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Ann Thorac Surg 2000;70:466-472
© 2000 The Society of Thoracic Surgeons
a Department of Anesthesiology, Utrecht University Medical Center, Utrecht, The Netherlands
b Heart–Lung Institute Utrecht, Utrecht University Medical Center, Utrecht, The Netherlands
Address reprint requests to Dr Nierich, Department of Anesthesiology, Room E03.511, Utrecht University Medical Center, Heidelberglaan 100, 3584 CX Utrecht, The Netherlands
e-mail: a.nierich{at}anest.azu.nl
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Abstract |
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Methods. The relationship between surgical exposure and hemodynamic management was assessed in 150 consecutive patients undergoing off-pump CABG utilizing the Octopus Tissue Stabilization System (Medtronic, Minneapolis, MN).
Results. Surgical exposure by anterolateral thoracotomy showed no significant hemodynamic changes. Through sternotomy, stroke volume was significantly reduced by dislocation at all target sites: by 6% at the left anterior descending artery (LAD), 25% at the diagonal branch artery (D), 14% at the right coronary artery (RCA), and 21% at the obtuse marginal artery (OM). The application of head-down positioning (LAD, 56%; D, 74%; RCA, 90%; OM, 96%) increased not only surgical exposure but also preload, producing correction of ventricular filling pressures and output. In a minority of cases, dopamine (3 to 5 µg · kg-1 · min-1) was added to maintain baseline hemodynamic values (LAD, 5%; D, 15%; RCA, 7%; OM, 28%).
Conclusions. Revascularization during anterolateral thoracotomy was uneventful. The sternotomy approach with heart displacement induced right heart compression. Mainly fluid redistribution was sufficient to correct cardiac output. Once stabilized, systemic circulation remained unchanged during revascularization.
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Introduction |
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TopAbstractIntroductionMaterial and methodsResultsCommentReferences |
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By using suction to take hold of a relatively small epicardial area, the Octopus Tissue Stabilization System (Medtronic, Minneapolis, MN) facilitates coronary surgery—specifically, microsurgery—on the beating heart without substantial interference with pump function. This suction fixation method helps to expose all sides of the heart and may be used through any access point [1].
Initial clinical experience shows that in a selected patient group, off-pump CABG is a good alternative to conventional bypass grafting with cardiopulmonary bypass in terms of graft patency [2], anesthesiologic management [3–5], cost [6], and clinical outcome [1]. The aim of this study was to further assess in 150 consecutive patients the hemodynamic consequences of cardiac dislocation and stabilization in relation to the location of the anastomosis and to gain insight in the mechanisms of the cardiovascular changes.
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Material and methods |
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TopAbstractIntroductionMaterial and methodsResultsCommentReferences |
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Surgical access
The surgical procedure has been described recently [1]. In brief, surgical access in most patients was either by anterolateral thoracotomy (ALT group) or by medial sternotomy (STERN group).
In the ALT group, the heart was not rotated to reach the left anterior descending artery (LAD) and only slightly rotated into the patient’s surgical incision wound to reach the diagonal branch artery (D).
In the STERN group, by contrast, the LAD was reached by placing two moisturized gauze pads (10 x 10 cm) between the pericardium and the left ventricle. This maneuver elevated and rotated the left ventricle toward the midsternal incision area, bringing the LAD into view. For grafting the diagonal coronary artery, the heart was retracted more to the midline by moving and rotating the tissue stabilizer to the right. The right coronary artery (RCA) was reached by placing the Octopus suction pods parallel to the RCA, elevating the right ventricle approximately 3 cm upward to gain better access and a better surgical view. The posterior wall was reached by placing the Octopus pods parallel to the obtuse marginal branch artery (OM), rotating the heart cranial and to the right. In this situation, the apex of the heart was lifted out of the thoracic cavity.
Anesthetic management and monitoring
Anesthetic management has recently been described in detail [3]. In brief, patients were treated up to the day of intervention with long-acting ß– blockers, calcium antagonists and nitrates. Perioperative monitoring consisted of a five-lead ECG with ST-segment trend analysis, capillary pulse oximetry, end tidal CO2 determination, invasive arterial blood pressure measurement, and right heart pressure measured by pulmonary artery catheter (Baxter Healthcare, Irvine, CA). Recorded variables were cardiac output (CO), mean arterial pressure (MAP), right atrial pressure, mean pulmonary arterial pressure (mPAP), mixed venous oxygen saturation (SvO2), and heart rate (HR). Cardiac output was determined by the thermodilution technique, using rapid injection of 10 ml of cold isotonic glucose. Stroke volume was calculated as CO/HR. Transesophageal echocardiography was used in most patients in order to record the physiologic consequences of cardiac displacement. During surgical preparation of the arterial conduits, a continuous infusion of a calcium blocker was started (nicardipine, 0.4 to 0.6 mg/h, or diltiazem, 6 to 8 mg/h). After mobilization of the internal mammary arteries but before the installation of the Octopus system, 1.5 mg/kg of heparin was given to the patient to produce an activated clotting time of more than 250 seconds. If regional ischemia occurred during clamping of the native coronary artery that was to be grafted, surgical preconditioning was performed (5 minutes occlusion, 5 minutes reperfusion, occlusion, and surgery).
