Importance of non-cardiovascular comorbidities in atrial fibrillation and heart failure with preserved ejection fraction.

AIMS: Atrial fibrillation (AF) and heart failure (HF) with preserved ejection fraction (HFpEF) are interlinked and frequently coexisting conditions. To date, patients with AF and HFpEF have limited evidence guiding their management. This study aimed to investigate the predictors of adverse outcomes among patients with AF and HFpEF. METHODS: The Fushimi AF Registry is a community-based prospective survey of AF patients in Fushimi-ku, Kyoto, Japan. From the registry, we explored predictors for a composite of cardiac death or HF hospitalization among AF patients with HFpEF (defined as having a prior HF hospitalization or New York Heart Association class ≥2 in association with heart disease and left ventricular ejection fraction ≥50%). Besides, we investigated whether the scoring using the predictors identified by the Fushimi AF Registry could stratify the outcomes in patients with AF and HFpEF registered in another independent Kyoto Congestive Heart Failure Registry. RESULTS: Of 755 patients with AF and HFpEF [mean age: 77.5 ± 9.9 years; female: 391 (52%); paroxysmal AF: 258 (34%); and mean CHA2DS2-VASc score: 4.5 ± 1.5], cardiac death or HF hospitalization occurred in 246 patients (33%) during the median follow-up period of 4.4 years in the Fushimi AF Registry. Using multivariate Cox regression analysis, age ≥75 years [hazard ratio (HR): 1.72, 95% confidence interval (CI): 1.26-2.36] and non-cardiovascular comorbidities such as anaemia (HR: 1.83, 95% CI: 1.37-2.46), chronic kidney disease (HR: 1.69, 95% CI: 1.27-2.26), diabetes mellitus (HR: 1.55, 95% CI: 1.15-2.09) and chronic obstructive pulmonary disease (HR: 1.87, 95% CI: 1.08-3.22) were independent predictors of adverse outcomes. Meanwhile, cardiovascular comorbidities including coronary artery disease, valvular heart disease or cardiomyopathy were not significantly associated with adverse outcomes. These results were also the case when analysed for patients with AF and HFpEF who registered in the Kyoto Congestive Heart Failure registry (N = 878). The score assigning 1 point for each five predictors (age, anaemia, chronic kidney disease, diabetes mellitus and chronic obstructive pulmonary disease; ranging 0-5 points) stratified the incidence of adverse outcomes among patients with AF and HFpEF registered in the Kyoto Congestive Heart Failure Registry as well as among those in the Fushimi AF Registry (both log-rank; P < 0.001). CONCLUSIONS: Non-cardiovascular comorbidities such as anaemia, diabetes mellitus and kidney or pulmonary disease in addition to advanced age were independent predictors of adverse outcomes in patients with AF and HFpEF. Our study suggests the importance of focusing on these non-cardiovascular comorbidities for individualized risk stratification and optimal management in patients with AF and HFpEF.

What is the Future Position of Factor XIa Inhibitors for Patients with Atrial Fibrillation?

Factor XIa (FXIa) may be involved in thrombus formation, but only to a lesser extent involved in haemostasis. Several novel FXIa inhibitors are under investigation, and Phase II trials demonstrated marked reduction of bleeding compared with standard treatment by factor Xa inhibitors. Asundexian is a small molecule that selectively inhibits FXIa. A large-scale Phase III clinical trial, OCEANIC-AF, has been initiated to compare the efficacy and safety between asundexian and apixaban. However, the OCEANIC-AF study was recently halted due to the inferior efficacy of asundexian versus the apixaban control arm. The present report describes up-to-date evidence of FXIa inhibitors and discusses the future position of FXIa inhibitors for patients with AF.

A Complex Interplay: Navigating the Crossroads of Tobacco Use, Cardiovascular Disease, and the COVID-19 Pandemic: A WHF Policy Brief.

