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Eur J Cardiothorac Surg 1999;16:647-652
© 1999 Elsevier Science NL

Minimally-invasive versus conventional aortic valve replacement – perioperative course and mid-term results

^a Klinik und Poliklinik für Thorax-, Herz- und Gefäßchirurgie, Westfälische Wilhelms-Universität Münster, Albert-Schweitzer-Strasse 33, 48149 Münster, Germany
^b Klinik und Poliklinik für Kardiologie und Angiologie, Westfälische Wilhelms-Universität Münster, Albert-Schweitzer-Strasse 33, 48149 Münster, Germany
^c Klinik und Poliklinik für Anästhesiologie und Operative Intensivmedizin, Westfälische Wilhelms-Universität Münster, Albert-Schweitzer-Strasse 33, 48149 Münster, Germany

Corresponding author. Tel.: +49-251-834-7401; fax: +49-251-834-8316

	Abstract

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion 5. Conclusions References

 
Objective: We performed a case-control-study to compare perioperative and mid-term results of minimally invasive with conventional aortic valve replacement. Methods: Between 8/96 and 7/97, 113 patients underwent isolated aortic valve replacement (minimally invasive: 29, conventional: 84) in our Department. Diagnosis, ejection fraction, pressure gradient/regurgitation fraction, age, gender and body-mass-index were used as matching criteria for the case-control-study. For qualitative data correspondence was requested, for quantitative data deviations up to 10% were accepted. With these criteria 25 patients of the minimally invasive group were matched to 25 patients of conventional group. All patients were reexplored 1 year after aortic valve replacement. Statistical analysis was done by the Fisher's exact test for qualitative data and the Mann–Whitney test for quantitative data. Results: We implanted 15 (20) bioprosthesis’ and 10 (five) mechanical prosthesis’ in the minimally invasive, respectively, conventional group. There were no statistically significant differences between both groups with respect to the perioperative course, only duration of surgery (mean 201.6 vs. 143.9 min, P<0.01) and extracorporeal circulation (mean 116.1 vs. 71.3 min, P<0.01) as well as aortic-cross-clamp-time (mean 77.9 vs. 46.9 min, P<0.01) were significantly longer in the minimally invasive group. Postoperative complications occurred in one patient of the minimally invasive group (dissection of the right coronary artery) and four patients of the conventional group (third degree AV block, pneumothorax, grand mal convulsion, cardiopulmonary resuscitation). Two patients, one of each group, died during follow-up for unknown reasons. Follow-up revealed no significant differences with respect to clinical and echocardiographic data, but the shorter skin incision was cosmetically more accepted by patients of the minimally invasive group. Minor paravalvular leaks occurred in four patients of the minimally invasive and three patients of the conventional group as diagnosed by transthoracic echocardiography. Conclusions: Both surgical techniques may be performed with comparable perioperative and mid-term results, but the better cosmetic result in the minimally invasive group is paid by a longer duration of surgery.

Key Words: Aortic valve replacement • Minimally invasive surgery • Cardiac surgery • Perioperative course • Mid-term results

	1. Introduction

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion 5. Conclusions References

 
During the last years, minimally-invasive operative techniques have been introduced in cardiac surgery. Many advantages, such as less postoperative pain, lower morbidity and mortality, faster recovery, shorter duration of operation and hospital stay associated with lower costs were described for these new techniques [1–11]. We performed this retrospective case-control-study to investigate, if perioperative and mid-term results of minimally invasive aortic valve replacement (AVR) are really better than those with conventional AVR.

	2. Materials and methods

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion 5. Conclusions References

 
2.1. Patients
From August 1996 to July 1997, 113 patients underwent isolated AVR, 84 in a conventional manner and 29 applying minimally invasive techniques in our department. After exclusion of patients with previous cardiac surgery, with additional surgical procedures, and with concomitant diseases of other heart valves, 25 patients of the minimally invasive group could be matched to patients of the conventional group with regard to age, gender, body-mass-index, diagnosis, ejection fraction, and pressure gradient/regurgitation fraction. Exact correspondence was requested for qualitative data, deviations up to 10% were accepted for quantitative data.

Both groups included 13 male and 12 female patients suffering from aortic valve stenosis in 17 and aortic valve insufficiency in eight cases. The matching criteria are presented in Table 1.

