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Ann Thorac Surg 2007;83:77-82
© 2007 The Society of Thoracic Surgeons

Original Articles: Cardiovascular

Superior Transseptal Approach to Mitral Valve Is Associated With a Higher Need for Pacemaker Implantation Than the Left Atrial Approach

Peter Lukac, MD, PhDa,*, Vibeke E. Hjortdal, MD, PhDb, Anders K. Pedersen, MD, DMSca, Peter T. Mortensen, MDa, Henrik K. Jensen, MD, PhDa, Peter S. Hansen, MD, PhDa

a Department of Cardiology, Aarhus University Hospital at Skejby, Aarhus, Denmark
b Department of Cardiothoracic Surgery, Aarhus University Hospital at Skejby, Aarhus, Denmark

Accepted for publication August 18, 2006.

* Address correspondence to Dr Lukac, Department of Cardiology, Skejby University Hospital, DK-8200 Aarhus N, Denmark (Email: lukacpe2{at}hotmail.com).


   Abstract
Top
 Abstract
Introduction
 Patients and Methods
 Results
 Comment
 Acknowledgments
 References
 
BACKGROUND: Several studies suggest that the superior transseptal approach to mitral valve surgery leads to sinus node dysfunction. The clinical consequences are not known.

METHODS: Consecutive patients undergoing surgery for mitral valve disease from November 16, 1994 through January 26, 2004 were retrospectively evaluated. The surgeons used either the superior transseptal (group A) or left atrial approach (group B). The risk of pacemaker implantation associated with the superior transseptal approach as compared with the left atrial approach was estimated using the multivariate Cox regression analysis to adjust for possible confounders.

RESULTS: We included 577 patients, 150 in group A and 427 in group B. Forty-four patients had a pacemaker implanted after the surgery; 17 in group A and 27 in group B (p = 0.010). The superior transseptal approach was an independent risk factor of pacemaker implantation in multivariate analysis (hazard ratio 2.2 [1.2 to 4.1], p = 0.014). Nineteen patients had a pacemaker implanted because of sinus node dysfunction; 9 in group A and 10 in group B (p = 0.017). Group A was an independent predictor of pacemaker implantation because of sinus node dysfunction in bivariate analyses. The risk of pacemaker implantation because of atrioventricular conduction disturbances was not different between the groups (p = 0.178).

CONCLUSIONS: The superior transseptal approach has a higher risk of clinically significant sinus node dysfunction than the left atrial approach.


   Introduction
Top
 Abstract
 Introduction
Patients and Methods
 Results
 Comment
 Acknowledgments
 References
 
The left atrial and the superior transseptal are the two main approaches to mitral valve surgery. Several authors [1–4] claim that the superior transseptal approach allows for better exposure of the mitral valve, especially when the left atrium is small. A wide application of this technique has been recommended [5]. Several centers use the superior transseptal approach as a standard. However, increased ischemia time, cardiopulmonary bypass, and cross-clamp time, and increased bleeding are possible drawbacks associated with this approach [2, 4].

Arrhythmias also are a concern when using the superior transseptal approach. Early atrial tachycardia is more frequent when the superior transseptal approach is used [6]. Several studies [2, 3, 7–9] suggest that the superior transseptal approach is associated with sinus node dysfunction. The problem of sinus node dysfunction after the superior transseptal approach obviously has implications for the surgeon’s choice of the approach. To assess if sinus node dysfunction really is a clinically significant problem, we retrospectively analyzed the need for pacemaker implantation on a large cohort of patients after mitral valve surgery with long-term follow-up.


   Patients and Methods
Top
 Abstract
 Introduction
 Patients and Methods
Results
 Comment
 Acknowledgments
 References
 
Patient Selection
The subjects of the study were consecutive patients who had surgery for mitral valve disease using either the superior transseptal (group A) or left atrial (group B) approaches at the Department of Cardiothoracic Surgery, Aarhus University Hospital at Skejby from November 16, 1994 through January 26, 2004. Patients who had an additional right atriotomy or a MAZE procedure as well as patients who had a pacemaker implanted before the operation were excluded. The Danish Data Protection Agency approved the study October 15, 2003.