The Coronavirus Disease 2019, commonly referred to as COVID-19, is responsible for one of the deadliest pandemics in human history. The direct, indirect and lasting repercussions of the COVID-19 pandemic on individuals and public health, as well as health systems can still be observed, even today. In the midst of the initial chaos, the role of tobacco as a prognostic factor for unfavourable COVID-19 outcomes was largely neglected. As of 2023, numerous studies have confirmed that use of tobacco, a leading risk factor for cardiovascular and other diseases, is strongly associated with increased risks of severe COVID-19 complications (e.g., hospitalisation, ICU admission, need for mechanical ventilation, long COVID, etc.) and deaths from COVID-19. In addition, evidence suggests that COVID-19 directly affects multiple organs beyond the respiratory system, disproportionately impacting individuals with comorbidities. Notably, people living with cardiovascular disease are more prone to experiencing worse outcomes, as COVID-19 often inherently manifests as thrombotic cardiovascular complications. As such, the triad of tobacco, COVID-19 and cardiovascular disease constitutes a dangerous cocktail. The lockdowns and social distancing measures imposed by governments have also had adverse effects on our lifestyles (e.g., shifts in diets, physical activity, tobacco consumption patterns, etc.) and mental well-being, all of which affect cardiovascular health. In particular, vulnerable populations are especially susceptible to tobacco use, cardiovascular disease and the psychological fallout from the pandemic. Therefore, national pandemic responses need to consider health equity as well as the social determinants of health. The pandemic has also had catastrophic impacts on many health systems, bringing some to the brink of collapse. As a result, many health services, such as services for cardiovascular disease or tobacco cessation, were severely disrupted due to fears of transmission and redirection of resources for COVID-19 care. Unfortunately, the return to pre-pandemic levels of cardiovascular disease care activity has stagnated. Nevertheless, digital solutions, such as telemedicine and apps, have flourished, and may help reduce the gaps. Advancing tobacco control was especially challenging due to interference from the tobacco industry. The industry exploited lingering uncertainties to propagate misleading information on tobacco and COVID-19 in order to promote its products. Regrettably, the links between tobacco use and risk of SARS-CoV-2 infection remain inconclusive. However, a robust body of evidence has, since then, demonstrated that tobacco use is associated with more severe COVID-19 illness and complications. Additionally, the tobacco industry also repeatedly attempted to forge partnerships with governments under the guise of corporate social responsibility. The implementation of the WHO Framework Convention on Tobacco Control could address many of the aforementioned challenges and alleviate the burden of tobacco, COVID-19, and cardiovascular disease. In particular, the implementation of Article 5.3 could protect public health policies from the vested interests of the industry. The world can learn from the COVID-19 pandemic to better prepare for future health emergencies of international concern. In light of the impact of tobacco on the COVID-19 pandemic, it is imperative that tobacco control remains a central component in pandemic preparedness and response plans.

Association of Regression from Sustained to Paroxysmal Atrial Fibrillation with Clinical Outcomes: The Fushimi AF Registry.

Some patients with atrial fibrillation (AF), albeit less frequently, may regress from sustained to paroxysmal type. We sought to investigate how the regression of AF is associated with outcomes. Among the AF patients enrolled in the Fushimi AF Registry who were identified as having sustained AF at baseline, conversion of sustained to paroxysmal AF during follow-up was defined as AF regression. Major adverse cardiovascular events (MACE) were defined as a composite of cardiac death, myocardial infarction, ischemic stroke, systemic embolism, or hospitalization due to heart failure. Among 2,261 patients with sustained AF at baseline, AF regression was observed in 214 (9.5%) patients over a median follow-up period of 5.8 years (1.78% per patient-year). The annual incidence of MACE in patients with AF regression was significantly lower than those without (3.47% vs. 6.59% per patient-year, P < 0.001; adjusted hazard ratio [HR], 0.53, 95% confidence interval [CI], 0.38-0.72). Furthermore, AF regression was significantly associated with reduced risk of MACE during and after the regression period from sustained to paroxysmal forms (during regression period: adjusted HR, 0.45; 95% CI, 0.22-0.90; after regression period: adjusted HR, 0.43; 95% CI, 0.26-0.67). The incidence of MACE was comparable between spontaneous regression (35/178: 19.7%) and therapy-associated regression (either receiving catheter ablation or antiarrhythmic drugs before the regression) (7/36: 19.4%) (P=0.98). Regression of AF was associated with a lower incidence of adverse cardiovascular events. The risk of adverse events decreased significantly during the regression period and its reduction level persisted after regression. URL: http://www.umin.ac.jp/ctr/index.htm Unique identifier: UMIN000005834.

Efficacy of highly bioavailable oral curcumin in asymptomatic or mild COVID-19 patients: a double-blind, randomized, placebo-controlled trial.

