Background

Cardiovascular diseases (CVDs) have been the global health problem with rising prevalence, incidence, and death rates. In 2017, 31.8% (17.79 million cases) of global deaths were attributed to CVDs, plus nearly 336 million disability-adjusted life-years (DALY) [1]. Ischemic heart disease (IHD) and stroke account for the highest standardized death rate among CVD causes [2]. Episodes of CVDs have complex, long term impacts on the life of patients, which is far beyond survivorship, since their consequences cause impairments in physical and cognitive functioning, which, in turn, limit the daily activities and social interactions of the survivors [3,4,5,6,7].

Achieving good quality of life (QOL), therefore, is crucial to patients suffering from heart and stroke diseases [3, 8]. According to the definition of World Health Organization on QOL, QOL is “affected in a complex way by the person’s physical health, psychological state, personal beliefs, social relationships and their relationship to salient features of their environment” [9]. QOL can be considered as one of the most important outcomes in healthcare, particularly among patients with CVDs [10]. Deterioration of QOL among CVD patients is positively correlated with higher rates of hospital readmission and fatality [11, 12]. Hence, assessing the QOL of CVD patients is critical when evaluating the effectiveness of CVD treatments and determining which aspects should be improved.

There is a remarkable growth in the body of literature regarding manners to improve the QOL of people with heart and stroke diseases. These implications range from healthier lifestyle encouragement [13] to the incorporation of mental health treatments into routine CVDs management [6]. Moreover, some initiatives have been implemented comprising: adoption of collaborative care models [14]; support and counseling of CVD specialists in the primary care setting to people at-risk of CVDs [15]; or adoption of surgical procedures, for instance, coronary artery bypass graft surgery (CABG) instead of percutaneous coronary intervention (PCI) [16].

Several systematic reviews worked on interventions that could improve the QOL of people with heart and stroke diseases. For example, life-style interventions at the workplace could decrease the risk of CVD [17], or community-based nursing interventions increase the outcome of treatment for people with CVD [18]. Besides, Widmer et al. confirmed the effectiveness of digital health interventions for the prevention of cardiovascular disease [19]. Despite the abundance of documents on the QOL and interventions targeting people with heart and stroke diseases, there is a lack of publications offering a ‘big picture’ of the interaction between interventions and QOL among CVD patients. This limits the ability of healthcare providers and policymakers to identify pathways to efficiently allocate scarce resources in CVD treatment.

The bibliometric approach has been proposed to be a potential solution given the capacity to provide a comprehensive and holistic investigation of the literature. By combining bibliometric approach and content analysis, we aimed at providing an interdisciplinary insights into research areas as well as characterizing the most common topics regarding interventions to improve QOL of CVD patients. Our findings can inform priority setting and policy development towards sustainable efforts of enhancing the lives of people with these conditions.

Methods

Search strategy, keywords, data download and extraction

The published works regarding the QOL of CVD patients were downloaded from the Web of Science (WOS). For bibliometric analysis, the WOS is superior to Scopus or Medline/Pubmed because it: 1) allows to extract a large number of with full information (e.g titles, author names, total citation, total download times); 2) covers citation of scientific publications since 1900; and 3) comprises high impact scientific journals worldwide [20, 21]. Data were collected in March 2019; thus, we excluded the publications from 1st January 2019 onwards. The analysis focused on English articles and reviews, therefore, other document types such as letter to editors, or conference abstracts in any other languages were excluded. Two steps of the search strategy were performed as follow:

  • Step 1: The terms “Quality of life”, and “well-being” were used to extract scientific research mentioning Quality of life on TS research in WOS (title, abstract, keywords, and topic) (see Additional file 1). Data were downloaded separately by two researchers and verified by a senior researcher. Any inconsistency between the data downloaded by the two researchers was solved by discussion and the data were re-downloaded when necessary. Papers which were 1) not articles and reviews; 2) not published in English; 3) written by anonymous authors. Final set of data was converted into txt format and transferred into STATA version 14.0 (STATACorp., Texas, USA) for further extraction and analysis.

