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Ann Thorac Surg 2006;81:509-513
© 2006 The Society of Thoracic Surgeons

Original article: Cardiovascular

Atrial Incision Affects the Incidence of Atrial Tachycardia After Mitral Valve Surgery

Peter Lukac, MD a , * , Vibeke E. Hjortdal, MD, PhD b , Anders K. Pedersen, MD, DMSc a , Peter T. Mortensen, MD a , Henrik K. Jensen, MD, PhD a , Peter S. Hansen, MD, PhD a

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

Accepted for publication July 26, 2005.

* 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: Atrial fibrillation is common after mitral valve surgery. We do not know the incidence of atrial tachycardia and how it depends on the surgical approach used.

METHODS: The subjects of the study were 213 consecutive patients who had surgery for mitral valve disease from January 1, 2001, through January 26, 2004. The surgeons used either the superior transseptal approach (69 patients, group A) or left atrial approach (144 patients, group B). An investigator, blinded for the approach used, analyzed all 12-lead electrocardiograms taken during the admission after the operation. The data were analyzed using the Cox regression analysis as time from the operation until documentation of atrial tachycardia or atrial fibrillation on a 12-lead electrocardiogram. Hazard ratio (95% confidence interval) is reported.

RESULTS: The superior transseptal approach (2.0 [1.1 to 3.5], p = 0.023), age 60 years or more (2.3 [1.2 to 4.6], p = 0.015), and male sex (2.6 [1.3 to 5.2], p = 0.007) were independent predictors of atrial tachycardia. Age 60 years or more was the only independent predictor of atrial fibrillation (2.0 [1.2 to 3.3], p = 0.007). Although atrial tachycardia was less frequent than atrial fibrillation in group B (p < 0.001), atrial tachycardia was as common as atrial fibrillation in group A (p = 0.149).

CONCLUSIONS: The superior transseptal approach has a higher risk of atrial tachycardia than the left atrial approach. Atrial tachycardia has different predictors than atrial fibrillation and constitutes a significant problem, especially after the superior transseptal approach. These results emphasize the need to distinguish between atrial tachycardia and atrial fibrillation—two entities with different pathophysiology, therapy, and also epidemiology.


   Introduction
Top
 Abstract
 Introduction
Patients and Methods
 Results
 Comment
 Acknowledgments
 References
 
Atrial fibrillation (AF) is common after mitral valve surgery [1]. The literature does not sufficiently distinguish between AF and atrial tachycardia (AT), two very different entities. That is why we do not know the incidence and risk factors of the less frequent AT. We have observed surprisingly many cases of AT after mitral valve surgery using the superior transseptal approach. In this retrospective cohort study, we compare the incidence of AT and AF after mitral valve surgery using the superior transseptal and left atrial approaches.


   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 approach (group A) or the left atrial approach (group B) at the Department of Thoracic Surgery, Skejby University Hospital, from January 1, 2001, through January 26, 2004. Patients, who had an additional right atriotomy or a MAZE procedure, were not included.

Surgical Procedure
The superior transseptal approach was used primarily in patients with small left atria. The atrial incision of this approach was begun anteriorly in the right atrium and continued superiorly (Fig 1). 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.


Figure 1
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  		Fig 1. The superior transseptal approach. Incisions in the free wall of the right atrium (RA) and in the interatrial septum (IAS) are connected and prolonged to the superior portion of the left atrium (LA). (IVC = inferior vena cava; SVC = superior vena cava; PV = pulmonary vein.)

 
The surgeons used two left atrial approaches. One was performed between the confluence of the right pulmonary veins and the interatrial groove; the other, and less frequent one, was 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.

Postsurgical Management and Data Acquisition
Patients were monitored continuously using bedside monitors or telemetry for the first 16 to 24 hours after the operation. A 12-lead electrocardiogram (ECG) was obtained at any clinical suspicion of arrhythmia.

The information system at Skejby University Hospital contains information on diagnosis, date of the operation, intervention performed (mitral valve replacement, mitral valve repair), sex, and age at operation. Operation note was available for all patients.

The Danish Data Protection Agency approved the study October 15, 2003.

