**Association of Increased Vascular Stiffness with Cardiovascular Death and Heart Failure Episodes Following Intervention on Symptomatic Degenerative Aortic Stenosis**

**Jakub Baran 1,2, Anna Kablak-Ziembicka 1,3, Pawel Kleczynski 1,2, Ottavio Alfieri 4, Łukasz Niewiara 2,5, Rafał Badacz 1,2, Piotr Pieniazek 2,6, Jacek Legutko 1,2, Krzysztof Zmudka 1,2, Tadeusz Przewlocki 2,6 and Jakub Podolec 1,2,\***


**Abstract:** Background. The resistive (RI) and pulsatile (PI) indices are markers of vascular stiffness (VS) which are associated with outcomes in patients with cardiovascular disease. We aimed to assess whether VS might predict incidence of cardiovascular death (CVD) and heart failure (HF) episodes following intervention on degenerative aortic valve stenosis (DAS). Methods. The distribution of increased VS (RI ≥ 0.7 and PI ≥ 1.3) from supra-aortic arteries was assessed in patients with symptomatic DAS who underwent aortic valve replacement (AVR, n = 127) or transcatheter aortic valve implantation (TAVI, n = 119). During a 3-year follow-up period (FU), incidences of composite endpoint (CVD and HF) were recorded. Results. Increased VS was found in 100% of TAVI patients with adverse event vs. 88.9% event-free TAVI patients (*p* = 0.116), and in 93.3% of AVR patients with event vs. 70.5% event-free (*p* = 0.061). Kaplan–Mayer free-survival curves at 1-year and 3-year FU were 90.5% vs. 97.1 % and 78% vs. 97.1% for patients with increased vs. lower VS. (*p* = 0.014). In univariate Cox analysis, elevated VS (HR 7.97, *p* = 0.04) and age (HR 1.05, *p* = 0.024) were associated with risk of adverse outcomes; however, both failed in Cox multivariable analysis. Conclusions. Vascular stiffness is associated with outcome after DAS intervention. However, it cannot be used as an independent outcome predictor.

**Keywords:** vascular stiffness; cardiovascular death; degenerative aortic stenosis; heat failure episodes; pulsatile index; resistive index; aortic valve replacement; transcatheter aortic valve implantation

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

#### **1. Introduction**

Resistive (RI) and pulsatile index (PI) are parameters corresponding to vascular stiffness (VS) which have been investigated in various clinical conditions, including renovascular and coronary atherosclerotic disease, hypertension, diabetes, and heart failure [1,2]. Vascular stiffness is a potential predictor of all-cause mortality, including cardiovascular mortality [3].

According to epidemiological data, even in young patients with increased VS, there is an increased risk of cardiovascular events, which carries with it a higher mortality rate [4]. Development and progression of degenerative aortic valve stenosis (DAS) is driven by

**Citation:** Baran, J.;

Kablak-Ziembicka, A.; Kleczynski, P.; Alfieri, O.; Niewiara, Ł.; Badacz, R.; Pieniazek, P.; Legutko, J.; Zmudka, K.; Przewlocki, T.; et al. Association of Increased Vascular Stiffness with Cardiovascular Death and Heart Failure Episodes Following Intervention on Symptomatic Degenerative Aortic Stenosis. *J. Clin. Med.* **2022**, *11*, 2078. https://doi.org/ 10.3390/jcm11082078

Academic Editor: Paolo Salvi

Received: 1 February 2022 Accepted: 5 April 2022 Published: 7 April 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

similar factors to those of VS, including aging, atherosclerosis, inflammation, fibrosis, calcification processes, and genetic susceptibility [5–7]. In addition, the data behind genetic predispositions in patients with ischemic heart disease have proven to favor its significant importance in progression of VS [7].

However, it is still unclear whether RI and PI might predict the incidence of cardiovascular death (CVD) and heart failure (HF) episodes following transcatheter (TAVI) or surgical (AVR) intervention on DAS [8].

Therefore, in the present study, we aimed to assess whether VS is associated with outcomes in post-intervention DAS patients.

#### **2. Materials and Methods**

#### *2.1. Study Population*

The study group comprised 246 consecutive patients with severe symptomatic DAS (aortic valve area, AVA < 1.0 cm2) referred for surgical or interventional treatment. From this group, 119 patients underwent transcatheter aortic valve implantation (TAVI), while 127 patients underwent surgical aortic valve replacement (AVR). Afterwards, patients were followed up for 36 months for the composite endpoint: CVD and HF episodes requiring hospital readmission.

Subjects were eligible if they (1) had preserved left ventricular ejection fraction (LVEF), (2) had never been diagnosed with stroke or transient ischemic attack (TIA), and (3) were ≥40 years of age. The exclusion criteria for both study groups included significant stenosis of any carotid or vertebral artery (exceeding 50% lumen reduction), persistent atrial fibrillation or other severe arrhythmia, significant concomitant valvular diseases, ongoing or recent myocardial infarction (<3 months), hemodynamic instability (NYHA class IV or acute heart failure), aortic dissection, and lack of informed consent.

Prevalence of cardiovascular risk factors including age, sex, hypertension, diabetes, and dyslipidemia was evaluated in compliance with guidelines of the European Society of Cardiology [9,10].

