Heart Lung Center Utrecht, University Medical Center, Utrecht, and Antonius Hospital, Nieuwegein, the Netherlands

Transcription

1 Ninety-Degree Anterior Cardiac Displacement in Off-Pump Coronary Artery Bypass Grafting: The Starfish Cardiac Positioner Preserves Stroke Volume and Arterial Pressure Paul F. Gründeman, MD, PhD, Cees W. J. Verlaan, Wim Jan van Boven, MD, and Cornelius Borst, MD, PhD Heart Lung Center Utrecht, University Medical Center, Utrecht, and Antonius Hospital, Nieuwegein, the Netherlands Purpose. In off-pump coronary surgery through sternotomy, exposure of posterior circumflex branches causes circulatory deterioration in both patients and pigs. We assessed cardiac pump function when displacing the pig heart anteriorly with a suction cardiac positioner. Description. Six pigs ( 80 kg) underwent sternotomy for hemodynamic instrumentation using catheter-tipped manometers and paced at 80 beats/min. Ultrasound flow probes were placed around the aorta and proximal coronary arteries. The heart was retracted anteriorly to 90 degrees with the Starfish cardiac positioner attached to the apex by means of suction ( 400 mm Hg). Retraction was guided by cardiac output monitoring. Evaluation. Anterior displacement to 90 degrees facilitated full exposure of posterior arteries. Stroke volume and mean arterial pressure decreased to 94% 13% (mean SD, p 0.135) and 95% 13% (p 0.09) of control values, respectively. Right and left ventricular end-diastolic pressure increased to 129% 37% (p 0.009) and to 128% 57% (p 0.235), respectively. Coronary flow remained unchanged. Additional 15-degree head-down positioning increased stroke volume to 113% 17% (p 0.015) and mean arterial pressure to 113% 25% (p 0.087) at the expense of further increased right and left ventricular end-diastolic pressure (186% 63%, p < and 157% 49%, p < 0.001, respectively). Conclusions. When lifting the porcine heart ninety degrees anteriorly, the Starfish cardiac positioner facilitated exposure of posterior branches and, when guided by cardiac output, preserved stroke volume and arterial pressure. (Ann Thorac Surg 2004;78:679 85) 2004 by The Society of Thoracic Surgeons Accepted for publication July 18, Address reprint requests to Dr Gründeman, Experimental Cardiothoracic Surgery, Experimental Cardiology Laboratory, Heart Lung Institute, Utrecht University Medical Center, Rm G02.523, Heidelberglaan 100, 3584 CX Utrecht, the Netherlands; exp.cardio@hli.azu.nl. In off-pump coronary surgery, lateral and posterior wall vessels are more difficult to approach than anterior wall vessels and the right coronary artery because of limited exposure and hemodynamic deterioration seen with cardiac displacement. Lifting the beating heart to expose circumflex branches decreases stroke volume (SV) by up to 40% in both patient [1, 2] and pig [3 5], which is attributed to right heart deformation [4] and impaired diastolic filling [4]. Several interventions will mitigate the stroke volume drop: the Trendelenburg maneuver [1 9] or by increasing preload otherwise [1, 2, 6 8], inotropic support [1, 2, 6], the increase in heart rate by pacing, preservation of right heart filling by pericardial incision [7, 8], efforts to drop the heart posteriorly in the right chest [7] or moderate right lateral decubitus body positioning [9]. The objectives of this study were (1) to assess exposure of the posterior wall by lifting the pig heart with the Starfish apical suction cardiac positioner; (2) to monitor the accompanying hemodynamic changes; and (3) to study the modifying effect of the Trendelenburg maneuver. Material and Methods Six Dutch land race pigs (range, 75 to 85 kg) were used. All animals received humane care in compliance with the Guide for the Care and Use of Laboratory Ani- Dr Borst discloses that he has a financial relationship with Medtronic by The Society of Thoracic Surgeons /04/$30.00 Published by Elsevier Inc doi: /s (03)

