever and is invariably accompanied by left heart valvular involvement. The pathology resembles mitral stenosis. Fatigue, a consequence of low cardiac output, is a prominent symptom, as are the other signs of right atrial hypertension including edema or anasarca, ascites, and hepatomegaly.
Diagnostic physical findings include large jugular a waves with sinus rhythm and sluggish y descent, which may be more palpable than visible if atrial fibrillation is present. The most helpful auscultatory finding is the diastolic decrescendo murmur to the left of the lower sternum, which is relatively high-pitched and easily misconstrued as aortic regurgitation. Echocardiography reveals leaflet thickening with reduced mobility and provides accurate assessment of the valvular gradient.
[edit] Tricuspid Regurgitation
Tricuspid regurgitation most often develops as a late consequence of left ventricular failure, regardless of etiology, as a result of sustained reactive pulmonary hypertension. Chronic right ventricular volume overload and dilation in atrial septal defect may induce secondary or “functional” tricuspid incompetence. Other primary causes of tricuspid regurgitation include trauma, carcinoid syndrome, endocarditis, rheumatic fever, myxomatous degeneration, and Ebstein's anomaly.
[edit] History and Physical Examination
Primary tricuspid regurgitation may be tolerated well for an indefinite period in the absence of pulmonary hypertension. Secondary regurgitation, however, serves only to exacerbate the manifestations of right ventricular failure. Examination discloses sustained ascent instead of descent of the jugular meniscus during systole and palpable hepatic pulsation. Echocardiography with Doppler confirms the diagnosis and clarifies etiology.
[edit] Management
Secondary tricuspid regurgitation usually responds to therapeutic measures directed at the principal offender (i.e., diuretics, and vasodilators in left ventricular failure), surgical correction of aortic or mitral valve disease, and measures intended to lower pulmonary pressures in the presence of lung disease. Indications for referral to a cardiologist include those previously indicated for any associated valvular disease, symptomatic primary tricuspid regurgitation, or recalcitrance to the medical therapy. Surgical tricuspid annuloplasty is the treatment of choice in refractory cases; valve replacement is reserved for circumstances in which satisfactory annular plication cannot be achieved.
Surgery for tricuspid stenosis is usually undertaken simultaneously with correction of the mitral and aortic valve abnormalities and most often consists of bioprosthetic valve replacement. Selected patients may be candidates for percutaneous commissurotomy.
[edit] VALVULAR DISEASE ASSOCIATED WITH APPETITE-SUPPRESSANT DRUGS
Recognition that the use of the anorectic agents phentermine, fenfluramine, and dexfenfluramine might produce a form of fibrosclerotic heart valve damage similar to that associated with ergotamine and methysergide has provoked a level of concern proportionate to the inordinate use of these agents. Published estimates vary considerably, but abnormalities of the aortic, mitral, or tricuspid valves may be detected in up to one third of patients who have received these agents alone or in combination for more than 4 months. The incidence of clinically significant valvular insufficiency is substantially lower, but the natural course of mild abnormalities awaits definition.
Routine echocardiographic screening of patients who have received these anorectic drugs is not recommended, but diagnostic evaluation is appropriate when a murmur, particularly a new murmur of aortic or mitral insufficiency, is detected on examination.
[edit] ENDOCARDITIS
Clinical features, bacteriologic aspects, and antibiotic therapy are discussed in detail in Chapter 69 . The combination of antibiotic therapy and timely surgical intervention has substantially reduced mortality with infective endocarditis. Questions regarding the need for and the timing of surgery, however, are often problematic because of the wide-ranging variability in the complexity and severity of the cardiac manifestations and the difficulty in balancing benefit-risk considerations. Relevant factors include valve type, heart failure, persistent infection, embolization, infecting organism, extravalvular extension, and other complications. Generally a cardiologist should be involved in the management of these patients.
Consideration of surgery in endocarditis must include a decision analysis that balances the risks of medical treatment with those of surgical intervention, which include not only operative mortality and morbidity, but the long-term complications of valvular prostheses and anticoagulation. Absolute indications for surgical intervention are advanced heart failure that is directly related to valve dysfunction and uncontrolled infection, including evidence of serious perivalvular extension. Relative indications for surgery include (1) perivalvular infection, (2) recurrent embolization, especially in the presence of large, mobile vegetations, (3) Staphylococcus aureus endocarditis, (4) infection with fungal or other resistant organisms, and (5) relapse after appropriate treatment.
