Mitral Stenosis: Introduction
- Itzhak Kronzon, MD
- Roberto M. Lang, MD
- Muhamed Saric, MD, PhD
- Roberto M. Lang, MD
The earliest description of mitral valve stenosis came from French and British anatomists who reported postmortem findings around the middle of the 17th century. “Extreme restriction of the mitral valve” in a 26-year-old man was recorded in 1668 by John Mayow (1640-1669), an Oxford physiologist. Several decades later, in 1715, Raymond de Vieussens of Montpelier, France, described and illustrated “ossification of the mitral valve,” which would be interpreted today as severe calcific mitral stenosis. As was the case with many pathologic findings diagnosed at autopsy, the ability to diagnose the condition during life lagged far behind. At least another 150 years passed before the first diagnoses of mitral stenosis by history and physical examination.
In 1806, the Frenchman J. N. Corvisart (1755-1821) was the first to describe a physical finding that had been observed during the life of a patient who was found later to have mitral stenosis at autopsy. Corvisart reported a “rustling or thrill palpable over the heart” and described it as a characteristic of the lesion. In fact, in the records of his student, it appeared that he compared the finding to that experienced by a hand while stroking a cat. Corvisart ascribed the finding to the passage of blood from the lungs and left atrium through the narrowed mitral orifice. It should be noted that this astute observation was made before the introduction of cardiac auscultation!
With the introduction of cardiac auscultation by Rene Laennec (1781-1819), there were many conflicting reports regarding the findings in patients with mitral stenosis. Laennec himself, who described a murmur, could not describe its timing during the cardiac cycle. He thought that the first heart sound was due to ventricular contraction, and the second to atrial contraction.
The first to realize that the murmur of mitral stenosis is diastolic (and presystolic) was Hilton Fauvel (1813-1884). His observation was not understood by many and was mocked by others. The master clinician Duroziez (1826-1897) referred to “that presystolic murmur of which everyone talks but no one understands.” Some claimed that it was extremely rare. Herbert Davis (1818-1895), an experienced clinician, stated that he never heard it. It is amazing that even today, although every medical student is theoretically familiar with the pathophysiology and the physical findings of mitral stenosis, only a few physicians can diagnose it solely by auscultation.
The invention of cardiac catheterization during the first half of the last century introduced a gold standard to this difficult diagnosis. This invasive technique was able to demonstrate a pressure gradient between the left atrium and left ventricle, which, together with flow measurement techniques developed later, led to the calculation of mitral valve area. The ability to correctly diagnose the condition occurred almost simultaneously with the development of surgical techniques of closed, and later open, mitral commissurotomy and mitral valve replacement.
The advent of echocardiography was driven by the fact that surgical findings in mitral stenosis patients sometimes were not predicted by previous cardiac catheterization. Inge Edler from Lund, Sweden (1911-2001), together with the German physicist Carl Helmut Hertz (1920-1990), began a venture to find a noninvasive way to better diagnose mitral valve disease. Their introduction of echocardiography in 1953 offered a revolutionary noninvasive technique to accurately diagnose mitral stenosis. The classical findings of mitral stenosis on M-mode, with decreased ejection fraction (EF) slope ( Fig. 107.1 , A ) and abnormal diastolic anterior motion of the posterior mitral leaflet, are indeed striking when compared with normal mitral valve motion. In fact, Edler felt that echocardiography should concentrate mainly on the mitral valve and doubted its usefulness for other cardiac disorders.
Almost every new technical development in echocardiography made during the following years had an important impact on the way we image and understand the physiology of mitral stenosis. Two-dimensional (2D) echocardiography allowed us to accurately measure mitral valve area and demonstrate the presence of commissural fusion and the “hockey-stick” deformity of the anterior mitral leaflet. The introduction of Doppler echocardiography had a remarkable impact on the accurate assessment of the hemodynamics of mitral stenosis, including gradients, valve area, and associated intracardiac pressures, while color Doppler allowed physicians to rapidly screen the frequently associated mitral regurgitation. This had been one of the main goals of Edler and Hertz in their initial quest.
