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Eur J Cardiothorac Surg 2003;24:762-769
© 2003 Elsevier Science NL
a Department of Cardiothoracic and Vascular Surgery, Skejby Sygehus, Aarhus University Hospital, Aarhus, Denmark
b Institute for Experimental Clinical Research, Skejby Sygehus, Aarhus University Hospital, Aarhus, Denmark
c Department of Anaesthesiology, Skejby Sygehus, Aarhus University Hospital, Aarhus, Denmark
d Department of Thoracic Surgery, Copenhagen University Hospital, Copenhagen, Denmark
Received 22 October 2002; received in revised form 24 April 2003; accepted 21 July 2003.
* Corresponding author. Department of Thoracic Surgery 2152, Rigshospitalet, Copenhagen University Hospital, 9 Blegdamsvej, DK-2100 Copenhagen, Denmark. Tel.: +45-3545-2516; fax: +45-3545-2548
e-mail: phughes{at}rh.dk
| Abstract |
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Key Words: Off pump coronary artery bypass Coronary artery bypass surgery Right heart assist
| 1. Introduction |
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Conventional coronary artery bypass surgery (cCABG) with cardiopulmonary bypass (CPB) has been regarded as the reference surgical technique for patients with coronary artery disease [5]. The use of a heartlung machine, however, involves risk of neurological, renal, and respiratory postoperative dysfunction, mainly due to a diffuse inflammatory response, and dysfunction of the coagulation system. Consequently, since the mid 1990s off-pump coronary artery bypass grafting (OPCAB) has been considered as a beneficial approach for selected patients [68].
Nierich et al. [9] investigated the haemodynamic profile for the OPCAB patients with target vessels on the anterior and lateral aspects of the heart. No significant haemodynamic changes were observed during this procedure. However, accessing these marginal arteries is hampered by space limitations that may compromise the quality of the anastomoses and often causes haemodynamic instability following manipulations of the heart. Dislocation of the heart leads to biventricular dysfunction because of kinking of the low-pressure right atrium and ventricle, which impairs blood flow in the pulmonary circulation. Accordingly, the low left ventricular preload leads to systemic circulatory failure. To provide sufficient preload to the left ventricle in such situations, a right-sided circulatory assist may be an alternative to the CPB.
Animal studies have verified that right heart assist (RHA) normalizes haemodynamics even with the heart maximally tilted [1013]. The feasibility of RHA has not yet been demonstrated in major clinical studies [14,15]. Therefore, the aim of this study was to evaluate RHA-CABG on 50 patients and compare the data of a similar-sized control group operated on with cCABG.
| 2. Materials and methods |
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2.2. Control group
Each RHA-CABG group patient was retrospectively matched to a control patient operated on by cCABG in the same period. Matching was performed on 50 patients according to, age, sex, 3VD, EuroSCORE [16], and EF by computer-aided selection from the local database. The operator was blinded to the patient outcome while selecting.
2.3. Management of anaesthesia and intensive care
After premedication with diazepam 0.10 mg/kg, the general anaesthesia was induced by propofol 1.52.5 mg/kg and sufentanil 35 µg/kg. Muscle relaxation was accomplished by pancuronium 0.1 mg/kg. Propofol 1.52.5 mg/kg per hour was given during surgery. Continuous mixed venous oxygen saturation (SvO2) supplemented by pump flow, pressure monitoring of left atrial pressure (LAP), and pulmonary artery pressure (PAP) were applied to monitor the circulatory status. Intravascular lines for continuous pressure monitoring were applied to monitor mean blood pressures from the radial artery (MAP) and central venous pressure (CVP) from the right internal jugular vein. Cardiac output (CO) of ten patients was measured in the aorta with a PiCCO catheter (ViCare DK) inserted through the right femoral artery [17]. The ST segment in the ECG was monitored continuously to detect signs of myocardial ischaemia and cardiovascular instability during cardiac manipulations, target artery immobilization, and flow interruption. Dobutamine and nitroglycerine as perfusion were administered as necessary to normalize haemodynamics.
