3. Q. Discuss with picture how do you Assess severity of MR with echo views and measurement? Answer: Assessment of Mitral regurgitation: To understand and appreciate aetiology, functional classification mitral regurgitation and its assessment of severity, we need to know cardiac anatomic relationships and functional aspects of mitral valve in cardiac cycle. Cardiac anatomic relationships: Parasternal long axis (PLAX): Anatomic section of LV from aortic root (right side) to the LV apex (left side). RV with trabeculation is seen anteriorly upward as it wraps around LV. Papillary muscles of LV emerge from ventricular free wall and give rise to chordae tendinae of two mitral valves. Secondary chordae is of surgical importance in severe MR due to broken mitral chordae and surgical repair is contemplated (seen in 3D echo view). Longer anterior mitral valve leaflet connects to right to aorta directly with the posterior aortic wall and aortic valve this is called mitral and aortic continuity in the left heart. Posterior mitral leaflet attached to mitral annulus along posterior ventricular free wall (mural leaflet). Left atria is posterior to aorta. Size of LA is approximately diameter of aorta. There is a pericardial sinus, transverse sinus between left atrial anterior wall and posterior aortic wall. Two large ostia of two left pulmonary veins are seen in superior portion of left atrial wall. Between two ostia and mitral valve apparatus is the ligament of Marshal (site of interest for RF ablation for atrial arrhythmias). Real time 3 D echo clearly shows relationship of pulmonary veins to the ligament of marshal, os of LAA, mitral annulus, and mitral leaflets (difficult with 2D). Behind LA is a descending aorta. Parasternal short axis: Conventional 2D echo views heart from its apex toward the base. The RV wrap around left and interventricular septum between both ventricles.inferomedial papillary sits at junction of septal and free walls at approximately eight o’clock on the ventricular short axis. Anterolateral papillary is located only on the ventricular free surface, attached only to free wall. The size of both papillary heads is roughly symmetric. Apical views: Traditionally, echo orients this views with apex of LV toward top of sector arch and both ventricles are juxtaposed and separated by intraventricular septum. The intraatrial septum between both atria and common septum shared by left ventricle and right atrium is atrioventricular septum (site for AV canal defect). Mitral valve apparatus is farther away from ventricular apex than tricuspid apparatus. Mitral and tricuspid valves can be differentiated by their position in relationship to cardiac apex and their attachments to ventricular walls. One of remarkable views of LV and mitral valve is seen from 3D echo frontal long axis view, here orientation of apex is toward bottom in a more anatomic presentation, with aorta and cardiac base oriented to top of figure. Length of LV is seen from base to apex while viewing back of heart and papillary muscles relationship to the mitral valve. Anterior mitral valve leaflet seen on enface as it moves forward and back toward and away from viewer when imaged in real time. Functional mitral valve anatomy: Functional anatomic segments: Functional classification of carpentier recognises three major regions of posterior mitral valve leaflet; begin at anterolateral commissure and extends extends clockwise to posterior medial commissure: P1 , P2 , P3 . Comprehensive evaluation of MR and Calculation of jet severity: Mitral regurgitatant jet have four basic components by colour flow Doppler. I. As flow converges in LV in systole just proximal to regurgitant orifice it forms into a 3D volume of flow converge. Here flow begins to accelerate in velocity. This is known as PISA for the derivation of EROA. Flow is organised as it moves into PISA. Proximal isovelocity surface area (PISA) method is based on law of conservation of flow. The law states the flow rate at two consecutive points is identical. The method uses the advantages of aliasing in colour Doppler imaging where flow is given red or blue if direction of flow is toward and away from the transducer. As the flow approaches its narrowest orifice (stenotic or regurgitant) its velocity increases, in a shape of an isovelocity hemispheric shell as blood flow converges from all directions toward the orifice. The flow rate at which surface of hemispheric shell is equal to the flow rate at the regurgitant orifice (law of conservation of flow). As the flow converges toward the orifice, it accelerates and aliasing occurs if the velocity exceeds the Nyquist