Carotid and vertebral arterial compliance parameters (RI and PI) of vascular stiffness indices and echocardiographic parameters of DAS were assessed. All measurements were done before final Heart Team qualification and performed by sonographers blinded to the subjects' characteristics.

The study protocol was consistent with the requirements of the Helsinki Declaration and approved by the local Institutional Ethics Committee. All subjects gave their informed consent for participation in the study.

#### *2.2. Echocardiographic Study*

All patients underwent a complete echocardiographic study in compliance with guidelines of the European Association of Cardiovascular Imaging [11]. Peak velocity and mean gradient across the aortic valve, AVA, and LVEF were assessed in all subjects.

#### *2.3. Arterial Compliance Assessment*

High-resolution B-Mode, color Doppler, and pulse Doppler ultrasonography of both carotid and vertebral arteries were performed with an ultrasound machine (TOSHIBA APLIO 450) equipped with a linear-array 5–10 MHz transducer on a patient lying in the supine position with head tilted slightly backward. Examinations were performed by experienced sonographers who were blinded to the subject's characteristics. Data comprised bilateral recording of peak systolic (PSV) and end diastolic velocities (EDV) measured within 1.0 to 1.5 cm of the proximal segment of the internal carotid artery and proximal V2 segment of the vertebral artery.

The averaged values of RI and PI from all assessed segments were calculated for each patient in accordance with the following equations: Resistive Index (RI) = [PSV − EDV/PSV], and Pulsatile Index (PI) = PSV − EDV/[(PSV + 2 × EDV)/3].

Frequencies of high RI (equal to 0.7 or higher) and high PI (equal to 1.3 or higher) from carotid and vertebral arteries were assessed [12,13].

#### *2.4. Follow-Up Period*

During an observation period of up to 36 months, the incidences of CVD and HF episodes were recorded. Cardiovascular disease was defined as fatal ischemic stroke, fatal myocardial infarction, fatal acute heart failure episode, or other CVD (i.e., any sudden or unexpected death unless proven as non-cardiovascular on autopsy). Heart failure episodes were defined as hospitalization for newly diagnosed or exacerbated congestive heart failure requiring administration of intravenous diuretics and/or vasoactive drugs (dopamine, dobutamine, epinephrine, or norepinephrine).

The final follow-up (FU) visit was conducted via telephone with the patient or an appointed family member. For all patients, data regarding patient vital status were obtained from the national health registry at the closing database.

#### *2.5. Statistical Analysis*

Data are presented as mean ± standard deviation or median (interquartile range) for continuous variables and as proportions for categorical variables. Differences between mean values were verified using the Student's *t* test and analysis of variance (ANOVA) test, while frequencies were compared using the chi squared test for independence, as appropriate. Normal distribution of the studied variables was determined using the Shapiro–Wilk test.

We assessed incidence of CVD and HF events in groups classified by high versus low PI and RI using the univariate Cox model, followed by the multivariable age-adjusted Cox models, with PI ≥ 1.3 and RI ≥ 0.7 as references [12,13]. We included age, sex, diabetes mellitus, hypertension, hyperlipidemia, previous myocardial infarction (MI), previous percutaneous coronary intervention (PCI), previous coronary artery bypass graft (CABG), chronic obstructive pulmonary disease (COPD), lower extremity artery disease (LEAD), LVEF, and pre-interventional AVA as factors which are potentially associated with the composite endpoint.

Results of the multivariate Cox proportional hazards analysis were expressed as hazard ratio (HR) and 95% confidence interval (CI). A two-sided value of *p* < 0.05 was considered statistically significant. The Kaplan-Mayer survival curves were constructed for groups with high vs. low VS. Statistical analyses were performed with Statistica version 13.3 software (TIBCO Software, Palo Alto, CA, USA) and with R Statistic Language 3.6.3 (R-Core Team, Vienna, Austria) [14].

#### **3. Results**

Out of 249 initially screened patients with severe DAS, 246 were eligible for follow-up evaluation. Three patients died from perioperative complications: 2 in the AVR and 1 in the TAVI groups.

Successful AVR was performed in 127 patients having a mean age of 69.3 ± 7.2 years (range: 53–86), including 75 (59.1%) females. Successful TAVI was performed in 119 patients having a mean age of 80.5 ± 5.8 years (range: 58–88), including 85 (71.4%) females.

The distribution of cardiovascular risk factors, including hyperlipidemia (*p* = 0.346), type 2 diabetes mellitus (*p* = 0.748), arterial hypertension (*p* = 0.292), history of previous MI (*p* = 0.833), and previous coronary interventions were similar between the AVR and the TAVI groups. Of note, patients referred for TAVI were older (*p* < 0.001) and more often were female (*p* = 0.042).

Patients with DAS referred for TAVI more frequently presented with symptoms corresponding to class 3 according to the New York Heart Association functional class (NYHA) when compared to AVR group (64.7% vs. 20.5%; *p* < 0.001).

All echocardiographic DAS parameters, as well as LVEF, were similar in both groups. Detailed study group characteristics are presented in Table 1.


