Accuracy of Impedance Cardiography in Acute Myocardial Infarction: A Literature Review

O cateter de Swan-Ganz é uma medida invasiva de monitorização hemodinâmica, indicado para situações clínicas, tais como: insuficiência cardíaca aguda (ex.: infarto agudo do miocárdio, complicado com hipotensão progressiva ou choque cardiogênico); complicações mecânicas do infarto agudo do miocárdio; infarto do ventrículo direito; insuficiência cardíaca congestiva refratária; Hipertensão pulmonar.1


Introduction
Hemodynamic monitoring of individuals with acute myocardial infarction, for evaluation of progression and prognosis of the patient's clinical picture, has been studied for years.
The Swan-Ganz catheter is an invasive hemodynamic monitoring measurement, indicated for clinical situations, such as acute heart failure (e.g.acute myocardial infarction, complicated by progressive hypotension or cardiogenic shock); mechanical complications of acute myocardial infarction; right ventricular infarction; refractory congestive heart failure; pulmonary hypertension. 1though there are indications, there is no consensus among them, since there is an enormous amount of work published on the clinical use of the Swan-Ganz catheter, but with doubtful methodology, allowing controversies regarding its true indications.Moreover, some authors have even published test results correlating the use of the Swan-Ganz catheter with increased mortality. 1,2ectrical impedance cardiography (ICG) or thoracic bioimpedance, among other forms of monitoring, is a noninvasive method for the estimation of hemodynamic variables.The method assumes that the thorax is a homogeneous fluid cylinder, composed of blood tissue, air and organs, with a specific resistance, and thus

Objectives
-To verify the accuracy of the use of impedance cardiography in patients with acute myocardial infarction.
-To compare the indications of the impedance cardiography with the Swan-ganz catheter in patients with acute myocardial infarction.

Method
It was a descriptive, retrospective research, based on a quantitative approach, conducted by means of literature review.For the survey of articles in the literature, a search was conducted in the following databases: Latin American and Caribbean Literature in Heath Sciences (LILACS), Medical Literature Analysis and Retrieval Sistem on-line (Medline), Cumulative Index to Nursing & Allied Health Literature (CINAHL) and COCHRANE LIBRARY.
The electronic search was guided by the PICO strategy.The PICO acronym stands for: Patient, Intervention, Comparison and Outcomes. 5Table 1 presents the components of the PICO strategy.
The collection of data occurred in the period from January to August 2015.The following controlled descriptors were used to find the articles in databases: myocardial infarction, cardiography impedance, catheterization, Swan Ganz, invasive hemodynamic monitoring and hemodynamics.The composition of the sample met the inclusion criteria: Articles in Portuguese, English and Spanish; Articles that compared bioimpedance cardiography and invasive hemodynamic monitoring; Population: adult patients (aged older than 18 years) in critical condition; Articles published between 2005 and 2015.And as exclusion criteria: Articles not available in full-text; Studies conducted with animals; Articles that compared bioimpedance cardiography with other methods; Revision articles.For data collection, an instrument was developed composed of data related to the journal (title, area, database, country, language, year of publication), the authorship (number of authors, profession of the authors) and to the study (place of research, sample identification, design, type of participants, type of publication, results and conclusions).
In the search, 108 articles were found in MEDLINE (02 articles were added due to similarity), 126 in CINAHL, 11 in LILACS, and 62 in COCHRANE, totaling 307 articles in an initial sample.
Following the eligibility criteria, 259 (84.36%) articles were excluded.A dynamic reading of the 48 (15.63%) remaining articles was taken, and 38 (12.37%) articles were excluded since they were related to heart failure or compared bioimpedance cardiography with other methods.10 articles were absorbed from the initial sample in order to develop this study.

Results
Ten articles were selected for review, among which eight (80%) were found in the Medline database and two (20%) in Cochrane.The USA and Lithuania were the countries that most published on the proposed outcome, totaling 60% of the results.It was found no indexed publication in Brazilian journals (Chart 1).
It was shown that 80% of the articles were developed by doctors, 10% by nurses and 10% by professionals of both categories (Chart 2).