limit. Flow rate can be calculated by multiplying the area by velocity (flow rate = area x velocity). The area incase of valve is circular so it is calculated as (Ω r2), but in case of hemisphere surface area is calculated as (2 Ω r2 or 6.28 r2 ), the r is the radius of the hemisphere which can be measured from the surface to the narrowest area of colour flow, which is closely related to regurgitant or stenotic orifice. The flow rate at hemisphere (PISA) surface is: flow rate = AV = 2 Ω r2 Valiasing = 6.28 r2 Valiasing and according to law of conservation of flow, flow rate at the regurgitant orifice is equal to flow rate at the surface of PISA. In mitral regurgitation, apical 4 c view (PLAX view if eccentric jet) with colour doppler with Nyquist limit shifted downward in direction of flow of MR jet, the velocity of PISA is measured at mid to late systole (the same time the maximum MR velocity occurs). Area (ERO) x Vmax MR = 6.28 r2 Valiasing Effective regurgitant orifice (ERO) = 6.28 r2 Valiasing / Vmax MR Flow rate is the product of area and TVI, this can be applied to calculate regurgitant volume. Here area is ERO and TVI is TVI of MR jet. Therefore: Mitral RV = ERO (PISA) x TVIMR (CW/Doppler) = (6.28 r2 Valiasing / Vmax MR) x TVIMR II. It then narrows into the fastest velocity (vena contracta) of a regurgitant jet where the flow accelerates (area of flow acceleration) through actual regurgitant orifice itself (the jet orifice). Diameter of this flow acceleration can be measured. Flow is also organised here into vena contracta. Width of vena contracta is a quantitative method to assess MR defined as the narrowest cross sectional area of jet, can be easily seen while obtaining zone of flow convergence, above the mitral valve on the LA side. Compared to continuity equation, vena contracta width of >5mm correlates well severe MR. III. Then, as the flow jet emerges from the regurgitant orifice into the LA the jet splays out into a large area of turbulence. This third area of turbulence is the first thing a viewer recognises when viewing a regurgitant jet in the LA. Flow into LA is quite disorganised and turbulent as it emerges from the regurgitant orifice, i. e. in severe MR, high energy transfer of a large volume of blood into LA producing jet in LA and can be seen by Colour flow doppler semiquatitative method which remains the easiest and best method to screen for MR. ratio of MR jet area to the total LA >40% is severe MR. It is the least reliable index and Jet area in LA depends on size and pressure of LA, residual blood in LA, eccentric jet, instrument settings, attenuation of ultrasound (reduce size), coanda effect/ wallhugger jet (regurgitant jet is directed from valve orifice directly adjacent atrial wall where it curls around LA) may overestimate jet size. IV. The fourth and last effect is the downstream effect of suppression or reversal of systolic flow into LA in systole through a pulmonary vein. When such suppression or reversal is noted, regurgitant jet is likely severe. PW doppler of left and right upper pulmonary vein is performed from the apical 4 c view. CW doppler of MR jet: If flow signal can be aligned parallel to the beam, in severe MR, the spectral doppler of jet appears uniformly dense throughout its duration and have a well-defined envelop. MR jet velocity does not correlate with severity. Calculation of mitral regurgitant volume: Continuity equation is based on the principle of conservation of mass. The principle states that, under conditions of cardiovascular stability without any regurgitations or shunts, the net blood volume at any part of circulation must equal the net blood volume at any other part next to it (what comes in must go out). This situation is true under certain assumptions: i. the two points are directly connected; ii. Blood is neither added nor removed from the system. Mitral valve stroke volume is equal to aortic valve stroke volume provided there is no mitral or aortic regurgitations. Calculation of volumetric flow rate is based on a simple hydraulic principle which states that the flow rate (Q) through a tube of a constant diameter is directly proportional to cross sectional area (CSA) of the tube and mean velocity of fluid moving through the tube (V) when orifice CSA is fixed and when the velocity is constant. However, in the heart velocity is not constant as blood flow is pulsatile and velocities are constantly changing with systole and diastole as well as throughout the flow period. Therefore, by instituting the velocity time integral (VTI) for the mean velocity, volumetric flow rather than volumetric flow rate is calculated in the