Validation of thoracic electrical bioimpedance as a porcine research tool

Transpulmonary thermodilution in patients treated with veno-venous extracorporeal membrane oxygenation

BACKGROUND

We tested the effect of different blood flow levels in the extracorporeal circuit on the measurements of cardiac stroke volume (SV), global end-diastolic volume index (GEDVI) and extravascular lung water index derived from transpulmonary thermodilution (TPTD) in 20 patients with severe acute respiratory distress syndrome (ARDS) treated with veno-venous extracorporeal membrane oxygenation (ECMO).

METHODS

Comparative SV measurements with transesophageal echocardiography and TPTD were performed at least 5 times during the treatment of the patients. The data were interpreted with a Bland-Altman analysis corrected for repeated measurements. The interchangeability between both measurement modalities was calculated and the effects of extracorporeal blood flow on SV measurements with TPTD was analysed with a linear mixed effect model. GEDVI and EVLWI measurements were performed immediately before the termination of the ECMO therapy at a blood flow of 6 l/min, 4 l/min and 2 l/min and after the disconnection of the circuit in 7 patients.

RESULTS

170 pairs of comparative SV measurements were analysed. Average difference between the two modalities (bias) was 0.28 ml with an upper level of agreement of 40 ml and a lower level of agreement of -39 ml within a 95% confidence interval and an overall interchangeability rate between TPTD and Echo of 64%. ECMO blood flow did not influence the mean bias between Echo and TPTD (0.03 ml per l/min of ECMO blood flow; p = 0.992; CI - 6.74 to 6.81). GEDVI measurement was not significantly influenced by the blood flow in the ECMO circuit, whereas EVLWI differed at a blood flow of 6 l/min compared to no ECMO flow (25.9 ± 10.1 vs. 11.0 ± 4.2 ml/kg, p = 0.0035).

CONCLUSIONS

Irrespectively of an established ECMO therapy, comparative SV measurements with Echo and TPTD are not interchangeable. Such caveats also apply to the interpretation of EVLWI, especially with a high blood flow in the extracorporeal circulation. In such situations, the clinician should rely on other methods of evaluation of the amount of lung oedema with the haemodynamic situation, vasopressor support and cumulative fluid balance in mind.

TRIAL REGISTRATION

German Clinical Trials Register (DRKS00021050). Registered 03/30/2020 https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00017237.

A percutaneous swine model of myocardial infarction

INTRODUCTION

The aim of this study was to develop a percutaneous, low risk, and reproducible technique of MI that simulates human disease.

METHODS

MI was induced in 44 swine (32.8+/-7.2 kg) by percutaneous embolization coil deployment in the left anterior descending coronary artery. Hemodynamic measurements, left heart catheterization, and echocardiography were performed pre, post, and 30 days after MI. 3D NOGA viability mapping was performed at baseline and 30 days. Excised hearts were examined histologically.

RESULTS

Pre-MI mortality was 6.8% and 24 h mortality was 13.6%. All pigs that survived 24 h after MI remained alive at 30 days. The mean left ventricular ejection fraction decreased from 58.4% to 42.1% (p<0.001) at 30 days. The average thrombolysis in myocardial infarction score was 3, 0, and 1.5 at baseline, post-MI, and 30 days, respectively. At 30 days, the end diastolic diameter, end diastolic volume, end systolic volume, and wall motion index increased from 3.76 to 3.89 cm, 32.5 to 50.0 ml, 14.9 to 27.0 ml, and 1.01 to 1.38, respectively (all p<0.05), while the ejection fraction decreased from 56.5% to 49.4% (p<0.01). Additionally, at 30 days, statistically significant reductions in both unipolar and bipolar voltage in the mid and apical regions of the left ventricle were observed. Postmortem pathology showed a transmural scar in the apical anteroseptal regions with fibrosis in the MI region, which accounted for 14.8% and 14.2% of the total left and right ventricular myocardial area and volume, respectively.

DISCUSSION

This model of MI is reliable, reproducible, has a pathophysiology similar to humans, and a lower mortality and ventricular fibrillation rates compared to other models. This model may be used to evaluate the effects of pharmacologics, gene therapy, and stem cell transplantation for the treatment of cardiovascular disease as well as studying mechanisms of cardiac remodeling.

Safety and feasibility of percutaneous autologous skeletal myoblast transplantation in the coil-infarcted swine myocardium

INTRODUCTION

Autologous skeletal myoblast transplantation (ASMT) for myocardial regeneration is a promising new treatment for patients with congestive heart failure secondary to myocardial infarction (MI). However, non-surgical delivery could broaden the utility of this approach. The present study was designed to evaluate the safety and feasibility of transplanting autologous skeletal myoblast (ASM) via endovascular delivery into the infarcted swine myocardium.

METHODS

Seven female Yorkshire swine successfully underwent induced left ventricular MI. ASM biopsies were obtained from the hind limb of each animal and myoblasts were expanded in vitro. In a pilot experiment, ASM were labeled with iridium and short-term retention and biodistribution was determined 2 h after ASM delivery via the MyoStar needle-injection catheter inserted through the femoral artery. At 30 days post-infarction, the remaining animals were divided into three groups containing 2 animals each for percutaneous catheter delivery into the infarcted zone: group 1 control animals were injected with media only, group 2 and 3 animals were injected with approximately 300 x 10(6) and 600 x 10(6) ASM, respectively. Sixty days post-transplantation, the swine hearts were harvested.