Three-dimensional echocardiography is now considered the imaging technique of choice in the assessment of mitral valve severity (see Fig. 107.1 , B ). 2- and 3D transthoracic and transesophageal echocardiography are essential in the evaluation, assessment, guidance, and follow-up of transcatheter balloon commissurotomy, which has replaced surgery in the treatment of many mitral stenosis patients.
The most common etiology of mitral stenosis has always been rheumatic fever. In developed countries, rheumatic fever has been essentially defeated by the introduction of better medical care and the use of antibiotics. We now educate generations of physicians who have never seen a patient with rheumatic fever and have rarely listened to a patient with mitral stenosis. However, mitral stenosis is still prevalent in third-world and developing countries.
In the near future, echocardiography will continue to be the technique of choice for the diagnosis and evaluation of mitral stenosis of any etiology. Given the rapid developments in cardiac imaging in recent decades, it is impossible to imagine or predict where the state of the art will take us. Undoubtedly, however, mitral stenosis will no longer be a condition of which “everyone talks but no one understands.”
Rheumatic Mitral Stenosis
- Muhamed Saric, MD, PhD
- Roberto M. Lang, MD
- Itzhak Kronzon, MD
- Roberto M. Lang, MD
Etiology of mitral stenosis
Rheumatic heart disease is the predominant but not the only cause of mitral stenosis. Mitral stenosis may result from a variety of congenital and acquired conditions. Congenital mitral stenosis is very rare (~ 1% of all mitral stenosis patients) and may be due to cor triatriatum, a supravalvular mitral ring, or a parachute mitral valve (typically as a part of the Shone syndrome) as discussed in detail in another chapter of this book.
| Parameter | Unit | Normal | Mild MS | Moderate MS | Severe MS | Method | Comments | |
|---|---|---|---|---|---|---|---|---|
| Primary determinant of severity | Mitral valve area (MVA) | cm 2 | 4.0-6.0 | > 1.5 | 1.0-1.5 | < 1.0 | Planimetry | Possibly the gold standard |
| Pressure half-time (PHT) | MVA underestimated: atrial septal defect or severe aortic regurgitation MVA overestimated: LV diastolic dysfunction with low LV compliance | |||||||
| Proximal isovelocity surface area (PISA) | Typically requires angle correction | |||||||
| Continuity equation | Not applicable with significant concomitant mitral regurgitation | |||||||
| Supportive findings | Mean gradient | mm Hg | Negligible | < 5 | 5-10 | > 10 | Mean gradient = average of 4V 2 measurements | Assuming a heart rate of 60-80 bpm. Mean gradient is directly proportional to heart rate and transvalvular flow |
| Pulmonary artery systolic pressure (PASP) | mm Hg | < 30 | < 30 | 30-50 | > 50 | PASP = 4V 2 + RAP | Caveat: A wide range of PASP has been observed for any given MVA |
Nonrheumatic causes of acquired mitral stenosis include lupus erythematosus, carcinoid, rheumatoid arthritis, radiation valvulitis, and age-related degenerative mitral annular calcifications. They are all rare except for mitral annular calcification, which is becoming the leading cause of acquired mitral stenosis in developed countries; this is further discussed in another chapter of this book.
Worldwide, rheumatic heart disease is by far the most common cause of mitral stenosis. The disease typically starts in childhood with a bout of acute rheumatic fever and is followed by lifelong progressive valvular damage. Acute rheumatic fever is triggered by infection with group A beta-hemolytic Streptococcus pyogenes , typically pharyngitis (“strep throat”). The exact mechanism by which the streptococcal infection causes acute rheumatic fever and subsequent progressive, lifelong valvular damage has not been fully elucidated.
