Heart Failure

Determining the Effectiveness of Impedance Monitoring in Heart Failure Patients with Implanted Cardiac Defibrillators

Amanda Franchuk, RN, BSN, DNP and Jaclyn Conelius, PhD, FNP-BC, FHRS
Fairfield University
Fairfield, Connecticut

Amanda Franchuk, RN, BSN, DNP and Jaclyn Conelius, PhD, FNP-BC, FHRS
Fairfield University
Fairfield, Connecticut


Heart failure (HF) is a serious health problem that plagues approximately 5.7 million adults in the United States.1 The Centers for Medicare and Medicaid Services (CMS) estimate that HF costs across the country are approximately $39.2 billion annually,1 and that HF is the primary cause of over 1.1 million hospital admissions each year. Heart failure remains among the top diagnoses for recurrent hospital admissions, with 20% or $17 billion paid for preventable readmissions.2 Furthermore, statistics published by the Centers for Disease Control and Prevention (CDC) show that one in nine deaths in 2009 included HF as a contributing cause, and that approximately 50% of all patients who develop heart failure die within five years of the diagnosis.3 
Symptoms such as fluid retention, shortness of breath, fatigue, and dyspnea upon exertion, inhibit those diagnosed with HF from leading normal, healthy lives.4 Considering the increasing prevalence, cost, and social burden to patients and families affected by heart failure, a therapeutic solution is necessary. As clinical management of these patients becomes increasingly complex, it is important to employ multi-modal interventions to best suit the needs of each individual patient. Interventions incorporating self-care methods coupled with effective medical treatments are critical to optimize patient health outcomes and improve overall well-being. 
Patients generally manage heart failure with a combination of treatment strategies. Adherence to medications, diet plan treatments, and symptom management are necessary to better control their disease processes. Education on these treatment strategies is pertinent to promote a patient’s self-care efforts and has become the cornerstone of HF disease management.4 Unfortunately, factors such as medication noncompliance and/or failure to seek medical attention in a timely manner after symptoms begin to worsen are directly linked to a decompensation of HF in a large number of patients. Thus, treatment plan adherence as well as timely symptom management are essential to improve a patient’s education and awareness to best control this crippling disease. This allows individuals to develop autonomy by contributing to their own healthcare strategies to maintain healthy functioning and well-being, leading to overall improved health outcomes.5 


The purpose of this study is to determine if implanted cardioverter-defibrillators (ICDs) with impedance monitoring appropriately measure hemodynamic changes in heart failure patients, and to assess patient perceptions of self-care maintenance, management, and confidence of his or her own heart failure diagnosis with the use of the Self-Care of Heart Failure Index (SCHFI) tool v.2.

Background and Significance

In performing a comprehensive literature search using CINAHL plus full text, PubMed, and Google Scholar, it is apparent that numerous studies have been performed to assess the reliability of intrathoracic impedance monitoring to determine exacerbations in heart failure patients. Many of these studies have yielded inconclusive results, requiring further testing. Many studies have also demonstrated that impedance monitoring not only can signal worsening HF, but also dehydration, cardiac arrhythmias, pleural effusions, and other causes of fluid retention.6 As a significant proportion of patients are faced with an acute decompensated HF episode, it is evident that direct links to dietary and medication noncompliance are the cause. A self-care intervention may assist in decreasing congestive symptoms and possible hospitalization.2,7 