heart assuming CSA has a circular geometry, flow is laminar and has a flat profile. Stroke volume is the volue of blood ejected during one cardiac cycle and can be calculated from SV= CSA x VTI, where SV= stroke volume (ml), VTI = distance of column of blood travels with each stroke (cm), CSA= cross sectional area (cm2). Aortic valve stroke volume is calculated by measuring aortic annulus diameter in PLAX view at maximum valve opening in systole. The TVI is obtained utilizing PW Doppler sample volume at the level of aortic annulus on the apical long axis or 5 c view. The AVA is assumed to be circular and hence, the area is calculated from obtained aortic annulus diameter (DAA) : AVA = Ω (DAA /2)2 = 0.785 DAA2 The stroke volume at the level of aortic valve is then calculated as: SVAA = AVA x TVIAA SVAA = 0.785 x DAA2 x TVIAA In calculating mitral valve stroke volume, mitral valve area is calculated either by assuming a circular or ellipsoid geometry. For practical purposes, the circular shape is the most often used. Mitral annulus diameter is obtained from apical 4c view at maximum valve opening in diastole. The TVI is obtained from same view by PW Doppler sample volume at the level of mitral annulus. MVA = 0.785 x DMA2 And therefore, SVMA = MVA x TVIMA SVMA = 0.785 x DMA2 x TVIMA Mathematically, continuity equation means that stroke volume through mitral valve is equal to stroke volume through aortic valve: TVI x Area 1 (mitral) = TVI 2 x Area 2 (aortic) 0.785 x DAA2 x TVIAA = 0.785 x DMA2 x TVIMA In MR, aortic stroke volume is less than forward mitral stroke volume because part of blood contained in LV at the end of diastole is ejected back to LA through regurgitant mitral valve: Aortic stroke volume = mitral stroke volume – mitral regurgitant volume (RV) Therefore, Mitral RV = mitral stroke volume – aortic stroke volume = (0.785 x DMA2 x TVIMA) - (0.785 x DAA2 x TVIAA) Mitral timing relationships: As the pressure rises in LV during mechanical systole, it exceeds that of LA and MV closes. This initiates a period of rising LV pressure with no movement of blood that preceeds the opening of aortic valve. This interval is known as period of isovolumic contraction. As the pressure in LV exceeds that in aorta the AV opens, mechanical systole ensues, and blood is ejected until LV pressure drops below aorta, when LV pressure drops below aorta, AV shuts, isovolumic relaxation period ensues as the ventricular pressure falls until MV opening. Relationship of spectral Doppler: Both aortic stenosis (AS) and mitral regurgitation (MR) are systolic events and both aortic regurgitation and mitral stenosis are diastolic events and these various regurgitations and due to proximity of aortic to mitral valve, these various regurgitations and stenosis may be confused for one another. The duration of MR is longer than AS because time for MV closing to MV opening is longer than from AV opening to closing. Use of Colour flow Doppler controls: MR during systole can be seen by colour flow Doppler in the LA in systole, e.g. mosaic in LA. Improper use of colour control can result in marked increased in jet size. Use of colour gain: Excessive colour gain is characterised by sparkling appearance of a variety of pixels. Hallmark of correct gain is detection of some low velocity flow in left ventricular outflow tract as well as lower velocity flows seen surrounding turbulence. The low velocity flows surrounding the turbulent jet reflect movement of red cells already present in LA that are engaged by regurgitation, known as entrainment. Altered Nyquist or scale factor: With lowering of Nyquist progressively lower velocities will be displayed with increased rightness, artifactually increasing jet size. Most international standard for display colour flow images of MR from apical 4 c view recommended scale factor in the 60cm/s range. Effect of frame rate and persistence: One should absolutely avoid widening of colour flow sector arc, thus slowing frame rate and obscuring flow dynamics. Neither 2D nor colour persistence should be used in echo as heart moves much too rapidly. Never to use persistence in any time when examining heart. Excess Image gain: Excess image gain encroaches on pixels occupied by colour and colour is eliminated, increase low amplitude image noise, displaced low velocity flow. Excess image gain as well as colour gain should be avoided in the conduct of any colour flow examination. System setting variability in jet size: Both excessive colour gain and low Nyquist should always be avoided. Jet Duration: Sample size of a jet in a still frame follow image can never be accurately relied upon as an