Permanent pacemaker insertion postmitral surgery: Do the atrial access and the origin of the sinoatrial node artery matter?

To determine whether the type of atrial access to the mitral valve (left atriotomy, superior trans‐septal, or limited trans‐septal) influenced postoperative permanent pacemaker implantation and to investigate the effect of the sinoatrial (SA) node artery origin (right coronary or circumflex arteries) on the rate of pacemaker insertion.


| INTRODUCTION
Traditionally, left atriotomy is the incision of choice to access the mitral valve. Guiraudon et al 1 were the first to report the extended vertical transatrial septal approach, also known as the superior transseptal approach. Early results were encouraging with excellent exposure of the mitral valve without inherent complications. Subsequently, the superior trans-septal approach was accepted and adopted due to the ease of access to the mitral valve, especially in cases when the left atrium is small. In our review, we found that the superior transseptal incision was safe and all papers except for one showed a similar rate of postoperative permanent pacemaker implantation (PPM) in comparison to the limited trans-septal approach and the standard left atriotomy. 2 Some authors hypothesized that due to its anatomical topography, the sinoatrial (SA) node artery was at risk of injury during the superior trans-septal approach. 3 In our study, we investigated the risk of postoperative PPM in three types of mitral valve approaches, the left atriotomy, the limited trans-septal, and the superior trans-septal incisions. We also studied the anatomical variation of the origin of the SA node artery on coronary angiography and the impact of this variation on the rate of postoperative PPM.

| Operative techniques
Following a median sternotomy, cardiopulmonary bypass was instituted with cannulation of the aorta and both venae cava.

| Left atriotomy
An incision is made just posterior and parallel to the interatrial groove (also known as Waterstonʼs or Sondergaardʼs groove). The incision is extended to the right superior pulmonary artery superiorly, and inferiorly to the back of the heart toward the mitral annulus to improve exposure while leaving a generous cuff for the closure.

| Limited trans-septal incision
The two caval snares are secured. An incision is made parallel to the atrioventricular (AV) groove, leaving a 1-cm atrial cuff to facilitate later atrial closure and to avoid injury of the right coronary artery (RCA). The incision is extended cephalad toward the right atrial appendage and caudad toward a midpoint between the inferior vena cava and the AV groove. A separate incision is made through the fossa ovale. It is extended caudad to the base of the fossa ovale and cephalad toward the base of the superior vena cava; care must be taken not to injure the aortic root by keeping the trans-septal incision medial.

| Superior trans-septal incision
Similar to limited trans-septal incision, the two caval snares are secured and a right atriotomy is made as described above. The transseptal incision through the fossa ovale is directed cephalad toward the dome of the left atrium and connected with the extended right atrial incision ( Figure 1).

| Choice of the type of atrial incision
The choice of the atrial incision was surgeon-dependent, irrespective of the size of the left atrium. Each surgeon opted toward a particular type of atrial incision due to familiarity with the technique. One surgeon changed his technique from the limited to the superior trans-septal incision in rare occasions when the left atrium was small.

| Postoperative period and follow-up
All patients had continuous electrocardiogram recordings (telemetry) during the first 48 to 72 hours after surgery and for a more extended period when indicated. Twelve lead electrocardiograms were recorded on day 1, day 4, and 6-weeks after hospital discharge.
Indications for permanent pacemaker insertion were in line with the American College of Cardiology/American Heart Association guidelines for implantation of cardiac pacemakers. 4 In all cases, the cardiologists were involved in the decision making of PPM.

| Statistics
The data are presented as means with standard deviation and medians with interquartile range (IQR). For comparing the three incision types, one-way analysis of variance test was used to compare the difference in means and χ 2 for binary or categorical   Tables 1 and 2. For comparing the baseline characteristics between the three groups (left atriotomy, limited trans-septal, and superior trans-septal approaches), only sex (female) and concomitant tricuspid valve surgery were significantly different between the three groups (P = .007, P < .0001, respectively). Over the last 2 years of this study, we tended to perform more concomitant tricuspid valve repairs in patients with moderate tricuspid regurgitation and also in tricuspid annular dilatation (more than

| Postoperative pacemaker insertion
In total, 25 permanent pacemakers were implanted (5.3%). The rate of PPM insertion was similar between the three incisions (left atriotomy; 5.3%, limited trans-septal; 5.3%, and superior trans-septal; 5.4%, P = 1.00). The causes of PPM insertion are summarized in Table 3. The median duration from time of surgery to PPM insertion was 13 days (IQR; 5).
On univariate analysis, only age and concomitant tricuspid surgery were the risk factors for PPM insertion, P = .004 and .015, respectively (Table 4). On multivariate analysis, age remained as a risk factor for PPM insertion (P = .015) while the type of atrial incision and the origin of the SA node artery were not the predictors of PPM insertion (Table 5).

