By: Dr. Ankur Gupta

Resident, Dept. of Cardiology

Dhiraj Hospital

ECHOCARDIOGRAPHY IN MITRAL STENOSIS

• Valve stenosis is a common heart disorder and an important cause of cardiovascular morbidity and mortality.

• Echocardiography - Key tool for diagnosis and evaluation of valve disease, and primary non-invasive imaging method for valve stenosis assessment.

• Essential in clinical practice to use an integrative approach when grading the severity of stenosis.

• Combine all Doppler and 2D data, and not rely on one specific measurement.

• Various conditions influence velocity and pressure gradients.

• Parameters vary depending on intercurrent illness of patients with low vs. high cardiac output.

• Irregular rhythms or tachycardia can make assessment of stenosis severity problematic.

MITRAL STENOSIS• Echo - Major role in decision making for MS.

• Confirmation of diagnosis,

• Quantitation of stenosis severity,

• Consequences, and

• Analysis of valve anatomy.

CAUSES AND ANATOMIC PRESENTATION• MS is the most frequent valvular complication of rheumatic fever.

• Rheumatic MS commissural fusion.

• Other anatomic lesions - chordal shortening and fusion, and leaflet thickening, and later in the disease course, superimposed calcification.

• This differs markedly from degenerative MS.

• Annular calcification.

• Old age. Associated with hypertension, atherosclerotic disease, and sometimes AS.

• Congenital MS - Abnormalities of the subvalvular apparatus.

• Other rare causes: inflammatory diseases (e.g. systemic lupus), infiltrative diseases, carcinoid heart disease, and drug-induced valve diseases.

• Leaflet thickening and restriction are common here, while commissures are rarely fused.

LA-LV gradient Elevated LA pressure

Elevated pressure in pulmonary capillaries Pulm. cong. / edema

PHT / reactive PHT TR

Right heart failure AF

NOTE: In mitral stenosis there is no ‘burden’ on the left ventricle(no pressure or volume over load).

Hemodynamics of MS

ECHO CHARACTERISTICS OF MS

Doming (diastolic bulging of the AML) Reduced valve opening

Commissural fusion Leaflet tip thickening

Secondary calcification Subvalvular involvement (thickened and fused tendinae)

Associated problemsThickened aortic valve Reduced LVF (rheumatic myocarditis)

Enlarged LA Pulmonary hypertension

Other valve involvement Aortic regurgitation

Tricuspid stenosis Thrombus

Risk of Thrombus

• Systemic embolism in 20% of all MS patients

• 80% of patients are in Afib

• 45% have spontaneous left atrial contrast

Most thrombi are seen in the left atrial appendage. Thus it can be easily missed on TTE

MV Area — Reference Values

Normal 4-6 cm²

Mild >1.5 cm²

Moderate (cm²) 1-1.5 cm²

Severe (cm²) <1 cm²

MITRAL STENOSIS ASSESSMENT• Based on literature review and expert consensus, these methods were categorized for

clinical practice as:

† Level 1 Recommendation: an appropriate and recommended method for all patients with stenosis of that valve.

† Level 2 Recommendation: a reasonable method for clinical use when additional information is needed in selected patients.

† Level 3 Recommendation: a method not recommended for routine clinical practice although it may be appropriate for research applications and in rare clinical cases.

MVA Planimetry (Level 1 Recommendation)

• Theoretically, advantage of being a direct measurement of MVA

• Unlike other methods, does not involve any hypothesis regarding flow conditions, cardiac chamber compliance, or associated valvular lesions.

• In practice, shows the best correlation with anatomical valve area.

• Therefore, considered as the reference measurement of MVA.

Indices of Stenosis Severity

• Planimetry measurement is obtained by direct tracing of the mitral orifice, including opened commissures, if applicable, on a PSAX view.

• Careful scanning from the apex to the base of the LV CSA is measured at the leaflet tips.

• Measurement plane should be perpendicular to the mitral orifice (elliptical shape).

• Gain setting - sufficient to visualize the whole contour of the mitral orifice.

