Transthoracic Echocardiogram

LEARNING OUTCOMES

• Comprehensively assess the mitral valve apparatus and the left ventricle to distinguish degenerative versus functional mitral regurgitation as they are different disease processes with different prognoses and different treatments.

• Evaluate the severity of mitral regurgitation using an integrated approach as no single parameter is accurate. It is essential to evaluate color-flow Doppler (flow convergence, vena contracta, color jet area), pulsed-wave Doppler (mitral inflow, pulmonary venous flow), and continuous-wave Doppler (mitral regurgitation envelope).

• Determine the compensatory mechanisms of the heart to a volume overloaded state. Assess left ventricular size and function, left atrial size, right ventricular size and function, and right ventricular systolic pressure. It is unlikely to have severe, chronic mitral regurgitation with normal-sized chambers.

• Resolve all hemodynamic issues (volume status, blood pressure, tachycardia, atrial fibrillation) before a final determination of mitral regurgitation severity is made.

• Consider additional testing such as transesophageal echocardiography, cardiac magnetic resonance imaging, and exercise echocardiography if there is discordance between 2D and Doppler findings, discordance between clinical assessment and MR severity, or suboptimal image quality.

.

Kollaborate link: https://www.kollaborate.tv/link?id=61ae2a9c70360

INTRODUCTION

Transthoracic echocardiography (TTE) is the best screening modality to assess the structure and function of the mitral valve and its hemodynamic effects on the left ventricle (LV), left atrium (LA), and the right heart. Accurate assessment of the severity and mechanism of the mitral valve pathology determines patient prognosis and the timing and type of intervention. It is important to identify whether the mitral regurgitation (MR) is due to an abnormal mitral valve (primary, degenerative), pathology of the ventricle, atria, or annulus (secondary, functional), or a combination of both (mixed etiology). Primary MR must be distinguished from secondary MR as surgical and transcatheter options may differ depending on the etiology. It is essential to use Doppler to assess multiple parameters for MR severity including regurgitant color-flow jet, vena contracta width (VCW), proximal isovelocity surface area (PISA), MR jet profile, mitral inflow, pulmonary vein flow, and flow quantitation. Additional testing may be required if the severity or mechanism of MR cannot be established despite a good quality, complete TTE. Transesophageal echocardiogram (TEE) should be performed if the mechanism of MR is unclear, but it should not be relied upon to assess MR severity due to the favorable hemodynamic changes that occur with the administration of sedation. If the severity is unclear, consider cardiac magnetic resonance imaging or stress testing.

STANDARD MITRAL VALVE EVALUATION

Meticulous interrogation of the mitral valve apparatus is essential to assess the mechanism and etiology of the pathology and to individualize the timing and treatment of the mitral valve disease. It is important to visualize leaflets, annulus, chordae, and papillary muscles to assess their contribution to the pathology. Abnormal leaflet pathology includes thickening, calcification, prolapse, flail, vegetation, and masses. Significant calcification of the mitral leaflets makes surgical and transcatheter valve repair difficult. Abnormal subvalvular morphology includes calcification, ruptured chordae, chordal fusion, vegetations, and masses. Mitral annulus must be evaluated for dilatation and calcification. If the mitral apparatus is normal, primary MR is unlikely.

The mitral valve should be evaluated in at least five views: parasternal long axis (PSLA), parasternal short-axis mitral valve level (PSSA), apical 4-chamber (A4C), apical 2-chamber (A2C), and apical long axis (ALA) for morphology ( Fig. 5.1 ) and regurgitation severity. Two-dimensional (2D) imaging is used to assess valvular structure while Doppler (color-flow, pulsed-wave, and continuous-wave) is used to assess the severity of MR ( Fig. 5.2 ). Three-dimensional (3D) applications have increased the accuracy of localization of valve pathology predominantly using TEE since the current lower spatial and temporal resolution has limited its evaluation during TTE. ^, There are several methods that should be used to assess the severity of the MR, and the final interpretation should integrate all the methods, as no single method should be completely relied upon. It is important to be aware of the strengths and limitations of each method ( Table 5.1 ). MR is very dynamic and responsive to loading conditions such as volume status, blood pressure, heart rate, medications, and pacemakers which all should be optimized before making the final decision about the severity of the mitral valve disease. ^,

Carpentier classification of the etiology of MR based on leaflet motion should be used to describe the precise anatomical pathology and mechanism. Carpentier type I represents MR with normal leaflet motion and includes perforation or cleft (primary MR) and MR due to dilated annulus (secondary MR). Carpentier type II includes excessive leaflet motion such as prolapse or flail (primary MR). Type IIIa describes rheumatic disease with leaflet restriction in both systole and diastole (primary MR). Type IIIb is seen in dilated cardiomyopathy with restricted motion only in systole (secondary MR) ( Fig. 5.3 ).

