Mitral Insufficiency

6 Mitral Insufficiency image



Goals of Echocardiography in Mitral Insufficiency




image To establish that mitral insufficiency is present


image To establish the severity of mitral insufficiency


image To determine the hemodynamic consequences of mitral regurgitation (MR), pulmonary venous flow, cardiac index (CI), and right ventricular systolic pressure


image To establish the underlying cause(s), when possible


• “Organic” causes: myxomatous causes (prolapse, flail), rheumatic, infective, papillary rupture

• “Functional” causes: ischemic, cardiomyopathy

image To determine the reparability of the valve lesion


image To verify adequacy of repair (intraoperative transesophageal echocardiography [TEE])


image To identify complications of MR (e.g., pulmonary hypertension, left ventricle [LV] dysfunction)


image To identify concurrent cardiac disturbances (e.g., other valve lesions, coronary artery disease)



Scanning Issues



Required Parameters to Obtain from Scanning




image Valve apparatus details to explain the cause of the MR


• Leaflets, chords, annulus

• Papillary muscle bodies and heads

• LV geometry and size, wall motion abnormality

image MR severity—quantified if more than moderate MR (i.e., not if mild)


• RVolume, RFraction

• Effective regurgitant orifice (ERO)

• Pulmonary venous systolic flow pattern

image LV size and systolic function


image Stroke volume (SV; net forward, not total) and CI


image Indirect volume/pressure overload descriptors


• Left atrium (LA) size, right ventricular systolic pressure

• Right ventricle (RV) size, systolic function, tricuspid regurgitation etiology if present and suitability of repair

image The height and weight for body surface area normalization


image Blood pressure, if ≥2+ MR



Valid Methods to Determine Severity of Mitral Regurgitation




image Proximal isovelocity surface area (PISA):ERO, RVolume


image Volumetric: RVolume, RFraction


image Pulmonary venous flow reversal



Scanning Notes




image If sinus rhythm: measure three spectral profiles


image If atrial fibrillation: measure five spectral profiles


image Spectral profiles should be two-thirds the height of the display and wide enough to show two to three per display.



Use Zoom Views Liberally




image For PISA depiction


image For mitral leaflet detail


image For papillary muscle detail


image For mitral annular diameter



Volumetric




image The volumetric method (using the left ventricular outflow tract [LVOT] as a standard) is unsuitable if there is ≥mild aortic insufficiency (AI).



For Proximal Isovelocity Surface Area




image Shift the color baseline down for MR (if transthoracic echocardiography [TTE]).


image Measure at mid-systole to correspond to peak MR velocity. PISA is measured at mid-systole by convention, although this may be less accurate when the regurgitant orifice is dynamic and mid-systole does not characterize its mean size.


image Record the aliasing velocity.


image VAliasing to 35-45-52 cm/sec to optimize depiction of PISA hemisphere


image The PISA method is unsuitable if there is frankly poor depiction of PISA.



Methods




image



where



image




image




image



where RF = regurgitant fraction and TVI = time velocity interval.


Total anterograde SV is determined from diastolic transmitral anterograde flow using Simpson’s method of the LV (in the absence of AI).



Grading of Mitral Regurgitation1


The most important distinction is to differentiate severe from moderate MR.



Reporting Issues




image Describe the cause of the MR.


image Describe the severity of the MR.


image If ≥2+, describe the hemodynamic effect of the MR:


• Pulmonary venous flow pattern

• Quantification of ERO, if >2+ MR

image Describe the LV


• Systolic function (overall and regional)

• End-systolic dimension

image Use of color Doppler flow mapping


• Establishes presence/absence of MR

• Does not alone establish the presence of severe MR

Severe


image Large ERO, RVolume, RFraction


image Severe hemodynamic effect (pulmonary venous flow reversal)


Severe MR


image ERO > 0.4 cm2


image PISA ≥ 1 cm at VAlias –40 cm/sec


image RVolume > 60 mL


image RF > 60%


image Pulmonary venous systolic flow reversal (for TTE)


• 60% sensitive

• 92% specific

image Describe the LV in detail: size, end-systolic diameter, end-systolic volume, ejection fraction, wall motion abnormality.


• Compare to previous studies

image Describe the RV in some anatomic detail, beyond the right ventricular systolic pressure


image Do not make assumptions about peak mitral velocity as it is quite variable.


image Pay attention to the aortic root if severe mitral valve prolapse (MVP), because Marfan syndrome may underlie both.


image Avoid the use of the term “trivial” in general and whenever the mitral valve is abnormal.


