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Eur J Cardiothorac Surg 2008;34:943-952. doi:10.1016/j.ejcts.2008.07.057
Copyright © 2008, European Association for Cardio-thoracic Surgery. Published by Elsevier. All rights reserved.
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Review

Minimally invasive mitral valve surgery: a systematic review and meta-analysis

Paul Modi, Ansar Hassan, Walter Randolph Chitwood, Jr.*

East Carolina Heart Institute, Greenville, NC, USA

Received 23 May 2008; received in revised form 19 July 2008; accepted 28 July 2008.

* Corresponding author. Address: East Carolina Heart Institute, East Carolina University, Pitt County Memorial Hospital, 600 Moye Boulevard, Greenville, NC 27834, USA. Tel.: +1 252 744 4822; fax: +1 252 744 3051. (Email: chitwoodw{at}ecu.edu).


   Abstract
Top
 Abstract
1. Introduction
 2. Overview of the...
 3. Patients and methods
 4. Results
 5. Special situations
 6. Endo-aortic balloon occlusion...
 7. Limitations of a...
 8. Conclusions
 References
 
The mitral valve has been traditionally approached through a median sternotomy. However, significant advances in surgical optics, instrumentation, tissue telemanipulation, and perfusion technology have allowed for mitral valve surgery to be performed using progressively smaller incisions including the minithoracotomy and hemisternotomy. Due to reports of excellent results, minimally invasive mitral valve surgery has become a standard of care at certain specialized centers worldwide. This meta-analysis quantifies the effects of minimally invasive mitral valve surgery on morbidity and mortality compared with conventional mitral surgery and demonstrates equivalent perioperative mortality (1641 patients, odds ratio (OR) 0.46, 95% confidence interval 0.15–1.42, p = 0.18), reduced need for reoperation for bleeding (1553 patients, OR 0.56, 95% CI 0.35–0.90, p = 0.02) and a trend towards shorter hospital stays (350 patients, weighted mean difference (WMD) –0.73, 95% CI –1.52 to 0.05, p = 0.07). These benefits were evident despite longer cardiopulmonary bypass (WMD 25.81, 95% CI 13.13–38.50, p < 0.0001) and cross-clamp times (WMD 20.91, 95% CI 8.79–33.04, p = 0.0007) in the minimally invasive group. Case-control studies show consistently less pain and faster recovery compared to those having a conventional approach. Data for minimally invasive mitral valve surgery after previous cardiac surgery are limited but consistently demonstrate reduced blood loss, fewer transfusions and faster recovery compared to reoperative sternotomy. Long-term follow-up data from multiple cohort studies are also examined revealing equivalent survival and freedom from reoperation. Thus, current clinical data suggest that minimally invasive mitral valve surgery is a safe and a durable alternative to a conventional approach and is associated with less morbidity.

Key Words: Surgical procedures • Minimally invasive • Thoracic surgery • Video-assisted • Mitral valve insufficiency


   1. Introduction
Top
 Abstract
 1. Introduction
2. Overview of the...
 3. Patients and methods
 4. Results
 5. Special situations
 6. Endo-aortic balloon occlusion...
 7. Limitations of a...
 8. Conclusions
 References
 
Minimally invasive mitral valve surgery (MIMVS) does not refer to a single approach but rather to a collection of new techniques and operation-specific technologies. These include enhanced visualization and instrumentation systems as well as modified perfusion methods, all directed toward minimizing surgical trauma by reducing the incision size [1]. In the majority of cases, MIMVS has been performed through either a right anterior minithoracotomy or a hemisternotomy. The belief that this results in less surgical trauma, blood loss, transfusion and pain, which translates into a reduced hospital stay, faster return to normal activities, less use of rehabilitation resources, and overall healthcare savings, has driven this development. Scepticism surrounding MIMVS has focused on the potential ‘trade-off’ of incision size against the safety and exposure of established techniques with proven durable long-term results. Despite criticism over the last decade, various institutions have adopted MIMVS and have published favorable results as single-center observational and comparative studies. A recent meta-analysis of minimal access aortic valve replacement suggested only marginal benefits for intensive care unit stay (ICU) and hospital stay over conventional surgery, despite longer operative times [2]. As yet, no such meta-analysis is available for MIMVS despite nearly 10 years of investigational data.