Discussion
In accordance with this study's objective, which refers to the identification of the accuracy of impedance cardiography compared to the Swan-Ganz catheter, this revision was concerned to elect clinical trial articles, considering their scientific magnitude to the scientific society, in addition to checking the journal's origin and its scientific relevance.
Impedance cardiography (ICG) is a reliable method for hemodynamic monitoring in cases of acute myocadial infarction without complications. 7

Review Article
The comparison of cardiac output (CO) accuracy determined by bioimpedance, thermodilution, and the Fick method led to the conclusion that the three techniques are not interchangeable in a heterogeneous population of critically ill patients.Measurements of CO by thermodilution were more significant than by bioimpedance.However, for each subject, the bioimpedance method varies less than the thermodilution method varies. 8G could decrease the need for placement of a pulmonary artery catheter in critically ill patients in coronary care units (CCU).The benefits of pulmonary artery catheter (PAC) may not justify the risks associated with invasive hemodynamic monitoring, such as the potential for infection and other complications associated with a catheter.Although ICG does not provide pulmonary artery pressure, it does provide reliable and reproducible measures of cardiac index, stroke volume, systemic vascular resistance, and other hemodynamic parameters.Clinicians utilizing ICG believe it aids medical decision-making and improves patient outcomes in coronary care units, and in the comparison of average hospital cost, it was found PAC 2165$ / ICG 34$ per procedure. 9G data could reflect the early cardiac functions of AMI patients, but the accuracy of ICG in evaluating cardiac Fuller 12 2006 The study examined the use of impedance cardiography to stimulate cardiac output in critically ill patients in the intensive care unit.Cardiac output was measured, concurrently, in 61 patients with a pulmonary artery catheter (PAC) and impedance cardiography (ICG).functions should be combined with detection of blood NT-proBNP, BNP and cTnT and echocardiography. 10e use of ICG made it possible to offer an integrated analysis with electrocardiogram to help identify the patients at risk of serious adverse events after STsegment.All-cause or cardiac mortality and in-hospital recurrent ischemia, recurrent nonfatal MI, and need for revascularization were considered as serious adverse events.A greater risk of cardiac death was observed within a 5-year period after STEMI. 5 Significant correlation of cardiac output values was observed between the impedance cardiography and the Swan-Ganz technique during intra-aortic balloon (IAB) usage.Noninvasive evaluation of hemodynamic indices by continuous monitoring of impedance cardiography during acute myocardial infarction complicated by cardiogenic shock and managed by an intra-aortic balloon is a reliable method for further application. 11ere is a low correlation between PAC and ICG in critically ill patients, but the exclusion of patients with valve regurgitation improves the results.The use of ICG led to a 71% reduction in PAC usage in critically ill patients.The support of clinicians for the introduction of any new technology is as important as the accuracy and reliability of that technology.Only with such support can impedance cardiography be accepted. 12pedance cardiography is a valid parameter to estimate stroke volume and to guide optimization of CRT timing in postinfarction patients.It has shown an advantage over the pulmonary artery catheter because it is a simple method of measuring daily hemodynamic data of patients. 13pedance cardiography, similarly to the pulmonary artery catheter, measures stroke volume, and in post-MI patients, it was possible to show the beneficial effect of stem cells usage in patients with depressed LV function using ICG, without the need for an invasive method. 14pedance cardiography provides contractility data that can increase traditional hemodynamic information.Current measure systems that measure thoracic impedance to electrical current are user friendly, easy to apply and safe.The use of impedance cardiography may enlarge the relationships between hemodynamic parameters and cardiovascular and circulation disorders that may subsidize patient care.

Conclusion
ICG has shown to be a reliable method for hemodynamic monitoring in cases of acute myocardial infarction without complications.This method enlarges the relationships between hemodynamic/ cardiovascular parameters and circulation disorders that may subsidize patient care.
It is emergent that we understand the importance of assisting the client based on clinical evidence.Our knowledge about the pathology and its hemodynamic repercussions assures the appropriate diagnosis identification, allowing the implementation of client care with quality and safety.

