Valvular Heart Disease
Garrick C. Stewart
Patrick T. O’Gara
The incidence of valvular heart disease continues to rise due to the increasing longevity of the population and remains a source of significant morbidity and mortality [1]. More than 5 million Americans are living with valvular heart disease and nearly 100,000 undergo valve surgery each year [2]. Patients with native or prosthetic valve disease constitute a significant proportion of intensive care unit (ICU) admissions. Many patients come to medical attention during an acute illness that triggers an abrupt change in cardiovascular physiology. While stabilization with medical management is possible for most patients with mild or moderate disease, surgery may be urgently required if severe disease is present. Prompt diagnosis often requires a high index of suspicion [3]. Timely cardiac imaging with transthoracic echocardiography (TTE) can define valve anatomy and lesion severity. Transesophageal echocardiography (TEE) may be required in select circumstances for better visualization and characterization. The need for an invasive hemodynamic assessment may follow. Early collaboration among intensivists, cardiologists, and cardiac surgeons is critical for optimizing patient outcome. This chapter will highlight an integrated approach to the diagnosis and treatment of the native and prosthetic valve diseases most commonly encountered in an ICU setting.
Aortic Stenosis
Aortic stenosis (AS) is a progressive disease for which there is no medical treatment. The ICU management of patients with AS may be quite challenging, particularly in the setting of concomitant medical illness. Characterizing the severity of stenosis is critical for determining the timing of surgical intervention and requires a careful history, physical examination, and initial imaging with TTE.
Etiology
AS accounts for one-quarter of all chronic valvular heart disease, with approximately 80% of symptomatic cases occurring in adult males (Fig. 34.1). Common etiologies of valvular AS include age-related calcific degeneration, stenosis of a congenitally bicuspid valve, and rheumatic heart disease. Age-related, degenerative calcific AS is the most common cause of AS among adults in the United States. More than 30% of adults older than 65 years exhibit aortic valve sclerosis, whereas only 2% have more significant valvular stenosis. The valve cusps are focally thickened or calcified in aortic sclerosis, with production of a systolic ejection murmur, but without significant outflow obstruction (peak jet velocity of < 2.5 m per second). Recent studies suggest calcific AS is the end result of an active disease process rather than the inevitable consequence of aging [4]. There may also be a genetic predisposition to calcific degeneration of trileaflet valves [5]. The histologic appearance of a sclerotic valve is similar to atherosclerosis, with inflammation, calcification, and thickening. Both calcific AS and aortic sclerosis appear to be a marker for coronary heart disease events [6]. Older age, male sex, smoking, diabetes mellitus, hypertension, chronic kidney disease, and hypercholesterolemia are risk factors for calcific AS. Despite the compelling connection between atherosclerosis and calcific valve degeneration, high-dose lipid lowering therapy has thus far not been shown to retard the progression of AS in randomized trials [7,8].
Congenitally bicuspid aortic valves are present in 1% to 2% of the population, with a 4 to 1 male predominance, and seldom result in serious narrowing of the aortic orifice during childhood [9]. Abnormal valve architecture makes the two cusps susceptible to hemodynamic stresses, ultimately leading to thickening, calcification, and fusion of leaflets, and narrowing of the orifice. AS develops earlier in bicuspid valves, usually in the fifth or sixth decades, compared with trileaflet aortic valves, which usually do not exhibit calcific AS until the sixth or seventh decade of life [10]. Bicuspid aortic valves are also associated with aortic regurgitation (AR) and aortic root/ascending aortic dilatation and coarctation (Fig. 34.2). Up to 25% to 40% of patients with bicuspid aortic valve will have an ascending aortic aneurysm unrelated to the severity of the valve lesion. Patients with bicuspid aortic valves are susceptible to aortic dissection [11]. Medial degeneration similar to that seen in Marfan syndrome is responsible for aneurysm development in patients with a bicuspid aortic valve [12].
Rheumatic disease may affect the aortic leaflets leading to commissural fusion, fibrosis, and calcification, with narrowing of the valve orifice. Rheumatic AS is almost always accompanied by involvement of the mitral valve and concomitant AR. Radiation-induced AS as a sequela of cancer radiotherapy often occurs in conjunction with proximal coronary artery disease (CAD). Rare causes of valvular AS include Paget’s disease of bone, rheumatoid arthritis, and ochronosis. By the time AS becomes severe, superimposed calcification may make it difficult to determine underlying valve architecture and the precise etiology.