INTRODUCTION: Even after the peak of the COVID-19 pandemic, the number of mild cases remains high, requiring continuous control. Curcumin, owing to its anti-inflammatory properties, can suppress vital proliferation and cytokine secretion in animal models. We developed a highly absorbable curcumin, curcuRouge® (cR), which is approximately 100 times more orally bioavailable than conventional curcumin. We evaluated the effect of cR on the inhibition of disease progression in asymptomatic or mildly symptomatic COVID-19 patients. METHODS: This study evaluated the effect of 7-day oral intake of cR (360 mg twice daily). Patients within 5 days of COVID-19 diagnosis were randomly assigned to a placebo or cR group in a double-blind manner. RESULTS: Primary endpoint events [body temperature (BT) ≥ 37.5 °C and saturation of percutaneous oxygen (SpO2) < 96%] were fewer than expected, and the rate of these events was 2.8% in the cR group (2/71) and 6.0% in the placebo group (4/67); hazard ratio (HR) = 0.532, 95% confidence interval (CI) 0.097-2.902. Patients receiving cR tended to take fewer antipyretic medications than those receiving placebo (HR = 0.716, 95% CI 0.374-1.372). Among patients with a normal range of BT at baseline, the BT change rate was significantly (p = 0.014) lower in the cR group (- 0.34%) versus placebo (- 0.01%). CONCLUSION: The relative suppression of event rates and antipyretic medications taken, and significant decrease of subclinical BT support the anti-inflammatory effects of cR in asymptomatic or mildly symptomatic patients with COVID-19. TRIAL REGISTRATION: Japan Registry of Clinical Trials (CRB5200002).

Five percent weight loss is a significant 1-year predictor and an optimal 5-year cut-off for reducing the number of obesity-related cardiovascular disease risk components: the Japan Obesity and Metabolic Syndrome Study.

Objective: This study aimed to identify the amount of weight loss needed in patients with obesity to improve metabolic syndrome (MetS), a risk factor for cardiovascular disease (CVD), over a long period of time. Methods: A total of 576 patients with obesity were enrolled in this study. Effects of continuous physician-supervised weight loss on the cumulative MetS components excluding abdominal circumference (defined as obesity-related CVD risk score) were investigated during a 5-year follow-up period. The extent of weight loss required to reduce the obesity-related CVD risk components was assessed using receiver operating characteristic (ROC) curve analyses. Results: Of the 576 participants, 266 completed 5-year follow-up, with 39.1% and 24.1% of them achieving ≥5.0% and ≥7.5% weight loss at the 5-year follow-up, respectively. The area under the ROC curve for reducing the obesity-related CVD risk components was 0.719 [0.662-0.777] at 1 year and 0.694 [0.613-0.775] at 5 years. The optimal cut-off value for weight loss was 5.0% (0.66 sensitivity and 0.69 specificity) and the value with 0.80 specificity was 7.5% (0.45 sensitivity) at 5 years. Greater reductions in weight were associated with greater improvements in the obesity-related CVD risk score at all follow-up periods (P-trend <0.001). Obesity-related CVD risk score was significantly improved by 5.0-7.5% and ≥7.5% weight loss at 1 year (P = 0.029 and P < 0.001, respectively) and ≥7.5% weight loss at 5 years (P = 0.034). Conclusions: A weight loss of ≥5.0% at 1 year and ≥7.5% at 5 years could reduce the number of obesity-related CVD risk components in patients with obesity.

Current frailty knowledge, awareness, and practices among physicians following the 2022 European consensus document on Frailty in Cardiology.

Aims: Aging-related cardiovascular disease and frailty burdens are anticipated to rise with global aging. In response to directions from major cardiovascular societies, we investigated frailty knowledge, awareness, and practices among cardiologists as key stakeholders in this emerging paradigm a year after the European Frailty in Cardiology consensus document was published. Methods and results: We launched a prospective multinational web-based survey via social networks to broad cardiology communities representing multiple World Health Organization regions, including Western Pacific and Southeast Asia regions. Overall, 578 respondents [38.2% female; ages 35-49 years (55.2%) and 50-64 years (34.4%)] across subspecialties, including interventionists (43.3%), general cardiologists (30.6%), and heart failure specialists (HFSs) (10.9%), were surveyed. Nearly half had read the consensus document (38.9%). Non-interventionists had better perceived knowledge of frailty assessment instruments (fully or vaguely aware, 57.2% vs. 45%, adj. P = 0.0002), exercise programmes (well aware, 12.9% vs. 6.0%, adj. P = 0.001), and engaged more in multidisciplinary team care (frequently or occasionally, 52.6% vs. 41%, adj. P = 0.002) than interventionists. Heart failure specialists more often addressed pre-procedural frailty (frequently or occasionally, 43.5% vs. 28.2%, P = 0.004) and polypharmacy (frequently or occasionally, 85.5% vs. 71%, adj. P = 0.014) and had consistently better composite knowledge (39.3% vs. 21.6%, adj. P = 0.001) and practice responses (21% vs. 11.1%, adj. P = 0.018) than non-HFSs. Respondents with better knowledge responses also had better frailty practices (40.3% vs. 3.6%, adj. P < 0.001). Conclusion: Distinct response differences suggest that future strategies strengthening frailty principles should address practices peculiar to subspecialties, such as pre-procedural frailty strategies for interventionists and rehabilitation interventions for HFSs.

