Wearable electronics or sensors, by definition, are devices designed to generate, transmit, modulate and detect electrical activity that are woven into a garment and comfortably worn, and serve a specific monitoring or measuring purpose.1 The general architecture for wearable electronics suggested by Tao1 incorporates sensors (input and output interfaces) to collect and display information, communication modules to transmit and receive information and energy sources and management technologies.1 Sensors are an integral part of the construction of wearable electronics and are used to collect a variety of physiological signals and to respond appropriately.1 Many basic physiological parameters such as temperature, electrocardiogram (ECG), heart rate, respiration rate, blood pressure, gait analysis, spinal posture, sweat rate, arm and limb motion as well as stress can be monitored with the aid of wearable sensors.2
Textiles, on the other hand, are the main interfacing mechanisms between the naked body and surrounding environment and commonly reflect the socio-cultural values of the society.3 As a newly emerging interdisciplinary field of research, electronic textiles, also known as e-textiles, consist of “fabrics that have electronics and interconnections woven into them”.4(p.4) Unlike “wearable technologies” in which the electronic components may simply be worn, the electronics in e-textiles are fully integrated into the material.2,5 Even though there are differences in reporting, scholars agree that the progenitor for e-textiles and wearable computing was initially proposed by Steve Mann in the 1980s, in the experimental labs of Massachusetts Institute of Technology.3 E-textiles utilizes the prime concepts of wearable computers.6
On top of their inherent familiarity by the patient, textiles have features such as wearability, flexibility to fit the human's body, softness and comfort to touch that make them acceptable for the patient.3 Textile integrated sensors for detecting a variety of physiological parameters are an active area of research. They have shown significant promise in ECG monitoring, and are also being investigated for use as bioimpedance, temperature, posture and motion sensing.5 Advantages of e-textiles include: no requirement for active patient involvement in the data collection process,7 minimal impact on daily living,8 the potential to address a large unmet clinical need,3 rapid technological advancements in electronic miniaturisation,9 wireless sensing technology reducing portability issues with current ECG monitors,7 gel-free electrodes with minimal skin irritation,5,10,11 potential for improved patient outcomes and reduced healthcare burden.12,13
The focus of this scoping review is on the use of e-textiles for ECG monitoring in cardiac patients.
Cardiovascular disease refers to a group of disorders of the heart and blood vessels which claim the lives of 17.7 million people every year, representing 31% of all global deaths. Cardiovascular disease continues to be the most deadly chronic disease across the globe, with the highest incidence in low- and middle-income countries.14,15 The global population continues to grow at a prolific rate and it is forecasted that there will be 10 billion people on the planet in the coming three decades.2 This is placing an unsustainable burden on healthcare systems around the world, where the traditional hospital infrastructure is no longer enough to satisfy the huge demands of the community. Hence, some new ways to administer healthcare to patients outside the traditional healthcare system need to be devised.1 If designed properly, wearable sensors and e-textiles could offer an alternative healthcare delivery solution. All these factors combined drive an increased demand for e-textile systems.9 E-textile-based patient care of cardiac patients may be a future alternative solution to traditional models of monitoring in-hospital and in the home.
There is a lack of detailed peer review published papers written on e-textile-based technologies applied in the field of cardiology.16-26 Although a recent scoping review5 has been found, the focus is on a general overview of e-textiles across a range of applications. It presents how e-textile sensors are used for clinical rehabilitation and highlights e-textile electrodes for ECG signal transduction. However, e-textile ECG systems and their clinical utility in the field of cardiology is not explored. This is important because there is a growing demand for continuous follow-up of patients with chronic diseases and home-based care and rehabilitation.9 The home-based nature of rehabilitation programs means minimal disruption for the patient, which could in turn provide mental wellbeing and recovery benefits. This scoping review will thus focus on e-textile-based ECG monitoring (resting, signal-averaged, ambulatory or exercise) for cardiac patients.
A preliminary search was conducted using the PCC (Population Concept Context) mnemonic to determine if any scoping reviews had been conducted on this topic. There were no scoping reviews on e-textile-based ECG monitoring (resting, signal-averaged, ambulatory or exercise) in hospital or at home for cardiac patients identified. The following platforms or databases were searched: Cochrane Database of Systematic Reviews, PubMed, Cumulative Index to Nursing and Allied Health Literature (CINAHL), JBI Database of Systematic Reviews and Implementation Reports (JBISRIR) and Institute of Electrical and Electronics Engineers (IEEE Xplore).
