Association of Echocardiographic Parameters with Nitric Oxide Levels in Overweight Patients with Coronary Artery Disease after Coronary Artery Bypass Grafting

Introduction

The metabolic syndrome – of which overweight and abdominal obesity are core components – is recognized as a major driver of cardiovascular disease (CVD) development and has been termed one of the defining noncommunicable “epidemics” of the 21st century [1, 2].

Overweight is an established predictor of adverse outcomes following CABG [3, 4].

Epicardial adipose tissue (EAT) is an important contributor to the development of atherosclerotic changes in the coronary arteries not only through its paracrine and vasoactive secretions but also via its anatomical proximity to the epicardial coronary arteries [5, 6].

Increased EFT is associated with biventricular hypertrophy, elevated myocardial workload, and left ventricular remodeling [7, 8]. Higher BMI values are associated with the development of atherosclerosis in grafts [9, 10].

Overweight patients following coronary interventions more frequently require prolonged hospitalization during rehabilitation and face an elevated risk of restenosis, associated with activation of inflammatory processes [11, 12]. Thus, obesity is regarded not only as a risk factor for the development of coronary artery disease (CAD) but also as a significant predictor of adverse outcomes after CABG.

Endothelial dysfunction is a key contributor to impaired vascular tone and atherosclerotic damage. Endothelial injury increases vascular permeability and activates the inflammatory cascade. The endothelium plays a central role in regulating vascular dilation and constriction, platelet adhesion, and smooth muscle cell proliferation [13]. Nitric oxide, the primary mediator of endothelium-dependent vasodilation, is central to this process. Reduced NO production or bioavailability is considered a sensitive biomarker of endothelial dysfunction and a predictor of atherosclerosic progression [14, 15].

Overweight patients who have undergone CABG represent a clinically relevant subgroup. Currently, data on the relationship between EFT, NO levels, and echocardiographic (ECHO) parameters in this population remain limited.

Objective: To investigate the relationship between echocardiographic parameters and NO levels in overweight patients during rehabilitation after CABG.

Material and Methods

Study Design

A prospective cohort study was conducted in accordance with Good Clinical Practice (GCP) standards and the principles of the Declaration of Helsinki from February 2021 to June 2022. The study protocol was approved by the Ethical Committee of Karaganda Medical University (Karaganda, Republic of Kazakhstan; Protocol No. 16, dated March 15, 2021).

Inclusion and Exclusion Criteria

Eligible participants met the following inclusion and exclusion criteria:

Inclusion criteria:

• Age 35-65 years
• Diagnosis of single-vessel coronary artery disease (CAD)
• Post-CABG status
• Provision of written informed consent

Exclusion criteria:

• Acute myocardial infarction
• Chronic heart failure (NYHA Class III-IV)
• Decompensated diabetes mellitus
• Class I-III obesity
• Acute cerebrovascular accident
• Severe comorbidities limiting participation

Group Formation

We enrolled 155 patients:

·        Group 1 (n=85): Post-CABG, overweight (BMI: 28.0±0.9 kg/m²; 48 men, 37 women);

·        Group 2 (n=70): Post-CABG, normal weight (BMI: 23.3±1.1 kg/m²; 39 men, 31 women);

·        Control group (n=30): Healthy, age-matched volunteers without acute or chronic disease (BMI: 20.4±0.7 kg/m²).

Rehabilitation Program

Cardiac rehabilitation was conducted in accordance with Orders No. 116 and No. 65 of the Ministry of Healthcare of the Republic of Kazakhstan and comprised three stages:

·        Stage 1: 1 to 3 months post-CABG;

·        Stage 2: 3 to 6 months;

·        Stage 3: more than 6 months after surgery.

All patients received standard medication therapy (antiplatelet, cardioprotective, antianginal, antihypertensive, and hypolipidemic). In addition, exercise therapy, massage, breathing exercises, and physiotherapy were applied.

Research Methods

Nitric Oxide. The concentration of NO metabolites was quantified spectrophotometrically using the Griess reagent (λ=370 nm), with nitrite anion (NO₂⁻) levels measured as stable metabolites of NO. Prior to analysis, serum proteins were precipitated using a 10% zinc sulfate solution, and the samples were pelleted by centrifugation at 3000 rpm for 10 minutes. Optical density was measured against a standard curve generated from sodium nitrite (NaNO₂) solutions [16].