Association of left atrial enlargement with heart failure events in non-valvular atrial fibrillation patients with preserved left ventricular ejection fraction.

Aims: Atrial fibrillation (AF) increases the risk of heart failure (HF); however, little is known regarding the risk stratification for incident HF in AF patients, especially with preserved left ventricular ejection fraction (LVEF). Methods and results: The Fushimi AF Registry is a community-based prospective survey of AF patients. From the registry, 3002 non-valvular AF patients with preserved LVEF and with the data of antero-posterior left atrial diameter (LAD) at enrolment were investigated. Patients were stratified by LAD (<40, 40-44, 45-49, and ≥50 mm) with backgrounds and HF hospitalization incidences compared between groups. Of 3002 patients [mean age, 73.5 ± 10.7 years; women, 1226 (41%); paroxysmal AF, 1579 (53%); and mean CHA2DS2-VASc score, 3.3 ± 1.7], the mean LAD was 43 ± 8 mm. Patients with larger LAD were older and less often paroxysmal AF, with a higher CHA2DS2-VASc score (all P < 0.001). Heart failure hospitalization occurred in 412 patients during the median follow-up period of 6.0 years. Larger LAD was independently associated with a higher HF hospitalization risk [LAD ≥ 50 mm: hazard ratio (HR), 2.36; 95% confidence interval (CI), 1.75-3.18; LAD 45-49 mm: HR, 1.84; 95% CI, 1.37-2.46; and LAD 40-44 mm: HR, 1.34; 95% CI, 1.01-1.78, compared with LAD < 40 mm) after adjustment by age, sex, AF type, and CHA2DS2-VASc score. These results were also consistent across major subgroups, showing no significant interaction. Conclusion: Left atrial diameter is significantly associated with the risk of incident HF in AF patients with preserved LVEF, suggesting the utility of LAD regarding HF risk stratification for these patients.

CRISPR-Cas9-guided amplification-free genomic diagnosis for familial hypercholesterolemia using nanopore sequencing.

Familial hypercholesterolemia is an inherited disorder that remains underdiagnosed. Conventional genetic testing methods such as next-generation sequencing (NGS) or target PCR are based on the amplification process. Due to the efficiency limits of polymerase and ligase enzymes, these methods usually target short regions and do not detect large mutations straightforwardly. This study combined the long-read nanopore sequencing and CRISPR-Cas9 system to sequence the target DNA molecules without amplification. We originally designed and optimized the CRISPR-RNA panel to target the low-density lipoprotein receptor gene (LDLR) and proprotein convertase subtilisin/kexin type 9 gene (PCSK9) from human genomic DNA followed by nanopore sequencing. The average coverages for LDLR and PCSK9 were 106× and 420×, versus 1.2× for the background genome. Among them, continuous reads were 52x and 307x, respectively, and spanned the entire length of LDLR and PCSK9. We identified pathogenic mutations in both coding and splicing donor regions in LDLR. We also detected an 11,029 bp large deletion in another case. Furthermore, using continuous long reads generated from the benchmark experiment, we demonstrated how a false-positive 670 bp deletion caused by PCR amplification errors was easily eliminated.

Fibroblast-specific PRMT5 deficiency suppresses cardiac fibrosis and left ventricular dysfunction in male mice.