2.2. Surgery
The operative technique was similar in all patients, except for the placement of external defibrillator patches, the different access, and the route of cardioplegia delivery. Conventional AVR was accomplished via a skin incision from the sternal notch to the xiphoid process and a complete median sternotomy. In the minimally invasive group, the length of the skin incision was limited to 6 cm and started at the sternal angle. Partial median sternotomy was performed in a J-shaped fashion and ranged from the sternal notch to the fourth right interspace. Conversion to a conventional approach was not necessary in any patient of the minimally invasive group. In all patients, the ascending aorta and the right atrial appendage were cannulated for institution of ECC. Blood cardioplegia was delivered via the retrograde route in the conventional group, whereas the patients of the minimally invasive group had an antegrade administration. All aortic valve prosthesis’ were implanted in an intraanular position using interrupted pledgeted mattress sutures. Transesophageal echocardiography was used to survey deairing of the heart and consecutive weaning from ECC in all patients. All minimally invasive operations were performed by the two most experienced surgeons.

2.3. Follow-up
Follow-up was done 1 year after AVR. During follow-up, two patients, one of each group, died of unknown causes. Five patients were lost at follow-up, two patients of the conventional group and three patients of the minimally invasive group, so that only 20 of the original 25 pairs could be reevaluated. We assessed clinical data and cardiac function by transthoracic echocardiography.

2.4. Statistical analysis
Statistical analysis was done by the Fisher's exact test for qualitative data and the Mann–Whitney test for quantitative data. P-values are presented with two significance levels (P<0.05 and P<0.01). Confidence intervals were computed for the most important differences.

	3. Results

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion 5. Conclusions References

 
3.1. Preoperative data
Frequency of risk factors, associated diseases and typical symptoms are presented in Table 2.

3.2. Operative data
In the minimally invasive group, 15 patients received a bioprosthesis’ and 10 a mechanical valve, as opposed to 20 bioprosthesis’ and five mechanical valves in the conventional group. Size of the implanted aortic valve prosthesis’, duration of surgery and ECC as well as aortic-cross-clamp-time and urgency of intervention are summarized in Table 3.

One patient of the minimally invasive group developed myocardial ischemia on the second postoperative day. Coronary angiography revealed dissection of the right coronary artery, necessitating emergency coronary artery bypass grafting (CABG). The patient had an uneventful recovery without developing myocardial infarction.

In the conventional group four patients suffered from postoperative complications:

The first patient required cardiopulmonary resuscitation on the day of operation for ventricular fibrillation probably due to a low level of serum potassium. The further postoperative course was uneventful and the patient was discharged on the twelfth postoperative day. The second patient required a pacemaker implantation for third-degree AV block. The third patient required insertion of an additional chest tube for pneumothorax, which was removed on the fourth postoperative day. The fourth patient developed a grand mal convulsion of unknown causes, which was controlled medically.

Two patients of the minimally invasive group and three patients of the conventional group developed neuropsychological alterations postoperatively, which were treated medically and regressed completely in the further postoperative course. Temporary pacemaker stimulation because of bradyarrhythmia was necessary in six patients of the conventional group and four patients of the minimally invasive group. In all patients, cardiac rhythm converted into a sinus rhythm, so that no permanent pacemakers had to be implanted. We did not observe myocardial, intestinal or cerebral infarctions, cerebral hemorrhage, mediastinitis or wound healing problems in our patients.

3.4. One year follow-up
Follow-up revealed no significant differences with respect to clinical and echocardiographic data. Patients of both groups demonstrated an average NYHA class of 1.5 (I–III) at follow-up, resulting in an average improvement of 1.4 in the minimally invasive and 1.6 in the conventional group. There were no differences with regard to laboratory values, electrocardiograms, pulmonary function and results of exercise testing. No patient with a mechanical prosthesis of either group had suffered from valve-related thromboembolism or anticoagulation-related bleeding complications. The quality of life as being judged by the patients on a scale from 1 (very good) to 6 (poor) was 1.5 on average in both groups (range 1–4), however, the shorter skin incision was repeatedly appreciated by patients of the minimally invasive group.

Transthoracic echocardiography demonstrated adequate function of all implanted prosthesis’. Minor paravalvular leaks without hemodynamic relevance and without increased serum parameters for hemolysis were detected in four patients of the minimally invasive group and in three patients of the conventional group. Mean pressure gradient, which was calculated by the Bernoulli formula (p=4x(V₂)²-4x(V₁)², V₁=flow velocity before the aortic valve, V₂=flow velocity behind the aortic valve), were 18.9 and 20.2 mmHg in the minimally invasive and conventional group, respectively.

