Feasibility of perflutren microsphere contrast transthoracic echocardiography in the visualization of ventricular endocardium during venovenous extracorporeal membrane oxygenation in a validated ovine model

Echocardiographic image quality deteriorates with the severity of cardiogenic shock

BACKGROUND

Transthoracic echocardiography (TTE) is the primary tool for assessing left ventricular (LV) function in cardiogenic shock (CS). However, inadequate image quality often hinders it. In this retrospective study, we investigated factors associated with LV image quality in patients admitted to the intensive care unit (ICU) with ischemic CS.

RESULTS

Two critical care physicians accredited in echocardiography independently reviewed the TTEs of 100 patients admitted to our tertiary cardiac ICU with ST-elevation myocardial infarction complicated by CS between October 2016 and September 2019. Endocardial border definition (EBD) was graded for each myocardial segment of the apical 4-chamber and 2-chamber views using a conventional scoring system (1 = good, 2 = suboptimal, 3 = poor, and 4 = not possible). The biplane EBD index (EBDi) was calculated by averaging all segments from both views. An average EBDi of both observers was correlated with clinical and echocardiographic parameters. The median age was 62 years [54, 73], and 78% were males. LV ejection fraction and cardiac index (CI) medians were 29% [20, 35] and 1.93 l/min/m2 [1.40, 2.51], respectively. The median biplane EBDi was nearly suboptimal (1.833 [1.542, 2.083]). There was no correlation between EBDi and age, sex, or body mass index. However, biplane EBDi demonstrated statistically significant correlations with PaO2 (r2 = 0.066, p = 0.01), mean arterial pressure (MAP, r2 = 0.055, p = 0.03), CI (r2 = 0.105, p < 0.01), tricuspid annulus systolic velocity (RV S', r2 = 0.092, p = 0.01), and tricuspid regurge maximum velocity (TR Vmax, r2 = 0.067, p = 0.01). In a multivariate model, only CI correlated independently with EBDi (r2 = 0.105, p < 0.01). The biplane EBDi predicted CI (area under the curve (AUC) 0.70, p = 0.001) with good sensitivity (71%) and reasonable specificity (61%).

CONCLUSIONS

The study suggests that in patients admitted to the ICU with ischemic CS, LV image quality by TTE deteriorates with the severity of shock, as indicated by CI.

Ultrasound-Enhancing Agent Safely Enhances Left Ventricular Visualization by Transthoracic Echocardiography in Patients on ECMO Support

OBJECTIVE

The authors investigated if the use of ultrasound-enhancing agents (UEA) can safely improve left ventricular (LV) image quality by transthoracic echocardiography (TTE) in patients on extracorporeal membrane oxygenation (ECMO).

DESIGN AND SETTING

This study was performed in a tertiary cardiothoracic and ECMO center in London, United Kingdom.

PARTICIPANTS

The authors included 18 prospectively identified consecutive patients requiring TEE supported on peripherally implanted ECMO.

INTERVENTION AND MEASUREMENTS

TTE was performed before and after the UEA administration. The authors assessed the LV image quality using the biplane (apical-4-chamber and apical-2-chamber views) endocardial border definition index (1 = good, 2 = suboptimal, 3 = poor, and 4 = unavailable), as well as the feasibility of LV ejection fraction (LVEF) measurement. The authors also gathered sequential clinical information for the next 24 hours.

MAIN RESULTS

The patients' median age was 47 years (35, 65), and 5 (28%) were women. The biplane endocardial border definition index improved from the suboptimal to the good range (2.167 [1.812, 3.042] v 1.500 [1.417, 1.792], p = 0.0004) after the use of UEA. The feasibility of LVEF tripled from 25% (n = 5) to 83% (n = 15) (p = 0.0008) with UEA use. The UEA did not set off the bubble alarm and did not impact clinical or ECMO parameters.