Changes in surgical indications, largely due to a better understanding of the natural history of organic mitral regurgitation and the increased use of repair techniques, have increased the number of minimally symptomatic patients with degenerative disease being referred for elective repair [3,4]. For MIMVS to become accepted widely, at least equivalent, if not better, short- and long-term outcomes must be demonstrated compared with sternotomy operations. This evidence should ideally come from large, multi-center prospective randomized controlled trials (RCT) that compare minimally invasive with conventional sternotomy-based mitral surgery. However, there are only two small RCTs, one of which reports data combined with minimally invasive aortic valve replacement [5,6]. The ability to conduct an effective RCT now would be compromised severely as patients and healthcare providers have preconceived notions about surgical approaches. This attitude would render patients unlikely to participate in a trial where randomization to sternotomy as a control cohort would be possible.

In the absence of large well-designed RCTs, data regarding short- and long-term outcomes are available from multiple case-control studies and observational studies. The aim of this report is to review the published randomized and nonrandomized comparative studies that compare minimally invasive endoscopic mitral valve surgery, excluding telemanipulation, to conventional approaches. Moreover, we integrate meta-analytical data to draw more useful conclusions about important short- and mid-term outcome metrics. Long-term outcomes are assessed using multiple large cohorts, to compare these to published sternotomy data.


   2. Overview of the evolution of minimally invasive mitral valve surgery
Top
 Abstract
 1. Introduction
 2. Overview of the...
3. Patients and methods
 4. Results
 5. Special situations
 6. Endo-aortic balloon occlusion...
 7. Limitations of a...
 8. Conclusions
 References
 
In the mid-1990s, surgeons began to explore the potential advantages of minimizing incision size during cardiac surgery. Cosgrove and Cohn independently showed that mitral valve operations could be performed safely and efficiently using either parasternal or hemisternotomy incisions. Complications including slower healing, increased lung herniation, and less cosmetically appealing results led to the former being abandoned [7,8]. Carpentier performed the first video-assisted mitral valve repair through a minithoracotomy in February of 1996 [9]. Soon after, the East Carolina University group performed the first mitral valve replacement through a minithoracotomy, using video-direction, a transthoracic aortic clamp, and retrograde cardioplegia [10,11]. In 1997, we presented our first experience with 31 video-assisted mitral operations, reporting a 30-day mortality rate of 3.2% and no major complications [12]. In 1998, Mohr reported the Leipzig University experience using port-access (PA) technology, which was based on endo-aortic balloon occlusion (EABO) rather than direct aortic clamping [13].

The next major development was the introduction of a voice-controlled robotic camera arm (AESOP 3000, Computer Motion Inc., Santa Barbara. CA, USA) which allowed precise tremor-free camera movements with less lens cleaning. This technology translated into reduced cardiopulmonary bypass (CPB) and cross-clamp (XC) times [14,15], and enabled even smaller incisions with better valve and subvalvar visualization. The next evolutionary leap in endoscopic mitral surgery was the development of three-dimensional (3D) vision and computer-assisted telemanipulation that could transpose surgical movements from outside the chest wall to deep within cardiac chambers. Currently, the most widely used system is the Da Vinci® telemanipulation system (Intuitive Surgical Inc., Mountain View, CA).


   3. Patients and methods
Top
 Abstract
 1. Introduction
 2. Overview of the...
 3. Patients and methods
4. Results
 5. Special situations
 6. Endo-aortic balloon occlusion...
 7. Limitations of a...
 8. Conclusions
 References
 
3.1 Literature search
The MEDLINE search strategy combined ‘Cardiac surgical procedure’ with the following MeSH terms: ‘Surgical procedures, minimally invasive’, ‘Thoracic surgery, video-assisted’, Endoscopy’ AND with ‘Mitral valve insufficiency’, ‘Mitral valve prolapse’, and ‘Mitral valve’. To reflect contemporary practice, the search was limited to the last 10 years and additional limits were English language citations and human subjects. The bibliographies of retrieved articles were searched for relevant articles. In addition, the ‘related articles’ function in PubMed was used as a further check of rigor. Where multiple cohort studies were published by a single institution, the largest or most informative study was included.