Moderate to severe heart failure caused by infective endocarditis and valve dysfunction confers a high mortality risk without corrective surgery. Medical therapy alone is associated with mortality rates of approximately 75% and can be reduced to about 25% with surgery. Thus patients with advanced heart failure should undergo operation before extreme or refractory hemodynamic deterioration develops. Failure to clear bacteremia after 3 to 5 days of appropriate antibiotic therapy or other clinical evidence that treatment has failed to control the infective process constitutes a strong indication for surgery.
Infection extends beyond the valve leaflets in 10% to 20% of patients with native valve endocarditis, and infections complicated by the formation of perivalvular abscesses and fistulas are notoriously resistant to antibiotic therapy. For this reason, evidence of such a complication is a strong indication for surgical intervention. Transesophageal echocardiography (TEE) is required in all instances where such complications are suspected (Fig. 66-10).
In older literature, the finding of vegetations on echocardiography was associated with a higher risk of death, congestive failure, or need for surgery during the course of endocarditis. Many, but not all, published reports on vegetation size indicate an increased probability of complications when vegetations measuring one centimeter or more in diameter are detected by echocardiography. Recent reports relating to vegetation size are not uniform: some suggest that large vegetations correlate with systemic emboli but not heart failure or mortality, others that size alone is a poor predictor of embolization. The decision to proceed to surgery should not be based solely on vegetation size. Other features of a vegetation may help to identify those more likely to produce embolization. Clearly, large vegetations combined with recurrent embolization in the treated patient present a strong indication for surgery.
Patients with severe valve dysfunction who respond to antibiotic therapy and who manifest evidence of no more than mild, nonprogressive heart failure should complete a full course of antibiotics before surgery is undertaken. If progressive heart failure occurs or evidence of other complications develops, surgery should be performed as soon as possible. An exception to this general guideline is the patient with cerebral embolization. Cardiac surgery and related anticoagulation increase the risk of additional neurologic damage. For this reason, surgery should be delayed 5 to 10 days in patients who have had an embolic stroke and at least twice that interval in those with evidence of intracranial hemorrhage.
[edit] POSTOPERATIVE VALVULAR PATIENTS
Current estimates place the number of heart valve operations above 50,000 annually, which cumulatively projects to a large population of patients who require vigilant follow-up care. Obviously, it is impractical to expect the physician to command the minute details of individual artificial valves, but design features allow manageable grouping, and the long-term complications are similar among all prostheses. Familiarity with fundamental aspects is essential, considering the high probability that postoperative valvular patients will be encountered in any practice.
Replacement heart valves are categorized by components as either mechanical or bioprosthetic. Two types of mechanical prostheses are currently available in the United States, caged-ball (Starr Edwards) valves, now seldom used, and tilting disk valves, which may have one (Medtronic Hall, Omniscience) or two (St. Jude, Carbomedics) pivoting disks. Bioprostheses include porcine valves, bovine pericardial valves, and homografts.
After successful surgery, complications may be grouped into three major categories: (1) prosthetic valve failure, (2) thromboembolism and the hazards of anticoagulation, and (3) prosthetic endocarditis.
[edit] Prosthetic Valve Dysfunction
Prosthetic valve dysfunction is usually not a consequence of structural failure of currently available mechanical prostheses. Thus the term most often implies prosthetic obstruction or regurgitation; the former usually results from pannus ingrowth or thrombosis, and the latter is actually periprosthetic. Bioprosthetic tissue is obviously subject to dysfunction by erosion or scarring. The current literature suggests an annual failure rate of about 1% over the first 5 years, with cumulative incidence of 20% for homografts and 30% for porcine heterografts by 10 to 15 years. Studies suggest lower failure rates for the newer bovine pericardial valves, approximately 5% at 10 years.
Auscultatory expectations vary with the type of prosthesis. More important than any a priori findings specified for a particular valve is a thorough and meticulous documentation of auscultation in the early postreplacement interval. Valvular dysfunction is typically heralded by the disappearance of previously audible clicks or the development of new murmurs that cannot be accounted for by changes in hemodynamic state, such as variable intensity of opening and closure sounds with atrial fibrillation or enhancement of murmurs by anemia. It is well recognized, however, that even severe prosthetic abnormalities may develop without detectable auscultatory evidence. When sinus rhythm is present, beat-to-beat alteration in prosthetic sound intensity always suggests dysfunction. Patients suspected to have prosthetic valvular dysfunction require referral for specialized evaluation.