2 680 GRÜNDEMAN ET AL Ann Thorac Surg TILTED HEART WITH SUCTION POSITIONER 2004;78: mals published by the National Institutes of Health (National Institutes of Health publication 85-23, revised 1985). The study protocol was approved by the Animal Experimentation Committee of the Utrecht University. assess the influence of changing the apex position from anatomic position into a 90-degree extraanatomic position relative to the spine. A paired Student s t test was used to assess the modifying effect of Trendelenburg compared with control values (supine position, phase 1). Anesthesia and Instrumentation The pigs were premedicated and anesthetized, and underwent midsternotomy to expose the heart for insertion of catheter-tipped manometers (Millar Instruments, Houston, TX) as described previously [3 5, 9]. After the administration of propranolol (range, 15 to 25 mg), pacing at a fixed rate of 80 beats/min was started. An ultrasound transit time flow probe (20 or 24 mm, Transonic Inc, Ithaca, NY) was placed around the ascending aorta for on-line measurement of the cardiac output (CO). Stroke volume was calculated by dividing CO by the heart rate. Flow probes were placed around the most proximal part of the main coronary vessels [5]. The heart was retracted anteriorly to 90 degrese with the Starfish cardiac positioner (Medtronic Inc, Minneapolis, MN). A personal computer based data acquisition system stored hemodynamic variables as described previously [3 5, 9]. Experimental Protocol The protocol was comparable with the one used in previous studies [3 5, 9]. Baseline cardiovascular values were recorded after stabilization after at least 15 minutes of pacing (phase 1, anatomic position). Subsequently, values were taken 3 (phases 2 to 5) and 15 minutes (phase 6) after each intervention. Phase 6 served as baseline for the second sequence of displacement. In phase 2, the suction cardiac positioner was fixed to the apex while the heart remained in its anatomic position. In phase 3 (displacement), the beating heart was hoisted with the Starfish cardiac positioner until a 90-degree extraanatomic position relative to the spine was achieved (apex pointing ventrally). To minimize hemodynamic deterioriation, displacement was guided by the instantaneous CO reading. In phase 4, after stabilization of hemodynamics, the operating table was tilted 15 degrees in the head-down position (Trendelenburg maneuver) without changing the position of the heart relative to the body. After return from Trendelenburg, the heart was released from the Starfish cardiac positioner and fell back into the pericardial cradle (phase 5 and 6, freely beating). Afterwards, the entire protocol was repeated once. Statistical Analysis The duplo data from each animal were averaged for analysis. In Table 1, data are presented as the mean value SD (absolute values). In the results section and in Figure 1, hemodynamic variables are presented as mean SEM of percentage of control values (the heart in anatomic supine position, phase 1). Statistical analysis was performed using multiple analysis of variance to Results All animals survived the entire procedure without the need to defibrillate or administer inotropic drugs. The results are summarized in Table 1 and Figure 1. The paced heart remained in the regular rate of 80 beats/min throughout the experiment. Phase 2: Attachment of the Cardiac Suction Positioner to the Apex Care was taken to avoid inclusion of the distal left descending coronary artery (LAD) in one of the three suction cusps of the Starfish cardiac positioner. After a couple of seconds of suction ( 400 mm Hg suction force), the heart became firmly fixed to the device, which occasionally elicited premature ventricular beats. No inadvertent detachment from the apical suction device occurred during the entire period of the protocol. Initially, SV and MAP decreased on average to 99% 2% and 95% 2% (p and 0.020, respectively (see Table 1). Right atrial pressure (RAP) and right ventricular end-diastolic pressure increased to 105% 4% (p 0.275) and 104% 5% (p 0.260), respectively. Left atrial pressure increased to 106% 4% (p 0.175) and left ventricular end-diastolic pressure increased to 102% 4% (p 0.956). Coronary flows remained unchanged. Phase 3: Cardiac Retraction With the Starfish Cardiac Positioner Displacement of the heart by the suction device was performed by first pulling the apex in the axial direction of the left ventricle and next moving it ventrally (Fig 2). Using the device, the maneuver was easy to perform. It resulted in a transient minor drop in MAP. The posterior aspect of the heart became fully