MITRAL REGURGITATION

Mechanism of Mitral Regurgitation

Primary Mitral Regurgitation (Degenerative)

MR is considered primary when there is abnormal structure of the mitral valve apparatus ( Table 5.2 ). In primary, degenerative MR, the specific pathology and location must be identified. It is important to methodically image the leaflets, chordae, and papillary muscle for thickening, prolapse, flail, tethering, and calcifications ( Fig. 5.4 ). Specific scallops can be identified on TTE, but only if on-axis views are obtained. The anterior and posterior leaflets are divided into three anatomic segments from medial to lateral (A3, A2, A1 and P3, P2, P1). The two leaflets meet at the medial and lateral commissures. Parasternal long-axis view shows the middle scallops of both leaflets (A2 and P2) (see Fig. 5.1 ). The parasternal short-axis view demonstrates medial scallops on the left (A3, P3) and lateral scallops on the right (A1, P1). The A4C usually demonstrates P1 and A2/A3, but angulation will change which scallops are visualized. Anterior angulation demonstrates A1/P1 while inferior angulation will show A3/P3. The A2C view shows posteromedial and anterolateral commissures and demonstrates P3, A2, P1 from left to right. More accurate localization of pathology requires a TEE. As treatment options increase, there will be specific treatment tailored to specific pathology. For example, if there is a torn chord, the treatment may be an insertion of synthetic chords, either surgically or transcatheter approach.

TABLE 5.2

Primary Versus Secondary Mitral Regurgitation ^a

		Secondary MR b
Primary MR b		Regional LV Dysfunction	Global LV Dysfunction
Etiology	Myxomatous or calcific leaflet degeneration	Inferior myocardial infarction	Nonischemic cardiomyopathy, large anterior or multiple myocardial infarctions
LV remodeling	Global, if severe chronic MR	Primarily inferior wall	Global dilation with increased sphericity
LA remodeling	Moderate to severe if chronic MR	Variable	Usually severe
Annulus	Dilated, preserved dynamic function	Mild to no dilation, less dynamic	Dilated, flattened, nondynamic
Leaflet morphology: Thickening Prolapse or flail Calcification	Yes/moderate, severe Usually present Variable	No/mild No No/mild	No/mild No No/mild
Tethering pattern	None	Asymmetric	Symmetric
Systolic tenting	None	Increased	Markedly increased
Papillary muscle distance	Normal	Increased posterior papillary-­ intervalvular fibrosa distance	Increased interpapillary muscle distance
MR jet direction	Eccentric or central	Posterior	Usually central
CWD	May be late systolic (if MVP) or uniform if flail or with calcific degeneration	Density usually uniform throughout systole	Biphasic pattern, with increased density in early- and late-systolic flow and mid-systolic dropout
PISA	Often hemispheric	Often not hemispheric	Often not hemispheric; may be biphasic

a In addition to evaluating the morphology of the mitral leaflets for thickening, prolapse, flail, and calcifications, the left ventricle must be assessed for size, ejection fraction, and regional wall motion abnormalities to aid in differentiating primary versus secondary MR.

b Primary and secondary MR may coexist. (From Zoghbi WA, et al. Recommendations for noninvasive evaluation of native valvular regurgitation: a report from the American Society of Echocardiography developed in collaboration with the society for cardiovascular magnetic resonance. J Am Soc Echocardiogr . 2017;30:303–371.) CWD, Continuous-wave Doppler; LA , left atrium; LV , left ventricle; MR , mitral regurgitation; MVP, mitral valve prolapse; PISA, proximal isovelocity surface area.