Rheumatic heart disease may be considered an autoimmune disease triggered by streptococcal infection mediated by cross-reactivity between the streptococcal M antigen (mucoid surface protein) and human epitopes in the heart, skin, and connective and nerve tissues. Streptococci do not invade and are not present in the affected tissues. Only certain strains of group A beta-hemolytic streptococci are rheumatogenic. In general, rheumatogenic strains are highly tropic for the throat and highly contagious via direct person-to-person contact.
Clinically, acute rheumatic fever is characterized by five major findings of a nonbacterial inflammatory process: (1) pancarditis (endocarditis, myocarditis, and pericarditis), (2) migrating arthritis of large joints, (3) subcutaneous nodules, (4) skin rash (erythema marginatum), and (5) Sydenham chorea (random rapid dancelike movements of the face and the extremities). There are also minor (nonspecific) signs of inflammation (such as fever, leukocytosis, or elevated erythrocyte sedimentation rate).
The so-called Jones criteria are used to establish the clinical diagnosis of acute rheumatic fever. In addition to evidence of a recent group A beta-hemolytic streptococcal infection (such as anti-streptococcal antibody titers), two major criteria or one major criterion plus two minor criteria are required for the diagnosis. From the historical perspective, the Jones criteria, published in 1944, pioneered the very concept of basing a clinical diagnosis on a set of major and minor criteria.
The index streptococcal infection, as well as subsequent reinfections, sets in motion a pathologic process of continued valve damage with lifelong progressive fibrosis and calcifications. Interestingly, clinical history of acute rheumatic fever cannot be elicited in a significant percentage of patients with rheumatic mitral stenosis.
Although any cardiac valve may be involved, the mitral valve is virtually always affected, and mitral stenosis with or without concomitant mitral regurgitation is the predominant chronic form. Mitral stenosis results primarily from commissural fusion along leaflet edges, with an additional contribution from chordal fusion and shortening. In general, leaflet thickening and calcification proceeds from leaflet tips toward leaflet bases. This is in contrast to mitral stenosis due to age-related mitral annular calcification, in which the process starts at the base of the posterior mitral leaflet.
Epidemiology
The prevalence of acute rheumatic fever and thus rheumatic mitral stenosis reflects the overall socioeconomic development as well as the adequacy of access to medical care in a given community. In developed countries, the incidence of rheumatic fever has declined dramatically since World War II. Although the introduction of antibiotics to treat streptococcal infection has played a major role, the prevalence of rheumatic fever started to decline well before that, at least in part due to elimination of overcrowding in living quarters.
In the developed countries, new cases of rheumatic fever are rare, with an incidence of less than 1 case per 100,000 people. Thus, most cases of rheumatic mitral stenosis in developed countries are found among immigrants from less developed parts of the world where the prevalence of rheumatic fever is much higher, perhaps as high as 150 cases per 100,000 people.
Rheumatic mitral stenosis also appears to progress more rapidly in developing countries, where severe symptomatic rheumatic mitral stenosis may be observed even in children and adolescents. In contrast, in developed countries mitral stenosis becomes symptomatic 20 to 30 years after the onset of rheumatic fever. This may be due to more frequent recurrences of streptococcal infections in developing countries.
Although acute rheumatic fever affects both sexes equally, women are at least twice as likely as men to develop rheumatic mitral stenosis. This may reflect the generally higher prevalence of autoimmune disorders in women compared with men. Rheumatic fever appears to occur exclusively in humans, as there are no known animal reservoirs.
Pathophysiology
Clinical manifestations of rheumatic mitral stenosis are due to progressive decrease in mitral valve area, development of atrial fibrillation, and clot formation in the left atrium and left atrial appendage. It appears that the characteristic clinical findings of rheumatic mitral stenosis were first reported in 1668 by the English physician John Mayow (1641-1679). Pathologic changes attributable to narrowing of the mitral orifice include elevation of left atrial pressure, pulmonary edema and other signs of left heart failure, pulmonary hypertension, right ventricular hypertrophy and dilation, secondary tricuspid regurgitation, and right heart failure.