**Table 1.** Study group clinical data.

Abbreviations: AVR, aortic valve replacement; CABG, coronary artery bypass graft; COPD, chronic obstructive pulmonary disease; LEAD, lower extremities artery disease; MI, myocardial infarction; PCI, percutaneous coronary intervention; TAVI, transcatheter aortic valve implantation.

Increased RI ≥ 0.7 and PI ≥ 1.3 were found in 91.6% of DAS patients in the TAVI group vs. 78.2% in the AVR group (*p* < 0.001) (Table 1).

After each valvular intervention, during a mean FU period of 29.3 ± 10.4 months, the composite endpoint occurred in 29 of 119 (24.4%) TAVI patients, including CVD in 21 (17.7%) and non-fatal HF episodes in 8 (6.7%) patients. In AVR patients, the composite endpoint occurred in 15 of 127 (11.8%) patients, including CVD in 7 (5.5%) and non-fatal HF episodes in 8 (6.3%) patients. A detailed comparison of patients with adverse events in TAVI and AVR groups is presented in Table 2.

Among patients with the composite endpoint compared to event-free patients, increased VS parameters (RI ≥ 0.7 and PI ≥ 1.3) were found in 29/29 (100%) vs. 80/90 (88.9%) patients in the TAVI group (*p* = 0.116), and in 14/15 (93.3%) vs. 79/112 (70.5%) in the AVR group (*p* = 0.061). In the entire study group (AVR plus TAVI), patients with increased VS more frequently suffered from a cardiovascular event when compared to patients with lower VS values (*p* = 0.011).

However, there was a large overlap of median and interquartile RI and PI values between event vs. event-free groups (Figure 1).

In the entire study group, Kaplan-Mayer free-survival curves at 1-year and 3-year FU were 90.5% vs. 97.1% and 78% vs. 97.1% for patients with increased VS compared to patients with lower RI and PI values (*p* = 0.014). Additionally, when TAVI and AVR groups were analyzed separately, patients with increased VS had lower free-survival curves when compared to patients with normal RI and PI values; however, this did not reach the level of statistical significance (Figure 2).


**Table 2.** Comparison of patients with composite endpoint and event-free patients in AVR and TAVI groups.

Abbreviations: AVR, aortic valve replacement; CABG, coronary artery bypass graft; COPD, chronic obstructive pulmonary disease; LEAD, lower extremities artery disease; MI, myocardial infarction; PCI, percutaneous coronary intervention; TAVI, transcatheter aortic valve implantation; VS, vascular stiffness.

**Figure 1.** Median and interquartile range for mean RI and PI in patients with the composite endpoint and in patients without the endpoint. Panel (**A**), AVR group; Panel (**B**), TAVI group; Panel (**C**), all study participants (AVR and TAVI patients). Abbreviations: PI, pulsatile index; RI, resistive index.

**Figure 2.** Kaplan-Meier survival curves showing time-to-event curves for 3-year cumulative survival to cardiovascular death and heart failure episodes dependent on increased vascular stiffness (defined as RI ≥ 0.7 and PI ≥ 1.3) compared to non-increased vascular stiffness. Panel (**A**), AVR group; Panel (**B**), TAVI group; Panel (**C**), all study participants (AVR and TAVI patients). Abbreviations: VS, vascular stiffness.

In univariate Cox analysis, factors potentially associated with increased risk of adverse outcomes included elevated VS (HR 7.97, 95% CI 1.10 to 57.9; *p* = 0.04), age (HR 1.05, 95% CI 1.01 to 1.09; *p* = 0.024), female gender (HR 1.90, 95% CI 0.94 to 3.85, *p* = 0.074), LEAD (HR 1.76, 95% CI 0.91 to 3.42; *p* = 0.094), and NYHA class III (HR 1.73, 95% CI 0.96 to 3.13; *p* = 0.069) (Table 3).

**Table 3.** Univariate and multivariate Cox proportional hazard analysis presenting risk of cardiovascular death and heart failure episodes for increased VS (RI ≥ 0.7 and PI ≥ 1.3 in all study group participants.


Abbreviations: CABG, coronary artery bypass graft; COPD, chronic obstructive pulmonary disease; LEAD, lower extremities artery disease; MI, myocardial infarction; LVEF, left ventricular ejection fraction; PCI, percutaneous coronary intervention; VS, vascular stiffness.

In multivariate Cox proportional hazard analysis, only LEAD (HR 2.22, 95% CI 1.12 to 4.39; *p* = 0.023) showed associations with risk of an adverse event, while increased VS failed to show an independent value (HR 7.12, 95% CI 0.97 to 52.5; *p* = 0.054) (Table 3).

#### **4. Discussion**

Our results support the hypothesis that high VS may be associated with risk of CVD and HF episodes in patients who underwent intervention for DAS, and that this risk can be elevated long after the intervention. Our findings are in line with studies by Makkar et al. and Mistiaen et al., who observed fatal cardiovascular events in patients with DAS and preserved LVEF, despite treatment of the valve [15,16].

Interestingly, the prognostic value of HF in patients with a preserved EF (HFpEF) in the TAVI population was presented by Seoudy et al. [17]. Importantly, the postulated multifactorial mechanisms of the HFpEF also may contribute to VS development and progression [18], while microvascular dysfunction underlies pathophysiological mechanisms of both VS and HF episodes despite a preserved systolic left ventricle contractility, constituting the main pathophysiological mechanism of recurrent HF episodes [19].

