MITRAL REGURGITATION

ETIOLOGY AND PATHOLOGY

Mitral regurgitation (MR) is caused by a myriad of conditions that may affect the leaflets, annulus, chordae tendineae, papillary muscles, or subjacent left ventricular (LV) myocardium. They include myxomatous replacement, rheumatic disease, IE, cardiomyopathy with LV remodeling, ischemia, congenital anomalies, and degenerative calcification of the mitral annulus. MR results in progressive LA and LV enlargement, which, in turn, causes more MR.

PATHOPHYSIOLOGY

It is important to recognize the pathophysiological differences between acute and chronic MR. In acute severe MR, a significant volume load is delivered into an unprepared and relatively noncompliant LA, resulting in a significant rise in LA pressure and symptoms and signs of pulmonary edema. In chronic severe MR, the LA enlarges gradually, and its compliance characteristics are maintained. LA pressure does not rise precipitously, and the volume overload may be well tolerated for many years. Eventually, however, the LV dilates, and its contractile performance declines, leading to hemodynamic derangements and symptoms of heart failure. The natural history of the disease may be punctuated by AF or some other insult (chordal rupture, MI, IE, etc.) with more abrupt clinical deterioration (acute on chronic MR).

SYMPTOMS

Acute severe MR may develop in the setting of an acute MI, IE, or blunt chest wall trauma. Symptoms are related chiefly to the resultant pulmonary edema and include severe dyspnea, air hunger, restlessness, diaphoresis, and apprehension. Early symptoms with chronic severe MR include fatigue and decreased exercise tolerance due to the progressive reduction in forward cardiac output. Eventually, symptoms of pulmonary congestion will develop.

PHYSICAL EXAMINATION

With acute severe MR, the LV apical impulse is hyperdynamic but neither displaced nor enlarged. A left parasternal pulsation transmitted from systolic LA expansion may be felt. The systolic murmur is of relatively short duration, decrescendo in its configuration, and of grade 3 or less intensity. It is best heard at the apex or toward the left lower sternal border. These characteristics derive from the rapid rise in LA pressure and the continued decline in the pressure gradient between the LV and LA during the first half of systole. The murmur may not be audible in a ventilated patient with a large chest. In chronic severe MR, the LV impulse may be enlarged and displaced laterally. A loud S2 suggests pulmonary hypertension. The murmur may be holosystolic in timing and plateau in configuration. Radiation of the murmur reflects the direction of the MR jet. With central MR, the murmur typically radiates into the axilla. In patients with posterior leaflet prolapse or flail, the jet is directed anteriorly, and thus the murmur radiates to the base, where it may masquerade as aortic stenosis. Anterior leaflet prolapse or flail is associated with a posteriorly directed jet and a murmur that can be heard in the axilla or back. There is great individual variability. MV prolapse may be accompanied by a nonejection click, heard after the onset of the carotid upstroke. With severe MR, a short diastolic filling complex may be heard, comprising a third sound followed by a low-pitched murmur, and is attributable to enhanced, rapid LV filling. Bedside maneuvers are often employed to help identify a systolic murmur as mitral in origin. With hand grip and an increase in LV afterload, the MR murmur becomes louder. The click and murmur of MV prolapse move closer to S1 with rapid standing from a squatting position, as LV preload is abruptly decreased. With squatting, the click and murmur move away from S1, signifying the later onset of leaflet prolapse with increased LV preload. The midsystolic murmur associated with hypertrophic obstructive cardiomyopathy (HOCM) behaves in a similar fashion.

LABORATORY EVALUATION

ECG signs of LA enlargement should be sought in the presence of sinus rhythm. AF occurs commonly in patients with severe MR and often marks the onset of symptoms. In the acute setting, the ECG may show signs of an inferior or posterior MI. Increased LV voltage owing to eccentric hypertrophy is often observed in patients with chronic severe MR. The CXR may show evidence of LA or LV enlargement, depending on the clinical context and chronicity of the MR. With acute severe MR, there is often dense alveolar pulmonary edema despite a normal heart size. On rare occasion, the edema may be asymmetric and follow the course of the regurgitant jet into one or the other upper lobe pulmonary veins (right > left). Pulmonary venous redistribution and Kerley B lines are indicative of chronically elevated left-sided filling pressures. TTE is indicated to define the mechanism and severity of the MR, assess chamber sizes and ventricular function, and estimate PA pressures. The findings often dictate the timing of surgery. Serial TTE studies are an important component of longitudinal follow-up. Transesophageal echocardiography (TEE) may be needed for greater clarification of the anatomic and physiological findings in some patients. Three-dimensional TEE is usually reserved for intraoperative assessment and surgical planning. Cardiac MRI can be used to provide an accurate and semiquantitative assessment of MR severity in patients with suboptimal echocardiographic studies. Left- and right-heart catheterization is pursued when there is a discrepancy between the clinical and noninvasive findings. Routine coronary angiography prior to anticipated surgery can be performed invasively or using computed tomography (CT) techniques. The clinical context might also dictate the need for invasive angiography, as for example, with post-MI acute MR or chronic, ischemic MR.

