Anterior versus posterior approach in peroral endoscopic myotomy (POEM): a systematic review and meta-analysis

• Abstract
• Introduction
• Methods
• Search strategy
• Study selection
• Data abstraction and quality assessment
• Outcomes assessed
• Assessment methodology and definitions
• Statistical analysis
• Results
• Search results and population characteristics
• Characteristics and quality of included studies
• Meta-analysis outcomes
• Validation of meta-analysis results
• Sensitivity analysis
• Heterogeneity
• Publication bias
• Quality of evidence
• Discussion
• References

Abstract

Background Peroral endoscopic myotomy (POEM) is increasingly being used as the endoscopic treatment option for achalasia. Data are limited as to the comparative efficacy of anterior vs. posterior myotomy.

Methods We searched multiple databases from inception to August 2019 to identify studies reporting on POEM. We selected studies that reported on the outcomes of POEM, along with information on myotomy approach. We performed a comparative analysis of clinical success, gastroesophageal reflux disease (GERD), and adverse events with anterior and posterior myotomy in POEM by meta-analysis.

Results 1247 patients from 18 studies were analyzed: 623 patients (11 cohorts) were treated via anterior myotomy and 624 patients (12 cohorts) via posterior myotomy. The pooled rate for clinical success gave an odds ratio (OR) of 1.02 (95 % confidence interval [CI] 0.52 – 2.0; I ² 0; P = 0.9); for GERD by esophagogastroduodenoscopy (EGD) was OR 1.02 (95 %CI 0.62 – 1.68; I ² 0; P = 0.9), and for GERD by pH was OR 0.98 (95 %CI 0.59 – 1.63; I ² 34; P = 0.9). The individual pooled rates of clinical success at 12 months and > 12 months, GERD (by symptoms, EGD, pH), and adverse events (mild, moderate, severe) were comparable. The pooled total procedure time with anterior myotomy was 82.7 minutes (95 %CI 69.0 – 96.4; I ² 98) and with posterior myotomy was 62.1 minutes (95 %CI 48.5 – 75.7; I ² 90).

Conclusion Anterior and posterior myotomy in POEM seem comparable to each other in terms of clinical success, GERD, and adverse events. The total procedure time with posterior myotomy seems to be shorter than with anterior myotomy.

Introduction

Achalasia is a progressive esophageal motility disorder of unknown etiology. The disease is characterized by the degeneration of inhibitor neurons that are involved in the phasic relaxation of the lower esophageal sphincter (LES). This results in a loss of propulsive peristalsis and a failure of normal, coordinated LES relaxation to occur. Clinical symptoms include dysphagia, chest pain, regurgitation, and weight loss [1]. Approximately 1 in 100 000 of the population per year is affected by this disorder [2]. If left untreated, achalasia can profoundly impair a person’s quality of life and can increase the risk of esophageal malignancy.

Treatment options for achalasia are focused on increasing the patency of the LES by means of endoscopic botulinum toxin injection (EBTI), endoscopic pneumatic balloon dilation (PBD), or surgical Heller’s myotomy of the LES. All of these treatments lower the functional resistance of the LES to food bolus progression. However, the effects of EBTI and PBD are temporary and repeat treatments are typically needed. In the modern era, myotomy has been performed laparoscopically and surgical Heller’s myotomy is considered to be a definitive treatment for achalasia. Recently, however, peroral endoscopic myotomy (POEM) has gained widespread popularity and is increasingly being used because of its minimally invasive nature.

The POEM procedure can be performed via a so-called “anterior” approach or “posterior” approach. Anterior myotomy involves performing POEM at the 1- to 2-o’clock position with patients in the supine position; posterior myotomy is performed at the 5- to 6-o’clock position [3] [4]. Theoretically, anterior myotomy may reduce the risk of damage to the angle of His and the sling muscle fibers located over the greater curvature, which support the natural antireflux mechanism. The posterior approach, on the other hand, may allow for superior alignment of the endoscopic tools used to perform the myotomy, as the working channel for most endoscopes is located over the 5- or 7-o’clock position. The posterior myotomy approach may risk damage to the sling muscles that are located around the 8-o’clock area and thereby disrupt the natural antireflux mechanism. Data comparing the clinical outcomes of anterior myotomy and posterior myotomy in POEM are limited.

The goal of this study was to conduct a systematic review and meta-analysis of studies on POEM pertaining to the myotomy approach and evaluate the clinical outcomes between these two myotomy approaches.

Methods

Search strategy

We conducted a comprehensive search of multiple databases from inception to August 2019. An experienced medical librarian using inputs from the study authors helped with the literature search. Controlled vocabulary supplemented with keywords was used to search for studies of interest. The full search strategy is available in Appendix 1s (available in online-only Supplementary Material). The PRISMA and MOOSE checklists were followed and are provided as Appendices 2s and 3s [5] [6]. Reference lists of evaluated studies were examined to identify other studies of interest.

