Anteriolateral versus anterior–posterior electrodes in external cardioversion of atrial fibrillation: A systematic review and meta‐analysis of clinical trials

Abstract The efficacy of anteriolateral versus anterior–posterior electrode positions in the success of atrial fibrillation's (AF) electrical cardioversion is unclear. Our aim is to perform a meta‐analysis to compare the success rate of both electrode positions. PUBMED, WOS, OVID, and SCOPUS were searched. Inclusion criteria were clinical trials that compared anterior–lateral with anterior–posterior electrodes in external cardioversion of AF. After the full‐text screening, 11 trials were included in the analysis. The total number of patients included in the study is 1845. The pooled analysis showed a statistically significant association between anterior–lateral electrode and increased cardioversion rate of AF (odds ratio [OR] = 1.40, 95% confidence interval [CI] = 1.02–1.92, p = .04). Subgroup analysis revealed a statistically significant association between the anterior–lateral electrode and increased cardioversion rate of AF in subgroups of less than five shocks, patients with 60 years old or more and patients with left atrial (LA) diameter >45 mm (OR = 1.72, 95% CI = 1.17–2.54, p = .006), (OR = 1.73, 95% CI = 1.18–2.54, p = .005), and (OR = 1.86, 95% CI = 1.04–3.34, p = .04), respectively. Anteriolateral electrode is more effective than anterior–posterior electrode in external cardioversion of AF, particularly in patients who have received less than 5 shocks, are 60 years old or older and have a LA diameter greater than 45 mm.


| INTRODUCTION
Atrial fibrillation (AF) is the most common arrhythmia worldwide. The global burden of AF has increased significantly due to the aging population. By 2030, the United States may have over 12 million people with AF. 1 AF has significant morbidity, linked to a threefold increased risk of heart failure, a fivefold increased risk of stroke, and a 1.5-1.9-fold increased chance of death. Rate or rhythm control, as well as anticoagulation to prevent thromboembolic complications, are the two basic techniques of controlling AF. The rate control strategy utilizes atrioventricular nodal blocking agents and long-term anticoagulation. In the rhythm control strategy, sinus rhythm is restored through either pharmacological, electrical, or catheter ablation. Rate control was the primary strategy over the last decade based on the data from the AFFIRM trial that showed no survival benefit from the rhythm control over the rate control. 2 However, recent data suggest that rhythm control, especially early in the disease, has fewer adverse cardiovascular outcomes. 3 Electrical cardioversion is the most popular method of rhythm control in cardiology practice. It effectively terminates the AF in more than 90% of the cases. 4 Electrical cardioversion can be safely done during the first 48 hours where the risk of clot formation is low. 5 If the duration is more than 48 hours or unknown, a transthoracic echocardiogram is warranted to exclude atrial thrombus or systemic anticoagulation for 3 weeks before and 4 weeks after the cardioversion. 5 Successful electrical cardioversion depends on proper patient selection, amount of electrical current delivery, number of shocks delivered, electrode size, and electrodeposition. 6 The most common positions in practice are anterior-posterior and anterior-lateral. The evidence comparing their efficacy is uncertain. Some evidence suggests that the anterior-posterior posture is optimal for the external cardioversion of AF. 7 On the other hand, others have shown no difference in cardioversion success between the two positions. 8 As a result, we conducted a meta-analysis of trials to see how the electrodeposition affects cardioversion success.

| METHODS
Ethical approval is not required as this study is a meta-analysis of published clinical trials. The present meta-analysis was performed in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and the Cochrane handbook. 9 We systematically searched PUBMED, Web of Science, OVID, and SCOPUS from inception to January 30, 2022. The search included the following key terms: "Anterior lateral" OR "anterolateral" AND "Electrode" AND "Anterior posterior" OR "Anteroposterior" AND "atrial fibrillation" OR "AF". We further reviewed the reference list of articles included in this review to include other relevant studies. Primary source studies published in peer-reviewed journals were eligible for inclusion if they met the below criteria.

| Eligibility criteria
Clinical trials that compared anterior-lateral electrode with anterior-posterior electrode in external cardioversion of AF.
We excluded cohort studies, case reports, editorials, conference abstracts, and animal studies. And thus, the PICO criteria for our meta-analysis will be: Population: Patients with AF.
Outcome: Cardioversion success rate between anterior-lateral electrodeposition group and the anterior-posterior group.
2.2 | Screening, data extraction, and risk of bias Initial title and abstract screening were conducted by two reviewers (S. S. and H. F.) and all disagreements were discussed to reach a consensus, otherwise, a third opinion from (K. R. M.) was obtained.
Potentially eligible articles were imported for full-text review and assessed for inclusion. We extracted data using an Excel sheet. Examples of data collected are study arms, number of patients in each group, age, sex (n), other baseline diseases, duration of AF, and baseline treatment.
We used the Cochrane tool (Risk of Bias 2) to assess the risk of bias in randomized trials. The following items were assessed (overall bias, selection of the reported result, measurement of the outcome, missing outcome data, deviations from intended interventions, and randomization process).

| Data analysis
We used the Review Manager Software version 5.4 to perform the meta-analysis; the dichotomous outcomes were presented as odds ratios (OR) with a 95% confidence interval. In case of heterogeneity (χ 2 p < .05), a random effect model was used otherwise, a fixed-effect model was employed, in general; the results were considered significant if the p value was less than .05.  Table 1.

