A Study on the Global Patterns in the Design and Development of Ventricular Assist Devices: A Visualization Approach

doi:10.21203/rs.3.rs-3488825/v1

A bibliometric analysis of 275 publications related to the design and development of Ventricular assist devices (VAD) has been conducted to analyze the developments in this research domain since 1990. This field of research has been witnessing a significant growth in terms of number of publications as more researchers are showing interest in this field, with the technological advancements in the past few years. This is first such bibliometric study in design and development of VAD, which uses data from both Scopus as well as Web of Science (WOS) databases. Research advancement in this domain can be divided into two stages: first stage (1990 to 2004) saw slow growth (N = 65) while second stage (from 2005 onwards) witnessed an increase in publications (N = 210). Most of the significant research work has been carried out in developed countries like USA, China, Germany, Japan, United Kingdom and France etc. This study presents a comprehensive examination of pivotal moments in the evolution of Ventricular Assist Device (VAD) research, along with potential avenues for future exploration in various VAD research domains such as the utilization of artificial intelligence and machine learning techniques to enhance the design, utilization, and data-driven optimization of VADs.

Physical sciences/Engineering/Biomedical engineering

Physical sciences/Engineering/Mechanical engineering

Health sciences/Cardiology/Cardiac device therapy

A Ventricular Assist Device (VAD) is a mechanical pump that assists the heart in circulating blood throughout the body. It is primarily used to treat individuals with heart failure, a condition in which the heart is unable to pump enough blood to meet the body's needs. There are two main types of VADs: Left Ventricular Assist Devices (LVADs)^1,2 and Right Ventricular Assist Devices (RVADs)^3–5. LVADs assist the left ventricle, which pumps blood to the rest of the body, while RVADs assist the right ventricle, which pumps blood to the lungs. LVADs, which are more commonly used, assist the left ventricle in pumping blood to the body. On the other hand, RVADs, which are less frequently used, help the right ventricle in pumping blood to the lungs. VADs can serve as a temporary solution while a patient awaits a heart transplant. They can also be used as a long-term or even permanent solution for treating heart failure, known as destination therapy. The implantation of a VAD^6,7 involves open-heart surgery. The pump is positioned within the chest or abdomen and connected to the heart via blood vessels. The device is powered by batteries or an external power cord. While VADs can be a lifesaving treatment for individuals with heart failure, they do come with certain risks, comprising bleeding, infection, and the formation of blood clots.

Bibliometric analysis has not been used till date to study the growth in the domain of design and development of VAD devices. To address this gap, the authors used bibliometric analysis to comprehensively study the important research trends in this field. Bibliometric analysis is a quantitative and qualitative approach used for studying the literature in a specific field using statistical and mathematical methods and it is helpful in recognizing the trends in a research area and the most prominent collaboration network between various authors, institutions and countries. In recent years, bibliometric analysis has been used to find emerging trends and collaborations in various scientific domains^8–11. Bibliometric analysis, in contrast to systematic reviews^12,13 that aim to provide answers to specific research queries on the basis of a limited number of publications, provides a comprehensive information related to the literature in a particular field. Similarly, bibliometric analysis differs from scoping reviews^14,15, which focus on identifying the nature and scope of research evidence. Despite these differences, bibliometric analysis remains a valuable tool for obtaining a snapshot of national and international contributions to the literature in a specific field, as well as identifying research gaps that future studies may address.

Over the past ten years, mechanical assist therapy has evolved from a distant goal to a practical reality. Improvements in device design, surgical techniques, and aftercare have made these devices a crucial treatment option for a challenging group of patients with heart failure¹⁶. Continuous-flow VADs, the type of VAD most commonly used today, can now last more than 10 years in a patient¹⁷. Over the past decade, the use of Left Ventricular Assist Devices (LVADs), a cutting-edge electro medical support system for patients with life threatening last stage heart failure, has seen a significant rise. These devices have become a primary treatment option for patients who have been on the heart transplant waiting list for an extended period of time, as well as for those who are not suitable candidates for transplantation^18–20. Drawing on information about the global collaboration network between authors, countries, and institutes, this paper aims to elucidate the research trends in the design and development of Ventricular assist devices (VAD). The findings will provide valuable references for future research. Furthermore, by gaining insights into the research trend topics in this domain, policymakers and funding agencies can make informed decisions about where to allocate research resources and prioritize future research efforts.