Surgical Procedure
We have previously published [10] the illustrations of the two surgical approaches to the mitral valve. The superior transseptal approach was used infrequently before 1999. The surgeons used this approach primarily in patients with small left atria. The superior transseptal approach was begun anteriorly in the right atrium and continued superiorly. A vertical incision was made in the septum starting in the fossa ovalis. The two incisions were connected superiorly and continued onto the superior portion of the left atrium.

The surgeons used two left atrial approaches. Neither of them disturbs the intraatrial septum. One was performed between the confluence of the right pulmonary veins and the interatrial groove, the other and less frequent one in the dome of the left atrium between the superior left and right pulmonary veins. We did not distinguish between these two left atrial incisions in the analysis. In all patients a cold crystalloid cardioplegia using the St. Thomas solution was used.

Postsurgical Management and Data Acquisition
Patients were monitored continuously using bedside monitors or telemetry for the first 16 to 24 hours after the operation, and further if clinically indicated. Pacemakers were implanted according to currently valid American College of Cardiology/American Heart Association/North American Society for Pacing and Electrophysiology indication criteria.

The information system at Aarhus University Hospital at Skejby contains information on date of the operation, age at operation, gender, diagnosis, intervention performed (mitral valve replacement, mitral valve repair), concomitant aortic valve replacement and coronary artery bypass grafting (CABG), survival status, and date of death. Operation note was available for all patients. The Danish Pacemaker Register [11] provided information on pacemaker implantation during follow-up, the date of pacemaker implantation, and indication (sinus node dysfunction or atrioventricular conduction disturbance).

Statistical Analysis
Survival curves of the time from operation to pacemaker implantation were estimated using the Kaplan-Meier method. Patients without pacemaker implantation during follow-up were censored at the end of follow-up or at time of death. The time from the first operation until a reoperation was used in patients with a reoperation during follow-up and no pacemaker implantation between the two operations. Follow-up was terminated on May 31, 2004.

The significance of differences between groups was examined by the log-rank test. The Cox regression analysis was used for multivariate analyses. To investigate, if the increased need for pacemaker and the increased need for pacemaker because of sinus node dysfunction associated with the superior transseptal incision were modified by other covariates, we first performed a series of Cox regression analyses with two covariates, where one of the selected variables was the surgical approach. Variables which influenced the hazard ratio of the superior transseptal approach were then included in a multivariate analysis of the risk of pacemaker (no such analysis was attempted for the risk of pacemaker because of sinus node dysfunction and because of atrioventricular conduction disturbances, as the number of end points was limited). Covariates studied were the following: age at operation (<60 vs ≥60 years), gender, mitral valve disease (mitral stenosis or mitral regurgitation; combined mitral stenosis and regurgitation was classified as stenosis), presence of active endocarditis, surgical approach (superior transseptal = group A versus left atrial = group B), atrial rhythm on the immediate preoperative electrocardiogram, procedure performed (mitral valve replacement versus mitral valve repair), associated aortic valve replacement and CABG, and documentation of atrial fibrillation or flutter during the postoperative stay in the hospital.

Comparison of proportions was performed using the {chi}2 test or the Fisher exact test, as appropriate. Comparison of continuous variables was performed using the Student t test or Wilcoxon rank sum test, as appropriate. All calculations were carried out using the statistical software Intercooled Stata Release 8 (Stata Corporation, College Station, TX). Median (25th and 75th percentiles) and hazard ratio (95% confidence intervals) are reported.


   Results
Top
 Abstract
 Introduction
 Patients and Methods
 Results
Comment
 Acknowledgments
 References
 
We included 577 patients; 150 in group A and 427 in group B. The clinical characteristics of the patients are summarized in Table 1.


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  		Table 1. Clinical Characteristics and Surgical Procedures: Comparison Between the Two Groups
 
A total of 44 patients had pacemakers implanted; 17 in group A and 27 in group B (p = 0.010) (Fig 1). Also, high age and postoperative atrial fibrillation or flutter were significant univariate predictors of pacemaker implantation (Table 2). The superior transseptal surgical approach remained an independent predictor of pacemaker implantation in the series of analyses with correction for one additional covariate (Table 2) and in a multivariate analysis including covariates influencing the hazard ratio; gender and postoperative atrial fibrillation or flutter (hazard ratio 2.2 [1.2 to 4.1], p = 0.014).


