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Ann Thorac Surg 2002;74:S1318-S1322
© 2002 The Society of Thoracic Surgeons
a Clinic for Heart Surgery, Heart Center, University of Leipzig, Leipzig, Germany
* Address reprint requests to Dr Doll, Heart Center, Clinic For Cardiac Surgery, University of Leipzig, Strumpellstrasse 39, 04289 Leipzig, Germany.
e-mail: dolln{at}medizin.uni-leipzig.de
Presented at the Eighth Annual Cardiothoracic Techniques and Technologies Meeting 2002, Miami Beach, FL, Jan 23–26, 2002.
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Abstract |
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METHODS: We reviewed prospectively gathered data on all patients who were undergoing first-time AVR, with or without replacement of the ascending aorta, over a 1-year period at our institution.
RESULTS: A total of 176 patients underwent minimal access and 258 underwent conventional AVR. The conventional group was older, had more incidence of diabetes, and more aortic stenosis (all p < 0.05). Eight minimal access AVR patients (2%) required conversion to a complete sternotomy. Minimal access AVR patients had longer aortic crossclamp times than conventional AVR patients (60 ± 22 vs 55 ± 23 minutes, p = 0.03) but similar CPB times (93 ± 38 vs 88 ± 42 minutes, p = 0.20). Postoperative creatine kinase–MB levels were similar for the two groups. Total postoperative blood loss was significantly lower in the minimal access group, and these patients received less red blood cell and fresh frozen plasma transfusions. Minimal access AVR patients were less likely to have postoperative respiratory failure (3% vs 10%); they had shorter intensive care unit stays (3.7 ± 5.4 vs 4.5 ± 5.6 days) and shorter hospital stays (10 ± 6 vs 12 ± 7 days, all p < 0.05). Mortality was lower in patients undergoing minimal access surgery (3% vs 9%, p = 0.008) by univariate analysis. Multivariate predictors of mortality were age, hypertension, and CPB time.
CONCLUSIONS: Although patient selection may have influenced some of the observed differences between our patient groups, minimal access surgery appears to be associated with decreased morbidity and resource use when compared to conventional AVR.
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Introduction |
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New surgical techniques require repetition and experience before optimal results are achieved [8]. The pattern of knowledge and proficiency acquisition is often referred to as the "learning curve." Our institution started performing minimal access valve surgery in 1997 [9, 10]. The purpose of this study was to compare outcomes in patients undergoing minimal access versus conventional AVR in a center with experience in minimal access techniques.
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Material and methods |
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Our exclusion criteria for minimal access AVR were significant coronary artery disease, renal failure, and preoperative cardiogenic shock or cardiopulmonary resuscitation. To make the two study groups comparable, we therefore excluded these same patients from the conventional AVR group. We also excluded patients undergoing reoperations and concomitant surgical procedures, with the exception of replacement of the ascending aorta.
The final analysis included 176 patients undergoing minimal access AVR and 258 patients undergoing conventional AVR. It should be stressed that the decision about whether patients received a minimal access or conventional procedure was entirely at the discretion of the attending surgeon. The percentage of patients who received a minimal access procedure, for those surgeons who performed more than 10 AVR operations during the study time period, ranged from 8% to 93%.
Perioperative management
A complete median sternotomy and standard surgical techniques were used for the conventional AVR group. Unless otherwise stated, the following methods pertain to the minimal access AVR group only.
External defibrillator pads were placed before draping. An incision was made over the sternal angle and extended inferiorly for 5 to 6 cm. The partial sternotomy was performed using a technique advocated by several other investigators [2, 4, 5, 11]. The J sternotomy approach was used in the majority of patients, with some receiving an inverted T sternotomy. The manubrium and upper sternum were divided with an oscillating saw and the sternotomy was extended as a J into the right third or fourth intercostal space, or as a T into the right and left intercostal spaces. Care was taken not to injure the mammary arteries or to enter the pleural spaces. Pericardial stay sutures were used to elevate the heart and great vessels.
After systemic heparinization, a straight, wire-reinforced arterial cannula (Edwards Fem-Flex; Irvine, CA) was inserted into the ascending aorta. An oval-shaped, wire-reinforced, two-stage venous cannula (Medtronic Oval VC2; Grand Rapids, MI) was inserted into the appendage of the right atrium. The proximal end of the venous cannula was brought out through a subxiphoid incision to minimize materials in the operative field. The subxiphoid incision was used at the end of the operation as a chest tube insertion site.
