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Ann Thorac Surg 2005;79:492-498
© 2005 The Society of Thoracic Surgeons

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Original article: Cardiovascular

Minimally Invasive Port Access Versus Conventional Mitral Valve Surgery: Prospective Randomized Study

Department of Thoracic and Cardiovascular Surgery, Johann Wolfgang Goethe University, Frankfurt am Main, Germany

Accepted for publication August 5, 2004.

^* Address reprint requests to Dr Dogan, Department of Thoracic and Cardiovascular Surgery, Johann Wolfgang Goethe University, Theodor Stern Kai 7, 60590 Frankfurt am Main, Germany (E-mail: s.dogan{at}em.uni-frankfurt.de).

	Abstract

Top Abstract Introduction Patients and Methods Results Comment References

 
BACKGROUND: We compared the port access mitral valve surgery with the conventional procedure through median sternotomy in a prospective randomized study.

METHODS: Forty elective patients with mitral valve disease were prospectively randomized to undergo minimally invasive (group I) or conventional (group II) mitral valve operation. The patients of group I had limited access through right small anterior thoracotomy and a femorofemoral cardiopulmonary bypass system using the endoclamp technique. To assess the efficiency and safety of the procedure, intraoperative and postoperative clinical data and markers of myocardial, cerebral, and lower limb ischemia were collected. Pulmonary function tests were performed to compare the preservation of pulmonary function. Neuropsychological tests were conducted for quantification of neurological and cognitive disorders.

RESULTS: Mitral valve reconstructions were performed in 28 patients (70%) in both groups. Intraoperative procedure-associated problems were experienced in 9 patients (45%) in group I, and 6 of them (30%) had to be converted to direct transthoracic aortic clamping. Markers of myocardial and cerebral damage as well as pulmonary and neuropsychological tests did not show statistically significant difference between groups.

CONCLUSIONS: The minimally invasive port access technique for mitral valve surgery can be done with similar clinical safety as procedures through median sternotomy. The problems with endoclamping have forced us to change our practice to the more simple and economic transthoracic aortic clamping technique.

	Introduction

Top Abstract Introduction Patients and Methods Results Comment References

 
Conventional mitral valve surgery (MVS) improves long-term survival with acceptable morbidity and mortality [1, 2]. Thus, it has been established as a procedure of choice for treatment of severe mitral valve disease [3].

Yet, the interest in minimally invasive MVS is continuing to evolve, with more centers reporting encouraging results [4–7]. This interest is primarily driven by the anticipated benefit for the patients, including achievement of the same quality of treatment with reduced operative mortality and morbidity, reduced pain, hospital stay and earlier return to full activities, superior preservation of the lung function, and improved cosmetics. In addition, the surgical quality must not be compromised and an equally good cerebral and myocardial protection as well as satisfactory peripheral perfusion must be guaranteed.

Cardiopulmonary bypass (CPB) cannot be avoided during intracardiac procedures. Therefore, the trauma can be reduced by limiting the incision. Several limited access techniques have been described [8–11]; all of them aim at avoidance of full sternotomy and preservation of the integrity of the chest. However, besides being more technically demanding and more time-consuming, these approaches may impose problems with intraoperative myocardial and cerebral protection [6, 12, 13].

We hypothesized that minimally invasive port access MVS is as safe and efficient as the conventional procedure through median sternotomy in terms of clinical results, and myocardial and cerebral protection.

	Patients and Methods

Top Abstract Introduction Patients and Methods Results Comment References

 
Forty consecutive adult patients with severe mitral valve disease scheduled for elective mitral valve operation were prospectively randomized over a period of 1 year to undergo either minimally invasive surgery (group I, n = 20) or operation through median sternotomy (group II, n = 20). The procedure for patients in group I had limited access through right anterior small thoracotomy and peripheral cannulation. The patients in group II had full median sternotomy and central cannulation for standard CPB. Exclusion criteria included hemodynamically significant coronary disease, internal carotid artery stenosis of greater than 70% luminal narrowing, bilateral external iliac or femoral artery stenosis, moderate or severe aortic valve disease and calcified ascending aorta. This study was approved by the ethics committee at our institution, and a written informed consent was obtained from every patient involved. Besides clinical results, primary end points included biochemical markers of myocardial and neurologic injury as well as neuropsychological tests.