• Excessive gain - underestimation of valve area (esp. when leaflet tips are dense or calcified).

• Image magnification (zoom mode) - useful to better delineate the contour of the mitral orifice.

• Optimal timing of the cardiac cycle to measure planimetry mid-diastole.

• Best performed using the cineloop mode on a frozen image.

• Perform several different measurements, esp. in

• Atrial fibrillation,

• Incomplete commissural fusion (moderate MS or after commissurotomy),

• Anatomical valve area may be subject to slight changes according to flow conditions.

MVA Plani: TTE, PSAX view.(A) Mitral stenosis. Both commissures fused. MVA 1.17 cm². (B) Unicommissural opening after BMV. Postero-medial commissure is opened. MVA 1.82 cm².(C) Bicommissural opening after BMV. MVA 2.13 cm².

Limitations of MVA planimetry

• Poor acoustic window

• Severe distortion of valve anatomy (severe valve calcifications of the leaflet tips).

• Technical expertise.

• Degenerative MS - planimetry is difficult and mostly not reliable because of the orifice geometry and calcification present.

Image quality Alignment

Timing Calcification

Atrial fibrillation Incompl. comm. fusion

Operator experience

Pressure gradient (Level 1 Recommendation)

• Estimation of the diastolic pressure gradient.

• Derived from the transmitral velocity flow curve.

• Simplified Bernoulli equation ∆P = 4v².

• Reliable estimation - good correlation with invasive measurement using transseptal catheterization.

• CWD is preferred to ensure maximal velocities are recorded.

• When PWD is used, the sample volume should be placed at the level or just after leaflet tips.

• Doppler gradient is assessed using the apical window (parallel alignment of the ultrasound beam and mitral inflow).

• Ultrasound Doppler beam should be oriented to minimize the intercept angle with mitral flow to avoid underestimation of velocities.

• Colour Doppler in apical view - useful to identify eccentric diastolic mitral jets - encountered in cases of severe deformity of valvular and subvalvular apparatus.

• In these cases, the Doppler beam is guided by the highest flow velocity zone identified by colour Doppler.

• Optimization of gain settings, beam orientation, and a good acoustic window are needed to obtain well-defined contours of the Doppler flow.

• Peak and mean mitral gradients are calculated by integrated software using the trace of the Doppler diastolic mitral flow waveforms on the display screen.

• Mean gradient is the relevant haemodynamic finding.

• Peak gradient is of little interest as it derives from peak mitral velocity, which is influenced by LA compliance and LV diastolic function.

• Heart rate at which gradients are measured should always be reported.

• AF - mean gradient - average of five cycles with the least variation of R–R intervals and as close as possible to normal heart rate.

• In addition, mean mitral gradient has its own prognostic value, in particular following BMV .

Mean gradient varies according to the length of diastole: it is 8 mmHg during a short diastole (A) and 6 mmHg during a longer diastole (B).

Determination of mean mitral gradient from Doppler diastolic mitral flow in a patient with severe mitral stenosis in atrial fibrillation.

Limitations of Pressure gradient

• Although reliable, not the best marker of the severity of MS.

• Dependent on MVA.

• Influenced by other factors: Transmitral flow rate, HR, cardiac output, associated MR.

Pressure half-time (Level 1 Recommendation)

• Time interval in milliseconds between the maximum mitral gradient in early diastole and the time point where the gradient is half the maximum initial value.

• Decline of the velocity of diastolic transmitral blood flow is inversely proportional to valve area (cm²).

• .

• PHT is obtained by tracing the deceleration slope of the E-wave on Doppler spectral display of transmitral flow and valve area is automatically calculated by the integrated software.

• Doppler signal used is the same as for the measurement of mitral gradient.

• As for gradient tracing, attention should be paid to the quality of the contour of the Doppler flow, in particular the deceleration slope.

MVA by PHT: MS in atrial fibrillation. Valve area is 1.02 cm².

• Deceleration slope is sometimes bimodal, the decline of mitral flow velocity being more rapid in early diastole than during the following part of the E-wave.