Intrathoracic Impedance

As a consequence of its progressive and unstable nature, many patients develop recurrent episodes of decompensated HF, requiring frequent hospital admissions. Once admitted, 25% of patients are readmitted in one month, and up to 50% are readmitted within six months.2 Research has shown that these recurrent exacerbations and hospital admissions are directly linked to fluid volume overload secondary to increased right ventricular filling pressures.7,8 To help prevent exacerbations and hospitalizations, alternative diagnostic options such as intrathoracic impedance monitoring have become more common.9
Intrathoracic impedance is defined when an electrical current is passed across the lungs. When there is an accumulation of intrathoracic fluid, the conductance is increased, as blood is among the most conductive fluids within the body. This hemodynamic change causes a corresponding decrease in impedance.10 Oftentimes, intrathoracic impedance can be monitored automatically through the use of an ICD, which measures intrathoracic impedance several times throughout the day using a vector between the ICD case and the right ventricular lead.10 The lower the impedance to the conduction of this current, the higher the fluid content of the lungs, signifying a change in pulmonary congestion.2
As the prevalence, cost, and social burden to patients and families affected all continue to steadily increase, it is mandatory that the HF patient population remain vigilant regarding compliance with diet and medication administration to successfully attain their goals of care. In comparison to daily weight measurements, which can provide poor sensitivity as a predictor of fluid retention,8,9 intrathoracic impedance monitoring is based on the pathophysiologic principle that the high impedance of normal air-filled lungs decreases as pulmonary congestion increases. Again, as fluid in the lungs builds, impedance decreases, indicating the possibility of decompensated heart failure.9 
Intrathoracic impedance not only can be used to measure changes in thoracic fluid content, but also measure change in intracardiac pressure, heart rate variability, physical activity level, and arrhythmias.11 Additionally, factors such as electrode placement, patient movement, skin moisture, blood composition, and body composition can affect the conductivity of the signals used to measure impedance.6 Therefore, even though the main goal of intrathoracic impedance monitoring is to aid in providing early detection of overt decompensated heart failure, it cannot been used to replace standard clinical practices since it is not exclusively specific to decompensated HF.
Vollmann et al12 evaluated the utility of intrathoracic impedance monitoring for detecting heart failure deterioration in patients with ICDs. Similarly, van Veldhuisen MD et al11 assessed if an early intervention with an audible alert by measurement of intrathoracic impedance would prevent hospitalizations for patients with an ICD. Although these studies were performed several years apart and by different investigators, results of both remained ambiguous in its value for predicting heart failure. Vollmann12 determined that approximately 40% of impedance alerts were false positives, deducing that further research is needed to determine if intrathoracic impedance monitoring can improve ambulatory management of chronic heart failure patients with an ICD. Unfortunately, the study performed by van Veldhuisen11 was terminated due to slow enrollment. However, a post hoc futility analysis performed after the end of the study indicated that a positive result would be unlikely. The authors concluded that the use of an implantable diagnostic tool to measure intrathoracic impedance did not improve patient outcomes, and that  both HF hospitalizations and outpatient visits related to HF increased.11 
Although several studies designed to assess the validity of intrathoracic impedance monitoring have yielded ambiguous results, it remains one of the most commonly used predictors of decompensated HF. 

Self-Care of Heart Failure Index

Combined with diagnostic interventions, practicing self-care is an important strategy in the long-term management of HF. These behaviors can result in reduced disability, fewer symptoms, and an improvement in health-related quality of life. One method to assess the strengths of a patient’s self-care is with the use of a valid and reliable tool. The SCHFI is a self-reported measure used to assess a patient’s perception of management of his or her own heart failure diagnosis.13 Riegel et al developed the tool in 2004 with the goal of improving outcomes of patients with heart failure. The latest version of the SCHFI is v.6.2, which is comprised of 22 items divided into three subscales.14 The subscales of self-care maintenance, self-care management, and self-care confidence are measured collectively to best assess the patient’s perceptions of their self-care. It was written at a sixth-grade reading level and takes approximately ten minutes or less to complete. Each item contains a best answer choice with a gradated forced-choice four-point response scale.13 This grading scale allows for assessment of the patient’s progress, in which higher scores indicate better self-care.13 A score of 70 or greater on each subscale is considered adequate self-care.14 Although the SCHFI addresses self-care within a time period of the prior 90 days, the interval can be adjusted for patient need and/or clinician preference.13 
The Self-Care of Heart Failure Index’s reliability and validity has been reassessed using both quantitative and qualitative approaches, yielding positive results.14 Reliability of the overall tool was adequate with a Cronbach’s alpha value of 0.76. Construct validity was further shown to be significant (P<0.05).13 Its multidimensional four-factor structure allowed for confirmatory factor analysis (CFA), providing a more precise measure of reliability.15 CFA yielded positive results, further authenticating the validity and reliability of the Self-Care of Heart Failure Index as sufficient to use in future clinical research.15 
Masterson Creber and colleagues utilized the SCHFI tool to assess improvements in patient self-care after a motivational interviewing intervention.16 Their study took place from January 2012 to December 2013, and involved 67 participants from varied backgrounds.16 Using the SCHFI, self-care was assessed at the start of the study and again at 90 days following a motivational interviewing intervention. The results indicated that the use of a nurse-led motivational interviewing intervention improved self-care assessments in patients with heart failure. The self-care confidence subcategory showed the greatest change (approximately 20 points). Overall, this novel study was successful in demonstrating that interventions using motivational interviewing are promising for improving confidence in self-care efforts and abilities in patients with heart failure.16


