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Ann Thorac Surg 2002;74:1537-1543
© 2002 The Society of Thoracic Surgeons
a Department of Thoracic and Cardiovascular Surgery, Johann Wolfgang Goethe University, Frankfurt, Germany
b Department of Anesthesiology, Intensive Care, and Pain Therapy, Johann Wolfgang Goethe University Frankfurt, Frankfurt, Germany
Accepted for publication June 20, 2002.
* Address reprint requests to Dr Dogan, Department of Thoracic and Cardiovascular Surgery, Johann Wolfgang Goethe University Frankfurt, Theodor Stern Kai 7, 60590 Frankfurt, Germany.
e-mail: s.dogan{at}em.uni-frankfurt.de
| Abstract |
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METHODS: In a prospective randomized study, 40 patients who required multivessel CABG were assigned to either conventional CABG via complete median sternotomy (group A) or port access CABG via minithoracotomy (group B). Control angiograms were performed in group B only. In addition, patients underwent neuropsychological testing after the operation. CK, CK-MB, and Troponin T levels were documented. S-100B protein and neuron-specific enolase (NSE) served to quantify cerebral injury. The terminal complement complex (C5b-9) and myeloperoxidase concentrations were determined to analyze inflammatory whole-body response after CPB.
RESULTS: There was no mortality. One patient suffered a retrograde aortic dissection immediately after onset of CPB, but had an uneventful postoperative course after surgical repair. Troponin T and CK-MB showed no difference between groups. CK and myoglobin were significantly higher in the minimally invasive cohort. Changes in complement activation (C5b-9) and myeloperoxidase during CPB markers of the whole-body inflammatory response were similar in both groups. S-100B concentrations in the port access group were significantly higher, whereas NSE levels were similar in both groups. Both groups did not display any significant difference in neuropsychological testing.
CONCLUSIONS: Minimally invasive multivessel CABG via minithoracotomy using port access technology is feasible and safe. Though prolonged operating and CPB times with significantly higher S-100B concentrations were observed in group B, equivalent myocardial and cerebral protection and similar whole-body inflammatory response were documented.
| Introduction |
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The use of the port access technique became indispensable for totally endoscopic cardiac operations because computer-enhanced telemanipulation systems finally facilitated totally endoscopic cardiac surgery [1114].
This study compares conventional coronary artery bypass grafting (CABG) with port access CABG via a left anterior small thoracotomy in patients requiring surgical multivessel revascularization. Clinical, neuropsychological, and angiographic outcomes were studied, as well as parameters of myocardial and cerebral protection and parameters of inflammatory response to evaluate potential differences in pathogenicity of CPB.
| Patients and methods |
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Port access CABG
The Heartport Port Access system (Redwood City, CA) was used for this procedure [1]. All patients had Doppler ultrasound of femoral vessels before randomization to rule out relevant calcification of the femoral artery cannulation site. Duplex sonography was conducted to detect potential stenoses of peripheral arteries. Transthoracic echocardiography was performed to evaluate the ascending aorta. Only after exclusion of relevant peripheral and central vascular disease, randomization for the study was carried out. Intraoperatively, the femoral artery was reassessed by palpation as well as the thoracic aorta by transesophageal echocardiography (TEE). Before skin incision, a pulmonary vent as well as a coronary sinus catheter were introduced through the jugular vein and advanced into their proper position under echocardiographic guidance. In single lung ventilation, the left internal thoracic artery (ITA) was dissected after a minithoracotomy approach in the fourth intercostal space. Meanwhile, the vein grafts were harvested. After dissection of the left groin, the femoral vessels were cannulated. A long venous drainage cannula was advanced into the right atrium. For the endoarterial return, the left femoral artery was cannulated in open technique and a guide wire was advanced into the descending aorta. The distal femoral artery was occluded during CPB. After onset of CPB, the endoaortic balloon clamp was guided into the ascending aorta. All intravascular maneuvers were performed under echocardiographic control. Proximal anastomoses were performed first through the minithoracotomy incision on the beating but decompressed heart after partial clamping of the aorta [15, 16]. Then, the intraaortic balloon was insufflated and antegrade as well as retrograde cold blood cardioplegia was administered. Distal anastomoses were performed on the arrested heart by exposing the target anastomotic site with sponges. After weaning from CPB, the femoral cannulas were removed and the thoracotomy was closed. Before transfer to the intensive care unit (ICU), the ventilation tube was changed.
