Mitral Stenosis

5 Mitral Stenosis



Goals of Echocardiography in Mitral Stenosis




image To establish that mitral stenosis (MS) is present


image To establish the level of obstruction


• Valvar

• Subvalvar

• Other (e.g., myxoma)

image To establish the hemodynamic parameters: gradient, area, cardiac index (CI), right ventricular systolic pressure (RVSP)


image To establish suitability for valvuloplasty


• Mass score, calcification

image To identify complications of mitral stenosis


• Pulmonary hypertension

• Atrial or appendage thrombosis

• Infective endocarditis

image To identify concurrent valvulopathies/pathologies


• Mitral regurgitation (MR)

• Aortic insufficiency (AI)

• Tricuspid regurgitation (TR)

• Tricuspid stenosis with tricuspid regurgitation (TS/TR)

• Tricuspid stenosis (TS)

• Aortic stenosis (AS)


Scanning Issues



Required Parameters to Obtain from Scanning




image Valve parameters


• Morphology, suitability for catheter balloon valvuloplasty (CBV)

• Mean gradient

• Area (same value by ≥2 methods)

• Proximal isovelocity surface area (PISA) variables: PISA radius, VAlias, VPeak

• MR severity

image Right ventricle size and systolic function


image Indirect pressure overload signs: left atrium (LA) size, RVSP


image Left ventricular outflow tract (LVOT)–derived cardiac output and stroke volume. Note that in the presence of AI, the stroke volume measured in the LVOT is the total forward stroke volume, not the net forward stroke volume.


image Height and weight for body surface area


image Has there been a commissurotomy within the last 3 months?



Valid Methods for Mitral Valve Area Determination (Need ≥2 Concordant)




image Continuity (if < mild AI)


image Pressure half time (PHT), if no factors are present that alter left ventricle (LV) compliance, such as left ventricular hypertrophy, left ventricular wall motion abnormalities, LV dysfunction, recent CBV, or more than mild AI


image Proximal isovelocity surface area (PISA)


image Planimetry


image Real-time three-dimensional (3D) echocardiography



Scanning Notes



Gradient




image Emphasize the mean gradient.


image Ensure that transmitral Doppler sampling is correctly aligned, and that continuous wave Doppler is being used with adequate gain settings.


image If sinus rhythm is present, measure three spectral profiles.


image If atrial fibrillation is detected, measure five spectral profiles.


image Ideally, measure 10 spectral profiles.


image Spectral profiles should be displayed at two-thirds the height of the display, and wide enough so that there are two or three per display.


image If the gradient is not severe, but the area is, consider provocative maneuvers (e.g., sit-ups) to increase flow and (thereby the gradient).




Planimetry




image Optimize the gain settings for planimetry—over-gain results in a falsely low estimation of mitral valve area (MVA) due to “blooming” of the margins.


image Measure the area at the narrowest part of the funnel-like orifice of MS—this may be at the level of the leaflet tips or at the subvalvar level.


image Be cautious if there was a prior commissurotomy—planimetry underrepresents area if the orifice has deep “splits” into the commissures (or leaflets), which are difficult so see by ultrasound, especially if they extend off the plane of imaging.



Pressure Half Time




image Do not accept PHT estimates of MVA if any of the following are present:


• Left ventricular hypertrophy

• Left ventricular wall motion abnormalities

• LV dysfunction

• Recent commissurotomy

• More than mild AI

All are factors that reduce the accuracy of the PHT relation to MVA.



Proximal Isovelocity Surface Area




image



where r = PISA radius.


The PISA method is based on the assumption that there is a hemisphere of flow acceleration such as would occur with a planar orifice. This often is not the case in mitral stenosis, however, particularly when the greatest stenosis is subvalvar. To adjust for the effect of the orifice on the volume of the PISA, use of an angle correction factor has been suggested (Fig. 5-1), multiplying the preceding calculation by α/180°. Not all echo systems carry angle measurement software.



image



where α = the measured angle of the “plane” of the orifice and r = PISA radius.


Transesophageal echocardiography (TEE) generally affords excellent depiction of PISA in mitral stenosis.



