Intraoperative assessment of mitral regurgitation

Angela L Pollak; Madhav Swaminathan

doi:10.4103/jiae.jiae_35_19

CONTEMPORARY TOPIC

Year : 2019 | Volume : 3 | Issue : 2 | Page : 66-70

Intraoperative assessment of mitral regurgitation

Angela L Pollak, Madhav Swaminathan
Department of Anesthesiology, Division of Cardiothoracic Anesthesiology and Critical Care Medicine, Duke University Health System, Durham, NC, USA

Date of Web Publication

29-Aug-2019

Correspondence Address:
Madhav Swaminathan
Department of Anesthesiology, Duke University Hospital, Box 3094/5691F HAFS, Erwin Road, Durham, NC 27710
USA

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jiae.jiae_35_19

Abstract

Since its advent, transesophageal echocardiography (TEE) has played an important role in the surgical management of patients undergoing mitral valve (MV) surgery. Mitral regurgitation (MR) assessment and surgical decision making remains one of the most challenging situations, especially when considered in the context of ischemic heart disease or when associated with another dominant lesions. Techniques for MV repair are becoming more and more intricate with outcome studies strongly supporting repair in contrast to replacement in patients with primary MV pathology. It is in these scenarios that a comprehensive intraoperative TEE is invaluable. Once MR is detected, it is vital to assess the valve for both qualitative and quantitative features. The following text discusses the approach, challenges and value of intraoperative TEE in the assessment of MR.

Keywords: Echocardiography, intraoperative, mitral regurgitation

How to cite this article:
Pollak AL, Swaminathan M. Intraoperative assessment of mitral regurgitation. J Indian Acad Echocardiogr Cardiovasc Imaging 2019;3:66-70

How to cite this URL:
Pollak AL, Swaminathan M. Intraoperative assessment of mitral regurgitation. J Indian Acad Echocardiogr Cardiovasc Imaging [serial online] 2019 [cited 2023 May 29];3:66-70. Available from: https://jiaecho.org/text.asp?2019/3/2/66/265752

Introduction

While multimodality imaging has become the preferred path for the diagnosis of valvular heart disease, echocardiography remains the most popular, robust, and frontline imaging modality. Since its introduction to the surgical arena, transesophageal echocardiography (TEE) has played an important role in surgical decision-making and perioperative management of patients undergoing mitral valve (MV) surgery. Surgical management of mitral regurgitation (MR) remains one of the most challenging decisions, especially when considered in the context of ischemic heart disease or when it is concurrent with another dominant lesion. Techniques for MV repair are becoming more and more intricate as we improve our understanding of valve function before and after the intervention. Outcome studies strongly support repair in contrast to replacement in patients with primary MV pathology ^[1],[2] and for the role of intraoperative TEE in MV repair. The following text discusses the approach, challenges, and value of intraoperative TEE in the assessment of MR.

Approach to Mitral Regurgitation Assessment

In the surgical setting, there are a few important questions to answer when assessing MR.

Is there MR? Ensuring that this is the right lesions being assessed and not due to related phenomena
How bad is it? Qualitative and quantitative assessment is key here
Why? Assessment of mechanism is critical to subsequent management.

Hemodynamics

The first question relates to the challenges of a cardiac surgical patient. Intraoperative assessment of any valve lesion is challenging given the frequent hemodynamic fluctuations typical of an acute care setting. This is in contrast to a stable ambulatory patient who presents to a clinic for the diagnosis of cardiogenic symptoms. Since valve lesions, particularly MR, are impacted by loading conditions, their assessment must account for and possibly correct for any hemodynamic irregularity prevailing at the time of assessment.^[3] The use of all echocardiographic modalities available with TEE, especially color flow Doppler (CFD), in all imaging planes for the MV will inform an echocardiographer about the presence of MR and its relationship to loading conditions. Supportive signs such as enlargement of the left atrium (LA), morphology of the MV, and integrity of the supportive subvalvular apparatus will also answer that first question about the presence of MR.

Assessment of Mitral Regurgitation Severity

The next question pertains to the qualitative and quantitative assessment of MR – the critical “How much MR is there?” question. The following text is a brief overview of the approach and appraisal of various intraoperative techniques for the assessment of MR.

There are several indicators of significant MR with simple two-dimensional (2D) imaging. Abnormal valvular morphology on 2D imaging indicates a more significant burden of MR. The hemodynamic consequences of MR lead to structural changes in adjacent cardiac chambers. Chronic MR leads to volume overloading of the left ventricle (LV), eventually resulting in LV dilatation and deterioration of LV function. Chronic pressure overload of the LA leads to increased LA pressure with subsequent enlargement of the LA, eventually leading to atrial fibrillation. The enhanced risk of clot formation in these patients should always prompt the search for thrombus within the LA appendage with TEE early during surgery since the surgical plan could be influenced by the finding of an LA appendage clot. Changes in right-sided chambers may also be seen and signal the presence of pulmonary hypertension from chronic MR. These changes, if observed in the preprocedure TEE examination, special care must be taken to prevent right heart failure after weaning from cardiopulmonary bypass.