In the present study, preoperative values of RI ≥ 0.7 and PI ≥ 1.3, corresponding to increased VS, were associated with a 7.97-fold risk increase (*p* = 0.040) in univariate Cox proportional hazard analysis and a 7.12-fold risk increase (*p* = 0.054) in the occurrence of the composite endpoint in multivariate analysis. Similarly, Saeed et al. showed that event-free survival was significantly lower in patients with PWV ≥ 10 m/s when compared to those with lower PWV (*p* = 0.015); however, they observed an impact of PWV on all-cause mortality only in univariate Cox analysis (HR 1.80, 95% CI 1.14 to 2.83; *p* = 0.012) and not in multivariate analysis (HR 0.91, 95% CI 0.48 to 1.74, *p* = 0.778) [20].

In patients who underwent AVR for symptomatic DAS, increased left ventricular filling pressures were associated with cardiovascular mortality after AVR [21].

Similarly, in TAVI patients, VS is proposed as an important risk factor for adverse outcomes [22,23].

Tanaka et al. assessed the impact of pre-procedural brachial-ankle pulse wave velocity (PWV) on 1-year post-TAVI adverse outcomes in a group of 161 patients with severe DAS [22]. In the group with increased PWV, the incidence of all-cause death and rehospitalization related to HF episodes was 3.42-fold greater (95% CI 1.62 to 7.85; *p* = 0.002) when compared to that of patients with lower PWV values [22]. Broyd et al. indicated an optimum cut-off for PWV higher than 11 m/s to be the only predictor of 1-year mortality following TAVI in 186 patients (OR 3.57, 95% CI 1.36–9.42, *p* = 0.01) associated with survival (log-rank *p* = 0.04) [23]. In line with these studies, our results indicate an important role for VS in the prediction of event-free survival at 1-year and 3-year FU, which were 90.5% vs. 97.1% and 78% vs. 97.1% for patients with increased VS when compared to patients with lower RI and PI values (*p* = 0.014).

Some researchers have investigated further, comparing VS parameters after DAS intervention. Musa et al. compared the impact of TAVI and AVR on VS as measured with PWV. They found that there was a further significant increase in PWV parameters following AVR at the 6-month FU, while in the TAVI arm, the postprocedural PWV increase did not reach the level of statistical significance [24]. However, in a TAVI population, Terentes-Printzios et al. showed that the arterial system exhibited increased stiffness in response to acute relief of the obstruction following intervention, which was retained in the long term [25]. Of note, in this high-risk subset of patients, such as patients referred for TAVI, the intervention on the valve has a beneficial effect on supra-aortic artery flow parameters during the orthostatic stress test, resulting from the alleviated obstruction to cerebral in-flow [26]. On the other hand, Cantürk et al. did not observe a significant change in PWV values following AVR [27].

In our study, we did not find a relationship between pre-interventional VS values and the NYHA class symptoms to the support findings of Kidher et al., which showed that PWV was an independent predictor of NYHA class pre-operatively (OR 8.3, 95% CI 2.27 to 33.33) and post-operatively (OR 14.44, 95% CI 1.49 to 139.31) [28]. Of interest, the baseline NYHA class (OR 1.02, 95% CI 1.005 to 1.041, *p* = 0.041) may be an independent predictor of improvement in PWV following AVR [28].

Our study shows the limitations of using VS parameters in daily clinical practice. The main disadvantage in result interpretation is the large overlap in median RI and PI values between groups with adverse events when compared to those without (Figure 1). A potential explanation for this finding is the presence of multifactorial associations between VS, traditional, and non-traditional cardiovascular risk factors [13,29].

Therefore, more data are required from studies in a larger scaled population to determine the role of VS in predicting outcome following aortic valve interventions. Recently published data from the OCEAN Japanese multicenter registry including 2588 patients who underwent TAVI demonstrated that male sex, body mass index, Clinical Frailty Scale, atrial fibrillation, peripheral artery disease, prior cardiac surgery, serum albumin level, renal function, and presence of pulmonary disease were independent predictors of 1-year mortality following TAVI [30]. However, in the registry of Yamamoto et al., arterial compliance was not investigated at all. Similarly, our present study showed LEAD to be an independent risk factor for CVD and HF episodes following aortic valve intervention. In summary, the Heart Team is at the center of the decision-making process in patients with DAS [31–33]. The gathered experience indicates that a multidimensional and multidisciplinary pre-procedural work-up in patients with severe DAS, including a thorough assessment of coexisting disorders, results in an optimal treatment strategy and can be associated with a superior prognosis when compared to conservative medical management [31–33].

Accordingly, future studies are required to elucidate whether routine VS assessment should be incorporated as an additional parameter in this risk stratification model.

Seoudy et al. showed the clinical importance of a potential role in routine assessment of patients with HFpEF using the novel diagnostics algorithm (HFA-PEFF score) among the DAS population [17], where the same VS advancement score could be beneficial for better patient monitoring and treatment.