Bibliometrics²¹ is a technique used to do quantitative analysis of large datasets of research publications of various types like articles, conference papers, review papers, books and book chapters. It makes use of statistical tools and techniques to analyze the pattern of publications and their impact on the research in the selected domain of study in terms of collaboration between authors, countries and various institutions and it also provides useful information related to latest trends in the research domain. The steps involved (refer to Fig. 1) include collection of data from relevant sources, then cleaning of this data to remove irrelevant and duplicate entries and then perform the analysis using a bibliometric tool which in our case in Biblioshiny²² (which is based on R and is a part of RStudio) and final step is plotting and explaining network plots, bar charts and line diagrams etc. to find research gaps and see the trend topics in this domain.

2.1 Data collection

For carrying out this study, data from two different databases has been used (Elsevier’s database Scopus²³ and Web of Science (WOS) from Clarivate Analytics). Both Scopus and WOS are well known databases for collecting data required for bibliometric analysis. A total of 331 papers from Scopus and 239 documents from WOS were downloaded using the keywords ventricular assist device, VAD, axial flow, centrifugal flow, design, model, computational fluid dynamics (CFD), simulation and computational fluid with a focus on getting papers related to work done in the field of VAD either experimentally or computationally for design, development or fabrication purposes.

2.2 Data merging and cleaning

For merging data from Scopus and WOS databases, use of RStudio was made. With the help of a code the two databases were merged²⁴ and data cleaned of duplicate entries as well. A total of 166 duplicate entries were removed. After merging and cleaning in RStudio the data file was exported to Microsoft Excel. Then in Microsoft Excel manual cleaning of data was done to remove entries with missing data involving author names etc. and also some duplicate entries were manually removed. Also some irrelevant papers which did not deal with design and development aspects of VAD were removed. Final cleaned data set consisted of a total of 275 documents of various kinds (articles, conference papers, review papers, and book chapters).

The data file was imported into Biblioshiny for doing the analysis of data and getting the various network plots. Upon examination, it was noted that several authors shared the same last name and first name initial, as both Scopus and WOS format author names as last name followed by first name initial in Biblioshiny. To clear up the uncertainty, an online search was made using the titles of the publications. This allowed for the identification of the full names and affiliations of the authors. To further distinguish between authors with the same name, a numerical identifier (e.g., 1, 2, 3) was appended to their last names. This ensured that Biblioshiny could generate accurate network plots involving authors.

The bibliometric analysis was performed on the cleaned dataset by making use of Biblioshiny and various network plots such as country collaboration network, institute collaboration network, author collaboration network etc. were made. There are multiple software choices available for doing bibliometric analysis (if data is from a single source) like CiteSpace, Gephi, Bib Excel, VOS-Viewer etc. But there is only one good option (Biblioshiny) available for getting network plots from merged data obtained from multiple databases such as Scopus and WOS. Biblioshiny is an open-source statistical tool having good graphical user interface^25,26. Microsoft excel was also used for plotting pie charts, bar charts etc.

2.3 Ethics approval and consent to participate. Ethical approval and informed consent were not required for this bibliometric research because the datasets were extracted directly from databases of Scopus (www.scopus.com) and Web of Science (www.webofscience.com) without any type of involvement of human participants.

3.1 Main information from data

An overview of the information from dataset is shown in Table 1. Data consists of a total of 275 publications and this data is from 105 different sources (journals, books etc.). Articles (N = 204) account for 74.18% of the total publication collection, there is no book available especially for this topic, conference papers (N = 41), review papers (N = 25) and book chapters (N = 5) account for 14.90%, 9.09% and 1.81% respectively. The first publication in this domain of research is from year 1990²⁷ where authors have investigated the use of first hemopump (a temporary VAD) on humans.

Figure 2 shows publications from year 1990 till 2023. The research in the design, development and use of VADs can be roughly divided into three phases. Early research phase (first phase) starting from 1950s till late 1990s, first VAD was used in humans in the year 1963²⁸. Second phase in the research related to design and development of VADs can be considered to be from the year 1998 when second generation of VADs were tested on humans for first time²⁹. Significant work in the design and development of the second generation VADS has been done by various scholars^30-34. These published works give a thorough summary related to the design and development of various 2^nd generation VADs, like HeartMate II, HeartWare HVAD, and Medtronic HVAD. They discuss the challenges that were faced in developing these devices, the design solutions that were implemented, and the preclinical and clinical testing that was performed.