In the adult, the normal mitral valve area is approximately 4 to 6 cm 2 , and the blood crosses the mitral valve without an appreciable transvalvular pressure gradient during diastole. Once the valve area drops below 2 cm 2 , an abnormal diastolic pressure gradient starts to develop between the left atrium (LA) and the left ventricle (LV). A high transvalvular gradient leads to elevated LA pressure, resulting in symptoms that may range from dyspnea on exertion to frank pulmonary edema at rest. This gradient is inversely proportional to the valve area and directly proportional to transvalvular flow. Conditions known to increase cardiac output, such as exercise, fever, and pregnancy, increase the blood flow and gradient across the valve. In addition, tachycardia (such as sinus tachycardia or atrial fibrillation) shortens the duration of diastole, which interferes with LA emptying and leads to a further increase in the LA-LV gradient.
Elevation of LA pressure in any patient with significant rheumatic mitral stenosis may lead to pulmonary venous hypertension (pulmonary artery pressure elevations with typically normal pulmonary vascular resistance, PVR). For poorly understood reasons, a subset of patients may also develop superimposed arterial pulmonary hypertension because of arteriolar spasm, medial hypertrophy, and intimal thickening (pulmonary hypertension with elevated PVR). In some patients, pulmonary artery pressure may reach or even exceed systemic levels, leading to low cardiac output and symptoms ranging from fatigue to poor organ perfusion and cardiac cachexia.
Pulmonary hypertension may increase right ventricular (RV) afterload and lead to RV dilation, secondary tricuspid regurgitation, elevation of RV diastolic and right atrial (RA) pressures, and signs of right heart failure: venous engorgement, leg edema, cardiac cirrhosis, ascites, and protein-losing enteropathy.
Patients with rheumatic mitral stenosis are at high risk for development of valvular atrial fibrillation and systemic thromboembolism. This risk is not directly proportional to the severity of mitral stenosis; one possible explanation is that left atrial enlargement and remodeling reflect not just elevated left atrial pressure but the underlying atrial myocarditis and patient’s age. Pathophysiology of mitral stenosis is summarized in Figure 108.1 . Quantification of transmitral pressure gradient and mitral valve area is discussed in a separate chapter.
Physical examination
By placing the palm of one’s hand on the precordium of a patient with rheumatic mitral stenosis, one can feel the diastolic valvular thrill. This palpable valvular thrill (“bruissement”) was the first physical exam finding reported in 1806 by the French physician Jean-Nicolas Corvisart (1755-1821). Because of its resemblance to a cat purr, the thrill was later referred to as frémissement cataire by the French physician René Laennec (1781-1821). The term was later Latinized to susurrus felinus . The invention of the stethoscope by Laennec led gradually to the description of the characteristic heart sounds and murmurs.
Typical auditory finding of rheumatic mitral stenosis obtained by cardiac auscultation and phonocardiography include loud S 1 , an opening snap (OS) following S 2 (originally described in French as claquement d’ouverture ), and a diastolic rumble. The first heart sound (S 1 ) is often loud. An OS is frequently heard after the second heart sound (S 2 ). The duration of the interval between the aortic component of the S 2 and the OS (referred to as S 2 -OS interval) is inversely proportional to the severity of mitral stenosis (shorter S 2 -OS interval suggesting severe mitral stenosis). S 2 -OS interval is roughly equivalent to the isovolumic relaxation time.
In the early years of echocardiography, a technique to measure the S 2 -OS interval was developed using M-mode recordings of the aortic valve and the left atrium ( Fig. 108.2 ). In severe mitral stenosis, S 2 -OS interval is typically less than 80 msec. This M-mode technique, though of historic significance, is not a part of the current mitral stenosis guidelines. A characteristic diastolic rumble is frequently heard best at the apex. In patients with normal sinus rhythm, there is also an end-diastolic (“presystolic”) accentuation of the rumble. Unfortunately, the auscultatory findings are subtle. They can be frequently missed by an inexperienced ear. When the cardiac output declines, the murmur may become softer. The pulmonic component of S 2 is loud in cases of pulmonary hypertension.