3.2 Inclusion criteria for meta-analysis
Intra-operative study variables included CPB and XC times, and postoperative ones were mortality, neurologic events (CVA), reoperation for bleeding, new atrial fibrillation (AF), intensive care unit (ICU) times, and hospital length of stay (LOS). The guidelines of the Meta-Analysis of Observational Studies in Epidemiology group were followed [16]. Both RCTs and case-control studies were used for the meta-analysis if they included at least one of the outcomes of interest. Reports presenting data for minimally invasive aortic and mitral valve surgery were only included if the mitral valve data were presented separately; studies reporting reoperative data were excluded from the meta-analysis. Studies in which data were not presented as mean and standard deviation (SD) or if this was not calculable were excluded from the analysis.

3.3 Statistical analysis
Meta-analyses were performed either using odds ratios (OR) or weighted mean differences (WMD) as the summary statistic for binary or continuous variables, respectively. The analyses were performed according to the recommendations of the Cochrane Collaboration and the Quality of Reporting of Meta-analyses guidelines [17]. An OR less than one or WMD less than one favors MIMVS over sternotomy. Random effects models were used as these assume variation between studies and are preferred for surgical data as selection criteria and risk profiles for patients differ between centers. Statistical significance was set at p < 0.05. Data were analysed using Review Manager version 4.2.10 (The Cochrane Collaboration, Oxford, England).


   4. Results
Top
 Abstract
 1. Introduction
 2. Overview of the...
 3. Patients and methods
 4. Results
5. Special situations
 6. Endo-aortic balloon occlusion...
 7. Limitations of a...
 8. Conclusions
 References
 
We identified 43 published reports and of these there were two RCTs, 17 case-control studies, and 24 cohort studies. Of these studies, one RCT and ten case-control studies, published between 1998 and 2005, met the inclusion criteria (Table 1 ). Cohort patients numbered 2827, with 1358 in the MIMVS group and 1469 in the conventional sternotomy group. One comparative series was excluded [12] as more recent inclusive data from the same group were found [14]. One report contained data from the Society of Thoracic Surgeons (STS) database as the control arm and therefore was excluded [18]. One report presented results for mitral valve repair (MVP) and replacement (MVR) separately without presenting a combined group; the data for each were therefore analysed as independent studies [19]. The only randomized study included in the meta-analysis was by Dogan et al. in which 20 patients in each arm were reported to have equivalent findings of ability to repair the valve, CPB and XC times, markers of myocardial and cerebral damage as well as pulmonary and neuropsychological tests [5]. Although the mean values for ventilation time, ICU time, hospital stay, and red blood cell transfusion were all lower in the MI group, these values did not reach statistical significance.


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  		Table 1 Studies comparing minimally invasive mitral valve surgery to sternotomy
 
4.1 Mortality
Of the 11 comparative studies evaluating mortality, none found a significant difference between the minimally invasive and conventional approaches [12,14,18–26]. In the largest study by Mihaljevic et al. 474 minimally invasive mitral operations (mostly lower sternotomy and right parasternal) were compared with 337 median sternotomy procedures. The perioperative mortality was 0.2% for the minimally invasive group and this compared favorably with 0.3% in the sternotomy cohort. However, the MIMVS patients were found to be a lower risk group (better ejection fraction, more repairs, less symptomatic) and no attempt was made to adjust for these differences [24]. Grossi et al. matched 88 patients undergoing minimally invasive aortic and mitral valve surgery over a 2.5-year period (through either a 2nd or 4th interspace incision) to patients having the same valve surgery via a sternotomy [25]. They demonstrated no significant difference in hospital mortality (3.7% vs 3.4%, respectively) between groups, even though mean CPB times were 30 min longer in the MI group. Six studies met the inclusion criteria for our meta-analysis and revealed no significant mortality difference between groups (1641 patients, OR 0.46, 95% CI 0.15–1.42, p = 0.18) (Fig. 1 , Table 2 ).