Reporting Issues


The mean gradient is the gradient seen, by the left atrium, on average, through diastole and is, as with AS, the only suitable expression of the physiologic pressure burden on the downstream chamber. Many MS profiles have an initial, brief, higher velocity/gradient that is not borne out through the rest of diastole. Therefore, emphasize the mean gradient, and avoid mentioning the peak gradient. It is clinically useful to offer the heart rate and rhythm, both of which are apparent on echocardiography, when stating the mean gradient: “The mean gradient was 13 mm Hg at an average heart rate of 75 bpm (atrial fibrillation).” When reporting, compare gradients, areas and RVSP, and rhythm to any previously recorded measurements.



Gradient Issues




image If there is a difference in gradient between current and previous echocardiographic determinations, then review the following variables:


• History (has there been a commissurotomy?)

• Rate differences

• Rhythm differences

• Sampling differences

image Recall that the accepted gradients for “severe” assume the absence of factors provoking higher output, such as the following:


• Tachycardia

• Anemia

• Fever

• Pregnancy

• Thyrotoxicosis

• Large dialysis shunt

image The 95% CI for mitral valve gradient is 3 mm Hg (vs. wedge:LV recordings).


image Direct left atrial pressure recording (LA:LV) typically leads to a lower mitral gradient, as it is without the phase delay of pulmonary capillary wedge tracings.



Area Issues




image Place less emphasis on the valve area, which is invariably calculated (other than by the planimetry method) and, therefore, is subject to larger error.


image Ensure MVA is concordant by at least two suitable methods.



Pressure Half Time Method




image The PHT relation (220) was validated in a relatively small series and is best applied for MVA between 1 and 1.5 cm2; r = 0.75.1 The actual precision of the correlation is less than has been thought.


image The 220 constant is actually different for both MVA <1 cm2 and MVA >1.5 cm2; therefore, use of the relationship at higher or lower areas is essentially an extrapolation of the known relationship, and assumes that a known variable (220) is a constant, which it is not.


image In the presence of AI, there are two ventricular inflows determining the spectral inflow:diastolic relationship. The PHT relation, therefore, is less representative of MS alone, in the presence of more than moderate AI. Correlation and SEE for MVA by PHT (vs. Gorlin) for patients both without and with AI are as follows:


• r = 0.69, SEE = 0.44 cm2 for patients with AI

• r = 0.91, SEE = 0.24 cm2 for patients without AI.2

image PHT is less accurate in patients older than 65 years of age, because of effects of hypertension on the ventricular diastolic properties, leading to overestimation of MVA.3


image PHT is less accurate for 3 months after CBV,4 because passive ventricular diastolic properties and atrial diastolic properties are adapting to the changes in load (i.e., less atrial/more ventricular).



Planimetry Method




image When images are amenable to planimetry, it is an accurate technique. It requires attention to scan extensively along the short axis of the orifice, to ensure sampling at the narrowest part. This may be at the leaflet tips, or in the subvalvar zone, which is important not to miss.


image Correlation for MVA by planimetry (vs. cardiac catheterization): r = 0.92 – 0.95.5,6


image Planimetry of MVA is an AI-independent technique.


image Planimetry is less accurate with prior commissurotomy,3,7,8 because the split often is eccentric: it may lead out onto another plane of imaging and be missed, or may go into a bright commissure that is difficult to visualize.



Continuity Method




image MVA by the continuity method is less accurate when the ideal reference site (the LVOT) has more than mild AI. The tricuspid reference site is harder to use, and is at least as likely to have TR. For all-comers, the correlation of continuity is very good: r = 0.91, SEE = 0.24 cm2,2 especially in the absence of AI: r = 0.93.2 However, in the presence of AI it is less: r = 0.84.2



Proximal Isovelocity Surface Area Method




image The utility of PISA depends on the clarity (quality) of the flow convergence signal. TEE regularly offers good-quality PISA. The most accurate PISA calculations are possible when the orifice is planar rather than within a curving and narrowing tunnel.


