Information sources and search strategy
A systematic literature search was performed using the database PubMed and repeated in Embase and Scopus. The last date of search was August 2, 2021.
The applied search strategy was “ventricular pacing wires OR temporary pacing wires OR TEPW”. In PubMed the search strategy was extended by “(((“Cardiac Pacing, Artificial*”[Mesh])) AND (temporary postoperative pacing))” to include MESH-terms. To ensure a broad inclusion “epicardial” and “myocardial” were used synonymously. No review protocol was made before the study.
The literature search and selection was performed by the first author, and verified by the co-authors, and all studies were consequently reviewed, and PRISMA guidelines  were followed and reported (Fig. 1).
Studies were eligible if they assessed whether a group of adult patients benefitted from having epi- or myocardial pacing electrodes inserted as a part of open-heart surgical procedures. Studies concerning transvenous-, transcutaneous-, transesophageal-, or transthoracic pacing were excluded. Studies only comparing different subtypes of pacing were excluded. Studies focusing only on atrial pacing for prevention of atrial fibrillation without depicting the type of cardiac surgery were excluded. Studies concerning congenital cardiac surgery alone were also excluded. The search included all types of studies apart from case reports. Studies were limited to articles published in English language between year 1980 and 2021.
Data collection process
The following information was obtained from each study: author, year of publication, type of surgery, study design, total number of included patients, number of patients having temporary pacemaker electrodes inserted, number of patients requiring temporary pacing, primary reason for pacing, significant factors predicting temporary pacing and conclusion.
The methodological quality of the included studies was assessed using the National Heart, Lung and Blood Institute’s checklists . Studies were considered of good quality if 60% or more of the criteria were met in the respective assessment tools. The individual assessments can be found in Additional file 1: Appendix 1. The studies were further assessed using the Effective Public Health Practice Project Quality Tool (EPHPP) [11, 12] (Additional file 1: Appendix 2). Selection bias, study design, confounders, blinding, data collection and withdrawals and drop-outs were scored to be either “weak,” “moderate,” or “strong,” resulting in a global rating to be either “weak,” “moderate,” or “strong.” Studies were rated “strong” if they received no “weak” scores, “moderate” if it received one “weak” score, and “weak” if it received more than one “weak” score.
Outcomes and prioritization
The aim was to identify studies reporting the use of temporary pacemaker electrodes and to investigate the extent of this use in clinical practice. Only studies with outcomes directly addressing number of patients receiving postoperative temporary pacing were included.
Results for selection of studies
The established database revealed 1.364 studies. The search identified 274 and 208 (MESH) results in PubMed, 383 results in Embase, 499 results in Scopus, and 0 in grey literature searches. After duplicates were removed, the number was reduced to 905 studies, of which 859 were excluded in the title and abstract screening due to eligibility criteria. Of the remaining 46 studies, 33 were excluded in the full-text screening due to eligibility criteria and type of paper. One study  were excluded since it was not possible to trace down the full-text online or by the Royal Danish Library, or the full-text was unsuccessfully requested by authors through ResearchGate.net. Hence, a total of 12 studies were included in the review (Table 1).
Results for study characteristics
The study material comprised five retrospective observational studies [14,15,16,17,18], six prospective observational studies [7, 19,20,21,22,23], and one systematic review . The individual study designs were not further labeled.
Alwaqfi , Abd Elaziz , and Ferrari  investigated the frequency of pacing among valve operated patients, while Bethea , Puskas , Imren , Asghar , and Khorsandi  focused on pacing after coronary artery bypass grafting (CABG) surgery. Cote , Kiely , Morin , and Takeda  included both CABG, valve surgery, and other procedures. Study design, type of surgery, total number of patients, number of patients having temporary pacemaker electrodes inserted, number of patients requiring temporary pacing, primary reasons for pacing, and conclusion are reported in Table 1. None of the studies reported on inclusion of patients subjected to minimal invasive surgery or aortic root surgery.
For most of the studies, patients were grouped according to insertion or non-insertion of temporary pacemaker electrodes, and were additionally subdivided according to the need for postoperative pacing.