Conditions to initiate fluid redistribution by the Trendelenburg maneuver were hemodynamic instability (MAP < 60 mm Hg; cardiac index < 2l · min-1 · m-2 or a mixed venous oxygen saturation of less than 60%), surgical improvement of exposure of the target area, or both.
If increase of preload did not restore hemodynamic values above the described limits, dopamine (3 to 5 µ g · kg-1 · min-1) was started to restore arterial pressure and cardiac output.
Hemodynamic data
Hemodynamic data were obtained before the incision was made, 3 minutes before positioning of the Octopus tentacles, 1 minute after placement of the stabilizer, directly at the start of the anastomosis, 3 minutes after beginning of grafting, and 1 minute after opening of the anastomosis before the release of the stabilizer. Event-related hemodynamic variables were stored by an IBM-compatible data acquisition system.
Statistical analysis
Hemodynamic data are presented as mean plus or minus the standard deviation. Only data completely registered for all events were analyzed by group mean comparison for repeated measurement differences compared with baseline and for differences compared with the previous value. Frequency of positioning interventions and dopamine therapy were compared by 
2 test. Statistical calculations were made with SPSS 7.5 for Windows (SPSS, Chicago, IL), and p values less than 0.05 were regarded as statistically significant.
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Results |
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In the D target-site group, preincision hemodynamic values were same as those in the LAD group. However, several values decreased significantly after fixation by the Octopus system: MAP fell from 71 to 66 mm Hg, CO from 4.9 to 4.4 L/min, and SV from 74 to 62 mL. During the events that followed, the postfixation values remained unchanged. Preincision lead II ST-segment elevation, right atrial pressure, mPAP, and SvO2 values did not change significantly during placement of the stabilizer or during operation on the diagonal branch.
STERN group
Baseline hemodynamics and hemodynamic changes during and after application of the Octopus stabilizer are summarized in Table 3. In the LAD target site group, the average lead II ST segment increased significantly from –0.16 mm before incision to 0.05 mm at the beginning of the anastomosis phase. From preincision to fixation with Octopus, HR increased from 65 to 71 beats/min, MAP decreased from 71 to 68 mm Hg, and SV decreased from 69 to 65 mL.
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In the RCA target-site group, HR increased from 67 to 75 beats/min, MAP decreased from 72 to 66 mm Hg, and SV decreased from 76 to 65 mL from preincision to fixation. Lead II ST-segment values increased significantly from a preincision value of –0.12 to 0.09 mm at the beginning of the anastomosis phase.
In the OM target-site group, the average lead II ST segment did not change significantly during the operation. Hemodynamic changes were as follows: an overall increase of HR from 69 to 74 beats/min and decreases of MAP (65 to 61 mm Hg), CO (4.7 to 4.0 L/min), SV (70 to 55 mL), and SvO2 (78% to 73%).
Figure 3 illustrates a situation of acute hemodynamic deterioration during surgical dislocation in order to position the Octopus stabilizer on the posterior wall.
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Comment |
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TopAbstractIntroductionMaterial and methodsResultsCommentReferences |
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Feasibility studies in the pig have shown that even with extreme displacement of the healthy pig heart, the circulation is not severely compromised, provided that subjects are placed in the Trendelenburg position [8]. Rotation and dislocation of the heart even with the apex out of the thoracic cavity did not obstruct coronary circulation [9]. Tilting the heart induces a reduction in CO that is primarily caused by impaired diastolic expansion of the right ventricle [8–10]. Treatment consists of elevation of right ventricular preload. Elevation of coronary perfusion pressure alone without an increase of right ventricular preload could not restore CO [10]. Experimental studies in the pig, however, do not per se reflect clinical situations produced by differences in anatomy and myocardial pathology in human patients and anesthetic corrections made to normalize circulatory homeostasis.
Therefore, it is important to analyze in detail perioperative effects on cardiac performance and global circulation in order to expand the use of the Octopus stabilization method without compromising the safety of the surgical procedure. Complicated hemodynamic management would make off-pump CABG with the Octopus less attractive.
The overall hemodynamic data show no clinically important deterioration in hemodynamic function of global circulation and no overall ischemic impairment of cardiac function during Octopus surgery. Ischemia was also not significant during the anastomosis phase. We observed no major decrease in contractility as reflected in unstable hemodynamics. Conversion due to hemodynamic instability or the use of a shunt was necessary in only two patients during interruption of RCA flow. Monitoring of ST-segment values in the dislocated heart is not reliable due to the loss of contact between the heart and the pericardium, which results in a decrease of ECG amplitude. Ischemia resulting in hemodynamic instability has recently been described elsewhere [11].
The act of displacing the heart, more than displacement itself, caused hemodynamic alterations, depending on the location of the target vessel. However, hemodynamic registrations were all obtained in the anesthesiologically stabilized situation after manipulation of the heart. These alterations are discussed by type of incision and by target native coronary artery site, together with their physiologic background. Baseline values differ among the different patient groups.