Second-generation VADs represented a significant advance in the treatment of advanced heart failure. They were smaller, more durable, and more reliable than first-generation devices, and they improved survival rates and quality of life for many patients. However, second-generation VADs were still associated with a number of complications, including stroke, infection, and pump thrombosis. Maximum number of publications equal to total of 180 (65.45%) are from the time domain of using 2^nd generation of VAD. The third phase in the design and development of VADs can be considered from 2017 till date. The third generation of VADs were used for first time in the year 2017. They were named HeartMate-3 LVADs, at University of Michigan³⁵. These are the latest series of VADs used in humans since 2017. A lot of research is still ongoing for further improvement in its design and working^36-39.

Table 1. An overview of data collected

Total Documents	275
Articles	204 (74.18%)
Books	0 (0.00%)
Book Chapters	5 (1.81%)
Conference Papers	41 (14.90%)
Review Papers	25 (9.09%)
Number of sources (Journals, Books etc.)	105
Time period	1990:2023
Average citations/document	29.97
Number of authors	1105
Authors of single-authored documents	10
Number of single-authored documents	13
Co-Authors/document	6.29
Annual Growth Rate %	6.88
International co-authorships %	8.00

Figure 3 shows the breakup of total publications in terms of number of articles, review papers, conference papers, books and book chapters from 1998 onwards showing the publications during 2^nd and 3^rd phases only. There were a total of 18 publications during 1^st phase (from 1990 to 1997) including 17 articles and 1 conference paper and these are not shown in Fig. 3. Annual publications entered into double figures for first time in year 2005 and since then it has shown increase in numbers as compared to previous years. From 1990 to 2004 total publications were 65 (23.64%). From the year 2005 onwards the number of publications till the year 2023 were 210 (76.36%) which shows a clear upward trend that more work is being done in this domain. Figure 4 shows total citations for various kinds of publications (articles, review papers, book chapters and conference papers). It clearly shows article papers are the most significant type of publications with total citations of 6668 (80.90%), followed by conference papers, review papers and book chapters with citations equal to 1006 (12.21%), 564 (6.84%) and 4 (0.05%) respectively.

3.2 Top contributing authors and their collaboration network

The top 10 authors based on their total publications are shown in Table 2. The author affiliation shown in this table has been obtained from their most recent publication in the data collected. Other information in this table includes the total citations, h-index value and the year these authors published their first as well as the latest paper. All the 10 top authors belong to USA which shows that most productive research work is being done or has been done in USA among all the countries in the world. Throckmorton A has maximum number of publications (N = 22), while Frazier O has got the highest number of citations (N = 1337) as well as the highest h-index of 15. Another important aspect from this table is that Throckmorton A and Frazier O are the only authors who are still actively involved in research publications related to this field in the last 5 years.

Table 2. Top 10 most productive authors

Author Name	Affiliation	No. of papers	Total Citations	h-index	Year of 1^st Publication	Year of last publication
Throckmorton A	BioCirc Research Laboratory, School of Biomedical Engineering, Science, and Health Systems, Drexel University, Philadelphia, Pennsylvania, USA	22	505	13	2003	2023
Frazier O	Innovative Design and Engineering Applications Laboratory, The Texas Heart Institute, Houston, Texas, USA	19	1337	15	1990	2023
Antaki J	Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, Pa, USA	15	550	13	1993	2015
Olsen D	Utah Artificial Heart Institute, Salt Lake City, UT, USA	14	476	12	1992	2010
Allaire P	University of Virginia \| UVa · ROMAC Laboratories, USA	12	374	9	1996	2008
Untaroiu A	Virginia Tech · Department of Biomedical Engineering and Mechanics, USA	12	335	8	2003	2013
Wood H	Professor of Mechanical and Aerospace Engineering, University of Virginia, USA	12	344	8	2003	2013
Gregoric I	University of Texas Health Science Center, USA	11	1091	11	2000	2017
Noon G	Department of Surgery, Baylor College of Medicine, Houston, Texas, USA	11	549	11	1993	2001
Benkowski R	MicroMed Technology, Inc., Houston, Texas, USA	10	461	10	1995	2010

Collaboration network between top 50 contributing authors is shown in Fig. 5 with each author having at least 5 publications. In this network, the nodes represent authors whereas the size of node is an indicator of the number of the publications and the lines joining these nodes represent the collaboration strength. Six different clusters can be seen in 6 different colours. Authors with strong collaboration can be seen in the same cluster. All of the top 10 authors shown in Table 2 can be seen in various clusters indicating that top 10 authors in Table 2 have strong collaboration networks. The largest cluster (red) consists of 14 authors, 13 from the USA and 1 from China. All authors from the second (brown) cluster (9 authors), third (orange) cluster (7 authors), fourth (green) cluster (10 authors), and fifth (blue) cluster (6 authors) are from the USA. This suggests that the majority of significant work in this field has been done in the USA, as most of the top authors are from there. As one author in these clusters is from China suggesting that some work in this field is also being done there.