The preoperative patient data from both groups are shown in Table 1. There was no significant difference between the groups in terms of preoperative status. Most of the patients were symptomatic (New York Heart Association [NYHA] class III) with a preserved left ventricular function. Pulmonary hypertension, defined as a systolic pulmonary pressure greater than 35 mm Hg, was the most common preoperative comorbidity.

The group I patients underwent a right anterior 5 to 7 cm thoracotomy through the fourth intercostal space. For port access (Heartport, Inc., Redwood City, CA) perfusion, the right femoral vessels were cannulated. Under transesophageal echocardiographic guidance, the endoaortic balloon catheter was advanced into the ascending aorta just proximal to the innominate artery. The catheter was used for aortic occlusion, aortic root venting, and antegrade delivery of cardioplegia through the central lumen. An endosinus catheter was not routinely used for retrograde administration of cardioplegia. The endopulmonary vent was introduced through the right internal jugular vein and advanced into the pulmonary artery. It was used for pulmonary artery venting and decompression of the right heart. After inverted T pericardiotomy just ventral to the right phrenic nerve, a left atriotomy was performed in the interatrial groove to expose the mitral valve. Core temperature was lowered to 28 to 30°C. Deairing was performed with a left atrial vent during the left atrial closure under increased pulmonary pressure, and through the aortic root. This was continued during reperfusion and weaning. Carbon dioxide was insufflated into the chest cavity using a Veress needle at a rate of 2 L/min.

For the group II patients a full median sternotomy was performed, and following systemic heparinization they underwent aortobicaval cannulation for standard CPB. After cross clamping of the aorta, intermittent cold blood cardioplegia infusion was administrated in antegrade fashion into the aortic root followed by retrograde infusion into the coronary sinus. The left atrium was opened at the interatrial groove and the mitral valve was exposed. The core temperature was brought down to 28 to 30°C. Deairing was performed through the apex of the left ventricle and the aortic root.

Mitral valve repair procedures were performed as described by Carpentier and coworkers [14, 15] and mitral valve replacement was carried out with preservation of the subvalvular apparatus [16]. A temporary right ventricular pacing wire was placed in all patients in both groups. Two senior surgeons performed all procedures

Clinical Assessment
Routine assessment included documentation of operative, CPB and cross-clamp times, as well as ventilation times, chest tube drainage, use of blood products, intensive care unit (ICU) stay and hospital stay. In addition, pulmonary function tests were conducted both 1 to 2 days preoperatively and on the sixth or seventh postoperative day. The recorded measurements included vital capacity (VC), forced vital capacity (FVC), and forced expiratory volume in first second (FEV₁). All intraoperative and postoperative complications were recorded. Morbidity and mortality is reported as currently recommended [17].

Assessment of Myocardial, Cerebral, and Lower Limb Ischemia
Biochemical markers were used in each patient for assessment of perioperative myocardial, cerebral, and lower limb ischemic injury. Blood sampling times for all markers except creatine kinase (CK) and CK-myocardial bound (CK-MB) fraction were before and after induction of anesthesia, after onset of CPB but before aortic cross-clamp, immediately before and 5 minutes after the release of the aortic cross-clamp, and at 1 hour, 24 hours, and 5 days after surgery.

For quantification of myocardial damage, CK, CK-MB fraction, and Troponin T and I the Enzymun-Test (Troponin T; Boehringer Mannheim Immundiagnostica, Mannheim, Germany) were used. Blood sampling times for CK and CK-MB were as follows: preoperative, immediately postoperative, and 8 and 24 hours postoperatively. The values of CK and Troponin T or I were considered increased if exceeding 80 U/L, 0.1 ng/mL, or 0.03 ng/mL, respectively.

Serum specimens were collected for determination of protein S-100B. Using a highly sensitive luminometric assay (Byk-Sangtec, Lund, Sweden), a selective measurement of the beta subunit (present in high concentration in glial and Schwann cells) was conducted [18]. Any value exceeding 0.15 µg/L was considered increased. Another marker of cerebral injury, the neuron-specific enolase (NSE) [19] was determined using the enzyme-linked immunosorbent assay test (Boehringer Mannheim Immundiagnostica). Normal values were considered if less than 10 µg/L.