When primary MR is accompanied by a normal-sized LV and LA, it is unlikely to be severe, unless an acute leaflet flail is present. Primary MR is unlikely if the mitral valve is normal.

Mitral valve prolapse (Carpentier type II)

Myxomatous degeneration is a spectrum of pathology that is the most common cause of primary MR in developed countries. It can range from fibroelastic deficiency with thin leaflets with one prolapsed/flailed segment to Barlow’s disease with billowy leaflets and multiple prolapsing segments. Mitral valve prolapse (MVP) is present when the body of the leaflet is displaced 2 mm beyond the mitral annular diameter into the LA as seen in the parasternal long-axis view (see Fig. 5.4B ). MVP should not be assessed in the apical views due to the saddle shape of the annulus which will result in a false appearance of the leaflets being displaced beyond the annular plane.

Barlow’s disease

Barlow’s disease results from an excess of myxomatous tissue leading to thick, bulky, redundant leaflets with elongated chordae resulting in bileaflet, multi segmental prolapse (see Fig. 5.4C ). The MR associated with Barlow’s disease is frequently late-systolic MR seen as a “flash” (not holosystolic) on color flow and a non holosystolic jet on continuous-wave Doppler interrogation of the MR jet ( Fig. 5.18C ). Transcatheter therapy of MR due to Barlow’s disease may differ from MVP as edge-to-edge repair may not be beneficial in these patients with multi segmental prolapse.

Flail leaflet (Carpentier type II)

Flail leaflets are part of the MVP spectrum and occur when the edge of the leaflet, not just the body, moves into the LA during systole. Rupture of the primary chords is usually present. Flail leaflet is usually associated with an eccentric jet of severe MR. The direction of the jet aids in determining the leaflet pathology. Although the regurgitant jet area (RJA) may not occupy 50% of the LA, the marked eccentricity of the jet is specific for severe regurgitation (see Figs. 5.4A , 5.5 , 5.7 , 5.10 , Videos 5.1 , 5.2 , 5.3 , 5.4 , 5.5 , 5.6 and 5.13 , 5.14 , 5.15 , 5.16 , 5.17 , 5.18 ).

Perforation, cleft (Carpentier type I)

There may be normal leaflet motion in patients with a congenital cleft or perforation due to healed endocarditis, but there is regurgitation through the defect in the leaflets. Identification of clefts usually requires a TEE. Currently, this is not amenable to percutaneous mitral valve repair.

Rheumatic (Carpentier type IIIa)

Rheumatic mitral leaflets demonstrate diffuse leaflet thickening and commissural fusion associated with some degree of mitral stenosis (MS). Both systolic and diastolic leaflet restriction is present due to fused commissures and retracted chordae. Classic hockey-stick morphology of anterior leaflet with restricted posterior leaflet is usually present (see Fig. 5.4D ) . Due to the presence of MS with thickened, calcified leaflets, percutaneous repair is currently not recommended in MR due to rheumatic disease.

Arrhythmic mitral valve prolapse

Although MVP is common and usually benign, with outcome predominantly determined by the severity of the MR, there is a rare form that is associated with sudden cardiac death. Our understanding of this malignant subset of MVP is incomplete, but it is associated with frequent ventricular arrhythmias, mitral annular disjunction (MAD), leaflet redundancy, and T-wave inversions and is independent of MR severity. MAD is an abnormal atrial displacement of the mitral valve leaflet hinge point in which the annulus becomes detached from the ventricular myocardium ( Fig. 5.6 ). Cardiac magnetic resonance to assess for presence and extent of myocardial fibrosis is necessary for risk stratification.