exposed, which included excellent view of the circumflex artery and its branches, distal RCA, the great cadiac vein, coronary sinus, inferior caval vein, and left lower pulmonary vein. In diastole, normal radial expansion of the left ventricle was observed. The head of the device rotated counterclockwise in synchrony with ventricular contraction. After stabilization, SV had decreased to 94% 4% (p 0.135) and MAP remained unchanged relative to phase 2 (95% 4%, p 0.09 vs base line) at the expense of (further) increased preloads. Coronary flows remained unchanged. Phase 4: Tilting Whole Body Head Down 15 Degrees (Trendelenburg) Stroke volume and MAP (over) normalized at the expense of further increased ventricular preloads (right ventricular end-diastolic pressure increased to 186% 19% (p 0.001)

3 Table 1. Hemodynamic Changes Upon Cardiac Displacement Using Suction Positioner Hemodynamic parameter Phase 1 Phase 2 Phase 3 Phase 4 Phase 5 Phase 6 Anatomic FIX p Value DIS p Value DIS TREN p Value Freely Beating for 3 Minutes p Value Freely Beating for 15 Minutes Heart rate (beats/min; paced) Stroke volume (ml/min) 46 (10) 46 (9) (12) (15) (9) (9) Cardiac output (L/min) 3.7 (1) 3.7 (1) (1) (1) (1) (1) Mean arterial pressure (mm Hg) 104 (22) 99 (22) (17) (24) (23) (22) Mean pulmonary artery pressure (mm Hg) 17 (4) 17 (4) (4) (3) (4) (4) Right atrial pressure (mm Hg) 6 (2) 6 (2) (2) (2) (2) (2) Right ventricular end-diastolic pressure (mm Hg) 4 (2) 4 (2) (2) (2) (1) (2) Left atrial pressure (mm Hg) 9 (3) 9 (3) (2) (3) (3) (3) Left ventricular end-diastolic pressure (mm Hg) 8 (3) 8 (3) (2) (4) (2) (3) Flow Left anterior descending coronary artery (ml/min) 38 (8) 37 (9) (10) (11) (9) (9) Flow Circumflex coronary artery (ml/min) 33 (14) 33 (15) (16) (17) (16) (17) Flow Right coronary artery (ml/min) 34 (8) 35 (9) (10) (11) (9) (8) Values are presented as mean; obtained from n 6 duplo data sets. Numbers in parentheses are SD. Symbols in phases 1 6 represent respectively: (1) heart in anatomic position, table horizontal; (2) FIX; (3) DIS; (4) DIS TREN; (5) anatomic position, table horizontal. DIS vertical displacement; FIX suction positioner fixed to apex; Freely Beating heart returned to anatomic position; suction positioner removed. TREN Trendelenburg maneuver. p Value Ann Thorac Surg GRÜNDEMAN ET AL 2004;78: TILTED HEART WITH SUCTION POSITIONER 681

4 682 GRÜNDEMAN ET AL Ann Thorac Surg TILTED HEART WITH SUCTION POSITIONER 2004;78: Fig 2. The porcine heart retracted with the Starfish cardiac positioner (apex pointing anteriorly). Caudal to craniad view on the posterior aspect exposing the distal right coronary artery and remote obtuse marginal branches of the circumflex coronary artery. and left ventricular end-diastolic pressure increased to 157% 15% (p 0.001). Coronary flows increased, which concurred with the increase in MAP (Table 1). Fig 1. Comparison of hemodynamics upon vertical displacement of the beating porcine heart with the Starfish cardiac positioner. Mean percentage of baseline values SEM. (A) Stroke volume. (B) Mean arterial pressure. (C) Right ventricular end-diastolic pressure (white bars) and left ventricular end-diastolic pressure (black bars). Compared with baseline: * p 0.05, $ p 0.01, #p Symbols from left to right represent respectively: suction positioner fixed to apex; vertical displacement; vertical displacement plus Trendelenburg maneuver; heart in anatomic position, table horizontal. Phase 5 to 6: Return of Table to Horizontal Position, Replacement of the Heart in the Anatomical Position, and Release From the Retractor The SV and MAP normalized. After detachment of the device, a superficial mashed dark discoloration was observed that outlined the contour of the suction device (total time attached to the heart was approximately 10 minutes). After 15 minutes (phase 6), the color of the suction lesion had turned to light red. Displacement of the Heart With Starfish Versus Octopus Retraction Exposure of the posterior wall by the apical suction device largely prevented the substantial drop in SV and MAP observed when similar exposure was achieved by the octopus stabilizer: SV diminished to 94% 13% (Starfish) versus 71% 6% (Octopus, mean SD) and 95% 13% (Starfish) versus 77% 8% (Octopus), respectively [ 4].