Echocardiography. All EFT measurements were performed by a single ultrasound specialist using a Vivid 8 echocardiography system (GE Healthcare, USA) in B- and M-modes. Standardization was achieved using the parasternal long-axis view at end-diastole, with values averaged over three cardiac cycles. Intra-observer reproducibility was assessed in 20 randomly selected patients, with repeat measurements performed 7-10 days later; the intraclass correlation coefficient (ICC) was 0.92 (95% CI: 0.87-0.96), indicating high consistency. Calculated parameters included left ventricular ejection fraction (LVEF, by the Teichholz formula), left ventricular myocardial mass (by the ASE method), and EFT, measured on the free wall of the right ventricle from the parasternal long-axis view at end-diastole and averaged over three cardiac cycles.

Ethical Aspects

All participants provided voluntary informed consent.

Statistical Analysis

Analyses were conducted using SPSS version 27.0 and MedCalc version 22. Normality of data distribution was assessed using the Kolmogorov-Smirnov test. Non-normally distributed variables are reported as median and interquartile range (IQR). Between-group comparisons were performed using the Mann-Whitney U test and Kruskal-Wallis H test, as appropriate. Within-group changes over time were evaluated using the Friedman test.

Receiver operating characteristic (ROC) analysis was employed to assess the diagnostic accuracy of BMI, with the area under the curve (AUC) and 95% confidence intervals (CI) reported.

Regression analysis

Multivariable logistic regression was performed to identify independent predictors of reduced NO levels and increased EFT, incorporating clinical and instrumental parameters as covariates. Statistical significance was defined as p<0.05.

Results

Table 1 presents the baseline demographic and clinical characteristics of the study groups, along with pharmacotherapy received during the rehabilitation period.

Table 1. Baseline Demographic and Clinical Characteristics of Patients by Group

Comparison of baseline characteristics between the two groups revealed no significant differences in demographic or clinical parameters. Mean age was 57.4±6.3 years in the overweight group (BMI≥25 kg/m²) and 56.1±7.1 years in the normal-weight group (BMI 18.5-24.9 kg/m²; p=0.34). The proportion of male participants was comparable (55.3% vs. 55.7%; p=0.96). Prevalence of comorbidities – including arterial hypertension (71.8% vs. 68.6%; p=0.67), type 2 diabetes mellitus (34.1% vs. 31.4%; p=0.78), and smoking (38.8% vs. 40.0%; p=0.88) – did not differ significantly between groups. Both groups received standard pharmacotherapy, including angiotensin-converting enzyme (ACE) inhibitors (89.4% vs. 91.4%; p=0.70), beta-blockers (95.3% vs. 95.7%; p=0.89), statins (94.1% vs. 94.3%; p=0.95), and antiplatelet agents (100% in both groups). The only parameter showing a statistically significant difference was BMI: 28.0±0.9 kg/m² in the overweight group compared to 23.3±1.1 kg/m² in the normal-weight group (p<0.001).

In Table 2, NO levels are presented in the study groups and the control group.

Table 2. Comparative Analysis of Echocardiographic Parameters and Plasma NO Levels in the Study Groups and the Control Group (Median [Q25; Q75])

As shown in Table 2, all parameters in Group 1 differed statistically significantly from those in Group 2 and the control group (p<0.05). Compared with the control group, Group 1 exhibited a 24% reduction in left ventricular ejection fraction (LVEF), a 187% increase in epicardial fat thickness (EFT), a 62% increase in left ventricular myocardial mass index (LVMMI), and a 36% decrease in plasma NO levels. Compared with Group 2, Group 1 had a 12% lower LVEF, 22% lower plasma NO, 43% higher EFT, and 25% higher LVMMI.

Further comparison of echocardiographic parameters and plasma NO levels in Group 1 and Group 2 across rehabilitation stages is presented in Figure 1.

Figure 1. Comparative Analysis of Echocardiographic Parameters and NO Levels Across Rehabilitation Stages in Study Groups (Median [Q25–Q75]).

According to our data, echocardiographic parameters in Group 1 were statistically significantly higher than those in Group 2 across all rehabilitation stages. Notably, in Group 2, all parameters demonstrated progressive improvement throughout the rehabilitation period: left ventricular ejection fraction (LVEF) showed a strong positive trend, while EFT and LVMMI decreased. In contrast, Group 1 exhibited a more complex pattern: although LVMMI and EFT initially decreased during early rehabilitation stages, both parameters demonstrated a statistically significant increase by the third rehabilitation stage. Concurrently, a statistically significant decline in LVEF was observed in Group 1 at the third stage.

