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A Game of Twister: What 3D TEE Rendering Tells Us About the Mitral Annulus During OPCAB
Journal of Cardiothoracic and Vascular Anesthesia ] (]]]]) ]]]–]]]
Contents lists available at ScienceDirect
journal homepage: www.jcvaonline.com
Editorial
A Game of Twister: What 3D TEE Rendering Tells Us About the Mitral Annulus During OPCAB Since the introduction of 3D transesophageal echocardiography (3D TEE) technology into clinical practice over 2 decades ago, this modality has developed into a powerful tool for the assessment of the mitral valve apparatus. Its significant contributions have enhanced our understanding of valve morphology, topography, geometry, spatial relationships, and annular dynamics. In addition to the ability to view the mitral valve en face from both atrial and ventricular sides in real time, sophisticated offline programs have enabled quantification of a number of important parameters. In 1989, Levine et al confirmed the annulus’ saddle shape using laborious 3D reconstruction from videotape images when they postulated that superior leaflet displacement in a 4-chamber view is below the highest annular points.1 Today, we understand that this saddle-shaped annulus undergoes geometric changes throughout the cardiac cycle, becoming more planar or flat at end-diastole, and losing its non-planarity in pathologic conditions, as demonstrated by annular flattening in both ischemic and degenerative chronic regurgitant states.2 These geometric alterations are highly dependent on the type of pathology and its source (eg, annular differences have been noted between anterior and inferior myocardial infarction in ischemic MR from heterogeneity of LV remodeling and infarct size).3 One aspect of 3D mitral annular morphology that has received less attention is what happens geometrically during multivessel off-pump coronary artery bypass (OPCAB). In this issue of the Journal of Cardiothoracic and Vascular Anesthesia, Toyama et al used real-time 3D echocardiography (RT3DE) and the Mitral Valve Quantification (MVQ) Program (Q-lab software v.7.2, Philips, Andover, MA) to assess mitral annular changes associated with cardiac dislocation during left circumflex (LCx) and right coronary artery (RCA) grafting.4 In this single-center experience, the authors were able to demonstrate a significant reduction in annular height during grafting of these vessels relative to the nondisplaced anatomical position, with the greatest height change occurring with worsening of baseline mitral regurgitation (MR) or development of new MR. Conversely, anteroposterior and intercommissural diameters, http://dx.doi.org/10.1053/j.jvca.2017.09.037 1053-0770/& 2017 Elsevier Inc. All rights reserved.
annular perimeter, and surface area were not significantly affected by positioning maneuvers. Furthermore, mitral annular height did not differ significantly between LCx and RCA grafting positions despite the greater hemodynamic effects of circumflex grafting. This new 3D information adds one more layer to our understanding of the etiology of hemodynamic derangements associated with OPCAB and the effects of verticalization and rotation of the heart on mitral annular geometry. We know from experience that hemodynamic derangements during OPCAB are multifactorial and most pronounced with posterior vessel grafting. The etiology of such derangements includes coronary ischemia, mechanical compression of the heart with impaired filling/decreased preload, and atrioventricular valve distortion with resultant regurgitation.5,6 The development of suction epicardial retractor/stabilization devices and apical suction retractors, along with the use of deep pericardial sutures to facilitate cardiac rotation, opening the right pleura, Trendelenberg positioning, and table rotation help to lessen the mechanical insult and support hemodynamics. Exposure of the LCx and obtuse marginal branches with the need to both elevate the apex and medially rotate the heart results in the greatest degree of compromise relative to the other territories. One can easily surmise that the early use of fork tine compression stabilizers induced even greater distortion than the current generation, though