Since the development of stabilization devices, there

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1 Mitral Annulus Distortion During Beating Heart Surgery: A Potential Cause for Hemodynamic Disturbance A Three-Dimensional Echocardiography Reconstruction Study Shane J. George, FRCP, FRCA, Sharif Al-Ruzzeh, FRCS, and Mohamed Amrani, FETCS, PhD Harefield Hospital, Royal Brompton & Harefield NHS Trust, Harefield, Middlesex, United Kingdom Background. Positioning for access to the coronary arteries leads to hemodynamic instability during offpump cardiac surgery. External changes have been well described, but a description of the intracardiac structures in humans has not been described. Methods. With multiplane intraoperative echocardiography, the mitral annulus at end diastole was reconstructed in the different positions and correlated with hemodynamic changes in the right heart and left atrium. Results. Significant distortion of the mitral annulus with enlargement of the left atrium and pulmonary veins was demonstrated, which correlated with high left atrial pressures. Conclusions. Mitral valve distortion can significantly contribute to hemodynamic instability during positioning for off-pump cardiac surgery. (Ann Thorac Surg 2002;73: ) 2002 by The Society of Thoracic Surgeons Since the development of stabilization devices, there has been increasing use of off-pump techniques for myocardial revascularization [1 9]. The problems for surgical success include access, visualization, and stabilization. This necessitates placing the heart in nonphysiologic positions, which can reduce cardiac output. A number of mechanisms [10, 11] may be postulated to be the cause of hemodynamic disturbance during this period, including coronary artery flow compromise, compression of the heart chambers, poor preload of the ventricles, and distortion of the cardiac valves. Little is known about the geometric changes of the mitral annulus when the heart is placed in a nonphysiologic position during a beating heart surgery. The aim of this study is to describe the distortion of the mitral ring and its effect on the hemodynamic variables with the use of intraoperative echocardiography with three-dimensional (3-D) reconstruction [12]. Material and Methods Accepted for publication Dec 30, Address reprint requests to Dr George, Department of Anaesthesia, Harefield Hospital, Harefield, Middlesex, UK, UB9 6JH; With institutional ethical approval and informed consent, 6 patients who were in sinus rhythm and required revascularization of the left anterior descending artery, posterior descending artery, and the circumflex artery were studied. After routine anesthetic induction the following monitors were placed: routine electrocardiogram monitoring, invasive arterial monitoring, a continuous cardiac output catheter with pulmonary artery and wedge pressure monitoring, intraoperative transesophageal echocardiography, and left atrial (LA) catheter. The transesophageal probe was left in the midesophagus as swabs and air between the heart and diaphragm resulted in inconsistent transgastric imaging. After sternotomy and conduit harvesting, measurements (Table 1) were taken with the heart in the physiologic position (with the sternum spread open); then the measurements were repeated after the heart was positioned for revascularizing the different arteries. The heart is stabilized using the suction and irrigation tissue stabilization system (Octopus 3; Medtronic Inc, Minneapolis, MN) [13, 14]. One deep pericardial retraction suture is placed at the posterior fibrous pericardium very close and medial to the most proximal part of the inferior vena cava (Fig 1). This suture is a personal modification of previously described deep pericardial retraction sutures. It acts as a lever that helps the surgeon manipulate and rotate the heart to vertical and lateral positions along with the Octopus system. A wet gauze swab is placed between the suture and the posterior surface of the heart to avoid tearing the myocardium or compressing the posterior coronary vessels. Mitral valve structure was reconstructed from the end diastolic frames of the transesophageal echo. With respiration paused, a cardiac cycle was taped at 20 degree intervals keeping the transducer still. Using the apex of the image as the origin, a two-dimensional coordinate system was allocated to the two points of the mitral annulus. Utilizing the angulation of the transducer, a 3-D coordinate system was generated for the mitral annulus 2002 by The Society of Thoracic Surgeons /02/$22.00 Published by Elsevier Science Inc PII S (02)