3.3 Bibliographic Coupling of institutions

Fig. 6 shows clustering by coupling which is a useful method of identifying the structure of scientific knowledge and it can be used by researchers to understand the latest advances and trends in a particular research domain. This method is based on the fact when any two published documents have some shared citations then the documents are linked intellectually. The clusters in Fig. 6 are for sources of publications, we are trying to group together sources where various authors are publishing work on similar themes. The biggest cluster (red in colour) consists of 18 different sources which have published papers on same theme (experience related to use of VAD). The second cluster (blue) consists of 3 sources and their common theme is work related to heart transplantation and heart failure. The remaining three clusters consists of 1 source each and are not as significant as the previous two clusters.

3.4 Most productive countries and their collaboration network

Top 10 most productive countries in terms of number of publications are shown in Table 3. Their total citations are also shown in the same table. USA is the most productive country in terms of number of publications (N = 160) which accounts for 76.93% of total publications. China is 2^nd ranked with a total of 22 publications and Germany is rank 3 with 16 publications. Japan and Austria are rank 4 and 5 with 10 and 7 publications respectively. Top countries have been identified on the basis of the corresponding authors for the publications. In terms of citations, only 5 countries have got more than 100 citations with USA at rank 1 with 6274 citations, Germany is rank 2 with 377 citations and Austria has rank 3 with 308 citations. UK and Japan are rank 4 and 5 with 133 and 117 citations respectively. From the country production, it is clearly obvious that most of the research related to design and development of VADs has been conducted in USA.

Out of a total of 34 countries who have published papers in this domain, country collaboration network of 21 countries has been shown in Fig. 7. Seven clusters can be seen in this figure out of which there are three big clusters, remaining 4 clusters have only 1 country and are not that significant. The biggest cluster (Red in colour) consists of 8 countries including USA, Germany, Japan, UK, Austria, Canada, Czech Republic, and Russia. The second cluster consists of 5 countries (Italy, Belgium, Switzerland, Bulgaria, and Lithuania). The 3^rd cluster consists of 4 countries (Netherlands, Poland, Paraguay, and Spain). All the top 10 most productive countries as shown in Table 3 can be seen in Fig. 7 also, which shows that all of the top 10 countries have good global research collaboration networks.

Table 3. Top 10 most prominent countries based on number of publications and citations

S.No	Country	Country Production	% Of Total Production	No Of Citations	% Citations
1	USA	160	58.18	6274	76.93
2	China	22	8.00	79	0.97
3	Germany	16	5.82	377	4.62
4	Japan	10	3.64	117	1.43
5	Austria	7	2.55	308	3.78
6	Italy	7	2.55	85	1.04
7	Singapore	6	2.18	67	0.82
8	UK	5	1.82	133	1.63
9	Canada	5	1.82	90	1.63
10	France	4	1.45	45	0.55

3.5 Most active journals and most cited publications

Maximum number of papers in the domain of VAD design and development have been published in the journals shown in Table 4. Out of the total 105 different sources whose data is collected for the present work, Table 4 shows the top 10 journals having highest number of publications. Rank 1 journal in the table with 54 publications is Artificial Organs. The rank 2 journal is Asaio Journal with 46 publications. Top 10 journals include 161 publications which accounts for 58.54% of the total publications (N = 275) and a total of 5151 citations which accounts for 62.50% of total citations (N = 8242). This clearly shows that these are the most significance sources of publications in this domain of research. Out of the top 10 journals, 5 are quartile 1 (Q1), 3 are quartile 2 (Q2) and 2 are quartile 3 (Q3) journals. All the top 10 journals are SCIE indexed as shown in Table 4.