the former were employed at a time when intraoperative TEE was not routinely used during OPCAB. We also know that heart displacement during OPCAB can cause MR. In a study of 60 consecutive elective OPCAB patients without MR and monitored with two-dimensional (2D) TEE, Ozay et al showed that grafting of the LCx resulted in the development of moderate MR in 38 of 45 patients (84.4%), with the greatest hemodynamic compromise occurring with grafting of this vessel (only 8/20 patients developed moderate MR with RCA grafting).7 No changes in mitral valve function were seen during left anterior descending (LAD) and diagonal grafting. These findings are in contrast to the present study where the incidence of MR was similar for both LCx and RCA territories.4 These differences could be due to a
2
Editorial / Journal of Cardiothoracic and Vascular Anesthesia ] (]]]]) ]]]–]]]
number of factors, including differences in surgical technique, patient characteristics, and order of grafting. When comparing OPCAB studies, it is difficult to control for numerous variables including volume status, use of vasoactive agents, Trendelenberg positioning, use of intracoronary shunts, collateral circulation, and presence of ischemia. In the study by Ozay et al, TEE showed an increase in wall motion score index only with grafting of the LCx (with return to baseline after operation), suggesting reversible regional dysfunction and leading the authors to conclude that mitral regurgitation was more likely due to positioning rather than ischemia.7 Despite these conclusions, hemodynamic instability during LCx and RCA grafting mandates ruling out ischemia, as not all MR is necessarily due to physical distortion of the valve.6 It has been shown that preoperative LV dysfunction might be a predictor of severe MR as a result of further increased left ventricular end-diastolic pressure (LVEDP) and mitral annular distortion during OPCAB. In the study by Akazawa et al, MR was the most severe during grafting of the LCx territory (p o 0.001).8 In their analysis, Tei index, serum B natriuretic peptide (BNP), and propagation velocity were significant predictors of moderate or severe MR when compared to patients who developed only mild or no MR. Distortion of the mitral annulus has been postulated in several studies where 2D TEE was the imaging modality, with the greatest distortion occurring with positioning to expose the back of the heart.5,6 This is mainly due to folding at the atrioventricular groove, leading to worsening MR or functional MS from obstructed left ventricular (LV) filling, and increased left atrial (LA) pressures. Al-Ruzzeh et al noted the greatest effect to occur in marginally abnormal valves that sustain greater distortion.9 These annular plane changes from folding at the atrioventricular groove can lead to significant regurgitation and altered hemodynamics as described by George et al.10 Further rotation to gain access to the lateral wall was shown to cause bending, folding, and twisting of the mitral annulus as demonstrated with 3D reconstruction from 2D TEE images taken at end-diastole.10 These changes were associated with left atrial and pulmonary vein enlargement and correlated with elevated left atrial pressures. Moderate MR was seen with circumflex grafting, reverting to mild with repositioning. Annular folding and twisting also were noted with RCA grafting. Using cardiac endoscopy and 3D ultrasound sonomicrometry in a simulated animal model of OPCAB where LVEDP was controlled, Koga et al were able to observe the mitral annulus and leaflets under varying conditions of cardiac displacement: displacement alone, with 15-minute occlusion of the LAD, and with 15-minute occlusion of the LCx.11 They found that displacement alone with maintained coronary perfusion caused no MR; occlusion of the LAD with displacement rarely caused MR from the anterolateral site; and occlusion of the LCx normally caused MR from the posteromedial site, with enlargement of the posteromedial annulus despite controlling LVEDP with a LV vent. RT3DE, which uses matrix 3D technology, offers a number of advantages over 2D imaging, including better spatial resolution and improved visualization of mitral valve morphology.