Figure 1
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  		Fig. 1. Overall meta-analysis of perioperative mortality, reoperation for bleeding and hospital length of stay. The diamond represents the summary odds ratio (OR) from the pooled studies with 95% confidence intervals (CIs) and is significant (p ≤ 0.05) if it does not touch the central vertical line. Squares for each study show point estimates of treatment effect (OR) with the size of the square representing the weight attributed to each study; horizontal bars show 95% CIs for these studies. df, degrees of freedom; MIS, minimally invasive surgery; MVP, mitral valve repair; MVR, mitral valve replacement.

 

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  		Table 2 Meta-analysis of outcomes
 
4.2 Neurological events
Due to restricted access with minimally invasive cardiac operations, there continues to be concern that inadequate deairing can cause a higher incidence of neurological events. In his early series, Mohr reported an 18% incidence of postoperative confusion; however, continuous CO2 insufflation was not used as in more recent series [13]. Ten studies reported no difference in the incidence of stroke [14,18–21,23–27], while two showed a reduced incidence with a minimally invasive approach [12,22]. There was no significant difference in neurological events on meta-analysis of six eligible studies (1801 patients, OR 0.66, 95% CI 0.23–1.93, p = 0.45). Schneider et al. used trans-cranial Doppler to detect cerebral microemboli in 21 MIMVS patients undergoing endoaortic balloon occlusion with continuous CO2 chest cavity insufflation. These were compared to 14 patients undergoing conventional mitral surgery [27]. They found no significant difference in the cerebral microembolic rate between either technique.

4.3 Operative times
There were consistent findings that CPB and XC times were longer with a minimally invasive approach. There was evidence suggesting that parity can be achieved with experience while certain high volume centers report shorter operative times with MIMVS [24]. Of the 16 studies reporting cardiopulmonary bypass times, 10 described longer durations for MIMVS. Seven of 14 groups reported longer aortic cross-clamp times [6,8,12,14,18–30]. Meta-analysis of eligible studies showed significantly longer CPB (871 patients, WMD 25.81, 95% CI 13.13–38.50, p < 0.0001) and XC times (671 patients, WMD 20.91, 95% CI 8.79–33.04, p = 0.0007) with the minimally invasive approach.

4.4 Bleeding, transfusion and re-exploration
A reduction in postoperative hemorrhage and transfusion requirements has been suggested as a potential advantage of minimally invasive valve surgery. This benefit is important given the significant morbidity and mortality associated with transfusions and re-exploration for bleeding [31]. Four comparative studies reported blood loss volume with three utilizing a minithoracotomy [12,14,21] and one selecting a parasternal approach [26]. Few of these series met the inclusion criteria for the meta-analysis. Chitwood et al. demonstrated no difference in blood loss or blood product transfusions in 31 videoscopic mitral procedures compared with a conventional sternotomy, despite fewer re-explorations for bleeding [12]. The addition of a voice-activated robotic camera arm (AESOP 3000, Computer Motion, Inc., Galeta, CA) led to a reduction in blood loss as well as CPB and XC times. Nevertheless, there was no significant difference either in the percentage of patients receiving transfusions or the amount of blood products transfused [14]. In a consecutive series of 41 patients undergoing either port access (n = 21) or sternotomy (n = 20) mitral surgery, Glower et al. demonstrated no significant difference in chest tube drainage or transfusion requirements despite longer CPB times in the former [21].