In addition to valvular AS, other causes of left ventricular (LV) outflow obstruction include hypertrophic obstructive cardiomyopathy (HOCM), a congenitally unicuspid aortic valve, discrete congenital subvalvular AS resulting from a fibromuscular membrane, and supravalvular AS. The various causes of LV outflow obstruction can be differentiated by careful physical examination and TTE.
Pathophysiology
Obstruction to LV outflow produces a pressure gradient between the LV and the aorta (Fig. 34.3). The ventricle responds to this pressure overload with concentric hypertrophy, which is initially adaptive because it reduces wall stress and preserves ejection performance. The law of Laplace states that wall stress is directly proportional to the product of LV pressure and radius and inversely proportional to LV wall thickness. Compensatory hypertrophy may accommodate a large pressure gradient for years before it becomes maladaptive and LV function declines, with chamber dilatation and reduced cardiac output [13]. In the setting of AS with preserved ejection fraction (EF),
cardiac output may be normal at rest but fail to rise appropriately with exercise. Coronary flow reserve may be reduced because of the increased oxygen demand of the hypertrophied LV and increased transmural pressure gradient, and the longer distance blood must travel to reach the subendocardial layer. Taken together, these factors can contribute to subendocardial ischemia even in the absence of epicardial CAD [14]. The loss of appropriately timed atrial contraction, such as occurs with atrial fibrillation (AF), may cause rapid progression of symptoms because of the reliance on atrial systole to fill the stiff, hypertrophied LV.
cardiac output may be normal at rest but fail to rise appropriately with exercise. Coronary flow reserve may be reduced because of the increased oxygen demand of the hypertrophied LV and increased transmural pressure gradient, and the longer distance blood must travel to reach the subendocardial layer. Taken together, these factors can contribute to subendocardial ischemia even in the absence of epicardial CAD [14]. The loss of appropriately timed atrial contraction, such as occurs with atrial fibrillation (AF), may cause rapid progression of symptoms because of the reliance on atrial systole to fill the stiff, hypertrophied LV.
 Figure 34.1. Transthoracic echocardiography of severe valvular aortic stenosis. A: Transthoracic echocardiogram parasternal long axis view of the aortic valve during systole. Aortic valve leaflets are thickened with severely restricted motion consistent with severe aortic stenosis. B: Transaortic continuous wave Doppler jet from the apical five-chamber view. Peak transaortic velocity is 4.68 m/sec, producing an estimated peak transaortic gradient of 87 mm Hg. |
 Figure 34.2. Bicuspid aortic valve and aortic root aneurysm. A: Transthoracic echocardiogram with parasternal short axis view at the level of the aortic valve reveals a bicuspid aortic valve with fusion of the left and noncoronary cusps. B: A 5.1-cm ascending aortic aneurysm in a 37-year-old man with bicuspid aortic valve disease and only moderate aortic stenosis (valve area, 1.2 cm2). Patients with bicuspid disease frequently develop aneurysms of the ascending aorta independent of the severity of hemodynamic valvular impairment and are at risk for aortic dissection. Resection is indicated for maximal aneurysm size larger than 5.0 cm, an increase in aneurysm size of more than 0.5 cm/y, or at the time of aortic valve replacement if the aneurysm size exceeds 4.5 cm. [From Libby P (ed): Essential Atlas of Cardiovascular Disease. New York, NY, Springer, 2009, p 216, Figure 9–6, with permission.] |
No single parameter of valve structure or function is sufficient to define the severity of AS. Integration of the clinical history, physical examination, and TTE is required to place the lesion in context [15]. The physical examination of AS in the ICU may be particularly challenging, contributing to the greater importance of timely TTE. Echocardiographic criteria for severe AS in patients with normal underlying LV function include
calcified leaflets with reduced excursion, maximal transaortic jet velocity of more than 4 m per second, mean transaortic gradient of more than 40 mm Hg, or an effective aortic valve orifice of less than 1 cm2 (Table 34.1). When there is underlying LV systolic dysfunction, severe AS may be present despite low transaortic velocity and mean gradient. Such patients are at particularly high risk for complications and require further evaluation to determine if true valvular AS is present or whether the reduced valve area relates to an underlying cardiomyopathy (pseudo-severe AS) [16].
calcified leaflets with reduced excursion, maximal transaortic jet velocity of more than 4 m per second, mean transaortic gradient of more than 40 mm Hg, or an effective aortic valve orifice of less than 1 cm2 (Table 34.1). When there is underlying LV systolic dysfunction, severe AS may be present despite low transaortic velocity and mean gradient. Such patients are at particularly high risk for complications and require further evaluation to determine if true valvular AS is present or whether the reduced valve area relates to an underlying cardiomyopathy (pseudo-severe AS) [16].