  • Step 2: A set of keywords related to CVDs was built, which based on the definition of World Health Organization (WHO), (“Coronary heart disease” OR “Heart failure” OR “Rheumatic Heart Disease” OR “Cerebrovascular disease”) [22], MeSH terms (“Cardiac arrhythmias” OR “Carcinoid heart disease” OR “Cardiac conduction system disease” OR “High cardiac output” OR “Low cardiac output” OR “Cardiomegaly” OR “Endocarditis” OR “heart aneurysm” OR “Heart arrest” OR “Congenital heart defects” OR “Heart neoplasms” OR “Heart rupture” OR “Heart attack” OR “Heart valve disease” OR “Myocardial ischemia” OR “Myocardial Ischemia” OR “Pericardial Effusion” OR “Pericarditis” OR “Ventricular Dysfunction” OR “Ventricular Outflow Obstruction” OR “Cardiovascular abnormalities” OR “Vascular malformations” OR “Cardiovascular infections”) [23], some systematic reviews (such as (“Ischemic heart disease” OR “Heart attack” OR “Stroke” OR “ischemic stroke” OR “Hemorrhagic stroke” OR “brain attack”) [24, 25]. Then, we used the terms “intervention*” or “trial*” to extract the papers regarding the intervention of this health problem (see Additional file 2).

Data analysis

First, basic characteristics of publications were described, which included 1) years of publication; 2) the number of papers per year; 3) total citations of each year up to 2018 (from 1990 to 2018); 4) a total of download times (total usage) and average download times per year (mean usage per year) in the last 6 months; and 5) total of download times (total usage) and the average number of citation per year (mean citation rate per year) in the last 5 years. A network graph showing the co-occurrence of authors’ keywords was generated by the VOSviewer software tool (https://www.vosviewer.com/). The Latent Dirichlet Allocation (LDA), a generative statistical model, was used for classifying publications into topics [26,27,28,29,30]. The LDA approach was selected because of its ability to group and explain trends and patterns in text content. The techniques used for each type of type are presented in Table 1.

Table 1 Summary of analytical techniques for each data types
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Results

Number of published items and publication trend

Table 2 reveals the characteristics of selected publications. The first paper was published in 1990. Then, there was a gradual increase in the number of interventions to improve QOL of patients with stroke and heart diseases during 1990–2018, resulting in a total of 6457 papers. Besides, the total number of download times (total usage), and the average number of download times (the mean use rate) in the last 5 years of papers published in 2013 were the highest compared with other years. Meanwhile, the total usage and the mean use rate last 6 months of the year 2019 were the highest figures compared with that of other years, which indicated the short-term interest of readers,

Table 2 General characteristics of publications
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The scope of studies was explored by using authors’ keywords, which was automatically mapped by the VOSviewer software tool. Figure 1 indicates four major clusters emerged from 164 most common keywords which appeared at least 200 times. Cluster 1 (red) refers to the quality of life, rehabilitation, and mental health illness of stroke patients. Cluster 2 (green) focuses on the daily exercise of patients with heart failure. Cluster 3 (yellow) includes types of analysis applied to identify the QOL among patients with heart diseases and stroke. Cluster 4 (blue) illustrates the risk factors, prevention, and cost-effectiveness of interventions for CVD.

Fig. 1
figure 1

Co-occurrence of authors’ keywords. Note: the weight of a keyword determined its size of the label. The length of the lines shows the relatedness of keywords

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Table 3 shows the most cited papers which had at least 400 citations. The title and abstract of each paper were reviewed by the research team and assigned to corresponding topics. Three major topics have been emerged encompassing: 1) Treatment of stroke or heart diseases (24/39 papers); 2) Preventions of stroke or heart diseases (8/39 papers), and 3) Others (systematic review and meta-analysis) (5/39 papers).

Table 3 Most cited papers
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The LDA was utilized to model the research topics based on texts in the abstracts and a total of ten major research topics was constructed (Table 4). Each topic was labeled by reviewing titles and abstracts of most cited papers within each group. Ten topics were divided into the following categories: 1) conventional therapies: topic 5, and topic 7; 2) other therapies: topic 2, topic 3, topic 4, topic 6, topic 8, topic 9, and topic 10. Figure 2 illustrates that recently, researchers have paid greater attention to two research topics focusing on biomedical therapies (topic 1), which are now under research and trial, as well as psychological and behavioral therapies for people with heart diseases (Topic 2).

