Elevated serum homocysteine has been reported to be an independent risk factor for cardiovascular and cerebrovascular diseases [6, 18, 19]. However, disputes [20] still exist regarding whether elevated homocysteine levels have predictive value for long-term prognosis in ACS patients. Therefore, this study sought to determine the relationship between homocysteine and long-term outcome in ACS patients undergoing PCI. The results unveiled that H-Hcy patients have higher all-cause mortality and cardiac death events than those without H-Hcy in ACS, regardless of hypertension. On the other hand, elevated serum homocysteine concentration is an independent predictor for long-term all-cause mortality after discharge in ACS patients with hypertension but not in ACS patients without hypertension.
Homocysteine is associated with plaque formation and atherosclerosis progression [3] by damaging vascular endothelial cells, altering lipid metabolism, and triggering inflammatory responses. In addition, it may be involved in acute coronary events by disrupting the balance between blood coagulation and fibrinolysis, leading to platelet aggregation and blood coagulation [21]. Thus, homocysteine has been identified as a prognostic factor for coronary heart disease. The study of Li, S et al. [22] revealed that H-Hcy (HR=1.075, 95% CI: 1.032-1.120, P<0.01) is an independent predictor of MACCE in patients with coronary heart disease (CHD) who underwent drug-eluting stent implantation. Moreover, a meta-analysis [6] of 19 cohort studies (4340 patients) revealed that elevated Hcy levels increased the risk of all-cause mortality by an average of 3.19-fold (HR = 3.19, 95% CI: 1.90-5.34, P<0.01), MACE by 1.51-fold (HR = 1.51, 95% CI: 1.23-1.85, P<0.01), and cardiac death by 2.76-fold (HR = 2.76, 95% CI: 1.44-5.32, P<0.01) in post-PCI patient. However, genetic background, eating habits, and living habits all affected the serum level of Hcy [23]. The mean Hcy levels varied between different studies. Simultaneously, the threshold for H-Hcy was inconsistent among various studies [22, 24]. Therefore, using definite cut-off values of Hcy concentration defined by guidelines or previous classical studies for risk stratification may underestimate the actual risk of patients. In addition, because homocysteine and hypertension have a synergistic effect on the prognosis of cardiovascular disease [9], homocysteine may have different effects on prognosis of ACS patients with complicated hypertension or not. As a result, we divided ACS patients into hypertension and non-hypertension groups and used ROC analysis to determine the optimal critical value of homocysteine for predicting long-term death in ACS patients in each of the two groups. The two groups were then subdivided into two subgroups based on the optimal cut-off value: an H-Hcy group and a normal Hcy group. As far as we know, the research method we adopted was more scientific and reasonable than those previously used.
In our study, Kaplan-Meier survival curves revealed that H-Hcy was associated with long-term mortality, including all-cause mortality and cardiac death, during 18-month median follow-up period in two groups, consistent with previous studies [4, 6]. Meanwhile, we observed that patients in the H-Hcy group were older and complicated with higher levels of serum BNP, creatinine, and uric acid levels and lower ejection fraction. These factors are variables of GRACE risk score, which is closely associated with the prognosis of ACS patients. Aslihan Calim et al. [5] recently reported a significant positive correlation between homocysteine and GRACE risk scores in ACS patients. Although controversies exist [25], most observational studies demonstrated that homocysteine is independent of other classic risk factors for cardiovascular diseases.
After adjusting for other risk factors, including H-Hcy, age, gender, serum creatinine, and ejection fraction, multivariate Cox regression analyses revealed that H-Hcy was strongly associated with long-term all-cause mortality in hypertension, but not in non-hypertension. Numerous possible explanations have been proposed, including the following. First, hypertension and homocysteine may have a synergistic effect on the prognosis of ACS. On the one hand, homocysteine plays a key role in atherosclerosis and plaque formation, strongly associated with long-term adverse events. On the other hand, ACS patients with hypertension have a poor long-term prognosis. Homocysteine is closely associated with hypertension development by activating angiotensin-converting enzyme. Thus, when hyperhomocysteine and hypertension are combined, the effect of “1 + 1 > 2” may occur. Second, the proportion of patients with heart failure (EF<40%) was higher in H-Hcy patients in the hypertension group, which is significantly linked to long-term prognosis of patients.
Furthermore, we found that the proportion of complicated strokes was higher in H-Hcy group than in N-Hcy group, consistent with the classical theory [26]. A case-control study conducted in six centers in China revealed that the risk of stroke in high Hcy population increased by 87% [27]. However, the study we conducted failed to establish a link between homocysteine and non-fatal stroke events in the long-term follow-up. This is due to the small sample size, short follow-up time, and few endpoints observed in this study.
However, our investigation has several limitations. First, this study only discussed the relationship between Hcy levels and long-term prognosis of ACS patients. There has been no discussion of whether lowering Hcy levels can improve the long-term prognosis of ACS patients, requiring additional research. Second, this was a retrospective study with relatively small sample size and relatively shorter follow-up duration, introducing bias. Third, there are differences in comprehensive management and treatment ability of ACS patients in different hospitals, which may influence observation results. Additionally, there may be discrepancies in the Hcy detection methods used in different hospitals. Finally, this paper did not discuss the impact of combined medication, including ACEI/ARB, antiplatelet drugs, statins, and β-receptor antagonists, on long-term cardiovascular events.