RESULTS

During the 60-day period between transplantation and harvest, no adverse events were recorded, and continuous rhythm monitoring revealed no arrhythmias. In the small sampling size, myocardial function assessments revealed a trend toward improvement in the treatment groups with respect to ejection fraction, viability, and cardiac index. However, histology of treated swine hearts identified no skeletal muscle cells.

DISCUSSION

Percutaneous ASMT into an infarcted swine myocardium is feasible and safe, and may contribute to overall improved heart function.

Pressure recording analytical method (PRAM) for measurement of cardiac output during various haemodynamic states

BACKGROUND

Cardiac output (CO) can be measured using the pressure recording analytical method (PRAM), which is a new, less invasive technique allowing beat-by-beat stroke volume monitoring from the pressure signals recorded in femoral or radial arteries.

METHODS

We investigated PRAM by comparing its cardiac output (PRAM-CO) with paired measurements obtained by electromagnetic flowmetry (EM-CO) and by standard thermodilution (ThD-CO) during various haemodynamic states in a swine model. Nine pigs were monitored with a pulmonary artery catheter and a femoral artery catheter at baseline, in a hyperdynamic state produced by administration of dobutamine and in a hypodynamic state induced by progressive exsanguination. Bland-Altman analysis was used.

RESULTS

One hundred and eight paired cardiac output values over a range of EM-CO of 1.8-10.4 litre min(-1) resulted. We found close agreement between the techniques. Mean bias between EM-CO and PRAM-CO was -0.03 litre min(-1) (precision 0.58 litre min(-1)). The 95% limits of agreement were -0.61 to +0.55 litre min(-1). Similar results between ThD-CO and PRAM-CO were found.

CONCLUSIONS

In a porcine model we have demonstrated accuracy of PRAM during various haemodynamic states. PRAM is a reliable tool to detect changes in cardiac output in pigs and has ability as a basic research tool.

Bench to bedside: electrophysiologic and clinical principles of noninvasive hemodynamic monitoring using impedance cardiography

The evaluation of the hemodynamic state of the severely ill patient is a common problem in emergency medicine. While conventional vital signs offer some insight into delineating the circulatory pathophysiology, it is often impossible to determine the true clinical state from an analysis of blood pressure and heart rate alone. Cardiac output measurements by thermodilution have been the criterion standard for the evaluation of hemodynamics. However, this technology is invasive, expensive, time-consuming, and impractical for most emergency department environments. Impedance cardiography (ICG) is a noninvasive method of obtaining continuous measurements of hemodynamic data such as cardiac output that requires little technical expertise. ICG technology was first developed by NASA in the 1960s and is based on the idea that the human thorax is electrically a nonhomogeneous, bulk conductor. Variation in the impedance to flow of a high-frequency, low-magnitude alternating current across the thorax results in the generation of a measured waveform from which stroke volume can be calculated by a modification of the pulse contour method. To adequately judge the possible role of this technology in the practice of emergency medicine, it is important to have a sufficient understanding of the basic scientific principles involved as well as the clinical validity and limitations of the technique.

Evaluation of a new advanced thoracic bioimpedance device for estimation of cardiac output

OBJECTIVE

This study is an evaluation of a new thoracic bioimpedance cardiac output monitoring system which incorporates a modified form of the Kubicek equation and a method of estimating the left ventricular ejection time from the time derivative bioimpedance signals.

METHODS

The performance of the new system was compared with conventional thermodilution in a porcine model. One hundred and ninety nine (n = 199) paired measurements of thermodilution cardiac output (TDCO) (range 1.20-18.00 L/min) and thoracic bioimpedance cardiac output (BICO) were collected in 7 pigs. The bioimpedance measurements were adjusted for the animal's weight and chest circumference, thus compensating for the differences in the anatomy of pigs when compared to humans. Data were compared using weighted correlation coefficient and Bland-Altman analysis.

RESULTS

The weighted correlation coefficient between TDCO and BICO values was 0.87 (n = 199). The Bland-Altman technique yielded a precision of the device of +/-1.69 L/min with a bias of 0.11 L/min.

CONCLUSION

The results from the porcine study show that the new system performed well over a wide range of cardiac outputs, comparing favorably with data from other new bioimpedance cardiac output devices currently available in the market.

A meta-analysis of studies using bias and precision statistics to compare cardiac output measurement techniques

INTRODUCTION

Bias and precision statistics have succeeded regression analysis when measurement techniques are compared. However, when applied to cardiac output measurements, inconsistencies occur in reporting the results of this form of analysis.

METHODS

A MEDLINE search was performed, dating from 1986. Studies comparing techniques of cardiac output measurement using bias and precision statistics were surveyed. An error-gram was constructed from the percentage errors in the test and reference methods and was used to determine acceptable limits of agreement between methods.

RESULTS

Twenty-five articles were found. Presentation of statistical data varied greatly. Four different statistical parameters were used to describe the agreement between measurements. The overall limits of agreement in studies evaluating bioimpedance (n = 23) was +/-37% (15-82%) and in those evaluating Doppler ultrasound (n = 11) +/-65% (25-225%). Objective criteria used to assess outcome were given in only 44% of the articles. These were (i) limits of agreement approaching +/-15-20%, (ii) limits of agreement of less than 1 L/min, and (iii) more than 75% of bias measurements within +/-20% of the mean. Graphically, we showed that limits of agreement of up to +/-30% were acceptable.

CONCLUSIONS

When using bias and precision statistics, cardiac output, bias, limits of agreement, and percentage error should be presented. Using current reference methods, acceptance of a new technique should rely on limits of agreement of up to +/-30%.