Table 4 Ten research topics classified by LDA
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Fig. 2
figure 2

Changes in research topics development in QOL of CVD patients

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Figure 3 presents the clusters of research areas in the interventions aiming to improve QOL of CVD patients. The horizontal axis shows the distance between research areas while the vertical axis shows the research areas based on WOS categories. The research areas in these interventions could be divided into three categories 1) Cardiovascular System; 2) Prevention, Treatment (Surgery, Internal Medicine, Pharmacy and Rehabilitation); 3) Health Policy and Economic evaluation. Overall, the dendrogram indicates that health services and economics studies have not been well studied. Also, holistic (e.g., system) factors and frontline interactions with patients (e.g., nursing) seem to have influential effects on QOL of CVD patients.

Fig. 3
figure 3

Dendrogram of coincidence of research areas using the WoS classifications

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Discussion

In this study, a total of 6457 papers was analyzed to identify the global trend and the development of research landscapes in the intervention to improve QOL of CVD patients from 1990 to 2018. The number of papers increased gradually since 2002 and reached a peak in the year of 2018. By applying text mining technique based on LDA, the interdisciplinary research topics and research areas were examined in detail. The most common topics were conventional treatment (surgery and medication), and psychological, behavioral interventions.

Our study proposed a novel approach for analyzing literature that overcomes the limitations of current systematic review/meta-analysis. Indeed, the traditional systematic review and meta-analysis cannot efficiently illustrate the research development trend as this method consumes time and human resources [31]. Meanwhile, scientometrics, when standing on its own, shows the productivity, collaborations among authors, organizations, or countries and co-occurrence of author keywords, however, the approach is unable to identify the research topics underlying the current literature [32]. By combining bibliometrics and text analysis, the study was able to explore the hidden patterns of information from the literature.

This study provides an overview of interdisciplinary research landscapes in the interventions to improve QOL of CVD patients. The majority of interventions for CVDs were conventional therapies, such as surgery and medication, or psychological and behavioral interventions. Historically, the use of medications has been a primary method of CVD treatment [33], given the lower costs of drug treatment compared to hospitalization and effectiveness in relieving symptoms, which mainly aim to slow down the disease progression and improve patients’ QoL [34]. The number of patients with end-stage heart diseases as well as the introduction of the heart-lung machine and cardiopulmonary bypass leads to the increase of surgical treatment and the number of papers mentioning this therapy, which was also confirmed by other studies [35]. Besides, several associated factors to CVDs, such as obesity, smoking, and sedentary lifestyle, have been proved in previous studies [36, 37], leading to a rise in the published works regarding interventions focusing in lifestyle changes to prevent the onset of CVD episode and elevate the patients’ QOL. Notably, traditional and alternative medicine gained the concern of scientists in the last 5 years (2014–2018). This result was in the same line with previous studies [38, 39]. It might be explained that patients believed in these approaches to reduce side-effects of conventional therapy [39], yet, there has been a lack of data for the pattern use of alternative therapy for CVDs [38]. In addition, the development of technology has enabled the research of gene therapy or robot-assistant in CVD treatment [40]. However, gene therapy has shown modest success in clinical translation [41]. Meanwhile, robot-assistant has been tried and is being investigated for rehabilitation among patients after stroke [42, 43].

Findings of this study have provided several important implications for setting priority in research, designing interventions, and improving quality of care for CVD patients. Firstly, we call for interdisciplinary approaches, specifically, the integration of research areas, such as health services in providing medical care, and psycho-socio-behavioral interventions at the individual, family, health facility, and community levels. Besides, more research should be focused on the economic aspects of interventions for CVD. Finally, there has been a lack of research on interventions to reduce mental problems (e.g., depression or stress) among people with CVD; hence, future research should focus on this phenomenon since mental issues were significant risk factors for CVD [44, 45].

Our study has several limitations. First, the choice of using WOS as the only database might limit the coverage of all possible publications in interventions to improve QoL of patients with CVD compared with Google Scholar [46], or Scopus [47]. However, a previous study recommended using WoS in the case of only one available database [48]. Second, only peer-reviewed publications in the English language were included, which might have resulted in a bias against non-English publications. Furthermore, only titles and abstracts were used for content analysis, which might not provide a deep insight intro research themes of the dataset. Hence, our findings should be interpreted with caution.

Conclusion

In conclusion, the number of scientific published works on the interventions to improve QOL among people with CVD has gradually increased from 1990 to 2018. The research areas in the field of the study emphasized the importance of interdisciplinary and inter-sectoral approaches in both evaluation and intervention. Conventional therapy (surgery and medication), and psychological and behavioral interventions were the common approach. Future research should focus on economic evaluation of intervention as well as interventions to reduce mental issues among people with CVD.