While jet area with CFD is commonly used to grade MR, this method is not very accurate due to a number of factors that may influence jet area for a specific MR grade. The jet is, after all, a 3D phenomenon, and the maximum area of the jet may fall outside of the plane of view and therefore underestimate the degree of severity. Eccentric jets lose momentum more rapidly and may appear smaller than central jets resulting in underestimation of MR severity.^[4] Large jets extending into the LA from small regurgitant orifices can often be seen in high afterload conditions common in the intraoperative setting. High LA pressure due to unrelated reasons may also reduce the jet area for a given degree of MR. Jet area, therefore, is not a preferred technique for MR assessment.^[5]

Vena contracta (VC) measurement, on the other hand, is generally considered to have the best predictive value in primary MR where the regurgitant orifice is circular. First, altered loading conditions have a limited effect in primary MR. Second, VC measurement remains valid in eccentric jets. However, it is less useful when the regurgitant orifice is oval in shape or when there are multiple jets.^[5]

With TEE, 3D echocardiography offers an exceptional view of the MV. It is also possible to acquire volumetric datasets with color Doppler using gated acquisition. The challenge in the surgical setting is the use of electrocautery that can interfere in gated imaging. The VC area can be measured using multiplane reconstruction with direct planimetry [Figure 1].^[6] Regurgitant volume (RV) derived from 3D VC area measurement shows a good correlation with cardiac magnetic resonance imaging-derived measurement of MR volume.^[7],[8]

Figure 1: Multiplanar reconstruction of a three-dimensional dataset with color flow Doppler demonstrating measurement of vena contracta area in the lower left panel

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The value of pulsed-wave Doppler (PWD) is limited in the assessment of MR. While the early (E) transmitral diastolic flow velocity is almost always elevated in significant MR, its absence excludes severe MR.^[9]

One measurement in which PWD may be more useful is in the ratio of MV velocity time integral (VTI) to aortic valve VTI. In significant MR, the MV VTI is greater than the AV VTI when there is no aortic valve regurgitation. A ratio of >1.4 indicates severe MR and a ratio <1.0 indicates mild MR.

Interrogation of the pulmonary veins using PWD can yield useful information. While normal pulmonary venous flow has a dominant systolic component, this wave gets progressively blunted with increasing severity of MR with reversal of systolic flow in severe MR [Figure 2]. Its absence, though, does not preclude severe MR, since eccentric jets may be directed toward one pulmonary vein and not the other.^[9]

Figure 2: Pulsed-wave Doppler spectral tracing of pulmonary vein flow demonstrating systolic flow reversal (arrow) in severe mitral regurgitation

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Continuous-wave Doppler (CWD) is useful for both qualitative and quantitative assessments of MR. A dense CWD trace indicates a more significant severity of MR. Quantitative assessment of MR can be performed using a combination of measurements. The proximal isovelocity surface area (PISA) method can be used to calculate the effective regurgitant orifice area (EROA) from which the RV and regurgitant fraction (RF) may be calculated by adding other quantitative information. The PISA method uses flow convergence, in which as flow accelerates, it gets closer to the regurgitant orifice until it reaches a maximum velocity at or just downstream to the anatomical orifice, thereby creating hemispheric shells of increasing velocity on the upstream side of the regurgitant orifice. The continuity principle is used to determine the EROA from this PISA method. Other measurements required include the PISA radius (r) of the MR jet [Figure 3], the aliasing velocity of the PISA shell (V_{max − ALV}), and the CWD peak MR velocity (V_maxMR). Once the EROA is known, the RV can be calculated once the MR VTI has been measured using the same CWD trace [Figure 4].

Figure 3: Zoomed in view of the mitral valve in the mid-esophageal four-chamber view with color flow Doppler showing the phenomenon of proximal flow convergence with the radius of the isovelocity shell measured (see text for details). Not the color baseline has shifted in the direction of flow

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Figure 4: Continuous-wave spectral Doppler waveform of a mitral regurgitation jet with measurement of the velocity time integral of the jet

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EROA = [2 πr ² × V_{max − ALV}]/V_maxMR

RV = EROA × VTI

However, PISA has several pitfalls:

Shape – The EROA does not always have a circular shape. Secondary MR generally has an oval-shaped orifice making the PISA surface hemiellipsoid rather than hemispherical. This underestimates the EROA. Automated 3D methods can more accurately measure the PISA to overcome this issue ^[10]
Timing – The largest PISA radius does not necessarily occur at the time of the highest pressure difference between LV and LA, especially since the EROA is dynamic throughout systole. This is specifically true in cases of secondary MR when PISA radius may be the largest at the initiation and conclusion of systole. The timing of measurement may, therefore, change the severity assessed. Therefore, the frame rate of acquisition becomes vital so that the correct frame can be reliably captured. Color M-mode can also help indicate the correct timing to measure the PISA radius.^[5] The American Society of Echocardiography guidelines recommend that PISA radius and MR velocity should be measured simultaneously in the regurgitant phase ^[4]
LV containment – In cases of severe MR, the PISA radius may be very large and containment by the LV wall may alter the shape of the flow convergence zone, thereby overestimating the PISA radius and subsequently MR severity.^[11]

Grading Mitral Regurgitation Intraoperatively

Data should be integrated from multiple sources to counterbalance the limitations of some methods and compensate for measurement errors.^[4] In the operating room, hemodynamics must be considered, along with the duration of MR. Supportive signs such as LV and LA enlargement offer invaluable clues to the chronicity or acuity of the MR jet and therefore its etiology.