absolute indicator of jet severity by itself. Size and jet duration must be taken together. MR is classically described as a holosystolic jet by physical examination. When MV shuts in early systole, and before aortic valve opens, LV is contracting prior to ventricular ejection (isometric /isovolumic contraction). Some blood is trapped in the closing mitral orifice, and when leaflets shut there usually is some movement of blood posteriorly into the LA that accompanies the closing velocity of the leaflets. This phenomenon is known as backflow / closing velocity / mitral flash which can be mistaken as MR by a frame detected in early systole with red blue pattern of systolic flow within LV. Hints from Spectral Doppler: The method for determining the severity of MR using spectral Doppler relies on subtle comparison of diastolic flow to the regurgitant systolic flow. Brightness of any Doppler signal reflects the number of red blood cells moving through a Doppler sample if spectral Doppler gain settings are properly set. Functional Classification of Mitral regurgitation: Typical Type II, P2 Leaflet Prolapse: 2D PLAX and apical views shows both leaflets and may demonstrate leaflet movement like billow back into LA in systole. Movement of both leaflet better appreciated by 3D views (TTE or TOE if poor image quality with TTE) with demonstration of features like bulging leaflet, chordal thickening, fibrotic, flail and gaping orifice of P2 segment, broken chordal tendinae. Colour flow during systole may show direction of jet is opposite the leaflet that prolapse. Most MR that comes to surgical repair is anteriorly directed, indicating that most type II MR is due to posterior leaflet prolapse. Typical Type II, A2 Leaflet Prolapse: Anatomic features of prolapse in any mitral valve segment can be visualised by 2 or 3 D echo. When there is a prolapse of anterior leaflet of an A2 segment, direction of MR jet is markedly posterior. Colour flow Doppler will demonstrate MR opposite the leaflet segment prolapse and directed posteriorly. Occasionally, callus like patches may be seen on the atrial walls at the impact site of MR jets and are known as McCallum’s patches. 3 D echo is helpful for surgical view of mitral valve and its apparatus in all spatial views. Ischaemic heart disease / coronary artery disease and Mitral regurgitation: Colour Doppler to assess presence and severity of MR, may be due to i. rupture of a part or entire papillary muscle commonly with inferoposterior infarction likely one vessel disease, ii. Ischaemic MR from papillary muscle dysfunction with small changes in spatial relation of papillary muscles and mitral valve leaflets and annulus due to RWMA and LV shape changes may produce incomplete mitral leaflet closure, resulting eccentric MR, common in inferoposterior MI as posterior papillary muscle has one vessel supply, iii. Multiple MIs or anterior aneurysm with low EF, central jet secondary to generalised ventricular and annular dilatation. Mitral regurgitation and congestive heart failure: Type 1 MR that results from dilatation of the mitral valve annulus. PSAX at mitral valve level with colour flow Doppler, in systole closed position from commissure to commissure, mitral valve coaptation are examined, and PlAX, apical views, dilated LA and LV can be appreciated in dilated cardiomyopathy. Three D echo LV frontal long axis view, anterior mitral leaflet is seen enface and compares orientation of papillary muscles in each of these patients. In dilated cardiomyopathy with severe MR papillary muscle can be seen laterally displaced and are pointed more medially. Mitral valve coaptation is not only a leaflet phenomenon, but is dependent upon the orientation of supporting structures such as papillary muscles and their relationship to the entire mitral valve apparatus. Pulmonary artery systolic pressure and tricuspid regurgitation: In severe decompensated MR, the tricuspid regurgitation peak velocity is increased as the result of pulmonary hypertension (RVSP also increased). TR velocity is derived from CW doppler mapping of TR jet, from apical 4c view or if eccentric jet, parasternal right ventricular inflow view. The velocity (m/sec) reflect the RV to RA pressure difference, ∆P, and when pulmonary stenosis is absent, RVSP is assumed to equal PASP, and is calculated through Bernoulli equation: PASP = RVSP = 4 (tricuspid regurgitant velocity: VTR)2 + right atrial pressure (RAP) In severe free flow TR, Bernoulli equation is not valid and TR velocity will underestimate the tricuspid pressure gradient.
Posted on: Mon, 18 Aug 2014 21:37:07 +0000
Trending Topics
Recently Viewed Topics
© 2015