#### **5. Conclusions**

Our data demonstrates that VS is common in patients with severe DAS. We have demonstrated that increased VS can be a predictor of post-procedure outcome. In patients with PI ≥ 1.3 or RI ≥ 0.7, there is an increased risk of cardiovascular death and heart failure episodes despite intervention on the aortic valve (AVR or TAVI). However, huge the large overlap of RI and PI values between patients with or without adverse events during follow-up may limit the clinical value of routine vascular stiffness assessment.

**Author Contributions:** Conceptualization, J.B., P.K., A.K.-Z. and J.P.; data curation, J.B., Ł.N., R.B., P.P., J.L. and K.Z.; formal analysis, Ł.N., J.P. and P.P.; funding acquisition, A.K.-Z. and J.P.; investigation, P.K., Ł.N., R.B., P.P. and A.K.-Z.; methodology, J.B., Ł.N., R.B., T.P. and A.K.-Z.; project administration, K.Z.; resources, J.B. and T.P.; software, J.B. and Ł.N.; supervision, A.K.-Z.; validation, O.A., J.L. and K.Z.; visualization, J.B., Ł.N. and R.B.; writing—original draft, J.B., P.K. and J.P.; writing—review and editing, O.A., J.L., K.Z., T.P. and A.K.-Z. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by grants from the Jagiellonian University (grant numbers: N41/DBS/000038 and N41/DBS/000437).

**Institutional Review Board Statement:** The study was conducted in accordance with the Declaration of Helsinki and approved by the Institutional Ethics Committee of the Jagiellonian University (KBET/118/B/2014 and KBET/1072.6120.148.2018).

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


## *Article* **Energy Drinks and Their Acute Effects on Arterial Stiffness in Healthy Children and Teenagers: A Randomized Trial**

**Pengzhu Li, Guido Mandilaras, André Jakob , Robert Dalla-Pozza, Nikolaus Alexander Haas and Felix Sebastian Oberhoffer \***

> Division of Pediatric Cardiology and Intensive Care, University Hospital, LMU Munich, 81377 Munich, Germany; pengzhu.li.extern@med.uni-muenchen.de (P.L.); guido.mandilaras@med.uni-muenchen.de (G.M.); andre.jakob@med.uni-muenchen.de (A.J.); robert.dallapozza@med.uni-muenchen.de (R.D.-P.); nikolaus.haas@med.uni-muenchen.de (N.A.H.)

**\*** Correspondence: felix.oberhoffer@med.uni-muenchen.de

**Abstract:** Adolescents are the main consumer group of energy drinks (ED). Studies suggest that acute ED consumption is associated with increased peripheral blood pressure. Little is known of the ED-induced effects on arterial stiffness. Therefore, this study aimed to investigate the acute effects of ED consumption on arterial stiffness in healthy children and teenagers by conducting a prospective, randomized, single-blind, placebo-controlled, crossover clinical trial. Study participants (*n* = 27, mean age = 14.53 years) consumed a body-weight-adjusted amount of an ED or a placebo on two consecutive days. Arterial stiffness was evaluated sonographically by two-dimensional speckle tracking of the common carotid artery (CCA) at baseline and up to four hours after beverage consumption. The ED intake led to a significantly decreased peak circumferential strain of the CCA (11.78 ± 2.70% vs. 12.29 ± 2.68%, *p* = 0.043) compared with the placebo. The results of this study indicate that the acute ED consumption might be associated with increased arterial stiffness in healthy children and teenagers. Minors, particularly those with increased cardiovascular morbidity, should be discouraged from ED consumption.

**Keywords:** energy drinks; arterial stiffness; pediatrics; prevention

#### **1. Introduction**

Energy drinks (EDs) are soft drinks that contain high amounts of sugar, caffeine, and other stimulant compounds such as guarana, taurine, or ginseng [1]. EDs were introduced in the 1960s and have become one of the fastest-growing beverages in the soft drink industry after widespread advertising in the 1990s [2]. EDs are particularly popular among teenagers and young adults. According to a review conducted by Seifert et al., 30% to 50% of adolescents and young adults consume EDs [3]. The main function of EDs is marketed as providing fatigue relief, physical performance enhancement, and concentration improvement [4]. However, heavy ED consumption is associated with a series of cardiovascular side effects, including arterial hypertension and arrhythmia in young adults [5–7]. Multiple studies demonstrated that heavy ED consumption is linked with increased blood pressure in young adults [5,8,9]. In addition, a recent publication by our department revealed that acute ED consumption significantly raised systolic and diastolic blood pressure in a pediatric cohort [10].

Arterial stiffness refers to the wall rigidity of the large arterial vessels, including the aorta, the carotid arteries, and the cervical arteries [11]. Healthy large arteries have a strong cushioning function. Arterial stiffening caused by aging and multiple cardiovascular risk factors (e.g., smoking, dyslipidemia, diabetes, excess weight) impairs this cushioning function [12]. The stiffness-induced increase in pulse pressure (PP) was shown to be an independent predictor of cardiovascular risk [13].