| Summary of studies
The cardioversion rate was compared between anterior-lateral and anterior-posterior electrode positions in the 11 studies.
Subgroup analysis was done according to the number of shocks, age, and left atrial (LA) diameter. The number of shocks subgroup was divided into two subgroups: five shocks or less than five shocks. The age subgroup was divided into two subgroups: 60 years old and more or less than 60 years old. The LA diameter subgroup was divided into two subgroups: more than 45 mm or 45 mm and less than 45 mm. The overall risk of bias was high in most of the studies, as we found significant bias in deviation from the intended interventions domain in six studies, missing outcome data domain in one study, and measurement of the outcome domain in three studies; however, we found no significant bias in randomization process domain in the included studies as shown in Figure 2.
The total number of patients included in the study is 1845 patients, 931 patients in the anterior-lateral electrode group, and 941 patients in the anterior-posterior electrode group, other baseline data are shown in Table 2.

| Overall cardioversion rate
The pooled analysis showed a statistically significant association between the anterior-lateral electrode and increased cardioversion rate of AF compared with anterior-posterior electrode (OR = 1.40, 95% CI = 1.02-1.92, p = .04), indicating that anterior-lateral electrodeposition is better than anterior-posterior electrodeposition in the external cardioversion of AF. We observed no heterogeneity among studies (p = .14, I 2 = 32%), Figure 3. No publication bias was observed, as shown in Figure 4.    ). There were no significant differences between groups in any safety outcomes.

| Subgroup analysis
The study concluded that AL electrode positioning was more effective than AP electrode positioning for the biphasic CV of AF. There were no significant differences in any safety outcome.
Stiell 2020 The study concluded that both the drug-shock and shock-only strategies were highly effective, rapid, and safe in restoring sinus rhythm for patients in the emergency department with acute AF, avoiding the need for a return to the hospital.
The drug infusion worked for about half of the patients and avoided the resource-intensive procedural sedation required for electrical CV. We also found no significant difference between the AL and AP pad positions for electrical CV. Immediate rhythm control for patients in the emergency department with acute AF leads to excellent outcomes.

Randomized controlled trial
The The study concluded that an AP electrodeposition is more effective in achieving restoration of sinus rhythm in lower energy shock levels compared to the AL position.

Kerber 1981
Randomized controlled trial United States Group 1: AL Group 2: AP Overall CV success rates with either paddle position were similar (greater than 90%). The larger paddles did not significantly reduce energy requirements for the CV of either arrhythmia. In AF, the majority of patients converted to normal sinus rhythm when given 100 or 200 J of energy. There were no significant differences in total success rates or in rates of success at any given energy level (i.e., energy requirements) when AP placement was compared with AP placement. When patients in each of these groups were subdivided into two smaller groups based on the size of the paddles, there still were no significant differences in overall success rates or energy requirements.
The study concluded that AL paddles are as effective as AP paddles for the elective CV of atrial arrhythmias and that there is no demonstrable advantage to using paddles that are larger than the standard size in either position (N Engl J Med.

| DISCUSSION
We found a statistically significant association between the anterior-lateral electrode and increased cardioversion rate of AF compared with the anterior-posterior electrode in the overall analysis.
Subgroup analysis showed no statistically significant difference between the anterior-lateral electrode and anterior-posterior electrode in patients who received five shocks, patients whose ages are less than 60 years old, and patients whose LA diameters are equal to and less than 45 mm.
Subgroup analysis showed a statistically significant association between the anterior-lateral electrode and increased cardioversion rate of AF compared with the anterior-posterior electrode in patients who received less than five shocks, patients whose ages are equal to and above 60 years old, and patients whose LA diameters are more than 45 mm.
Our data suggest that the anterior-lateral approach is associated with higher cardioversion rates than the anterior-posterior approach. An  Moreover, the progression of A.fib is associated with poor outcomes after transcutaneous ablation. [15][16][17] Surprisingly, our analysis reports better efficacy of anterior-lateral electrode positioning in patients with LA enlargement with a diameter greater than 45 mm when compared to anterior-posterior positioning. Additionally, the anterior-lateral position is associated with higher success rates in patients receiving less than five shocks. This denotes the superiority of the anterior-lateral position in managing this hard-to-treat subset of the A.fib population.
Second, a divergent patient population seems to be a valid prognostication factor in determining the safety and efficacy of various approaches. Our pooled analysis revealed that anterior-lateral position is more likely to attain higher success chances in patients aged 60 years old or more.
Third, it is essential to consider that some medical practices have been recently obsolete and are no longer clinical guidelines.
One is the use of monophasic shocks in cardioversion which have been widely replaced with biphasic shocks that have shown optimal efficacy in managing different types of arrhythmias. 10 self-adhesive electrodes. It is recommended to apply pressure on anterior-lateral electrodes for higher efficacy. 20,21 Given the current data, it is reasonable to consider the anterior-lateral position as a first-line modality in AF cardioversion, given the relatively higher success rates, especially in elderly patients and those with enlarged left atrium indicating LA remodeling. Additionally, the anterior-lateral position has anatomical convenience and easier accessibility, particularly in critically ill patients.
Nevertheless, our study has some limitations. Variable protocols for cardioversion have been applied. While some papers followed the step-up energy levels approach, others used initial high-energy levels of 200 J and higher on failed attempts.
We found some bias in deviation from the intended interventions, missing outcome data, and measurement of the outcome domains in some studies; however, we found no significant bias in the randomization process domain in the included studies. Lastly, our included articles had variable proportions of persistent and permanent AF, which are hard to treat and might alter the outcomes.

| CONCLUSION
Our meta-analysis revealed that anterior-lateral electrodeposition is more effective and better than anterior-posterior electrodeposition in external cardioversion of AF, particularly in patients who have received less than five shocks, are 60 years old or older, and have a LA diameter greater than 45 mm. More multicenter randomized clinical trials are warranted to support our findings.