Blood myoglobin level was used as a biochemical indicator of lower limbs ischemic injury. It was considered elevated if measured 70 ng/mL or above.

Neuropsychological Testing
Neuropsychological tests were performed 1 day before, and 5 days and 2 months after the operation. The test battery used was in accordance with the "Statement of Consensus on Assessment of Neurobehavioral Outcomes after Cardiac Surgery [20]. This included the Mosaik Test (problem-solving strategies), Benton Test (visual memory reproduction), Figures Repeating Test, Digit Span Test (figures and short-term memory), D2 Test (concentration and care at speed), and Beck's Depression Inventory (quantifying state of mood, motivation, self esteem, and vitality).

For purposes of this study, we have examined changes in individual performance over time as recommended [21]. Any postoperative score drop of more than 20% was considered a neuropsychological impairment.

Postoperative Anticoagulation Protocol
All patients were maintained on Coumarin for the first 3 months after the operation; the medication was discontinued in patients with sinus rhythm and patients that underwent reconstruction or bioprosthetic valve replacement. In patients with atrial fibrillation or mechanical valve replacement, however, oral anticoagulation was maintained.

Statistical Analysis
Data were presented as mean values ± standard deviation (SD), unless indicated otherwise. Differences of variables between both groups were calculated with the Mann-Whitney U test. Analysis was conducted using the StatView software package (SAS Institute Inc., Cary, NC) for repeated assessment of neuropsychological test scores and biochemical values. A p value of less than 0.05 defined statistical significance.

	Results

Top Abstract Introduction Patients and Methods Results Comment References

 
There was no hospital mortality in either group. All perioperative data are listed in Table 2. The operative and CPB times were longer in group I, whereas the cross-clamp times were slightly longer in group II; however the difference did not reach statistical significance. Most of the patients had mitral valve repair. Replacements were done in 6 patients (30%) in each group. Intraoperatively, the antegrade delivery of cardioplegia by the endoclamp has failed initially to provide sufficient cardiac arrest in 3 patients of the group I; therefore, direct cannulation of the coronary sinus for retrograde delivery of the cardioplegia was performed and successful cardiac arrest achieved. In 4 other patients of the same group, inadequate aortic cross-clamp was observed due to balloon migration (n = 3) or rupture (n = 1). In these patients, conversion to direct transthoracic aortic clamping was performed as described by Chitwood and coworkers [10]. The clamp (Scanlan International, Inc., Minneapolis, MN) was introduced through a 5-mm incision into the third right intercostal space at the anterior axillary line. In 2 other patients of the same group, the advancement of the endoaortic balloon catheter was impossible due to nonobstructive severe calcification of the common iliac artery. These patients were converted to the transthoracic aortic clamping technique as well. Therefore 6 of 20 patients (30%) required conversion of aortic clamping technique from failed endoclamping to direct transthoracic aortic clamping. There was not a single incisional conversion to median sternotomy.

The ventilation times, the ICU, and hospitalization times were shorter in group I; however, again, the difference did not reach statistical significance. We did not find statistical significance between the groups in terms of early extubation (postoperative ventilation time shorter than 6 hours), short ICU stay (less than 24 hours), and short hospital stay (less than 6 days).

There was no significant difference between the groups in terms of chest tube drainage or postoperative ventilatory function.

Complications in the postoperative period in group I included 1 patient who developed Pseudomonas aeruginosa-induced pneumonia that successfully resolved with antibiotics, 2 patients with inguinal lymphocele, and 1 patient with a groin hematoma, all of them without signs of wound infection. One patient in group II required implantation of a permanent pacemaker due to sustained ventricular bradycardia. A transient ischemic attack was observed in 1 patient in each group; the event resolved in 24 hours of occurrence. Left heart decompensation was also observed in 1 patient in each group; inotropic support was sufficient and no patient required insertion of intraaortic balloon. Other complications noted in group II included pericardial effusion requiring fenestration (1 patient), infection-free sternal instability that had to be restabilised (1 patient), rethoracotomy for surgical bleeding (1 patient), and pneumothorax in 1 patient. The other patients had an uneventful postoperative course.