As stated in the works of Petticrew and Roberts,27 one of the problems facing current researchers undertaking scoping reviews is the explosion of information. Hence, keeping track of all resources is difficult unless the researcher is concentrated in a more focused field. One of the methods used to combat such problems is the development of precise inclusion and exclusion criteria.27 In this regard, the following inclusion criteria are suggested based on the PCC mnemonic.
In this scoping review, only papers that include cardiac patients who are qualified for cardiac rehabilitation programs or continuous ambulatory monitoring will be considered. Patients who have experienced one (or more) of the following cardiac events will be included: i) heart failure; ii) cardiomyopathy conditions; iii) medically managed acute myocardial infarction (MI) (STEMI [ST-elevation myocardial infarction] or non-STEMI), which includes or excludes post-MI revascularization; iv) medically managed coronary artery disease (CAD) (e.g. stable angina); v) revascularization procedures, including percutaneous coronary interventions and/or coronary artery bypass graft surgery; vi) post-insertion of implantable defibrillator and permanent pacemaker; vii) repair and replacement of valve device(s); viii) device implant for ventricular assist; and ix) heart transplant.
The key concepts that will be addressed are resting, signal-averaged, ambulatory or exercise ECG monitoring based on e-textile technologies or e-textile-based cardiac rehabilitation. The following are working definitions of concepts utilized in the scoping review:
Signal-averaged electrocardiogram (ECG)
Signal-averaged ECG is a procedure similar to a standard resting ECG, however, the electrical activity of the heart is recorded for a longer period of time (usually between 15 and 20 minutes) in order to identify cardiac abnormalities that may not be spotted during a standard ECG test.28
Ambulatory ECG (AECG) “is a small portable device that is used to continuously record heart's rhythm during daily activities of a person for a duration of at least 24 hours using a special portable device called HOLTER monitor”.29(p.137),30(p.521) The advantages of AECG include not only the diagnosis of mild infrequent and undetectable cardiac episodes like atrial fibrillation but also fatal abnormal arrhythmias for which the patient has no plausible symptoms otherwise.31 From an equipment point of view, most HOLTER monitors use fewer leads to reduce circuit complexity, compared to standard 12-lead ECG. Additionally, limb electrode sites in the standard ECG are approximated in HOLTER monitors by attachments mapped to the trunk.32
Ambulatory ECG monitoring in cardiac patients
The need for long-term ECG monitoring is still emerging as ventricular dysrhythmias continue to be the major etiologic factors responsible for cardiac death while atrial fibrillation is a precursor to heart failure and the onset of stroke.33,34 Hence, there are three common forms of clinical ECG usage;
- i) Twelve-lead resting ECG, exercise stress ECG and long-term ECG monitoring.33 The 12-lead resting ECG is the baseline measurement. However, stress ECG can provide several clinical advantages over ambulatory ECG monitoring. For instance, exercise stress testing is more appropriate for initial assessment of intermittent stable angina.35
- ii) Post-hospital follow-up of patients after myocardial infarction is necessary and conducted via ambulatory ECG monitoring to identify cardiac ailments leading to sudden cardiac death.36 Patients who do not have a graded exercise test prior to starting rehabilitation, especially those with stable angina or recovering from a recent myocardial infarction, can benefit from ambulatory monitoring. Additionally, people with a history of myocardial infarction complicated by cardiogenic shock or heart failure, or left ventricular dysfunction with or without heart failure, can benefit from extended cardiac monitoring.37
- iii) Patients who have demonstrated exercise-induced ischemia, atrial fibrillation, or a ventricular arrhythmia appearing or increasing during their pre-cardiac rehabilitation stress test are also eligible for HOLTER monitoring. Moreover, partial-program or full program telemetry monitoring has unprecedented importance for survivors of sudden cardiac death and for individuals who are unable to self-monitor heart rate because of physical or mental impairment.37
Exercise ECG is used to follow-up changes in electrical activity of the heart during exercise. Exercise ECG (also clinically known as stress ECG) has various clinical applications besides routine health screening or assessment prior to the commencement of an exercise program.37 For instance, exercise ECG can determine if a person has heart disease or is likely to get it, can estimate the likelihood of coronary artery disease in asymptomatic people with a high risk factor profile for ischemic heart disease, and can measure exercise capacity and the progression of disease in people with other cardiac abnormalities (e.g. valvular disease and cardiomyopathy).38
