Introduction

Obesity is an independent risk factor for cardiovascular diseases and may cause various changes in heart morphology that predispose to ventricular dysfunction and development of heart failure (HF).1 According to previous studies, obesity most often leads to development of HF with preserved ejection fraction (HFpEF).2,3 Overweight and obese patients have respectively by 38% and 56% higher risk of HFpEF, independent of other risk factors, than persons with normal body mass index (BMI).4 Diagnosing HFpEF is often difficult, which is why the search for new echocardiographic parameters enabling early detection of subclinical HF is ongoing. In recent years, global longitudinal strain (GLS) and myocardial work (MW) have been increasingly used. The role of new echocardiographic parameters in the assessment of cardiac dysfunction in people with obesity has not been fully established yet. It is particularly important in this population to document improvement in cardiac function after weight loss.

Several studies to date have confirmed a correlation between normalization of body weight and improvement of echocardiographic parameters in patients undergoing bariatric surgery.5-8 Clinical confirmation of these observations may be a significant reduction in the incidence of cardiovascular complications in patients treated with bariatric surgery as compared with those treated conservatively.9

The aim of this study was to assess the value of the MW parameters in people with obesity, and to investigate the impact of weight loss after bariatric surgery on the MW components.

Patients and methods

Study population

Consecutive adult patients (>18 years) with BMI above 40 kg/m2 or BMI above 35 kg/m2 and concomitant risk factors (diabetes and / or hypertension and / or coronary artery disease) were enrolled in the Department and Division of Surgery of the Jan Kochanowski University in Kielce, Poland, from December 2022 till June 2023.

The exclusion criteria included: previous myocardial infarction and revascularization, expected lack of cooperation with the patient and the possibility of not completing follow-up visits, significant acquired or congenital valvular disease or previous correction of a heart defect, hypertrophic cardiomyopathy, left ventricular ejection fraction (LVEF) below 50%, pregnancy or postpartum period, alcohol or substance abuse, and active or prior cancer. The patients signed informed consent, and the study was approved by a local bioethics committee (70/2021).

Echocardiographic examinations

Standard echocardiography with assessment of all basic parameters was performed with additional MW analysis and evaluation of global constructive work (GCW), global wasted work (GWW), global work index (GWI), and global work efficiency (GWE) before the surgery and 3 and 6 months after the surgery by the same experienced cardiologist and echocardiography specialist (AP). The MW parameters were assessed using the VIVID-95 GE echocardiographic device and EcoPAC GE, software version 204 (GE Healthcare, Horten, Norway). Echocardiographic data were verified by an independent core laboratory analyst. First, LV GLS was assessed using speckle-tracking echocardiography in optimized apical 2-, 3-, and 4-chamber views at a frame rate of 50–80 frames/s. The aortic valve closure time was calculated using automatic function imaging in the apical 3-chamber view. Using the EchoPAC software, peak LV GLS was then assessed and a bull’s eye chart was created showing peak LV GLS for each segment of the myocardium. Before starting echocardiographic examination, blood pressure was measured. The system used these data to plot MW by segment and calculate an average GWI for all segments. The software then generated a pressure-strain loop based on the speckle tracking data and calculated the remaining parameters. The area under the curve, that is, the total work from the mitral valve closure to the mitral valve opening, represented the GWI. GCW is the work performed by the myocardium that was needed to achieve LVEF, which is a combination of LV shortening during systole and LV elongation during isovolumic relaxation. GWW defined work that was unproductive for LVEF, which was a combination of lengthening during systole and shortening during isovolumic relaxation. The ratio of constructive work to total work (both constructive and wasted) was reflected by GWE.