Heparin (300 U/kg) was administered for systemic anticoagulation in both groups. CPB was instituted with a Jostra Quadrox capillary membrane oxygenator and tubing set (Jostra Medizintechnik AG, Hirrlingen, Germany). All patients were cooled to a rectal temperature of 32°C.
Intraoperative and clinical assessment
Bypass time, aortic cross-clamp time, and time of the operation were documented. The latter one is defined as total time in the operating room including induction of anesthesia. Further times of mechanical ventilation, postoperative blood drainage (24 hours), ICU stay, and hospital stay were analyzed. Patients in group B received invasive coronary angiograms before discharge to assess anastomotic quality and graft function. In group A, anastomotic quality and graft function were not specifically examined, because open sternotomy and arrested heart cases are considered to be the gold standard for coronary anastomoses.
Biochemical parameters
In addition to CK and CK-MB, troponin T levels were documented to quantify myocardial damage (Enzymun-Test Troponin T; Boehringer Mannheim Immundiagnostica, Mannheim, Germany). Myoglobin was analyzed to determine the quantity of limb ischemia and reperfusion damage after femoral cannulation with an immunoassay (Beckmann, Essen, Germany).
S-100B protein and neuron-specific enolase (NSE) served to quantify cerebral injury. Protein S-100B was determined in serum specimens using a sensitive luminometric assay (Byk-Sangtec, Lund, Sweden), which selectively measures the beta subunits (present in glial and Swann cells) [17]. NSE is a sensitive indicator of neuronal cell destruction clinically evident as stroke [18] and was determined with an enzyme-linked immunosorbent assay (ELISA) (Boehringer Mannheim Immundiagnostica).
The terminal complement complex (C5b-9) and myeloperoxidase (MPO) concentrations were determined to quantify the inflammatory whole-body response of CPB [19]. C5b-9 was analyzed with an ELISA (Gambro, Hechingen, Germany) and MPO with an ELISA (Calbiochem-Navibiochem, San Diego, CA).
Neuropsychological testing
Patients underwent neuropsychological testing 1 day before, 5 days after, and 2 months after the operation. Testing required about 1 hour and was performed on the ward or the outpatient clinic, respectively.
The test battery used was in accordance with the "Statement of Consensus on Assessment of Neurobehavioral Outcomes after Cardiac Surgery" [20]. This includes the Block Design Test (problem-solving strategies and recognition and analysis of forms), the Trail Making Test (cognitive achievement at speed), and the Digit Span Test (short-term memory and memory of figures). In addition, the Benton Test (visual constructive abilities), the d2 Test (concentration and care at speed), and the Becks Depression Inventory (quantifying state of mood, motivation, self esteem, and vitality) were employed. Testing was carried out by the same two physicians.
Statistical analysis
Statistical analysis was carried out using the StatView software package (Abacus Concepts, Berkeley, CA) for repeated assessment of neuropsychological test scores and biochemical values. Data are presented as means ± standard deviation of means. Comparison between groups was performed using the Mann-Whitney U test. Differences were considered significant when the p value was below 0.05. Spearman-Rank-Test was used to correlate neuropsychological testing results with laboratory results, and CPB time with S-100B concentrations.
| Results |
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| Comment |
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This leads to an increasing interest in reevaluation of this technique. Testing of biochemical parameters such as parameters for myocardial tissue damage, skeletal muscle damage, brain damage, and inflammatory response [19] were conducted by our group to justify further application of the port access technique.
CPB using the port access cannulation system is a complex method in which venous and arterial cannulation and handling of the endoaortic balloon may be difficult in regards to placement and migration [24, 25]. The risk of retrograde aortic dissection constitutes a serious threat for the patient [26]. In our overall institutional experience of more than 150 port access cases, the aortic dissection cited in group B was the only dissection that occurred. In these cases of aortic dissection, a high mortality is reported [21]. Therefore, careful preoperative evaluation of femoral vessels (size, quality of vessel wall at cannulation site) by doppler and duplex ultrasound along with pre- and intraoperative assessment by transthoracic and transesophageal echocardiography, respectively, is necessary to identify candidates who are at risk for dissection and thus not suitable for port access surgery. Of course, a patient displaying severe medionecrosis will always stay undetected. In addition, the perfusionist has to monitor the arterial line pressure carefully. Early detection is crucial; therefore, constant TEE control during and after port access system placement is mandatory. Immediate weaning from CPB, instant implementation of antegrade perfusion, and immediate surgical repair is essential to master such a complication.