AlWaqfi  and Morin  inserted temporary pacemaker electrodes based on an individual evaluation, while other authors [15, 20, 22] had clearly stated criteria for temporary pacemaker electrode insertion. Hence, Abd Elaziz did not insert temporary pacemaker electrodes in patients with (1) young age with no preoperative history of risk factors, (2) isolated single valve replacement with minimal calcification, or (3) easy weaning from cardiopulmonary bypass and stable vital parameters on minimum inotropic support.
Puskas  inserted temporary pacemaker electrodes if the patients required pacing prior to chest closure.
Asghar , Bethea , Takeda , Cote , Ferrari , and Kiely  inserted temporary pacemaker electrodes in all patients and assessed the need for pacing afterwards. The year of publication ranged from 1982 to 2020.
Primary reasons for postoperative pacing
The most frequent reasons for postoperative pacing were bradycardia (30–82%) and atrioventricular block (46–67%) (Table 1). Junctional rhythm was the most common reason for postoperative pacing in Morin et al.’s study  with a frequency of 42% and were reported as a primary reason for pacing for Alwaqfi, Puskas and Imren [14, 20, 22] as well.
Other reported reasons for postoperative pacing
were low cardiac output [14, 15, 20], asystole [7, 14, 15, 19, 21], atrial
fibrillation [16, 19, 22], and bundle branch block [19, 21, 22].
Except from the review publication, the studies included a total of 15.980 patients. Of these, 14.757 patients had temporary pacemaker electrodes inserted and 2.639 (18%) required pacing in the postoperative period (Table 1). From this latter group, 64 patients [20, 22] only had temporary pacemaker electrodes inserted if pacing was required at the time of chest closure or if arrhythmias occurred intraoperatively. Hence, the two studies found a higher pacing rate (70%, 100%) compared with the remaining studies where the pacing rate ranged from 3 to 35%.
The studies, where only valve surgery patients were studied [14, 15, 18] found a higher pacing rate (24%, 20%, 17%) compared with the two remaining studies where only coronary artery bypass grafting surgery patients were included [19, 21] (3% and 9%). Kiely  found that 26% required pacing in the aortic valve repair group, while this number was 25% in the non- aortic valve repair group.
Imren  assessed the need for pacing between on-pump and off-pump CABG patients and found that 31 patients need pacing, of which 20 were on-pump patients and eleven were off-pump operated patients.
The number of the patients not receiving temporary pacemaker electrodes but requiring pacing in the postoperative period was one and two respectively [7, 22], equivalent to 3% and 0.3%. Puskas  reported that none of the patients in whom temporary pacemaker electrodes were not inserted developed a need for pacing nor suffered any complications due to the absence of temporary pacemaker electrodes. The remaining studies did not address this issue.
Predictors for need of postoperative pacing
Besides studying the frequency of pacing, most studies also investigated factors predicting the need for postoperative pacing (Table 2, Fig. 2). Predicting factors were not assessed for Takeda  and Kiely , while Khorsandi  did not report the level of statistical significance.
For two of the studies reporting on valve surgery [14, 15] the factors which were statistically significant associated with temporary cardiac pacing were age, New York Heart Association (NYHA) class III-IV, pulmonary artery pressure ≥ 45 mmHg /≥ 50 mmHg , preoperative use of digoxin, multiple valve surgery, aortic cross-clamp time ≥ 60 min /≥ 65 min  and annulus calcification. Ferrari  found age > 60 years, mitral valve surgery, biological prosthesis, length of hospital stay, preoperative antiarrhythmic drugs and β-blocker to be predisposing factors for atrioventricular block and temporary cardiac pacing.
For the CABG surgery studies [19,20,21,22], the most frequent factors included preoperative arrhythmias, long aortic cross-clamp time, pacing required to wean from cardiopulmonary bypass, and time on cardiopulmonary bypass appearing at three out of six studies. Older age was a predicting factor in two of the studies, and use of antiarrhythmic drugs upon leaving the operating room, previous CABG surgery, number of coronary arteries bypassed, gender, and hypertension were statistically significant predicting factors in one of the six studies.