2 Ann Thorac Surg GEORGE ET AL 2002;73: MITRAL DISTORTION IN BEATING HEART SURGERY 1425 Table 1. Hemodynamic Measurements Before and After Positioning for Revascularization of the Left Anterior Descending Artery Posterior Descending Artery Circumflex Left Anterior Descending Artery Normal Position Change in Parameter Parameter Mean arterial pressure (SD) (min-max) mm Hg 78.8 ( 3) Mean % decrease in arterial pressure ( SD) 25% ( 3%) 27% ( 2%) 26% ( 3%) (70 90) (min-max) (17% 33%) (2% 33%) (14% 47%) Mean systolic PA pressure (SD) (min-max) mm Hg 35 ( 1.8) Mean % increase in systolic PA pressure ( SD) 3.5% ( 5.2%) 10% ( 4%) 11% ( 8%) (30 40) (min-max) ( 17% 15%) (0% 23%) (0% 51%) Mean CVP (SD) (min-max) mm Hg 10 ( 1.1) Mean % increase in CVP ( SD) (min-max) 2% ( 5%) 42% ( 6%) 72% ( 16%) (6 13) ( 23% 16%) (23% 66%) (23% 133%) Mean LA pressure (SD) (min-max) mm Hg 12 ( 0.5) Mean % increase in LA pressure ( SD) 13% ( 6%) 51% ( 6.5%) 66% ( 8%) (11 14) (min-max) ( 15% 28%) (28% 72%) (36% 91%) Mean cardiac output (SD) (min-max) L/min 5.48 ( 0.34) Mean % decrease in cardiac output ( SD) 3% ( 1.8%) 11% ( 3.3%) 20% ( 5%) ( ) (min-max) ( 10% 2.4%) (1.7% 23%) (5% 36%) Mean SVO2 (SD) (min-max) % 71 ( 2.2) Mean % decrease in SVO2 ( SD) (min-max) 4.6% ( 0.4%) 9% ( 2%) 9.5% ( 4%) (68 75) (0% 5%) (5% 13%) (4% 14%) AP arterial pressure; CVP central venous pressure; LA mean left atrial pressure; min-max minimum-maximum; PA pulmonary artery pressure; PCWP pulmonary capillary wedge pressure; SVO2 pulmonary artery oxygen saturation; SAO2 arterial oxygen saturation; SD standard deviation. Fig 1. Deep pericardial suture placement. (IVC inferior vena cava.) at end diastole. The mitral annulus was reconstructed from these points using computer software (DesignCAD Pro 2000; Viagrafix Corp, Oklahoma City, OK). Once the image was reconstructed, software smoothing of the edges generated the final image. The image generated for the normal position correlated well with previous descriptions of the mitral valve annulus. We therefore proceeded to generate similar images for the mitral valve when the heart was held in other positions. Results Normal Table 1 shows the mean base line hemodynamic measurements and its changes during the various positions. Figure 2 shows the normal appearance of the mitral valve and the left atrium. This shows the normal left atrial dimension of 4 cm and the direction of the mitral valve toward a4o clock direction. Reconstruction of the mitral annulus at end diastole is shown in Figure 3. The previously described saddle shape is clearly seen and provides some validation of our reconstruction technique. Left Anterior Descending Artery Revascularization There was minimal distortion of the mitral valve as there was only minimal rotation, and the application of the stabilizer had little effect. The 3-D image generated (Fig 4) was no different from the normal one, and therefore it was not reproduced. Hemodynamic measurements are shown in Table 1. Posterior Descending Artery Revascularization The prime movement in accessing the right coronary artery and posterior descending artery is verticalization of the heart. We frequently open the right pleura and these images are generated with the right pleura open (Fig 5). The hemodynamic changes seen are shown in Table 1. Reconstruction of the mitral valve annulus (Fig 6) shows the mitral valve to be bent over. This is reflected in

3 1426 GEORGE ET AL Ann Thorac Surg MITRAL DISTORTION IN BEATING HEART SURGERY 2002;73: Fig 2. Selected images of left atrium and mitral valve while in the normal sternotomy position. Note the depth of the image (12 cm, each white dot on the side representing 1 cm). Note the left atrial dimension, which is normal at 4 cm. the hemodynamic changes and the appearance of the dilated pulmonary veins, with the LA dimension increased to 6 to 7 cm; the mean increase was 50%. The pulsed wave Doppler pattern (Fig 7) suggests a restrictive filling pattern with a mean reduction of E:A ratio of 30%, suggesting that compression of the left ventricle may play a significant role in the hemodynamic changes. Circumflex Revascularization Access to the back of the heart requires the most distortion of the heart s position. Typically, this requires both a vertical and rightward rotation. Again, with the right pleura open, the heart can be displaced into the right thorax with less compression of the right side (Fig 8). The increased LA dimension of 6 cm (mean increase 50%), and the raised LA pressures suggest dynamic mitral stenosis or mitral regurgitation. The color Doppler images showed minimal mitral regurgitation in the normal position in 2 patients. When positioned for access to the circumflex artery, mitral regurgitation had deteriorated to moderate regurgitation. On repositioning, the mitral regurgitation reverted to being mild. The hemodynamic changes seen are shown in Table 1. The restrictive pattern seen with the vertical position is not seen in this additionally rotated position (Fig 9). Reconstruction of the mitral annulus (Fig 10) suggests folding and twisting of the mitral valve. In two patients there was significant increase in LA and CV pressures. Fig 3. Three-dimensional reconstruction of the annulus and its plane (not the whole mitral valve) at end diastole with representations of the result from different perspectives.