Table 4. Top 10 journals with maximum number of publications

Rank	Journals	Publishing House/Country	No. of Publications	No. of Citations	Scopus Quartile	WOS
1	Artificial Organs	Wiley Online Library, UK	54	1228	Q2	SCIE
2	Asaio Journal	Lippincott Williams & Wilkins, USA	46	1166	Q1	SCIE
3	Journal Of Heart And Lung Transplantation	Elsevier Science Inc. ,USA	17	1078	Q1	SCIE
4	Annals Of Thoracic Surgery	Elsevier Science Inc. ,USA	10	778	Q1	SCIE
5	Texas Heart Institute Journal	Texas Heart Institute, USA	9	472	Q3	SCIE
6	International Journal Of Artificial Organs	Sage Publications Ltd, England	8	107	Q3	SCIE
7	Journal Of Thoracic And Cardiovascular Surgery	Mosby-Elsevier, USA	6	138	Q1	SCIE
8	Current Opinion In Cardiology	Lippincott Williams & Wilkins, USA	4	66	Q2	SCIE
9	European Journal Of Cardio-Thoracic Surgery	Oxford Univ Press Inc, USA	4	97	Q1	SCIE
10	Bioengineering-Basel	MDPI , Switzerland	3	21	Q2	SCIE

Table 5 shows top 10 most cited publications along with other information such as their first author, year of publication, digital object identifier (DOI), total citations, average citations per year and normalized total citations. These publications are from year 2000 to 2019. Normalized total citation is a measure of the citation impact⁴⁰ of a research paper when compared to other papers published in the same research domain⁴¹. It is the ratio of citations of a research paper and the expected number of citations a research paper should receive in the same research domain and this expected number is usually obtained on the basis of average number of citations received by publications in the same research domain and in the same year⁴².

The titles of the papers are not mentioned in the tabular form but are given here in the text. The 1^st paper in Table 5 titled ‘A Fully Magnetically Levitated Left Ventricular Assist Device- Final Report’ is a comparative study between the performance of centrifugal and axial flow type left ventricular assist device (LVAD) devices and it suggest that the use of centrifugal type is better for avoiding pump thrombosis⁴³. The 2^nd paper in this table titled ‘A Fully Magnetically Levitated Circulatory Pump for Advanced Heart Failure’ discusses about magnetically levitated centrifugal pump and its role in reducing pump thrombosis while using LVAD devices⁴⁴. The 3^rd paper titled ‘Intrapericardial Left Ventricular Assist Device for Advanced Heart Failure’ presents a comparative study of use of centrifugal and axial flow devices for patients who did not meet eligibility criteria for transplant⁴⁵. The 4^th article titled ‘HeartMate II left ventricular assist system: from concept to first clinical use’ discusses about design aspects related to the left ventricular assist device (LVAD) named Heartmate II in terms of its evolution and use⁴⁶. The 5^th paper titled ‘Axial and centrifugal continuous-flow rotary pumps: A translation from pump mechanics to clinical practice’ discusses about comparison of axial and centrifugal pumps, also bearing design is discussed in terms of their reliability and biocompatibility⁴⁷. The 6^th paper titled ‘Design concepts and principle of operation of the HeartWare ventricular assist system’ deals with design aspects and working of HeartWare VSD device and it consists of a centrifugal type pump⁴⁸. The 7^th publication titled ‘Fully Magnetically Levitated Left Ventricular Assist System for Treating Advanced HF: A Multicenter Study’ focusses on the assessment of the performance and safety aspects of a Levitated Left Ventricular Assist System (LVAS)⁴⁹. The 8^th publication titled ‘Clinical experience with the MicroMed DeBakey ventricular assist device’ discusses about understanding the working and performance of MicroMed DeBakey VAD device which is an axial flow VAD⁵⁰. The 9^th paper titled ‘Effects of centrifugal, axial, and pulsatile left ventricular assist device support on end-organ function in heart failure patients’ discusses about centrifugal, axial, and pulsatile LVADs with respect to circulatory support in patients inching towards heart failure⁵¹. The 10^th paper titled ‘First Clinical Experience with the DeBakey VAD Continuous-Axial-Flow Pump for Bridge to Transplantation’ discusses DeBakey VAD axial-flow pump for using it as a bridge before transplantation⁵².

