Measurement of cardiac output with non-invasive Aesculon® impedance versus thermodilution

Induction of aggressive arterial and venous dilation therapy in addition to pulmonary dilation therapy (super-Fontan strategy) improves Fontan circulation both at rest and during treadmill exercise

Objective

Methods

Results

Conclusions

Usefulness of Optimization of Interventricular Delay Using an Electrical Cardiometry Method in Patients with Cardiac Resynchronization Therapy Implantation

There are no studies examining interventricular (VV) delay optimization by an electrical cardiometry method in relation to subsequent cardiac function in cardiac resynchronization therapy (CRT) -implanted patients. This study aimed to compare the VV delay in CRT-implanted patients by the dp/dt and electrical cardiometry and to examine the optimization of VV delay and improvement of cardiac function. We examined 19 consecutive CRT-implanted patients. The protocol included biventricular stimulation with either simultaneous or sequential pacing, and we evaluated systolic volume (SV) using an electrical cardiometry and the dp/dt of the left ventricle. The optimal VV delay was determined by the maximum SV using the electrical cardiometry. Two groups were defined, those whose increase in SV was at or above the median and those whose SV increase was below the median; changes in left ventricular ejection fraction (LVEF). The correlation between the VV delay optimized by the electrical cardiometry and dp/dt methods was high (R = 0.61, P = 0.006). Compared to the baseline SV (43.4 mL), the SV increased to 47.8 mL with simultaneous biventricular pacing (versus baseline P = 0.008) and further increased to 49.8 mL with optimized VV delay (versus simultaneous biventricular pacing P = 0.020). LVEF after 6 months significantly improved in the above-median SV increase group (37.6 versus 28.2%, P = 0.041), but not in the below-median SV increase group (26.5 versus 26.5%, P = 0.985). In conclusion, the optimal VV delay by electrical cardiometry method was almost concordant with that by the dp/dt method. Cardiac function significantly improved in the group with the above-median SV increase.

Implications of Doppler Echocardiography-guided Heart Rate Modulation Using Ivabradine

Objective Heart rate modulation therapy using ivabradine reduces both morbidity and mortality in patients with systolic heart failure. However, the target heart rate for this patient population remains to be elucidated. Methods In this prospective observational study, we included patients with heart failure and a reduced ejection fraction who received 5.0 mg/day of ivabradine for three days. At baseline and three days later, the overlap length between E-wave and A-wave using trans-mitral Doppler echocardiography, as well as the cardiac output using AESCLONE mini, were simultaneously measured. The associations between Δ overlap length and Δ cardiac output were then investigated. Results Eight patients [77 (53, 87) years old, 2 men] were included. The heart rate decreased from 81 (69, 104) bpm down to 64 (57, 79) bpm (p=0.012). The overlap length increased in four patients and decreased in the other four patients. During the time period of ivabradine therapy, patients who had a greater decrease in overlap length had a greater increase in cardiac output (r=0.84, p=0.009). Conclusion Decreases in the overlap length between E-wave and A-wave by Doppler echocardiography were associated with an increase in the cardiac output while on ivabradine therapy. The implications of Doppler echocardiography-guided heart rate modulation therapy targeting a minimal overlap length therefore require further evaluation in larger, prospective studies.

Combination therapy using trans-catheter aortic valve implantation and adaptive servo-ventilation in patient with aortic stenosis and heart failure

Severe aortic stenosis sometimes accompanies advanced heart failure with reduced cardiac contractility (i.e. low-flow low-gradient aortic stenosis). The therapeutic strategy for the remaining heart failure following trans-catheter aortic valve implantation remains unknown. An 84-year-old man with six hospitalizations due to aortic stenosis and congestive heart failure with reduced ejection fraction was admitted to our institute. Heart failure remained following trans-catheter aortic valve implantation. Additional adaptive servo-ventilation therapy with optimal pressure setting determined by the ramp test further improved his heart failure symptoms. Combination therapy using trans-catheter aortic valve implantation and adaptive servo-ventilation might be a promising therapeutic tool to ameliorate heart failure with severe aortic stenosis. <;Learning objective: Adaptive servo-ventilation might be a promising therapy in patients with persistent congestive heart failure following trans-catheter aortic valve implantation for severe aortic stenosis.>.