TREATMENT

Surgery is required for treatment of acute severe MR (box 79.1). The type of operation is dictated by the anatomic findings and the presence or absence of coronary artery disease (CAD). Repair is preferred over replacement whenever possible given its more favorable effect on LV function, lesser need for anticoagulation, and greater preservation of native valve tissue. Temporizing medical measures include diuretics for pulmonary congestion, sodium nitroprusside for rapid preload and afterload reduction, inotropic therapy as required, and intra-aortic balloon counterpulsation if needed. Management of chronic MR is focused on early identification of the indications for elective surgery in appropriate candidates, including onset of symptoms, LV ejection fraction (EF) ≤0.60, and/or LV end-systolic dimension ≥4.0 cm. Surgery is also reasonable in asymptomatic patients with PA hypertension or recent-onset AF. Some authorities advocate surgery for patients with severe MR who have none of these other indications provided there is a high likelihood of successful and durable repair at low operative risk in experienced hands. Vasodilators are not indicated in the absence of systemic hypertension or LV systolic dysfunction. Rhythm management is similar to that for patients with MS; anticoagulation is provided once AF intervenes. Treatment of angina for patients with ischemic MR follows standard principles.

Box 79.1 MITRAL REGURGITATION: INDICATIONS FOR SURGERY

MITRAL VALVE PROLAPSE

ETIOLOGY AND PATHOLOGY

Mitral valve prolapse (MVP) occurs in 1–2% of the general population with a female predominance and has a variable clinical course. The etiology is most often related to myxomatous replacement of mitral leaflet tissue. MVP occurs in patients with Marfan syndrome and similar connective tissue diseases but most often develops spontaneously. Two types of myxomatous change are described: fibroelastic deficiency (classic MVP) and Barlow disease, which refers to an extreme form of leaflet redundancy and billowing. Myomatous MV disease is by far the most common cause of MR for which surgery is required.

PATHOPHYSIOLOGY

Prolapse is defined by the superior displacement of one or both MV leaflets above the annular plane at end-systole. Lack of leaflet coaptation leads to MR, the severity of which can worsen with chordal rupture, flail, and/or annular dilatation. The MR is usually eccentric and directed opposite to the involved leaflet. With bileaflet prolapse, the MR can be central or eccentric. Changes in LA and LV size and function then follow along the same course as expected for MR of other etiology.

SYMPTOMS

The clinical course is frequently benign. Patients may experience premature ventricular or atrial contractions and paroxysmal supraventricular (including PAF) and ventricular tachycardia, precipitating palpitations, lightheadedness, or syncope. Sudden death is very rare. Patients may report chest pain, although the mechanism is unclear. A variety of other disorders have been associated with MVP, including migraine, stroke, transient ischemic attacks (TIAs), hypercoagulability, and panic, though a cause-and-effect relationship has not been consistently established. Many patients have hypermobile joints, thoracic spine disease, or inguinal hernias. IE can be the presenting illness.

PHYSICAL EXAMINATION

Classically, auscultation reveals a mid- to late systolic click murmur complex best heard at the lower left sternal border or apex. The changes in the timing of the click and murmur with standing and squatting as previously described are useful adjuncts to correct bedside diagnosis.

LABORATORY EVALUATION

The ECG is usually unremarkable but may show biphasic or inverted T waves in the inferior and apical leads. The diagnosis is confirmed with TTE, which also allows characterization of MR severity, ventricular function, and suitability for valve repair if indicated. TEE can provide superior visualization if needed for clinical decision making.

TREATMENT

Most patients do not require any specific therapy. Treatment of symptomatic arrhythmias may be required, and often beta blockers will be of use. Indications for MV repair are as discussed previously. Posterior leaflet repair is technically easier and more durable than anterior or bileaflet repair. The latter often requires construction of neochordae and/or chordal transposition. Posterior leaflet repair should be feasible in >95% of patients with this anatomy.