Non-linear decreasing slope of the E-wave. The deceleration slope should not be traced from the early part (left), but using the extrapolation of the linear mid-portion of the mitral velocityprofile (right).

• In rare patients - concave shape of the tracing - PHT measurement may not be feasible.

• AF - tracing should avoid mitral flow from short diastoles and average different cardiac cycles.

PITFALLS OF MVA PHT

• Gradient and compliance are subject to important and abrupt changes (Immediately after BMV)

• Discrepancies between the decrease in mitral gradient and the increase in net compliance.

• Rapid decrease of mitral velocity flow, i.e. short PHT can be observed despite severe MS.

• In patients with low LA compliance.

• Severe AR Shortens PHT.

• Early diastolic deceleration time is prolonged with impaired LV relaxation, while shortened in case of decreased LV compliance.

• Impaired LV diastolic function is a likely explanation of the lower reliability of PHT to assess MVA in the elderly.

• Elderly rheumatic MS, degenerative calcific MS often associated with AS and hypertension and, thus, impaired diastolic function.

• Hence, the use of PHT in degenerative calcific MS may be unreliable and should be avoided.

Diastolic dysfunction Aortic regurgitation

Following BMV Concave shape of tracing

Degenerative calcified MS Additional AR where the AR signal interferes with MV inflow signal

Continuity equation (Level 2 Recommendation)

• Based on the conservation of mass, stating in this case that the filling volume of diastolic mitral flow is equal to aortic SV.

where D is the diameter of the LVOT (in cm) VTI (cm).

• Accuracy and reproducibility of the continuity equation for assessing MVA are hampered by the number of measurements increasing the impact of errors of measurements.

• Cannot be used in AF or associated significant MR or AR.

Proximal isovelocity surface area (PISA) method (Level 2 Recommendation)

• Based on the hemispherical shape of the convergence of diastolic mitral flow on the atrial side of the mitral valve, as shown by colour Doppler.

• Enables mitral volume flow to be assessed and, thus, to determine MVA by dividing mitral volume flow by the maximum velocity of diastolic mitral flow as assessed by CWD.

where r is the radius of the convergence hemisphere (in cm), Valiasing is the aliasing velocity (in cm/s),

peak VMitral the peak CWD velocity of mitral inflow (in cm/s), and α is the opening angle of mitral leaflets relative to flow direction

• Can be used in the presence of significant MR.

• Technically demanding and requires multiple measurements.

• Accuracy is impacted upon by uncertainties in the measurement of the radius of the convergence hemisphere, and the opening angle.

• Use of colour M-mode improves its accuracy, enabling simultaneous measurement of flow and velocity.

Other indices of severity: Mitral valve resistance (Level 3 Recommendation)

• Ratio of mean mitral gradient to transmitral diastolic flow rate, which is calculated by dividing SV by diastolic filling period.

• Alternative measurement of the severity of MS

• Correlates well with pulmonary artery pressure.

• Not shown to have an additional value for assessing the severity of MS as compared with valve area.

• Estimation of pulmonary artery pressure, using Doppler estimation of the systolic gradient between RV and RA, reflects the consequences of MS rather than its severity itself.

• Advised to check its consistency with mean gradient and valve area, as there may be a wide range of pulmonary artery pressure for a given valve area.

• Pulmonary artery pressure is critical for clinical decision-making and it is therefore very important to provide this measurement.

OTHER ECHOCARDIOGRAPHIC FACTORS IN THE EVALUATION OF MITRAL STENOSIS Valve anatomy

• Major component of echo assessment of MS because of its implications on the choice of adequate intervention.

• Commissural fusion is assessed from the PSAX view.

• Degree of commissural fusion is estimated by echo scanning of the valve.

• Commissural anatomy may be difficult to assess, in particular in patients with severe valve deformity.

• Commissural fusion is an important feature to distinguish rheumatic from degenerative MS.

• Complete fusion of both commissures generally indicates severe MS.

• Lack of commissural fusion does not exclude significant MS.

• In degenerative aetiologies or even rheumatic MS, restenosis after previous commissurotomy may be related to valve rigidity with persistent commissural opening.

