Atrial approaches in mitral valve surgery: a propensity analysis of differences in the incidence of clinically relevant adverse effects

Despite the fact that minimally invasive surgery is perhaps the first alternative for the surgical treatment of mitral valve disease [1], the open approach plays a fundamental role, especially given the need for concomitant coronary artery revascularization procedures and/or intervention in multiple valves. It is necessary to be familiar with the different atrial approaches used in open surgery and to know the potential adverse effects derived from their use. There are multiple surgical methods to expose the mitral valve (MV), but the most used are the left lateral atrial and transseptal approaches or their extended superior transseptal version [2‐5].

The most used incision is through the left atrium behind the interatrial groove, which provides satisfactory exposure of the valve and subvalvular apparatus. However, there are circumstances that limit the versatility of this type of access, such as the presence of a small left atrium, a deep thorax or simply the need for a greater degree of tissue dissection in the context of reoperation [1, 6].

The superior transeptal (TS) approach offers optimal exposure of the MV complex, even in the presence of hostile anatomical conditions and the event of reoperations, and it limits the need to extend the release of pleuropericardial, mediastinal adhesions or both, facilitates exposure and theoretically reduces the risk of bleeding. This approach was associated with a variety of complications, especially postoperative heart rhythm disorders, but the evidence is contradictory [7‐12].

The lack of evidence of complications using either approach leaves the choice of exposure to the surgeon’s preference, based on individual experience, speed, ease, and quality of exposure, and less need for dissection in reoperations.

The present study approaches the problem from a different perspective to establish the association with clinically significant outcomes that lead to the need for additional therapeutic interventions, such as chronic anticoagulation due to arrhythmia, use of antiarrhythmic medication and electrical cardioversion, implantation of devices for rhythm control or both. The establishment of causal relationships between the type of surgical approach used for MV exposure and the development of postoperative complications will provide objective and useful elements when planning the strategy for open MV surgery.

Between January 2006 and July 2018, 652 patients who met the inclusion criteria underwent first-time isolated or combined MV surgery. Associated procedures included CABG, aortic valve replacement (AVR) and TV repair/replacement. A total of 391 patients received an LA approach (Group LA), and 261 patients received a TS approach (Group TS). We excluded 18 patients because of the type of surgical approach (minimally invasive) and 424 patients who had incomplete preoperative critical data, such as echocardiographic measures (Fig. 1).

We obtained a new sample of 96 patients in the LA group and 69 patients in the TS group after PSM. Standardised differences were obtained, and an improvement in the sample heterogeneity was achieved because the post-PSM standardised differences were lower than 0.1 [13] (Fig. 2).

The preoperative and perioperative variables are illustrated in Table 1.

Before matching, no statistically significant differences were found, except for PASP (p = 0.001) and tricuspid intervention (p = 0.007). No differences were observed in the distributions of other variables, such as the type and severity of MV dysfunction, aortic valve disease, comorbidity profile and intraoperative characteristics, such as type of mitral intervention, type of cardioplegia solution and cross-clamp and CPB time. Of the patients who underwent simultaneous AVR, only 0.95% received a mechanical prosthesis, with no differences in distribution between groups. All tricuspid valves were repaired.

The primary analysis according to PSM yielded 69 patients in the TS group and 96 in the LA group, with no significant differences between cohorts, except for a longer ICU stay (p = 0.002) and an increased prevalence of nodal rhythm in TS patients (p = 0.008). Table 2.

There were 24 deaths during the entire follow-up time (mean time from surgery 11.6 years for the LA group and 10.6 years for the TS group), but no significant differences were found between the type of surgical approach in the survival analysis (log-rank test p = 0.073) (Fig. 3).

The secondary analysis divided the sample according to the mean follow-up time into 2 groups. The first sub analysis included the date of surgery from January 2006 to July 2011, and the second subgroup was from July 2011 to December 2016. No significant differences were found between patients, except for a longer ICU stay (p = 0.04) and an increased prevalence of nodal (p = 0.023) and other SV arrhythmias (X² p = 0.045) in TS patients for the first sub analysis group (Table 3).

For the second sub analysis group, no significant differences were found between patients, except for longer ICU stay (p = 0.04) and an increase cross-clamp (p = 0.024) and CPB time (p = 0.049) in TS patients (Table 4).

No significant differences in the perioperative or overall mortality were found in either group. However, a noticeable difference was observed in the mortality figures in each of the intervention groups between the two periods.

There were significant differences in the myocardial protection strategies used in each time. During the first time, HTK solution (Custodiol) was used in 19.5% of interventions and blood cardioplegia with Del Nido solution was used in 27.4%. During the second, they were used in 0% and 11.5% respectively. Likewise, during the first period there was a tendency to use retrograde cardioplegia more frequently as a complementary route of administration.

Since the first description of the TS approach by Guiraudon and colleagues in 1991 [4, 8], there has been controversy on its relationship with postoperative heart rhythm disorders, the need for PPM, and postoperative bleeding. Available evidence primarily comes from retrospective studies and a few randomised prospective studies without adequate power, which explains why it is contradictory and not widely applicable [14].