This holds particularly true in the case of degenerative mitral valve disease.12 With 2D echocardiography, assessment of the mitral valve annulus is limited to 2 perpendicular diameters with limited spatial orientation, making it difficult to determine the precise site for accurate measurement. While RT3DE provides a more realistic view of the mitral valve, multiplanar reconstruction of 2 orthogonal 2D sections is necessary, without the ability to take direct measurements on the 3D model itself. The MVQ Program solves this problem, thereby creating a 3D topographic model of the mitral valve and allowing for quantitative assessment of the valve apparatus. A valve model is generated when the operator obtains a series of 2D sections from the acquired 3D data set, defines the annulus and commissures, and then traces the leaflets. This program was able to characterize mitral annulus characteristics in different types of regurgitant lesions (ischemic, isolated prolapse, and Barlow’s) when compared to normal control valves.13 When compared to a normal control group, patients with ischemic MR had increased annular diameter, perimeter, and area of minimal surface spanning the annulus, while annular height did not differ significantly. The mitral annulus height index (the ratio between MV annulus and perimeter) was significantly lower versus controls.13 Mitral regurgitation in ischemic heart disease is due to annular flattening, which in turn is dependent on the degree of MR and LV dysfunction.3 In the present study, only annular height was altered, suggesting an actual mechanical distortion as opposed to any functional or structural issue, though this finding alone cannot be used to rule out ischemia.4 Jensen et al have demonstrated that regardless of the etiology, annular flattening leads to out-of-plane tension on the annulus, valve leaflets, and chordae.14 Through complex interactions, these stresses can create a vicious cycle of altered mechanics and coaptation geometry that can result in progressively worse MR.15 It is believed that the systolic annular saddle shape affords better withstanding of stresses created by left ventricular pressures, with leaflet stress being inversely proportional to the annular height-to-commissural width ratio (AHCWR), an offline-derived measure of annular nonplanarity with a higher ratio implying a more saddle-shaped annulus.16 Ryan et al have demonstrated that leaflet stress is at a minimum between AHCWR values of 15% to 30%, increasing exponentially as this ratio approaches zero and the annulus becomes more planar (ie, less saddle-shaped).17 Of note, the nonplanarity angle (between the planes of the anterior and posterior MV annular horns at the level of the commissure) obtained from 3D TEE data sets18 has been shown to correlate well with the more time-consuming mathematically derived AHCWR with an observed increase in angle correlating with a less saddle-shaped MV annulus.19 In the current study, the measurement of the annular height with MVQ software was used as a surrogate for the assessment of the MV annular nonplanarity despite its limited use. Clearly, one of the limiting factors of topographic MV apparatus evaluation with the MVQ program is the modeling of the dynamic saddleshaped annulus in only one end-systolic frame; however, parametric volumetric and 3D multiplanar reconstruction can
Editorial / Journal of Cardiothoracic and Vascular Anesthesia ] (]]]]) ]]]–]]]
point out specific tethering sites along the coaptation line that contribute to abnormal leaflet coaptation, thus guiding the choice of intervention.20 This enables detection of differences in tethering between different valve regions (from anterolateral to posteromedial), correlating with the decrease in specific coronary blood flow distribution. Indeed, as noted experimentally, occlusion of the LAD rarely caused MR on the anterolateral side, while occlusion of the LCx caused MR on the posteromedial side despite maintaining normal LVEDP (thus avoiding myocardial ischemia), suggesting incremental morphologic deformation of the MV annulus.11 Despite not knowing the actual status of coronary perfusion during the procedure, the present study adds to the fact that positioning and procedural technique during OPCAB diminishes the physiologic nonplanar conformation of the MV annulus and increases MR severity. Unlike the United States, where there has been a decline in the overall use of OPCAB (17% in 2012 v 23% in 2002), the proportion of OPCAB among total CABG cases in Japan has exceeded 60% based on reports from the Japanese Associate for Coronary Artery Surgery (65% in 2013).21 The widespread use of OPCAB in Japan makes the findings of this study particularly relevant to regions where this is the predominant technique for coronary revascularization. It seems intuitive that the cardiac acrobatics imposed by lifting, compression, and rotation during OPCAB would affect cardiac structures such as the atrioventricular valves, leading to valvular insufficiency, or what might be aptly referred to as distortional MR. Quantitative 3D imaging and analysis have given us a means to characterize not only pathologic annular geometry, but also the effects of physical deformation on annular dynamics, as has been nicely illustrated in the highlighted study. Michelle Capdeville, MD Andrej Alfirevic, MD, FASE Department of Cardiothoracic Anesthesia Cleveland Clinic Cleveland, OH
References 1 Levine RA, Handschumacher MD, Sanfilippo AJ, et al. Three-dimensional echocardiographic reconstruction of the mitral valve, with implications for the diagnosis of mitral valve prolapse. Circulation 1989;80:589–98. 2 Mahmood F, Matyal R. A quantitative approach to the intraoperative assessment of the mitral valve for repair. Anesth Analg 2015;121:34–58. 3 Watanabe N, Ogasawara Y, Yamaura Y, et al. Mitral annulus flattens in ischemic mitral regurgitation: Geometric differences between inferior and anterior myocardial infarction: A real-time 3-dimensional echocardiographic study. Circulation 2005;112(9 Suppl):I458–62.
