Results of beating heart mitral valve surgery via the trans-septal approach

Objective: Mitral valve surgery can be performed through the trans-atrial or the trans-septal approach. Although the trans-atrial is the preferred method, the trans-septal approach has also been used recently and has a particular value in beating-heart mitral valve surgery. Herein we report our experience with beating-heart mitral valve surgery via trans-septal approach, and discuss its advantages and pitfalls. Methods: Between 2000 and 2007, 214 consecutive patients were operated upon utilizing beating heart technique for mitral valve surgery. The operation was performed via transseptal approach with the aorta unclamped, the heart beating, with normal electrocardiogram and in sinus rhythm. Results: Mean age was 56.03 ± 13.93 years (range: 19-86 years; median: 56 years). There were 131 (61.2%) males Endereço para correspondência: Tomas A. Salerno 1611 nw ‘12th Avenue, Miami, Florida USA 33136. E-mail: tsalerno@med.miami.edu Artigo recebido em 13 de janeiro de 2009 Artigo aprovado em 20 de fevereiro de 2009


INTRODUCTION
Although beating heart surgery had been used in the early days of cardiac surgery, it was only recently that several surgical groups including ours [1,2] reported mitral valve surgery without cardioplegia.The operation is performed on a beating heart, minimizing or eliminating ischemia-reperfusion injury due to aortic cross-clamping and myocardial ischemia.Several surgical approaches to the mitral valve have been proposed in the literature.When cold blood cardioplegic arrest and cross-clamping of the aorta are used, mitral valve surgery is most commonly performed via the trans-atrial approach.
The type of surgical approach to the mitral valve is particularly important in beating-heart mitral valve surgery.Although initially performed via conventional trans-atrial approach, our beating-heart approach to the mitral valve has evolved into the trans-septal approach [3] because retraction of the atrial wall during the trans-atrial approach often caused aortic insufficiency.Several types of transseptal approach have been reported previously [4].These include the technique in which a transverse incision is made that extends medially from the right superior pulmonary vein to the right atrium, and through the inter-atrial septum, as described previously by Dubost et al. [5], the conventional posterior inter-atrial groove incision perpendicular to the septum and the right atrium [6], and the superior trans-septal approach through the right atrium, the left atrium, and the inter-atrial septostum extended to the inferior portion of the fossa ovalis [7].
To our knowledge, there have been no reports focusing on the type of surgical approach to mitral valve surgery using beating-heart technique.As we believe this is an important aspect of this type of surgery, we reviewed our experience with beating-heart, trans-septal, mitral valve operations, discussing its advantages and pitfalls.
Conclusions: Beating-heart mitral valve surgery is an option for myocardial protection in patients undergoing mitral valve surgery.This technique is facilitated by the trans-septal approach due to reduced aortic insufficiency and improved visualization of the mitral apparatus.

Surgical procedure
Procedures were performed at systemic temperature of 34 o -35 o C.After heparinization, the ascending aorta and both cavae were cannulated [3].Cardiopulmonary bypass (CPB) was initiated and the cavae were snared.The right atrium was open longitudinally and the heart was then briefly fibrillated.A longitudinal incision was made into the fossa ovale, with extension superiorly toward the superior vena cava, and inferiorly to the area just behind the coronary sinus, so as to gain access to the left atrium and expose the mitral valve (Figure 1).A suction catheter was passed through the mitral valve into the left ventricle (Figure 2).The heart was then defibrillated.The remainder of the valve procedure (repair or replacement) was performed with the heart beating [8,9].In no patients it became necessary to cross-clamp the aorta.In the cases that required valve replacement, every effort was made at preserving the posterior subvalvular apparatus, unless it was involved by calcific process or vegetations.As the inter-atrial septum was closed, the heart was again briefly fibrillated and gently massaged, the ascending aorta was vented, the lungs were briefly inflated, and the inter-atrial suture line was secured when there was no evidence of retained air in the left ventricle.Only then was the heart defibrillated.As complementary maneuvers, the patient was placed in a Trendelenburg position during this period.
Occasionally, a suction catheter was inserted in the left ventricle through the apex, as an alternative to inducing ventricular fibrillation when the inter-atrial septum was opened.This also facilitated removal of air from the heart at the end of the procedure.Throughout the procedure the heart was monitored via trans-esophageal echocardiography to ensure that there was no residual air in the atrial or ventricular cavities.There was no evidence of ejection of air into the ascending aorta in any of these patients during surgery.
During combined mitral and aortic valve surgery, both cavae were cannulated and were snared once CPB was initiated.The right atrium was opened and a purse-string was placed around the mouth of the coronary sinus, which was then cannulated.After snaring of the purse-string, perfusion of the coronary sinus was initiated with warm blood at mean pressure of 55 mmHg and flows > 250 ml/ min.The aorta was then cross-clamped and opened.Both coronary ostia were cannulated with Polystan cannulae, and the heart was perfused via inflow from the cannula in the ascending aorta.The aortic valve was decalcified and the annulus size was measured.Attention was then directed to the inter-atrial septum which was opened, as described previously.The mitral valve procedure was performed.After the inter-atrial septum had been closed, attention was directed to the aortic valve.The left ventricle was decompressed either via the right superior pulmonary vein, the apex of the heart or through the aortic valve.The aortic valve was replaced and the aorta was closed, utilizing similar  de-airing maneuvers as previously described.If needed, tricuspid repair was performed with the heart beating and the aorta unclamped.
In combined mitral valve and coronary artery bypass surgery, coronary bypass was usually performed off-pump, after which the patient was placed on CPB.In case of hemodynamic instability, coronary revascularization was completed on-pump, while the heart was maintained beating and continuously perfused.During the period of the mitral valve surgery, all grafts were left open with the aorta unclamped.In cases in which there was mild aortic insufficiency not requiring intervention, pressure on the root of the aorta from the outside usually eliminated aortic insufficiency.