3.5. Statistical analysis
Differences between both groups, using the Mann–Whitney test, could not be detected based on the power of this test (Table 1). Also all evaluated parameters did not show any significant differences, only duration of operation, ECC and aortic-cross-clamp-time were significant longer in the minimally invasive group (P<0.01; Table 3) than in the conventional group. In Tables 1, 3 and 4 the presented values are depicted as ‘mean’ and ‘range’.

	4. Discussion

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion 5. Conclusions References

 
Several advantages, such as less lower mortality and faster recovery with consecutive earlier discharge and lower costs as well as less postoperative pain have been attributed to many minimally-invasive cardiosurgical procedures [1–11], mainly to those avoiding ECC. In AVR, however, ECC cannot be avoided. In these patients, major advantages include better cosmesis and preserved pulmonary function resulting in less respiratory complications whereas reduction of surgical trauma, wound complications, and postoperative blood loss vary considerably with surgical techniques employed and therefore are a matter of ongoing discussion [3,4,10]. For many patients, the favorable cosmesis due to the shorter skin incision is the most important factor for decision making (own experiences [4,7,8]).

In contrast to Cosgrove [3,4], we could not demonstrate a diminished use of analgetics due to less postoperative pain after minimally-invasive AVR. This finding is in accordance with the experiences of other authors [6,9,12] and may be explained by the different minimally-invasive operative accesses: Cosgrove [3] chose a right parasternal incision from the second to the fifth costal cartilage, whereas Aris [12], Konertz [6] and our group used a partial sternotomy. According to Cosgrove [3], avoidance of sternotomy is associated with absence of retraction and stress on the ribs and therefore should reduce postoperative pain, whereas Konertz [6] described increased postoperative pain following complete or partial rib removal and minithoracotomy. This experience is confirmed by others: ‘a median sternotomy is the more comfortable incision than any type of thoracotomy and perhaps the least painful surgical incision’ [13,14]. Perhaps another minimally-invasive access, called the reversed C-incision [8,9], may help to reduce patient's discomfort and pain postoperatively due to a stable chest wall, particularly a stable upper chest wall. Pain levels may be reduced further by infiltration of the wound with local anesthetics [4,8]. Additionally, these steps may help to reduce respiratory compromise and complications [4] due to an improved pulmonary function postoperatively. Particularly patients, who are at high risk for postoperative pulmonary complications (for example patients with a severe chronic obstructive pulmonary disease) may benefit from the reversed C-incision, because the stable upper and lower chest wall leads to a better postoperative pulmonary function reducing the rate of respiratory complications [9].

Another advantage of partial median sternotomy in contrast to transverse sternotomy or a parasternal access is the preservation of the internal thoracic arteries (ITA), which are important conduits, if a second surgical intervention is necessary for coronary artery disease. Cosgrove [3] had to ligate the right ITA when using the right parasternal approach and even both ITAs are sacrificed when a transverse sternotomy is used [1,15]. Furthermore, sternum and chest wall instabilities as well as lung herniation after resection of several costal cartilages occurred with these approaches [1,4,5,16], so that Cosgrove's [4] incision of choice is now a ministernotomy extended into the fourth interspace on the right. With this approach, we did not see any sternum instabilities or lung herniations in our patients.

Our access led to an excellent exposure of the aortic root and the left ventricular outflow tract. This experience is shared by Konertz [6], who used a slightly paramedian sternotomy from the sternal notch to the fourth interspace. He explains the excellent exposure of the aortic valve by the fact, that the anterior mediastinum is not dissected completely and therefore the heart remains in a relatively anterior position compared with the conventional approach. Whether the dissection of the right coronary artery in a patient of the minimally invasive group was related to the AVR procedure, cannot be answered finally. Although an iatrogenic cause seems likely, we assume, that atherosclerotic alteration of the aortic wall close to the ostium of the right coronary artery may have triggered the complication.

Meanwhile, minimally-invasive operative techniques for AVR underwent such an improvement, that not only simple AVRs are performed via the different minimal accesses but also much more difficult operations such as patch enlargement of the aortic valve ring according to Manouguian, reconstruction of the aortic valve, the Ross operation, a total root replacement, hemiarch repair, the maze procedure, composite valve grafts including reoperations and transanular mitral valve replacements [2,6,8].