Mechanism of Mitral Regurgitation

The final relevant question in the intraoperative assessment of MR pertains to its mechanism. Surgical decision-making relies on the precise determination of etiology of the MR, especially when it presents either as an unexpected lesion or when the decision to address it has not yet been made in the operating room. This is a critical step since the mechanism of MR will usually decide the surgical technique to be deployed. While the factors that determine repair versus replacement are beyond the scope of this brief review, the echocardiographer is charged with reporting all the findings that will contribute to the surgical management decision, and mechanism is perhaps the most important.

Carpentier's classification of MR,^[12] which remains valid today when planning surgery of the MV, describes the pathology in terms of the motion of the leaflet. One fundamental feature of an MR jet can help triage the etiology – direction and origin of the MR jet with CFD are often helpful when describing the underlying mechanism. A modification of Carpentier's classification with a more detailed description of MR etiology to aid surgical decision-making is described in [Table 1].^[11]

Table 1: Modified Carpentier's functional classification of mitral regurgitation

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Type I

The MV has normal leaflet motion, and MR is the result of annular dilatation or leaflet perforation. Annular dilatation is characterized by a central MR jet, while leaflet perforation will show a variable direction of the jet originating from a leaflet defect and not the coaptation line.

Type II

There is an increased leaflet motion, thereby resulting in a jet directed away from the affected leaflet. The etiology usually is localized prolapse or a ruptured chord (flail) which results in excursion of the affected leaflet beyond the annulus level. When multiple scallops are affected, such as in Barlow's valve, symmetrical prolapse may result in a central jet [Figure 5]a, [Figure 5]b, [Figure 5]c.

Figure 5: Images from a patient with Barlow's mitral valve disease showing a mid-esophageal four-chamber view (a). The same view with color flow Doppler showing the regurgitant jet (b). The corresponding three-dimensional dataset showing the same mitral valve in an en face view in systole (c)

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Type III

Restricted leaflet motion is typical of this type of lesion. There is further subclassification into Type III A, B, and C lesions.

Type IIIA is characterized by restricted leaflet motion during systole and diastole and is typically seen in rheumatic MVs. The eccentric MR jet will usually be seen in the direction of the restricted leaflet but may be central when both leaflets are equally affected.

Systolic restriction seen in dilated cardiomyopathy results in a central MR jet that is typical of Type IIIB. Leaflets are tethered from displacement of the papillary muscles resulting in coaptation more apically.

Type IIIC lesions are characterized, in contrast, by unequal or asymmetric systolic restriction due to localized left ventricular ischemic insult, resulting in tethering of a leaflet with relative prolapse of the opposing unrestricted leaflet. The jet is usually directed toward the affected leaflet.

Type IV

The typical pathology for this type is dynamic obstruction of the LV outflow tract resulting in systolic anterior motion (SAM) of the anterior mitral leaflet causing MR. The jet is most prominent later in systole when SAM is at its worst. This type of MR is most often seen with hypertrophic cardiomyopathy [Figure 6]a and [Figure 6]b but may also be seen following MV repair or when a hypertrophic LV is also hypovolemic and hyperdynamic.

Figure 6: Mid-esophageal four-chamber view in a patient with hypertrophic cardiomyopathy with systolic anterior motion of the mitral valve (a). The same view with color flow Doppler demonstrating mitral regurgitation (b)

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Type V

When multiple etiologies are present, such as rheumatic heart disease with leaflet perforation, or dilated cardiomyopathy leading to a tethered leaflet that later has a ruptured chord resulting in a flail leaflet, the lesion is classified as a Type V MR.

The severity of MR can also be classified based on symptoms or sound and texture analysis, but the most popular and useful remains the Carpentier's classification based on mechanism and pathology.

Summary

MR frequently presents itself for assessment in patients undergoing a variety of cardiac surgeries. While it is generally imaged comprehensively prior to a planned repair or replacement, MR can present unexpectedly in patients undergoing unrelated surgery, most commonly coronary artery bypass grafting and/or aortic valve replacement. It is in these cases that a comprehensive intraoperative TEE is invaluable. Once detected, it is vital to assess the valve for both qualitative features and quantity of the RV. The qualitative assessment will aid in the decision of whether to repair, replace, or defer, whereas the quantitative assessment will be important to firmly conclude the need for surgical treatment. Intraoperative assessment of MR remains challenging for several reasons. Fluctuating hemodynamics can significantly influence the degree of MR, emphasizing the importance of a thorough and accurate assessment using multiple approaches.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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