Statistical analysis
All numerical values were expressed as mean + standard deviation.Statistical comparisons for selected numerical variables were made by using the two-tailed chi square Fisher's test.P values of less than 0.05 were considered significant.
There was one case of triple valve surgery performed with concomitant CABG.Mean prosthetic mitral valve size was 28.6 mm ± 1.7 (range: 25-33 mm) and 29.4 mm ± 2.3 (range: 25-33 mm) for biological and mechanical valve prostheses, respectively.The cardiopulmonary bypass time for this group of patients was 93.9 + 47.9 minutes.Postoperative complications are listed in Table 3.These were identified in 20.5% of 214 patients.The most frequent was mediastinal bleeding requiring re-exploration in five (2.3%) cases, and CHF in five (2.3%) cases.Six (2.2%) patients who developed complications died early postoperatively.
Based on the CT appearance of a localized area of ischemia, it is unlikely that this was due to air embolism.It is more consistent with a particulate matter embolization from the valve.We did not observe any complications resulting from the insertion of catheters in the coronary ostia during aortic valve surgery in patients requiring combined mitral and aortic valve operations.Also, we did not observe any cases of postoperative right ventricular failure or postoperative stroke resulting from intra-operative air embolization.

DISCUSSION
Mitral valve surgery is most commonly performed using the trans-atrial approach under aortic cross-clamping and cardioplegic arrest conditions.Several reports have appeared in the literature regarding surgical procedures utilizing beating-heart techniques in which aortic crossclamping and cardioplegic arrest were not used [3,10,11].Advantages of this method of myocardial protection include avoidance of ischemia-reperfusion injury, performance of surgery in a more physiologic state of the heart, decreased use of inotropic medications, and shorter hospital stay [10][11][12].Potential concerns related to this technique may include performance of surgery in a relatively blood-filled field, limited surgical precision due to difficult exposure, risk of air embolization, and limited ability to perform complex mitral valve repair procedures on the beating heart.We initially used the trans-atrial approach for this type of surgery and subsequently evolved to using the trans-septal approach.Reasons for the change in surgical strategy include better exposure of the mitral valve especially in small atria and redo operations, avoidance of aortic insufficiency induced by the mitral retractor, and technically easier de-airing of the heart at the end of the procedure [4].Potential concerns about this type of surgical approach through the atrial septum include the increased incidence of atrial arrhythmias and complete heart block, as well as residual atrial septal defect due to dehiscence of the atrial suture line.However, in our patients we did not observe either complication, although the incidence of atrial fibrillation remained significant in the range of 20-25%.
Trans-septal beating-heart mitral valve surgery may be especially useful in patients with dilated cardiomyopathy and decreased left ventricular systolic function, as previously confirmed by others [13].Conventional myocardial protective strategies may result in postoperative left ventricular dysfunction, especially in patients with preoperative myocardial dysfunction and in those requiring prolonged periods of aortic cross-clamping.Experimental studies by our group [14,15] demonstrated decreased accumulation of extracellular fluid, diminished lactate production, and greater preservation of high energy stores when a strategy of myocardial protection with simultaneous antegrade/retrograde continuous normothermic, normokalemic blood perfusion was used as compared to conventional cardioplegic arrest.
The beating-heart technique eliminates the detrimental effects of ischemia-reperfusion injury and allows for sustained normal myocardial energy metabolism during the period of intra-cardiac repair.This approach to mitral valve surgery has also been found to be useful in patients requiring mitral valve reoperations [16], as well as in those with ischemic mitral insufficiency [17,18], since myocardial ischemic injury is minimized.