Cardiac rehabilitation (CR) program
The primary aim of cardiac rehabilitation program is to improve the day-to-day physical activities and autonomous functioning of patients, provide symptom relief, risk factor modification i.e. smoking reduction or cessation, improve exercise tolerance and reduce the risk of mortality.39 Individualized exercise and early ambulation play a vital role in the rehabilitation process for many cardiac patients as both physiological and psychological improvements can be achieved.40 People who have heart failure, peripheral artery and coronary artery diseases benefit from prescribed rehabilitation exercise programs as do those who have undergone post-myocardial infarction, revascularization after coronary artery bypass grafting and percutaneous interventions as well as some selected patients with angina. Moreover, patients before and after they undergo heart transplant can benefit from exercise-based cardiac rehabilitation therapy.39,40
Electronic textile (e-textile)
E-textiles are fabrics (or clothing) that contain electronic elements or circuits woven directly into the material and are an emerging interdisciplinary field of research.4 In general, electronic garments differ from one another based on the level of integration of electronic components into the garment. For the purpose of the review, there are three types of electronics to textile integration to be considered:3
- i) Embedded electronics: a result of on the shelf or custom-made electronic components which are attached to the textile.
- ii) Textronics: an electronic component made up of textile and produced through the textile production system.
- iii) Fibertronics: e-textile of basic electronic components, such as transistors incorporated into yarns.
Electrocardiogram measurement using e-textile system (any number of leads) will be considered as an outcome measure.
The context for this scoping review will be the global published research of e-textile use for patients as an in-hospital patient or outpatient and home-based exercise or long-term ambulatory monitoring.
Types of studies
This review will consider both experimental and quasi-experimental study designs including randomized controlled trials, non-randomized controlled trials, before and after studies and interrupted time-series studies. In addition, analytical observational studies including prospective and retrospective cohort studies, case-control studies and analytical cross-sectional studies will be considered for inclusion. This review will also consider descriptive observational study designs including case series, individual case reports and descriptive cross-sectional studies for inclusion. Guidelines, non-peer reviewed articles such as gray-literature will also be used to minimize any publication biases. Even though there is no definite timeline, the concept of smart fabrics (e-textiles) was initially proposed by Tao41 in the year 2001 and further refined in 2004 by Strese and co-workers mentioned in Tao.1 Thus, this review will consider any form of article, study, report, dissertation, or book related to the topic and published between January 2000 to March 2018. This represents a period of increasing availability and acceptance of e-textile technology and their incorporation into research protocols. Due to time and resource constraints, only studies written in English will be considered. Papers will not be considered if they are focused on any of the following aspects of the e-textile ECG system:
- i) E-textile electrodes/active electrodes design
- ii) De-noising / signal reconstruction algorithms
- iii) Graphics User Interface (GUI) design, Web socket or Application program development
- iv) Study of (optimal) placement of electrodes
- v) Wireless sensor topology/body area network/healthcare network.
The proposed scoping review will be conducted in accordance with the Joanna Briggs Institute methodology for scoping review.42
The search strategy will aim to find both published and unpublished studies. An initial limited search in PubMed and IEEE Xplore using keywords (see Table 1) will be undertaken followed by analysis of the text words contained in the title and abstract, and of the index terms used to describe the article. This will inform the development of a search strategy which will be tailored to each information source. A preliminary search strategy for the approved information sources database MEDLINE is provided in Appendix I. The reference list of all selected studies will be screened for additional studies.
The following sources of research will be scoped for this review:
Electronic databases: MEDLINE, PubMed Central, Institute of Electrical and Electronics Engineers (IEEE Xplore), CINAHL, Cochrane Database of Systematic Reviews, Web of Science, Scopus, Expanded Academic ASAP, ProQuest, ProQuest Dissertations and Theses Global, SPORTDiscus, ENGINE - Australian Engineering Database (Informit) and Google Scholar.