Table 5. Top ten most cited publications

S.No	Paper (1^st Author, Year, Journal)	DOI	Total Citations	Average Citations per year	Normalized total citations
1	Mehra MR, 2019, New Engl J Med	10.1056/NEJMoa1900486	630	126.00	6.52
2	Mehra MR, 2017, New Engl J Med	10.1056/NEJMoa1610426	503	71.86	6.18
3	Rogers JG, 2017, New Engl J Med	10.1056/NEJMoa1602954	499	71.29	6.13
4	Griffith BP, 2001, Ann Thorac Surg	10.1016/S0003-4975(00)02639-4	230	10.00	2.78
5	Moazami N, 2013, J Heart Lung Transpl	10.1016/j.healun.2012.10.001	218	19.82	7.65
6	Larose JA, 2010, Asaio J	10.1097/MAT.0b013e3181dfbab5	190	13.57	5.21
7	Netuka I, 2015, J Am Coll Cardiol	10.1016/j.jacc.2015.09.083	180	20.00	4.19
8	Noon GP, 2001, Ann Thorac Surg	10.1016/S0003-4975(00)02634-5	153	6.65	1.85
9	Kamdar F, 2009, J Heart Lung Transplant	10.1016/j.healun.2009.01.005	136	9.07	5.45
10	Wieselthaler GM, 2000, Circulation	10.1161/01.CIR.101.4.356	128	5.33	3.49

3.6 Keyword Co-occurrence Network

The network related to co-occurrence of keywords is a graphical way of showing the relation between different keywords in publications and is very useful in highlighting important themes in the given research area⁵³. Each node represents a keyword while its size indicates frequency of that keyword in the database. The thickness of various lines connecting nodes shows the strength of the co-occurrence of keywords. Fig. 8 shows five clusters in the keyword co-occurrence network. 1^st cluster (green in colour) has 22 nodes with each node representing a keyword. Most important keywords in this cluster are heart-assist devices, humans, assisted circulation, hemodynamics⁵⁴, heart failure and, equipment design⁵⁵. It clearly shows that research revolves around design, development and use of VAD device to prevent human heart failure and also to support it. The other keywords in this cluster which are significant from research domain point of view are computer simulation, blood flow velocity, heart transplantation, thrombosis⁵⁶ and blood pressure as these keywords play a vital role in the design and development of the VAD equipment. Second big cluster (purple) has 13 nodes with most frequently used keywords being blood pump, blood, axial flow⁵⁷ left ventricular assist devices and Computational fluid dynamics^58,59. It again shows that research is focussed on design, development and use of VAD device to pump blood. Axial flow device are widely used and Computational fluid dynamics is also made use of to design and optimize these devices. The third cluster (blue) has 5 nodes with most frequently used keyword being ventricular assist device along with other keywords like mechanical circulatory support⁶⁰, implantation and device indicating that research in this domain is focussed on using mechanical circulatory support systems for design, development and use of VAD devices. Fourth cluster (red) has five nodes and it has bridge⁶¹, support, transplantation, experience and system as keywords showing this cluster involves research related to implantation of the VAD device for supporting human heart on short term or long term basis. Last cluster (orange) has only one node named design indicating it deals with designing of the VAD device.

3.7 Thematic and trend analysis

3.7.1 Thematic Evolution

The thematic evolution plot is a visual representation of how the main topics in a field of study change with passage of time. It is based on a statistical analysis of the most common keywords in the domain of research. This analysis projects the keywords onto a simplified space, while keeping as much of the original information as possible. The thematic evolution figure then plots the keywords in each time slice, providing color-coding on basis of year. Figure 9 shows the thematic evolution of various topics related to VAD design and development with the passage of time. It can been divided into three time zones. First time zone is 1990 to 2001 which shows early research work in this domain. Important keywords during this time zone were heart assist device, nonhuman, system, blood pump, performance, safety, support and transplantation. These keywords shows that early research work focussed on design and development of heart assist device then testing was done on nonhuman species to check for their performance. During this time domain VAD 1^st generation and VAD was used and also VAD 2^nd generation was introduced in year 1998. Second time zone shown is from year 2002 till 2020 and important keywords used during this time zone are pumps, support, ventricular assist device, design, humans, and total artificial-heart. It shows continued trend from previous time domain but here human keyword means use of VAD was made during this time period and its outcomes were studied, design was improved as 3^rd generation VADs were introduced in year 2017. Some new keywords like total artificial-heart can be seen in this time zone as comparted to the previous one. Third time zone is from 2021 till the date of collection of data for this work. It shows the latest trends in the field of research. The main keywords are prediction, children, implantation, bridge, axial flow and factor degradation. It shows that it is still a very active domain of research and researchers are trying to improve the existing design of VAD for short term and long term use in human patients including children.

