Strategies to Test for Rheumatic Heart Disease
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Rheumatic heart disease remains a major public health problem in many parts of the world. While the incidence and prevalence of ARF and RHD have been decreasing in developed countries since the early twentieth century, they continue to be major causes of morbidity and mortality among young people in developing nations. It is estimated that there are more than 15 million cases of RHD worldwide, with 282,000 new cases and 233,000 deaths annually.
Globally, India contributes nearly 25%-50% of newly diagnosed cases, deaths, hospitalizations and burden of RHD.The earliest reporting of RHD was done in 1910. Even during the 1980s, hospital admission data suggested that RF and RHD accounted for nearly one-half to one-third of the total cardiac admissions at various teaching hospitals all over India. A more recent survey across various tertiary care hospitals found that hospital admission rates of RHD had declined (5%-26% of cardiac admissions). Population-based epidemiological data to ascertain the prevalence of RHD and their impact on community in India are lacking. A properly planned population study in 1993 reported a prevalence of 0.09% for RHD.
Most of the epidemiological studies are school-based surveys. The reported prevalence of RHD varied from 1.8 to 11/ 1000 schoolchildren (average 6/1000) during the 1970s and 1980s, and 1-3.9/1000 during the 1990s.Studies using echocardiographic validation of clinical diagnoses show a much lower prevalence of RHD. The surveys conducted by the Indian Council of Medical Research (ICMR) also indicate a decline in the prevalence of RHD over decades.
The epidemiology of rheumatic heart disease in India is of special interest as it may help to understand the effects of economic transition on this particular enigmatic disease. Critical appraisal of the published literature suggests the possibility of a real decline in the occurrence of the disease in some parts of the country, but a continuing onslaught in several other regions. The rate of decline seems to correlate more with improved public health facilities than with economic growth alone. However, the cumulative burden of the disease remains high, and sustained efforts for the prevention of rheumatic heart disease needs special attention .
Rheumatic fever is the most common cause of mitral stenosis. Other less common etiologies of obstruction to left atrial outflow include congenital mitral valve stenosis, , mitral annular calcification with extension onto the leaflets, cor triatriatum, rheumatoid arthritis, systemic lupus erythematosus, left atrial myxoma, and infective endocarditis with large vegetations. Pure or predominant MS occurs in approximately 40% of all patients with rheumatic heart disease and a past history of rheumatic fever. In other patients with rheumatic heart disease, lesser degrees of MS may accompany mitral regurgitation (MR) and aortic valve disease. In temperate climates and developed countries, the incidence of MS has declined considerably over the past few decades due to reductions in the incidence of acute rheumatic fever. However, it remains a major problem in developing nations, especially in tropical and semitropical climates.
In normal cardiac physiology, the mitral valve opens during left ventricular diastole, to allow blood to flow from the left atrium to the left ventricle. This flow direction will be maintained as long as the pressure in the left ventricle is lower than the pressure in the left atrium and the blood flows down the pressure gradient. Mitral stenosis (MS) is a mechanical obstruction during blood flow from the left atrium to the left ventricle. Obstruction happens due to thickening and immobility of the leaflets, thickening and fusion of the chorda tendinae or mitral annular and commissural calcification.
In rheumatic MS, the valve leaflets are diffusely thickened by fibrous tissue and/or calcific deposits. The mitral commissures fuse, the chordae tendineae fuse and shorten, the valvular cusps become rigid, and these changes, in turn, lead to narrowing at the apex of the funnel-shaped ("fish-mouth") valve. Although the initial insult to the mitral valve is rheumatic, the later changes may be a nonspecific process resulting from trauma to the valve caused by altered flow patterns due to the initial deformity. Calcification of the stenotic mitral valve immobilizes the leaflets and narrows the orifice further. Thrombus formation and arterial embolization may arise from the calcific valve itself, but in patients with atrial fibrillation (AF), thrombi arise more frequently from the dilated left atrium (LA), particularly from within the left atrial appendage.