**Citation:** Li, P.; Mandilaras, G.; Jakob, A.; Dalla-Pozza, R.; Haas, N.A.; Oberhoffer, F.S. Energy Drinks and Their Acute Effects on Arterial Stiffness in Healthy Children and Teenagers: A Randomized Trial. *J. Clin. Med.* **2022**, *11*, 2087. https:// doi.org/10.3390/jcm11082087

Academic Editors: Andrea Grillo and Paolo Salvi

Received: 28 February 2022 Accepted: 5 April 2022 Published: 7 April 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

The current gold standard for the assessment of arterial stiffness is considered to be carotid-femoral pulse wave velocity (cfPWV) measurement [14]. Other techniques, such as performing an ultrasound of the great arteries, have been recently applied to evaluate arterial stiffness: two-dimensional speckle tracking (2DST) is an advanced, non-invasive imaging technique, which has been widely used to analyze left ventricular function [15]. Recently, 2DST has been applied to assess arterial stiffness by tracking the ultrasonic speckles of the arterial wall during systole and diastole. Through the calculation of the vessel's deformation (strain), arterial stiffness can be visualized [16,17].

Current studies support the hypothesis that caffeine increases arterial stiffness and thus has an impact on the cardiovascular system [18]. To the best of our knowledge, the acute effects of caffeine-containing ED consumption on arterial stiffness have not been investigated yet.

The aim of this study was to evaluate the acute effects of caffeine-containing ED consumption on arterial stiffness in healthy children and teenagers.

#### **2. Materials and Methods**

#### *2.1. Ethical Statement*

This study was conducted according to the guidelines of the Declaration of Helsinki and approved by the Ethics Committee of the Ludwig Maximilians University Munich (Munich, Germany) (protocol code: 20-0993, date of approval: 12 January 2021). We obtained prior written informed consent from all study participants. For minor study participants we additionally obtained prior written informed consent from parents or legal guardians.

#### *2.2. Study Population*

In total, 27 healthy children and teenagers aged 10–18 years were prospectively enrolled for this study. Study participants were examined for eligibility through personal interviews, clinical examination, conventional echocardiography, 24-h Holter ECG, and 24-h blood pressure monitoring before inclusion. The exclusion criteria were as follows: the presence of chronic diseases such as congenital heart disease, arterial hypertension, presence of severe dysrhythmia, family history of sudden cardiac death, allergies to beverage ingredients, regular use of medication with effects on cardiovascular function, regular use of drugs including smoking and alcohol consumption, and pregnancy.

In study participants <18 years, weight classification was assessed according to the body mass index (BMI, kg/m2) percentiles (P.) established by Kromeyer-Hauschild et al. [19]. In study participants ≥18 years, normal weight was defined as BMI < 25 kg/m2, overweight as BMI ≥ 25 kg/m<sup>2</sup> but < 30 kg/m2, and obesity as BMI ≥ 30 kg/m2.

The caffeine consumption behavior of study participants was assessed in accordance with Shah et al.: rare caffeine consumers if <1 caffeinated beverage per month, occasional caffeine consumers if 1 to 3 caffeinated beverages per month, frequent caffeine consumers if 1 to 6 caffeinated beverages per week, and daily caffeine consumers if ≥1 caffeinated beverage per day [5]. In addition, study participants' ED consumption behavior was investigated as described above.

#### *2.3. Study Design*

This study was a prospective, randomized, single-blind (study participants), placebocontrolled, crossover clinical trial conducted by the Division of Pediatric Cardiology and Intensive Care, University Hospital, LMU Munich (Munich, Germany), from April 2021 to October 2021. The study was registered in the German Clinical Trials Register (https://www.drks.de/drks\_web/DRKS00027580 (accessed on 27 February 2022)).

Detailed information on the study design was described in a recent publication by our department [20]. In short, eligible study participants were randomized into two groups (Group I: day 1: ED, day 2: placebo; Group II: day 1: placebo, day 2: ED) and received either an ED or a placebo drink on two consecutive days. The administered ED amount was adjusted according to the maximal daily caffeine consumption for healthy children and teenagers (3 mg caffeine per kilogram of body weight per day) as recommended by the European Food Safety Authority [21]. The amount of the administered placebo drink was matched with the ED and did not contain typical ED ingredients such as caffeine, guarana, or taurine. ED and placebo had a similar sugar content and taste. The beverages were administered in an identical and masked drinking bottle at room temperature on both study days.

Participants were required not to consume any sources of caffeine or drugs 48 h before and 24 h after study participation. An overnight fast (apart from water) was requested before every study day. Study participants were asked not to consume any food or liquids during each examination duration. Lastly, after complete data collection, to assess blinding quality, study participants were asked to guess on which study day the ED beverage was administered.