In our patients postoperative survival using the beatingheart approach was comparable to contemporary series from the literature [19,20].The statistically significant difference in early mortality, 44% in patients requiring "salvage" operations and 3.2% in urgent or emergent cases, confirms that surgical outcomes in critically ill patients with multiple co-morbid conditions and multi system organ failure remain poor.It also raises the question as to whether some of these patients requiring "salvage" procedures should be treated medically and be excluded altogether from surgical intervention, irrespective of the surgical approach used.
Possible contraindications to beating-heart mitral valve surgery may include the inability to adequately expose the mitral valve, as well as the presence of large and mobile vegetations in patients with infective endocarditis or large left atrial thrombi, due to the risk of embolization.Should this be the case, the surgeon has the option of using conventional myocardial protection with aortic crossclamping and cardioplegic arrest.Alternatively, the aorta may be cross-clamped and continue myocardial perfusion may be provided by using a perfusion catheter inserted into the aortic root.Another technique that can help in reducing the risk of systemic embolization is the placement of a left ventricular suction catheter directly through the apex of the left ventricle.This strategy can result in effective left ventricular decompression, may facilitate de-airing of the ventricle, and it may eliminate the need to induce ventricular fibrillation for a short period while entering the left atrium.It is not possible to determine with certainty whether minor neuro-cognitive disorders due to microembolization occurred.We have not performed neurocognitive evaluation in these patients, but this is an important aspect that needs to be further investigated.
The presence of aortic insufficiency may also result in significant blood accumulation in the left ventricle as the mitral retractor is applied, and may represent a relative contraindication to beating-heart mitral valve surgery.In general, however, we have observed that aortic valve distortion, and consequent insufficiency, has been reduced by using a trans-septal approach as compared to a trans-atrial approach.When proper visualization of the mitral valve cannot be obtained, the surgeon has the option of cross-clamping the aorta and proceeding with cardioplegic arrest.This situation was not encountered in this series of patient.
In regard to the type of mitral valve procedure (repair versus replacement), in our experience the indications for performing a valve repair procedure are unchanged when using the beating-heart technique as compared to conventional cardioplegic arrest.When performing beating heart mitral valve replacement, preservation of the subvalvular apparatus is important to prevent ventricular dysfunction [21].The relatively low proportion of mitral valve repairs in this series (31%) as compared to mitral valve replacement was largely based on the fact that a variety of mitral valve disease processes were observed with significant frequency other than myxomatous degeneration and ischemic mitral valve disease, premiere indications for valve repair procedures.We do recognize, however, that in some cases in which complex repair procedures are needed, the beating-heart technique is technically more difficult and involves a significant learning curve.
We acknowledge that our study has several important limitations.In addition to the relatively small number of patients, we were unable to compare beating-heart patients with patients receiving conventional cardioplegic techniques.The clinical variables affecting outcomes in patients with mitral valve disease are numerous.The small sample size would have precluded a meaningful analysis in a patient population where many variables could have affected outcomes (different valve disease processes, age, EF, risk factors, etc.).Our study suggests that the beating-heart approach to mitral valve surgery has comparable survival to contemporary series in which conventional myocardial protective strategies were used.In fact, it confirms that surgical mortality for critically ill patients requiring salvage operations remains significant, probably as a result of powerful preoperative risk factors and co-morbidities.However, our experience suggests that the beating-heart mitral valve surgery is facilitated by using the trans-septal approach.Further studies are needed before the clinical benefits of the beating-heart technique can be demonstrated as compared to conventional myocardial protective strategies.

Fig. 1 -
Fig. 1 -General anatomy of the heart during mitral valve surgery.Note the fossa ovale, where the incision into the inter-atrial septum is initially made