In normal adults, the area of the mitral valve orifice is 4-6 cm2. In the presence of significant obstruction, i.e., when the orifice area is reduced to < âˆ¼2 cm2, blood can flow from the LA to the left ventricle (LV) only if propelled by an abnormally elevated left atrio-ventricular pressure gradient, the hemodynamic hallmark of MS. When the mitral valve opening is reduced to <1 cm2, often referred to as "severe" MS, a LA pressure of âˆ¼25 mmHg is required to maintain a normal cardiac output (CO). The elevated pulmonary venous and pulmonary arterial (PA) wedge pressures reduce pulmonary compliance, contributing to exertional dyspnea. The first bouts of dyspnea are usually precipitated by clinical events that increase the rate of blood flow across the mitral orifice, resulting in further elevation of the LA pressure.
To asscess the severity of obstruction hemodynamically, both the transvalvular pressure gradient and the flow rate must be measured. The latter depends not only on the CO but also on the heart rate. Increase in heart rate causes shortening of diastole proportionately more than systole and diminishes the time available for flow across the mitral valve. Therefore, at any given level of CO, tachycardia, including that associated with rapid AF, augments the transvalvular pressure gradient and elevates further the LA pressure. The LV diastolic pressure and ejection fraction (EF) are normal in isolated MS.
In MS and sinus rhythm, the elevated LA and PA wedge pressures exhibit a prominent atrial contraction pattern (a wave) and a gradual pressure decline after the v wave and mitral valve opening (y descent). In severe MS and whenever pulmonary vascular resistance is significantly increased, the pulmonary arterial pressure (PAP) is elevated at rest and rises further during exercise, often causing secondary elevations of right ventricular (RV) end-diastolic pressure and volume.
In temperate climates, the latent period between the initial attack of rheumatic carditis and the development of symptoms due to MS is generally about two decades; most patients begin to experience disability in the fourth decade of life. Studies carried out before the development of mitral valvotomy revealed that once a patient with MS became seriously symptomatic, the disease progressed continuously to death within 2-5 years.
In patients whose mitral orifices are large enough to accommodate a normal blood flow with only mild elevations of LA pressure, marked elevations of this pressure leading to dyspnea and cough may be precipitated by sudden changes in the heart rate, volume status, or CO, as, for example, with excitement, severe exertion, fever, severe anemia, paroxysmal AF and other tachycardias, sexual intercourse, pregnancy, and thyrotoxicosis. As MS progresses, lesser degrees of stress precipitate dyspnea, the patient becomes limited in daily activities, and orthopnea and paroxysmal nocturnal dyspnea develop. The development of permanent AF often marks a turning point in the patient's course and is generally associated with acceleration of the rate at which symptoms progress.
Hemoptysis results from rupture of pulmonary-bronchial venous connections secondary to pulmonary venous hypertension. It occurs most frequently in patients who have elevated LA pressures without markedly elevated pulmonary vascular resistances and is rarely fatal. Recurrent pulmonary emboli, sometimes with infarction, are an important cause of morbidity and mortality rates late in the course of MS. Pulmonary infections, i.e., bronchitis, bronchopneumonia, and lobar pneumonia, commonly complicate untreated MS, especially during the winter months.