 Figure 34.3. Pathophysiology of aortic stenosis. Left ventricular (LV) outflow obstruction results in a gradual increase in LV systolic pressure, an increase in LV ejection time (LVET), an increase in LV diastolic pressure, and a decrease in mean aortic (Ao) pressure. Increased LV systolic pressure results in compensatory LV hypertrophy (LVH), which may lead to LV dysfunction and failure. Increased LV systolic pressure, LVH, and prolonged LVET increase myocardial oxygen (O2) consumption. Increased LVET results in a decrease in LV diastolic time (myocardial perfusion time). Increased LV diastolic pressure and decreased Ao diastolic pressure decrease coronary perfusion pressure, thereby decreasing myocardial supply. Increased myocardial O2 consumption and decreased myocardial O2 supply produce myocardial ischemia, which further compromises LV function. [Adapted from Bonow R, Braunwald E: Valvular heart disease, in Zipes D, et al. (eds): Braunwald’s Heart Disease. Philadelphia, Elsevier, 2005, p 1585, with permission.] |
Clinical Presentation
History
The cardinal symptoms of AS are dyspnea, angina, and syncope [17]. Exertional dyspnea is typically the first reported symptom and reflects an elevation in LV end-diastolic pressure transmitted to the pulmonary venous circulation. Some patients, particularly the elderly, may report generalized fatigue and weakness rather than dyspnea. Angina occurs in two thirds of patients with AS and is similar to that reported by patients with flow-limiting coronary atherosclerosis [18]. Syncope is effort related and due to cerebral hypoperfusion from a decrease in mean arterial pressure produced by the combination of peripheral vasodilatation in the presence of a fixed cardiac output or an inappropriate baroreceptor reflex. Severe AS is also rarely associated with acquired von Willebrand’s disease related to sheering of von Willebrand multimers passing through the stenotic orifice [19]. As a result, gastrointestinal bleeding, epistaxis, or ecchymoses may be present in some patients.
Table 34.1 Severity of Aortic Stenosis | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
Most patients with AS have gradually increasing LV obstruction over many years, producing a long latent phase. During this clinically silent period, there is a very low risk of sudden death (< 1% per year) [20]. The rate of AS progression is variable, with an average increase in mean gradient of 7 mm Hg and reduction in valve area of 0.1 cm2 per year [21]. Symptoms from valvular AS are rare until the valve orifice has narrowed to approximately less than 1 cm2. The onset of symptoms is a critical turning point in the natural history of the disease, usually indicates severe AS, and heralds the need for surgical evaluation and treatment because of the markedly reduced survival [17] (Fig. 34.4). An abrupt change in the natural history of AS may occur with AF, endocarditis, or myocardial infarction (MI), each of which may trigger acute decompensation [22].
Physical Examination
The hallmark of AS is a carotid arterial pulse that rises slowly to a delayed peak, known as pulsus parvus et tardus. In the elderly, stiffened carotid arteries may mask this finding. Similarly, patients with AS and concomitant AR may have preservation of the arterial upstroke due to an elevated stroke volume. The LV apical impulse may be displaced laterally with a sustained contour due to LV hypertrophy (LVH) and prolonged systolic ejection.
The murmur of AS is a systolic ejection murmur commencing shortly after S1, rising in intensity with a peak in mid ejection, then ending just before aortic valve closure. It is
characteristically low-pitched, harsh, or rasping in character and best heard at the base of the heart in the second right intercostal space. The AS murmur radiates along the carotid arteries, though may sometimes be transmitted downward to the apex where it may be confused with the murmur of mitral regurgitation (MR) (Gallavardin effect). The murmur of AS is diminished with Valsalva maneuver and standing, in contrast to the murmur of hypertrophic cardiomyopathy which gets louder with these maneuvers. Often S2 becomes paradoxically split in severe AS because of prolonged LV ejection. An S4 is audible at the apex and reflects LVH with an elevated LV end-diastolic pressure. An S3 gallop generally occurs late in the course of AS when LV dilatation is present. Murmur intensity does not necessarily correspond to AS severity. The best predictors of AS severity on physical examination are a late peaking systolic murmur, a single S2 (absent aortic valve closure sound), and pulsus parvus et tardus. In patients with heart failure and a low cardiac output, the findings related to AS are less impressive.