Statistical analysis

All analyses were performed using the data analysis software system Statistica version 13.3 (Tibco Software Inc., Palo Alto, California, United States). Due to a drop-down in the number of patients during follow-up, only the patients for whom complete follow-up data were obtained were included in the final analysis (n = 24). Distribution of quantitative variables was examined by histogram assessment and the Shapiro–Wilk test. Variables for which the histogram shape clearly deviated from the Gaussian curve (mainly extremely asymmetric or U-shaped histograms) were not subjected to the Shapiro–Wilk test. For quantitative variables with normal distribution, mean values with SD were calculated, while for the variables with other than normal distribution median with interquartile range were provided. For repeated measurements with normal distribution of differences between each measurement, the t test for dependent (paired) samples was used. For repeated measurements with other than normal distribution of differences, the Wilcoxon signed-rank test was used. The Holm–Bonferroni method was used to counteract the problem of multiple comparisons. The effect of weight loss on echocardiographic heart function parameters was assessed with the Pearson correlation test and linear regression model. The significance level was set at a P value below 0.05.

Results

The study involved 40 patients with obesity who were qualified for bariatric surgery. One patient withdrew their consent, 39 were included in the analysis, and they were 32 women and 7 men, at a mean (SD) age of 42.3 (12) years. As many as 15 patients were treated for hypertension, 7 for diabetes, 10 for hypothyroidism, and 2 patients were diagnosed with ischemic heart disease.

Four types of bariatric surgery were performed: sleeve gastrectomy (87.18%), intragastric ballon (7.69%), mini gastric bypass (2.56%), and single anastomosis sleeve ileal bypass (2.56%).

The examinations were performed in 39 patients before the surgery, 33 patients after 3 months (women, 81.82%), and 26 patients after 6 months (women, 80.77%). Twenty-four patients were examined at all 3 checkpoints.

Mean (SD) BMI decreased at consecutive measurements from 40.29 (5.6) kg/m2 before the surgery, to 34.58 (5.65) kg/m2 after 3 months, and 32.07 (5.05) kg/m2 after 6 months (P <⁠0.001 for comparison before the surgery and after 3 months, and after 3 and 6 months). Mean (SD) LVEF increased during follow-up from 59.08% (4.81) before the surgery, to 61% (4.82) after 3 months, and 61.25% (4.66) after 6 months (P = 0.048 for comparison before the surgery and after 6 months). Improvement was seen in all MW parameters after the surgery (Table 1).

Table 1. Changes observed during follow-up in heart function parameters (group limited to the patients examined at all 3 checkpoints: before the surgery and after 3 and 6 months; n = 24)

Parameter

Before the surgery

3 months postsurgery

6 months postsurgery

P valuea

P valueb

P valuec

GLS

–14.31 (2.47)

–16.72 (2.21)

–18.07 (2.33)

<⁠0.001

<⁠0.001

0.001

GCW

1807.21 (387.98)

1889.54 (287.66)

2091.17 (360.05)

0.16d

0.002

0.003

GWW

182.5 (130–286.25)

110 (90.25–186.25)

118.5 (73.75–150.5)

0.002

<⁠0.001

0.15d

GWI

1357.63 (338.17)

1505.92 (245.4)

1697.04 (273.02)

0.04d

<⁠0.001

<⁠0.001

GWE

88 (84–92)

92.5 (88–94)

94 (92–95)

<⁠0.001

<⁠0.001

0.02d

Data are presented as mean (SD) or median and interquartile range.

a Before the surgery and 3 months postsurgery

b Before the surgery and 6 months postsurgery

c Between 3 and 6 months postsurgery

d Nonsignificant, adjusted with the Holm–Bonferroni method

Abbreviations: GCW, global constructive work; GLS, global longitudinal strain; GWE, global work efficiency; GWI, global work index; GWW, global wasted work

We found a correlation between BMI change in the first 3 months after the surgery and GLS change between 3 and 6 months of follow-up (R = 0.4686; P = 0.03). This linear regression model explained the change in GLS in the abovementioned period in 19.17%. A correlation was also demonstrated between the BMI change at 3 and 6 months of follow-up and GWW change in the same period (R = 0.4342; P = 0.04). This linear regression model explained the change in GWW in 18.86%.

