Exploring the association of erythrocytic NO-ferroheme, a surrogate marker of endothelial function with perioperative cardiovascular events in low/intermediate risk patients undergoing elective non-cardiac surgery

Purpose

Pre-operative assessment of cardiovascular risk currently relies on scores, such as the American Society of Anesthesiologists (ASA) score, biased towards high-risk, but neglecting middle/lower risk patients. Endothelial dysfunction is a precursor to cardiovascular events (CVEs), due to impaired nitric oxide (NO) bioavailability. We previously showed that the erythrocytic NO-ferroheme including the 5-coordinated NO-heme-α-hemoglobin (HbNO), a complex between NO and deoxyhemoglobin correlates with endothelial function assessed by digital tonometry. The aim of this study was to evaluate if HbNO is associated with the different cardiovascular risk factors and to explore its association with CVE in patients undergoing elective non-cardiac surgery.

Methods

We conducted a prospective, monocentric study in adult patients scheduled for elective non-cardiac surgery. At preoperative visit, blood samples were collected, and erythrocytes isolated to measure baseline HbNO levels, along with other biomarkers routinely used to evaluate pre-operative risk factors. NO-ferroheme signals were quantified using electron paramagnetic resonance spectroscopy. Follow-up visits and data analysis using electronic health records were conducted at 1-, 3-, 6- and 12- months postoperatively. The primary endpoint was the occurrence of a composite of CVE, including arrhythmias, chest pain/unstable angina, myocardial infarction/ischemia, pulmonary edema, pulmonary embolism, stroke, deep venous thrombosis, cardiac failure and death of any cause.

Results

Between November 2019 and June 2022, 2,500 patients were screened and 1,066 patients underwent an elective non-cardiac surgery. Among the 1,066 patients kept for the final analysis, 23 subjects developed a peri-operative CVE up to 30 days after surgery (p-30d CVE). Linear regression analysis revealed several independent factors significantly correlated with HbNO levels, including hemoglobin, anticoagulant usage, and smoking status. Patients who developed p-30d CVE exhibited lower mean HbNO levels (124.2 ± 96.6 nM) compared to those who did not (154.8 ± 104.1 nM; p = 0.028). Using a threshold of 124 nM for HbNO, levels below this cutoff (HbNO < 124 nM) were associated with an increased risk of p-30d CVE (OR [95% CI] = 4.21 [1.55–11.41]), as did classification in ASA III or higher (OR [95% CI] = 3.23 [1.38–7.59]). However, after excluding patients at high risk of CVE a priori, HbNO < 124 nM remained associated to p-30d CVE (OR [95% CI] = 5.52 [1.57–19.33]) while the association to ASA-score was no longer significant (OR [95% CI] = 0.89 [0.20–3.97]).

Conclusion

In patients scheduled for non-cardiac surgery, known cardiovascular risk factors, such as active smoking independently and negatively correlates with erythrocytic NO-ferroheme including HbNO. In patients without severe comorbidities, despite the limited number of CVEs observed, HbNO levels under 124 nM were independently and positively associated with p-30d CVE up to 30 days after surgery, while the ASA score was no longer correlated to p-30d CVE. HbNO measurements could help to improve the preoperative evaluation of low/intermediate risk patients.

Trial registration

Registered at ClinicalTrials.gov on June 19, 2019 (NCT03994900).