• “Trivial” MR is within normal finding and therefore does not need to be recorded.


Role of Transesophageal Echocardiography in Mitral Regurgitation




image To define pathologies responsible for MR that are not evident on some TTE examinations—such as infective endocarditis, flail chordae


image To determine severity when TTE and clinical or angiographic assessment are discordant


image To determine suitability of MV to surgical repair, if TTE is unclear



When the Grade of Mitral Regurgitation is Different on Serial Echocardiographic Studies




image If the change is >1 grade, it probably is a true change.


image None/mild/moderate/severe is the most logical grading system. The greater the number of grades, the greater the intraobserver, interobserver, and interstudy reclassification rates. Therefore, using fewer categories yields more consistent grading.


image When serial studies suggest difference in grade, a careful review of the basis of grading of each study should be entertained. If the studies have different components (e.g., one without pulmonary venous flow) then true comparison is not possible.


image When apparent changes have occurred, it is important to evaluate the likelihood of improvement. Some pathologies responsible for MR are unlikely to change: for example, a flail leaflet nearly always results in severe MR, and the associated degree of MR is unlikely to be altered by medical therapy. Conversely, peri-infarction MR often is evanescent, and “functional MR” associated with chronic ischemic cardiomyopathy and with dilated cardiomyopathy, may be significantly improved with load alteration on the LV via medical therapy or blood pressure changes.


image TEE is able to record pulmonary venous flow patterns in all cases; TTE under-detects abnormalities of pulmonary venous flow because of less successful interrogation of the pulmonary veins. Since pulmonary venous systolic flow reversal is a criterion to establish severe MR, TEE will more often establish that MR is severe than will TTE.


image TEE is more sensitive than TTE to record MR flow mapping, and, therefore, for any given MR jet, the MR generally looks worse by TEE.



Echocardiography–Catheterization Discordance of the Assessment of Mitral Regurgitation Severity



When Echocardiographic Assessment of Mitral Regurgitation Differs from the Contrast Ventriculographic Assessment of Mitral Regurgitation




image Contrast ventriculography may underrepresent the severity of MR.


• The most common error in angiographic assessment of MR is underestimation of the severity of MR due to poor opacification (usually because of increased LV and LA volumes, and because not enough contrast dye was used).

• Cine-angiographic “panning” must show the left atrium adequately to allow assessment of opacification. Sometimes, it does not.

image Contrast ventriculography may overrepresent the severity of MR:


• Premature ventricular contractions may cause MR.

• Catheter entrapment of chordal or leaflet elements may cause MR.

image Inter- and intraobserver agreement of the “middle” grades of MR are not consistent. Differentiation of 2+ from 3+ MR may influence management, as 3+ MR may be operated upon at some centers.


image Echocardiographers who rely on color Doppler flow mapping, and who subscribe to 1985-derived color Doppler metrics of MR severity, will systematically describe the extent of MR as worse than it really is.


image TEE is more likely to agree with contrast ventriculographic assessment, because it is less likely to misclassify severe MR. TEE remains superior to TTE in sampling pulmonary venous flow.



V-Waves on the Pulmonary Capillary Wedge Pressure Tracing and Mitral Regurgitation Grading


The erroneous notion that large V-waves are sensitive and specific for severe MR is widespread. V-waves are neither sensitive nor specific for severe MR.



image V-waves may be produced by pathologies other than severe MR:


• Ventriculoseptal defect

• Mitral stenosis

• Left ventricular failure

• Stiff LA

image Errors in catheterization technique can confuse the issue as well:


• Excessive tubing length, small catheter bore, and overdamping can obscure large V-waves.

• Underdamping can exaggerate a V-wave.

• Dye dilution techniques are less accurate when the CO is <2.5 L/min, or if severe tricuspid regurgitation is present.2


Surgical Reparability of the Mitral Valve


Formerly, TEE was considered necessary to define mitral anatomy in sufficient detail to determine accurately the chances of successful surgical repair. However, this convention is being challenged.