Morin  and Cote  studied multiple types of surgeries and disclosed aortic cross-clamp time, preoperative arrhythmia, preoperative renal failure, low ejection fraction, and preoperative use of calcium channel blocker as predicting factors for use of postoperative pacing. Larger volume of cardioplegic solution was also reported as a predicting factor. This is supported by the study of Imren , which found that almost twice as many on-pump CABG operated patients as off-pump operated patients were paced.
Digoxin is used in the treatment of atrial flutter, why this factor is an expression for preoperative arrhythmia. Age, preoperative arrhythmias and long aortic cross-clamp time were the most frequent predicting factors throughout all the studies (Table 2).
Ashgar found that 1% of patients required temporary cardiac pacing following standard isolated CABG, if the following three main predictors were addressed before hand: Bundle branch block, pacing when weaning from cardiopulmonary bypass and use of antiarrhythmic upon leaving the operation room.
Routine use of temporary pacemaker electrodes?
Of the 12 included studies, eight concluded that it is unnecessary to routinely place temporary pacemaker electrodes in all patients [14, 15, 17, 19,20,21,22,23]. Morin  concluded that temporary pacemaker electrodes always should be inserted, while the rest concluded that pacing is useful in the postoperative period, but did not take a stand on the frequency of which temporary pacemaker electrodes should be inserted. Cote  found that 14% of the isolated CABG patients potentially could have avoided temporary pacemaker electrode insertion.
None of the studies reported any severe complications from the use of temporary pacemaker electrodes. However, severe complications have been described in literature, including tamponade and electrode migration [25,26,27].
Quality assessment of included studies
With regard to the hierarchy of evidence to reflect questions of effectiveness  the studies mostly belonged to the middle, counting observational cohort studies, cross-sectional studies and a case-control study. Khorsandi  was the only study scoring high in the hierarchy of evidence being a systematic review.
Due to the heterogeneity of the study designs, the studies could not all be assessed using the same tool. Khorsandi  was scored following the tool for Systematic Reviews created by the National Heart, Lung and Blood Institute . It provided quality assessment tools for most study designs, however these checklists are not nearly as comprehensive as the EPHPP tool, why this was used to assess the quality in the remaining studies.
Khorsandi et al.  were considered of good methodological quality by fulfilling > 60% of the National Heart, Lung and Blood Institute’s respective checklist . The quality assessment using the EPHPP tool resulted in nine studies [7, 14, 15, 17,18,19,20,21,22] receiving a strong global rating, and two studies [16, 23] receiving a moderate global rating (Additional file 1: Appendix 2).
To reduce the risk of selection bias, the studies were scored based on how well the study population represented the target population. All the included studies scored “very likely” since the study groups were patients going through different kinds of open-heart surgical procedures, hence fulfilling international standardized criteria for the respective surgical procedures [29, 30]. Thus, the study groups were considered homogeneous across the studies and therefore, securing a high external validity.
The studies were all categorized to be ‘cohort analytics’ or ‘case-control study’ and hence received a moderate rating. The categorization was based on the EPHPP dictionary description, since none of the studies labeled their study design further than being a retrospective or prospective observational or cross-sectional study.
The study group in this review consist of patients varying in age, gender, comorbidities and intraoperative factors, why all the studies scored ‘yes’ in the question of important differences between groups prior to the intervention. Most of the studies [7, 14, 15, 17,18,19,20,21,22] analyzed risk factors resulting in a strong score where most of the relevant confounders were controlled. Takeda  and Kiely  received a weak score, because only few or none of the factors were assessed. None of the studies discussed confounders explicitly in the text, but only addressed the significant associations.
Blinding was not explicitly described in the studies except Puskas , and all studies received a moderate score equivalent to ‘can’t tell’ or only partial blinding.
Data collection methods
Data was estimated to be valid and reliable for all the included studies, since it consisted of objective data retrieved by researchers or medical records.
Withdrawals and drop-outs
Withdrawals and drop-outs were not explicitly described in the studies, but number of deaths in the early postoperative days was reported by Kiely , Imren , Asghar  and Bethea .
Imren  reported that one patient from the non-paced group developed a need for pacing. It is not elaborated whether any of these patients were withdrawn from the statistics.
Alwaqfi , Abd Elaziz , Takeda , Cote  and Ferrari  received a moderate score due to their retrospective design while the remaining studies received a strong score.
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