This study was performed at a large private cardiology practice in the Northeast from June 2016 to March 2017, after IRB approval. Prior to the start of the study, permission from the lead electrophysiologist was obtained. Participants were taken from a convenience sample of established patients at our cardiology practice; inclusion criteria included patients with a biventricular ICD with intrathoracic impedance monitoring capabilities, a concurrent diagnosis of heart failure, were aged 20-100 years old, and who spoke English. Participants were excluded from the study if their implantable device did not have thoracic impedance monitoring capabilities, if they did not speak or understand English, or if they either intentionally or unintentionally left a question blank on the SCHFI tool. If the SCHFI is not completed in its entirety, it is impossible to assess if it provides an accurate measure. 
Participants were recruited from June 2016 to September 2016, during a device interrogation of their ICD or over the phone if the impedance alert was triggered. In the initial meeting, consent was obtained, the SCHFI v.6.2 tool was administered, and a participant demographics sheet was completed. Consent was assumed upon completion of the surveys, and anonymity was maintained by de-identifying all patient-related information. At this time, participants were also informed that he or she would still receive regular care by their cardiologist, and they were provided a detailed information sheet outlining the goals of this research study, the principle investigator contact information, and options to withdraw. 
After 30 days, a chart review was performed using the cardiology practice’s preexisting electronic medical record to assess if any intervention occurred in direct relation to the patient’s heart failure management. Interventions such as medication changes, diagnostic imaging, telephone encounters, office visits, and/or hospitalizations were all assessed in relation to the participant’s HF. Participants were then re-administered the SCHFI v.6.2 tool to assess changes in management, maintenance, and confidence in relation to their self-care methods. 
Strict participant confidentiality was maintained through the completion of this study. A participant identification code for each subject was created by the PI and all forms were matched according to code. Only the principal investigator and co-principal investigator had access to any information collected for the purposes of this study. Participants were placed at minimal to no risk during the course of this study. Participants were given the option to withdraw themselves from the study at any point in time, and could ask questions or discuss concerns with the research being conducted at any time during the study. 


Both pre and post test SCHFI scores were calculated according to the formula provided in the directions of the SCHFI v.6.2 tool. Data was then inputted into Microsoft Excel for organization and preparation for paired t-testing using SPSS software. After running G-power analyses to find n=25 for statistically significant data with the use of a P≤0.05, the statistician performed a paired two-sample means t-test utilizing SPSS software. Data was analyzed to compare the scores of the initial SCHFI tool and the results after the 30-day retrospective chart review. Descriptive statistics were used to report demographic data. 