#### *2.4. Two-Dimensional Speckle Tracking of the Common Carotid Artery*

An iE33 xMatrix and an Epiq 7G ultrasound machine (Philips, Amsterdam, The Netherlands) were used for examination. Both common carotid arteries (CCA) were recorded in short-axis view just below carotid bifurcation with a 3–8 MHz sector array transducer. During the entire examination period, study participants were in supine position, and the neck was extended to a 45◦ angle and turned to the opposite side of examination. Three consecutive loops were acquired under constant three-lead ECG tracking. Recorded clips were then transferred to a separate workstation (QLAB cardiovascular ultrasound quantification software, version 11.1, Philips, Amsterdam, The Netherlands). Peak circumferential strain (CS, %) and peak strain rate (SR, s−1) of both CCAs were measured semi-automatically through the software's function "SAX-A". The vascular region of interest was manually adjusted. Speckles of the vessel wall were then two-dimensionally tracked, as visualized in Figure 1. A masked investigator analyzed the recorded loops three consecutive times, and an average was then calculated. Arterial distensibility (mmHg−<sup>1</sup> × <sup>10</sup><sup>−</sup>3) was defined as

Arterial distensibility = (2 × Peak Circumferential Strain)**/**(Systolic Blood Pressure − Diastolic Blood Pressure)

**Figure 1.** Two-dimensional speckle tracking of the common carotid artery. The arrow indicates (**A**) peak circumferential strain (CS, %) and (**B**) peak strain rate (SR, s<sup>−</sup>1).

Data on ambulatory blood pressure, which were used for the calculation of arterial distensibility, were given in a recent publication by our department [10]. CS, SR, and arterial distensibility of the right and left CCA were averaged.

#### *2.5. Endpoints Measurement*

The endpoints were CS, SR, and arterial distensibility. For each study day, the endpoints were assessed at baseline as well as 30, 60, 120, and 240 min after beverage consumption.

#### *2.6. Statistical Analysis*

As this study was a pediatric pilot study, pediatric reference values for ED-induced changes in arterial stiffness did not exist and could not be considered in a power analysis. To test for normal distribution of continuous variables, histograms, QQ-plots, and the Shapiro–Wilk test were applied. Mean and standard deviation were used for all continuous variables. Ordinal and nominal variables are presented as percentages and counts. Sqrt or Ln data transformation was used if data were not normally distributed. A paired *t*-test was applied to compare baseline parameters between the ED and the placebo group. A two-way repeated-measures analysis of variance (ANOVA) was performed to evaluate the main effects of "beverage", "time", and interaction of "beverage and time" on CS, SR, and arterial distensibility. The Bonferroni-adjusted pairwise test was used for post hoc testing. Data analyses were performed independently by a masked statistician using SPSS (IBM SPSS Statistics for Windows, version 26.0. IBM Corp., Armonk, NY, USA). A *p*-value < 0.05 was considered statistically significant.

#### **3. Results**

#### *3.1. Patient Characteristics*

A total of 27 healthy children and teenagers were included in the analysis. The characteristics of participants are shown in Table 1. None of the subjects had chronic health conditions or was receiving medication. The parameters of arterial stiffness were not significantly different between the two groups at baseline (Table 2). Thirteen of the twenty-seven study participants (48.15%) correctly guessed the day of ED administration, indicating an appropriate blinding quality.


**Table 1.** Study Participants' Characteristics (*n* = 27).

<sup>a</sup> Rare caffeine consumer if <1 caffeine-containing drink per month, occasional caffeine consumer if 1 to 3 caffeinecontaining drinks per month, frequent caffeine consumer if 1 to 6 caffeine-containing drinks per week, and daily caffeine consumer if ≥1 caffeine-containing drink per day [5]. <sup>b</sup> Rare energy drink (ED) consumer if <1 ED per month, occasional ED consumer if 1 to 3 EDs per month, frequent ED consumer if 1 to 6 EDs per week, and daily ED consumer if ≥1 ED per day.


**Table 2.** Parameters of Arterial Stiffness at Baseline (*n* = 27).

CCA, common carotid artery; CS, peak circumferential strain; SR, peak strain rate. Mean ± standard deviation were used for normally distributed parameters.

#### *3.2. Acute Effects of Energy Drinks on CS, SR, and Arterial Distensibility*

The Shapiro–Wilk test revealed a non-normal distribution for the CS at time points baseline, 120 min, and 240 min within the ED group. It revealed a non-normal distribution for the SR at time point 30 min within the placebo group and at time points baseline and 120 min within the ED group. For arterial distensibility, a non-normal distribution was assessed at time points baseline, 60 min, and 120 min within the placebo group and at time points 30 min and 120 min within the ED group. To achieve a normal distribution, the original CS and SR data were transferred into Sqrt-form, and the original arterial distensibility data were transferred into Ln-form. According to Mauchly's sphericity hypothesis test for the interaction term "beverage and time", the variance and covariance matrices of the dependent variables were equal (*p* > 0.05).

The interaction between the variables "beverage and time" had no statistically significant effect on the CS, the SR, and arterial distensibility (*p* > 0.05). Hence, the main effect of "beverage consumption" was chosen.

A two-way repeated-measures ANOVA demonstrated that the CS was significantly lower after ED consumption compared with placebo intake (Table 3, Figure 2). In addition, the SR tended to be lower after ED consumption but did not reach statistical significance (Table 3). Regarding arterial distensibility, no significant differences were assessed between both groups (Table 3).



CCA, common carotid artery; CS, peak circumferential strain; SR, peak strain rate. \* *p* < 0.05.

**Figure 2.** Peak Circumferential Strain (CS, %) of the Common Carotid Artery after Energy Drink and Placebo Consumption.