A statistically significant difference in NO levels was observed between Group 1 and Group 2 only at the third rehabilitation stage.

To evaluate the relationship between NO levels and echocardiographic parameters across rehabilitation stages in overweight patients who had undergone reperfusion therapy, a correlation analysis was performed (Table 3).

Table 3. Correlation Analysis of NO and Echocardiographic Parameters Across Rehabilitation Stages in Study Groups

Correlation analysis revealed both positive and negative associations between NO levels and echocardiographic parameters at Stage 0 and during the first and second rehabilitation stages. By the third rehabilitation stage, strong and consistent correlations emerged between all echocardiographic parameters and NO levels.

A regression model was constructed to assess the influence of BMI on echocardiographic parameters and NO levels.

Receiver operating characteristic (ROC) analysis was conducted to evaluate the diagnostic utility of BMI in predicting combined alterations in NO levels and echocardiographic parameters (Tables 4-7).

Table 4. Regression Model (Rehabilitation Stage 2)

Table 5. Characteristics of the ROC Curves (Rehabilitation Stage 2)

Table 6. Regression Model (Rehabilitation Stage 3)

Table 7. Characteristics of the ROC Curves (Rehabilitation Stage 3)

Summarizing the data, at Rehabilitation Stage 2, BMI was identified as an independent predictor of reduced NO levels and adverse echocardiographic changes (OR=1.797; 95% CI: 1.038-3.110; p=0.036).

Figure 2 presents the ROC curve for Rehabilitation Stage 2 (AUC=0.734; 95% CI: 0.575-0.858). At Rehabilitation Stage 3 (Figure 3), the diagnostic value of BMI was higher (AUC=0.867; 95% CI: 0.714-0.956; p<0.001). The optimal BMI threshold was 28.08 kg/m², at which sensitivity reached 83.3% and specificity was 100%.

Figure 2. ROC Curve for Predicting the Development of Combined Adverse Changes in NO Levels and Echocardiographic Parameters Among Study Patients at Rehabilitation Stage 2. AUC and p-values for statistically significant predictors are indicated on the graph.

Figure 3. ROC Curve for Predicting the Development of Combined Adverse Changes in NO Levels and Echocardiographic Parameters Among Study Patients at Rehabilitation Stage 3. AUC and p-values for statistically significant predictors are indicated on the graph.

Thus, the analysis demonstrated that overweight in patients after CABG is associated with reduced NO levels, increased EFT, elevated left ventricular myocardial mass, and decreased cardiac contractile function.

BMI serves as an independent predictor of these changes and demonstrates diagnostic utility in predicting the risk of endothelial dysfunction, as reflected by NO levels.

Discussion

Our study demonstrates that overweight patients after CABG exhibit significantly increased EFT, reflecting impaired lipid metabolism in the epicardium. EFT was higher in the overweight cohort compared to normal-weight controls (p<0.05), reinforcing that obesity promotes not only visceral adiposity but also pathological fat deposition in the epicardium.

The American Heart Association recognizes obesity as an independent risk factor for coronary artery disease (CAD) [17, 18]. Large-scale studies further corroborate the association between excess body weight and adverse clinical outcomes after CABG [3, 4].

Notably, our study identified a significant further increase in EFT and left ventricular myocardial mass (LVMM) at the late (third) rehabilitation stage in patients with excess body weight. This likely reflects sustained metabolic and inflammatory dysregulation due to inadequate lifestyle modification, persistent dyslipidemia, and reduced physical activity after hospital discharge. Furthermore, decreased NO bioavailability and persistent endothelial dysfunction may contribute to myocardial remodeling and the paracrine activation of epicardial adipose tissue. These findings underscore the need for an individualized approach to patient management during late-stage cardiac rehabilitation, one that incorporates an understanding of the metabolic mechanisms underlying cardiac remodeling.

Analysis of the Society of Thoracic Surgeons (STS) database indicates that severe obesity in women after CABG does not elevate in-hospital mortality but is associated with a higher incidence of wound complications and rehospitalizations [19]. In contrast, several authors have identified obesity as an independent predictor of increased long-term mortality following myocardial revascularization [20-22].