Among 279 patients, Monin et al.1 predicted valve repair versus replacement:



image By TTE in 97% of cases


image By TEE in 98% of cases


Among patients with degenerative (myxomatous) MR, agreement of localization by echocardiography with surgery was:



image 91% by TTE (κ 0.81)


image 93% by TEE (κ 0.85)


A posterior leaflet angle >45% (see later discussion) predicts failure to annuloplasty repair of ischemic MR (Fig. 6-1).3



Notes on Specific Causes of Mitral Regurgitation


A clear attempt to identify the specific cause of MR should be made in each case. MR is often grouped into “functional” (e.g., in nonmitral chords, leaflets and papillary muscles; the suspension of the chords, leaflets, and papillary muscles is the problem—i.e., the LV is the problem) and “organic” (i.e., diseased chords, leaflets, and papillary muscles). In general, functional MR is less likely to be severe, and often goes hand-in-hand with impaired LV systolic function and geometry and, therefore, is of higher surgical risk. Axiomatically, the chance of having a good LV is greater with organic MR, because in that case the LV is not the cause of the MR.



image Altered LV geometry (regional or global cavitary dilation) causing mitral apparatus distortion often is referred to as “functional MR” (as the mitral apparatus components are not diseased themselves) and is the most common cause of MR in patients with coronary artery disease and dilated cardiomyopathy. Lateral and apical displacement of the papillary muscles exerts radial and longitudinal traction on the mitral leaflet tips, reducing and then resulting in loss of coaptation. The mitral apparatus appears “tented” in systole as the leaflet tips are apically displaced; the leaflets appear as structurally normal. The extent of tenting (which can be described as the area in the triangle formed by the mitral leaflets and a line across the mitral annulus) roughly correlates (r = 0.74; P < 0.0001) with the ERO.4 The same study established that there was a wide range of ERO, and that ERO was not related to EF% (P = 0.32). Papillary muscle tethering length has been shown in at least one study to be an independent cause of severe MR.5


image Severe wall motion abnormality (e.g., infarction, stunning)


• Some MR is present in 20% of infarction cases, and establishes a higher mortality.

• Apical (r = 0.75; P < 0.0001) and lateral (r = 0.70; P < 0.0001) LV geometric alterations (displacement of papillary muscles), especially, are associated with increased ERO size.4

• LV dysfunction without alteration of geometry is unlikely to produce significant MR,6 underscoring that the attachments (papillary muscle position and annulus) of the mitral apparatus are of paramount importance in the development of functional MR.6

image Papillary muscle rupture (PMR)*


• PMR is seen in <1% of MI cases, but accounts for 1% to 5% of deaths. It is an essential diagnosis, because it generally is fatal in a few days if operation is withheld. As long as the patient is operable, there is a high rate of salvage. Almost invariably, PMR is associated with severe (or very severe) MR. Operation is best performed quickly before oliguria develops.

image Ischemia* alone may result in transient MR, although this is not nearly as common as the term “ischemic MR” would indicate. That term leads to confusion, as it implies that ischemia is the cause of the MR, but where the term is generally relevant is in CAD-related MR.


image Myxomatous disease of the mitral valve* includes MVP, MVP with flail, and flail leaflets. Myxomatous degeneration of the mitral valve is the leading cause for mitral valve surgery in North America, and the only common indication for valve repair at most centers.


• Mitral prolapse can be viewed as occurring with a thickened mitral valve due to myxomatous infiltration/degeneration (“classic MVP”) and also with a normal-appearing valve (“nonclassical MVP”). The distinction is important, as nonclassical MVP is very unlikely to evolve into infective endocarditis, worsened MR requiring surgery, or sudden death.7,8

• Flail leaflets almost invariably cause severe MR and constitute an important subgroup of causes of MR both because this is a classically reparable lesion and because there is some concern that the natural history is prone to high, possibly excess, mortality,9 with a mortality of 6.4%/year. At 10 years (unoperated) the rates of heart failure, atrial fibrillation, or surgery/death were 63 ± 8%, 30 ± 12%, and 90 ± 3%, respectively.9 In multivariate analysis, surgery was associated with a significant reduction in mortality (RR = 0.29, P < 0.001).9 There is a sudden death rate of approximately 2% per year with mitral valve flail. Although 40% of the sudden deaths in mitral flail leaflet cases occurred in people who had been class 1 at baseline, most who die have heart failure symptoms first.10 Atrial fibrillation complicating the course of a flail mitral leaflet is independently associated with a RR of death or heart failure of 2.2.11

• Nomenclature of the mitral leaflets (surgical perspective: LAA at 10 o’clock and LVOT at 2 o’clock)

