Invited commentary: Bovine or porcine valve in tricuspid position—is there a difference?

In this issue, Sohn et al. [1] addressed an absolutely interesting topic in their article: Is there a difference regarding the reoperation rate of porcine versus bovine bioprostheses in tricuspid valve (TV) position? In fact, very little can be found regarding this topic in the literature so far.

The present article shows a higher reoperation rate in patients with bovine versus porcine bioprostheses in tricuspid position with no effect on ‘long-term-clinical outcomes, including all-cause mortality, cardiac death, ischaemic stroke, haemorrhagic stroke and endocarditis’ [1]. The take-home message is: ‘For patients undergoing bioprosthetic TVR, porcine valves might be more beneficial than bovine valves in terms of reoperation’ [1].

What is the basis of the study? The recruitment of data was based on the Korean National Health Insurance Service. The patient's diagnoses known were those coded within 1 year prior to surgery. The following patients were excluded: congenital vitia/Ebstein anomaly, patients with previous TV surgery and patients <19 years of age. The retrospective study period was from 2002–2018. A total of 562 patients were included in the study, 342 patients with bovine TV replacement (TVR) and 199 patients with porcine TVR. In around 50% of the patients, surgery on the TV was performed as a concomitant procedure. Due to the nature of the data collection, more detailed information, such as the genesis of the TV disease, or factors that could estimate the risk of surgery (such as left ventricular ejection fraction (EF), right ventricular EF, pulmonary hypertension, echocardiography) were not available. The risk factor analysis performed on the available factors identified bovine TV as a risk factor for reoperation (Hazard ratio (HR) 4.54, P = 0.005). The discussion of the data is plausible; ultimately, the authors attribute the increased reoperation rate in the group with bovine TVR to the increased pliability of the porcine prosthesis, which may offer advantages over the bovine prosthesis (which is flow-dependent in terms of valve opening), especially in the low flow area.

After reading the study with its limitations, however, the question arises: is the data situation sufficient for the interpretation of the calculations?

Already in 2021, a study with the same topic, but based on the retrospectively analysed data from their own clinic, was published by the predominantly same authors [2]. The study is considered a reference for the authors' argumentation in the present study and is quoted as follows: ‘A previous study reported that the cumulative incidence of structural valve deterioration (SVD) was significantly higher in bovine TVR than in porcine TVR (HR 17.544), and the cumulative incidence of TV reoperation was also higher in the bovine TVR group (HR 38.5)’ [2].

To clarify, 106 bovine prostheses and 26 porcine prostheses were implanted in tricuspid valve position during the period 1996–2018, favouring the bovine valves during the mentioned period. The diagnosis of SVD was made echocardiographically and/or intraoperatively, whereas the definition of SVD was not standardized. In the propensity score-adjusted multivariate analysis, the valve type showed—just significantly and with a large dispersion of the 95% confidence interval (CI)—an influence on the SVD of the bioprostheses [17. 544 (95% CI 1.070–243.902), P = 0.045], but also coronary artery disease [HR = 17.349, 95% CI (2.931–102.689), P = 0.002] and dyslipidaemia [HR = 5.627, 95% CI (2.493–12.699), P < 0.001].

The effect of bovine versus porcine bioprosthesis on the reoperation rate is reported (without PS adjustment and without P-value) as HR 38.462 (95% CI 2.591–476.190). Are these results actually suitable to serve as the above-mentioned reference for the present study?

Which patients, however, are referred for a TV reoperation after TVR? Epidemiologically, the genesis of tricuspid regurgitation in Korea is secondary in 90.2% [3]. Together with the above-mentioned factors—including the fact that a TV repair was not considered possible/meaningful—it would be reasonable to assume that the patient data analysed are predominantly a patient population with a significantly increased operative risk profile with long-standing secondary TV failure—clinically often associated with severe dilatation of the TV annulus and/or restriction of the leaflets with dilatation of the right ventricle with/without right heart failure. This risk profile is reflected in the perioperative mortality of ∼10% in the present study.

What are the reasons for TV reoperation after TVR despite the high operative risk—isolated degeneration, or endocarditis of the TV prosthesis, or infection of an pacemaker lead? Or was there another primary indication for surgery (e.g. mitral valve regurgitation), so that the TV reoperation was also performed concomitantly? How many patients with an indication for reoperation at the TV were not reoperated on due to comorbidities—and what influence does this have on the results of the study? These questions cannot be answered by the present study.

In summary, the results and discussion of the present study by Sohn et al. [1] are clinically relevant. However, due to the limitations, the results do not appear as clear-cut as they are discussed. However, due to the small number of patients with an indication for TVR, it will be difficult to conduct a prospective and at the same time numerically meaningful study in the future. Perhaps, however, the evaluation of retrospective data after TVR from different cardiac surgery centres can add more information, whether the use of a porcine valve versus a bovine valve makes a difference in the tricuspid valve position.

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