Three of 10 studies showed reduced transfusion requirements with a minimally invasive approach, compared to conventional surgery [8,23,25] whilst the others showed no difference [6,12,14,19,21,26,32]. Too few studies met the inclusion criteria for meta-analysis (percent transfused, two studies; units transfused, three studies). In patients 70 years or older, Grossi et al. reported reduced plasma transfusions with a minimally invasive (n = 111) compared to a conventional (n = 259) approach [23]. However, the minimally invasive cohort had a lower preoperative risk profile (e.g. fewer redo operations), and there was no attempt to adjust for this baseline difference in the analysis. More convincing evidence came from a subsequent study by the same group that showed 13% fewer total transfusions with 1.8 fewer units of red blood cells using a minithoracotomy compared to a sternotomy [25]. Similar data from Cohn et al. confirm that patients undergoing minimally invasive valve surgery are transfused 1.8 units less compared to a conventional cohort [8].

Two of seven studies [12,14] demonstrated a reduced need for reoperation for bleeding with a minimally invasive approach [18,19,23,24,26]. Five studies met the inclusion criteria for the meta-analysis that showed a significant reduction in reoperation for bleeding with a MI approach (1553 patients, OR 0.56, 95% CI 0.35–0.90, p = 0.02).

4.5 Atrial fibrillation (AF)
It has been suggested that a less traumatic surgical approach would be a less potent trigger of postoperative AF. Five of six studies, however, demonstrated this not to be the case [12,14,18,19,21,29], and on meta-analysis of four eligible studies, there was no significant difference between minimally invasive and sternotomy approaches (539 patients, OR 0.86, 95% CI 0.59–1.27, p = 0.45). Asher et al. addressed this question specifically in a cohort of 100 patients having elective primary minimally invasive aortic or mitral valve surgery and compared them to a matched control group undergoing a median sternotomy [29]. They found a similar prevalence of postoperative AF using either method, even when stratified for valve type. However, the PAIR registry reported a 10% incidence of new onset atrial fibrillation with the port access technique which is lower than that expected for sternotomy [33].

4.6 Septic complications
The incidence of septic wound complications is less with thoracotomy than median sternotomy. Of the three studies of mini-thoracotomy mitral valve surgery that reported wound complications compared to median sternotomy, Grossi et al. reported an incidence of 0.9% and 5.7% for mini-thoracotomy and sternotomy cases, respectively (p = 0.05) [25]. This increased to 1.8% and 7.7%, respectively, in elderly patients (p = 0.03) [23], whereas Felger et al. reported no significant difference [14].

4.7 Pain and speed of recovery
Of all the potential benefits of MIMVS, a reduction in pain and faster return to normal activity is the most consistent finding. All four studies that measured postoperative pain levels reported less compared to sternotomy [8,21,28,32] and both studies reporting time to return to normal activities noted a significant advantage for a minimally invasive approach [8,21]. In a nonrandomized study, Walther et al. reported equivalent pain for the first two postoperative days when a minithoracotomy approach was compared to sternotomy with a subsequent significant reduction of pain in the MI group from day 3 onwards, a difference which progressively widened with time [32]. Better stability of the bony thorax led to earlier mobilization and a faster return to activities of daily living. Glower reported that postoperative pain tended to resolve more quickly with a minimally invasive approach and that these patients returned to normal activity 5 weeks more rapidly than those having a median sternotomy (4 ± 2 weeks vs 9 ± 1 weeks, p = 0.01) [21]. Cohn's data is concordant with less pain in hospital and after discharge, less analgesic usage, greater patient satisfaction and a return to normal activity 4.8 weeks ahead of sternotomy patients [8]. Vanermen reported that 94% of his patients report no or mild postoperative pain, 99.3% feel they have an aesthetically pleasing scar, 93% would choose the same procedure again if they had to have redo surgery and 46% are back at work within 3 weeks [34]. However, perhaps the most insightful piece of evidence for patient preference of MIMVS comes from two studies reporting that those who have had a MI approach as their second procedure all felt that their recovery was more rapid and less painful than their original sternotomy [14,35].