Less specific findings include malar flush and sign of left and right heart failure as well as signs of low cardiac output. Left atrial enlargement, which may be massive in rheumatic mitral stenosis, occasionally compresses the left recurrent laryngeal nerve to cause hoarseness (Ortner syndrome). A combination of atrial septal defect and rheumatic mitral stenosis is sometimes referred as Lutembacher syndrome .
Electrocardiography
Electrocardiography (ECG) may demonstrate signs of LA enlargement (P mitrale ) with wide, saddle-shaped P wave in leads I and II, as well as late, deep P wave inversion in lead V1. In more advanced cases, there is also evidence of RV hypertrophy. Atrial fibrillation is a frequent finding in patients with rheumatic mitral stenosis. In 1749, the French physician Jean-Baptiste de Sénac (1693-1770) was the first to postulate a correlation between rheumatic mitral stenosis and the irregular pulse of “rebellious palpitations” or delirium cordis . With the advent of electrocardiography, the British physician Thomas Lewis (1881-1945) recognized, in 1909, this irregular rhythm of rheumatic mitral stenosis as auricular (atrial) fibrillation.
Chest radiography
Chest x-ray usually demonstrate LA enlargement with straightening of the left cardiac silhouette due to the enlargement of the LA appendage. Some combination of mitral valve calcifications, pulmonary venous engorgement, pulmonary edema, and right ventricular enlargement may also be seen.
Transthoracic echocardiography
In the 1950s, rheumatic mitral stenosis was the very first heart disease visualized echocardiographically by the inventors of echocardiography, Inge Edler (1911-2001) and Carl Hertz (1920-1990). In this section we concentrate on echocardiographic analysis of mitral valve morphology and secondary cardiac changes in rheumatic mitral stenosis ( Fig 108.3 /Video 108.3, A-D ). Quantification of mitral valve area, transvalvular mitral gradient, and right heart pressures is discussed in detail in another chapter of this book.
During bouts of acute rheumatic fever, which are exceedingly rare in developed countries, mitral regurgitation is the primary echocardiographic finding. In contrast, during chronic phase, rheumatic mitral stenosis with or without concomitant mitral regurgitation is the norm. The rheumatic process affects both mitral leaflets and chordae. Leaflet thickening, leaflet calcifications, decreased leaflet mobility, and commissural fusions are the hallmarks of rheumatic mitral stenosis together with chordal fusion and shortening. Leaflet thickening and calcification start at leaflet tips and extends toward leaflet bases over time. Similarly, chordal thickening and fusion start at leaflet tips and then extend distally toward papillary muscles. This orderly progression of rheumatic disease in the tip-to-base leaflet direction and the tip-to-papillary muscle direction along the chordae is pathognomonic and forms the foundation for grading the severity of rheumatic mitral stenosis and eligibility for percutaneous mitral balloon valvuloplasty (see “Treatment,” later). Leaflet thickening can be observed in any two-dimensional (2D) echocardiographic view of the mitral valve, although leaflet thickness is typically measured in the parasternal long-axis view. In this view, one can also observe decreased mobility of the posterior mitral leaflet and the characteristic doming resulting in a hockey-stick appearance of the anterior leaflet (see Fig. 108.3 /Video 108.3, A ).
On the 2D parasternal short-axis view at the level of the mitral valve, one appreciates commissural fusions resulting in a fish-mouth appearance of the mitral orifice (see Fig. 108.3 /Video 108.3, B ). It is in this view that 2D planimetry of the mitral orifice is performed—with the caveat that on 2D, one may not be able to identify true leaflet tips because in rheumatic mitral stenosis, the orifice may be eccentric and separate from the 2D short-axis plane. The eccentricity of the orifice can often be appreciated in 2D apical views of the mitral valve. Three-dimensional (3D) echocardiography, especially multiplane reconstruction techniques, overcomes limitations of 2D echocardiography and allows for precise orifice planimetry exactly at leaflet tips as described in the chapter on quantification of mitral stenosis. Chordal involvement is best seen still in the apical transthoracic views, especially the apical two-chamber view or its transesophageal echocardiography (TEE) equivalents, such as the transgastric two-chamber view (see Fig. 108.3 /Video 108.3, C ).