Trial registries: Cochrane Central Register of Controlled Trials, ClinicalTrials.gov, Australian New Zealand Clinical Trials Registry (ANZCTR) and Clinical Trials Connect (CTC).
Unpublished studies: the search for unpublished studies will include reference lists, book chapters, and theses as well as conference papers.
Study selection, in general, is an iterative process that involves literature searching, modifying search strategy and articles review for study inclusion.43 Given the contemporary and multidisciplinary nature of the topic under investigation, a large number of citations are expected. All identified citations will be collated and uploaded in Endnote V8.1 (Clarivate Analytics, PA, USA) with duplicates removed. Titles and abstracts will be screened by two independent reviewers for assessment against the inclusion criteria for the review. Studies that may meet the inclusion/exclusion criteria will be retrieved in full and their details imported into the Joanna Briggs Institute's System for the Unified Management, Assessment and Review of Information (JBI SUMARI).42 The full text of selected studies will be retrieved and assessed in detail against the inclusion criteria. Full-text studies that do not meet the inclusion criteria will be excluded and reasons for exclusion will be provided in an appendix in the final systematic review report. The results of the search will be reported in full in the final report and presented in a Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flow diagram.44 Any disagreements that arise between the reviewers will be resolved through discussion or with a third reviewer.
“Extraction of results” in a scoping review can be defined as charting the results.27 Charting the results provides readers with a summary of the results that is descriptive and logical in nature, which aligns with the review question(s) and objectives.27 Data will be extracted from papers included in the review using the standardized data extraction tool available in JBI SUMARI42 by two independent reviewers. The data extracted will include specific details about the interventions, populations, study methods and outcomes of significance to the review question and specific objectives. Considering the keywords and based on the contributions of Franzon et al. (2017, unpublished data) and Fleury et al.,5 a modified preliminary charting tool is proposed (see Appendix II). The suggested data extraction tool may be refined by collective discussion among the reviewers. If further data extraction categories are needed or missing data emerges, consultation with the research team will guide the decisions. During the time of data extraction, any disagreements that arise between the reviewers will be resolved through discussion or referred to a third reviewer. Authors of the primary studies will be contacted to request missing or additional data or clarify doubts as required.
According to the PCC framework that has been outlined in the scoping review protocol, the mapped data may be presented in tabular or graphical format combined with appropriate narration. The narrative summary included will describes the aims, objectives, concepts and results of the review question.34 Information extracted will be presented in categories as described in Appendix II, any additional information will be categorized appropriately at the time of review. An overall description of the included studies will be presented as a Summary of Findings. The scoping review will address the PCC elements in depth and point out the gaps for further research, if any. A PRISMA flow diagram will be adapted to report the result of the search.
The authors thank CINOP Global, and Addis Ababa Institute of Technology through Nuffic funded NICHE project NICHE/ETH/246 for supporting this work.
RC is supported by a Heart Foundation Future Leader Fellowship (APP100847). MT received financial assistance through the Heart Foundation Tom Simpson Trust Fund (Equipment Grant) 2017.
Appendix I: Search strategy
Ovid MEDLINE(R) Epub Ahead of Print, In-Process & Other Non-Indexed Citations, Ovid MEDLINE(R) Daily, Ovid MEDLINE and Versions(R)
- (e-textile∗ or etextile∗ or textile-based).tw.
- ((smart adj1 fabric∗) or (smart adj1 garment∗) or (smart adj1 cloth∗) or (sensori?ed adj1 garment∗) or (conductive adj1 fabric∗) or electronic cloth∗ or e-cloth∗ or ecloth∗ or e-fabric∗ or efabric∗ or e-garment∗ or egarment∗).tw.
- (textronics or fibertronics or Vivometrics LifeShirt system or textro or e-shirt or eshirt or h-shirt or MagIC-SCG).tw.
- Electrocardiography/ or Electrocardiography, Ambulatory/
- (electrocardio∗ or ECG or EKG).tw.
- (holter∗ or cardiac event monitor∗ or loop recorder∗).tw.
- Rehabilitation/ or Cardiac Rehabilitation/
- 10 or 13
- 6 and 14
- limit 15 to yr = “2000 -Current”
Appendix II: Modified data extraction tool
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