characteristically low-pitched, harsh, or rasping in character and best heard at the base of the heart in the second right intercostal space. The AS murmur radiates along the carotid arteries, though may sometimes be transmitted downward to the apex where it may be confused with the murmur of mitral regurgitation (MR) (Gallavardin effect). The murmur of AS is diminished with Valsalva maneuver and standing, in contrast to the murmur of hypertrophic cardiomyopathy which gets louder with these maneuvers. Often S2 becomes paradoxically split in severe AS because of prolonged LV ejection. An S4 is audible at the apex and reflects LVH with an elevated LV end-diastolic pressure. An S3 gallop generally occurs late in the course of AS when LV dilatation is present. Murmur intensity does not necessarily correspond to AS severity. The best predictors of AS severity on physical examination are a late peaking systolic murmur, a single S2 (absent aortic valve closure sound), and pulsus parvus et tardus. In patients with heart failure and a low cardiac output, the findings related to AS are less impressive.
 Figure 34.4. The onset of symptoms in patients with aortic stenosis initiates a rapid rise in the risk of mortality. Patients with angina have a better prognosis than those with syncope. [From Ross J Jr, Braunwald E: Aortic stenosis. Circulation 38(1S5):61–67, 1968, with permission.] |
Investigations
Electrocardiography
Most patients with severe AS will have evidence of LVH on electrocardiogram (ECG). Left atrial (LA) enlargement is common. Nonspecific ST and T wave abnormalities may be seen or evidence of LV strain may be apparent. Rarely, atrioventricular conduction defects may develop due to extension of perivalvular calcium into the adjacent conduction system. This finding is more common after aortic valve replacement (AVR). There is poor correlation between ECG findings and AS severity.
Chest Radiography
The chest radiograph may be normal in severe AS. There may be “poststenotic” dilation of the ascending aorta or a widened mediastinum if aortic aneurysmal dilatation is present in patients with a bicuspid aortic valve. LV chamber size is usually normal, though aortic valve calcification may be seen, especially on the lateral film. Valvular calcium deposits can be visualized using fluoroscopy during cardiac catheterization, chest computed tomography (CT), or TTE. A normal radiograph does not exclude severe AS. In the later stages of AS, the LV dilates leading to a widened cardiac silhouette, often accompanied by pulmonary congestion.
Echocardiography
TTE with Doppler is indicated for assessing the severity of AS. TTE visualizes aortic valve structure, including the number of cusps, degree of calcification, leaflet excursion, annular size, and supravalvular anatomy. Eccentric valve cusps are characteristic of congenitally bicuspid aortic valves, often accompanied by aneurysmal enlargement of the root or ascending aorta. TTE is also useful for identifying coexisting valvular disease, differentiating valvular AS from other forms of LV outflow tract obstruction, assessing pulmonary artery systolic pressure, and evaluating underlying biventricular function. The peak transvalvular jet velocity on continuous wave Doppler is critical for assessing AS severity. Peak and mean transvalvular gradients are derived from the jet velocity using the modified Bernoulli equation and the aortic valve area is estimated from the continuity equation. The dimensionless index, which is the ratio of LV outflow tract velocity to peak aortic velocity, can also be used to estimate AS severity when measurement of LV outflow tract diameter is difficult due to extensive calcification. A dimensionless index less than 0.25 is consistent with severe AS [15].
Cardiac Catheterization
Noninvasive assessment with TTE is now standard, but catheterization may be helpful if there is a discrepancy between the clinical and echocardiographic findings. Calculation of aortic valve area by invasive hemodynamic assessment requires accurate assessment of the transvalvular flow and mean transvalvular pressure gradient to calculate effective orifice area using the Gorlin formula [23]. Concerns have been raised about the risk of cerebral embolization during attempts to cross the aortic valve and directly measure the transaortic gradient. Angiography is indicated to detect CAD in patients older than 45 years who are being considered for operative treatment of severe AS [24]. Coronary CT angiography is likely to be performed more often for this indication in patients with a low pretest likelihood of CAD.