• MVP was formerly vastly over-diagnosed at the bedside and by echocardiography. Using criteria of “classical MVP” (defined as superior displacement of the mitral leaflets of ≥2 mm in systole and mitral leaflet thickness in diastole ≥5 mm), only 2.4% of the offspring of the Framingham cohort had MVP, and the incidence of symptoms of chest pain, dyspnea, and ECG abnormalities was no different from those without prolapse. Patients with MVP were leaner (P < 0.001) and had more MR than those without MVP, but the degree of MR was usually only mild or trace.12 Furthermore, when examined carefully with the current more stringent criteria of MP, there is no association of MVP and stroke in younger individuals.13 When “nonclassical MVP” is present (defined as superior displacement of the mitral leaflets of ≥2 mm in systole but mitral leaflet thickness in diastole <5 mm), the prognosis appears better, because presumably there is less (or no) leaflet disease and less likelihood of progression.14

• The ERO of an MVP valve increases through systole,15 and there is a tendency to overestimate MR severity with a single measurement.15


image Rheumatic MR is caused by rheumatic-incited scarring of the mitral leaflets that has left them so “frozen” that they cannot coapt. The ERO is fixed, and by virtue of the immobility of the leaflets, the S1 is muffled.


image Mitral annular calcification (MAC) is unlikely to produce more than mild or moderate MR, as the leaflets are seldom involved enough to reduce coaptation. MAC, however, is a challenge for surgeons, because seating a prosthesis is more difficult, and prone to paraprosthesis insufficiency.


image Annular dilation, by itself, does not usually cause severe MR.5


image Endocarditis* is a necrotizing infection of valve leaflets, annuli, and chordae that will, in time, lead to leaflet perforation, chordal tearing, or annular disruption. Some cases are not associated with severe insufficiency, but most do have at least moderate insufficiency. Extensive involvement of the valve, as can be depicted by large or multiple vegetations, usually is associated with extensive necrosis and severe insufficiency. Some of what appears to be valve insufficiency is insufficiency through the annulus and is even more ominous.


image Congenital


• Cleft mitral valve is a congenital anomaly of the anterior mitral leaflet that may (rarely) be isolated or, more commonly, occurs in association with other congenital anomalies, for example, endocardial cushion defects. The two-dimensional image is characteristic, showing a discontinuity of the linear appearance of the anterior mitral leaflet—the “cleft.” The anterior mitral leaflet is usually divided by a couple of millimeters into two even-sized components. Accessory chordae may be visualized.

• ASD-related

image Fibrosis of the medial half of the anterior leaflet is common with


• Anorexigens

• Marantic, system lupus erythematosus

• Hypertrophic obstructive cardiomyopathy (HOCM) and HOCM-like

This list should lead to the conclusion that several factors may participate in MR, especially in cases of “functional MR.”



Mitral Regurgitation and Progression


In the presence of “organic” causes, MR is a progressive lesion, but the rate of progression is highly variable. On average, the progression is as follows16:



image RVolume: 7.4 mL/year


image RFraction 2.9%/year


image ERO: 6 mm2/year


New flail leaflets (P = 0.0001) and progressive annular dilation (P = 0.0001) were the best predictors of progression. Regression was possible (in 11% at 2 years apart), and was associated with decreased blood pressure (P = 0.008).16



Notes on the Pathophysiology of Mitral Regurgitation




image Volume (over)load of the LA and LV


image Leads to remodeling (increased compliance and dilation) of the LA and LV.


• Normalizes the filling pressures

• Normalizes the stroke volume. As total stroke volume (forward and regurgitant stroke volume) increases, the forward stroke volume is restored/normalized. For example, if the total stroke volume is now 175 mL, then despite an 80-mL regurgitant volume, there is still a normal stroke volume of 90 mL.

image Sarcomeres replicate in series (wall thickness increases little, but overall LV mass increases—“eccentric hypertrophy”), therefore O2 demand increases. As LV mass is determined by wall thickness and cavitary size, generally, in chronic severe MR (where LV volumes are about twice normal but wall thickness is normal) myocardial mass is about twice normal (158 g/m2 vs 86 g/m2).17


image Coronary (myocardial O2 supply) flow is seldom a problem (in the absence of CAD), as the aortic diastolic pressure is normal (unlike AI).


image Systemic afterload dependence: increasing impedance to ejection increases the regurgitant volume. Factors that reduce afterload (e.g., pregnancy) are well tolerated, but hypertension is not.


• With the above in mind, the expected morphologic adaptation to severe MR is obvious (dilation of the left heart chambers).

image MR may remain compensated for years, or may progress. Progression depends on many factors:


• Progression of the organic pathology—e.g., necrosis by endocarditis, myxomatous degeneration

• Loss of LV systolic function entails rising LV diastolic pressures and cardiac output.