3
4 Toyama Y, Kanda H, Igarashi K, et al. Morphologic evaluation of the mitral annulus during displacement of the heart in off-pump coronary artery bypass surgery. J Cardiothorac Vasc Anesth (this issue). 5 Couture P, Denault A, Limoges S, et al. Mechanisms of hemodynamic changes during off-pump coronary artery bypass surgery. Can J Anaesth 2002;49:835–49. 6 Chassot PG, van der Linden P, Zaugg M, et al. Off-pump coronary artery bypass surgery: Physiology and anesthetic management. Br J Anaesth 2004;92:400–13. 7 Ozay B, Sargun M, Abay G, et al. The severity of positional mitral regurgitation during off-pump coronary artery bypass grafting. Heart Surg Forum 2008;11:E145–51. 8 Akazawa T, Iizuka H, Aizawa M, et al. The degree of newly emerging mitral regurgitation during off-pump coronary artery bypass is predicted by preoperative left ventricular function. J Anesth 2008;22: 13–20. 9 Al-Ruzzeh S, Athanasiou T, George S, et al. Methodological approach in adopting off-pump coronary artery bypass surgery in a British cardiothoracic unit: Harefield experience. Perfusion 2004;19:S61–6. 10 George SJ, Al-Ruzzeh S, Amrani M. Mitral annulus distortion during beating heart surgery: A potential cause for hemodynamic disturbance—A three-dimensional echocardiography reconstruction study. Ann Thorac Surg 2002;73:1424–30. 11 Koga S, Okazaki Y, Kataoka H, et al. Configurations of the mitral valve during off-pump coronary artery bypass grafting: Endoscopic and threedimensional analysis. J Heart Valve Dis 2007;16:602–7. 12 Agricola E, Oppizzi M, Pisani M, et al. Accuracy of real-time 3D echocardiography in the evaluation of functional anatomy of mitral regurgitation. Int J Cardiol 2008;127:342–9. 13 Kovalova S, Necas J. RT-3D TEE. Characteristics of mitral annulus using mitral valve quantification (MVQ) program. Echocardiography 2011;28: 461–7. 14 Jensen MO, Hagege AA, Otsuji Y, et al. The unsaddled annulus. Mechanical culprit in mitral valve prolapse? Circulation 2013;127: 766–8. 15 Lee AP, Hsiung MC, Salgo IS, et al. Quantitative analysis of mitral valve morphology in mitral valve prolapse with real-time-3-dimensional echocardiography. Importance of annular saddle shape in the pathogenesis of mitral regurgitation. Circulation 2013;127:832–41. 16 Salgo IS, Gorman 3rd JH, Gorman RC, et al. Effect of annular shape on leaflet curvature in reducing mitral leaflet stress. Circulation 2002;106: 711–7. 17 Ryan LP, Jackson BM, Enomoto Y, et al. Description of regional mitral annular nonplanarity in healthy human subjects: A novel methodology. J Thorac Cardiovasc Surg 2007;134:644–8. 18 Warraich HJ, Chaudary M, Maslow A, et al. Mitral annular nonplanarity: Correlation between height/commissural width ratio and the nonplanarity angle. J Cardiothorac Vasc Anesth 2012;26:186–90. 19 Ahmad R, Gillinov AM, McCarthy PM, et al. Annular geometry and motion in human ischemic mitral regurgitation: Novel assessment with three-dimensional echocardiography and computer reconstruction. Ann Thorac Surg 2004;78:2063–8. 20 Lang RM, Tsang W, Weinert L, et al. Valvular heart disease. The value of 3-dimensional echocardiography. J Am Coll Cardiol 2011;58:1933–44. 21 Kuroda K, Kato TS, Kuwaki K, et al. Early postoperative outcome of offpump coronary artery bypass grafting: A report from the highest-volume center in Japan. Ann Thorac Cardiovasc Surg 2016;22:98–107.