Our study addressed this problem using a cohort model in which the differences in prognosis of MV surgery were analysed after the use of the left atrial vs. superior transseptal approach. Because there was a non-random distribution between groups, conditions that could influence the selection of the technique, such as reoperations or emergency surgeries, were excluded from the analysis. Patients with a history of arrhythmia, chronic anticoagulation or PPM were also excluded because the objective of this study was to precisely elucidate the effects of the use of the two main mitral approach strategies in the development of rhythm disturbances, the need for PPM, and the use of postoperative anticoagulation and antiarrhythmic medication. We used PSM to further minimise biases inherent to retrospective analyses.

After matching with propensity scores, no significant differences were observed in the postoperative incidence of Afib/flutter or other types of supraventricular arrhythmias between groups. There was a higher incidence of nodal rhythm (p = 0.008) and length of stay in the ICU (p = 0.04) in patients undergoing a TS approach. However, these rhythm disorders were mostly transitory. Therefore, they did not result in a significant difference in the need for PPM implantation. Similar findings were reported in other studies and reflect the benign behaviour of early rhythm disorders related to the TS approach [15, 16]. Because we found no differences in the incidence of Afib/flutter and the use of anticoagulation and antiarrhythmic medications, the need for postoperative electrical cardioversion was the same between groups. Our results are consistent with the observations of the prospective randomised study by Gaudino et al., who did not identify significant differences in the incidence of cardiac rhythm disturbances in patients whose preoperative rhythm was a normal sinus rhythm [17]. In contrast, Rezahosseini et al., in a retrospective cohort analysis performed via pairing with propensity scores that gathered 815 patients, observed a significant increase in the prevalence of postoperative Afib in patients who received the TS mitral approach (36.8% vs. 27.5%, p = 0.019), with no differences in the need for a perioperative temporary pacemaker between the groups. Although it was essentially a transient dysfunction, our higher early incidence of nodal rhythm partially contributed to the longer stay in the ICU with the TS approach. However, it is clear that the definition of this outcome was due to a multifactorial origin. Turkyilmaz and Kavala, in a retrospective analysis using propensity scores, identified a significant increase in ICU stay (p < 0.001) and hospitalisation (p < 0.001) associated with the TS approach despite a lack of significant differences in the prevalence of postoperative rhythm disturbances. They instead identified perioperative bleeding as the main factor influencing this outcome (p < 0.001) [16].

The rhythm disturbances correlated with the TS approach may be explained because of the proximity of the sinus node artery, which is easily injured and leads to ischaemia and resultant nodal dysfunction. The incision also causes internodal pathway disruption, and scar formation may block impulses from the sinus node [18].

Nienabber et al., in a retrospective analysis of 531 patients comparing the LA approach with the so-called mini-transseptal access, limited to the interatrial septum without extension to the atrial roof, observed a significant increase in the incidence of junctional rhythm (8.7% vs. 4.2%, p = 0.035) and the need for PPM (10.5% vs. 5.1%, p = 0.025). However, multivariate analysis showed that TS access was not an independent predictor for the development of rhythm alterations or the need for PPM, and the latter is specifically related to the presence of redo sternotomy [19]. Lukac et al. also identified a greater need for PPM in their retrospective cohort analysis of 577 patients (p = 0.010) undergoing the TS approach, which was primarily related to a higher incidence of sinus node dysfunction (p = 0.017) [20]. In the long-term follow-up of our cohorts, clinical stability was evidenced without significant differences in the incidence of arrhythmias, the need for antiarrhythmic medication, the use of oral anticoagulation in non-carriers of mechanical valves, or the incidence of cerebrovascular events. The need for late PPM implantation was also similar between groups.

We did not observe a significant difference in perioperative (p = 0.204) or late (p = 0.211) mortality associated with the use of a TS approach. Gaudino et al. [17] and Aydin et al. [15] specifically evaluated the outcome of mortality without being able to establish a relationship with the type of atrial approach. No evidence is available from prospective studies showing an association between the use of the ST approach and an increase in mortality [14]. The recent meta-analysis by Harky et al. compared the outcomes in MV surgery of these two types of approaches, but it included limited transseptal access and superior transseptal access in the TS group. A total of 4537 patients were included and evaluated for primary outcomes, operative mortality and PPM implantation. The mortality outcome was similar between the groups, unlike the need for PPM implantation and the incidence of new-onset AF, which were higher in the TS group. Analysis of the isolated MV surgery subgroup did not show any significant difference. Unlike our study, the distribution of other concomitant valve procedures was not symmetrical, which could influence the higher incidence of postoperative rhythm disorders and the need for PPM [21].

The high mortality rate observed in both intervention groups is striking. However, both isolated mitral procedures and procedures combined with valve interventions in other locations and/or with coronary revascularisation were included in the present analysis. The secondary analysis in different periods showed that these high mortality values were primarily conditioned by the results obtained in the initial period. Important factors that may have influenced the improvement of the postoperative prognosis likely include improvements in surgical technique and anaesthesia and advances in cardiopulmonary bypass technology and intensive care management.

This is a retrospective study based on observational data and is therefore limited by the biases inherent in this type of analysis. Strict criteria were used for the inclusion of patients in the final propensity analysis obtaining two completely comparable populations with a homogeneous distribution of variables, however this significantly reduced the sample size. More studies are needed in this subject.

This study did not find significant differences in the postoperative incidence of permanent heart rhythm disorders or any other clinically significant adverse outcome in relation to the type of atrial approach. Therefore, the superior trans septal approach represents an useful and safe alternative for mitral valve exposure.