#### **4. Discussion**

To the best of our knowledge, this is the first study investigating the acute effects of ED consumption on arterial stiffness in healthy children and teenagers. In total, 27 children with a mean age of 14.53 years were included for strain imaging of the CCA. After ED consumption, a significant decrease in the CS was observed. In addition, the SR tended to be lower after ED intake. Therefore, the results of this study suggest an acute elevation of arterial stiffness in a cohort of healthy children and teenagers after ED consumption.

#### *4.1. Pathophysiological Considerations and Clinical Implications*

The ED-induced effects on arterial stiffness can mainly be attributed to the high content of caffeine and guarana in EDs. Caffeine is thought to increase peripheral vascular resistance through sympathetic stimulation and consequently effect arterial stiffness [18,22]. Interestingly, a recent publication by our department reported a significant increase in peripheral systolic and diastolic blood pressure in the same pediatric cohort after ED consumption [10]. The results of this study suggest that the increased peripheral vascular resistance may result in an elevation of arterial stiffness visualized by a significant decrease in CS after ED consumption.

For this study, the administered amount of caffeine corresponded to the maximal daily dose (3 mg caffeine per kilogram of body weight per day) recommended for healthy children and teenagers by the European Food Safety Authority [21]. Presumably, the cardiovascular system might respond even more severely to higher amounts of caffeinated EDs. Besides caffeine and guarana, other substances such as taurine, glucuronolactone, and vitamins are commonly added to EDs. It has been suggested that taurine may lower blood pressure and have a positive effect on arterial stiffness [23–26]. The potential impact of glucuronolactone and vitamins on the cardiovascular system, however, requires further research.

Increased arterial stiffness is associated with elevated cardiovascular risk: the literature suggests that increased arterial stiffness is linked with altered coronary perfusion, elevated left ventricular afterload, left ventricular dysfunction, and left ventricular hypertrophy [12,27]. Therefore, further studies investigating the acute and chronic effects of ED consumption on left ventricular function and morphology are required. Moreover, pediatric studies indicate that increased arterial stiffness leads to structural vascular changes early in life [28]. Besides caffeine, EDs are high in sugar and calories. In particular, chronic ED consumption can increase the risk for glucose metabolism disorders, excess weight, and arterial hypertension. All of these cardiovascular risk factors were shown to be involved in the process of arterial stiffening [11,29,30]. As EDs negatively affect the cardiovascular system, minors, particularly those with already present cardiovascular risk factors (e.g., arterial hypertension, diabetes, excess weight, congenital heart disease), should be discouraged from ED consumption. In the future, studies are needed that evaluate the cardiovascular morbidity, including arterial stiffness, of chronic ED consumers.

#### *4.2. Limitations*

The limitations of the study design were reported in previous publications of our department [10,20]. The sample size of this study can be considered relatively low, as only 27 study participants were included. As 2DST of the CCA is a relatively new method to evaluate arterial stiffness, pediatric reference values do not exist and could not be elaborated in the current study. In addition, solely healthy children and teenagers were included in the present study. Minors with pre-existing health conditions (e.g., arterial hypertension, congenital heart disease) might react more profoundly to ED ingestion. Further, the relatively small sample size did not allow for an analysis of the influence of sex and habitual caffeine consumption on the parameters studied. Moreover, the ED amount was matched with body weight instead of lean body mass. Lastly, only the acute ED-induced effects on arterial stiffness were investigated, and only one specific ED product

was utilized for this study. Hence, further studies are required that take the abovementioned limitations into consideration.

#### **5. Conclusions**

The acute ED consumption is associated with a significant increase in arterial stiffness in healthy children and teenagers. Minors, particularly those with pre-existing health conditions such as arterial hypertension, diabetes, overweight, or congenital heart disease, should be discouraged from ED consumption. Further studies are required that evaluate the chronic effects of ED consumption on cardiovascular morbidity in children and teenagers.

**Author Contributions:** Conceptualization, R.D.-P., N.A.H. and F.S.O.; methodology, G.M., R.D.-P., N.A.H. and F.S.O.; software, G.M., R.D.-P., N.A.H. and F.S.O.; validation, G.M., R.D.-P., N.A.H. and F.S.O.; formal analysis, P.L. and F.S.O.; investigation, P.L., G.M. and F.S.O.; resources, A.J., R.D.-P., N.A.H. and F.S.O.; data curation, P.L., G.M. and F.S.O.; writing—original draft preparation, P.L., G.M. and F.S.O.; writing—review and editing, all authors; visualization, P.L., G.M., R.D.-P., N.A.H. and F.S.O.; supervision, G.M., A.J., R.D.-P., N.A.H. and F.S.O.; project administration, G.M. and F.S.O. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study (project title: EDUCATE Study: Energy Drinks—Unexplored Cardiovascular Alterations in TEens and TwEens) was supported by the German Heart Foundation/German Foundation of Heart Research.

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki and approved by the Ethics Committee of the Ludwig Maximilians University Munich (Munich, Germany) (protocol code: 20-0993, date of approval: 12 January 2021).

**Informed Consent Statement:** Prior written informed consent was obtained from all study participants. For minor study participants prior written informed consent from parents or legal guardians was additionally obtained.

**Data Availability Statement:** The data presented in this study are available upon reasonable request from the corresponding author.

**Acknowledgments:** We would like to thank Megan Crouse for editorial assistance.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