Figure 1
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  		Fig 1. Kaplan-Meier curves showing cumulative event rates of pacemaker implantation. (Group A = the superior transseptal approach; group B = the left atrial approach.)

 

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  		Table 2. Predictors of the Need for Pacemaker Implantation in the Univariate Analysis (Log-Rank Test), Bivariate Analysis With Group as a Covariate and the Hazard Ratio of the Superior Transseptal Approach After Adjustment for the Respective Predictor
 
Sinus Node Dysfunction
Nineteen patients had pacemakers implanted because of sinus node dysfunction; 9 in group A and 10 in group B (p = 0.017) (Fig 2). Median time from the operation to pacemaker implantation was 11 (8, 15) days in group A and 12 (8, 188) days in group B (p = 0.653). The clinical characteristics of these patients are summarized in Table 3. None of the patients had a tricuspid intervention, a repeat operation, an ablative arrhythmia operation, a mitral valve annular reconstruction, or cold blood cardioplegia (Table 4). The superior transseptal surgical approach remained a significant predictor also after adjustment for all the other covariates in bivariate analyses (Table 5).


Figure 2
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  		Fig 2. Kaplan-Meier curves showing cumulative event rates of pacemaker implantation because of sinus node dysfunction. (Group A = the superior transseptal approach; group B = the left atrial approach.)

 

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  		Table 3. Clinical Characteristics of Patients With Sinus Node Dysfunction
 

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  		Table 4. Surgical Procedures and Complications in Patients With Sinus Node Dysfunction
 

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  		Table 5. Predictors of the Need for Pacemaker Implantation Because of Sinus Node Dysfunction in the Univariate Analysis (Log-Rank Test), Bivariate Analysis With Group as a Covariate and the Hazard Ratio of the Superior Transseptal Approach After Adjustment for the Respective Predictor
 
Atrioventricular Conduction Disturbances
Twenty-five patients had a pacemaker implanted because of atrioventricular conduction disturbances; 8 in group A and 17 in group B (p = 0.178) (Fig 3). The only significant univariate predictor of pacemaker implantation because of atrioventricular conduction disturbances was age 60 years or greater (p = 0.037).


Figure 3
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  		Fig 3. Kaplan-Meier curves showing cumulative event rates of pacemaker implantation because of atrioventricular conduction disturbances. (Group A = the superior transseptal approach; group B = the left atrial approach.)

 

   Comment
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
Acknowledgments
 References
 
The main finding of the present study is that the superior transseptal approach in comparison with the left atrial approach is associated with an increased need for pacemaker implantation. While the superior transseptal approach was associated with a higher need for pacemaker because of sinus node dysfunction, the difference in the need for pacemaker implantation because of atrioventricular conduction disturbances was not different between the two groups. The higher need for pacemaker implantation was independent of the age, gender, mitral pathology, the presence of endocarditis, preoperative rhythm, associated CABG and aortic valve replacement, postoperative atrial fibrillation and flutter, and whether the valve was replaced or repaired. It is unlikely that other known risk factors for pacemaker implantation influence the results, as these were not present in our patients with sinus node dysfunction [12]. The need for pacemaker implantation because of atrioventricular conduction disturbances was not different between the two approaches.

Previous Studies
Several studies smaller than ours noted signs of early sinus node dysfunction with the use of the superior transseptal approach in univariate [2, 3] and multivariate analyses [8, 9]. Sinus node dysfunction manifested as transient or persistent junctional rhythm and need for temporary pacing in these studies. The only randomized study [4] addressing this issue also found a trend toward a higher incidence of early junctional rhythm in the group with the superior transseptal approach on 146 patients (p = 0.065). On the other hand, Misawa and colleagues [13] did not observe any sign of sinus node dysfunction on 52 patients.

After the superior transseptal approach, some of the patients showed abnormal sinoatrial conduction time and abnormal intrinsic heart rate 12 to 26 months after the surgery [7]. Shin and colleagues [14] found normal mean values of different invasive indices of sinus node function. However, their study does not report the individual values and lacks data from a control group operated using the left atrial approach.