image Correlation and SEE for MVA by PISA9


• Versus planimetry: r = 0.91, SEE 0.21 cm2

• Versus PHT: r = 0.89, SEE 0.24 cm2

• Versus Gorlin: r = 0.86, SEE 0.24 cm2

• PISA appears not to be influenced by AI.9

• Versus surgical standard

Planimetry: r = 0.95, SEE 0.06 cm2

PHT: r = 0.87, SEE 0.09 cm2

PISA: r = 0.90, SEE 0.09 cm2


Real-Time Three-Dimensional Echocardiography


The real-time 3D technique allows depiction of the mitral orifice on any plane, and thus should assist with the task of planimetry. Although studies are limited to date, real-time 3D echocardiography shows very good correlation with Gorlin (average difference of 0.08 cm2), and low inter- and intraobserver variability (κ of 0.84 and 0.96, respectively), which in comparative studies was better than with other methods.10



Descriptors of Mitral Stenosis Severity




image After it has been established that MS is present, the next important task is to determine its severity. This involves a composite assessment of symptoms, physical findings, and hemodynamics. It must be recalled that MVA < 1 cm2 always indicates severe MS, but larger patients or those with higher cardiac output (CO) needs are commonly “severe” above an area of 1 cm2 and receive intervention for average MVAs of 1.2 or 1.3 cm2.


image Distinguishing moderate from mild is really of little consequence, as both are “nonsevere” and would not prompt intervention.


image “Severe” = mean gradient >12 mm Hg at rest, and an area of <1.3 cm2.


• A subset of clinically severe cases have MVA > 1 cm2 (1.2–1.3 cm2).

image “Critical” = mean gradient > 12 mm Hg at rest, and an area of <1.0 cm2


image Moderate = mean gradient < 12 mm Hg at rest, and an area of ≥1.3 cm2



Suitability for Valvuloplasty and Commissurotomy Issues




image Suitability for commissurotomy is determined by the following:


• Mass score < 8

• No contraindications: no significant MR, no LA or left atrial appendage (LAA) clot

image Use the mass score


image Calcification, especially of commissures, is a marker of higher short- and long-term mortality with CBV.


image Commissurotomy is generally unsuitable if there is MR >2+.


image There is substantial risk of arterial embolism if there is clot within the body of the left atrium, because valvuloplasty wires invariably are in the body of the atrium. There is a smaller risk of embolism if clot is within the LAA, because the wires that must traverse the LA body may avoid the LAA. TEE is clearly superior to evaluate for the presence of LA and LAA clot.



Surgical Issues




image Establish the degree of submitral (annular) calcification. There is a greater risk of periprosthesis (paravalvar) MR when submitral (annular) calcification is severe.


image Determine the degree of AI: in severe MR, IABP should not be used if there is concurrent AI ≥2+.


image Describe the RV in detail (RVH/systolic dysfunction/size), as well as the RVSP.


image RA size is a reasonable descriptor of RV diastolic function, if neither TR nor atrial fibrillation is present.



Provocative Testing to Enhance Transmitral Gradients and Right Ventricular Systolic Pressure


Simple bedside maneuvers (e.g., a few sit-ups) or more sophisticated ones (e.g., supine bicycle, upright treadmill testing, or dobutamine) may be used to increase the heart rate and cardiac output, and thereby enhance the mitral gradient and RVSP. The role of such testing is unclear: in mitral stenosis the gradient would be expected to increase, and generally it does, about two-fold, when patients are subjected to a Bruce or modified Bruce protocol: from 9 ± 7 mm Hg at rest to 17 ± 8 mm Hg, as does the RVSP, from 41 ±1 9 mm Hg to 70 ± 32 mm Hg.11 The optimal interpretation of the provoked hemodynamics is unclear. Advocates suggest that it better describes the basis of exertional symptoms and may be contributory when the resting hemodynamics are less striking than the (exertional) symptoms and findings.


Dobutamine stress echo (a gradient cut-off of 18 mm Hg) has been shown to predict clinical events (90% sensitivity, 87% specificity, and 90% accuracy) over a 5-year period, and increases the detection of medium- and higher-risk cases.12 Dobutamine stress echocardiography may assist with the evaluation of patients whose symptoms are out of proportion to the calculated valve area, and who may benefit from “medical or invasive intervention.”13



Notes on Mitral Stenosis



Etiologies of Mitral Stenosis



Congenital




image Congenital valvular MS is rare.


image Cor triatriatum sinister also is rare. It is a baffle-like ridge across the mid-LA that obstructs flow across the atrium, not at the mitral valve level.