5 Ann Thorac Surg GRÜNDEMAN ET AL 2004;78: TILTED HEART WITH SUCTION POSITIONER 683 Comment The principal findings of the study were, first, that displacement of the beating heart by the apical suction positioner was easy and safe. Second, fixing the positioner to the apex hardly influenced heart function. Third, 90-degree anterior displacement provided full exposure of the circumflex territory and caused only a 6% or less decrease in SV and MAP. Fourth, the Trendelenburg maneuver resulted in an overshoot in SV and MAP at the expense of significantly elevated ventricular preload pressures. Cardiac Retraction With the Suction Cardiac Positioner The major advantage of displacing the heart with the apical suction positioner is the separation of exposure and stabilization of the target coronary artery as well as the improvement in cardiac function. In 1995, in addition to cardiac displacement with the Octopus [3, 6, 11], we explored in the pig model two alternative ways to expose the back side of the heart, one using a rigid prototype apical suction device and one using apically placed traction sutures (unpublished results). It was noted that when the heart was vertically displaced, using either approach, by pulling at the apex, MAP was surprisingly well preserved. In the present study, guided by the on-line cardiac output readings from the ultrasound aortic probe, a substantial drop in SV by overstretching the heart too much in the long-axis direction was avoided and the optimal position with respect to cardiac output for posterior wall exposure could be selected. The crucial observation was that a 1- to 2-cm change in apical position could improve cardiac output by up to 10% to 15%. The lateral and posterior aspects of the left ventricle became well exposed and were readily accessible for placement of a local wall stabilizer (Fig 2). Visually, the right ventricle was displayed unhindered, filling down to its apex. The left ventricle showed proper radial diastolic expansion circumferentially. The positioner moved in synchrony with the natural motion of the apex with a counterclockwise rotation. Compared with our previous studies [3 5] using the suction-based Octopus tissue stabilizer for retraction of the heart, obtaining 90-degree ventral position with the Starfish resulted in easier exposure of the back side of the heart with a significantly smaller decrease in stroke volume ( 6% compared with 29% [4]) and arterial pressure ( 5% compared with 23% [4]). Right ventricular preload, however, was again enhanced, suggesting some right heart dysfunction. It is likely that compression of the thin-walled right ventricle by surrounding tissue contributed to the marginally decreased right ventricular function. It is inferred that keeping the left ventricle in its normal anatomical shape by gently pulling at the apex when it points ventrically largely preserved left ventricular diastolic and systolic function. As a result, the Trendelenburg maneuver caused an overshoot in SV and arterial pressure. It is conceivable that according to Laplace s law, midventricular enddiastolic wall tension was reduced owing to its smaller short-axis luminal diameter achieved by pulling at the apex. Recently, George and associates [10] provided clinical evidence for another mechanism of the SV decrease upon vertical displacement. The authors demonstrated with three-dimensional echocardiography in patients undergoing off-pump coronary surgery that mitral valve annulus distortion may significantly contribute to hemodynamic instability during positioning for posterior wall grafting. In that study, however, no apical suction retraction was employed and compression stabilization may have contributed to the loss of cardiac output. The patient s heart may have become temporarily ischemic when the target coronary vessel was occluded, inducing papillary muscle dysfunction in addition to mechanical interference with valve funtion. In the present pig model, ischemic valve dysfunction originating from the papillary muscle is highly unlikely because coronary flow was not interrupted for coronary surgery and it followed the changes in arterial pressure. Previously, in both patients [1, 6] and animal [4], no valvular incompetence was observed that could explain the substantial drop in arterial pressure seen after full cardiac retraction for exposure of the posterior and lateral wall. Mean coronary flow in the three proximal major branches varied according to changes in MAP (ie, with afterload). In the Trendelenburg position, for instance, when arterial pressure showed an overshoot to 115%, coronary flow increased to 117% to 125%. From this observation, we conclude that coronary flow was unimpeded throughout all maneuvers. In contrast to an earlier study [5], where lateral wall exposure was performed with the aid of a suction stabilizer, blood flow in the proximal circumflex coronary artery was slightly more reduced compared with coronary flow in the right and left anterior descending coronary artery when afterload was reduced, but the comparison did not reach level of significance. We have no indication that circumflex flow to the postero-lateral territory was adversely influenced by gently stretching the heart in the long-axis direction. Clinical Implications Cardiac displacement by the Starfish positioner will facilitate exposure of posterior arteries. Provided that cardiac displacement is guided by cardiac output or MAP, full exposure of posterior arteries will be feasible with limited adverse hemodynamic consequenses. Because the exposure of the base of the heart was excellent, it is conceivable that other cardiac procedures can also be facilitated by the use of the cardiac positioner (eg, atrial tissue ablation on the beating heart, retraction of the right ventricle for access to the proximal aorta, limited access pacemaker lead placement, and, eventually, endoscopic positioning for closed-chest coronary surgery). Limitations Cardiac retraction was carried out in the normal healthy pig heart with its apex slightly pointing rightwards. The pig s chest cavity conformation is carinad -shaped compared with the barrel -shaped human chest cavity.