Changes associated with rheumatic mitral stenosis include often a very marked left atrial enlargement (which is not necessarily proportional to the degree of mitral stenosis), aortic and tricuspid regurgitation, right heart enlargement, and elevation of left atrial and right heart pressures. Left ventricle typically has normal size and systolic function.
Many of the previously mentioned changes can also be seen on M-mode echocardiography. The severity of mitral stenosis can be semiquantitatively assessed on M-mode echocardiography by measuring either the EF slope of the mitral valve (see Fig. 108.2 , A ) or the rate of left atrial emptying (see Fig. 108.2 , B ). Normally, EF slope is steep (> 8 cm/sec). The flatter the EF slope, the more severe the mitral stenosis. Similarly, the slower the rate of LA empting during diastole, the more severe the mitral stenosis. Although of historical importance, these M-mode techniques are imprecise and are not part of the current American Society of Echocardiography (ASE) valvular stenosis guidelines.
Transesophageal echocardiography
The routine echocardiographic evaluation of rheumatic mitral stenosis does not require TEE. However, TEE should be considered when the image quality and the Doppler information are suboptimal or do not correlate with the clinical impression ( Fig. 108.4 /Video 108.4, A ). TEE is especially useful in the evaluation of complications of rheumatic mitral stenosis (such as LA clot or endocarditis) and in guiding percutaneous mitral balloon valvuloplasty. Patients with rheumatic mitral stenosis are at a high risk for developing intracardiac thrombus. This is particularly the case in those with atrial fibrillation; however, LA stasis with smoke, sludge, and thrombus formation often occurs in such patients even in sinus rhythm. In rheumatic mitral stenosis, the majority of thrombi are in the left atrial appendage (LAA) (see Fig. 108.4 /Video 108.4, B ); however, a substantial proportion occurs in the body of the left atrium (see Fig. 108.4 /Video 108.4, C ). According to one surgical series, 57% of thrombi were in the LAA versus 43% in the LA. This is contrast to nonvalvular atrial fibrillation, in which thrombi outside the LAA are unusual.
Therapy
Rheumatic mitral stenosis is a progressive lifelong disease. Without treatment, the 10-year survival is less than 15% once significant symptoms develop, and in those who develop severe pulmonary hypertension, mean survival drops to less than 3 years.
Medical Therapy
There is no effective medical therapy that alters the progression of valvular disease except for long-term antibiotic prophylaxis of recurrent streptococcal pharyngitis in endemic areas. Medical therapy with diuretics and heart-rate controlling agents (beta blockers, calcium channel blockers, and digoxin) provides symptomatic relief. It appears that the very first clinical use of digoxin was in patients with atrial fibrillation and rheumatic mitral stenosis, as reported in 1785 by the British physician William Withering (1741-1799), who discovered digitalis.
Management of atrial fibrillation (including chemical and electrical cardioversion) should follow standard guidelines. Chronic anticoagulation to prevent thromboembolism is recommended in patients with atrial fibrillation and may be considered even in patients with sinus rhythm. In contrast to nonvalvular atrial fibrillation, efficacy of anticoagulation in rheumatic mitral stenosis has not been proven in a randomized trial; nonetheless, anticoagulation is recommended based on several retrospective studies. Although patients with rheumatic mitral stenosis are at risk for mitral valve endocarditis, current guidelines do not recommend routine antibiotic prophylaxis for endocarditis. Significant rheumatic mitral stenosis is a mechanical disorder that requires a mechanical treatment for effective symptom relief and improvement in survival.