Postoperative ventilatory support continued until stable haemodynamic conditions were ensured. Chest drain blood was auto-transfused whenever necessary during the first 8 postoperative hours. In both groups criteria for transfusion of red blood cells were identical namely at a haematocrit <25% during operation, or <30% postoperatively.
2.4. Surgical technique in the RHA-CABG group
After midline sternotomy, the left internal mammary artery (LIMA) was harvested. When the pericardium was opened, the LIMA was anastomosed to the left descending artery (LAD). The venous grafts were anastomosed immediately afterwards. Generally, the distal anastomoses were completed before the proximal ones. The coronary arteries were snared proximally with a suture and a tourniquet to prevent bleeding during the distal anastomosis. An Octopus Stabilization System (Medtronic, Grand Rapids, MI) was used to immobilize the exposed target coronary artery. An RHA was established before performing the distal anastomosis to the marginal coronary arteries. A 28-F two-stage inlet catheter (Jostra, Germany) was placed in the right atrium. A 14-F outlet cannula (Jostra) was placed through a purse string suture directly in the pulmonary trunk. After completion of the last distal anastomosis and taking the heart back to its normal position, the perfusion cannulae were removed. All bypass grafts were immediately quality controlled by flow measuring by means of a Doppler transit time flow probe (CardioMed, Norway). During the procedure the patients were kept normothermic using a Bair Hugger Temperature Management System (Augustine Medical Inc., MN).
2.5. Right heart assist
A BioMedicus centrifugal pump head (80 ml) with 3/8-inch tubings was primed with 400 ml lactated Ringer solution and connected to the venous catheter and the arterial cannula. Initially, the pump was set at 2.5 l/min per 3000 rpm displacing the blood from the inlet to the outlet cannula (Fig. 1)
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2.6. Surgical techniques for the control group
After cannulation of the aorta and right atrium, CPB was initiated to allow aortic cross-clamping and antegrade cold crystalloid cardioplegic (St. Thomas II). Central anastomoses were performed after distal by means of a side clamp. After completion of the distal anastomoses the patients were gradually weaned from CPB. The blood remaining in the heartlung machine was re-transfused.
2.7. Cardiopulmonary bypass (CPB)
The circuit comprised a membrane oxygenator (Quadrox, Jostra), a softbag venous reservoir (Safe II, Polystan, Denmark), cardiotomy reservoir (Gish, USA), silicone tubings (Polystan), and an arterial filter (Pall, UK). The HLM (Polystan) had occlusive roller pumps.
Prime consisted of 1800 ml of lactated Ringer solution with an addition of 5000 IU of heparin. CPB was conducted at 34 °C. During perfusion, the pump flow was maintained at a cardiac index at 2.4 l/m2 per minute maintaining SvO2>70% (CDI 100, 3M, USA). Acidbase balance followed an alpha-stat regime [18]. During CPB the haematocrit was kept between 0.25 and 0.30.
Anticoagulation was achieved by administering 300 IU heparin/kg body weight to an ACT level>480 s. To neutralize the heparin after surgery 1 mg protamine sulphate (Leo) pr. 100 IU heparin was administered.
2.8. Outcome measures
We studied peri- and postoperative course and complications and also worked out a 3-month postoperative status for the RHA-CABG group. As for the control group, we studied peri- and postoperative course and complications during admission. The peri- and postoperative outcome measures were defined as mortality and cardiac, pulmonary, cerebral, renal, and bleeding complications according to these definitions: AMI (defined as Q-wave changes or loss of R-wave in the electrocardiogram and creatine kinase (CK)-MB release >40 µg/l), atrial fibrillation, need for inotropic support >1 day, ventilatory support >24 h, major neurological deficit as coma, stupor or paresis, se-creatinine >200 µmol/l, need for haemofiltration, need for re-operation due to bleeding, need for allogenic transfusion of red blood cells. The 3-month follow-up consisted of data on survival, reappearance of angina, cardiac-related hospitalization and intervention, and the requirement anti-angina medication.