Study selection

In this meta-analysis, we included studies that evaluated the clinical outcomes of anterior myotomy and posterior myotomy in patients undergoing POEM for the treatment of achalasia. Studies were included irrespective of inpatient/outpatient setting, size of study sample, follow-up time, abstract/manuscript status, and geography, as long as they provided the appropriate data needed for the analysis.

Our exclusion criteria were as follows: (i) studies that did not differentiate the clinical outcomes based on the myotomy approach; (ii) studies done in a pediatric population (age < 18 years); and (iii) studies not published in English. In cases of multiple publications from a single research group reporting on the same patient and same cohort and/or overlapping cohorts, data from the most recent and/or most appropriate comprehensive report were retained. When needed, authors were contacted via email for clarification of data and/or study-cohort overlap. The retained studies were decided by two authors (B.P.M., S.C.) based on the publication timing (most recent) and/or the sample size of the study (largest).

Data abstraction and quality assessment

Data on study-related outcomes from the individual studies were abstracted independently onto a standardized form by at least two authors (B.P.M., S.R.K.), and two authors (B.P.M., S.C.) did the quality scoring independently. The primary study authors were contacted via email as and when needed for further information and/or clarification on data.

The Newcastle – Ottawa scale for cohort studies was used to assess the quality of studies [7]. This quality score consists of eight questions, the details of which are provided in Table 1s.

Outcomes assessed

1. Anterior myotomy vs. posterior myotomy: pooled odds ratio (OR) of clinical success and pooled OR of gastroesophageal reflux disease (GERD).

2. Pooled rate of clinical success with anterior myotomy and pooled rate of clinical success with posterior myotomy.

3. Pooled rate of GERD with anterior myotomy and pooled rate of GERD with posterior myotomy.

4. Pooled rate of adverse events with anterior myotomy and pooled rate of adverse events with posterior myotomy.

Predetermined meta-regression analyses were planned based on achalasia type and prior treatments in POEM to assess potential causes of heterogeneity and predictors of clinical outcomes.

Assessment methodology and definitions

The collected data were matched between the groups (anterior myotomy and posterior myotomy) before statistical analysis. Comparison analysis was performed by two methods: (i) pooled OR for clinical outcomes were calculated from studies that compared anterior myotomy and posterior myotomy “head-to-head,” and (ii) subgroup comparison analysis was performed between the pooled outcomes of anterior and posterior myotomy. This model of comparison is comparable to a retrospective case – control study with matched groups and has been previously reported [8] [9] [10] [11] [12].

Clinical success after the POEM procedure was defined by an Eckardt’s score ≤ 3 [13]. GERD was measured subjectively by standardized patient symptom-based questionnaires [14] [15] [16] [17]. It was also measured objectively by EGD findings, based on the Los Angeles classification of esophagitis (> B), and by pH measurement [18] [19] [20]. Adverse events were recorded as mild, moderate, and severe, as defined by the American Society for Gastrointestinal Endoscopy (ASGE) lexicon [21].

Statistical analysis

We used meta-analysis techniques to calculate the pooled estimates in each case following the methods suggested by DerSimonian and Laird, using the random-effects model [22]. When the incidence of an outcome was zero in a study, a continuity correction of 0.5 was added to the number of incident cases before statistical analysis [23]. We assessed heterogeneity between study-specific estimates using the Cochran Q statistical test for heterogeneity, 95 % prediction interval, which deals with the dispersion of the effects [24] [25] [26], and the I ² statistic [27] [28]. In this, values of < 30 %, 30 % – 60 %, 61 % – 75 %, and > 75 % were suggestive of low, moderate, substantial, and considerable heterogeneity, respectively [29].

Publication bias was ascertained, qualitatively, by visual inspection of the funnel plot and, quantitatively, by the Egger test [30]. When publication bias was present, further statistics using the fail-Safe N test and Duval and Tweedie’s “Trim and Fill” test were used to ascertain the impact of the bias [31]. Three levels of impact were reported based on the concordance between the reported results and the actual estimate if there were no bias. The impact was reported as: minimal if both versions were estimated to be the same; modest if the effect size changed substantially but the final finding would still remain the same; and severe if the basic final conclusion of the analysis was threatened by the bias [32].

A P value of ≤ 0.05 was used “a-priori” to define the significance of the difference between the compared groups, as provided by the statistical software. All analyses were performed using Comprehensive Meta-Analysis (CMA) software, version 3 (BioStat, Englewood, New Jersey. USA).