Utley and colleagues [9] reported an increased rate of pacemaker implantation with the superior transseptal approach in univariate analysis, but did not study the indications for pacemaker implantation. They could not use multivariate analysis because they had only 14 patients with pacemakers. Masiello and colleagues [2] reported the same finding, but concerning temporary pacemakers. Utley and colleagues [9] made an important observation that the superior transseptal approach is associated with a higher risk of loss of sinus rhythm. Apart from the sinus node dysfunction, atrial tachycardia and flutter are known complications after the superior transseptal approach leading to the loss of sinus rhythm [6]. On the other hand, the incidence of atrial fibrillation is no higher with the superior transseptal approach than with the left atrial approach [6].

Another approach to mitral valve, not used in the present study, is the vertical transseptal approach, which respects the roof of the right atrium. Sinus node dysfunction probably does not complicate this approach, but the data are limited [15].

Influence of Other Factors
Gordon and colleagues [12] defined independent risk factors predicting permanent pacemaker implantation after a cardiac operation on a group of 10,421 consecutive patients. We adjusted for several of these risk factors in multivariate analyses (age, the presence of endocarditis, mitral valve replacement, and aortic valve replacement). Other risk factors (tricuspid replacement surgery, repeat operation, ablative arrhythmia operation, mitral valve annular reconstruction, cold blood cardioplegia) were not present in our patients with sinus node dysfunction. Only two patients had preoperative renal failure. Therefore, the higher need for pacemaker implantation because of sinus node dysfunction in our patients after the superior transseptal approach was not the result of bias by these known risk factors.

Patients with ischemic heart disease may be at risk for bradycardia because of the involvement of the sinus node, the conduction system, and because of the effects of medication. Not surprisingly, concomitant CABG was associated with an increased need for pacemaker implantation and pacemaker implantation because of sinus node dysfunction in the present study. The superior transseptal approach remained an independent risk factor also after adjustment for concomitant CABG.

Similarly, atrial fibrillation is frequently associated with sinus node dysfunction and antiarrhythmic medication prescribed for atrial fibrillation can cause bradycardia. Postoperative atrial fibrillation and flutter was associated with an increased need for pacemaker implantation and pacemaker implantation because of sinus node dysfunction in the present study. The superior transseptal approach remained an independent risk factor also after adjustment for preoperative and postoperative atrial fibrillation and flutter.

Pathogenesis of Sinus Node Dysfunction After Superior Transseptal Approach
Berdajs and colleagues [16] showed that the damage to the sinus node artery, with resulting ischemia of the sinus node region, is very probable during the superior transseptal approach. Another explanation for the high incidence of sinus node dysfunction, suggested in the literature, is that the region of the posterior right atrium, including the sinus node, becomes electrically isolated after placement of the extensive incision. We observed this phenomenon in one of 10 patients after the superior transseptal approach undergoing radiofrequency catheter ablation of atrial flutter [10]. The clinical relevance of electrical isolation of the sinus node region is not very likely, however, because independent P waves coming from the isolated part of the atrium should then be visible at least in some of the patients with junctional rhythm. These P waves should not be difficult to see because the junctional rhythm is typically slow without any visible atrial activity or with P waves coincident with the QRS complex. We did not observe isolated P waves in these patients, neither are we aware of any reports mentioning this phenomenon.

Statistical Analysis
In the present study, the data have been analyzed as time-to-event. This type of analysis, in comparison with logistic regression analysis used in other studies [8, 9], has the advantage of compensating for differences in the occurrence of end points caused by shorter follow-up time in one of the groups. In the subanalysis of implantations because of sinus node dysfunction a full multivariate analysis was not feasible due to the limited number of end points. Instead, we adjusted for several possible confounding variables one at a time.

Limitations
This is not a randomized study and selection bias toward patients at higher risk of sinus node dysfunction due to unknown factors in the group with the superior transseptal approach cannot be completely excluded. However, we adjusted for several risk factors and other known risk factors were not present in patients who received a pacemaker because of sinus node dysfunction. A prospective randomized study is needed to prove definitively that the superior transseptal approach causes sinus node dysfunction.