ALT group
Grafting the LAD using anterolateral thoracotomy produced few hemodynamic changes. This is the least compromising situation for the heart during off-pump grafting, because there is no dislocation by the stabilizer and the heart remains in its natural cavity, the pericardium.
In cases in which additional grafting of the diagonal branch was necessary, the surgeon first performed side-to-side anastomosis. To retract the diagonal artery in the surgical field, the heart was rotated towards the anterolateral incision by manipulation of the stabilizer. This meant slight compression of the left ventricle, which was reflected in a decrease of SV and CO compared with values occurring before fixation. Right atrial pressure did not change. Treatment was normally not necessary since hemodynamics remained well within acceptable levels. After finishing anastomosis of the diagonal and left internal mammary artery, suction was released and the heart rotated back to the left side to allow end to side grafting of the LAD.
STERN group
Sternotomy is the most practical incision for multiple grafting because it provides access to all sides of the heart. It allows easy harvesting of intrathoracic arterial grafts, and conversion to cardiopulmonary bypass, if needed, is simple. Hemodynamic values in patients undergoing sternotomy are different from those in the patients undergoing a limited-access procedure due to the location of the coronary arteries in relation to the incision area. In the STERN group, strategy during surgery was always to graft first the anterior wall or the right coronary artery because accessing these areas did not necessitate excessive tilting of the heart, in contrast with the posterior wall. The decision as to which vessel to graft first depended on the rate of occlusion within the native vessel. A fully occluded artery was grafted first to allow collateral perfusion to the next operated coronary artery during occlusion.
To reach the anterior wall (LAD, D) the surgeon placed two to three moistened gauze pads measuring 10 x 10 cm behind the left ventricle to elevate and to rotate the left ventricle into the midline. However, this caused compression of the right heart, which was squeezed between the thick, bulky left ventricle and the right pericardium. That resulted in a drop in right ventricular output, which was reflected in a decrease of mPAP, MAP, and CO. Treatment consisted of elevation of right heart filling by fluid loading or fluid redistribution through the Trendelenburg maneuver. Exposure of the diagonal artery area caused additional compression, suction, and rotation of the left ventricle to the right with additional right heart compression. This resulted in a significant reduction of SV and an increase by 15% in incidence of inotropic support (Fig 2). After finishing both anterior wall anastomoses, the moistened gauze pads were removed before continuation to the right or posterior wall.
To allow a good surgical view of the RCA and its distal branches, the operating table was placed in the head-down position and both suction arms were moved ventrally in order to elevate the target area 3 to 5 cm. This resulted in a tremendous increase in surgical view, but it also caused some obstruction of the tricuspid orifice. Transesophageal echocardiography as well as monitoring of right atrial pressure were helpful in identifying the limit of elevation in order to prevent tricuspid valve blockage or insufficiency.
The most challenging site to graft on the beating heart is the posterior wall. In order to view this invisible area from the sternotomy approach, the heart must be tilted out of the pericardial cradle. In the first phase of rotating and elevating the heart in order to inspect the OM vessels, compression of the heart and premature ventricular beats caused hemodynamic deterioration. Figure 3 illustrates the acute phase before the stabilized position of the heart. The mechanism is the same as in the anterior area but more pronounced. The right ventricle is squeezed between the pericardium and the muscular left ventricle, and a situation of an acute low cardiac output syndrome is created, different from that of the clinical syndrome: filling pressures did not increase but left ventricular filling pressures decreased. This was reflected in decreased mPAP, MAP, CO, and SvO2. Monitoring by TEE during this period showed a bulging of the intraatrial septum to the left side, no dilatation of the left ventricle, and a crumpled small aspect of the right ventricle (Fig 4). Ischemia monitoring was not of value, since the amplitude decreased by the loss of contact between the heart and pericardium. At the same time both stabilizer arms were placed parallel to the OM. In cases in which suction was installed, the hand of the surgeon did not compress the heart anymore and in most patients hemodynamics came back to normal values. This unstable period persisted in most instances for fewer than 30 seconds. Compared with LAD and RCA grafting, coronary circulation was only impaired in the OM area, since the other areas had already been bypassed. This means that flow over these grafts must be normalized after tilting by increasing the coronary perfusion pressure by an 
-constrictor or low doses of an inotropic drug. Normalization of MAP will restore residual myocardial blood flow, as well as flow through the grafts on the anterior and inferior wall, and this situation of acute low cardiac output syndrome will disappear. It is very important to avoid overshooting with inotropic drugs, especially ß-adrenergic drugs. This may compromise local cardiac wall stabilization, the accuracy of the anastomosis, and cardiac performance because of increased oxygen demand. Our hemodynamic measurements were all made in the stabilized period, and hemodynamic values were normalized before grafting, without important efforts to increase contractility. There was a decrease of SV and of MAP, but within physiologic limits.
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A limitation of this study is that these data were collected from a patient group that did not have severely impaired left ventricles. However, the present data show that off-pump multiple vessel grafting is quite feasible and suggest that this technique may be well controlled and applicable to a substantial proportion of the coronary artery surgery patients.
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Acknowledgments |
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