Protein arginine methyltransferase 5 (PRMT5) is a well-known epigenetic regulatory enzyme. However, the role of PRMT5-mediated arginine methylation in gene transcription related to cardiac fibrosis is unknown. Here we show that fibroblast-specific deletion of PRMT5 significantly reduces pressure overload-induced cardiac fibrosis and improves cardiac dysfunction in male mice. Both the PRMT5-selective inhibitor EPZ015666 and knockdown of PRMT5 suppress α-smooth muscle actin (α-SMA) expression induced by transforming growth factor-ß (TGF-ß) in cultured cardiac fibroblasts. TGF-ß stimulation promotes the recruitment of the PRMT5/Smad3 complex to the promoter site of α-SMA. It also increases PRMT5-mediated H3R2 symmetric dimethylation, and this increase is inhibited by Smad3 knockdown. TGF-ß stimulation increases H3K4 tri-methylation mediated by the WDR5/MLL1 methyltransferase complex, which recognizes H3R2 dimethylation. Finally, treatment with EPZ015666 significantly improves pressure overload-induced cardiac fibrosis and dysfunction. These findings suggest that PRMT5 regulates TGF-ß/Smad3-dependent fibrotic gene transcription, possibly through histone methylation crosstalk, and plays a critical role in cardiac fibrosis and dysfunction.

Nicotine and Cardiovascular Health: When Poison is Addictive - a WHF Policy Brief.

Nicotine is universally recognized as the primary addictive substance fuelling the continued use of tobacco products, which are responsible for over 8 million deaths annually. In recent years, the popularity of newer recreational nicotine products has surged drastically in many countries, raising health and safety concerns. For decades, the tobacco industry has promoted the myth that nicotine is as harmless as caffeine. Nonetheless, evidence shows that nicotine is far from innocuous, even on its own. In fact, numerous studies have demonstrated that nicotine can harm multiple organs, including the respiratory and cardiovascular systems. Tobacco and recreational nicotine products are commercialized in various types and forms, delivering varying levels of nicotine along with other toxic compounds. These products deliver nicotine in profiles that can initiate and perpetuate addiction, especially in young populations. Notably, some electronic nicotine delivery systems (ENDS) and heated tobacco products (HTP) can deliver concentrations of nicotine that are comparable to those of traditional cigarettes. Despite being regularly advertised as such, ENDS and HTP have demonstrated limited effectiveness as tobacco cessation aids in real-world settings. Furthermore, ENDS have also been associated with an increased risk of cardiovascular disease. In contrast, nicotine replacement therapies (NRT) are proven to be safe and effective medications for tobacco cessation. NRTs are designed to release nicotine in a slow and controlled manner, thereby minimizing the potential for abuse. Moreover, the long-term safety of NRTs has been extensively studied and documented. The vast majority of tobacco and nicotine products available in the market currently contain nicotine derived from tobacco leaves. However, advancements in the chemical synthesis of nicotine have introduced an economically viable alternative source. The tobacco industry has been exploiting synthetic nicotine to circumvent existing tobacco control laws and regulations. The emergence of newer tobacco and recreational nicotine products, along with synthetic nicotine, pose a tangible threat to established tobacco control policies. Nicotine regulations need to be responsive to address these evolving challenges. As such, governments should regulate all tobacco and non-medical nicotine products through a global, comprehensive, and consistent approach in order to safeguard tobacco control progress in past decades.

Anserine, a Histidine-Containing Dipeptide, Suppresses Pressure Overload-Induced Systolic Dysfunction by Inhibiting Histone Acetyltransferase Activity of p300 in Mice.

Anserine, an imidazole dipeptide, is present in the muscles of birds and fish and has various bioactivities, such as anti-inflammatory and anti-fatigue effects. However, the effect of anserine on the development of heart failure remains unknown. We cultured primary cardiomyocytes with 0.03 mM to 10 mM anserine and stimulated them with phenylephrine for 48 h. Anserine significantly suppressed the phenylephrine-induced increases in cardiomyocyte hypertrophy, ANF and BNP mRNA levels, and histone H3K9 acetylation. An in vitro histone acetyltransferase (HAT) assay showed that anserine directly suppressed p300-HAT activity with an IC50 of 1.87 mM. Subsequently, 8-week-old male C57BL/6J mice were subjected to transverse aortic constriction (TAC) and were randomly assigned to receive daily oral treatment with anserine-containing material, Marine Active® (60 or 200 mg/kg anserine) or vehicle for 8 weeks. Echocardiography revealed that anserine 200 mg/kg significantly prevented the TAC-induced increase in left ventricular posterior wall thickness and the decrease in left ventricular fractional shortening. Moreover, anserine significantly suppressed the TAC-induced acetylation of histone H3K9. These results indicate that anserine suppresses TAC-induced systolic dysfunction, at least in part, by inhibiting p300-HAT activity. Anserine may be used as a pharmacological agent for human heart failure therapy.

Impact of smoking initiation age on nicotine dependency and cardiovascular risk factors: a retrospective cohort study in Japan.