4 Ann Thorac Surg GEORGE ET AL 2002;73: MITRAL DISTORTION IN BEATING HEART SURGERY 1427 Fig 4. Selected images of left atrium and mitral valve while positioned for the revascularization of the left anterior descending artery. Comment Using a 3-D reconstruction technique, we have demonstrated that the mitral valve undergoes profound changes. The distortion of the heart when positioning for coronary artery access during off-pump myocardial revascularization has been grossly appreciated externally. However, the distortion of intracardiac structures has not been fully addressed, and the most useful tool to investigate this is intraoperative transesophageal echocardiography. However, because of the deliberate separation of the inferior surface of the heart from the diaphragm, transgastric images are not always obtained, so we are Fig 5. Selected images of left atrium and mitral valve while positioned for the revascularization of the posterior descending artery (vertically). Note the depth had to be increased; the left atrial dimension increased to 6 cm, and the pulmonary veins are dilated. Note also the distortion of the left atrium and how in some views the two ends of the mitral annulus are close together.

5 1428 GEORGE ET AL Ann Thorac Surg MITRAL DISTORTION IN BEATING HEART SURGERY 2002;73: Fig 6. Three-dimensional reconstruction of the annulus and its plane (not the whole mitral valve) at end diastole, in the vertical position, with representations of the result from different positions. left to interpret images only from the transesophageal positions. We have used additional monitoring with intraoperative echocardiography to delineate the changes that occur during the abnormal positioning of the heart. We use the Octopus system with suction on the myocardial wall to achieve stability. The data from the normal position have been used to delineate base line and to corroborate our results (ie, the 3-D reconstruction of the mitral annulus) with other results [12]; this was used as a validation of our technique of demonstrating the mitral architecture. In addition to the previously described factors that have been implicated in the hemodynamic disturbance seen with positioning [3, 10, 11, 15], we have identified the role of Fig 7. Left ventricular inflow Doppler trace suggesting restrictive flow when the heart is held vertically. distortion of the mitral valve to be another cause of hemodynamic instability. The greatest distortion seems to occur during the positioning to access the back of the heart. The data suggest that the intracardiac structures are folded primarily at the atrioventricular groove, giving rise to either a functional mitral stenosis or worsening mitral regurgitation resulting in raised left atrial pressures. The most profound effect seemed to be on marginally abnormal valves, which became more distorted and gave rise to the most marked hemodynamic changes seen. The left atrium was clearly seen to increase in length from a base line of 4 cm to a base line of 6 to 7 cm. Although this may only be a distortion of the left atrium, the dilation of the pulmonary veins and the rise in LA pressure suggest this is a real process. In addition, there seems to be a functional difference according to the position. Indeed, during verticalization, the pulsed wave Doppler suggests that the distortion gives rise to a restrictive pattern probably corresponding with compression of the left ventricle. Surprisingly, this pattern is not seen when the heart is rotated for the circumflex approach. This is probably because there is less ventricular compression, as the pleura is open and the heart can lie in the right thoracic cavity. Gründeman and colleagues [16] used echocardiography in a pig model and showed distortion primarily to the right side, but failed to show two-dimensional changes on the mitral valve or changes in the left atrial pressure. Their failure to demonstrate similar changes may reflect species differences or less aggressive manipulation of the heart. Similarly, Nierich and colleagues [11] used routine pulmonary artery catheters that did not show any significant changes in the mean pulmonary artery pressures. These authors did not report on wedge or left atrial pressures; although in the discussion there is a suggestion that wedge pressures were lower than base line. The differences between their findings and ours may be explained by technical differences in approach or by our more aggressive manipulation of the heart; we currently perform 95% of elective and urgent cases off pump.