2.9. Statistical analysis
In the statistical analysis, haemodynamic changes between baseline values and values on RHA were analysed by means of a MannWhitney U-test or a paired Student t-test, depending on distribution. The clinical outcome data were compared with an unpaired Student's t-test or a chi-square test. Statistically significant differences were defined as the level at which the P-value was less than 0.05. SPSS statistical software (SPSS Inc., Chicago) and Microsoft Excel 2000 was used for statistical analysis and graphical presentation.
| 3. Results |
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The haemodynamic parameters during RHA support are shown in Figs. 26 . The RHA procedure lasted 18 min (626), with a blood flow on the pump set at 2 l/min (1.62.4). The mean arterial pressure decreased significantly during the first 10 min of RHA from 78 mmHg (±11) (mean (SD)) to 69 mmHg (±13) and was restored hereafter to reference values (Fig. 2).
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The CVP, LAP, and PAP increased significantly during RHA, and did not normalize until the heart was brought back to its normal position and the pump was stopped (Figs. 46).
The cardiac index was measured on the last ten patients and showed no significant change during the procedure, as there was no significant change in the heart rate during the procedure.
3.3. Postoperative outcome
The postoperative outcome measures are shown in Table 2. The patients in the RHA-CABG group had significantly less chest drain bleeding 14 h postoperatively than the control group (722 ml (2002200) vs. 1214 ml (1502725)). There was no significant difference in the frequency of re-operations in the two groups (n=2 vs. 8) as there was no significant difference in the frequency of patients receiving allogenic red blood cells (n=25 vs. 34). In the RHA-CABG group the patients were on ventilator significantly shorter time (5.7 h (018) vs. 7.9 (317)) (long-term ventilation not included), and the CK and brain CK (CKB) levels were significantly lower compared to those of the control group (CK=455 (1271245) vs. 909 (1793642) µg/l; (CKB=17.3 µg/l (652) vs. 29.2 (652)). No significant difference was found in the number of patients having a postoperative level of se-creatinine >200 µmol/l (n=1 vs. 4), as no difference was found between the groups in terms of length of hospitalization (5.7 days (312) vs. 6.2 (421)).
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In the control group, one patient died 7 days postoperatively from untreatable atrial fibrillation, universal intestinal ischaemia and sepsis. Three patients suffered from major cerebral complications after the operation. One patient had facial palsy and hemi weakness; one had severe cerebral damage and never regained consciousness. Additionally, one patient suffered from hemiparesis due to a hypotensive crisis 2 days after surgery. Forty-six patients (92%) were discharged from the hospital in good health.
3.5. Description of RHA-CABG group at 3-month follow up
Three months postoperatively one patient suffering from severe diabetes mellitus was admitted again due to re-angina. An angiography revealed an occluded graft and a stent was inserted. Preoperatively 20% of the patients were medicated with beta-blockers/ACE inhibitors, nitrates, and calcium antagonists. After 3 months, none of the patients received three-drug anti-anginal medication. Preoperatively 44% were medicated for anti-angina with two drugs; this number was reduced to 16% after 3 months.
Forty patients responded to a questionnaire. Out of these, 38 patients described their situation as better/almost no symptoms, and two reported unchanged. Two patients had died, and eight did not respond.
| 4. Discussion |
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4.1. Postoperative outcome in terms of safety and complications
We found that MAP decreased significantly compared with baseline values 2 min after pump start, but normalized within 8 min. The CO and HR remained constant. The SvO2 saw a significant decrease during pump time but not to critically low values and the SvO2 normalized shortly after termination of RHA. PAP, CVP and LAP increased during RHA. This indicates that the left ventricle is not fully able to overcome the workload in a displaced position. Evidently, a pump flow of 2 l/min was not an inadequate support of the right ventricle, since CVP increased. However, an increase of the pump flow will cause the left atrium to overload and the LAP and PAP to further increase, thus straining the left ventricle. This might be due to mitral valve insufficiency caused by the kinking of the heart. Surgery was completed on the majority of the patients (80%) without inotropic support, and indicating that the circulatory system is able to adjust to the situation. For 18% of the patients it was necessary to use a slight stimulation with a beta-agonist to maintain acceptable values of MAP, SvO2 and CO.