Percutaneous Mitral Balloon Valvuloplasty
In eligible patients, percutaneous mitral balloon valvuloplasty (PMBV) is the treatment of choice; surgery is reserved for those who cannot undergo valvuloplasty. Currently, approximately 1500 PMBVs are performed in the United States annually. The PMBV technique was perfected in the 1980s by Kanji Inoue of Japan, who developed an ingenious balloon (Inoue Balloon, Toray Industries Inc, San Mateo, CA), which remains the preferred balloon for PMBV.
Transthoracic echocardiography allows selection of appropriate candidates for valvuloplasty using four parameters: three related to mitral leaflets (thickening, mobility, and calcification) and one related to the degree of chordal involvement. From these, the so-called Wilkins score is derived. Each parameter is scored on a scale from 0 (normal) to 4 (severe); thus the Wilkins score ranges from 0 (normal valve) to 16 (poorly mobile, severely calcified leaflets with severe chordal fusion and shortening). Good valvuloplasty candidates should have a Wilkins score of 10 or less and preferably 8 or less ( Table 108.1 ).
| Grade | 0 | 1 | 2 | 3 | 4 |
|---|---|---|---|---|---|
| Leaflet mobility | Normal | Highly mobile with only leaflet tip restricted | Leaflet mid and base portions have normal mobility | Valve continues to move in diastole, mainly from the base | No or minimal forward leaflet motion in diastole |
| Valve thickness | Normal | Near normal thickness (4-5 mm) | Mid-leaflets normal; thickened leaflet tips (5-8 mm) | Entire leaflet thickened(5-8 mm) | Marked thickening of entire leaflet (> 8-10 mm) |
| Leaflet calcification | None | Single area of echo brightness | Scattered areas of brightness at leaflet margins | Brightness extends to mid leaflets | Extensive brightness throughout leaflets |
| Subvalvular thickening | None | Minimal chordal thickening just below leaflet tips | Thickening from leaflet tips to up to <SPAN role=presentation tabIndex=0 id=MathJax-Element-1-Frame class=MathJax style="POSITION: relative" data-mathml='1/3′>1/31/3 1 / 3 of chordal length | Thickening extending to the distal third of chordae | Extensive chordal thickening down to papillary muscle |
TEE plays an essential role in the refinement of patient selection ( Fig. 108.5 /Video 108.5, A ), guidance of percutaneous valvuloplasty (see Fig. 108.5 /Video 108.5, B ), and assessment of postvalvuloplasty results (see Fig. 108.5 /Video 108.5, C , D ). In the absence of contraindications, PMBV is recommended in the following instances: (1) in symptomatic patients with moderate or severe mitral stenosis; (2) in asymptomatic patients with moderate or severe mitral stenosis when pulmonary artery systolic pressure is greater than 50 mm Hg at rest or greater than 60 mm Hg with exercise, or when there is new-onset atrial fibrillation; and (3) in symptomatic patients with mild stenosis (valve area > 1.5 cm 2 ) when pulmonary artery systolic pressure is greater than 60 mm Hg, pulmonary artery wedge pressure is greater than 25 mm Hg, or mean mitral valve gradient is greater than 15 mm Hg during exercise. Contraindications for PMBV include unfavorable mitral valve Wilkins score (≥ 10), more than moderate mitral regurgitation, and the presence of intracardiac thrombus.
TEE plays an essential role in guiding PMBV, including guidance of transseptal puncture, visualization of wires and catheters, and proper placement of the valvuloplasty balloon across the mitral orifice, as well as in the assessment of procedure outcomes. A favorable outcome is characterized by leaflet separation along commissural lines with a concomitant increase in mitral valve area and a decrease in transvalvular gradient (see Fig. 108.5 /Video 108.5, C ). Leaflet tear is the most feared complication of PMBV, as it may lead to severe acute mitral regurgitation necessitating urgent mitral valve surgery (see Fig. 108.5 /Video 108.5, C ).