Implication of heart rate optimization in patients with heart failure

Prognostic impact of heart rate reduction therapy using ivabradine, a selective inhibitor of I_f channel that purely reduces heart rate, in patients with heart failure with reduced ejection fraction and sinus tachycardia has been demonstrated. However, ideal heart rate remains unknown. We experienced an 80-year-old woman with reduced left ventricular ejection fraction who was hospitalized due to congestive heart failure. Following the ivabradine administration that decreased her heart rate from 100 bpm down to around 60 bpm, the "overlap" between E-wave and A-wave in the trans-mitral Doppler echocardiography diminished, accompanied by an improvement in cardiac output. Heart rate optimization targeting to diminish the overlap between E-wave and A-wave might maximize cardiac output and improve the clinical course via facilitated cardiac reverse remodeling. Further studies are warranted to validate the implication of therapeutic strategy to aggressively minimize the echocardiographic "overlap" by heart rate reduction therapy in heart failure patients.

Bioimpedance analysis as a tool for hemodynamic monitoring: overview, methods and challenges

Recent advances in hemodynamic monitoring have seen the advent of non-invasive methods which offer ease of application and improve patient comfort. Bioimpedance Analysis or BIA is one of the currently employed non-invasive techniques for hemodynamic monitoring. Impedance Cardiography (ICG), one of the implementations of BIA, is widely used as a non-invasive procedure for estimating hemodynamic parameters such as stroke volume (SV) and cardiac output (CO). Even though BIA is not a new diagnostic technique, it has failed to gain consensus as a reliable measure of hemodynamic parameters. Several devices have emerged for estimating CO using ICG which are based on evolving methodologies and techniques to calculate SV. However, the calculations are generally dependent on the electrode configurations (whole body, segmental or localised) as well as the accuracy of different techniques in tracking blood flow changes. Blood volume changes, concentration of red blood cells, pulsatile velocity profile and ambient temperature contribute to the overall conductivity of blood and hence its impedance response during flow. There is a growing interest in investigating limbs for localised BIA to estimate hemodynamic parameters such as pulse wave velocity. As such, this paper summarises the current state of hemodynamic monitoring through BIA in terms of different configurations and devices in the market. The conductivity of blood flow has been emphasized with contributions from both volume and velocity changes during flow. Recommendations for using BIA in hemodynamic monitoring have been mentioned highlighting the suitable range of frequencies (1 kHz-1 MHz) as well as safety considerations for a BIA setup. Finally, current challenges in using BIA such as geometry assumption and inaccuracies have been discussed while mentioning potential advantages of a multi-frequency analysis to cover all the major contributors to blood's impedance response during flow.

Implication of Ivabradine in Up-titrating Beta-blocker in a Patient with Advanced Heart Failure

Titration of beta-blockers is a gold-standard therapy in patients with heart failure and a reduced ejection fraction but is sometimes challenging to administer, given symptomatic hypotension. Ivabradine is a recently introduced selective I_f channel inhibitor that purely reduces the heart rate. We encountered a patient with advanced heart failure in whom a beta-blocker could not be up-titrated given his symptomatic hypotension. Following the initiation of ivabradine, an increase in blood pressure due to heart rate optimization, probably via an improvement in the cardiac output, allowed for the further up-titration of carvedilol, followed by a successful clinical course. Ivabradine might be a novel therapeutic tool to facilitate the up-titration of beta-blockers in patients with heart failure and hypotension.

The implication of optimal heart rate in patients with systolic dysfunction following TAVR

Heart rate reduction therapy using ivabradine has demonstrated its prognostic implication in patients with heart failure with reduced ejection fraction. However, the target heart rate with optimal clinical outcomes, particularly for those with systolic dysfunction following a transcatheter aortic valve replacement (TAVR), remains unknown. Consecutive patients with left ventricular ejection fraction (LVEF) < 50% and sinus rhythm following TAVR received transthoracic echocardiography at index discharge. The ideal heart rate was calculated using a formula: 93 - 0.13 × (deceleration time [ms]). Those whose actual heart rates at discharge were within 10 bpm of the calculated ideal heart rate were assigned to the optimal heart rate group, and their prognosis was compared with those without. Twenty-four patients (83 [78, 85] years old, LVEF 41% [35%, 44%], 16 males) were included. The median difference between actual heart rate and ideal heart rate was 12 (0, 16) bpm and 11 patients were assigned to the optimal heart rate group. One year later, the optimal heart rate group achieved more improvement in LVEF (24% [15%, 28%] vs. 7% [7%, 12%], p = .003) and had lower heart failure readmission rates (0.059 vs. 0.116 events/year; p = .49). In conclusion, an optimal heart rate might be associated with cardiac reverse remodeling and prevention of heart failure recurrences in patients with systolic dysfunction following TAVR. The implication of deceleration time-guided heart rate optimization therapy for such cohorts remains the next concern.

Effect of Endovascular Treatment on Systemic Vascular Resistance in Patients with Lower-Limb Peripheral Artery Disease

Objective: Endovascular treatment (EVT) for lower-limb peripheral artery disease patients reduces blood pressure (BP) and improves prognosis. This study retrospectively examined hemodynamics during EVT to clarify the mechanism. Materials and Methods: Systemic vascular resistance (SVR) was measured using a noninvasive continuous cardiac output monitoring system during EVT. Furthermore, ankle brachial index was measured before and after EVT. Results: The study included 88 lesions of 56 patients (hypertension in 98%). SVR significantly decreased from 2409.1±746.8 dynes·s·cm^-5 to 2033.7±635.0 dynes·s·cm^-5 (p<0.0001). The difference in SVR before and after EVT was significantly greater in the Fontaine IV group than in the Fontaine IIa group (554.7±406.6 dynes·s·cm^-5 vs. 312.9±245.7 dynes·s·cm^-5, p=0.0151). The change in SVR was correlated with a change in mean BP in the upper limb (p=0.0026). When the change in pressure gradient between the upper limb and the diseased lower limb was large, mean BP of the upper limb significantly decreased (p=0.0022). Conclusion: EVT can reduce SVR and BP by canceling the pressure gradient between central BP and diseased lower-limb BP.

Safety Monitoring for Obstructive Hypertrophic Cardiomyopathy During Exercise

Patients with hypertrophic cardiomyopathy (HCM) are prohibited from engaging in intensive exercise, to avoid sudden death. Given that patients with HCM, even those without left-ventricular outflow tract obstruction at rest, potentially have exercise-induced obstruction, reasonable monitoring methods during exercise are required. We present the case of a woman with HCM with exercise-induced obstruction whose hemodynamics during stress echocardiography were under observation using noninvasive cardiac output monitoring. Stroke volume declined during exercise before the manifest elevation of the left-ventricular outflow tract pressure gradient. As shown here, a noninvasive monitoring method can be useful in monitoring hemodynamics during exercise in HCM patients.

Use of a Non-invasive Cardiac Output Measurement in a Patient with Low-output Dilated Cardiomyopathy

A 49-year-old man was diagnosed with acute cardiac insufficiency based on evidence of congestive heart failure. The non-invasive measurement of the cardiac output using an AESCULON^® mini showed low cardiac output (CO, 3.9 L/min). We administered an intravenous diuretic for cardiac edema and dobutamine drip for low cardiac output. Soon after starting dobutamine at 3.2 γ (microg/kg/min), the CO improved to 6.8 L/min. Combination therapy of diuretic and dobutamine resolved the heart failure. CO measurement by an AESCULON^® mini was safe, cost-effective, and convenient. Data output correlates with the CO by Swan-Ganz catheterization. The non-invasive measurement of the CO permitted a smooth recovery without recurrence in this patient.

Effect of hemodialysis on impedance cardiography (electrical velocimetry) parameters in children

BACKGROUND

Pediatric hemodialysis (HD) patients have a high incidence of cardiovascular morbidity and mortality. The study aim was to investigate whether impedance cardiography (electrical velocimetry, EV) is suitable as a hemodynamic trend monitoring tool in pediatric patients during HD.

METHODS

Measurements by EV were obtained before, during, and after HD in a prospective single-center pediatric observational study. In total, 54 dialysis cycles in four different pediatric patients with end-stage kidney disease on chronic HD were included. EV parameters analyzed were heart rate (HR), stroke volume (SV), stroke volume index (SI), cardiac output (CO), cardiac index (CI), thoracic fluid content (TFC), index of contractility (ICON), stroke volume variation (SVV), variation of ICON (VIC), R-R interval (TRR), pre-ejection period (PEP), left ventricular ejection time (LVET), and systolic time ration (STR). Systemic vascular resistance index (SVRI) was calculated.

RESULTS

EV did measure significant changes in cardiovascular parameters associated with HD. The following parameters increased after HD: HR (9%), SVV (19%), VIC (33%), PEP (8%), and STR (18%). A decrease after HD was measured in SV (18%), SI (18%), CO (10%), CI (10%), TFC (10%), ICON (7%), TRR (7%), LVET (8%), and LVET (8%). SVRI was not affected by HD. The changes were correlated to ultrafiltration. HD cycles without fluid withdrawal also altered cardiovascular parameters.

CONCLUSIONS

Pediatric HD with and without fluid withdrawal changes hemodynamic EV monitoring parameters. Possibly EV may be useful to optimize HD management in pediatric patients.

Accuracy and precision of non-invasive cardiac output monitoring by electrical cardiometry: a systematic review and meta-analysis

Cardiac output monitoring is used in critically ill and high-risk surgical patients. Intermittent pulmonary artery thermodilution and transpulmonary thermodilution, considered the gold standard, are invasive and linked to complications. Therefore, many non-invasive cardiac output devices have been developed and studied. One of those is electrical cardiometry. The results of validation studies are conflicting, which emphasize the need for definitive validation of accuracy and precision. We performed a database search of PubMed, Embase, Web of Science and the Cochrane Library of Clinical Trials to identify studies comparing cardiac output measurement by electrical cardiometry and a reference method. Pooled bias, limits of agreement (LoA) and mean percentage error (MPE) were calculated using a random-effects model. A pooled MPE of less than 30% was considered clinically acceptable. A total of 13 studies in adults (620 patients) and 11 studies in pediatrics (603 patients) were included. For adults, pooled bias was 0.03 L min^-1 [95% CI - 0.23; 0.29], LoA - 2.78 to 2.84 L min^-1 and MPE 48.0%. For pediatrics, pooled bias was - 0.02 L min^-1 [95% CI - 0.09; 0.05], LoA - 1.22 to 1.18 L min^-1 and MPE 42.0%. Inter-study heterogeneity was high for both adults (I² = 93%, p < 0.0001) and pediatrics (I² = 86%, p < 0.0001). Despite the low bias for both adults and pediatrics, the MPE was not clinically acceptable. Electrical cardiometry cannot replace thermodilution and transthoracic echocardiography for the measurement of absolute cardiac output values. Future research should explore it's clinical use and indications.

A Retrospective Study of Hemodynamic Changes in Patients After Off-Pump Coronary Artery Bypass Graft Surgery Using Impedance Cardiography

Background

This study aimed to investigate the role of impedance cardiography (ICG) to evaluate hemodynamic changes in patients after off-pump coronary artery bypass graft (OPCABG) surgery.

Material/Methods

One-hundred and sixty patients who had undergone OPCAGB were enrolled and assessed using New York Heart Association NYHA functional class (II, II, and IV). ICG was used to measure the stroke volume (SV), stroke volume index (SI), cardiac output per minute (CO/min), cardiac index (CI), end-diastolic volume (EDV), pre-ejection period (PEP), left ventricular ejection time (LVET), systolic time ratio (STR), left ventricular ejection fraction (LVEF), acceleration index (ACI), systemic vascular resistance (SVR), and thoracic fluid content (TFC). The ICG parameters were correlated with brain natriuretic peptide (BNP) and echocardiography parameters using multivariate regression analysis.

Results

The levels of CO, ACI, TFC, SVR, and BNP compared with ICG showed differences between NYHA functional class, with CO showing a significant difference (p<0.05). There were no significant differences between SV, SI, EDV, and LVEF before and after OPCAGB. Using ICG, the parameters of CI, LVEF, EDV, and TFC showed no significant correlation with BNP. SV, SI, CO, ACI, and LVET, which were negatively correlated with BNP. SVR, PEP, and STR were positively correlated with BNP (P<0.05).

Conclusions

In patients who had OPCABG, the findings from ICG were significantly correlated with BNP levels and the results from echocardiography for the evaluation of cardiac hemodynamic changes. ICG might have a role in the assessment of cardiac function in clinical practice.

Diagnostic and Outcome Prediction Value of Transthoracic Impedance Cardiography in Heart Failure Patients During Heart Failure Flare-Ups

BACKGROUND This study aimed at evaluating the diagnostic and outcome prediction value of transthoracic impedance cardiography (ICG) in heart failure (HF) patients admitted for in-hospital treatment due to flare-ups of their condition. MATERIAL AND METHODS In total, 120 patients of intensive care units who were admitted due to HF flare-ups were involved to the study. The findings of ICG were compared to data obtained by other methods used for diagnosing HF. RESULTS Statistically significant (p<0.001) results were obtained when evaluating differences in ICG data between admission and discharge from the intensive care unit. In addition, a correlation was detected between brain natriuretic peptide (BNP) and thoracic fluid content index (r=0.4, p<0.001). Differences in ICG values, and BNP data emerged after the participants were grouped according to NYHA classes (p<0.05). The evaluation of lethal outcome during 6 months after the discharge yielded statistically significant results: BNP ≥350 pg/mL (Odds Ratio (OR) 4.4), thoracic fluid content ≥34 1/kOhm (OR 4.3), and systolic time ratio ≥0.55 (OR 2.9), p<0.05. CONCLUSIONS ICG data might be applied for the diagnosis and prognosis of HF, although the links between ICG and HF need further evaluation.

Non-invasive measurement of cardiac output in children with repaired coarctation of the aorta using electrical cardiometry compared to transthoracic Doppler echocardiography

OBJECTIVE

To evaluate the equivalence of the ICON^® electrical cardiometry (EC) haemodynamic monitor to measure cardiac output (CO) relative to transthoracic Doppler echocardiography (TTE) in paediatric patients with repaired coarctation of the aorta (CoA).

APPROACH

A group of n  =  28 CoA patients and n  =  27 matched controls were enrolled. EC and TTE were performed synchronously on each participant and CO measurements compared using linear regression and Bland-Altman analysis. The CoA group was further subdivided into two groups, with n  =  10 and without n  =  18 increased left ventricular outflow tract velocity (iLVOTv) for comparison.

MAIN RESULTS

CO measurements from EC and TTE in controls showed a strong correlation (R  =  0.80, p  <  0.001) and an acceptable percentage error (PE) of 28.1%. However, combining CoA and control groups revealed a moderate correlation (R  =  0.57, p  <  0.001) and a poor PE (44.2%). We suspected that the CO in a subset of CoA participants with iLVOTv was overestimated by TTE. Excluding the iLVOTv CoA participants improved the correlation (R  =  0.77, p  <  0.001) and resulted in an acceptable PE of 31.2%.

SIGNIFICANCE

CO measurements in paediatric CoA patients in the absence of iLVOTv are clinically equivalent between EC and TTE. The presence of iLVOTv may impact the accuracy of CO measurement by TTE, but not EC.

Impact of Obesity on Noninvasive Cardiac Hemodynamic Measurement by Electrical Cardiometry in Adults With Aortic Stenosis

OBJECTIVES

There are substantial potential benefits to noninvasive cardiac monitoring methods, such as electrical cardiometry (EC), over more invasive methods, including significantly reduced risk of complications, lower up-front and operational costs, ease of use, and continuous monitoring. To take advantage of these technologies, clinical equivalence to currently established methods must be determined. The authors sought to determine if the noninvasive measurement of cardiac index (CI) by EC was clinically equivalent to thermodilution (TD) in adult patients with aortic stenosis (AS).

DESIGN

This is a cross-sectional study comparing measurement devices in a single patient group.

SETTING

Single-center, university teaching hospital.

PARTICIPANTS

The study included 52 adult patients with aortic stenosis undergoing right heart catheterization.

INTERVENTIONS

Cardiac output (CO) was measured concurrently using EC with an ICON device and TD in 52 participants with AS. CI values were to determine the accuracy and precision of EC in reference to TD. Percentage error (PE) was used to assess their clinical equivalence. The participants were divided further into groups (normal and overweight/obese) based on body mass index and the analysis was repeated.

MEASUREMENTS AND MAIN RESULTS

CO measurement made by EC in adult patients with obesity or overweight was reduced significantly relative to TD. This was not observed in normal-weight adult AS patients. EC provided clinically equivalent measurements to TD for measuring CI in normal-weight adult AS patients (PE = 25.0%), but not for those adult AS patients with overweight or obesity (PE = 42.3%).

CONCLUSION

Overall, the ICON device produced lower CO and index measurements relative to TD in adult patients with AS. Overweight and obesity also significantly affected the relative precision and accuracy of the ICON electrical cardiometric device to measure CI in these patients.

Comparison of bioreactance non-invasive cardiac output measurements with cardiac magnetic resonance imaging

Impedance cardiography measurement of cardiac output gained wide interest due to its ease of use and non-invasiveness. However, validation studies of different algorithms yielded diverging results. Bioreactance (BR) as a recent adaption differs fundamentally as the flow signal is derived from phase shifts. Our aim was to assess the accuracy and reproducibility of BR, as compared to the non-invasive gold standard--cardiac magnetic resonance imaging (CMR). We prospectively included 32 stable patients. BR was performed twice in the supine position and averaged over 30 seconds. Mean bias was 0.2 ± 1.8 l/minute (1 ± 28%, percentage error 55%) with limits of agreement ranging from  -3.4 to 3.7 l/minute. Reproducibility was acceptable with a mean bias of 0.1 ± 0.9 l/minute (1 ± 14%, 27%). Low cardiac output was significantly overestimated (-1.1 ± 1.5 l/minute), while high cardiac output was underestimated (1.5 ± 1.7 l/minute), (P=0.001), although reproducibility was unaffected. Bias and weight were moderately correlated in men (r = 0.50, P=0.02). No differences for accuracy were found in nine patients who had an arrhythmia (0.3 ± 1.4 versus 0.1 ± 2.0 l/minute, P=0.76), while clinically relevant differences were found in patients with mild aortic valve disease (1.9 ± 2.2 versus -0.3 ± 1.7 l/minute, P=0.02). Overall, BR showed insufficient agreement with CMR, overestimating low and underestimating high cardiac output states. Reproducibility was acceptable and not negatively affected by the circulatory condition. Consequently, absolute values acquired with BR should be interpreted with caution and must not be used interchangeably in clinical practice.

Identification of the State of Maximal Hyperemia in the Assessment of Coronary Fractional Flow Reserve Using Non-Invasive Electrical Velocimetry

Previous research revealed that, in patients with coronary pressure-derived fractional flow reserve (FFR) in the 'grey zone' (0.75-0.85), repeated FFR assessments sometimes yield conflicting results. One of the causes of the fluctuations in FFR values around the grey zone may be imprecise identification of the point where maximal hyperemia is achieved. Identification of the state of maximal hyperemia during assessment of FFR can be challenging. This study aimed to determine whether non-invasive electrical velocimetry (EV) can be used to identify the state of maximal hyperemia.Stroke volume (SV), SV variation (SVV), and systemic vascular resistance index (SVRI) were determined by EV in 15 patients who underwent FFR assessment. Time intervals from initiation of adenosine infusion to achieving maximal hyperemia (time^mFRR), as well as to achieving maximal cardiac output (CO), SV, SVV, and SVRI (time^mCO, time^mSV, time^mSVV, and time^mSVRI, respectively), were determined. Time^mCO and time^mSVV were closer to time^mFRR than other values (time^mSVV/time^mFRR versus time^mSVRI/time^mFRR = 1.03 ± 0.2 versus 1.36 ± 0.4, P < 0.05). The maximum of SV was difficult to determine owing to considerable variations, but the maximum of SVV was clearly recognized. Time^mCO and time^mSVV were significantly correlated with time^mFFR, with time^mSVV showing a stronger correlation than time^mSV (time^mSVV: r = 0.92, P < 0.01; time^mCO: r = 0.80, P < 0.01).Maximal SVV is reached close to maximal hyperemia. Monitoring of SVV with non-invasive EV during FFR assessment can help identify the state of maximal hyperemia.

Applicability of Impedance Cardiography During Heart Failure Flare-Ups

BACKGROUND Heart failure (HF) accounts for about 5% of all causes of urgent hospital admissions, and the overall mortality of HF patients within 1 year after hospitalization is 17-45%. Transthoracic impedance cardiography (ICG) is a safe, non-invasive diagnostic technique that helps to detect various parameters that define different cardiac functions. The aim of this study was to investigate the value of ICG parameters in patients hospitalized due to HF flare-ups. MATERIAL AND METHODS The study included 60 patients (24 women and 36 men) who were admitted to intensive care units because of an acute episode of HF without signs of myocardial infarction. The diagnosis of HF as the main reason for hospitalization was verified according to the universally accepted techniques. ICG data were compared to those obtained via other HF diagnostic techniques. RESULTS A moderately strong relationship was found between the ejection fraction (EF) and the systolic time ratio (STR) r=-0.4 (p=0.002). Findings for STR and thoracic fluid content index (TFCI) differed after dividing the subjects into groups according to the EF (p<0.05). A moderately strong relationship was found between brain natriuretic peptide and TFCI r=0.425 (p=0.001), left cardiac work index (LCWI) r=-0.414 (p=0.001). Findings for TFCI, LCWI, and cardiac output differed after dividing the subjects into groups according to HF NYHA classes (p<0.05). CONCLUSIONS Transthoracic impedance cardiography parameters could be applied for the diagnostics and monitoring of HF, but further studies are required to evaluate the associations between ICG findings and HF.

Influence of electrode positioning on accuracy and reproducibility of electrical velocimetry cardiac output measurements

Electrical velocimetry (EV) is one of the most recent adaptions of impedance cardiography. Previous studies yielded diverging results identifying several factors negatively influencing accuracy. Although electrode arrangement is suspected to be an influencing factor for impedance cardiography in general, no data for EV is available. We aimed to prospectively assess the influence of electrode position on the accuracy and reproducibility of cardiac output (CO) measurements obtained by EV. Two pairs of standard electrocardiographic electrodes were placed at predefined positions of the thorax in 81 patients. The inter-electrode gap was varied between either 5 or 15 cm by caudal movement of the lowest electrode. Measurements were averaged over 20 s and performed twice at each electrode position. Reference values were determined using cardiac magnetic resonance imaging (CMR). Mean bias was 1.2  ±  1.6 l min(-1) (percentage error 22  ±  28%) between COCMR and COEV at the 5 cm gap significantly improving to 0.5  ±  1.6 l min(-1) (8  ±  28%) when increasing the gap (p  <  0.0001). The mean difference between repeated measurements was 0.0  ±  0.3 l min(-1) for the 5 cm and 0.1  ±  0.3 l min(-1) for the 15 cm gap, respectively (p  =  0.3). The accuracy of EV can be significantly improved when increasing the lower inter-electrode gap still exceeding the Critchley and Critchley recommendations. Therefore, absolute values should not be used interchangeably in clinical routine. As the reproducibility was not negatively affected, serial hemodynamic measurements can be reliably acquired in stable patients when the electrode position remains unchanged.

Non-Invasive Determination of Cardiac Output in Pre-Capillary Pulmonary Hypertension

Background

Cardiac output (CO) is a major diagnostic and prognostic factor in pre-capillary pulmonary hypertension (PH). Reference methods for CO determination, like thermodilution (TD), require invasive procedures and allow only steady-state measurements. The Modelflow (MF) method is an appealing technique for this purpose as it allows non-invasive and beat-by-beat determination of CO.

Methods

We aimed to compare CO values obtained simultaneously from non-invasive pulse wave analysis by MF (CO_MF) and by TD (CO_TD) to determine its precision and accuracy in pre-capillary PH. The study was performed on 50 patients with pulmonary arterial hypertension (PAH) or chronic thrombo-embolic PH (CTEPH). CO was determined at rest in all patients (n = 50) and during nitric oxide vasoreactivity test, fluid challenge or exercise (n = 48).

Results

Baseline CO_MF and CO_TD were 6.18 ± 1.95 and 5.46 ± 1.95 L·min^-1, respectively. Accuracy and precision were 0.72 and 1.04 L·min^-1, respectively. Limits of agreement (LoA) ranged from -1.32 to 2.76 L·min^-1. Percentage error (PE) was ±35.7%. Overall sensitivity and specificity of CO_MF for directional change were 95.2% and 82.4%, (n = 48) and 93.3% and 100% for directional changes during exercise (n = 16), respectively. After application of a correction factor (1.17 ± 0.25), neither proportional nor fixed bias was found for subsequent CO determination (n = 48). Accuracy was -0.03 L·min−1 and precision 0.61 L·min⁻¹. LoA ranged from -1.23 to 1.17 L·min⁻¹ and PE was ±19.8%.

Conclusions

After correction against a reference method, MF is precise and accurate enough to determine absolute values and beat-by-beat relative changes of CO in pre-capillary PH.

Propofol effect on cerebral oxygenation in children with congenital heart disease

Propofol is a short-acting, intravenously administered hypnotic agent which is used in procedural sedation in children. Propofol is known to decrease systemic vascular resistance, arterial blood pressure and can lead to desaturations and decreased systemic perfusion in children with cardiac shunting. This may result in a reduction in cerebral blood flow and oxygenation. Near-infrared spectroscopy (NIRS) can monitor cerebral tissue oxygenation in the frontal neocortex. The objective of our study was to measure the changes in cerebral oxygen and blood supply after Propofol infusion in children with congenital heart disease. Propofol infusion may reduce cerebral oxygenation in children with congenital heart disease. The study group consisted of 32 children (f:m = 18:14), with median age of 49 (5-112) months and median weight of 15 (5-34) kg. We performed NIRS derived continuous measurement of cerebral oxygenation and cardiac output using Electrical velocimetry for 5 min before and after sedation with Propofol (1-2 mg/kg i.v.) for cardiac catheterization. Simultaneously, non-invasive arterial blood pressure and transcutaneous oxygen saturation were measured. Propofol sedation led to a significant decrease in mean arterial pressure (79 ± 16 vs. 67 ± 12 mmHg) (p = 0.01) and cardiac index (3.2 ± 0.8 vs. 2.9 ± 0.6 ml/min/m(2)) (p = 0.03). In contrast, cerebral tissue oxygenation index, increased significantly from 57 ± 11 to 59 ± 10 % (p < 0.05). Sedation with Propofol increased cerebral tissue oxygenation despite a decrease in cardiac index and arterial blood pressure. This may be caused by a decreased oxygen consumption of the sedated brain with intact cerebral auto-regulation.