Aims: Initiating smoking in early adolescence results in challenges with smoking cessation and is associated with high risk of cardiovascular disease. Recently, the initiation of smoking has transitioned from adolescence to young adulthood. However, there are few reports on the impact of initiating smoking at a later age. This study investigated the impact of the age of smoking initiation on nicotine dependency, smoking cessation rates, and cardiovascular risk factors, using a cut-off point of 20 years, within the Japanese population. Methods and results: This retrospective cohort study encompassed 1382 smokers who sought smoking cessation treatment at Kyoto Medical Centre Hospital between 2007 and 2019. Clinical indicators were evaluated by adjusting for age at the time of hospital visit and sex. The smoking cessation rate was further adjusted for treatment medication. The group with a smoking initiation age of <20 years reported a higher number of cigarettes/day (P = 0.002), higher respiratory carbon monoxide levels (P < 0.001), a higher Fagerström Test for Nicotine Dependence (FTND) score (P < 0.001), and a higher Self-rating Depression Scale score (P = 0.014). They also reported lower diastolic blood pressure (P = 0.020) and a lower successful smoking cessation rate [odds ratio: 0.736, 95% confidence interval (0.569, 0.951)] than the group with a smoking initiation age of ≥20 years. When smokers were divided into four groups based on the age they started smoking, the FTND score for those who started at 20-21 years was significantly higher than the score for those who started at 22 years or older. Conclusion: In young adulthood, initiating smoking later (beyond 20 years old) was associated with lower nicotine dependency and fewer depressive tendencies, as well as a higher success rate in smoking cessation among Japanese smokers. The results might suggest that raising the legal smoking initiation age from 20 to 22 years old or older could be effective in reducing nicotine dependency in smokers.

KUS121, a VCP modulator, has an ameliorating effect on acute and chronic heart failure without calcium loading via maintenance of intracellular ATP levels.

AIMS: As heart failure (HF) progresses, ATP levels in myocardial cells decrease, and myocardial contractility also decreases. Inotropic drugs improve myocardial contractility but increase ATP consumption, leading to poor prognosis. Kyoto University Substance 121 (KUS121) is known to selectively inhibit the ATPase activity of valosin-containing protein, maintain cellular ATP levels, and manifest cytoprotective effects in several pathological conditions. The aim of this study is to determine the therapeutic effect of KUS121 on HF models. METHODS AND RESULTS: Cultured cell, mouse, and canine models of HF were used to examine the therapeutic effects of KUS121. The mechanism of action of KUS121 was also examined. Administration of KUS121 to a transverse aortic constriction (TAC)-induced mouse model of HF rapidly improved the left ventricular ejection fraction and improved the creatine phosphate/ATP ratio. In a canine model of high frequency-paced HF, administration of KUS121 also improved left ventricular contractility and decreased left ventricular end-diastolic pressure without increasing the heart rate. Long-term administration of KUS121 to a TAC-induced mouse model of HF suppressed cardiac hypertrophy and fibrosis. In H9C2 cells, KUS121 reduced ER stress. Finally, in experiments using primary cultured cardiomyocytes, KUS121 improved contractility and diastolic capacity without changing peak Ca2+ levels or contraction time. These effects were not accompanied by an increase in cyclic adenosine monophosphate or phosphorylation of phospholamban and ryanodine receptors. CONCLUSIONS: KUS121 ameliorated HF by a mechanism totally different from that of conventional catecholamines. We propose that KUS121 is a promising new option for the treatment of HF.

Coalescence and mixing dynamics of droplets in acoustic levitation by selective colour imaging and measurement.

Acoustic levitation is well-suited to 'lab-on-a-drop' contactless chemical analysis of droplets. Rapid mixing is of fundamental importance in lab-on-a-drop platforms and many other applications involving droplet manipulation. Small droplets, however, have low Reynolds numbers; thus, mixing via turbulence is not possible. Inducing surface oscillation is effective in this regard, however, the relationship between internal flow and mixing dynamics of droplets remains unclear. In this study, we conducted a set of simultaneous optical measurements to assess both the flow field and the distribution of fluid components within acoustically levitated droplets. To achieve this, we developed a technique to selectively separate fluorescent particles within each fluid, permitting the measurement of the concentration field based on the data from the discrete particle distribution. This approach revealed a relationship between the mixing process and the internal flow caused by surface oscillation. Thus, the internal flow induced by surface oscillation could enhance droplet mixing. Our findings will be conducive to the application and further development of lab-on-a-drop devices.