Special Case: Low-Output/Low-Gradient Aortic Stenosis
The evaluation and management of patients with AS and a depressed EF can be vexing. Patients with anatomically severe AS and reduced EF (< 40%) often have a relatively low-pressure gradient (< 30 mm Hg) due to a weakened ventricle and afterload mismatch. The true severity of AS can be difficult to determine when the cardiac output and transaortic gradient are low. If the ventricle itself is diseased and unable to generate sufficient systolic force to open the leaflets adequately, a reduced aortic valve area may be present at rest, overestimating AS severity. This condition is known as pseudo-severe AS [25]. In such cases, LV dysfunction is the predominant pathology and may be caused by prior MI or a primary cardiomyopathy. Patients either with true severe AS with reduced EF or pseudo-severe AS have a low-flow state with low transaortic gradients contributing to calculated aortic valve areas less than 1 cm2. Pseudo-severe AS patients must be distinguished from those with true severe AS and poor LV function, since patients with true severe AS and contractile reserve will usually benefit from valve surgery, whereas patients with pseudo-severe AS are not operative candidates [26,27,28].
Dobutamine stress echocardiography has a well-defined diagnostic role in this setting [29] (Fig. 34.5). The inotropic effects of low-dose dobutamine will increase transvalvular flow in patients with a contractile reserve [30]. Contractile reserve is defined as an increase in stroke volume with inotropic infusion of more than 20%. Dobutamine infusion, particularly at doses ≤ 20 μg per kg per minute, is generally well tolerated but should only be performed in experienced centers with a cardiologist in attendance. In patients with true severe AS and LV dysfunction, dobutamine will increase cardiac output and mean transvalvular gradient, but the calculated aortic valve area will remain low (< 1 cm2). Patients with pseudo-severe AS will have an increase in aortic valve area into a range no longer considered severe (> 1.2 cm2) with little change in transvalvular gradient. Some patients will not show contractile reserve to dobutamine, signaling a poor prognosis [31]. Surgery is indicated in true severe AS with contractile reserve after dobutamine challenge, and generally contraindicated for patients with pseudo-severe AS or those without contractile reserve [32]. Patients with low-gradient AS undergoing AVR have a significantly higher perioperative and long-term mortality if multivessel CAD is present [27,33].
Intensive Care Unit Management
Surgery with AVR is the preferred treatment strategy for patients with symptomatic severe AS and for asymptomatic patients with severe AS who have a reduced EF (< 50%).
In contrast, surgery may be postponed in patients with severe, asymptomatic AS and normal LV function, as these patients may do well for years [34]. AVR is also indicated for patients with moderate AS who require other cardiac surgery, such as coronary artery bypass grafting (CABG) or aortic aneurysm repair. Patients with severe AS and cardiogenic shock may be considered for percutaneous aortic balloon valvuloplasty (PABV) as a bridge to AVR. Transcatheter aortic valve implantation (TAVI) has been performed in more than 5,000 patients worldwide and promises to be a viable treatment alternative for patients with severe AS who are considered too high risk for conventional surgery.
In contrast, surgery may be postponed in patients with severe, asymptomatic AS and normal LV function, as these patients may do well for years [34]. AVR is also indicated for patients with moderate AS who require other cardiac surgery, such as coronary artery bypass grafting (CABG) or aortic aneurysm repair. Patients with severe AS and cardiogenic shock may be considered for percutaneous aortic balloon valvuloplasty (PABV) as a bridge to AVR. Transcatheter aortic valve implantation (TAVI) has been performed in more than 5,000 patients worldwide and promises to be a viable treatment alternative for patients with severe AS who are considered too high risk for conventional surgery.
 Figure 34.5. Decision making in low-flow, low-gradient aortic stenosis (AS). Dobutamine stress echocardiography aids decision making in low-flow AS. Contractile reserve is defined as an increase in stroke volume of > 20%. When contractile reserve is elicited, patients with true severe AS have an increase in transvalvular gradient (Δ P) with a persistently low calculated valve area (AVA). One can also determine the projected AVA at a standardized normal flow rate (AVAproj), with an AVAproj ≤ 1 cm2 consistent with true severe AS. Management decisions are more challenging if contractile reserve is absent. AVR, aortic valve replacement; CABG, coronary artery bypass grafting; LV, left ventricle. [From Picano E, Pibarot P, et al: The emerging role of exercise testing and stress echocardiography in valvular heart disease. J Am Coll Cardiol 54:2251–2260, 2009, with permission.] |
Medical Management
Medical interventions in severe AS are largely supportive until surgery is feasible. In patients with severe AS with heart failure or cardiogenic shock, management should be guided by invasive hemodynamic monitoring with a pulmonary artery catheter. Gentle diuresis may relieve pulmonary congestion, but patients with severe AS have a preload-dependent state, so overdiuresis can cause a severe drop in blood pressure. For patients in cardiogenic shock, arterial pressure should be supported with inotropes and/or vasopressors until valve surgery can be performed. Vasodilators are generally contraindicated, except in select patients with depressed EF [35]. In these
select patients with EF less than 35%, severe AS and cardiogenic shock accompanied by high systemic vascular resistance, sodium nitroprusside infusion has been shown to modestly improve hemodynamics and can serve as a bridge to the operating room [36].
select patients with EF less than 35%, severe AS and cardiogenic shock accompanied by high systemic vascular resistance, sodium nitroprusside infusion has been shown to modestly improve hemodynamics and can serve as a bridge to the operating room [36].