4.8 Hospital stay, costs and discharge disposition
Does a more rapid recovery translate into a shorter stay in hospital and therefore reduced costs? Eight of 14 studies reported less time in hospital with a MI approach [8,12,14,19,21–29,32]. Only five studies were eligible for meta-analysis and although the trend indicated this to be the case, the result was not statistically significant (350 patients, WMD –0.73, 95% CI –1.52 to 0.05, p = 0.07) (Fig. 1). Chitwood, Cohn and Cosgrove equated this to a 34%, 20% and 7% cost saving, respectively [8,12,36]. Moreover, these patients had fewer requirements for post-hospital rehabilitation, which is a significant advantage in terms of healthcare savings with 91% being discharged home compared to 67% with a conventional approach [8,24].

4.9 Intermediate- and long-term results
Comparing a consecutive cohort of 100 minithoracotomy mitral valve operations to the previous 100 sternotomy mitral valve procedures, Grossi et al. found comparable 1-year freedom from reoperation (96.8% vs 94.4%, p = 0.38, respectively) with similar net improvement in functional class [20]. Mihaljevic et al. reported significantly better actuarial survival at 5 years for minimally invasive compared to sternotomy patients (95% vs 86%), but this may be explained by a lower risk profile [24]. Many of the cohort studies are temporally updated results from a few select high-volume centers such as the Cleveland Clinic, the Brigham and Women's Hospital, New York University, University of Leipzig, OLV Clinic (Aalst, Belgium) and East Carolina University. Therefore, only the most recent data from 10 cohorts with 6479 patients are considered, herein (Table 3 ) [1,33,34,37–42]. The crude unadjusted mortality rates for the entire cohort are 1.1% for mitral valve repair and 4.9% for mitral valve replacement. The corresponding data from the Society of Thoracic Surgeons (STS) Fall 2007 report are 1.5% for MVP and 5.5% for MVR (Table 4 ). The neurological event rates for the entire cohort are lower than STS data. With regard to long-term survival, we found seven studies reporting from 100% survival at a mean of 2.3 years to 83% at 6.8 years postoperatively (Table 5 ) [34,39–44]. This compares favorably to 5-year survivals of 86.4% reported by the Mayo Clinic [45] and 82% reported by the Cleveland Clinic [46]. Five studies reported freedom from reoperation ranging from 99.3% at 3.2 years to 91% at 4 years [34,40–42,44]. The longest follow-up was 6.3 years with 96.2% freedom from reoperation. Again this compares favorably to the Mayo Clinic data which indicates a risk of reoperation of between 0.5% per year for isolated posterior leaflet prolapse to 1.64% per year for isolated anterior leaflet prolapse [45].


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  		Table 3 Most recent observational cohort studies of minimally invasive mitral valve surgery
 

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  		Table 4 Summary data derived from above cohort studies compared to data from STS Fall 2007 report
 

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  		Table 5 Studies reporting long-term results of minimally invasive mitral valve surgery
 

   5. Special situations
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 Abstract
 1. Introduction
 2. Overview of the...
 3. Patients and methods
 4. Results
 5. Special situations
6. Endo-aortic balloon occlusion...
 7. Limitations of a...
 8. Conclusions
 References
 
5.1 Reoperative surgery
The greatest potential benefit of a right mini-thoracotomy is the avoidance of sternal re-entry and limited dissection of adhesions, avoiding the risk of injury to cardiac structures or patent grafts, and limiting the amount of postoperative bleeding [47]. This consistently translates into reduced blood loss, less transfusions and faster recovery. There are seven important studies (three case-control and four cohort) describing a right minithoracotomy approach for reoperative valve surgery [35,48–53] and one describing a left posterior approach [54] (Table 6 ).


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  		Table 6 Studies reporting a minithoracotomy approach for reoperative mitral valve surgery
 
The case-control studies all demonstrated superiority of the right mini-thoracotomy versus a reoperative sternotomy. The largest series from Sharony et al. demonstrated equal mortality (5% for isolated mitral operations), fewer wound infections, less blood product utilization, decreased hospital length of stay, and slightly more favorable mid-term outcomes with a mini-thoracotomy approach for reoperative mitral and aortic valve surgery [48]. In 71 reoperative mitral valve operations of which 38 were done through a minithoracotomy, Bolotin et al. noted no difference in mortality or CPB times but significantly reduced intubation times, blood transfusion and hospital stay with a minimally invasive approach [49]. In a retrospective study from Duke University, patients undergoing a right mini-thoracotomy for redo mitral surgery had lower mortality, less blood loss and fewer transfusions than via a redo sternotomy or an antero-lateral thoracotomy [50].