Contents lists available at ScienceDirect
journal homepage: www.jcvaonline.com
Editorial
A Game of Twister: What 3D TEE Rendering Tells Us About the Mitral Annulus During OPCAB Since the introduction of 3D transesophageal echocardiography (3D TEE) technology into clinical practice over 2 decades ago, this modality has developed into a powerful tool for the assessment of the mitral valve apparatus. Its significant contributions have enhanced our understanding of valve morphology, topography, geometry, spatial relationships, and annular dynamics. In addition to the ability to view the mitral valve en face from both atrial and ventricular sides in real time, sophisticated offline programs have enabled quantification of a number of important parameters. In 1989, Levine et al confirmed the annulus’ saddle shape using laborious 3D reconstruction from videotape images when they postulated that superior leaflet displacement in a 4-chamber view is below the highest annular points.1 Today, we understand that this saddle-shaped annulus undergoes geometric changes throughout the cardiac cycle, becoming more planar or flat at end-diastole, and losing its non-planarity in pathologic conditions, as demonstrated by annular flattening in both ischemic and degenerative chronic regurgitant states.2 These geometric alterations are highly dependent on the type of pathology and its source (eg, annular differences have been noted between anterior and inferior myocardial infarction in ischemic MR from heterogeneity of LV remodeling and infarct size).3 One aspect of 3D mitral annular morphology that has received less attention is what happens geometrically during multivessel off-pump coronary artery bypass (OPCAB). In this issue of the Journal of Cardiothoracic and Vascular Anesthesia, Toyama et al used real-time 3D echocardiography (RT3DE) and the Mitral Valve Quantification (MVQ) Program (Q-lab software v.7.2, Philips, Andover, MA) to assess mitral annular changes associated with cardiac dislocation during left circumflex (LCx) and right coronary artery (RCA) grafting.4 In this single-center experience, the authors were able to demonstrate a significant reduction in annular height during grafting of these vessels relative to the nondisplaced anatomical position, with the greatest height change occurring with worsening of baseline mitral regurgitation (MR) or development of new MR. Conversely, anteroposterior and intercommissural diameters, http://dx.doi.org/10.1053/j.jvca.2017.09.037 1053-0770/& 2017 Elsevier Inc. All rights reserved.
annular perimeter, and surface area were not significantly affected by positioning maneuvers. Furthermore, mitral annular height did not differ significantly between LCx and RCA grafting positions despite the greater hemodynamic effects of circumflex grafting. This new 3D information adds one more layer to our understanding of the etiology of hemodynamic derangements associated with OPCAB and the effects of verticalization and rotation of the heart on mitral annular geometry. We know from experience that hemodynamic derangements during OPCAB are multifactorial and most pronounced with posterior vessel grafting. The etiology of such derangements includes coronary ischemia, mechanical compression of the heart with impaired filling/decreased preload, and atrioventricular valve distortion with resultant regurgitation.5,6 The development of suction epicardial retractor/stabilization devices and apical suction retractors, along with the use of deep pericardial sutures to facilitate cardiac rotation, opening the right pleura, Trendelenberg positioning, and table rotation help to lessen the mechanical insult and support hemodynamics. Exposure of the LCx and obtuse marginal branches with the need to both elevate the apex and medially rotate the heart results in the greatest degree of compromise relative to the other territories. One can easily surmise that the early use of fork tine compression stabilizers induced even greater distortion than the current generation, though the former were employed at a time when intraoperative TEE was not routinely used during OPCAB. We