3.7.2 Thematic Map

Biblioshiny thematic maps are visualizations of the thematic structure of a research field. They are created by analysing the keywords in a collection of scholarly documents and grouping them into clusters based on their similarity. The size and position of each cluster on the map represent its importance and relationship to other clusters.

To understand and interpret a thematic map, the following terminology is important:

Cluster size: Bigger clusters are more noteworthy since they cover more keywords and are more frequently cited by other documents. These clusters signify the core themes of the research field, while the smaller and less significant clusters recognize emerging or niche themes

Cluster position: Clusters that are nearer are more closely linked, whereas clusters that are further apart are less closely linked.
Cluster labels: The labels of the clusters indicate their general topic, but they are automatically labelled and may not be correct so manual explanation labelling is needed sometimes.

From Fig. 10 we can see there are four different parts of the thematic map as explained below:

Motor themes are the most important and well-established themes in a research field. They are characterized by their large size, central position on a thematic map, and strong connections to other themes. Motor themes are the themes that drive the field forward. From Fig .10 we can see the motors themes are left ventricular assist device, assisted circulation, heart-assist devices, hemolysis, equipment design and blood pump etc.

Niche themes are smaller and less important themes in a research field. They are characterized by their smaller size, peripheral position on a thematic map, and weaker connections to other themes. Niche themes may be new and emerging, or they may be specialized and focused on a particular aspect of the field. From Fig. 10 we can see that Niche themes are multicentre, therapy, trial and circulatory pump. So this indicates a focused and emerging theme in this domain of research is multicentre trial of VAD related equipment⁶².

Basic themes are fundamental themes that are common to many different research fields. They are characterized by their large size, central position on a thematic map, and strong connections to other themes. Basic themes are the foundational themes upon which other research is built. From Fig. 10 we can see that basic themes for this research domain are ventricular assist device, pump, flow, axial-flow pump etc. indicating that the research revolves around design of ventricular assist device for flow of blood with the help of either axial or centrifugal type of pumps.

Emerging or declining themes are themes that are either new and growing, or old and declining. They are characterized by their relatively small size and weak connections to other themes. Emerging themes may represent new areas of research, while declining themes may represent areas of research that are becoming less important. From Fig. 10 we can see that emerging terms in this field of research include themes like wireless⁶³, intraaortic balloon pump, machine learning⁶⁴, acute myocardial-infarction⁶⁵, miniaturization and cardiogenic-shock⁶⁶.

3.7.3 Trend Topics

Trend topic plots in single-quadrant mode is shown in Fig. 11. Single-quadrant trend topic plots show all terms in the same quadrant, with the size of the circles representing the frequency of the terms. The terms with the largest circles represent most frequently used terms in the field. In trend topic plot if a particular term is becoming more common over time, this means that the field is moving in that direction. Limitations of single-quadrant trend topic plots is that these plots are useful for getting a high-level overview of the most frequently used terms in a field. However, they do not provide sufficient information about the importance of the terms. Fig. 11 shows the trends topics in the field of research of VAD design and development are blood pump, hemodynamics, fibre optic sensors, axial-flow pump, ventricular assist device, centrifugal flow, miniaturization, machine learning, wireless, shear flow etc. Figure 12 presents a word cloud of the 50 most frequently used keywords in this field of study.

To the best of our knowledge, this is the first bibliometric analysis to use merged data from Web of Science and Scopus databases to study the evolution of VAD device design and development using experimental and computational techniques, also including human trials^67-69. These techniques are playing an increasingly important role in biomedical research, and it is exciting to see how they are being used to improve the development of VAD devices. Our analysis provides insights into the latest trends and advances in this field, which is essential for saving the lives of patients with heart failure or those who need a heart transplant. While many developing and some developed countries are still exploring this research area, the top ten productive journals in the field are all SCIE indexed and Scopus quartile 1 (Q1), quartile 2 (Q2) or quartile 3 (Q3) journals, indicating that high-quality research is being conducted in this domain. This bibliometric study will help to identify the latest trends and developments in the field of VAD device design and development, and to highlight the areas where more research is needed. This information is essential for driving innovation in this field and for improving the lives of patients who rely on VAD devices. Many researchers have published papers on VAD design, development and use related topics since the year 2005 (N = 210). Most of the publications are either journal articles, conference papers or review papers, with very few book chapters directly addressing the main topic of this paper. This is the time zone after use of 2^nd generation VAD devices started and research was focussed on further improvements in its design which resulted in 3^rd generation of VADs starting from year 2017 onwards. Since then researchers are focussing to improve its design, use and maintenance by using machine learning and artificial intelligence techniques along with some other design improvements.