Acute mitral regurgitation Careful assessment of the LV, LA, right ventricle, and right ventricular (RV) systolic pressure is essential in determining the severity of the MR and its chronicity. Acute MR is less common than chronic MR and patients usually present in hemodynamic distress. Acute MR is usually due to ruptured chordae tendinae, ruptured papillary muscle, or leaflet destruction due to endocarditis. If the LV and LA are normal sizes, significant chronic MR is unlikely, but acute MR may be present ( Fig. 5.7 ). ^, Doppler assessments of color RJA, effective regurgitant orifice area (EROA), regurgitant volume (RVol), regurgitant fraction (RF), and mitral inflow will be inaccurate due to low driving pressure from high left atrial pressure and hypotension. Imaging of a flail leaflet with a normal-sized LV, hyperdynamic systolic function associated with decreased stroke volume (SV), and systolic reversal in pulmonary veins should confirm the diagnosis of acute, severe MR even if a large MR jet is not seen by color-flow imaging. Careful measurements of the LA and LV volumes performed according to the American Society of Echocardiography (ASE) Guidelines by 2D method of disks (modified Simpson’s method) or 3D is crucial for differentiating acute versus chronic MR ( Fig. 5.8 ). ^, All measurements should be indexed to body surface area. Chronic MR is almost always associated with dilated left-sided chambers (see Video 5.1 , 5.2 , 5.3 , 5.4 , 5.5 , 5.6 ).

Secondary Mitral Regurgitation (Functional)

Secondary (functional) MR is a distinct disease process due to ventricular pathology in which the valve leaflets and chordae are structurally normal, although minimal abnormalities such as nonspecific leaflet thickening and mild calcification may be present. Secondary MR is much more complicated because the left ventricular dilatation and systolic dysfunction are frequently the cause rather than the result of the MR. In some patients, it may be an indicator of a diseased ventricle, whereas in others, it may contribute to further progression of LV dysfunction. Functional MR is associated with a worse prognosis than degenerative MR.

Functional MR is usually a consequence of LV remodeling with ventricular dilatation, annular dilatation, papillary muscle displacement, leaflet tethering, and malcoaptation of leaflets due to chordal stretching (see Table 5.2 ). In the presence of a dilated cardiomyopathy, it may be difficult to determine whether the MR is the cause of the dilated cardiomyopathy or a result of the dilated cardiomyopathy and simply a marker of poor prognosis. As the LV dilates, the papillary muscles become displaced and restrict leaflet mobility, resulting in more MR. “MR begets MR” as the saying goes. Proportionate MR refers to the “appropriate” amount of MR you would expect after considering the LV end-diastolic volume, ejection fraction, and RF. Disproportionate MR, when the MR severity is more severe than would be predicted by the size of the LV alone, may differentiate those patients who will benefit from an intervention from those whose ventricles will not recover. Functional MR may occur with normal leaflet motion (Carpentier type I) due to a dilated annulus, but it may also be seen with restricted leaflets (Carpentier type IIIb) due to adverse LV remodeling from ischemic or nonischemic cardiomyopathy. Symmetric bileaflet tethering due to LV remodeling occurring in nonischemic cardiomyopathies usually results in a central jet. Asymmetric posterior leaflet tethering due to inferior wall remodeling in an ischemic cardiomyopathy frequently results in a posteriorly directed jet ( Fig. 5.9 ). A significant posterior jet may also be seen with an isolated inferior/inferolateral infarction due to a restricted posterior leaflet despite relative preservation of LV size and function. If the posterior leaflet is restricted with the anterior leaflet overriding it, this is still considered secondary MR. Several methods have been proposed to assess the amount of leaflet restriction including tenting area, a measurement of the area between the leaflet tips and the annulus, and coaptation depth, the maximal distance from the leaflet tip to the annular plane. ^, Secondary MR is significantly affected by preload, afterload, and heart rate/rhythm. Atrial fibrillation may worsen secondary MR due to increased atrial stretch and annular dilatation. Functional MR is extremely sensitive to loading conditions and the MR severity should be re-evaluated after guideline-directed medical therapy has been instituted and cardiac resynchronization therapy has been considered. Anesthetic agents tend to optimize LV filling and decrease MR which necessitates that secondary MR severity be assessed by TTE rather than TEE (see Videos 5.7 , 5.8 , 5.9 , 5.10 , 5.11 , 5.12 and 5.19 , 5.20 , 5.21 , 5.22 , 5.23 ).

Mixed Etiology

Mixed MR due to both primary and secondary causes is also possible. A sudden onset of shortness of breath in a patient with a dilated, ischemic cardiomyopathy may signal a ruptured chordae with a flail leaflet ( Fig. 5.10 ). Also, long-standing untreated severe MR due to prolapse may result in dilated cardiomyopathy (see Videos 5.13 , 5.14 , 5.15 , 5.16 , 5.17 , 5.18 ).