Another correlation was detected between the BMI change before the surgery and 6 months of follow-up and LVEF, GLS, and GWE changes in the same period (R = –0.4741; P = 0.03; and R = 0.6318; P <⁠0.001; and R = –0.4086; P = 0.04, respectively). The correlations based on BMI before the surgery and after 6 months of follow-up explained the changes in LVEF in 22.68%, in GLS in 30.43%, and in GWE in 16.07%.

Discussion

MW is a new parameter that can be measured noninvasively during echocardiography, and which has become a valuable heart muscle function assessment tool.10 It is more sensitive in detection of early heart muscle dysfunctions independent of LVEF.3,11,12 Previous studies have evaluated MW in healthy athletes and in patients with LV systolic asynchrony qualified for cardiac resynchronization therapy, and nowadays the first papers on MW evaluation in patients with obesity, diabetes, and cardiovascular risk factors are also published.13-15 This study assessed MW parameters in a group of patients with obesity with normal LV systolic function, and showed relatively low values of GCW, GWI, and GWE and increased GWW. These results are consistent with a recently published work assessing a correlation of MW components with obesity.14 A comparison of MW parameters in obese and normal-weight patients showed significantly lower GCW, GWW, and GWE values and higher GWW in the patients with obesity. Moreover, that study confirmed that these values correlate with the degree of obesity, as individual components differed significantly in the patients with mild, moderate, and severe obesity.14

The underlying mechanism of development of obesity-induced HF is complex and not fully understood. Obesity predisposes to HF through several direct pathophysiologic mechanisms including hemodynamic changes, neurohormonal activation, hormonal effects of dysfunctional adipose tissue, ectopic fat deposition resulting from lipotoxicity, and microvascular dysfunction. Hemodynamic alterations associated with obesity, such as increased plasma volume and decreased systemic vascular resistance promote adaptive cardiac remodeling.16 According to previous studies,17-20 many hemodynamic alterations and changes in cardiac morphology associated with obesity are reversible after significant weight loss. In severely obese patients with hyperdynamic circulation, significant weight loss is associated with a reduction in central blood volume, myocardial oxygen consumption, and cardiac performance. Bariatric surgery is probably more effective in reversing the adverse effects of obesity on cardiac efficiency and morphology than other weight loss methods, primarily because it is reserved for patients with severe obesity who are most profoundly affected by obesity-related cardiovascular changes, and also because the amount of weight loss is greater than that resulting from diet and exercise.21 Our study confirmed a significant improvement in the MW parameters in the patients who achieved a significant weight loss as a result of bariatric surgery. Significant improvement in GCW, GWI, and GWE with a decrease in GWW were observed already 3 months postsurgery, with further effects visible after another 3 months. It should be emphasized that our study group also showed improvement in LVEF and GLS, and the correlation of these parameters with changes in BMI was confirmed. However, both LVEF and GLS values depend on afterload, which is of great importance in patients with obesity.22,23 Moreover, only the patients with normal LVEF were included in this study, and thus MW parameters allowed for identification of patients with obesity-related subclinical HF. A particularly important parameter affecting the demonstrated improvement in cardiac efficiency after bariatric surgery is GWW. GWW reflects negative work (segment extension) during contraction and positive work (shortening section) during isovolumic relaxation.23 We showed a correlation between the decrease in BMI and GWW in the period of between 3 and 6 months after bariatric surgery. The reduction in GWW may indicate reverse, positive cardiac remodeling after bariatric surgery.

Limitations

Major limitations of this study are the facts that it was a single-center study with a small number of patients, and that a majority of the group were women.

Conclusions

MW is a new noninvasive parameter useful in the assessment of subclinical LV systolic dysfunction in patients with obesity. In patients undergoing bariatric surgery, myocardial performance improves soon after the surgery, that is, already within 3 months. MW components, especially GWW and GWE, correlate with a decrease in BMI and may be very useful in predicting improvement in LV function after bariatric surgery.