Chart 1 -Chart 2 -
Characterization of the country and language of publication of articles.Distribution of articles according to the author's professions.Doctors Nurses Both Silva et al.Impedance cardiography in myocardial infarction International Journal of Cardiovascular Sciences.2018;31(3)282-289 The study has found a low correlation between PAC and ICG in critically ill patients, with 95% confidence interval, but the exclusion of patients with valve regurgitation and adjustment for hematocrit and skinfold thickness improved agreement.The support of clinicians for the introduction of any new technology is as important as the accuracy and reliability of that technology.Only with such support can impedance cardiography be accepted.The use of bioimpedance led to a 71% reduction in PAC usage in critically ill patients.Keuhne et al.13 2013Fifteenpostinfarction patients, with symptomatic heart failure and akinetic or dyskinetic segment were included in the study.During the implantation of a cardiac resynchronization therapy (CRT) device, stroke volume was measured via impedance cardiography.It has shown an advantage over the pulmonary artery catheter because it is a simple method for measuring daily hemodynamic data of patients.Impedance cardiography is a valid parameter to estimate stroke volume and to guide optimization of CRT timing in postinfarction patients.Silva et al.Impedance cardiography in myocardial infarction International Journal of Cardiovascular Sciences.2018;31(3)282-289 Review Article Piepoli et al. 14 2010 It used impedance cardiography, and not the pulmonary artery catheter, to assess stroke volume, in post-MI patients, and the use of bone marrow stem cells to improve cardiac function.The study showed the beneficial effect of stem cells usage in post-MI patients with depressed LV function.Albert 15 2006 Comparison between hemodynamic variables: Cardiography impedance Stroke volume / stroke index; cardiac output / cardiac index; systemic vascular resistance; left cardiac work / left cardiac work index.Other contractility parameters: -Systolic time ratio; Pre-ejection period; Left ventricular ejection time; Velocity index; Thoracic fluid content.Pulmonary Artery Catheter -Stroke volume / stroke index; cardiac output / cardiac index; left cardiac work / left cardiac work index; systemic vascular resistance and peripheral vascular resistance index; pulmonary vascular resistance and pulmonary vascular resistance index; pulmonary artery pressure; right atrial pressure.. Impedance cardiography provides contractility data that can increase traditional hemodynamic information.Current measure systems that measure thoracic impedance to electrical current are user friendly, easy to apply and safe.The use of impedance cardiography may enlarge the relationships between hemodynamic and cardiovascular parameters and circulation disorders that may subsidize patient care.Silva et al.Impedance cardiography in myocardial infarction International Journal of Cardiovascular Sciences.2018;31(3)282-289 Review Article

Chart 3 -Description of Results
9  2005The hypothesis was that ICG could decrease the need for placement of a pulmonary artery catheter in critically ill patients in coronary care units (CCU).After evaluating the need for hemodynamic monitoring of 107 patients admitted to the CCU, 14 were judged to have indications, and all patients were monitored by ICG.ICG parameters were provided to the patients; unsuccessfully, in 1 patient, who died within the first 18 hours.Half of patients underwent cardiac surgery within the first two weeks.Mortality rate was 68%.A total of 109 paired measurements were carried out in 16 patients in accordance with different IABP stages.Monitoring of cardiac output, cardiac index, systemic vascular resistance and systolic volume were compared by the two methods, every 12 hours.
15mparison between hemodynamic variables: Cardiography impedance -Stroke volume / stroke index; cardiac output / cardiac index; systemic vascular resistance; left cardiac work / left cardiac work index.Other contractility parameters: -Systolic time ratio; Preejection period; Left ventricular ejection time; Velocity index; Thoracic fluid content.Pulmonary Artery Catheter -stroke volume; stroke index; cardiac output; cardiac index, left cardiac work; left cardiac index; systemic vascular resistance and peripheral vascular resistance index; pulmonary vascular resistance and pulmonary vascular resistance index; pulmonary artery pressure; right atrial pressure.15