6 684 GRÜNDEMAN ET AL Ann Thorac Surg TILTED HEART WITH SUCTION POSITIONER 2004;78: Despite this anatomic difference, inferences made from previous porcine heart displacement studies [3 5, 9] turn out to be fairly well applicable to the human [1, 2, 6 8]. In the present study, no stabilizer was placed along a coronary artery in addition to the use of the suction positioner. Provided that forcefully pushing the myocardium laterally was avoided, in three experiments (unpublished), additional local wall stabilization by the Octopus suction stabilizer did not have a negative impact on stroke volume and arterial pressure. Conclusions Exposure of posterior vessels through sternotomy was greatly facilitated by lifting the porcine heart with the Starfish apical suction positioner. At the expense of marginally augmented right and left ventricular preload, SV and MAP decreased on average by only 6% or less upon ninety-degree anterior displacement of the beating heart. Disclosures and Freedom of Investigation The University Medical Center Utrecht (UMCU) receives royalties from Medtronic for this invention; however, this research was performed independently, funded with academic grants. The present study was funded by a grant from the UMCU to Dr Borst. The UMCU receives royalties from the sales of the Octopus stabilizer and the Starfish positioner. As inventors, Drs Grundeman and Borst have received compensation from the UMCU. The authors have performed a free and in-depth evaluation of this new technology. The authors acknowledge the technical contributions by Merel Schurink and Ricardo Budde. References 1. Nierich AP, Diephuis J, Jansen EWL, et al. Embracing the heart: perioperative management of patients undergoing off-pump coronary artery bypass grafting using the Octopus tissue stabilizer. J Cardiothorac Vasc Ann 1999;13: Mathison M, Edgerton JR, Horswell JL, Akin JJ, Mack MJ. Analysis of hemodynamic changes during beating heart surgical procedures. Ann Thorac Surg 2000;70: 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(Suppl):S 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: Gründeman PF, Borst C, van Herwaarden JA, Verlaan CWJ, Jansen EWL. Vertical displacement of the beating heart by the Octopus stabilizer: influence on coronary flow. Ann Thorac Surg 1998;65: Jansen WL, Borst C, Lahpor JR, et al. Coronary artery bypass grafting using the Octopus method: results in the first hundred patients. J Thorac Cardiovasc Surg 1998;116: Hart JC, Spooner TH, Pym J, Flavin TF, Edgerton JR, Mack MJ, Jansen EW. A review of 1,582 consecutive Octopus off-pump coronary bypass patients. Ann Thorac Surg 2000; 70: Spooner TH, Dyrud PE, Monson BK, Dixon GE, Robinson LD. Coronary artery bypass on the beating heart with the Octopus: a North American experience. Ann Thorac Surg 2000;66: Gründeman PF, Borst C, Verlaan CW, Damen S, Mertens S. Hemodynamic changes with right lateral decubitus body positioning in the tilted porcine heart. Ann Thorac Surg 2001;72: 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: Borst C, Jansen EWL, Tulleken CAF, et al. Coronary artery bypass without cardiopulmonary bypass and without interruption of native coronary flow using a novel anastomosis site restraining device ( Octopus ). J Am Coll Cardiol 1996; 27: Disclaimer The Society of Thoracic Surgeons, the Southern Thoracic Surgical Association, and The Annals of Thoracic Surgery neither endorse nor discourage use of the new technology described in this article. INVITED COMMENTARY Early efforts at beating heart surgery were decidedly low-tech, utilizing at most a simple stabilizer, a few pericardial sutures, and conventional anastomotic techniques [1]. These critical early steps represented more of a philosophical advance and paradigm shift than a technologic breakthrough. More importantly, a door was opened, and the imagination of surgeons and engineers were stimulated to develop new enabling technologies that would reinvent coronary artery bypass surgery. Starting with the original Octopus stabilizer, Drs Gründeman and Borst and colleagues from the Utretcht group have been pioneers in developing such technologies. Enabling technologies are now available to facilitate all aspects of off-pump coronary artery bypass (OPCAB) surgery, including positioning the heart with hemodynamic stability (apical suction devices), coronary stabilization (vacuum and rigid stabilizers), coronary visualization, and hemostasis (intracoronary shunts), as well proximal and distal anastomotic devices. The first, and often most challenging, step in performing a beating heart anastomosis is positioning the heart so that the coronary target is well visualized and accessible, while maintaining hemodynamic stability. The ideal system permits access to all targets, especially on the lateral wall, with a normal blood pressure and cardiac output for as long as is necessary to perform a technically precise anastomosis. In a recent study, hemodynamic compromise during cardiac positioning was the most common obstacle to achieving complete revascularization during OPCAB [1]. The introduction of apical suction devices in large part eliminates this issue, allowing motivated surgeons with appropriate training and experience to now perform complete revascularization offpump in most patients by The Society of Thoracic Surgeons /04/$30.00 Published by Elsevier Inc doi: /j.athoracsur