• Loss of atrial systolic function (atrial fibrillation) will also raise the filling pressures.

• Ongoing and severe LV dilation may dilate the annulus, further impairing the leaflet coaptation and increasing the MR volume.

• Development of hypertension


Notes on Mitral Repair and Mitral Replacement




image Several issues render mitral repair conceptually attractive:


• The operative mortality is lower for mitral repair than it is for replacement.

• Successful repair, in the absence of atrial fibrillation, does not need anticoagulation, whereas mechanical MVR does.

• LVEF% is better preserved with repair than (non–chordal-sparing) MVR.

image Pathologies that are amenable to repair include some complications of myxomatous disease:


• Flail is highly amenable to repair, with good results.

• P2 prolapse is highly amenable to repair, with good results.

• Anterior prolapse amenable to repair

• Localized perforations from infective endocarditis are often amenable to repair.

image Pathologies that are not well suited to repair include the following:


• Extensive (bileaflet) myxomatous degeneration

• Prolapsing segments at the commissures

image Chordal sparing is now the norm, with mitral replacement surgery, as long as the leaflets and chordae are not rheumatic. Chordal transsection is avoided when possible for the reasons listed in Table 6-318:


image LVEF% falls with chordal severing because of


• Elimination of the low impedance ejection pathway (elimination of the MR)

• Changes in LV volume and wall stress

• Other reasons to be determined


What is the Single Best Technique to Describe Mitral Regurgitation Severity?


The question is so academic that it is irrelevant. As MR is influenced by many variables, no single technique is reliable enough to describe by itself the severity of MR. A composite (of parameters) assessment is needed. The predominance of results determines the estimation of severity.


The clinical impact of MR is heavily influenced by the regurgitant orifice, the compliance of both the LV and the LA, systemic hemodynamics, and the systolic function of the LV and the LA, and the reactivity of the pulmonary vasculature. Therefore, one cannot expect a single parameter from any single test to be sufficiently insightful to describe MR. The more pathophysiologic aspects of the MR that are characterized, the better the understanding of the MR.


The importance of grading is to distinguish the severe cases that may benefit from surgery from the moderate cases that would not. The distinction of mild and moderate is relatively unimportant.


In the ideal (most straightforward) case of severe MR, each of the following would be present:



image Lesions that typically result in severe MR


• Flail

• Papillary muscle rupture

• Infective endocarditis with large vegetations

• Other severe organic disease

image Pulmonary venous flow reversal (often obtainable by TTE, but TEE is sometimes needed to establish that MR is severe)


image Large ERO


image Large regurgitant volume


image Large regurgitant fraction


image LV dilation (if chronic—note that all of the above lesions are acute, and therefore generally without much LV dilation)


image LA dilation (if chronic), and LA systolic bulging, unless there is an equal amount of tricuspid regurgitation


image Pulmonary pressures elevated moderately or more (unless the LA is a huge reservoir)


In the end, no single isolated parameter should be used to establish the severity of MR. Multiple parameters, and a balance of Doppler, 2D, and clinical assessment should be used. Otto19 states that Doppler means alone should not be used.



Caveats Concerning Descriptors of Mitral Regurgitation



Color Doppler Flow Mapping


Color Doppler flow mapping of MR is a “low-tech” means to evaluate MR and is fraught with potential error. Unfortunately, color Doppler flow mapping is also the easiest and fastest technique, validated over a decade ago,20,21 and therefore is often used alone, or over–relied-upon to evaluate MR. Flow mapping with current equipment is prone to overestimating MR severity, especially as the now antiquated criteria are out of date for flow mapping by current equipment, which detects more flow, and therefore displays MR jets as larger than would older equipment. As well, color Doppler flow mapping is machine factor dependent (Va, color Doppler gain), chamber dependent (compliance), and jet dependent (best suited to central jets, and poorly suited to eccentric jets). TTE is notoriously insensitive to insufficiency of an MVR as the jet is shadowed by the prosthesis and its sewing ring.


The optimal use of color Doppler flow mapping is to



image Alert the sonographer to the presence of MR, and roughly estimate its severity. If the MR appears by flow mapping and pulmonary venous flow to be moderate or more than moderate, then quantitative methods should be employed.

Related posts:

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

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Jun 12, 2016 | Posted by in CARDIOLOGY | Comments Off on Mitral Insufficiency

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