.9%, 0.80 (0.64 to 1.00). Tricuspid repair was also associated with lower in-hospital acute renal failure 12.4% vs 15.6%, 0.82 (0.72 to 0.93) and pacemaker implantation 9.4% vs 21.0%, 0.37 (0.24 to 0.58), but higher stroke rate 1.5% vs 0.9%, 1.63 (1.10 to 2.41). There were no differences in rates of prolonged ventilation, mediastinitis, return to operating room or late mortality. Conclusion Isolated tricuspid valve repair was associated with significantly reduced in-hospital mortality, renal failure and pacemaker implantation compared with replacement and is therefore recommended where feasible for isolated tricuspid valve disease, although its higher stroke rate warrants further research.

► Isolated tricuspid valve surgery is uncommonly performed making up to 20% of tricuspid valve surgery, because of poor outcomes compared with other single valve surgery. Surgical repair and replacement are two strategies to address isolated severe tricuspid valve disease with mixed results from the literature.

What does this study add?
► This is the first meta-analysis comparing isolated tricuspid valve repair and replacement, pooling 16 cohort studies and 15 069 patients. We found that isolated tricuspid valve repair was associated with reduced operative mortality (8.4% vs 9.9%) as well as lower rates of renal failure and pacemaker implantation, but a higher rate of stroke.
How might this impact on clinical practice? ► The findings support recommendations of performing surgical repair where feasible in isolated tricuspid valve disease. Isolated tricuspid surgery remains a high risk procedure regardless of whether repair or replacement is undertaken. Given this clinical scenario being increasingly encountered, percutaneous tricuspid valve interventions, if effective, may play an important role in the future to fill this unmet need.

ABSTRACT
Objectives Tricuspid valve disease is increasingly encountered, but surgery is rarely performed in isolation, in part because of a reported higher operative risk than other single-valve operations. Although guidelines recommend valve repair, there is sparse literature for the optimal surgical approach in isolated tricuspid valve disease. We performed a meta-analysis examining outcomes of isolated tricuspid valve repair versus replacement. There were no differences in rates of prolonged ventilation, mediastinitis, return to operating room or late mortality. Conclusion Isolated tricuspid valve repair was associated with significantly reduced in-hospital mortality, renal failure and pacemaker implantation compared with replacement and is therefore recommended where feasible for isolated tricuspid valve disease, although its higher stroke rate warrants further research.

IntROduCtIOn
The 'forgotten' tricuspid valve has lost its label over the last decade due to increased recognition that severe tricuspid regurgitation is associated with worse prognosis. [1][2][3] The gold-standard treatment remains open heart surgery, indicated in those with severe tricuspid valve disease who present with either symptoms of right sided heart failure or progressive right ventricular dilation or systolic dysfunction. 1 4 The threshold for performing isolated tricuspid valve surgery is higher in part because of the markedly higher operative mortality risk compared with other single valve surgery, approximately 9% vs 2%-3%. 5 6 This presents a challenging clinical decision, and isolated tricuspid valve surgery only makes up 20% of all tricuspid valve surgeries. 7 Although guidelines suggest that tricuspid repair is preferred when feasible over replacement similar to for mitral valve surgery, this is based on a limited number of observation studies only. 1 To address this, we performed a meta-analysis of the outcomes of patients undergoing isolated tricuspid valve repair versus replacement.

MetHOds search criteria
Ethical approval was not required for the conduct of this meta-analysis with no individual-level patient data collected. The PRISMA guidelines for meta-analysis protocol were used for this study. Medline, Embase, Scopus and Cochrane electronic databases and reference lists of relevant searched articles during 1 January 1980 to 30 June 2019 were searched for adult human original clinical studies comparing tricuspid valve repair with replacement. The search terms used were (tricuspid) AND (repair OR annulopasty) AND (replacement OR bioprosthetic OR mechanical). Isolated tricuspid valve surgery was defined as either surgical repair or replacement of the tricuspid valve without concurrent valvular heart surgery within the same procedure (such as mitral or aortic valve operations). For inclusion, studies needed to report separate outcomes for isolated tricuspid valve repair and replacement arms and have at least 10 patients in each group. Studies describing exclusively congenital tricuspid valve disease warranting surgery were excluded. Reviews, editorials and guidelines were excluded.