Cardiopulmonary bypass (CPB) was instituted with vacuum assistance (-30 to -50 mm Hg) to achieve a flow of 2.0 to 2.5 Lmin-1m-2. The CPB circuit consisted of a hard-shell venous and cardiotomy reservoir, a membrane oxygenator, an arterial line filter, and roller pumps. Systemic temperature was lowered to 33°C at the start of CPB and then rewarmed to 36°C at the end of CPB.
Our method of myocardial protection was identical in minimal access and conventional AVR patients. After application of the aortic crossclamp, 1.5 L of cold Bretschneider crystalloid cardioplegia was administered into the aortic root or, if significant aortic insufficiency was present, directly into the coronary ostia. Further doses of cardioplegia were given if the crossclamp time was prolonged (>90 minutes). Blood cardioplegia, containing potassium chloride and magnesium sulfate, was used only in patients with significant ventricular dysfunction. Venting of the left ventricle was achieved through the right superior pulmonary vein or the main pulmonary artery, according to surgeon preference.
Standard surgical techniques were used to replace the aortic valve in both study groups. No special surgical equipment was necessary to replace the aortic valve in the minimal access group.
Carbon dioxide was insufflated into the surgical field while the aorta and heart were open in patients undergoing minimal access AVR. Deairing was achieved by filling the heart with blood before tying the aortotomy suture, by applying gentle suction to the ascending aorta before and after crossclamp release, and by sticking a needle directly into the roof of the left atrium, if necessary.
Statistical analysis
All statistical analyses were performed with SAS version 8.1 (SAS Institute, Cary, NC). Data are displayed as percentages for categorical variables and as means ± standard deviations for continuous variables unless otherwise stated. Postoperative outcomes were defined according to the guidelines for reporting morbidity and mortality after cardiac valvular operations [12]. Comparisons of group proportions were made with 
2 or Fisher’s exact tests where appropriate. Comparisons of group means were made with t or Wilcoxon rank sum tests where appropriate. Stepwise logistic regression analysis was used to determine the independent predictors of mortality. Statistical significance was considered at the level of p less than 0.05.
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Results |
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Intraoperative characteristics of the two groups of patients are displayed in Table 2. The types of valves inserted were similar for the two groups of patients, as was the percentage of patients undergoing concomitant replacement of the ascending aorta. Aortic crossclamp and total operating times were significantly longer in the minimal access group, but CPB times were not. Conventional AVR patients were more likely to require defibrillation after release of the aortic crossclamp, but the average number of defibrillations required was not significantly different between groups. The total energy required for defibrillation was higher in the minimal access group (306 ± 406 vs 56 ± 153 Joules, p < 0.001), because external defibrillation was usually used in these patients.
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Comment |
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TopAbstractIntroductionMaterial and methodsResultsCommentReferences |
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Minimal access AVR has been described by several investigators over the last few years, with some reporting significant advantages over conventional AVR [1–5], some finding minimal or no advantage [13, 14], and some describing significantly worse outcomes than with surgery through a full sternotomy [15, 16]. A possible explanation for the discrepancy in results is the level of experience of the centers involved. Minimal access surgery is more technically demanding than conventional cardiac surgery. The "learning curve" of knowledge and skill acquisition for new surgical techniques requires that a minimum number of procedures be performed before optimal results are achieved [8].
In 1997 we introduced minimal access surgery at our institution [9, 10, 17]. The current study was undertaken to determine whether minimal access AVR offers benefits over conventional AVR in a center that is experienced in minimal access techniques. We examined all patients undergoing isolated AVR, with or without replacement of the ascending aorta, at our institution over a 1-year period. We excluded patients with significant coronary artery disease, renal failure, or cardiogenic shock because these are our exclusion criteria for minimal access surgery.
We found that minimal access and conventional AVR patients were similar in regard to preoperative characteristics, with the exception that conventional AVR patients were older and were more likely to have diabetes and aortic stenosis. Such differences were likely due to surgeon patient selection, since type of operative procedure performed was entirely at the discretion of the surgeon. This patient selection may have also affected some of our observed differences in patient outcomes.
Our comparison of intraoperative variables revealed significantly longer operating times in the minimal access group, reflecting the increased technical demands of this procedure. However, the increase in times was small—an average of 5 minutes for aortic crossclamping and 14 minutes for the entire operative procedure. The clinical significance of such modest increases in operating times is unclear.