According to the literature, EFT<7 mm is associated with subclinical atherosclerosis, whereas EFT>7 mm is reliably associated with an increased risk of coronary artery disease (CAD) [7, 5]. Corradi et al. demonstrated that EFT positively correlates with left ventricular myocardial mass, atrial size, and diastolic dysfunction; this parameter is significantly elevated in the setting of myocardial hypertrophy [23]. Similar findings have been reported by other investigators, who noted that a pronounced increase in EFT contributes to ventricular remodeling and hypertrophy of the left heart chambers [8].

In our study, a significant correlation between EFT and NO levels was observed, suggesting the development of an inflammatory process linked to endothelial dysfunction. In patients with atherosclerosis, reduced NO bioavailability – resulting from endothelial dysfunction – impairs coronary blood flow [15, 24]. This mechanism is largely attributable to tetrahydrobiopterin (BH₄) deficiency, a critical cofactor for endothelial nitric oxide synthase (eNOS), alongside elevated levels of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of NO synthesis whose concentrations increase under the influence of oxidized low-density lipoproteins [14, 24].

Notably, during the late (third) rehabilitation stage, we observed very high correlation coefficients between NO levels and echocardiographic parameters (r=0.908 for LVEF and r=-0.947 for LVMMI). These findings indicate a strong pathophysiological link between endothelial function and myocardial remodeling: diminished NO bioavailability is accompanied by increased myocardial mass and reduced contractility. This suggests that, at this stage, endothelial dysfunction may be the primary driver of remodeling severity in overweight patients.

Our results illustrate that dynamic changes in echocardiographic parameters and NO levels in overweight patients reflect a complex interplay of metabolic and endothelial mechanisms. The renewed increase in EFT and LVMMI during Rehabilitation Stage 3, coinciding with declining NO levels, points to persistent endothelial dysfunction and a chronic subclinical inflammatory milieu. These observations align with data from Virdis et al. (2016) [25] and Oikonomou and Antoniades (2019) [26], underscoring the role of oxidative stress and adipokine imbalance in advanced stages of myocardial remodeling in obese patients. Consequently, our study reinforces the necessity for long-term metabolic and anti-inflammatory management within cardiac rehabilitation programs following CABG.

The identified BMI threshold (>28.08 kg/m²) has practical significance for risk stratification in post-CABG patient management. A BMI exceeding this threshold may serve as a marker of an increased likelihood of reduced NO bioavailability and the development of endothelial dysfunction, justifying more aggressive lifestyle modification and intensification of pharmacological therapy. Specifically, such patients should be advised to adhere to strict body weight control, participate in expanded physical rehabilitation programs, and receive intensified hypolipidemic and antioxidant therapy – approaches consistent with contemporary guidelines from the American Heart Association (AHA, 2021) and the European Association for Cardiovascular Prevention and Rehabilitation (EACPR, 2023) for managing patients with obesity and coronary artery disease.

Conclusions

Overweight in patients after CABG is associated with increased EFT, reduced NO levels, and impaired myocardial diastolic function. The obtained data confirm the role of obesity as a significant predictor of endothelial dysfunction and adverse cardiac remodeling in the postoperative period.

Limitations

This study has several limitations that should be considered when interpreting the results. First, it was a single-center study with a limited sample size, which may restrict the generalizability of the findings to broader populations.

Second, the relatively small sample size may have limited statistical power to detect weaker or modest associations.

Third, the study had an observational design, which does not allow for the full establishment of causal relationships between overweight, EFT, NO levels, and echocardiographic parameters.

Furthermore, some potential confounders – including physical activity levels, dietary patterns, and the degree of medication adherence – were not formally assessed and may have influenced the observed associations.

Moreover, the limited follow-up duration precludes assessment of long-term clinical outcomes in this patient cohort.

Ethical Approval and Consent to Participate

The study was conducted in accordance with the ethical standards of the institutional research committee and the 1964 Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from all participants prior to enrollment. The study protocol was approved by the Ethics Committee of Karaganda Medical University (Karaganda, Republic of Kazakhstan; Protocol No. 16, March 15, 2021).

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Conflict of Interest

The authors declare no conflicts of interest.

Disclosure of AI Use

The authors confirm that no artificial intelligence tools or technologies were used in the preparation of this manuscript.