AORTIC STENOSIS

ETIOLOGY AND PATHOLOGY

Bicuspid aortic valve and its congenital variants (e.g., unicuspid valve) are now recognized as the most common causes of aortic stenosis requiring valve replacement surgery. Bicuspid disease is often familial and may be accompanied by an aortopathy characterized by root or ascending aortic aneurysm disease in up to 30% of patients. Coarctation occurs less frequently. Age-related calcific degeneration of a trileaflet valve is the second most common cause of AS. Rheumatic disease is rarely encountered in developed countries. Degenerative valve disease and atherosclerosis share several common risk factors, histopathologic characteristics, and pathogenetic traits. In older adults with AS, the prevalence of significant CAD exceeds 50%.

PATHOPHYSIOLOGY

The obstruction to LV outflow produces a systolic pressure gradient between the LV and the aorta. Concentric LV hypertrophy develops gradually in response to the pressure overload to normalize wall stress. Initially, cardiac output is preserved, and LV chamber dimensions are preserved. Diastolic performance is altered by the hypertrophy and interstitial fibrosis; LV diastolic pressure is increased. Ultimately, with unrelieved obstruction of sufficient magnitude, the LV pump failure occurs with dilation of the cavity and reduction in cardiac output. Severe AS is defined by a valve area of <1.0 cm². In the presence of normal LV systolic function, severe AS is also characterized by a peak transvalvular jet velocity of ≥4 m/sec and mean valve gradient of ≥40 mm Hg.

SYMPTOMS/NATURAL HISTORY

Symptoms are rarely present until the valve obstruction is severe because of the ability of the hypertrophied LV to maintain a normal stroke volume. Although the rate of progression of AS varies among individual patients, longitudinal echocardiographic studies have suggested an average increase in mean gradient of 7 mm Hg/year and decrease in valve area of 0.1 cm²/year. Both the peak jet velocity and the severity of valve calcification are predictive of event-free survival. The cardinal symptoms of AS are exertional dyspnea, angina, and syncope. Although these symptoms are usually not apparent in patients with degenerative, trileaflet AS until the sixth to eighth decade, an insidious history of decreasing exercise tolerance and fatigue is often elicited, as may also be the case with younger patients with bicuspid disease. Symptoms or signs of more advanced left- or right-heart failure are ominous.

    The natural history of untreated severe AS has been well documented. The average time to death from the onset of angina, syncope, and dyspnea are 5 years, 3 years, and 2 years, respectively. Heart failure and ventricular arrhythmias are the most common causes of death. Sudden death as the manifestation of severe AS in adult patients is very rare.

PHYSICAL EXAMINATION

The carotid or brachial artery pulse is characteristically reduced in amplitude and rises slowly to its peak (pulsus parvus et tardus), although arterial wall stiffening may mask this finding in the elderly. LV hypertrophy can be detected by a forceful, sustained apical impulse. A systolic thrill present at the base of the heart that tracks along the carotid arteries suggests significant stenosis. As AS progresses, LV systole is prolonged, moving the closure of the aortic valve (A2) closer to that of the pulmonic valve (P2). Eventually, A2 becomes inaudible and S2 single. Paradoxical splitting of S2 may also occur. An S4 is invariably present in sinus rhythm secondary to LV hypertrophy. An S3 signifies elevated LV end-diastolic pressures in a dilated ventricle. The murmur of AS is typically a loud (at least grade III/IV) diamond-shaped ejection murmur that begins after S1 and is heard best at the base of the heart in the right second intercostal space with radiation to the carotid arteries. It is important to note that in patients with severe stenosis and LV failure, the murmur may be soft and brief due to reduced transvalvular flow rates. A systolic ejection click is audible in many young patients with bicuspid disease. A diastolic murmur of aortic regurgitation signifies mixed disease.

LABORATORY EVALUATION

The ECG commonly shows LV hypertrophy with associated repolarization abnormalities (“LV strain pattern”). The chest may be unremarkable. Calcium in the region of the aortic valve should be assessed on the lateral film. Dilatation of the ascending aorta may signify aneurysm. Signs of aortic coarctation should be sought in young patients with bicuspid disease. TTE is essential in the diagnosis and management of AS. Leaflet number, morphology, calcification, and excursion are noted. Measurement of the trans-aortic valve velocity with continuous wave Doppler can be used to estimate AS severity. LV size and function are important in clinical management, as is the presence or absence of concomitant ascending aorta dilatation. Left-heart catheterization and coronary angiography are routinely performed in older adult patients with severe AS referred for surgery or in patients with AS and symptoms of myocardial ischemia.

TREATMENT

The medical treatment is quite limited, and AS should be thought of as a surgical disease (box 79.2). Patients with severe AS should be advised to avoid strenuous physical activity.

Box 79.2 MANAGEMENT OF AORTIC STENOSIS

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