Duration of ICU and hospital stay are gaining more and more importance, because they are the most important determinants of costs in cardiac surgery [17]. Therefore, all steps are welcome to accelerate patient's recovery in order to shorten hospital stay and with it reduce overall costs. Unfortunately, we cannot confirm the results of Cosgrove [3,4] and Svensson [9], who reported a reduction of direct hospital costs of about 19% due to earlier extubation and reduced length of stay in the ICU since we did not apply a fast track protocol. All these parameters were similar in both groups of our study (Table 4). This finding is in agreement with the results of Aris’ study [12] and may be explained partly by the longer duration of surgery, ECC and aortic-cross-clamp-time in the minimally invasive group than in the conventional group because of our learning curve. Analysis of surgery times for the next 25 patients, who underwent minimally invasive AVR in our Department, confirmed this supposition: duration of surgery and ECC as well as aortic-cross-clamp-time decreased significantly and is now similar between both groups. This experience was also made by others, when new operative techniques were introduced [9,14] They demonstrated, that time for surgery may approximate to usual values for conventional AVR with increasing experience [7].

Lesser wound complications and blood loss are discussed in minimally invasive access surgery [3,4,10]. Our patient cohort is too small to investigate differences in frequency of wound infections or disturbances in wound healing between both groups. Therefore, studies with greater patient cohorts are necessary to answer this question.

With respect to blood loss, our study and the investigation done by Aris [12] failed to demonstrate significant differences between both groups. Some authors [4,5] reported, that blood loss after minimally invasive AVR is markedly reduced in comparison to conventional AVR. According to these authors, reasons may be: (1) avoidance of complete sternotomy (because bleeding will continue, even after reapproximation of the sternum); (2) avoidance of mediastinal dissection (which leads to diffuse bleedings); and (3) the smaller operative access. Our and Aris’ results [12] may be explained by the fact, that blood loss is not only determined by the kind and size of operative access, but also by the perioperative management of anticoagulation or duration of surgery and ECC, which was markedly longer in the minimally invasive group than in the conventional group. Although patients of the minimally invasive group demonstrated a slightly higher blood loss than patients of the conventional group, the number of applicated blood products was similar in both groups. This result is supported by Svensson [9].

Follow-up examinations one year after AVR demonstrated good mid-term results and failed to point out any significant differences between both groups. As mentioned above, the shorter skin incision was repeatedly appreciated by patients of the minimally invasive group. The only striking finding was the incidence of paravalvular leaks, which did not differ between both groups, but appears high. In fact, the reported incidence of paravalvular leaks only ranges from 0 to 4.4% (18–20), but this means the incidence for major paravalvular leaks, requiring reoperation in almost all cases. Reasons for paravalvular leaks are severe calcified aortic annuli, preoperative endocarditis, annulo-aortic ectasia in conjunction with aortic regurgitation, annuloprosthetic mismatch, myxomatous aortic valve leaflets, inadequate fibrous ingrowth into the aortic annulus, and inaccurate suture techniques [19,20]. Furthermore, the incidence of paravalvular leaks is dependent on the kind of the implanted prostheses [19]. The incidence of paravalvular leaks may be reduced by a meticulous suture technique, thorough decalcification of the annulus and, in special cases, by inserting the prosthesis in the supra-annular position [20]. Other publications, focusing on the value of echocardiography in the evaluation of aortic valve protheses, report higher incidences of periprosthetic leakage (1.1–21.0% [21–23]). But the most important finding of these studies is, that transthoracic as well as transesophageal echocardiography demonstrated prosthetic aortic valve insufficiency even in clinically normal aortic valve prostheses (7.7–13.3% [21,23]). These data clearly demonstrate, that prosthetic aortic valve insufficiency is overestimated in a considerable number of patients. Therefore, the overall incidence of paravalvular leaks, including minor and major periprosthetic leakage, is probably higher than reported in surgical publications [18–20] and lower than in echocardiographic reports [21–23], so that the 14%-incidence of paravalvular leaks in our study (without a major periprosthetic leakage) may approximate the true overall incidence.

	5. Conclusions

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion 5. Conclusions References

 
Our study demonstrates, that perioperative and mid-term results of minimally-invasive and conventional AVR are comparable. Improved cosmesis is paid by longer time requirements. Investigations with greater patient cohorts and longer follow-up are necessary in order to finally evaluate the new techniques.

	Footnotes

 
This paper was presented in part at the 116th Congress of the German Society for Surgery, Munich, Germany, April 11th 1999.

	References

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion 5. Conclusions References

 

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Christiansen, S. Articles by Hammel, D. Search for Related Content PubMed PubMed Citation Articles by Christiansen, S. Articles by Hammel, D.