Twelve patients (24%) had short episodes (seconds) of atrial or ventricular fibrillation during surgery. This phenomenon may be related to the surgery on a non-occluded artery on which the snare is tightened around the vessel proximal to the stenoses. In this way, the myocardium suffers from ischaemia, which may give rise to arrhythmia. In all cases but one sinus rhythm was achieved either spontaneously or by a single defibrillation. Even though CABG with RHA on patients with 3VD entails short episodes of compromised haemodynamics, it does not seem to affect the overall postoperative outcome compared to the patients in the control group patients operated on with HLM.
4.2. Postoperative bleeding
The patients in the RHA-CABG group had significantly less chest drain bleeding, although there was no significant difference of frequency of re-operation for bleeding. There was no difference between the two groups regarding the need for allogenic blood transfusion, a confirmation of data from Nader et al. [20].
However, the use of RHA implicates less contact by blood to foreign surfaces, less haemodilution, no autotransfusion from suctions from the operative field, and less heparinization. This approach is likely to retain the platelet function and coagulation ability of the blood postoperatively as compared to patients operated on using cCABG.
4.3. Cardiac complications
The control group had a significantly higher peak of plasma level of CK and CKB postoperatively than the RHA-CABG group, indicating a higher degree of diffuse myocardial damage. Three control group patients suffered from perioperative acute myocardial infarction compared to one patient in the RHA-CABG group (not significant). In the control group, 16 patients were medicated for postoperative atrial fibrillation compared to nine in the study group (not significant). These indicators seem to point in the same direction, that RHA-CABG is less traumatic to the myocardium than the cCABG procedure.
4.4. Complications to the CNS
To perform a cCABG, aortic cross-clamping and cannulation of the aorta is necessary. Patients with ischaemic heart disease tend to have some degree of atherosclerosis in the aorta. Manipulation of the aorta involves the risk of tear of the atherosclerotic debris, which may subsequently end up as an embolus in the brain or other vital organs [21]. In our study, three control group patients had severe neurological damage while in hospital. None of the patients in the study group showed damage to the CNS (no significant difference). Svenmarker et al. [19] report cognitive dysfunction in 50% of the cCABG cases; some of this might be due to the anaesthesia and the general stress on the body. Diegeler et al. [22] proved in a randomized study (n=40) between OPCAB/cCABG that, 1 week postoperatively, 90% of the cCABG had postoperative impairment of the cognitive function versus no impairment in the off-pump group. Their findings confirm the association between cerebral microembolism and impairment in postoperative cognitive tests.
CABG with RHA is not a completely pump-less approach but the cannulation sites are both on the right side. Accordingly, the risk of systemic embolization caused by the perfusion system is significantly reduced.
4.5. Limitations of the study
The study was a feasibility study including 50 patients. After closing the study, we formed a control group according to specific criteria. Had the groups been chosen by random, the question of a true difference of the surgical approach might have been answered. A discussion of any difference in the quality of the anastomosis between the two groups is only possible if angiographies are performed postoperatively. This, however, was not the perspective of this study. The same consultant operated on all patients in the RHA-CABG group. This gives a one-surgeon experience, which can be defended by the fact that this is a new technique, but more surgeons in the control group probably results in more scattered data making the comparison difficult.
Accordingly, this study can be considered as a valid justification for conduction of a large-scale prospective randomized clinical controlled study.
4.6. Conclusion
The present non-randomized study demonstrates a significant difference between the RHA-CABG group and the control group in terms of postoperative bleeding, myocardial enzyme release, and postoperative ventilation time. Other data might indicate a positive trend for the RHA approach as regards CNS protection, reduced frequency of perioperative AMI, and a reduced requirement for allogenic blood products transfusion. We conclude that revascularization on patients with 3VD by means of the beating heart procedure and RHA is a safe technique, which will provide high-quality results in comparison to what can be achieved by cCABG.
| Acknowledgments |
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| References |
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