Echocardiography plays an important role in follow-up of postoperative valvular patients, and a baseline study should be obtained prior to hospital discharge or soon thereafter without exception. Imaging and Doppler evaluation are very helpful when valvular dysfunction is suspected, and the superior resolution of transesophageal study may provide important additional information, particularly when mitral prosthetic function is at issue. Although some hemolysis occurs with all mechanical prostheses, an increase in the degree of hemolysis may occur with valve dysfunction. Determination of lactic dehydrogenase (LDH) and haptoglobin levels once patients have fully recovered from surgery establishes a potentially useful reference base.
[edit] Thromboembolism
For anticoagulated patients, the risk of thromboembolism from a mechanical aortic prosthesis averages 1% per year or less; the risk is about double this for a mitral prosthesis. Patients with bioprostheses in normal sinus rhythm do not require anticoagulation beyond the immediate postoperative period, and this is the most attractive feature of these valves. However, atrial fibrillation and severe left ventricular dysfunction remain as indications for long-term anticoagulation in patients with bioprosthetic valves. An isolated thromboembolic event need not occasion extensive evaluation in the absence of other indications of valve dysfunction. Recurrent embolization in the presence of a therapeutic INR may be managed by addition of aspirin or other antiplatelet agents. Although advocated by some, routine use of low-dose aspirin in addition to warfarin for mechanical prostheses is not the practice of most authorities.[5] Estimates of significant hemorrhage in anticoagulated patients range as high as about 6% annually, with severe episodes in 2% and related fatality in about 0.5%.
Anticoagulation should be temporarily withheld following embolic stroke until the possibility of a hemorrhagic component can be clarified. For major surgery, dental extractions, gynecologic procedures, or diagnostic procedures that may eventuate in surgery, anticoagulation is usually discontinued 3 to 5 days beforehand and resumed as soon as possible thereafter. The administration of vitamin K is discouraged. Relevant literature neither strongly supports nor refutes the interim use of intravenous or low-molecular- weight heparin for these short terms, but parenteral anticoagulation is indicated when the INR falls below 2 for 5 days. The potential for embryopathy and the unpredictable need for restitution of normal coagulation at delivery provides the rationale for the substitution of subcutaneous heparin for warfarin during the first trimester and again immediately before term in pregnant women with prostheses.
[edit] Prosthetic Endocarditis
The annual rate of prosthetic valvular infection approaches 1%. Infection that develops within 2 months of valve replacement (early PVE) is most often caused by coagulase-negative staphylococci, S. aureus, or gram-negative bacilli. The mortality rate, despite antibiotic therapy, remains high (50% to 75%). Late PVE is more often of streptococcal etiology and carries a lower mortality risk (40% to 50%). Antibiotic cures may be achieved with PVE, and are most likely when there is evidence of bioprosthetic leaflet involvement and maintenance of perivalvular integrity. Infection of mechanical prostheses is perivalvular, and the probability of successful eradication with antibiotics, except with an organism displaying high antibiotic susceptibility, is low. Most patients will require surgery, which is usually preceded by a period of drug therapy. Removal of an infected prosthesis is indicated if there is persistent bacteremia despite appropriate therapy, evidence of valve dehiscence or dysfunction, and relapse after treatment.
Patients with prosthetic valves share a higher risk of endocarditis following bacteremia and should be imbued with a strong sense of the need for antibiotic prophylaxis for dental and other procedures (see Chapter 69 ). Embolization may be an indication of prosthetic infection, and this possibility should always be considered. The limited data available suggest that cerebrovascular morbidity is higher if anticoagulation is stopped during the course of prosthetic endocarditis; thus warfarin should be continued unless another specific contraindication arises.
[edit] REFERENCES
- ↑ RO Bonow, B Carabello, AC de LeonJr,et al.: ACC/AHA guidelines for the management of patients with valvular heart disease: executive summary. A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee on Management of Patients with Valvular Heart Disease). Circulation 1993; 98:1949 - 1986.
- ↑ BA Carabello, FA Crawford: Valvular heart disease. N Engl J Med 1997; 337:32 - 41.
- ↑ JJ Glazier, ZG Turi: Percutaneous balloon mitral valvuloplasty. Prog Cardiovasc Dis 1997; 40:5 - 26.
- ↑ HJ Levine, WH Gaasch: Vasoactive drugs in chronic regurgitant lesions of the mitral and aortic valves. J Am Coll Cardiol 1996; 28:1083 - 1091.
- ↑ DJ Tiede, RA Nishimura, DA Gastineau,et al.: Modern management of prosthetic valve anticoagulation. Mayo Clin Proc 1998; 73:665 - 680.