| Origin of the sinoatrial node artery
Coronary angiograms were performed in 376 cases, the SA node artery originated from the right coronary ( Figure 3) and the left circumflex ( Figure 4) arteries in 66.5% and 30.8%, respectively. In 0.8% of cases, the SA node artery had a dual origin from both the right coronary and the circumflex arteries. It was not possible to assess the origin of the SA node artery due to concomitant significant coronary artery disease in 1.9% of the cases. On univariate and multivariate analysis, the origin of the SA node artery from the circumflex was not a risk factor for PPM implantation (Table 4; Figure 5).

| DISCUSSION
In this large study, there was no difference in the rate of PPM between left atriotomy, limited trans-septal, and superior transseptal approaches. The patient age was a risk factor for PPM. The SA node artery originated from either the RCA, the left circumflex, or had a combined origin. The origin of the SA node artery was not a risk factor for postoperative PPM implantation. to the mitral valve, and it was used regardless of the size of the heart. In our recent review paper, we found no difference in PPM insertion between the trans-septal approach and the left atriotomy and that the superior trans-septal approach could be associated with a higher rate of PPM implantation due to sinus node dysfunction. 2 Lukac et al 6 conducted a large study whereby there was a higher incidence of PPM insertion in the superior trans-septal approach in comparison to the standard left atriotomy due to sinus node dysfunction, whereas PPM implantation due to AV node dysfunction did not differ. Other studies did not corroborate the findings of Lukac et al and did not find a significantly higher incidence of PPM implantation with the superior trans-septal approach. [7][8][9] The origin and the course of the SA node artery have been extensively reported. In a large meta-analysis, Vikse et al 10 showed that the SA node artery originated from the RCA in the majority of cases (68%), followed by the left circumflex (22%), common origin from RCA, and left circumflex or other types of combined origins (ie, RCA and left coronary artery, RCA, and bronchial artery). Three main courses of the SA node artery were also described: retrocaval (47.1%), precaval (38.9%), or pericaval course (14%). The precaval course was found to be associated with a lower incidence of SA node artery injury during the superior trans-septal approach. Another paper reported a detailed anatomical study of 50 human hearts, whereby the SA node artery relationship with the interatrial septum was studied. The SA node artery originated either from the RCA (66%) or the left coronary artery (34%).
The SA node artery crossed the superior posterior border of the interatrial septum (retrocaval course) in all 17 cases of the left SA node artery (34%), whereas, the right SA node artery crossed the superior posterior border in only 10 cases (20%). The authors concluded that there is potentially a high risk of intraoperative injury to the SA node artery during the superior trans-septal approach, especially when the SA node originates from the left coronary artery. 3 Guiraudon et al 1 suggested that the blood supply from the SA node artery does not seem essential to maintain sinus node function.
Noncoronary blood supply contributes considerably to atrial myocardial revascularization, and this argument is supported by the fact This observation tallies up with the findings of our review whereby we concluded that the incidence of transient junctional rhythm was higher in the superior trans-septal approach. 4 Progression from junctional to sinus rhythm in some cases of the superior trans-septal approach could be explained by a change of the site of the sinus impulse to a different region as described in the experimental study conducted by Sealy et al, 11 or by the fact that the SA node does not rely entirely on the SA node artery for blood supply as suggested by Guiraudon et al. 1 We acknowledge that our study is limited by its retrospective nature, and also, the sample size did not allow for full risk adjustment, which is a major limitation.

| CONCLUSIONS
In summary, we found no significant difference in the rate of PPM between the three atrial incisions. The origin of the SA node artery F I G U R E 5 Operative view through a median sternotomy showing the artery to the sinus node, which in this case originates from the circumflex coronary artery and extends across the dome of the left atrium did not influence the rate of pacemaker implantation. It is the surgeonʼs choice to decide on the type of atrial incision to access the mitral valve.

AUTHOR CONTRIBUTIONS
AB contributed in concept/design, data collection, data analysis/ interpretation, drafting article, critical revision of article, approval of article, and statistics. DN performed data collection, article drafting, critical revision of article, and approval of article. AS contributed in concept/design, critical revision of article, and approval of article. DR contributed in concept/design, critical revision of article, and approval of article.