Mitral valve assessment with echocardiography should include the pattern of valve involvement and calcification, severity of stenosis, associated mitral regurgitation and other co-existent valve lesions and atrial chamber dilatation and function. Mitral stenosis can be assessed in parasternal, apical or subcostal views. As with any stenotic valve the main diagnostic feature in the parasternal long axis view. As in rheumatic MS, the anterior mitral leaflet (AMVL) shows diastolic doming or hockey-stick shape and the posterior mitral leaflet (PMVL) has restricted motion or is totally immobile. This doming is due to the reduced mobility of the valve tips compared to the base of the leaflets. Echocardiography can also adequately assess the Subvalvular apparatus changes such as thickening, shortening, fusion of chordal calcification. Color Doppler in this view with diastolic turbulence across the mitral valve confirms the diagnosis. On the other hand, Parasternal short axis view of the mitral valve is used for assessing the leaflets thickening, fusion and calcification of commissures. The parasternal short axis view is also used to assess the mitral valve orifice area by planimetry of the mitral leaflets at the level of tips. The Following are different means of measurements by echocardiography to ascess the severity of MS. Planimetry of mitral valve at the level of the leaflets tips is done in parasternal short axis view. This method is a very familiar technique by 2D echocardiography but the same method can also be used in 3D echocardiography en-face view of mitral valve. However, newly developed QLAB software in 3D echo is now available for calculation of mitral valve orifice area which requires further validation. Calculation of mitral valve area (MVA) by pressure half-time (P1/2t) should be done in an apical four chamber view using continuous wave. Doppler Pressure half-time method is not valid immediately after percutaneous balloon mitral the Doppler curve. The gradient can be measured by tracing the dense outline of mitral diastolic inflow and the mean pressure gradient is automatically calculated. The severity can be assessed as mild (<5), moderate (5-10) and severe (>10) .
Both qualitative and quantitative evaluation of valvular heart disease can be improved by 3D echocardiography. Anyplane and paraplane analysis of a stenotic valve allows an accurate planimetry of the smallest orifice area. Zamorano et al demonstrated that 3DTTE is a feasible, accurate and highly reproducible technique for assessing the mitral valve area in patients with rheumatic MV stenosis. In a consecutive series of 80 patients, MV area was assessed by conventional echo Doppler methods and by 3DTTE, and results were compared with those obtained invasively.Compared with all other echo-Doppler methods, 3DTTE had the best agreement with the invasively determined MV area, and intra- and inter-observer variability of the method was very good. Zamorano et al also studied 29 patients undergoing percutaneous balloon mitral valvuloplasty. 3DTTE had the best agreement with the invasively determined MV area, particularly in the immediate post procedural period; therefore, the method could be proposed as an ideal one throughout this procedure and could make invasive evaluation unnecessary in this setting. As part of these very important quantitative data, 3DTTE can be integrated with 2D evaluation in the qualitative morphology assessment of the MV. Commissures, leaflets, annulus calcifications and subvalvular structures can be visualized from different and unique planes facilitating the understanding of this complex apparatus. Vegetations, commissural diseases, subvalvular pathologies (tip of the leaflets/chordae/papillary muscles), clefts can be accurately diagnosed.
So assessment of the severity of mitral valve stenosis requires accurate measurements of the Mitral valve orifice area (MVA). Direct measurement of the MVA can be performed by planimetry using two-dimensional echocardiography (2-D echo). Mitral valve area determined by planimetry reflects the anatomic orifice area and is largely independent of hemodynamic variables, left ventricular compliance and concomitant valvular disease. However, planimetry by 2-D echo requires significant experience and operator skill to define the correct image plane that displays the true mitral valve orifice. In addition, planimetry requires a parasternal short axis view of the mitral valve and is therefore limited to patients with favorable image quality from a parasternal window. To bypass the difficulty of a parasternal short axis view, Doppler traces of the diastolic transmitral flow is obtained from a four-chamber apical view and the mitral valve area is estimated using the pressure half-time (PHT). However PHT is influenced by hemodynamic variables, left ventricular compliance and concomitant valvular disease.
Real-time three-dimensional echocardiography (3-D echo) is a novel imaging technique that is expected to enhance the ability to perform planimetry of the mitral valve. 3D echo utilizes a matrix array echo probe to scan a pyramidal volume in real time. A precise cross-section of mitral valve orifice at the tips of the leaflets with correct plane orientation may provide more accurate assessment of MS severity than two-dimensional echocardiography. Thus it can eliminate one of the principle limitations of 2DE in determining MVA by planimetry. There is less inter- and intra-observer variation also during MVA calculation. Therefore, real-time 3D echo can be used as a practical and accurate method for planimetry of mitral valve areas.
This study will be performed to evaluate the feasibility, reproducibility and accuracy of 3-D echo for the assessment of MVA over conventional 2D planimetry & Doppler PHT methods.
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