Surgical Treatment
AVR is the preferred treatment for severe symptomatic AS [32,37]. Choice of valve prosthesis depends on patient age, anticipated lifespan, and preference for and tolerance of anticoagulation [38]. The perioperative mortality for isolated AVR ranges from less than 1% in healthy, younger patients with normal LV systolic function to 10% or more in elderly patients with coexisting CAD and reduced EF. Age alone is not a contraindication to AVR. Other factors associated with reduced survival after AVR include chronic kidney disease, obstructive lung disease, reoperation, emergency operation, and age older than 65 years. The overall 10-year survival for patients with AVR is approximately 60%. Surgical risk for valve replacement can be estimated using one of several online calculators (Society for Thoracic Surgeons, EuroSCORE, or others) [39,40,41].
Percutaneous Aortic Balloon Valvuloplasty and Percutaneous Valve Replacement
PABV is often used instead of an operation in children and young adults with congenital, noncalcific AS. During the procedure in adults, a balloon is placed across the stenotic aortic valve and inflated to high pressure to fracture adherent calcium and increase effective orifice area [42]. A technically successful procedure can reduce the transaortic valve gradient to a mild degree but rarely increase valve area to more than 1 cm2. Valvuloplasty is not widely used in adults with severe calcific AS because of high restenosis rates, frequent embolic complications (particularly stroke), and the development of AR [43]. In adults with acutely decompensated AS, PABV is particularly high risk and has no proven long-term benefits [44]. Given these risks, PABV is seldom used even in a palliative setting. In rare cases, it may be used as a bridge to AVR in patients with severe LV dysfunction and shock who are too ill to tolerate surgery without a period of metabolic recovery. PABV should not be considered as a substitute for AVR.
TAVI has generated considerable enthusiasm because it can eliminate the incremental risks conferred by sternotomy, cardiopulmonary bypass, and general anesthesia. TAVI can now be achieved in select patients and is undergoing active clinical investigation [45,46,47,48]. The procedure involve preparatory PABV followed by deployment of a balloon or self-expanding stented valve across the stenotic orifice. An antegrade, retrograde or LV transapical approach may be used. The retrograde approach is preferred but depends critically on whether relatively large diameter catheters can be successfully manipulated through the arterial system. Lower profile devices are under active development. There are several potential complications, though results with TAVI have been improving steadily and are quite promising [49]. TAVI will likely to have a major impact on management of AS in elderly, high-risk patients [50,51].
Aortic Regurgitation
Acute severe AR may occur in previously normal or only mildly diseased valves and often results in abrupt hemodynamic decompensation and respiratory compromise requiring ICU admission. Acute valvular regurgitation is a surgical emergency, but accurate diagnosis may be a challenge because examination findings may be subtle and the clinical presentation nonspecific [52]. Patients with acute AR appear gravely ill and have tachycardia, significant dyspnea, and often hypotension. The presentation of acute AR may even be mistaken for other acute conditions like sepsis, pneumonia, or nonvalvular heart failure. In marked contrast, chronic severe AR may be asymptomatic or minimally symptomatic and is rarely encountered in the ICU setting. In cases of acute valvular regurgitation, a high index of suspicion is required, along with timely TTE, and prompt surgical consultation.
Etiology
Most cases of acute severe AR are caused by infective endocarditis (IE), but other causes include aortic dissection and blunt chest trauma. Staphylococcus has emerged as the most important causative organism of native valve endocarditis [53,54]. Patients with antecedent aortic valve disease or a congenital bicuspid valve are at increased risk for IE, though organisms like Staphylococcus aureus can infect a normal trileaflet valve. IE is a particular problem among injection drug users, patients with indwelling catheters, and those on hemodialysis. Acute severe AR from IE is the consequence of tissue destruction, leaflet perforation, or bulky vegetations impairing leaflet coaptation [55].