Acquired




image Rheumatic origin is by far the most common cause of MS (>99% of all cases).


image Severe mitral annular calcification may cause mild/moderate MS but very rarely causes severe MS.


image LA myxoma/thrombus is an uncommon cause of MS (<1%).


image A mitral annuloplasty ring may overly narrow the orifice.


image Malignant carcinoid, rheumatoid arthritis, systemic lupus erythematosus, and other tumors are very rare causes.



Pathophysiology




image The normal mitral valve area is 4.5 to 6 cm2. A diastolic transmitral valve gradient occurs with loss of about half of the original area. There is increased left atrial pressure at rest with MVA of 1.5 cm2.


image Two thirds (at least) of MS cases occur in women. Of all cases of rheumatic heart disease, 25% are pure MS and 40% are mixed MS/mitral insufficiency.


image The course of disease proceeds as follows:


• There is a 5- to 15-year latent period after rheumatic fever before early findings (auscultatory abnormalities) become apparent.

• Usually, a decade of asymptomaticity (with auscultatory abnormalities) passes before symptoms develop.

• Over 5 years, most patients with NYHA Class 2 symptoms progress to Class 3 to 4.

• Ten-year survival of patients with NYHA Class 2 symptoms is about 80%; for patients with NYHA Class 3 symptoms, it is about 38%. A more rapid progression has been noted among certain groups, such as in the subtropical areas of India and the Philippines, and among the Inuit.


Role of Transthoracic and Transesophageal Electrocardiography in Mitral Stenosis



Transthoracic Echocardiography


Nearly all cases of MS can be hemodynamically assessed using TTE alone. Both apical and lower esophagus sampling sites are, however, ideally aligned for Doppler interrogation, and generally generate accurate estimates of gradient. However, if the plane of the mitral orifice is oblique (because of LA dilation), TEE may struggle to achieve optimal alignment for sampling.


Mitral valve scoring is better performed by TTE than TEE, because posterior long-axis and apical views show subvalvar (chordal) involvement better than TEE does. TEE images from the esophagus, acquired through thickened (and potentially calcified) leaflets, fail to clearly depict subvalvar disease. Transgastric long-axis views may afford adequate views of the important subvalvar apparatus.


TEE is better than TTE for the following:



image Detection of LAA and LA thrombus, which is necessary information when contemplating CBV


image Estimation of MR severity (TTE may underestimate MR severity)


image The rare truly technically difficult study case


TEE is not superior for the evaluation of subvalvar disease. The thickened and often calcified leaflets impair subvalvar imaging from the esophagus. Transgastric views are helpful to circumvent this imaging problem.



Cardiac Catheterization for Assessment of Mitral Stenosis



Usual Technique




image Pulmonary artery (PA) catheter(s) for right-sided pressures and thermodilution-estimated CO


image Femoral arterial access for retrograde cannulation into the LV via the aorta


• LV to aortic (femoral) pressure gradients

• Diastolic filling period (DFP): the average width (time) of the gradients

image Verification of pressure waveforms (see later discussion)



Gorlin Equation




image The Gorlin equation is employed, using the following variables: CO, DFP, HR, gradient. These variables are readily obtained at cardiac catheterization.


image Historically, the Gorlin equation constant was developed for MS, because there is less flow dependence with MS than for AS.14


image In a small initial validation (11 cases), variation of serial measurements averaged ±0.0 cm2, but ranged from +0.2 to –0.4 cm2.15


image In the initial series, autopsy standard was ±0.5 to ±0.1 cm2 and the variation against autopsy was ≤0.2 cm2.14


image The Gorlin equation purportedly estimates anatomic, not effective, orifice, because it was validated against surgery and autopsy, but there is evidence that it does not truly reflect anatomic area.


image The Gorlin equation is less accurate in the presence of the following:

Related posts:

  1. The Aortic Valve
  2. Coronary Artery Disease: Ischemia, Infarction, and Complications
  3. Pericardial Diseases
  4. Mitral Insufficiency

Stay updated, free articles. Join our Telegram channel
Tags:
Jun 12, 2016 | Posted by in CARDIOLOGY | Comments Off on Mitral Stenosis

Full access? Get Clinical Tree
Get Clinical Tree app for offline access