also know that heart displacement during OPCAB can cause MR. In a study of 60 consecutive elective OPCAB patients without MR and monitored with two-dimensional (2D) TEE, Ozay et al showed that grafting of the LCx resulted in the development of moderate MR in 38 of 45 patients (84.4%), with the greatest hemodynamic compromise occurring with grafting of this vessel (only 8/20 patients developed moderate MR with RCA grafting).7 No changes in mitral valve function were seen during left anterior descending (LAD) and diagonal grafting. These findings are in contrast to the present study where the incidence of MR was similar for both LCx and RCA territories.4 These differences could be due to a
2
Editorial / Journal of Cardiothoracic and Vascular Anesthesia ] (]]]]) ]]]–]]]
number of factors, including differences in surgical technique, patient characteristics, and order of grafting. When comparing OPCAB studies, it is difficult to control for numerous variables including volume status, use of vasoactive agents, Trendelenberg positioning, use of intracoronary shunts, collateral circulation, and presence of ischemia. In the study by Ozay et al, TEE showed an increase in wall motion score index only with grafting of the LCx (with return to baseline after operation), suggesting reversible regional dysfunction and leading the authors to conclude that mitral regurgitation was more likely due to positioning rather than ischemia.7 Despite these conclusions, hemodynamic instability during LCx and RCA grafting mandates ruling out ischemia, as not all MR is necessarily due to physical distortion of the valve.6 It has been shown that preoperative LV dysfunction might be a predictor of severe MR as a result of further increased left ventricular end-diastolic pressure (LVEDP) and mitral annular distortion during OPCAB. In the study by Akazawa et al, MR was the most severe during grafting of the LCx territory (p o 0.001).8 In their analysis, Tei index, serum B natriuretic peptide (BNP), and propagation velocity were significant predictors of moderate or severe MR when compared to patients who developed only mild or no MR. Distortion of the mitral annulus has been postulated in several studies where 2D TEE was the imaging modality, with the greatest distortion occurring with positioning to expose the back of the heart.5,6 This is mainly due to folding at the atrioventricular groove, leading to worsening MR or functional MS from obstructed left ventricular (LV) filling, and increased left atrial (LA) pressures. Al-Ruzzeh et al noted the greatest effect to occur in marginally abnormal valves that sustain greater distortion.9 These annular plane changes from folding at the atrioventricular groove can lead to significant regurgitation and altered hemodynamics as described by George et al.10 Further rotation to gain access to the lateral wall was shown to cause bending, folding, and twisting of the mitral annulus as demonstrated with 3D reconstruction from 2D TEE images taken at end-diastole.10 These changes were associated with left atrial and pulmonary vein enlargement and correlated with elevated left atrial pressures. Moderate MR was seen with circumflex grafting, reverting to mild with repositioning. Annular folding and twisting also were noted with RCA grafting. Using cardiac endoscopy and 3D ultrasound sonomicrometry in a simulated animal model of OPCAB where LVEDP was controlled, Koga et al were able to observe the mitral annulus and leaflets under varying conditions of cardiac displacement: displacement alone, with 15-minute occlusion of the LAD, and with 15-minute occlusion of the LCx.11 They found that displacement alone with maintained coronary perfusion caused no MR; occlusion of the LAD with displacement rarely caused MR from the anterolateral site; and occlusion of the LCx normally caused MR from the posteromedial site, with enlargement of the posteromedial annulus despite controlling LVEDP with a LV vent. RT3DE, which uses matrix 3D technology, offers a number of advantages over 2D imaging, including better spatial resolution and improved visualization of mitral valve morphology.