AR is present in up to 65% of patients with Stanford Type A aortic dissection [56]. Ascending aortic dissection may be seen in Marfan syndrome, bicuspid aortic valve, or following CABG or AVR surgery. Retrograde extension of the dissection flap into the annulus may cause prolapse or eversion of the aortic valve leaflets. Type A aortic dissection with AR is a surgical emergency requiring prompt diagnosis and intervention [57]. Aneurysmal enlargement of the aortic root without dissection may also lead to AR. Although AR is usually chronic when produced by aortic root dilatation, an acute-on-chronic decompensation may occur if there is superimposed dissection or abrupt aneurysm enlargement [58]. Important causes of aortic root pathology producing AR include connective tissue disorders (Marfan syndrome and Ehlers-Danlos syndrome) and vasculitis (syphilis aortitis, giant cell arteritis, or Takayasu’s arteritis). Aortic leaflets tears, perforation, or detachment producing AR may also follow blunt chest trauma or occur as a complication of PABV for AS [59].
Pathophysiology
Unlike in chronic AR, the LV in acute AR has not had time to develop compensatory eccentric hypertrophy in response to elevated afterload and preload (Fig. 34.6). The nondilated, noncompliant left ventricle receives a significant diastolic volume load from the regurgitant flow, resulting in an abrupt rise in LV end-diastolic pressure. This pressure may in turn be transmitted to the pulmonary bed resulting in pulmonary edema. Since the LV cannot dilate acutely in response to the volume load, forward stroke volume is decreased and tachycardia develops to maintain cardiac output. Impaired forward stroke volume leads to decreased systolic pressure and relatively narrow pulse pressure. Patients may present with signs of impending cardiogenic shock. LV diastolic pressure may equilibrate with aortic pressure during the latter half of diastole (diastasis), resulting in attenuation of the AR murmur in the acute setting. The elevation in end-diastolic pressure and tachycardia can increase myocardial oxygen demand and, when coupled with decreased diastolic coronary blood flow, can reduce myocardial perfusion and result in coronary ischemia. Ischemia from AR can be compounded by impairment in coronary flow from
preexisting atherosclerosis or an aortic dissection flap. In acute severe AR, LV failure and cardiogenic shock develop if surgery is not promptly performed.
preexisting atherosclerosis or an aortic dissection flap. In acute severe AR, LV failure and cardiogenic shock develop if surgery is not promptly performed.
 Figure 34.6. Pathophysiology of acute aortic regurgitation. LV, left ventricle; LVEDP, left ventricular end diastolic pressure. [Adapted from Bonow R, Braunwald E: Valvular heart disease, in Zipes D, et al. (eds): Braunwald’s Heart Disease. Philadelphia, Elsevier, 2005, with permission.] |
Clinical Presentation
History
Acute AR may present with little or no warning. Symptoms of weakness, profound dyspnea, angina, and presyncope are common. Antecedent valve disease, fever, and skin findings may suggest IE. Severe, ripping chest or back pain with hypertension may indicate aortic dissection. Signs of blunt chest trauma may be disarmingly subtle. The natural history of acute severe AR is one of LV failure and death in the absence of rapid intervention. Patients with chronic AR may present acutely with a sudden worsening of their underlying pathology.
Physical Examination
The classic eponymous signs observed in chronic AR are attenuated or absent in acute AR. Patients are often tachycardic with low or low-normal blood pressure. Pulse pressure may underestimate AR severity in the acute setting. Tachypnea, accessory muscle use, and hypoxemia are worrisome findings and pulmonary rales are common. LV apical impulse is not displaced unless prior LV dysfunction was present. The first heart sound (S1) is often soft due to premature closure of the mitral valve from the rapid LV diastolic pressure rise. There is often a low-pitched systolic ejection murmur from increased flow across the aortic valve, whereas the diastolic regurgitant murmur is of grade 1 or 2 intensity and of short duration. A pulse deficit or relative decrease may be appreciated in the setting of AR from aortic dissection.
Investigations
Electrocardiography
Sinus tachycardia is often present, though the ECG may be entirely normal in acute severe AR. In contrast, LVH is a feature of chronic AR. Nonspecific ST-segment and T-wave abnormalities or signs of LV strain are common. In IE, if there is paravalvular extension of the infection in the region of the atrioventricular node, heart block of varying degree may be present. In the setting of acute heart failure, supraventricular and ventricular tachycardias may occur.
Chest Radiography
The cardiac silhouette may be normal unless AR is chronic or there was preexisting heart disease. Pulmonary edema is common and characterized by cephalization of interstitial markings and Kerley B lines. A widened mediastinum may signify aortic dissection or thoracic aortic aneurysm.