The markers of myocardial injury in the perioperative period revealed similar values in both groups. The differences between the values rarely reached statistical significance. The rare occasions where the observed values between the groups reached statistical significance included increased Troponin T levels (Fig 1) in group II after onset of CPB but before aortic cross-clamp, increased Troponin I levels in group II 1 hour postoperatively (Fig 2). In addition, the CK levels were significantly increased in group I at all times; however, there was no statistically significant difference of the more specific CK-MB values at any time (Fig 3).

View larger version (8K): [in this window] [in a new window]   Fig 1. Perioperative changes in serum concentration of Troponin T. Blood sampling was performed (a) before and (b) after induction of anesthesia, (c) after onset of cardiopulmonary bypass but before aortic cross-clamp, immediately (d) before and (e) 5 minutes after the release of the aortic cross-clamp, and at (f) 1 hour, (g) 24 hours, and (h) 5 days after surgery. The difference observed reached statistical significance at time point c only. --•-- = group I; –•– = group II.

View larger version (8K): [in this window] [in a new window]   Fig 2. Perioperative changes in serum concentration of Troponin I. Blood sampling was performed (a) before and (b) after induction of anesthesia, (c) after onset of cardiopulmonary bypass but before aortic cross-clamp, immediately (d) before and (e) 5 minutes after the release of the aortic cross-clamp, and at (f) 1 hour, (g) 24 hours, and (h) 5 days after surgery. Statistical significance was reached at point f only. --•-- = group I; –•– = group II.

View larger version (6K): [in this window] [in a new window]   Fig 3. Perioperative changes in serum concentration of CK-MB. Blood sampling times for CK-MB were preoperative (a), immediately (b), 8 hours (c), and 24 hours (d) postoperatively. Statistical significance was reached at no point. The preoperative CK-MB (time point a) was below measurable levels. --•-- = group I; –•– = group II.

View larger version (7K): [in this window] [in a new window]   Fig 4. Perioperative changes of serum concentrations of neuron-specific enolase (NSE). Blood sampling was performed (a) before and (b) after induction of anesthesia, (c) after onset of cardiopulmonary bypass but before aortic cross-clamp, immediately (d) before and (e) 5 minutes after the release of the aortic cross-clamp, and at (f) 1 hour, (g) 24 hours, and (h) 5 days after surgery. Statistical significance was reached at points b, g, and h. --•-- = group I; –•– = group II.

View larger version (8K): [in this window] [in a new window]   Fig 5. Perioperative changes in serum concentration of S100B. Blood sampling was performed (a) before and (b) after induction of anesthesia, (c) after onset of cardiopulmonary bypass but before aortic cross-clamp, immediately (d) before and (e) 5 minutes after the release of the aortic cross-clamp, and at (f) 1 hour, (g) 24 hours, and (h) 5 days after surgery. Statistical significance was reached at point c only. --•-- = group I; –•– = group II.

Clinical signs of acute lower limb ischemia were not observed in the postoperative period in either group. However, myoglobin levels were significantly increased in group I in time interval from moments before the release of the aortic cross-clamp up to 24 hours postoperatively (Fig 6).

View larger version (9K): [in this window] [in a new window]   Fig 6. Perioperative changes in serum concentration of myoglobin. Blood sampling was performed (a) before and (b) after induction of anesthesia, (c) after onset of cardiopulmonary bypass but before aortic cross-clamp, immediately (d) before and (e) 5 minutes after the release of the aortic cross-clamp, and at (f) 1 hour, (g) 24 hours, and (h) 5 days after surgery. The difference reached statistically significant value at time points d, e, f, and g. --•-- = group I; –•– = group II.

	Comment

Top Abstract Introduction Patients and Methods Results Comment References

The minimally-invasive limited-access approach is reported to be more time consuming [5, 6, 8]. This is primarily due to the groin cannulation, balloon endoclamping, and more difficult exposure of the surgical field including areas such as coronary sinus and atrial roof as compared with the conventional technique. In our study, the difference in operating times was not statistically significant. The CPB and cross-clamp time were similar, reflecting the excellent visualization of the mitral valve itself from the right-sided approach.