   Acknowledgments
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
 Acknowledgments
References
 
Dr. Peter Lukac has been supported by a Training Fellowship of the European Society of Cardiology, the Slovak Society of Cardiology, the Danish Research Agency, the Ejnar and Aase Danielsens Fund, the Dagmar Marshalls Fund, and Grant No. 04-10-B38-A155-22202 of the Danish Heart Foundation. The authors would like to thank Joan Lisbeth Christensen from the Department of Cardiology for secretarial support and Professor Michael Vaeth from the Department of Biostatistics, University of Aarhus, for statistical advice.


   References
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
 Acknowledgments
 References
 

  1. Masuda M, Tominaga R, Kawachi Y, et al. Postoperative cardiac rhythms with superior-septal approach and lateral approach to the mitral valve Ann Thorac Surg 1996;62:1118-1122.[Abstract/Free Full Text]
  2. Masiello P, Triumbari F, Leone R, Itri F, Del Negro G, Di Benedetto G. Extended vertical transseptal approach versus conventional left atriotomy for mitral valve surgery J Heart Valve Dis 1999;8:440-444.[Medline]
  3. Kumar N, Saad E, Prabhakar G, De Vol E, Duran CM. Extended transseptal versus conventional left atriotomy: early postoperative study Ann Thorac Surg 1995;60:426-430.[Abstract/Free Full Text]
  4. Gaudino M, Alessandrini F, Glieca F, et al. Conventional left atrial versus superior septal approach for mitral valve replacement Ann Thorac Surg 1997;63:1123-1127.[Abstract/Free Full Text]
  5. Alfieri O, Sandrelli L, Pardini A, et al. Optimal exposure of the mitral valve through an extended vertical transeptal approach Eur J Cardiothorac Surg 1991;5:294-298.[Abstract]
  6. Lukac P, Hjortdal VE, Pedersen AK, Mortensen PT, Jensen HK, Hansen PS. Atrial incision affects the incidence of atrial tachycardia after mitral valve surgery Ann Thorac Surg 2006;81:509-513.[Abstract/Free Full Text]
  7. Takeshita M, Furuse A, Kotsuka Y, Kubota H. Sinus node function after mitral valve surgery via the transseptal superior approach Eur J Cardiothorac Surg 1997;12:341-344.[Abstract]
  8. Tambeur L, Meyns B, Flameng W, Daenen W. Rhythm disturbances after mitral valve surgery: comparison between left atrial and extended trans-septal approach Cardiovasc Surg 1996;4:820-824.[Medline]
  9. Utley JR, Leyland SA, Nguyenduy T. Comparison of outcomes with three atrial incisions for mitral valve operationsRight lateral, superior septal, and transseptal. J Thorac Cardiovasc Surg 1995;109:582-587.[Abstract/Free Full Text]
  10. Lukac P, Pedersen AK, Mortensen PT, Jensen HK, Hjortdal V, Hansen PS. Ablation of atrial tachycardia after surgery for congenital and acquired heart disease using an electroanatomic mapping system: which circuits to expect in which substrate? Heart Rhythm 2005;2:64-72.[Medline]
  11. Danish pacemaker and ICD register1999. Pacing Clin Electrophysiol 2000;23:S1-S93.[Medline]
  12. Gordon RS, Ivanov J, Cohen G, Ralph-Edwards AL. Permanent cardiac pacing after a cardiac operation: predicting the use of permanent pacemakers Ann Thorac Surg 1998;66:1698-1704.[Abstract/Free Full Text]
  13. Misawa Y, Fuse K, Kawahito K, Saito T, Konishi H. Conduction disturbances after superior septal approach for mitral valve repair Ann Thorac Surg 1999;68:1262-1264.[Abstract/Free Full Text]
  14. Shin H, Yozu R, Higashi S, Kawada S. Sinus node function after mitral valve surgery using the superior septal approach Ann Thorac Surg 2001;71:587-590.[Abstract/Free Full Text]
  15. McGrath LB, Levett JM, Gonzalez-Lavin L. Safety of the right atrial approach for combined mitral and tricuspid valve procedures J Thorac Cardiovasc Surg 1988;96:756-759.[Abstract]
  16. Berdajs D, Patonay L, Turina MI. The clinical anatomy of the sinus node artery Ann Thorac Surg 2003;76:732-735.[Abstract/Free Full Text]



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