Even though suturing for proximal and distal anastomoses was performed under technically demanding circumstances in the minithoracotomy group, postoperative angiography did not show any compromise in surgical quality. Except for longer operating times in group B, which are due to the small-access approach, all patients had a good clinical outcome, including the 1 with the aortic dissection.
Postoperative treatment on the ICU was similar for both groups of patients. Applying the same extubation criteria to both cohorts, patients in group B had significantly longer ventilation times. This may be due to single-lung ventilation and a prolonged CPB time in this group. It also has to be considered that 1 patient of group B suffered a severe pneumonia and had to be mechanically ventilated for 127 hours.
A mild increase in troponin T (peak 0.53 µg/L in group B vs 0.64 µg/L in group A) and CK-MB (peak 17 U/L in group B vs 15 U/L in group A) concentrations after cardiac arrest were documented in the conventional as well as in the minimally invasive cohort. In our study, cross-clamp time has been comparable in both groups. No significant differences in troponin T and CK-MB levels were found between groups. This shows that myocardial protection is sufficient in using port access technology.
Significantly higher CK and myoglobin concentrations after CPB were documented in the minimal invasive cohort and were interpreted as consequences of partial lower limb ischemia due to femoral cannulation. Whether additional musculoskeletal trauma caused by the thoracotomy adds to elevated CK and myoglobin levels remains open. Because the length of incision was only 7 cm on average and the muscle was mainly divided parallel to the fibers, we believe that the amount of muscle trauma from the thoracotomy is of minor relevance. Clinically, no serious reperfusion syndromes were detected in hypoperfused limbs.
Levels of C5b-9 and MPO were elevated in both groups without a significant difference. This indicates a similar reaction of these mediators between groups, although CPB time was markedly prolonged in the minimally invasive cohort. Higher numbers of intravascular cannulas and catheters necessary using port access technology did not cause a difference in inflammatory markers.
Longer CPB times, the potential risks of balloon placement, and retrograde blood flow are making this technique especially prone to cerebrovascular incidents [25, 27]. S-100B was found to be four times higher in the port access group. This protein is a marker of blood-brain barrier damage [18, 27]. Thus, cerebral swelling can be detected after use of CPB [28], and is part of the inflammatory whole-body response due to blood-surface and blood-air contact. The longer CPB times certainly contribute to this findings [29], but cannot explain this pronounced increase of S-100B levels after release of the aortic cross-clamp. We could not find any correlation between CPB time and peak S-100B levels in either group.
We believe that higher S-100B levels in the port access group are mainly caused by retrograde aortic blood flow. As a further potential cause, endoaortic balloon placement seems to be an unlikely source for microemboli, because none of the patients in the port access group displayed aortic plaques on echocardiography. Recently, publications showed a dependency of S-100B levels on different methods of intraoperative blood processing [29, 30]. Because this was handled completely equally between groups and even the postoperative amount of chest tube drainage did not differ, no influence by this matter should have occurred.
As a very sensitive, CPB-independent marker for neuronal cell lesions, NSE concentrations were measured [31]. Although there is a theoretical risk for focal neurologic injury due to retrograde perfusion in port access technique, NSE levels did not differ between groups. The isolated increase of S-100B underlines our assumption that increased blood-brain barrier damage in group B is due to microemboli generated by retrograde blood flow in the abdominal and descending thoracic aorta.
No clinically detectable neurologic deficit occurred. Though two neuropsychological tests showed significant differences before and after CPB within groups A and B, neither of the neuropsychological tests yielded significant results between the port access and the conventional group. These biochemical and neuropsychological results demonstrate that damage of the blood-brain barrier is reversible and elevation of biochemical markers of neurologic injury only expresses a subclinical deficit.
The present study has the shortcoming of a small sample size. Because multivessel revascularization via the LAST approach using port access technology is a demanding procedure, also necessitating a great amount of personal resources, large numbers cannot be achieved easily. We do believe, though, that tendencies shown by randomized trials with small patient numbers are still of scientific value, taking these issues into account.
Safety and feasibility of port access technology supporting minimally invasive bypass grafting via a minithoracotomy are shown in this preliminary study. Though prolonged operating and CPB times as well as significantly higher S-100B concentrations are evident in the port access group, no differences in myocardial and cerebral protection and similar inflammatory whole-body response were found. This advocates for the use of port access technology for a totally endoscopic cardiac surgery program.
| References |
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