The myocardial protection protocol in group II included both antegrade and retrograde delivery of cardioplegia, in contrast to the mainly antegrade route used in the group I patients. In the minimally invasive setting, percutaneous placement and advancement of coronary sinus catheter for retrograde cardioplegia is not always possible. No patient demonstrated clinical evidence of myocardial ischemia, or myocardial wall dysfunction with subsequent low cardiac output syndrome in our series. The analysis of myocardial injury markers in our study did not reveal statistically significant difference, indicating nearly identical quality of myocardial protection in both groups. However, 3 patients in group I did require additional retrograde cardioplegia administration due to incomplete occlusion of the aorta or failure to achieve satisfactory cardiac arrest with the endoclamp.

Satisfactory deairing in minimally invasive procedures may be difficult due to the limited access to the ascending aorta and the apex of the heart [13]. Mohr and coworkers have reported incomplete deairing of the heart and high incidence of postoperative confusion in their series [6]. In our experience, no permanent neurologic deficit was noted in either group. The analysis of markers of neurologic injury has failed to indicate clear superiority or inferiority of either method, as well. In addition, the results of the neuropsychological tests further support this conclusion, as the neurobehavioral performance of the patients returned to normal values at 2 months postoperatively. Schneider and colleagues [22] reported similar experience as they have also observed no significant differences in the embolic stress rates between patients operated on through port access or conventional surgery.

In group I we observed few typical complications of groin cannulation (hematoma, lymphocele), but no clinically apparent malperfusion of the limb. However, analysis of myoglobin levels indicated some subclinical injury to the peripheral muscle tissue in the second half of the procedure. Other potential drawbacks of the femoral cannulation, such as wound infection, arterial injury requiring reconstruction, aortic dissection, and atheroembolism [5, 23–25], were not experienced in our series. In concern for these groin cannulation-related complications, some groups have moved from peripheral to central cannulation for CPB [5, 23, 26].

Importantly, in group I we observed a high rate of intraoperative procedure-related problems. In 3 of 20 patients (15%) it was impossible to arrest the heart by antegrade cardioplegia delivery through the endoclamp. Further, in 4 patients (20%) either the balloon position in the ascending aorta was not stable or one balloon ruptured, so that a conversion of cardioplegic technique to transthoracic aortic clamping was necessary. In 2 other patients we could not advance the endoclamp even though retrograde perfusion was unremarkable. In summary, these technical handling problems of the endoclamp constitute a relevant disadvantage of this procedure, and in part account for the lack of widespread adoption of port access technique for the mitral valve procedures. Balloon migration is rare but troublesome complication. Proximal translocation may injure the aortic valve, whereas migration of the balloon distally may occlude the innominate artery [6]. Migration can be prevented by continuous monitoring of the balloon position with transesophageal echocardiography during the operation, but this modality is not optimal when the left atrium is open. In our experience, the single case of balloon rupture in group I occurred during placing a suture on the mitral annulus for mitral valve replacement.

In most problematic cases of this series, a simple cross-clamp and perfusion technique, as described by Chitwood and associates [10], was applied that avoided an incisional conversion to median sternotomy, which is reported to be between 3% and 12% [6, 27].

The rate of postoperative complications was similar in both groups. The types of the complications reflected the specific procedures undertaken. There were no cases of serious procedure-related complications like retrograde aortic dissection or acute purulent mediastinitis in either group. Transient ischemic attack was observed in 1 patient in each group; the neurologic deficit resolved within 24 hours. The other clinical measurements did not differ significantly between the patients, including ventilation and stay times, and chest tube drainage. These findings are in accordance with the reports from others [28, 29].

Postoperative pulmonary function was assessed in every patient and compared between groups. Even though superior postoperative values of the VC, FVC, and FEV₁ were noted in group I patients, this difference has not reached statistical significance and did not influence hospital stay.

The results of our study could not show significant advantages or superiority of the minimally invasive port access operative technique, which leaves the main advantage of improved cosmetics. However, the rate of intraoperative procedure-related problems was high. Due to the complexity of the port access technique and the costs we have changed the minimally invasive mitral valve approach to the more acceptable operation as described by Chitwood and coworkers [10], which is to use direct transthoracic aortic clamping.

Our study has certain limitations. The cumulative experience with the minimally invasive port access technique for MVS before randomization was suboptimal and some of the technical problems experienced in these series may be attributed to the learning curve. In addition, each group is rather small to detect any statistically significant differences in clinical as well as biochemical and neuropsychological variables.

	References

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