Vanermen recently reported 80 adults undergoing endoscopic MV and TV reoperative surgery with an operative mortality of 3.8% [51]. There was one intra-operative and two postoperative strokes. Survival at 1 and 4 years was 93.6 ± 2.8% and 85.6 ± 6.4% respectively, and there was one late reoperation at five years. At the University of Michigan, Bolling et al. used a 5–10 cm right anterior 5th interspace thoracotomy in 22 patients for reoperative mitral and tricuspid valve surgery with no 30-day mortality [35]. Patients were weaned from ventilation at a mean of 5 h and received 1.3 ± 1 units of blood. There were no re-explorations for bleeding. The important message from this study was that all patients interviewed considered that their recovery was more rapid and less painful than their original sternotomy.

Onnasch et al. reported 39 patients undergoing redo mitral valve surgery through a right minithoracotomy with a mortality of 5.1% [53]. One patient experienced transient hemiplegia due to migration of the aortic balloon endoclamp. This group concluded that a MI approach offers excellent exposure and minimizes the need for mediastinal dissection and optimizes patient comfort. Their updated series described 97 patients undergoing mitral reoperations since 1996 with an in-hospital mortality of 5.6% [52].

Finally, the New York University group have described a left posterior minithoracotomy approach in 40 patients in whom a right thoracotomy was precluded, e.g. right mastectomy/irradiation [54]. They concluded this approach to be a valuable option in complicated reoperative mitral procedures with acceptable perioperative morbidity and mortality.

5.2 Low ejection fraction
Previously considered by many as a contraindication to a minimally invasive approach, Mohr has treated 68 patients having a dilated cardiomyopathy (EF 21 ± 8%) with MI mitral valve repair and 11 with a replacement with an overall 8.8% mortality [52]. Severe pulmonary hypertension was present in 45.6%. Postoperatively, 6.3% developed renal failure and 7.9% had low cardiac output. Despite successful mitral valve repair, seven patients required transplantation during follow-up.

5.3 Elderly patients
Two studies have looked at the application of MI techniques specifically to elderly patients. Grossi et al. reviewed 111 patients undergoing MI valve surgery who were at least 70 years old and compared these to 259 patients having a sternotomy [23]. The MI group had a significantly lower incidence of sepsis and wound complications, required less frozen plasma transfusions, and had a shorter length of hospital stay. They concluded that this approach can be used safely in operations on the elderly population with excellent results. Also, Tabata et al. recently reported 123 cases of MI mitral valve repair in patients aged 70 years and older with 1.6% operative mortality as well as 5-year actuarial survival of 87% and 5-year freedom from reoperation of 93% [55].


   6. Endo-aortic balloon occlusion versus transthoracic clamping
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 Abstract
 1. Introduction
 2. Overview of the...
 3. Patients and methods
 4. Results
 5. Special situations
 6. Endo-aortic balloon occlusion...
7. Limitations of a...
 8. Conclusions
 References
 
One of the most significant risks of endo-aortic balloon occlusion (EABO) is aortic dissection, and as a consequence, many surgeons have abandoned this technique. In the first PAIR report, the incidence of aortic dissection was 1.3% in the first half of the study compared to 0.2% in the second half, a difference attributable to experience, better techniques, and improved technology [56]. In comparison to transthoracic clamping (TTC), EABO is more expensive, and the clamp position is less stable. Proximal balloon dislodgement can cause innominate artery occlusion with neurological injury. Monitoring by transesophageal echocardiography and transcranial Doppler should be done routinely [57,58]. Balloon prolapse into the left ventricle can lead to inferior myocardial protection, ventricular distension or aortic valve injury.