6 Ann Thorac Surg GEORGE ET AL 2002;73: MITRAL DISTORTION IN BEATING HEART SURGERY 1429 Fig 8. Selected images of left atrium and mitral valve while positioned for the revascularization of the circumflex (verticalized and rotated). Note the depth had to be increased, and the left atrial dimension increased to 6 cm. Note also the distortion of the left atrium and the change in orientation of the mitral valve opening. As with the posterior descending artery, in some views the two ends of the mitral annulus are close together. Fig 9. Left ventricular inflow pattern suggests a more normal pattern with faster flow when the heart is allowed to fall into the right thorax while positioning for access to the circumflex artery. Although the mitral valve is clearly involved in the deformation, the folding of the mitral annulus was not recognized until the 3-D reconstruction. This could significantly contribute to intraoperative hemodynamic instability. Whether it contributes to longer-term dysfunction has not been demonstrated. However, mitral distortion is relatively short and would not be expected to cause prolonged dysfunction, except possibly in patients with poor lung function. In conclusion, we have observed significant changes of the left atrium and left atrial pressures associated with distortion of the mitral annulus geometry at the end diastolic phase of the cardiac cycle during positioning of the heart for off- pump myocardial revascularization. We suggest that distortion of the mitral valve can result in either functional mitral stenosis or increased mitral regurgitation with subsequent raised left atrial pressures. This may be a significant contributor to the hemodynamic disturbance seen during the procedure. Whether these findings are more marked or comparable with compression devices remains to be shown. Recent developments, such as the apical suction device, may play a beneficial role in reducing the distortion of the mitral valve. Fig 10. Three-dimensional reconstruction of the annulus and its plane (not the whole mitral valve) at end diastole, in the verticalized and rotated position, with representations of the result from different positions. Note the folding of the mitral annulus in two separate areas representing the vertical rotation.

7 1430 GEORGE ET AL Ann Thorac Surg MITRAL DISTORTION IN BEATING HEART SURGERY 2002;73: References 1. Ovrum E, Tangen G, Oystese R, Dragsund S, Nitter-Hauge S. Coronary surgery at the Heart Center in Oslo Tidsskr Nor Laegeforen 2000;120(6): Ricci M, Karamanoukian HL, Abraham R, et al. Stroke in octogenarians undergoing coronary artery surgery with and without cardiopulmonary bypass. Ann Thorac Surg 2000;69: Hart JC, Spooner TH, Pym J, et al. A review of 1,582 consecutive Octopus off-pump coronary bypass patients. Ann Thorac Surg 2000;70: Hernandez F, Clough RA, Klemperer JD, Blum JM. Offpump coronary artery bypass grafting: initial experience at one community hospital. Ann Thorac Surg 2000;70: Ascione R, Lloyd CT, Underwood MJ, Lotto AA, Pitsis AA, Angelini GD. Economic outcome of off-pump coronary artery bypass surgery: a prospective randomized study. Ann Thorac Surg 1999;68: Turner WF, Jr. Off-pump coronary artery bypass grafting: the first one hundred cases of the Rose City experience. Ann Thorac Surg 1999;68: Spooner TH, Hart JC, Pym J. A two-year, three institution experience with the Medtronic Octopus: systematic offpump surgery. Ann Thorac Surg 1999;68: Holubkov R, Zenati M, Akin JJ, Erb L, Courcoulas A. MID- CAB characteristics and results: the CardioThoracic Systems (CTS) registry. Eur J Cardiothorac Surg 1998;14 (Suppl 1):S Olsen PS, Thiis JJ, Stentoft P, et al. Coronary bypass surgery at the Rigshospitalet Results after consecutive operations. Ugeskr Laeger 1997;159(6): Gründeman PF, Borst C, van Herwaarden JA, Mansvelt Beck HJ, Jansen EWL. Hemodynamic changes during displacement of the beating heart by the Utrecht Octopus method. Ann Thorac Surg 1997;63:S Nierich AP, Diephuis J, Jansen EW, et al. Embracing the heart: perioperative management of patients undergoing off-pump coronary artery bypass grafting using the octopus tissue stabilizer. J Cardiothorac Vasc Anesth 1999;13(2): Flachskampf FA, Franke A, Job FP, Krebs W, Terstegge A, Klues HG, et al. Three-dimensional reconstruction of cardiac structures from transesophageal echocardiography [Review]. Am J Card Imaging 1995;9(2): Anyanwu A, Al-Ruzzeh S, George SJ, Patel R, Yacoub M, Amrani M. Conversion to off pump coronary bypass without increased morbidity or change in practice. Ann Thorac Surg 2002; (in press). 14. Al-Ruzzeh S, George SJ, Bustami M, Nakamura K, Yacoub M, Amrani M. The early clinical and angiographic outcome of the sequential coronary artery bypass grafting using the off-pump technique. J Thorac Cardiovasc Surg 2002;123: (in press). 15. Bergsland J, D Ancona G, Karamanoukian H, Ricci M, Schmid S, Salerno TA. Technical tips and pitfalls in OPCAB surgery: the Buffalo experience. Heart Surg Forum 2000;3(3): Gründeman PF, Borst C, Verlaan CWJ, Meijburg H, Mouës CM, Jansen EWL. Exposure of circumflex branches in the tilted, beating porcine heart: echocardiographic evidence of right ventricular deformation and the effect of right or left heart bypass. J Thorac Cardiovasc Surg 1999;118: