Transthoracic Impedance Cardiography: A Noninvasive Method of Hemodynamic Assessment

Differential hemodynamic adaptations to tilt test in patients with idiopathic atrial fibrillation

The hemodynamic response during the transition from the supine to standing position in idiopathic atrial fibrillation (AF) patients is not completely understood. This study aimed to analyze the hemodynamic changes that occur during the head-up tilt test in idiopathic AF patients. We investigated the hemodynamic changes during the head-up tilt test with impedance cardiography in 40 AF patients (12 with AF rhythm-AFr and 28 with sinus rhythm-AFsr) and 38 non-AF controls. Patients with AFr had attenuated SVI decrease after standing when compared to AFsr and non-AF [ΔSVI in mL/m2: -1.3 (-3.4 to 1.7) vs. -6.4 (-17.3 to -0.1) vs. -11.8 (-18.7 to -8.0), respectively; p < 0.001]. PVRI decreased in AFr but increased in AFsr and non-AF [ΔPVRI in dyne.seg.m2/cm5: -477 (-1148 to 82.5) vs. 131 (-525 to 887) vs. 357 (-29 to 681), respectively; p < 0.01]. Similarly, compared with non-AF patients, AFr patients also had a greater HR and greater CI increase after standing. The haemodynamic response to orthostatic challenge suggests differential adaptations between patients with AF rhythm and those reverted to sinus rhythm or healthy controls. Characterizing the hemodynamic phenotype may be relevant for the individualized treatment of AF patients.

Effect of cardiac function in patients with gastrointestinal cancer with or without acute kidney injury assessed using a non-invasive impedance cardiography: a case-control study

OBJECTIVES

This study aimed to analyze the possible causes of changes in cardiac function and investigate the feasibility of clinical assessment of gastrointestinal cancer in patients with or without acute kidney injury (AKI) assessed using a non-invasive impedance cardiography (ICG, Bioz. Cardio Dynamics, USA) to identify independent risk factors.

METHODS

Patients admitted to the Fourth Hospital of Hebei Medical University, China, between May 1, 2019, and February 15, 2022, were included in this study. A total of 51 patients with gastrointestinal cancer (31 men and 20 women, mean age 61.1 ± 10.9 years) with or without AKI were evaluated for ICG. A total of 19 patients underwent ultrasound cardiography (UCG) and ICG evaluations.

RESULT

There was a significant positive correlation between cardiac output (CO), cardiac index (CI), stroke volume (SV), left cardiac work index (LCWI), and ejection fraction (EF) measured using UCG and ICG. The relationship was observed between COICG and COUCG (r = 0.707, P = 0.001), CIICG and CIUCG (r = 0.718, P = 0.001), SVICG and SVUCG (r = 0.837, P < 0.001), and LCWIICG and EFUCG (r = 0.540, P = 0.017). Cardiac function parameters measured using ICG were statistically different between patients with gastrointestinal cancer with or without AKI (P ≤ 0.05). Multivariate analysis revealed that AKI independently affects cardiac function in patients with gastrointestinal cancer.

CONCLUSIONS

UCG and ICG methods are significantly associated with cardiac function in patients with or without AKI, and patients with gastrointestinal cancer with AKI are worse than those without AKI. AKI is an independent risk factor for cardiac function in patients with gastrointestinal cancer.

Monitoring Resistance Training in Real Time with Wearable Technology: Current Applications and Future Directions

Resistance training is an exercise modality that involves using weights or resistance to strengthen and tone muscles. It has become popular in recent years, with numerous people including it in their fitness routines to ameliorate their strength, muscle mass, and overall health. Still, resistance training can be complex, requiring careful planning and execution to avoid injury and achieve satisfactory results. Wearable technology has emerged as a promising tool for resistance training, as it allows monitoring and adjusting training programs in real time. Several wearable devices are currently available, such as smart watches, fitness trackers, and other sensors that can yield detailed physiological and biomechanical information. In resistance training research, this information can be used to assess the effectiveness of training programs and identify areas for improvement. Wearable technology has the potential to revolutionize resistance training research, providing new insights and opportunities for developing optimized training programs. This review examines the types of wearables commonly used in resistance training research, their applications in monitoring and optimizing training programs, and the potential limitations and challenges associated with their use. Finally, it discusses future research directions, including the development of advanced wearable technologies and the integration of artificial intelligence in resistance training research.

MONITORIA: The start of a new era of ambulatory heart failure monitoring? Part I - Theoretical Rationale

Heart failure (HF) is a multifactorial chronic syndrome with progressive increasing incidence causing a huge financial burden worldwide. Remote monitoring should, in theory, improve HF management, but given increasing morbidity and mortality, a question remains: are we monitoring it properly? Device-based home monitoring enables objective and continuous measurement of vital variables and non-invasive devices should be first choice for elderly patients. There is no shortage of literature on the subject, however, most studies were designed to monitor a single variable or class of variables that were not properly assembled and, to the best of our knowledge, there are no large randomized studies about their impact on HF patient management. To overcome this problem, we carefully selected the most critical possible HF decompensating factors to design MONITORIA, a non-invasive device for comprehensive HF home monitoring. MONITORIA stands for MOnitoring Non-Invasively To Overcome mortality Rates of heart Insufficiency on Ambulatory, and in this paper, which is part I of a series of three articles, we discuss the theoretical basis for its design. MONITORIA and its inherent follow-up strategy will optimize HF patient care as it is a promising device, which will essentially adapt innovation not to the disease but rather to the patients.

Point of Care Ultrasonography for Objective Assessment of Heart Failure: Integration of Cardiac, Vascular, and Extravascular Determinants of Volume Status

BACKGROUND

Lingering congestion portends poor outcomes in patients with heart failure (HF) and is a key target in their management. Studies have shown that physical exam has low yield in this setting and conventional methods for more precise assessment and monitoring of volume status (e.g., body weight, natriuretic peptides, and chest radiography) have significant inherent shortcomings.

SUMMARY

Point of care ultrasonography (POCUS) is a noninvasive versatile bedside diagnostic tool that enhances the sensitivity of conventional physical examination to gauge congestion in these patients. It also aids in monitoring the efficacy of decongestive therapy and bears prognostic significance. In this narrative review, we discuss the role of focused sonographic assessment of the heart, venous system, and extravascular lung water/ascites (i.e., the pump, pipes, and the leaks) in objective assessment of fluid volume status. Key Messages: Since each of the discussed components of POCUS has its limitations, a combinational ultrasound evaluation guided by the main clinical features would be the key to reliable assessment and effective management of congestion in patients with HF.

MONITORIA: The start of a new era of ambulatory heart failure monitoring? Part I - Theoretical Rationale

Heart failure (HF) is a multifactorial chronic syndrome with progressive increasing incidence causing a huge financial burden worldwide. Remote monitoring should, in theory, improve HF management, but given increasing morbidity and mortality, a question remains: are we monitoring it properly? Device-based home monitoring enables objective and continuous measurement of vital variables and non-invasive devices should be first choice for elderly patients. There is no shortage of literature on the subject, however, most studies were designed to monitor a single variable or class of variables that were not properly assembled and, to the best of our knowledge, there are no large randomized studies about their impact on HF patient management. To overcome this problem, we carefully selected the most critical possible HF decompensating factors to design MONITORIA, a non-invasive device for comprehensive HF home monitoring. MONITORIA stands for MOnitoring Non-Invasively To Overcome mortality Rates of heart Insufficiency on Ambulatory, and in this paper, which is part I of a series of three articles, we discuss the theoretical basis for its design. MONITORIA and its inherent follow-up strategy will optimize HF patient care as it is a promising device, which will essentially adapt innovation not to the disease but rather to the patients.

A Novel Non-Invasive Assessment of Cardiac Hemodynamics in Patients With Heart Failure and Atrial Fibrillation

Background

Heart failure (HF) and atrial fibrillation (AF) often coexist. The hemodynamic alterations induced by AF in patients with HF are well studied; however we lack reliable and non-invasive means to study these hemodynamic alterations in ambulatory patients. We sought to evaluate the clinical utility of impedance cardiography (ICG) as a novel and non-invasive tool to evaluate cardiac hemodynamics in ambulatory patients with HF and AF.

Methods

This was a single-center observational study. A convenient sample of ambulatory patients with chronic HF underwent non-invasive electrocardiogram (ECG) and hemodynamic monitoring using BioZ Dx impedance cardiographer. Hemodynamics were automatically computed and ECG data were interpreted by an independent reviewer.

Results

A total of 32 patients (62 ± 14 years of age; 66% male; ejection fraction 33±13%) were enrolled. There were no baseline demographic or clinical differences between those with AF (28%) and those without AF (72%). However, patients with AF exhibited lower stroke volume (60 ± 7 vs. 89 ± 29, P = 0.008), left ventricular work (33 ± 9 vs. 45 ± 13, P = 0.016), cardiac contractility (30 ± 8 vs. 40 ± 13, P = 0.037), and arterial elasticity (13 ± 5 vs. 21 ± 5, P = 0.012), as well as higher cardiac afterload (203 ± 57 vs. 151 ± 49, P = 0.015).

Conclusions

Using non-invasive ICG, we have shown that it is feasible to characterize hemodynamics in ambulatory HF patients. We show that AF compromises left ventricular function in patients with HF and is associated with excess afterload and reduced arterial elasticity.

Arterial Stiffness Is Associated With QTc Interval Prolongation in Patients With Heart Failure

BACKGROUND

A prolonged corrected QT (QTc) interval is a known risk factor for adverse cardiac events. Understanding the determinants and physiologic correlates of QTc is necessary for selecting proper strategies to reduce the risk of adverse events in high-risk patients. We sought to evaluate the role of arterial stiffness in heart failure as a determinant of QTc prolongation.

METHOD

This was an observational study that recruited ambulatory heart failure patients (New York Heart Association Classes I-II) from an outpatient heart failure clinic. In the supine resting position, consented patients underwent noninvasive 12-lead electrocardiograph (ECG) and hemodynamic monitoring using BioZ Dx impedance cardiography. ECGs were evaluated by a reviewer blinded to clinical data, and QTc interval was automatically computed. Patients with pacing or bundle branch block (BBB) were analyzed separately. Strengths of associations were evaluated using Pearson's r coefficients and multivariate linear regression.

RESULTS

The final sample ( N = 44) was 62 ± 13 years of age and 64% male with ejection fraction of 34% ± 12%. At univariate level, QTc interval moderately ( r > .50) correlated with cardiac output, left cardiac work index, systemic vascular resistance, and total arterial compliance in patients with intrinsically narrow QRS complexes. At the multivariate level, increasing systemic vascular resistance and decreasing total arterial compliance remained independent predictors of widening QTc interval in this group ( R² = .54). No significant correlations were seen in patients with pacing or BBB.

CONCLUSIONS

In the absence of conduction abnormalities, magnitude of arterial stiffness, an indirect measure of endothelial dysfunction, is associated with QTc interval prolongation.

Reduced Systolic Volume: Main Pathophysiological Mechanism in Patients with Orthostatic Intolerance?

Background

Orthostatic intolerance patients' pathophysiological mechanism is still obscure, contributing to the difficulty in their clinical management.

Objective

To investigate hemodynamic changes during tilt test in individuals with orthostatic intolerance symptoms, including syncope or near syncope.

Methods

Sixty-one patients who underwent tilt test at - 70° in the phase without vasodilators were divided into two groups. For data analysis, only the first 20 minutes of tilting were considered. Group I was made up of 33 patients who had an increase of total peripheral vascular resistance (TPVR) during orthostatic position; and Group II was made up of 28 patients with a decrease in TPVR (characterizing insufficient peripheral vascular resistance). The control group consisted of 24 healthy asymptomatic individuals. Hemodynamic parameters were obtained by a non-invasive hemodynamic monitor in three different moments (supine position, tilt 10' and tilt 20') adjusted for age.

Results

In the supine position, systolic volume (SV) was significantly reduced in both Group II and I in comparison to the control group, respectively (66.4 ±14.9 ml vs. 81.8±14.8 ml vs. 101.5±24.2 ml; p<0.05). TPVR, however, was higher in Group II in comparison to Group I and controls, respectively (1750.5± 442 dyne.s/cm⁵ vs.1424±404 dyne.s/cm⁵ vs. 974.4±230 dyne.s/cm⁵; p<0.05). In the orthostatic position, at 10', there was repetition of findings, with lower absolute values of SV compared to controls (64.1±14.0 ml vs 65.5±11.3 ml vs 82.8±15.6 ml; p<0.05). TPVR, on the other hand, showed a relative drop in Group II, in comparison to Group I.

Conclusion

Reduced SV was consistently observed in the groups of patients with orthostatic intolerance in comparison to the control group. Two different responses to tilt test were observed: one group with elevated TPVR and another with a relative drop in TPVR, possibly suggesting a more severe failure of compensation mechanisms.

Evaluation of patients with heart failure

Heart failure is one of the most prevalent cardiovascular diseases in the United States, and is associated with significant morbidity, mortality, and costs. Prompt diagnosis may help decrease mortality, hospital stay, and costs related to treatment. A complete heart failure evaluation comprises a comprehensive history and physical examination, echocardiogram, and diagnostic tools that provide information regarding the etiology of heart failure, related complications, and prognosis in order to prescribe appropriate therapy, monitor response to therapy, and transition expeditiously to advanced therapies when needed. Emerging technologies and biomarkers may provide better risk stratification and more accurate determination of cause and progression.

Elevated levels of interleukin 6 and C-reactive protein associated with cognitive impairment in heart failure

There is abundant evidence on inflammatory mechanisms in heart failure (HF) that are used for prognostication of the disease; however, data are lacking regarding the association between elevated cytokines, C-reactive protein (CRP), and cognition in HF. A cross-sectional pilot study of 38 patients with HF, aged 62 years (standard deviation± 9 years), predominantly men (68%) and Caucasian (79%) were screened for cognitive function using the Montreal Cognitive Assessment (MoCA). The study aimed to examine cognitive scores on MoCA with cytokines, interleukin 6 [IL-6] and tumor necrosis factor α [TNF-α], and CRP as indicators of early cognitive changes in HF. The result showed no direct correlation between cardiac variables and the MoCA score. The MoCA score, however, was inversely associated with IL-6 (r=-0.53, P=.001) and CRP (r=-0.34, P=.04), with no association to TNF-α. Regression analysis on the MoCA score and log-transformed IL-6 accounted for an additional 11% variation and remained statistically significant (P=.008) after controlling for covariates of education, living arrangements, and loneliness. The large effect size (R(2) =0.87) found in this pilot study provides rationale for a larger exploratory study to examine associations between cognitive function, cytokines, and CRP levels and help design future intervention studies.

Usefulness of lung impedance-guided pre-emptive therapy to prevent pulmonary edema during ST-elevation myocardial infarction and to improve long-term outcomes

Patients sustaining an ST-segment elevation myocardial infarction (STEMI) frequently develop pulmonary congestion or pulmonary edema (PED). We previously showed that lung impedance (LI) threshold decrease of 12% to 14% from baseline during admission for STEMI marks the onset of the transition zone from interstitial to alveolar edema and predicts evolution to PED with 98% probability. The aim of this study was to prove that pre-emptive LI-guided treatment may prevent PED and improve clinical outcomes. Five hundred sixty patients with STEMI and no signs of heart failure underwent LI monitoring for 84 ± 36 hours. Maximal LI decrease throughout monitoring did not exceed 12% in 347 patients who did not develop PED (group 1). In 213 patients LI reached the threshold level and, although still asymptomatic (Killip class I), these patients were then randomized to conventional (group 2, n = 142) or LI-guided (group 3, n = 71) pre-emptive therapy. In group 3, treatment was initiated at randomization (LI = -13.8 ± 0.6%). In contrast, conventionally treated patients (group 2) were treated only at onset of dyspnea occurring 4.1 ± 3.1 hours after randomization (LI = -25.8 ± 4.3%, p <0.001). All patients in group 2 but only 8 patients in group 3 (11%) developed Killip class II to IV PED (p <0.001). Unadjusted hospital mortality, length of stay, 1-year readmission rate, 6-year mortality, and new-onset heart failure occurred less in group 3 (p <0.001). Multivariate analysis adjusted for age, left ventricular ejection fraction, risk factors, peak creatine kinase, and admission creatinine and hemoglobin levels showed improved clinical outcome in group 3 (p <0.001). In conclusion, LI-guided pre-emptive therapy in patients with STEMI decreases the incidence of in-hospital PED and results in better short- and long-term outcomes.

Bedside assessment of cardiac hemodynamics: the impact of noninvasive testing and examiner experience

BACKGROUND

Knowledge of cardiac filling pressures is critical in the diagnosis and management of patients with dyspnea or heart failure. Echocardiography and B-natriuretic peptide (BNP) testing are commonly used to estimate these pressures, but their incremental value beyond physical examination remains unknown.

METHODS

Right and left heart filling pressures were prospectively estimated as "normal" or "abnormal" by staff cardiologists and cardiovascular trainees based upon physical examination findings alone, or examination coupled with echocardiographic and BNP data in patients referred for cardiac catheterization. Net reclassification improvement was calculated to determine whether echocardiographic/BNP data had incremental value in the determination of right and left heart pressures.

RESULTS

Two hundred fifteen observations were made by 9 examiners in 116 consecutive patients. Right and left heart pressures were accurately predicted from examination alone in 71% and 60% of observations, respectively. Examination-based accuracy was greater for staff cardiologists compared with trainees for right heart (82 vs 67%, P=.03) and left heart pressures (71% vs 55%, P=.03). Exposure to echocardiographic and BNP data did not enhance accuracy beyond bedside examination alone, both for left heart pressures (net reclassification improvement=-0.004; 95% confidence interval, -0.12-0.12) and right heart pressures (net reclassification improvement=0.02, 95% confidence interval, -0.09-0.13).

CONCLUSIONS

Cardiac filling pressures can be estimated from physical examination with modest accuracy, which is enhanced with experience. While echocardiographic and BNP data predict cardiac filling pressures, they may not provide information of incremental value beyond examination alone. Rigorous teaching and practice of cardiac examination skills should continue to be emphasized during medical training.

Effects of alcohol withdrawal on cardiovascular system

Alcohol withdrawal syndrome (AWS) develops after cessation of alcohol intake in alcoholic patients characterizing psychiatric symptoms and changes in autonomous nervous systems. We studied cardiovascular changes during different phases of AWS (1, 2, 3 and 10 days after admission for detoxification; n=34) and compared them with those in early recovery (at least 1 month of abstinence; n=30). The results study showed that cardiovascular system underwent significant changes during AWS characterizing the decrease of heart rate, systolic and diastolic blood pressures, and total peripheral resistance. Stroke index was lower during AWS than in early recovery. As the decreased stroke index was compensated by increased heart rate, cardiac index did not differ during AWS from that in early recovery. Increased functioning of noradrenaline (along with other central and peripheral regulating mechanisms) may be an important factor associated with cardiovascular changes in AWS. Normalization of this function after AWS leads to returning of cardiovascular parameters to baseline levels.

Refractory acute decompensated heart failure: an observational study on a noninvasive hemodynamic monitoring system aimed at improving the therapeutic approach

BACKGROUND

Inotropic agents should only be administered in acute decompensated heart failure (ADHF) refractory to vasodilators at optimal doses because they are associated with adverse outcome. In this setting a noninvasive hemodynamic monitoring system (NHMS) could be useful for optimizing treatment.

METHODS

INCLUSION CRITERIA

advanced chronic heart failure, ejection fraction 30% or less, admission for ADHF with systolic blood pressure 115 mmHg or less and inadequate response at 48 h of therapy. Patients were evaluated with a NHMS: with vascular systemic resistance (VSR) greater than 1500 dyne x s/cm we used vasodilators at increasing doses, with VSR less than 1500 and cardiac index (CI) less than 2.4 l/min per m inotropic agents were used.

RESULTS

The study population consisted of 20 patients (mean age 67 + or - 12 years) with ejection fraction 20 + or - 7%. After 48 h of clinical-guided therapy, none of the patients achieved VSR 1500 or less, and 12 patients had a CI less than 2.4 l/min per m. After hemodynamic-guided therapeutic optimization there was a significant reduction of dyspnea at rest (7.7 + or - 1.25 versus 2.44 + or - 1.33 on the 10-point Likert scale, P < 0.001) and 'cold' presentation (12 patients before and 1 patient after, P = 0.0004). Daily urinary volume was higher (1217 + or - 369 versus 2260 + or - 797 ml, P = 0.001) without renal function deterioration (creatinine 1.56 + or - 0.52 versus 1.34 + or - 0.61 mg/dl, P = 0.012).The nitroprusside dosing was increased after NHMS (0.13 + or - 0.19 versus 0.4 + or - 0.310 microg/kg per min, P = 0.044), whereas doses of inotropic agents, diuretics and beta-blockers did not change significantly.

CONCLUSIONS

In refractory ADHF a NHMS improves significantly symptoms and renal function, with a better use of vasodilators.

Monitoring in resuscitation: comparison of cardiac output measurement between pulmonary artery catheter and NICO

AIM

The cardiac output and coronary perfusion pressure generated from chest compressions during resuscitation manoeuvres can predict effectiveness and successful outcome. Until now, there is no good method for haemodynamic monitoring during resuscitation. Noninvasive partial carbon dioxide rebreathing system (NICO, Novametrix Medical Systems, Inc., Wallingford, CT, USA) is a relatively new non-invasive alternative to thermodilution for measuring cardiac output. The accuracy of the NICO system has not been evaluated during resuscitation. The aim of this study is to compare thermodilution cardiac output method with NICO system and to assess the utility of NICO during resuscitation.

METHODS AND DESIGN

Experimental study in 24 Yorkshire pigs. Paired measurements of cardiac output were determined during resuscitation (before ventricular fibrillation and after 5, 15, 30 and 45 min of resuscitation) in the supine position. The average of 3 consecutive thermodilution cardiac output measurements (10 ml 20 degrees C saline) was compared with the corresponding NICO measurement.

RESULTS

Bland and Altman plot and Lin's concordance coefficient showed a high correlation between NICO and thermodilution cardiac output measurements although NICO has a tendency to underestimate cardiac output when compared to thermodilution at normal values of cardiac output.

CONCLUSIONS

There is a high degree of agreement between cardiac output measurements obtained with NICO and thermodilution cardiac output during resuscitation. The present study suggests that the NICO system may be useful to measure cardiac output generated during cardiopulmonary resuscitation.

Emerging trends in minimally invasive haemodynamic monitoring and optimization of fluid therapy

BACKGROUND

For decades the pulmonary artery catheter has been the mainstay of cardiac output monitoring in critically ill patients, and pressure-based indices of ventricular filling have been used to gauge fluid requirements with acknowledged limitations. In recent years, alternative technologies have become available which are minimally invasive, allow beat-to-beat cardiac output monitoring and permit assessment of fluid requirements by volumetric means and by allowing assessment of heart-lung interaction in mechanically ventilated patients.

METHODS

A qualitative review of the basic science behind the transpulmonary dilution technique used in the measurement of cardiac output, global end-diastolic volume and extravascular lung water; the basic science and validation of pulse contour analysis methods of real-time cardiac output monitoring; the application and limitations of these technologies to guide rational fluid therapy in surgical and critically ill patients.

RESULTS

Transpulmonary dilution techniques correlate well with pulmonary artery catheter-derived measurement of cardiac output. Volumetric measures of preload appear to be superior to central venous and pulmonary artery occlusion pressures. Dynamic indices of preload responsiveness such as stroke volume variation are more useful than static measures in mechanically ventilated patients.

CONCLUSION

In fully mechanically ventilated patients, dynamic measurements of heart-lung interaction such as stroke volume variation are superior to static measures of preload in assessing whether a patient is volume-responsive (i.e. will increase stroke volume in response to a fluid challenge). For patients who are not fully mechanically ventilated, pulse contour analysis allows real-time assessment of increases in cardiac output in response to passive leg-raising.