The top 10 nations leading the charge in this field of research are predominantly developed countries, with India being the notable exception (refer to Table 3). The citation count further underscores the dominance of these developed nations, indicating that the majority of significant research in this domain originates from these countries. This suggests that developing nations have considerable ground to cover in advancing their technology in this field. Among the developing nations, only India, Iran, Malaysia, and Thailand have made contributions to the research in VAD design and development, with each of the latter three contributing a single paper.

From the keyword co-occurrence network (see Fig. 8) we see a gradual increase in the number of themes being covered under this domain. More and more relevant areas of concern related to VAD design and development are being explored with the passage of time. The first few early publications focussed on a very preliminary design. As more researchers started working in this domain we see more new topics being explored related to VAD such as hemodynamics, fibre optic sensors, miniaturization, machine learning, wireless, shear flow etc. as also can be observed from Fig. 11. VAD designers are also working to improve designs to reduce blood damage by optimizing the interaction between blood and VAD equipment. Thematic analysis shown in Fig. 12 helped us in answering the following questions related to research work. It helped us to understand the following things based on the collected data from the past work done in this domain such as:

Most important topics related to this area are left ventricular assist device, assisted circulation, heart-assist devices, hemolysis, and equipment design.
Another important information we got from thematic analysis is regarding the evolution of different topics connected to technology involved in the design process with new keywords appearing in research like miniaturization, machine learning, artificial intelligence and centrifugal pumps etc.
The themes appearing in four groups of thematic map (Motor, Niche, Basic and Emerging) help us to understand that few themes are totally isolated and focusses on a particular area of research only such as multicentre, trials etc. and also help us to identify trending topics in this research domain such as machine learning, artificial intelligence, hemodynamics, fibre optic sensors, axial-flow pump and centrifugal-flow pumps etc.

This paper presents the first ever bibliometric analysis of the design and development of VAD devices using merged data from the Scopus and WoS databases. The study provides a comprehensive overview of the research in this domain, including the most influential authors, publications, and emerging themes. The authors faced a challenge in that other bibliometric tools, such as VOS-Viewer and CiteSpace, could not read the merged data file, so they were limited to using Biblioshiny and Microsoft Excel. Despite this limitation, the study provides valuable insights into the field and highlights the need for continuous exploration to keep up with rapidly changing technologies. The study also identifies several emerging themes in this digital age, such as Miniaturization, artificial intelligence, machine learning, wireless, shear flow etc., which warrant further investigation to better understand the new challenges in this field. Ventricular assist device (VAD) technology is rapidly advancing, with new devices being developed all the time. One promising area of research is wireless VADs, which would eliminate the need for a percutaneous driveline, making them more comfortable and reducing the risk of infection. Another promising area of research is implantable VADs powered by the patient's own blood flow, which would eliminate the need for a bulky external battery pack and allow patients to be more active and independent. Another possibility of development in future lies in using artificial intelligence and machine learning that can learn from information about patients and then adapt as per the patients’ requirements. The modern developments in VAD design and surgery are making them a more practicable choice for more patients^70,71. Ventricular assist devices (VADs) have radically enhanced the quality of life for patients with heart related issues needing treatment. VADs can support patients in living longer and more active lives, and they can also serve as a bridge to heart transplantation for needy patients.

VAD Ventricular Assist Device

LVAD Left Ventricular Assist Device

RVAD Right Ventricular Assist Device

WOS Web of Science

CFD computational fluid dynamics

HVAD HeartWare Ventricular Assist Device

Author’s contributions: AKS- Data collection, Literature review, Figures, Analysis, Manuscript preparation; AKPR- Conceptualization and final editing.

Data availability statement: Data will be provided by the corresponding author, upon request.

Additional Information: Authors declare no conflict(s) of interest of this work.

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No competing interests reported.

A Study on the Global Patterns in the Design and Development of Ventricular Assist Devices: A Visualization Approach

Status:

Version 1

Abstract

Figures

1. Introduction

2. Methodology

2.1 Data collection

2.2 Data merging and cleaning

3. Results

4. Discussion

5. Conclusions and Future Scope

Abbreviations

Declarations

References

Additional Declarations

Status:

Version 1