This holds particularly true in the case of degenerative mitral valve disease.12 With 2D echocardiography, assessment of the mitral valve annulus is limited to 2 perpendicular diameters with limited spatial orientation, making it difficult to determine the precise site for accurate measurement. While RT3DE provides a more realistic view of the mitral valve, multiplanar reconstruction of 2 orthogonal 2D sections is necessary, without the ability to take direct measurements on the 3D model itself. The MVQ Program solves this problem, thereby creating a 3D topographic model of the mitral valve and allowing for quantitative assessment of the valve apparatus. A valve model is generated when the operator obtains a series of 2D sections from the acquired 3D data set, defines the annulus and commissures, and then traces the leaflets. This program was able to characterize mitral annulus characteristics in different types of regurgitant lesions (ischemic, isolated prolapse, and Barlow’s) when compared to normal control valves.13 When compared to a normal control group, patients with ischemic MR had increased annular diameter, perimeter, and area of minimal surface spanning the annulus, while annular height did not differ significantly. The mitral annulus height index (the ratio between MV annulus and perimeter) was significantly lower versus controls.13 Mitral regurgitation in ischemic heart disease is due to annular flattening, which in turn is dependent on the degree of MR and LV dysfunction.3 In the present study, only annular height was altered, suggesting an actual mechanical distortion as opposed to any functional or structural issue, though this finding alone cannot be used to rule out ischemia.4 Jensen et al have demonstrated that regardless of the etiology, annular flattening leads to out-of-plane tension on the annulus, valve leaflets, and chordae.14 Through complex interactions, these stresses can create a vicious cycle of altered mechanics and coaptation geometry that can result in progressively worse MR.15 It is believed that the systolic annular saddle shape affords better withstanding of stresses created by left ventricular pressures, with leaflet stress being inversely proportional to the annular height-to-commissural width ratio (AHCWR), an offline-derived measure of annular nonplanarity with a higher ratio implying a more saddle-shaped annulus.16 Ryan et al have demonstrated that leaflet stress is at a minimum between AHCWR values of 15% to 30%, increasing exponentially as this ratio approaches zero and the annulus becomes more planar (ie, less saddle-shaped).17 Of note, the nonplanarity angle (between the planes of the anterior and posterior MV annular horns at the level of the commissure) obtained from 3D TEE data sets18 has been shown to correlate well with the more time-consuming mathematically derived AHCWR with an observed increase in angle correlating with a less saddle-shaped MV annulus.19 In the current study, the measurement of the annular height with MVQ software was used as a surrogate for the assessment of the MV annular nonplanarity despite its limited use. Clearly, one of the limiting factors of topographic MV apparatus evaluation with the MVQ program is the modeling of the dynamic saddleshaped annulus in only one end-systolic frame; however, parametric volumetric and 3D multiplanar reconstruction can
Editorial / Journal of Cardiothoracic and Vascular Anesthesia ] (]]]]) ]]]–]]]
point out specific tethering sites along the coaptation line that contribute to abnormal leaflet coaptation, thus guiding the choice of intervention.20 This enables detection of differences in tethering between different valve regions (from anterolateral to posteromedial), correlating with the decrease in specific coronary blood flow distribution. Indeed, as noted experimentally, occlusion of the LAD rarely caused MR on the anterolateral side, while occlusion of the LCx caused MR on the posteromedial side despite maintaining normal LVEDP (thus avoiding myocardial ischemia), suggesting incremental morphologic deformation of the MV annulus.11 Despite not knowing the actual status of coronary perfusion during the procedure, the present study adds to the fact that positioning and procedural technique during OPCAB diminishes the physiologic nonplanar conformation of the MV annulus and increases MR severity. Unlike the United States, where there has been a decline in the overall use of OPCAB (17% in 2012 v 23% in 2002), the proportion of OPCAB among total CABG cases in Japan has exceeded 60% based on reports from the Japanese Associate for Coronary Artery Surgery (65% in 2013).21 The widespread use of OPCAB in Japan makes the findings of this study particularly relevant to regions where this is the predominant technique for coronary revascularization. It seems intuitive that the cardiac acrobatics imposed by lifting, compression, and rotation during OPCAB would affect cardiac structures such as the atrioventricular valves, leading to valvular insufficiency, or what might be aptly referred to as distortional MR. Quantitative 3D imaging and analysis have given us a means to characterize not only pathologic annular geometry, but also the effects of physical deformation on annular dynamics, as has been nicely illustrated in the highlighted study. Michelle Capdeville, MD Andrej Alfirevic, MD, FASE Department of Cardiothoracic Anesthesia Cleveland Clinic Cleveland, OH
References 1 Levine RA, Handschumacher MD, Sanfilippo AJ, et al. Three-dimensional echocardiographic reconstruction of the mitral valve, with implications for the diagnosis of mitral valve prolapse. Circulation 1989;80:589–98. 2 Mahmood F, Matyal R. A quantitative approach to the intraoperative assessment of the mitral valve for repair. Anesth Analg 2015;121:34–58. 3 Watanabe N, Ogasawara Y, Yamaura Y, et al. Mitral annulus flattens in ischemic mitral regurgitation: Geometric differences between inferior and anterior myocardial infarction: A real-time 3-dimensional echocardiographic study. Circulation 2005;112(9 Suppl):I458–62.