There are three pertinent studies, all non-randomized consecutive series from Germany, demonstrating superiority of TTC over EABO. Onnasch et al. demonstrated a significantly higher risk of neurological complications with EABO (8.1% vs 1.8%, p < 0.05) and higher mortality (5.2% vs 3.1%, respectively). Mohr subsequently abandoned EABO for primary mitral valve procedures [59]. In 58 patients, Aybek et al. demonstrated similar results with faster operations, fewer technical difficulties, less blood loss and lower costs using the transthoracic clamp [60]. Reichenspurner et al. confirmed shorter operative times with TTC in 120 patients and with fewer complications (reduced bleeding, wound problems and fewer femoral artery reconstructions) and he showed a reduction in costs of disposables by $2800 [61].


   7. Limitations of a minimally invasive approach
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 1. Introduction
 2. Overview of the...
 3. Patients and methods
 4. Results
 5. Special situations
 6. Endo-aortic balloon occlusion...
 7. Limitations of a...
8. Conclusions
 References
 
Clearly, there is a learning curve for the surgeon as well as the anesthetists, perfusionists and nursing teams. Mohr reported a high mortality (9.8%) in his early port access cases, partially procedure-related with two of 51 patients suffering an aortic dissection [13]. After simplification of the surgical procedure the mortality decreased to 3%. Vanermen demonstrated that ICU and hospital stays decrease with increasing experience [62].

There are potential vascular risks with femoral cannulation, especially with the larger port access femoral cannula. Groin seromas can be problematic but are kept to a minimum by dissection only of the anterior surface of the vessels as well as clipping lymphatics. When the pericardium is opened too posteriorly, phrenic nerve palsy has been reported and can be avoided by placing the pericardiotomy at least 3 cm anterior to it. Excess tension by pericardial retraction sutures should be avoided. Although some have suggested that a small anterior thoracotomy is associated with equal or greater postoperative pain [63,64], there is good evidence as detailed above that it actually reduces postoperative discomfort and enhances recovery [21,25,65].


   8. Conclusions
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 1. Introduction
 2. Overview of the...
 3. Patients and methods
 4. Results
 5. Special situations
 6. Endo-aortic balloon occlusion...
 7. Limitations of a...
 8. Conclusions
References
 
Over the last decade there has been a transformation in the way cardiac surgeons, cardiologists and patients decide the approach to cardiac therapies. Less invasive procedures are demanded but at the same time proven safety, efficacy and durability are expected. There is no prior level one evidence to justify switching to minimally invasive mitral valve surgery. All the reviewed evidence demonstrates that minimally invasive mitral valve surgery is associated with equal mortality and neurological events despite longer cardiopulmonary bypass and aortic cross-clamp times. However, there is less morbidity in terms of reduced need for reoperation for bleeding, a trend towards shorter hospital stay, less pain and faster return to preoperative function levels than conventional sternotomy-based surgery. This would be expected to translate into improved utilization of limited healthcare resources. With follow-up now of almost 7 years it is clear that long-term outcomes are equivalent to those of conventional surgery. Data for minimally invasive mitral valve surgery after previous cardiac surgery is limited but consistently demonstrates reduced blood loss, fewer transfusions and faster recovery compared to reoperative sternotomy. Almost all patients who undergo a minimally invasive mitral valve operation as their second procedure feel their recovery is more rapid and less painful than their original sternotomy.

As for the future, minimally invasive cardiac surgery is likely to become more widely adopted as growth in this niche market and cardiac surgery as a whole is often patient-driven, much in the same way that percutaneous intervention for multivessel disease has been. That is, patients do not want a sternotomy and it is important as a surgical community that we realize this. However, despite enthusiasm, caution cannot be overemphasized as traditional cardiac operations still enjoy proven long-term success and ever-decreasing morbidity and mortality and remain our measure for comparison.


   References
Top
 Abstract
 1. Introduction
 2. Overview of the...
 3. Patients and methods
 4. Results
 5. Special situations
 6. Endo-aortic balloon occlusion...
 7. Limitations of a...
 8. Conclusions
 References
 

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