Results

Search results and population characteristics

From an initial 6285 studies, 2169 records were screened and 43 full-length articles were assessed. The final analysis included 18 studies, of which four compared anterior myotomy and posterior myotomy [33] [34] [35] [36], six reported on outcomes with POEM done exclusively via an anterior myotomy approach [37] [38] [39] [40] [41] [42], and eight reported on outcomes with POEM done exclusively via a posterior myotomy approach [43] [44] [45] [46] [47] [48] [49] [50]. Overall, we had 11 cohorts that underwent anterior myotomy (four cohorts from anterior vs. posterior studies and seven from exclusively anterior approach studies) and 12 cohorts that underwent posterior myotomy for this analysis (four cohorts from anterior vs. posterior studies and eight from exclusively posterior approach studies).

A schematic diagram demonstrating our study selection is illustrated in Fig. 1s. Six studies had overlapping cohorts and the most comprehensive cohort was included for analysis [51] [52] [53] [54] [55] [56].

Baseline population characteristics were comparable between the anterior myotomy and posterior myotomy cohorts. The mean and/or median age ranged from 33 to 63 years in the anterior myotomy cohorts and from 38 to 68 years in the posterior myotomy cohorts, with a predominantly male population (55 % in anterior myotomy and 53 % in posterior myotomy). Further details along with the population characteristics are described in Table 1s.

Characteristics and quality of included studies

Three studies were multicenter in nature [33] [41] [48]. Four studies were randomized controlled trials (RCTs) [33] [34] [35] [36]. The detailed assessment of study quality can be found in Table 2s. Overall, 14 studies were considered high quality and the remaining four were considered medium quality. There were no low quality studies.

Meta-analysis outcomes

A total of 1247 patients were included in the analysis from 18 studies: 623 patients underwent anterior myotomy (11 cohorts) and 624 patients underwent posterior myotomy (12 cohorts).

The pooled OR of clinical success at 12 months was 1.02 (95 %CI 0.52 – 2.0; I ² 0; P = 0.9) ([Fig. 1]), of GERD by EGD was 1.02 (95 %CI 0.62 – 1.68; I ² 0; P = 0.9) ([Fig. 2]), and of GERD by pH was 0.98 (95 %CI 0.59 – 1.63; I ² 0; P = 0.9) ([Fig. 3]).

At 12-month follow-up, the pooled clinical success rate with anterior myotomy was 91.1 % (95 %CI 87.8 % – 93.6 %; I ² 0) and with posterior myotomy was 93.1 % (95 %CI 89.8 % – 95.4 %; I ² 0) (Fig. 2s). The pooled clinical success rate of anterior myotomy with follow-up of > 12 months was 88.8 % (95 %CI 73.5 % – 95.8 %; I ² 81) and with posterior myotomy was 92.7 % (95 %CI 85.6 % – 96.4 %; I ² 43) (Fig. 3s).

The pooled rates of GERD (each individual pooled rate by symptoms, pooled rate by EGD, and pooled rate by pH) and the pooled rates of adverse events are summarized in [Table 1] and Figs. 4s – 9s The total procedure time with anterior myotomy was 82.7 minutes (95 %CI 69.0 – 96.4 minutes; I ² 98) and with posterior myotomy was 62.1 minutes (95 %CI 48.5 – 75.7 minutes; I ² 90).

Meta-regression analyses based on achalasia types (I, II, III) and prior treatments (PBD, EBTI, Heller’s myotomy) did not reveal any significant predictor effect on the pooled rate of clinical outcomes with either anterior myotomy or posterior myotomy. The statistical two-tailed P values are summarized in [Table 1].

Validation of meta-analysis results

Sensitivity analysis

To assess whether any one study had a dominant effect on the meta-analysis, we excluded one study at a time and analyzed its effect on the main summary estimate. On this analysis, no single study significantly affected the outcome or the heterogeneity. This was true for both the RCTs and the cohort groups.

Heterogeneity

We assessed dispersion of the calculated rates using the prediction interval and I ² percentage values. The prediction interval gives an idea of the range of the dispersion and I ² tell us what proportion of the dispersion is true vs. chance [26]. The calculated prediction intervals are reported with the pooled rates in [Table 1]. The calculated prediction interval was narrow for the calculated pooled rates of clinical success at 12-month follow-up, with no I ² heterogeneity.

Publication bias

Based on visual inspection of the funnel plot (Fig. 10s), as well as quantitative measurement using the Egger regression test (two-tailed P value = 0.07), there was no evidence of publication bias. A separate publication bias assessment for the RCTs was not done, as the number of studies was less than 10.

Quality of evidence

The quality of evidence was rated for results from the meta-analysis according to the GRADE working group approach [57]. Observational studies begin with a low quality rating and, based on the risk of bias, indirectness, heterogeneity, and publication bias, the quality of this meta-analysis would be considered as low quality evidence.