Atrial Tachycardia and Atrial Fibrillation
Patients who had chronic AF postoperatively (only AF on all ECGs) and patients who had no ECG obtained postoperatively were excluded from the analysis. An investigator (P.L.), blinded for the incision used, analyzed 12-lead ECGs taken immediately before operation and during the admission after the operation. Atrial tachycardia was defined as a sustained regular monomorphic atrial rhythm at a constant rate greater than 100 per minute originating outside the sinus node, documented on the whole length of a 12-lead ECG (10 seconds; Fig 2). The ratio or regularity of atrioventricular conduction was irrelevant to the diagnosis of AT; only the atrial activation had to be regular. Typical atrial flutter is the most frequent subgroup of AT [2].


Figure 2
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  		Fig 2. An example of atrial tachycardia. The regularity of the atrial rhythm is best appreciated in lead V1, where regular monomorphic negative P waves (their beginning is marked with the calipers), separated by a slightly descending plateau, can be appreciated. The cycle length is 220 ms. In this case, the differential diagnosis against atrial fibrillation might be difficult, if the ventricular rate was not regular. However, ventricular activation may not always be regular during atrial tachycardia.

 
Statistical Analysis
Incidence of atrial tachycardia
Curves of the time from operation to first AT documentation were calculated according to the method of Kaplan and Meier. The time from operation until discharge/death during admission, or start of AF that lasted until the end of admission was taken instead in patients without AT.

Incidence of atrial fibrillation
Curves of the time from operation to first AF documentation were calculated. The time from operation until discharge/death during admission was taken instead in patients without the documentation of AF. The time from the first operation until the reoperation was taken instead in patients who were reoperated on using an atriotomy and who did not have AT or AF between the two operations.

The significance of differences was examined by the log-rank test. The Cox regression analysis was used for multivariate analyses of risk of AT and AF during admission. Covariates studied were age at operation (less than 60 and 60 years or older), sex, preoperative rhythm (sinus rhythm/atrial paced rhythm versus atrial fibrillation), surgical approach (superior transseptal [group A] versus left atrial [group B]) and intervention performed (mitral valve replacement versus mitral valve repair). Comparison of proportions was performed using the {chi}2 test or Fisher's exact test, as appropriate. Comparison of continuous variables was performed using the Wilcoxon rank-sum test. All calculations were carried out using the statistical software Intercooled Stata Release 8 (Stata Corporation, College Station, Texas). Median (interquartile range) and hazard ratio (95% confidence intervals) are reported.


   Results
Top
 Abstract
 Introduction
 Patients and Methods
 Results
Comment
 Acknowledgments
 References
 
Of 236 patients included, 77 were in group A and 159 in group B. Postoperative ECG documentation was not available for 9 patients, and 14 patients had chronic AF postoperatively (only AF on all postoperative ECGs). Therefore, the analysis of AT and AF predictors was performed on 213 patients, 69 from group A and 144 from group B (Table 1). Age at operation was not different between the groups. Proportion of men was higher in group A. Preoperative atrial fibrillation and mitral valve repair tended to be more frequent in group B. Pacemakers were equally frequent in both groups.


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  		Table 1. Patient Characteristics
 
Atrial tachycardia developed in 48 patients, 24 in group A and 24 in group B (p = 0.006; Fig 3). Age 60 years or more, male sex, and group A were predictors of AT in univariate and multivariate analyses (Table 2).


Figure 3
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  		Fig 3. Kaplan-Meier curves showing cumulative event rates of atrial tachycardia for both groups. (Group A = superior transseptal approach; Group B = left atrial approach.)

 

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  		Table 2. Multivariate Analysis of Predictors of Atrial Tachycardia
 
The majority of AT had the morphology of typical atrial flutter. The shortest cycle length was 180 ms, the longest 370 ms. The cycle length and morphology of AT were not different between groups A and B (Table 3).


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  		Table 3. Characteristics of Atrial Tachycardia, by Group
 
Ninety patients had AF, 31 in group A and 59 in group B (p = 0.633; Fig 4). The same variables were tested in univariate and multivariate analyses as for AT. Preoperative AF and age more than 60 years were predictors of AF in univariate analysis. The only predictor of AF in multivariate analysis was age 60 years or more (Table 4).


Figure 4
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  		Fig 4. Kaplan-Meier curves showing cumulative event rates of atrial fibrillation in both groups. (Group A = superior transseptal approach; Group B = left atrial approach.)

 

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  		Table 4. Multivariate Analysis of Predictors of Atrial Fibrillation
 
While AT was less frequent than AF in group B (p < 0.001), AT was as common as AF in group A (p = 0.149; Fig 5).