Determination of cardiac output with dynamic contrast-enhanced computed tomography

Cardiac output (CO) is an important diagnostic and prognostic factor in the haemodynamic evaluation of patients. The gold standard for CO measurement, thermodilution, requires an invasive right-heart catheterisation (RHC). In this pilot study we aimed to determine the accuracy of non-invasive CO determination from dynamic contrast-enhanced computed tomography (CT) compared to thermodilution. Patients who underwent diagnostic or follow-up RHC due to suspected or known pulmonary vascular disease at our department and required a thoracic CT between June 2011 and August 2012 were included. CO was determined from CT attenuation-time curves in the pulmonary artery and the ascending aorta using a dynamic contrast-enhanced CT sequence. CO determined in N = 18 patients by dynamic CT in the pulmonary artery was in very good agreement with thermodilution data (r = 0.84). Bland-Altman analysis showed a systematic overestimation of 0.7 ± 0.6 l/min compared to thermodilution. Data from the ascending aorta also showed a good correlation, but with a larger scattering of the values. The average effective dose for the dynamic investigation was 1.2 ± 0.7 mSv. CO determined with dynamic contrast-enhanced CT in the main pulmonary artery reliably predicts the values obtained by thermodilution during RHC. This non-invasive technique might provide an alternative for repeated invasive right-heart catheter investigations in the follow-up of pulmonary arterial hypertension patients.

Hemodynamic monitoring in the critical care environment

Hemodynamic monitoring is essential to the care of the critically ill patient. In the hemodynamically unstable patient where volume status is not only difficult to determine, but excess fluid administration can lead to adverse consequences, utilizing markers that guide resuscitation can greatly affect outcomes. Several markers and devices have been developed to aid the clinician in assessing volume status with the ultimate goal of optimizing tissue oxygenation and organ perfusion. Early static measures of volume status, including pulmonary artery occlusion pressure and central venous pressure, have largely been replaced by newer dynamic measures that rely on real-time measurements of physiological parameters to calculate volume responsiveness. Technological advances have lead to the creation of invasive and noninvasive devices that guide the physician through the resuscitative process. In this manuscript, we review the physiologic rationale behind hemodynamic monitoring, define the markers of volume status and volume responsiveness, and explore the various devices and technologies available for the bedside clinician.

Cardiac parameters in children recovered from acute illness as measured by electrical cardiometry and comparisons to the literature

Electrical cardiometry (EC) is a non-invasive cardiac output method that can assess cardiac index (CI) and stroke index (SI) but there are no reference values for children per se. The primary aim of this study was to develop reference values for clinical application. The secondary aim was to compare the EC measurements to published values. We performed a prospective observational study in patients (<21 years of age) without structural heart disease who had recovered from an acute illness. EC recordings in children that had normal heart rate and mean arterial blood pressure at discharge were eligible for analysis. The relationship of CI or SI and age in children was performed by regression analysis. Similar analysis was performed comparing measurements by EC to cardiac parameters values compiled from reference sources to assess bias in EC. Eighty-three children (2 weeks-21 years of age) were studied. There was a significant curvilinear relationship between CI or SI and age by EC (F-test, p < 0.05). Regression curves of cardiac parameters reported in the literature using 6 Fick's method, thermodilution, echocardiography and cardiac MRI were the same or higher than (0-19.6 %) values obtained with EC, with higher values being statistically significant (p < 0.05 all). There is a curvilinear relationship of CI or SI and age by EC in normal children. Cardiac parameters reported in the literature using alternative methods are different from those obtained with EC but are within acceptable ranges, with EC biased to underestimate CI. Adjustment of target value is required for EC goal-directed therapies.