Discussion

In a US Agency for Healthcare Research and Quality database review of 5,234 patients who underwent TVS from 2003 to 2012, operative mortality was 13.9%.9 The 9.8% operative mortality in our series was similar to previously published studies.10–17
The key finding is that MELD-Na correlates well with operative mortality after triple valve surgery and exhibits superior diagnostic accuracy over EuroSCORE. The association remains significant after risk adjustment. A possible explanation is that the key driver of operative mortality was multiorgan failure in the valvular heart failure population; this is in contradistinction to the CABG population, in whom operative mortality was driven by low cardiac output syndrome.18 Just as EuroSCORE is the quid pro quo litmus test of ventricular recovery after cardiopulmonary bypass, MELD-Na may serve the litmus test of organ reserve.
In polyvalvular heart failure, right ventricular function and hepatorenal function are delicately intertwined. Both acute and chronic dysfunctions in one organ can initiate and perpetuate dysfunction in the others through complex neurohormonal feedback systems. This complex system of crosstalks between failing organs is collectively referred to as cardiorenal and cardiohepatic syndromes.19,20 A key message for cardiac surgeon sis that treating the valvular dysfunction may not necessarily lead to recovery in organ function. In fact, the deleterious effects of prolonged cardiopulmonary bypass may precipitate a potent immunogenic cascade leading to frank multiorgan failure and death.
Due to a substantial portion of missing data regarding right ventricular systolic function, the impact of chronic right ventricular dysfunction on hepatorenal dysfunction cannot be quantified in this study. Using the data available, right ventricular systolic dysfunction did correlate with operative mortality on univariate analysis. Volumetric assessment with MRI, right ventricular dimension, as well as strain imaging may provide more accurate assessment of right ventricular function compared with two-dimensional echocardiography. Nonetheless, we believe this is a promising avenue for future research because strategies to mitigate post-bypass right ventricular dysfunction and ensuing organ failure remain limited.
We would like to highlight the importance of including hyponatremia in the risk score. Hyponatremia in heart failure is mediated by increased activity of anti-diuretic hormone and activation of the renin-angiotensin-aldosterone system. Aggressive diuresis may also have played a role. As demonstrated in the OPTIMISE-HF registry, hyponatremia in patients hospitalized for heart failure was associated with higher rates of in-hospital and follow-up mortality.21Although it is unclear whether hyponatremia contributes to poor prognosis or serves simply as a marker of disease severity, the presence and severity of hyponatremia should alert the surgeon to the severity of the underlying heart failure.22
This study was retrospective in nature and suffered from weaknesses inherent to all retrospective studies, including selection bias and confounding. The number of subjects was small. The findings generated were at best hypothesis-generating and would benefit from verification in a sizable regional or national database.
In Papworth’s landmark publication regarding the EuroSCORE back in 1999, the authors commented that “the true test of such a system is in its widespread application in the field”, and that its use should be routine for all cardiac surgical patients.2 In the modern era, MELD-Na can be easily calculated by inputting the four biochemical parameters into mobile applications on smartphones and tablet computers. We believe that it is not a stretch to imagine that the adoption of MELD-Na can become widespread and find its rightful place in risk stratifying patients with valvular heart failure.