Figure 5
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  		Fig 5. Kaplan-Meier curves showing cumulative event rates of atrial tachycardia and atrial fibrillation after the superior transseptal approach.

 

   Comment
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
Acknowledgments
 References
 
The present study shows that the superior transseptal approach has a higher risk of AT than the left atrial approach. Atrial tachycardia was very frequent after the superior transseptal approach. The predictors of AT were different from those of AF.

Incidence of Atrial Tachycardia After Surgery for Mitral Valve Disease
There are no data on the incidence of AT after mitral valve surgery. In our patients, the incidence of AT during admission after the left atrial approach (17%) corresponds well with the incidence found in patients after coronary artery bypass grafting, which was remarkably constant at 15% to 17% [3–5]. In our patients, after the superior transseptal approach, AT constituted a much greater problem (35%). In fact, AT was as frequent as AF in this group. Atrial tachycardia was more frequent in our patients after the superior transseptal approach than in patients undergoing the very arrhythmogenic Fontan operation (10%) [6]. The prognosis of AT arising during admission is not known. Studies are needed to determine whether it is predominantly a short-lived or a life-long problem and how it relates to AF. The results of these studies will show if we should start to think about a specific antiarrhythmic intervention to prevent AT in conjunction with mitral valve surgery using the superior transseptal approach.

Predictors of AT and AF
The majority of our patients had P-wave morphology during AT consistent with typical atrial flutter. The results of intracardiac mapping of AT after mitral valve surgery also suggest that typical atrial flutter is the most frequent circuit [7, 8]. Therefore, our study not surprisingly reproduced the results of Granada and colleagues [9], who showed that higher age and male sex are risk factors of typical atrial flutter in general population. The extensive right atrial incision forms a long proarrhythmogenic posterior line of block in typical atrial flutter [10] and the central obstacle in incisional AT, which may explain the high incidence of AT after the superior transseptal approach.

Distinction must be made between AT and AF after mitral valve surgery because their pathophysiology and therapy are fundamentally different. Atrial tachycardia, in contrast to AF, is typically based on a fixed reentry around surgical and anatomical obstacles and can be cured with radiofrequency catheter ablation of a crucial isthmus in the circuit [7, 8, 11]. Atrial tachycardia can be, in contrast to AF, acutely terminated by rapid atrial pacing, a treatment that is frequently available through temporary epicardial wires after heart surgery [5]. Possible surgical strategies, therapeutic and preventive, are also different from those applicable to AF [6, 12, 13]. The present study shows that also the epidemiology of these two entities is different. The only predictor of AF was higher age, corresponding to the findings in a large study of unselected patients undergoing cardiac surgery [1] and patients after mitral valve surgery [14]. In agreement with Utley and associates [14] and Tambeur and coworkers [15], the approach used was not a predictor for AF in our study.

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, has the advantage of compensating for differences in the occurrence of endpoints caused by shorter follow-up time in one of the groups.

Limitations
This is not a randomized study, and selection bias toward patients at higher risk of AT in the group with the superior transseptal approach cannot be excluded. However, several facts suggest that not other factors but the arrhythmogenicity of the incision is responsible for the higher incidence of AT in patients after the superior transseptal approach. (1) We adjusted, besides other variables, for two important risk factors of AT [11] in the multivariate analysis—age and sex. (2) The surgeons used the superior transseptal approach in patients with small left atria, where the access to the mitral valve may be difficult using the left atrial approach. That and the lower prevalence of AF before the operation suggest that the patients operated on with the superior transseptal approach were not those with more advanced mitral valve disease. (3) The superior transseptal approach was not a risk factor for atrial fibrillation.

The occurrence of AT and AF during admission was determined based on the documentation of the arrhythmia on a 12-lead ECG. We certainly missed some episodes, especially the short and asymptomatic ones. On the other hand, short bursts of AF and AT, documented by chance because they occurred exactly at the time of ECG recording, played probably not an important role in the analysis. The majority of them would start or end on a 10-second 12-lead ECG tracing and would therefore be excluded. This selection bias toward longer and more severe arrhythmias might be advantageous in that our analysis describes a more clinically significant phenomenon.

In summary, the superior transseptal approach has a higher risk of AT than the left atrial approach. Atrial tachycardia constitutes a significant clinical problem after the superior transseptal approach. The surgeon should take this into account when choosing the superior transseptal approach. The high incidence of AT after mitral valve surgery emphasizes the need to distinguish between AT and AF—two entities with different pathophysiology, treatment, and also epidemiology.