3
4 Toyama Y, Kanda H, Igarashi K, et al. Morphologic evaluation of the mitral annulus during displacement of the heart in off-pump coronary artery bypass surgery. J Cardiothorac Vasc Anesth (this issue). 5 Couture P, Denault A, Limoges S, et al. Mechanisms of hemodynamic changes during off-pump coronary artery bypass surgery. Can J Anaesth 2002;49:835–49. 6 Chassot PG, van der Linden P, Zaugg M, et al. Off-pump coronary artery bypass surgery: Physiology and anesthetic management. Br J Anaesth 2004;92:400–13. 7 Ozay B, Sargun M, Abay G, et al. The severity of positional mitral regurgitation during off-pump coronary artery bypass grafting. Heart Surg Forum 2008;11:E145–51. 8 Akazawa T, Iizuka H, Aizawa M, et al. The degree of newly emerging mitral regurgitation during off-pump coronary artery bypass is predicted by preoperative left ventricular function. J Anesth 2008;22: 13–20. 9 Al-Ruzzeh S, Athanasiou T, George S, et al. Methodological approach in adopting off-pump coronary artery bypass surgery in a British cardiothoracic unit: Harefield experience. Perfusion 2004;19:S61–6. 10 George SJ, Al-Ruzzeh S, Amrani M. Mitral annulus distortion during beating heart surgery: A potential cause for hemodynamic disturbance—A three-dimensional echocardiography reconstruction study. Ann Thorac Surg 2002;73:1424–30. 11 Koga S, Okazaki Y, Kataoka H, et al. Configurations of the mitral valve during off-pump coronary artery bypass grafting: Endoscopic and threedimensional analysis. J Heart Valve Dis 2007;16:602–7. 12 Agricola E, Oppizzi M, Pisani M, et al. Accuracy of real-time 3D echocardiography in the evaluation of functional anatomy of mitral regurgitation. Int J Cardiol 2008;127:342–9. 13 Kovalova S, Necas J. RT-3D TEE. Characteristics of mitral annulus using mitral valve quantification (MVQ) program. Echocardiography 2011;28: 461–7. 14 Jensen MO, Hagege AA, Otsuji Y, et al. The unsaddled annulus. Mechanical culprit in mitral valve prolapse? Circulation 2013;127: 766–8. 15 Lee AP, Hsiung MC, Salgo IS, et al. Quantitative analysis of mitral valve morphology in mitral valve prolapse with real-time-3-dimensional echocardiography. Importance of annular saddle shape in the pathogenesis of mitral regurgitation. Circulation 2013;127:832–41. 16 Salgo IS, Gorman 3rd JH, Gorman RC, et al. Effect of annular shape on leaflet curvature in reducing mitral leaflet stress. Circulation 2002;106: 711–7. 17 Ryan LP, Jackson BM, Enomoto Y, et al. Description of regional mitral annular nonplanarity in healthy human subjects: A novel methodology. J Thorac Cardiovasc Surg 2007;134:644–8. 18 Warraich HJ, Chaudary M, Maslow A, et al. Mitral annular nonplanarity: Correlation between height/commissural width ratio and the nonplanarity angle. J Cardiothorac Vasc Anesth 2012;26:186–90. 19 Ahmad R, Gillinov AM, McCarthy PM, et al. Annular geometry and motion in human ischemic mitral regurgitation: Novel assessment with three-dimensional echocardiography and computer reconstruction. Ann Thorac Surg 2004;78:2063–8. 20 Lang RM, Tsang W, Weinert L, et al. Valvular heart disease. The value of 3-dimensional echocardiography. J Am Coll Cardiol 2011;58:1933–44. 21 Kuroda K, Kato TS, Kuwaki K, et al. Early postoperative outcome of offpump coronary artery bypass grafting: A report from the highest-volume center in Japan. Ann Thorac Cardiovasc Surg 2016;22:98–107.