• Evaluates leaflet thickening and mobility in long-axis parasternal view.

• Chordal shortening and thickening - PLAX and apical views.

• Increased echo brightness - calcification.

• Impairment of mitral anatomy is expressed in scores combining different components of mitral apparatus or using an overall assessment of valve anatomy.

Associated lesions

1) LA thrombus

• Quantitation of LA enlargement - Evaluating LA area or volume.

• M-mode lacks accuracy because enlargement does not follow a spherical pattern in most cases.

• LA spontaneous contrast on TEE - better predictor of the thrombo-embolic risk than LA size.

• TEE has much higher sensitivity than TTE to diagnose LA/LA appendage clot.

2) Associated MR

• Rheumatic MR - Restriction of leaflet motion.

• Post BMV MR - leaflet tearing is frequent.

• Choice of intervention.

• Quantitation should combine semi-quantitative and quantitative measurements.

• Careful for intermediate MR - more than mild MR is a relative contraindication for BMV.

• Analysis of the mechanism of MR is important in patients presenting with moderate-to-severe MR after BMV.

• Presence of MR does not alter the validity of the quantitation of MS, except for the continuity-equation valve area.

3) Other valve diseases

• MS SV aortic gradient underestimating AS severity.

• Severe AR PHT method for assessment of MS is not valid.

• To look for rheumatic involvement of TV.

• More frequently, associated tricuspid disease is functional TR.

• Diameter of the tricuspid annulus >40 mm seems to be more reliable than quantitation of regurgitation to predict the risk of severe late TR after mitral surgery.

GRADING OF MITRAL STENOSIS• Routine evaluation of MS severity – A combination of measurements of mean gradient

and valve area using planimetry and PHT.

• In case of discrepancy - Planimetry.

• Associated MR should be accurately quantitated, esp. when moderate or severe.

• Intervention - considered when moderate MS ± moderate MR + symptoms.

• Consequences of MS include - quantitation of LA size and estimation of PASP.

• The description of valve anatomy is summarized by an echocardiographic score.

• Severity assessment of rheumatic MS should rely mostly on valve area.

• Multiple factors influence other measurements, in particular mean gradient and systolic pulmonary artery pressure.

• Mean gradient and systolic pulmonary artery pressure supportive signs.

• Cannot be considered as surrogate markers of MS severity.

• Normal resting values of pulmonary artery pressure may be observed even in severe MS.

• In degenerative MS, mean gradient can be used as a marker of severity given the limitations of planimetry and PHT.

• Multivariate analyses performed in studies reporting a follow-up of at least 10 years identified valve anatomy as a strong predictive factor of event-free survival.

• Indices of the severity of MS or its haemodynamic consequences immediately after BMV

• Predictors of event-free survival,

• MVA, mean gradient, and left atrial or pulmonary artery pressure.

• Strong predictors of long-term results of BMV

• Degree of MR following BMV,

• Baseline patient characteristics - age, functional class, and cardiac rhythm.

IN NUTSHELL

Color Doppler , PISA and Continuity EquationCandle flamePISA for quantificationMVA = Mitral volume flow/ Peak velocity of diastolic mitral flowContinuity Equation (does not work if AR and MR are both present)

Quantifification of Mitral Stenosis in Atrial Fibrillation

Planimetry Several different measurements

Mean gradients Average 5 cycles with small variation of R-R intervals close to normal HR

PHT Avoid mitral flow from short diastoles/ averagedifferent cardiac cycles

Valvuloplasty• Indication• Clinically significant MS (valve area <1.5 cm² or <1.8 cm² in

unusually large patients)

• Results• Good immediate results (valve area >1.5 cm² with no

regurgitation).

NOTE: PHT method is not reliable immediately after valvuloplasty!

Prevalvuloplastic Echo-evaluation

Mobility Subvalvular thickeningValve thickening CalcificationCalcification of commissures Thrombus

Mitral regurgitation Tricuspid regurgitation

Finally, echocardiographic measurements of valve stenosis must be interpreted in the clinical context of the individual patient.

Thank you