Mitral Valve Surgery
Surgical options include closed or open commissurotomy, mitral valve replacement, and occasionally mitral valve repair. In the 1920s, Henry Souttar (1875-1964) in England and Elliot Cutler (1888-1947) in the United States led the first attempts to perform surgical relief of rheumatic mitral stenosis using what would later be termed closed commissurotomy . Their technique was improved soon after World War II by the American surgeons Charles Bailey (1910-1993) and Dwight Harken (1910-1993); Bailey called the procedure “mitral commissurotomy,” whereas Harken called it “mitral valvuloplasty.” In developed countries, open commissurotomy requiring cardiac arrest and cardiopulmonary bypass is preferred over closed commissurotomy, which is performed on a beating heart. Because of its simplicity, closed commissurotomy is still widely performed in developing countries. In the 1960s, rheumatic mitral stenosis was the first valvular disease to be treated with a prosthetic valve replacement using the mechanical mitral valve developed by Albert Starr (born 1926) and Lowell Edwards (1898-1982). For further discussion of surgical options in rheumatic mitral stenosis, the reader is referred to appropriate treatment guidelines.
Quantification of Mitral Stenosis
- Muhamed Saric, MD, PhD
- Roberto M. Lang, MD
- Itzhak Kronzon, MD
- Roberto M. Lang, MD
Echocardiography is the modality of choice for the diagnosis of mitral stenosis. The joint American Society of Echocardiography and European Association of Echocardiography guidelines for native valvular stenosis feature an exhaustive review of echocardiographic methods for quantitative assessment of mitral stenosis. Full echocardiographic evaluation of mitral stenosis includes the following three sets of parameters: (1) mean diastolic transmitral pressure gradient; (2) mitral valve area (MVA); and (3) secondary changes including measurements of relevant chamber sizes and estimation of right heart pressures. Most modern ultrasound systems contain built-in software packages for determining these parameters. Major methods for quantification of mitral stenosis are presented in Figures 109.1 and 109.2 . In most instances, evaluation of mitral stenosis by invasive methods of cardiac catheterization is not necessary unless there is a discrepancy between clinical and echocardiographic findings.
Mean pressure gradient measurements
Mean diastolic pressure gradient is inversely related to MVA; that is, the more severe the mitral stenosis, the higher the mean diastolic pressure gradient across the mitral valve. This gradient can be easily measured by pulsed and continuous wave Doppler. The best approach for transmitral flow evaluation and gradient determination should be with the transducer at the apex, imaging in four-chamber or two-chamber views. Color flow imaging can be helpful for the assessment of the exact direction of the transmitral flow. The angle between the interrogating beam and the transmitral jet should be 0 degrees.
Gradient can be assessed by pulsed-wave Doppler with the sample volume at the tips of the leaflets or by continuous wave Doppler. By tracing the spectral Doppler-derived diastolic transmitral flow velocity envelope and with the use of built-in algorithms available in most modern ultrasound imaging systems, one can obtain the mean MV gradient (see Fig. 109.1 , A ). To calculate the mean gradient, the system first calculates instantaneous pressure gradients using the simplified Bernoulli equation (see Eq. 109-4 , later) and then averages them out:
where ΔP is the mean diastolic transmitral pressure gradient, V is the instantaneous transmitral velocity, and n is the number of instantaneous gradients measured.
In the presence of atrial fibrillation, mean diastolic gradient should be averaged from multiple (typically five) cardiac cycles. When the mitral valve is normal, there is no significant diastolic transmitral pressure gradient. In severe mitral stenosis, the mean gradient is typically greater than 10 mm Hg, in moderate stenosis it is between 5 and 10 mm Hg, and in mild stenosis it is less than 5 mm Hg. It is important to emphasize that these cutoff values assume a normal transmitral flow (a normal stroke volume and a normal heart rate). Mean diastolic gradient is strongly influenced by changes in transmitral flow:
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