This study found that the highest pre-ECMO implantation, pre-ECMO weaning, and pre-discharge NT-pro BNP levels were higher in CS patients who had died than in those who were undergoing rehabilitation. Pre-discharge NT-pro BNP levels were the best predictor of patient prognosis.
CS is a state of inadequate tissue perfusion due to cardiac dysfunction. The pathophysiology of CS involves a “downward spiral”: ischemia causes myocardial dysfunction, which, in turn, worsens ischemia.10 VA-ECMO introduces blood from the right atrium into the extracorporeal circulation through a catheter; this blood is fully oxygenated by a membrane oxygenator and then re-infused from the arterial end to the aorta. VA-ECMO thus increases effective circulation and ensures perfusion of vital organs.11 However, patients with CS receiving VA-ECMO often have severe underlying diseases, myocardial cell damage, and necrosis. Heart function may steadily deteriorate despite VA-ECMO support, resulting in disease progression and even death.12 In this study, the etiology of CS of patients receiving ECMO included heart failure (55.84%), fulminant myocarditis (15.58%), and malignant arrhythmias (23.38%) along with critical primary disease. Therefore, it is important to analyze the associated factors and evaluate the prognosis of CS patients receiving VA-ECMO support to improve their clinical outcomes and more appropriately use medical resources.
BNP is mainly synthesized and secreted by ventricular myocytes. BNP is an important endocrine factor that can promote sodium excretion and diuresis. BNP has strong vasodilatory effects, counteracts the renin-angiotensin-aldosterone system, and protects the body against volume overload and hypertension. The precursor of BNP, NT-proBNP, has a longer half-life and better stability and is an important diagnostic and prognostic value in heart failure, especially in cases of CS.13 NT-pro BNP can also be used for physical screening in elderly and high-risk groups since it has greater diagnostic and prognostic value in the early detection and intervention of heart failure.13,14
When VA-ECMO is used in patients with CS, an early and accurate assessment of tissue perfusion is critical for adjusting therapy and determining patient prognosis. The closed-loop system of the body circulation is disrupted by ECMO and the use of sedative, analgesic, and vasoactive drugs. Traditional tissue perfusion indicators (such as heart rate and urine volume) and invasive hemodynamic monitoring (such as Swan-Ganz balloon float catheters and pulse-indicated continuous cardiac output monitoring) cannot accurately measure and respond to tissue perfusion. Sometimes, even critical care ultrasound technology cannot accurately evaluate tissue perfusion.15,16 NT-pro BNP changes in adults treated with ECMO have rarely been studied except for a few reports in children [17, 18]. This study found that pre-ECMO implantation, pre-ECMO weaning, and pre-discharge NT-pro BNP values were lower in patients undergoing rehabilitation from CS than in those who had died of CS. These results are consistent with a study by Huang et al., which found significantly lower BNP levels in children who had survived CS than in those who had died of CS.19 Moreover, the difference between NT-pro BNP values in the death versus rehabilitation groups gradually increased as the patients’ conditions deteriorated, indicating that continuous monitoring of NT-pro BNP levels may be useful for patients receiving ECMO.
This study also showed that NT-pro BNP levels prior to ECMO weaning and discharge were predictive of patient death, of which NT-pro BNP levels prior to discharge were the best predictor of patient death. The high predictive value of pre-discharge NT-pro BNP level may be because patients in the rehabilitation group had significantly improved cardiac function and reduced blood NT-pro BNP levels at the time of ECMO weaning and discharge, while those in the death group (with varying degrees of persistent cardiac dysfunction) displayed continuous high-level secretions of NT-pro BNP. At the time of discharge (when the intergroup difference was greatest), the differences in the ROC curves and patient prognosis were also the most accurate. These results suggest that NT-pro BNP has an important diagnostic and predictive role at each treatment stage in adult CS patients receiving VA-ECMO assistance. The most predictive NT-pro BNP values for patient prognosis were those at discharge.
In addition, age; SOFA score; Cr, PLT, BUN, TBIL, PLT, and LA levels; MAP; pre-ECMO weaning Cr level, pre-discharge NT-pro BNP level, and LVEF% were reliable predictors of patient death. This study found that pre-discharge NT-pro BNP values were the best predictors of patient death among all variables; however, our results differ from those of previous studies. This different result could be due to differences in inclusion and exclusion criteria, participant selection, and sample size among studies.20,21
This study has several limitations. First, this study was retrospective in nature. Thus, prospective studies are required to validate our results. Second, the statistical efficacy was relatively limited owing to the small sample size. Finally, NT-pro BNP levels were recorded at only four key time points throughout this study. In the future, sample sizes and time points should be expanded upon when obtaining continuous values to further investigate the relationship between changes in NT-pro BNP levels and patient prognosis.