Echocardiography
Urgent TTE is mandated whenever acute AR is suspected. Echocardiography can determine etiology and hemodynamic severity of AR while providing information on underlying LV function, aortic size, and coexisting valvular heart disease (Fig. 34.7). Severe AR is characterized by a wide regurgitant jet (vena contracta > 6 mm) and holodiastolic flow reversal in the descending thoracic aorta [60]. The rapid rise in LV diastolic pressure with acute severe AR produces short pressure half time (< 250 milliseconds) and premature mitral valve closure [61]. CT angiography has become the preferred imaging test to assess for acute dissection, but TEE may be indicated if the study is nondiagnostic and can be crucial for surgical planning [62,63].
Cardiac Catheterization
Establishing the hemodynamic severity of AR seldom requires catheterization, which can delay surgery [64]. Younger patients without coronary risk factors may proceed directly to emergency valve replacement without angiography. Patients with Type A dissection should proceed directly to surgical repair.
Intensive Care Unit Management
Medical Management
Acute severe AR has a high mortality rate. Medical management should not delay urgent or emergent surgery. Congestive heart failure and cardiogenic shock are the principle targets of acute medical therapies. Use of vasodilators, particularly sodium nitroprusside, and diuretics are the mainstays of medical therapy, if the systemic blood pressure allows [65]. Inotropes such as dopamine or dobutamine may be used to augment cardiac output. Pulmonary edema from acute AR frequently requires intubation and mechanical ventilation. Intra-aortic balloon counterpulsation (IABP) is strictly contraindicated. Beta-blockers should only be considered in cases of acute aortic dissection. Antibiotics are indicated for IE, but surgery must not be delayed once heart failure intervenes [24].
Surgical Treatment
Surgery is indicated for acute severe AR unless overwhelming patient comorbidities dictate otherwise. AVR is most commonly performed, but valve repair may be possible in
cases of leaflet perforation. Most surgeons favor the use of homograft material for management of aortic valve/root IE given the low reinfection rates with cadaveric tissue. A composite valve-graft conduit may be used when disease dictates replacement of both the aortic root and valve [66]. Perioperative risk depends on age, preoperative LV function, etiology, and urgency of the surgery. Debridement of periaortic abscess or aortic root replacement compounds operative risk.
cases of leaflet perforation. Most surgeons favor the use of homograft material for management of aortic valve/root IE given the low reinfection rates with cadaveric tissue. A composite valve-graft conduit may be used when disease dictates replacement of both the aortic root and valve [66]. Perioperative risk depends on age, preoperative LV function, etiology, and urgency of the surgery. Debridement of periaortic abscess or aortic root replacement compounds operative risk.
 Figure 34.7. Echocardiographic appearance of severe aortic regurgitation. A: Transthoracic echocardiogram apical four-chamber view with severe aortic regurgitation from infective endocarditis. Color Doppler shows ventricular filling from the aorta during diastole. B: Pulse wave Doppler of the descending thoracic aortic reveals holodiastolic flow reversal consistent with severe aortic regurgitation. |
Mitral Stenosis
Widespread use of programs to detect and treat Group A streptococcal pharyngitis have reduced the incidence of rheumatic fever in the developed world, the leading cause of MS [67]. The burden of rheumatic valve disease in the developing world remains considerable and is a significant cause of premature death. Most cases of rheumatic MS in the United States are seen in patients who have recently emigrated from endemic areas [1]. Symptomatic MS requires mechanical relief of LV inflow obstruction. ICU management goals include treatment of heart failure, rate control of AF, and preparation for valvotomy or valve replacement surgery.
Etiology
Rheumatic fever produces valvular inflammation and scarring, though nearly half of patients may not recall history of acute rheumatic fever or chorea. Two thirds of patients with rheumatic MS are female and 40% of patients with rheumatic valvular disease will have isolated MS [68]. Screening TTE in endemic areas may detect up to 10 times as many cases of rheumatic valve disease compared with clinical screening alone [69]. By contrast, in developed countries, MS is more commonly produced by calcific degeneration of the annulus and mitral leaflets, congenital abnormalities, or collagen vascular diseases such as lupus or rheumatoid arthritis [70]. Atrial myxoma may mimic MS by causing obstruction to LV inflow. The natural history of MS is often dependent on the patient’s nationality: in developing countries, patients tend to be younger with a more pliable valve, whereas in developed countries, patients are older with comorbid conditions [71].
Related posts:
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