This study included 25 participants, in which all participants were administered pre and post test within the study’s time frame. The mean participant age was 69.5, with a range of 34 to 90 years old. Sixteen percent (n=4) were female, and 84% (n=21) were male. Each participant’s heart failure was also categorized according to the New York Heart Association (NYHA) Functional Classification. Twenty-five percent (n=7) were NYHA class I, 48% (n=12) were NYHA class II, 24% (n=6) were NYHA class III, and 0% (n=0) was NYHA class IV. Class I patients demonstrate no limitation of physical activity and ordinary physical activity does not cause undue fatigue, palpitation, or dyspnea. Class II have a slight limitation of physical activity, are comfortable at rest, and ordinary physical activity results in fatigue, palpitation, or dyspnea. Class III patients demonstrate marked limitation of physical activity, are comfortable at rest, and have less than ordinary activity causes fatigue, palpitation, or dyspnea. Lastly, class IV patients are unable to carry on any physical activity without discomfort, they exhibit symptoms of heart failure at rest, and if any physical activity is undertaken, discomfort increases.17 
The SCHFI v.6.2 is divided into three categories: maintenance, symptom perception, and management. Each category was scored according to the directions of the tool. Parts A and C measuring maintenance and management, respectively, were calculated using a paired two-sample mean t-test. Part B, symptom perception, was not calculated using a paired two-sample mean t-test due to the lack of self-reporting of HF symptoms. Part B began with a “yes” or “no” question, and if the participant answered “no,” they were instructed to skip the rest of the section and continue onto Part C. Due to this, the data was unable to be compared, as some participants completed the section once, twice, or none at all, depending on if they were currently experiencing subjective symptoms of HF. 
Part A measuring maintenance was not significant (P=0.31) using a paired t-test (Figure 1). Part C, measuring management, demonstrated a significant increase (P<0.05) in confidence of participants managing their HF symptoms over the 30-day period (Figure 2).  


There were several limitations to this study. One limitation was that data collection only occurred at one site in a multisite office. Time constraint was a limitation in this research study. Due to the constraints working within an academic year, time allotted for participant recruitment was limited from June 2016 through September 2016. Additionally, attrition rates were high for the phone recruitment at the time of the initial recruitment period, making for a smaller total sample. 


Considerable medical costs of patients with heart failure are directly related to hospitalization secondary to decompensated symptoms.12 Dyspnea on exertion and fatigue are indicative of early signs of worsening heart failure, whereas more typical signs of edema and pulmonary congestion are consistent with the later progression of a HF exacerbation.12 Along with the previous symptoms of dyspnea, fatigue, and edema, the leading cause of most heart failure hospitalizations is excessive pulmonary fluid accumulation.9 Therefore, meticulous surveillance and self-monitoring of fluid status are an integral part in not only preventing hospital readmissions, but also increasing patient confidence in relation to caring for their heart failure. As a result, early detection of fluid overload and pulmonary congestion may aid in avoiding HF decompensation.9 This, in turn, may potentially prevent HF-associated morbidity and mortality while keeping associated costs down.9 It may also possibly lead to an improved self-awareness of symptoms and confidence by recognizing a decline in their own healthcare, prompting a provider evaluation before late decompensation signs set in.


Along with diagnostic interventions, self-care is an important strategy in long-term HF management. Self-care can result in reduced disability, fewer symptoms, and an improvement in health-related quality of life. The need to create innovative care systems for HF patients is obvious from the increasing healthcare burden of this rampant disease. Interventions incorporating self-care methods, coupled with effective medical treatment, are critical to optimize patient health outcomes and improve overall well-being. Current evidence for intrathoracic impedance technologies requires further research. 
This study demonstrated that heart failure patients had an increase in confidence at 30-day follow-up after an intrathoracic impedance alert. There were no correlations between a change in impedance and prediction of heart failure exacerbations, since management did not significantly change with the impedance alert. However, the study did show a significant increase in confidence in self-care methods, which may lead to decreased exacerbations. This demonstrates that with a simple intervention, such as the one performed during this research study, patient confidence in their abilities to recognize and manage their heart failure can potentially lead to reduced hospital admissions, recurrent decompensated episodes, and an overall healthier lifestyle.
Disclosures: The authors have no conflicts of interest to report regarding the content herein.   


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