   Acknowledgments
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
 Acknowledgments
References
 
Doctor Peter Lukac has been supported by a Training Fellowship of the European Society of Cardiology, the Slovak Society of Cardiology, the Danish Research Agency, Ejnar and Aase Danielsen's Fund, Dagmar Marshall's Fund, and Grant 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, Signe Holm Larsen from the Department of Thoracic Surgery for the help with the analysis of preoperative rhythm, and Ken Kragsfeldt from the Audiovisual Department, Aarhus University Hospital for the illustration in Figure 1.


   References
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
 Acknowledgments
 References
 

  1. Creswell LL, Schuessler RB, Rosenbloom M, Cox JL. Hazards of postoperative atrial arrhythmias Ann Thorac Surg 1993;56:539-549.[Abstract]
  2. Saoudi N, Cosio F, Waldo A, et al. A classification of atrial flutter and regular atrial tachycardia according to electrophysiological mechanisms and anatomical basesa statement from a joint expert group from the Working Group of Arrhythmias of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. Eur Heart J 2001;22:1162-1182.[Free Full Text]
  3. Mori SS, Fujii GG, Ishida HH, Tomari SS, Matsuura AA, Yoshida KK. Atrial flutter after coronary artery bypass graftingproposed mechanism as illuminated by independent predictors. Ann Thorac Cardiovasc Surg 2003;9:50-56.[Medline]
  4. Taylor AD, Groen JG, Thorn SL, Lewis CT, Marshall AJ. New insights into onset mechanisms of atrial fibrillation and flutter after coronary artery bypass graft surgery Heart 2002;88:499-504.[Abstract/Free Full Text]
  5. Waldo AL, MacLean WA, Cooper TB, Kouchoukos NT, Karp RB. Use of temporarily placed epicardial atrial wire electrodes for the diagnosis and treatment of cardiac arrhythmias following open-heart surgery J Thorac Cardiovasc Surg 1978;76:500-505.[Abstract]
  6. Collins KK, Rhee EK, Delucca JM, et al. Modification to the Fontan procedure for the prophylaxis of intra-atrial reentrant tachycardiashort-term results of a prospective randomized blinded trial. J Thorac Cardiovasc Surg 2004;127:721-729.[Abstract/Free Full Text]
  7. 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 systemwhich circuits to expect in which substrate?. Heart Rhythm 2005;2:64-72.[Medline]
  8. Schalij MJ, de Groot NM, Chan WK, Rahatianpur M, Van der Wall EE. Post-operative atrial tachycardias in patients with mitral valve diseasewhat is the location of the arrhythmogenic substrate [abstract]?. Heart Rhythm 2005;2(Suppl):S2.
  9. Granada J, Uribe W, Chyou PH, et al. Incidence and predictors of atrial flutter in the general population J Am Coll Cardiol 2000;36:2242-2246.[Abstract/Free Full Text]
  10. Chan DP, Van Hare GF, Mackall JA, Carlson MM, Waldo AL. Importance of atrial flutter isthmus in postoperative intra-atrial reentrant tachycardia Circulation 2000;102:1283-1289.[Abstract/Free Full Text]
  11. Markowitz SM, Brodman RF, Stein KM, et al. Lesional tachycardias related to mitral valve surgery J Am Coll Cardiol 2002;39:1973-1983.[Abstract/Free Full Text]
  12. Henglein D, Cauchemez B, Bloch G. Simultaneous surgical treatment of atrial septal defect and atrial flutter using a simple modification of the atrial incision Cardiol Young 1999;9:197-199.[Medline]
  13. Rodefeld MD, Gandhi SK, Huddleston CB, et al. Anatomically based ablation of atrial flutter in an acute canine model of the modified Fontan operation J Thorac Cardiovasc Surg 1996;112:898-907.[Abstract/Free Full Text]
  14. Tambeur L, Meyns B, Flameng W, Daenen W. Rhythm disturbances after mitral valve surgerycomparison between left atrial and extended trans-septal approach. Cardiovasc Surg 1996;4:820-824.[Medline]
  15. Utley JR, Leyland SA, Nguyenduy T. Comparison of outcomes with three atrial incisions for mitral valve operations. Right lateral, superior septal, and transseptal J Thorac Cardiovasc Surg 1995;109:582-587.[Abstract/Free Full Text]



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