data collection
For all studies meeting the inclusion criteria, data were extracted for analysis separately for valve repair and replacement. Study characteristics recorded include author and year of publication, surgical cohort date and location, number of patients undergoing surgical repair and replacement, aetiology of tricuspid valve disease requiring surgery, demographics (age and sex) and follow-up duration. The primary outcomes of interest were operative mortality defined as in-hospital and/or within 30 days. Other outcomes studied include in-hospital morbidities and longer-term mortality after the operative period during follow-up.
statistical analysis Review Manager V.5.3 (Cochrane Collaboration, Oxford, England) was used for performing pooled analysis. Estimated effect measures were performed for binary outcomes using the Mantel-Haenszel statistical method and random effect models. The OR with 95% CI calculated in this study are based on the odds of an event for tricuspid valve repair compared with replacement, for example, OR less than 1.0 indicates lower event rate for surgical repair. Outcomes are only pooled if they are reported by over three studies. Heterogeneity of the outcomes reported across studies were assessing using the Cochrane Q χ² statistic and I 2 statistic, the former with p values and the latter considered significant heterogeneity if >50%. Funnel plots were used to evaluate for publication bias. The significance level was set at 5% and all tests were two-tailed. The meta-analysis was performed using the PRISMA guidelines.
In terms of postoperative complications, the three with significant differences by surgical technique are shown in figure 3. Tricuspid valve repair was associated with higher rate of stroke (1.5% vs 0.9%, OR 1.63 95% CI 1.10 to 2.41), but lower rates of renal failure (12.4% vs 15.6%, OR 0.82 95% CI (0.72 to 0.93)) and pacemaker implantation (9.4% vs 21.0%, OR 0.37 95% CI (0.24 to 0.58)). Long-term morbidities such as stroke, recurrent tricuspid valve disease, repeat operations and endocarditis were rarely reported and were not pooled.    Heterogeneity of studies in reporting adverse events was detected for pacemaker implantation, and to a lesser degree for early and late mortality, prolonged ventilation and return to operating room. Funnel plots were symmetrical without suggesting evidence of publication bias. Figure 4 illustrates the Funnel plot for operative mortality.
dIsCussIOn This is the first meta-analysis comparing the outcomes of isolated surgical tricuspid valve repair versus replacement. Combining 16 observational studies and over 15 000 patients, we found that isolated tricuspid valve repair was associated with 20% lower operative mortality than replacement, with lower rates of in-hospital acute renal failure and pacemaker implantation, but a higher rate of stroke. There were no differences in other in-hospital complications or late mortality.
Tricuspid repair had lower rates of operative mortality than replacement. Possible reasons from the surgical point of view include preservation of the tricuspid annulus which contributes to right heart function and risk of thromboembolism and bleeding from anticoagulation for prosthetic heart valves. Nevertheless, these patients form a high risk surgical group with 8.4% operative mortality for repair and 9.9% for replacement. Compared with  data from the Society of Thoracic Surgeon's Database, this mortality is much higher versus the 2%-3% mortality for isolated aortic and mitral valve surgeries 5 and is more comparable to endocarditis surgery that has a reported risk of 8.2%. 14 Possible factors contributing to the high risk of isolated tricuspid valve surgery include high prevalence of previous cardiac surgery, atrial fibrillation, heart failure, right ventricular dilation and/or dysfunction, pulmonary hypertension, non-cardiac comorbidities and late presentation for surgery. 6 17 Long-term mortality was less often reported and no differences by type of operation were seen in our analysis.
In terms of in-hospital complications, tricuspid repair had lower rates of renal failure and pacemaker implantation. The former parallels the trend for lower operative mortality and is an important endpoint with prognostic, length of stay, cost and quality of life implications. 22 The need for pacemaker is related to the close proximity of the atrioventricular node to the septal leaflet of the tricuspid valve, meaning interventions, manipulation and trauma to the tricuspid valve can lead to heart block, expectedly higher for valve replacement (in fact 21% in our metaanalysis), with underlying heart rhythm disturbance and endocarditis being other important predictors of pacemaker requirement. 23 Conduction disturbance needs to be anticipated as transvenous pacemaker lead implantation is not feasible in some types of prosthetic tricuspid valves meaning epicardial leads may be required, sometimes as part of the initial operation. On the other hand, the higher rate of stroke in tricuspid repair was surprising, demonstrating an opposite trend to other endpoints. The reasons for this are unclear. Although prosthetic valves are associated with thromboembolism, in tricuspid valve surgery,