Discussion

Our study demonstrates that POEM whether performed by anterior myotomy or posterior myotomy seems to have comparable clinical outcomes in terms of the clinical success, post-procedure GERD, and adverse events. With 1247 total patients from 11 anterior myotomy cohorts and 12 posterior myotomy cohorts, this is the most current and largest meta-analysis of anterior myotomy and posterior myotomy in the treatment of achalasia by POEM to date.

Based on our analysis, we report a non-significant OR for clinical success rates at 12-month follow-up (OR 1; P = 0.9). In addition, the pooled individual clinical outcomes with anterior and posterior myotomy were comparable as well. The clinical success at 12 months with anterior myotomy was 91 % vs. 93 % for posterior myotomy, and the clinical success at follow-up beyond 12 months with anterior myotomy was 89 % vs. 93 % for posterior myotomy. No heterogeneity was noted with the calculated 12-month pooled rate of clinical success; however, the pooled clinical success at > 12 months was limited by considerable heterogeneity, which is to be expected because of the varying follow-up times.

Patients can report new development of GERD following POEM, which makes sense given their recent myotomy. The pooled OR of reporting symptomatic GERD as diagnosed by EGD was 1 (P = 0.9) and the pooled OR of GERD by pH measurement was 0.9 (P = 0.9), both being non-significant. The pooled rate of GERD by symptom questionnaire (28 % vs. 17 %), by EGD findings (22 % vs. 19 %), and by pH measurement (34.5 % vs. 40 %) seemed to be similar for both anterior and posterior myotomy, albeit limited by considerable heterogeneity in the values.

Our pooled results on the adverse events, as defined by the ASGE lexicon, seemed comparable (mild 2 % vs. 5.5 %; moderate 8 % vs. 5 %; severe 2 % vs. 3 %). Our study reinforces the fact that POEM is a highly safe procedure and the myotomy approach does not make any difference.

The pooled rate of procedure time was noted to be longer with anterior myotomy when compared with posterior myotomy (83 minutes vs. 62 minutes). This study is the first to report these data and it is a key finding. The difference may be best explained by the fact that the posterior approach allows for better alignment of the endoscopic accessories with the working channel of the endoscope, thereby allowing faster and easier completion of the POEM procedure and shorter incision closure time, when compared with the anterior approach. However, the heterogeneity was high and we do not know if operator experience and partial or full thickness myotomy, which is a key factor for operation time, were balanced between the anterior and posterior studies.

How does our study compare to currently published data? Studies with head-to-head comparison between anterior and posterior myotomy have reported comparable clinical outcomes, akin to this study [33] [34] [35] [36]. However, those studies were usually limited by small sample size and inadequate study power. At the time this study was completed, there was only one other published meta-analysis, which significantly differed from this study in the methodology of comparison and the reported outcomes [58]. Unlike in this study, the total procedure time was comparable in that study.

The strengths of this review are as follows: systematic literature search with well-defined inclusion criteria, careful exclusion of redundant studies, inclusion of good quality studies with detailed extraction of data, and rigorous evaluation of study quality. Our pooled rates are calculated from 623 patients treated with anterior myotomy and 624 patients treated with posterior myotomy.

There are limitations to this study, most of which are inherent to any meta-analysis. The included studies were not entirely representative of the general population and community practice, with most studies being performed in tertiary referral centers. Our analysis had studies that were retrospective in nature contributing to selection bias. Our analysis has the limitation of retrospective comparison and heterogeneity. We were unable to ascertain a cause for the observed heterogeneity based on our meta-regression analysis; however, we hypothesize that the observed heterogeneity is primarily due to interobserver variability, variability in GERD symptom questionnaires, and differences in follow-up time.

Owing to the many differences in the characteristics of the study population, providers, healthcare environments, and study protocols across independent study cohorts, our method of comparison suffers from extreme biases. Therefore, we do not comment on the subgroup P values and superiority and/or inferiority of one approach over the other based on the subgroup analysis of anterior vs. posterior myotomy in this study. Nevertheless, our study is the best currently available estimate in the literature thus far with respect to the clinical outcomes of anterior and posterior myotomy in POEM for the treatment of achalasia.

In conclusion, based on our meta-analysis, anterior and posterior myotomy seem to be comparable in terms of clinical success, GERD, and adverse events. Posterior myotomy has a shorter procedure time than anterior myotomy. Achalasia type and prior treatments do not seem to influence reported outcomes.

Competing interests

The authors declare that they have no conflict of interest.

Acknowledgments

We wish to thank Emily Glenn (Associate Director, Education & Research Services, McGoogan Library of Medicine, University of Nebraska Medical Center, Omaha, Nebraska, USA) for help with the systematic literature search.

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Corresponding author

Publication History

Received: 05 September 2019

Accepted: 09 December 2019

Article published online:
20 January 2020

© Georg Thieme Verlag KG
Stuttgart · New York

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• Supplementary Material