One of the concerns about minimal access AVR is the capability for deairing the heart the end of the procedure [18]. Although deairing of the heart is more difficult than through a full sternotomy, we did not observe any increased clinical sequelae of air emboli in the patients undergoing minimal access AVR. That is, we failed to detect any significant increases in ventricular fibrillation, CK-MB release, delirium, or stroke. We believe that meticulous deairing can be achieved through a ministernotomy. We also believe that flooding of the operative field with carbon dioxide may be beneficial, since carbon dioxide is more soluble in blood than room air.
Postoperatively, we found that minimal access AVR patients had less blood loss than did conventional AVR patients and required less red blood cell and fresh frozen plasma transfusions. It should be noted that our threshold for blood transfusion (hemoglobin <8 g/dL) was the same for the two groups of patients. Several other investigators have also described decreased blood loss and transfusion requirements for minimal access AVR [1, 3, 19]. The ministernotomy approach may lead to lower blood loss because of decreased surgical trauma to the tissues.
We also found that the risk of respiratory failure was lower after minimal access AVR, and that ICU and hospital lengths of stay were shorter. Several other studies have also described these findings [1, 4, 20]. Decreasing lengths of stay is an important aspect of resource use, since ICU and hospital times are the major determinants of cost after cardiac surgery [21]. We also found that patients were quicker to mobilize after the ministernotomy approach, an observation that agrees with those in other surgical centers [3, 4, 20]. Minimal access AVR patients may ambulate faster because of decreased pain from the incision or shorter duration of chest tube drainage [1, 4, 9].
Finally, univariate analysis revealed that minimal access AVR patients had a lower risk of mortality than conventional AVR patients. However, when we accounted for other risk factors (ie, age, hypertension, and CPB time), minimal access surgery was no longer a predictor of survival. It is therefore likely that our observed difference in mortality rates between the two groups of patients was due to differences in patient selection.
In summary, minimal access through a partial sternotomy represents a significant shift in the approach to aortic valve surgery. Minimal access AVR is more technically demanding than conventional AVR and takes slightly longer to perform. Although the retrospective nature of our study is subject to patient selection bias, we can conclude that minimal access AVR is at least as safe as conventional surgery and may even lead to decreased morbidity and resource use. Once proficiency is acquired, the minimal access approach may be the procedure of choice for AVR.
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References |
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This article has been cited by other articles:
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  A. Yilmaz, A. Rehman, U. Sonker, and G. T.L. Kloppenburg Minimal access aortic valve replacement using a minimal extracorporeal circulatory system. Ann. Thorac. Surg., March 1, 2009; 87(3): 720 - 725. [Abstract] [Full Text] [PDF]
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 M. L. Brown, S. H. McKellar, T. M. Sundt, and H. V. Schaff Ministernotomy versus conventional sternotomy for aortic valve replacement: a systematic review and meta-analysis. J. Thorac. Cardiovasc. Surg., March 1, 2009; 137(3): 670 - 679.e5. [Abstract] [Full Text] [PDF]
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K.-M. Chiu, C.-C. Wu, M.-J. Wang, C.-W. Lu, J.-S. Shieh, T.-Y. Lin, and S.-H. Chu Local infusion of bupivacaine combined with intravenous patient-controlled analgesia provides better pain relief than intravenous patient-controlled analgesia alone in patients undergoing minimally invasive cardiac surgery. J. Thorac. Cardiovasc. Surg., June 1, 2008; 135(6): 1348 - 1352. [Abstract] [Full Text] [PDF]
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B. Murtuza, J. R. Pepper, R. DeL Stanbridge, C. Jones, C. Rao, A. Darzi, and T. Athanasiou Minimal Access Aortic Valve Replacement: Is It Worth It? Ann. Thorac. Surg., March 1, 2008; 85(3): 1121 - 1131. [Abstract] [Full Text] [PDF]
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K. Ak, T. Aybek, G. Wimmer-Greinecker, F. Ozaslan, F. Bakhtiary, A. Moritz, and S. Dogan Evolution of surgical techniques for atrial septal defect repair in adults: A 10-year single-institution experience J. Thorac. Cardiovasc. Surg., September 1, 2007; 134(3): 757 - 764. [Abstract] [Full Text] [PDF]
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 M. Glauber, A. Farneti, M. Solinas, and J. Karimov Aortic valve replacement through a right minithoracotomy MMCTS, November 10, 2006; 2006(1110): 1826. [Abstract] [Full Text] [PDF]
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