CONCLUSION

The use of UEA significantly improved the quality of LV biplane images by transthoracic echocardiography, transforming them from suboptimal to good in patients supported with peripherally implanted ECMO. UEA use tripled the feasibility of measuring LVEF by TTE without affecting clinical and ECMO parameters.

Contrast-Enhanced Echocardiography Application in Patients Supported by Extracorporeal Membrane Oxygenation (ECMO): A Narrative Review

Extracorporeal membrane oxygenation (ECMO) is a lifesaving intervention increasingly used to support patients with severe respiratory and cardiac dysfunction. Echocardiography is an important tool, aiding implantation and monitoring during ECMO therapy, but often its use is limited by poor acoustic windows. This limitation may be overcome by the use of echocardiography contrast agents to improve diagnostic yield and reduce the need for other imaging modalities that may require patient transfer, involve ionizing radiation and, occasionally, nephrotoxic radio-opaque contrast medium. In this article the authors review the literature addressing the use of contrast-enhanced echocardiography (CEE) in ECMO-supported patients. The authors discuss the role of CEE in guiding implantation of ECMO, cardiac assessment and diagnosis of complications during ECMO therapy, as well as the safety of ultrasound-enhancing agents in this cohort of patients.

Cardiorespiratory physiological perturbations after acute smoke-induced lung injury and during extracorporeal membrane oxygenation support in sheep

Background: Numerous successful therapies developed for human medicine involve animal experimentation. Animal studies that are focused solely on translational potential, may not sufficiently document unexpected outcomes. Considerable amounts of data from such studies could be used to advance veterinary science. For example, sheep are increasingly being used as models of intensive care and therefore, data arising from such models must be published. In this study, the hypothesis is that there is little information describing cardiorespiratory physiological data from sheep models of intensive care and the author aimed to analyse such data to provide biological information that is currently not available for sheep that received extracorporeal life support (ECLS) following acute smoke-induced lung injury. Methods: Nineteen mechanically ventilated adult ewes undergoing intensive care during evaluation of a form of ECLS (treatment) for acute lung injury were used to collate clinical observations. Eight sheep were injured by acute smoke inhalation prior to treatment (injured/treated), while another eight were not injured but treated (uninjured/treated). Two sheep were injured but not treated (injured/untreated), while one received room air instead of smoke as the injury and was not treated (placebo/untreated). The data were then analysed for 11 physiological categories and compared between the two treated groups. Results: Compared with the baseline, treatment contributed to and exacerbated the deterioration of pulmonary pathology by reducing lung compliance and the arterial oxygen partial pressure to fractional inspired oxygen (PaO 2/FiO 2) ratio. The oxygen extraction index changes mirrored those of the PaO 2/FiO 2 ratio. Decreasing coronary perfusion pressure predicted the severity of cardiopulmonary injury. Conclusions: These novel observations could help in understanding similar pathology such as that which occurs in animal victims of smoke inhalation from house or bush fires, aspiration pneumonia secondary to tick paralysis and in the management of the severe coronavirus disease 2019 (COVID-19) in humans.

Contrast-Enhanced Ultrasound in Extracorporeal Support: In Vitro Studies and Initial Experience and Safety Data in the Extreme Premature Fetal Lamb Maintained by the Extrauterine Environment for Neonatal Development

OBJECTIVES

To evaluate the effects of ultrasound contrast agent (UCA) administration on hemodynamic parameters and support equipment in in vitro and in vivo models of extracorporeal support.

METHODS

In vitro, incrementally increasing bolus doses of a UCA were administered proximal to a membrane oxygenator, and ultrasound cine clips were obtained. The rates of microbubble destruction across the oxygenator and over time were calculated from time-intensity-curves. Measurements across the membrane oxygenator were recorded and compared by a repeated-measures analysis of variance. In vivo, 7 premature fetal lambs were transferred from placental support to the extrauterine environment for neonatal development. Contrast agent boluses were administered for contrast-enhanced ultrasound (CEUS) examinations. Hemodynamic parameters and serum laboratory values were evaluated before and after the examinations by paired t tests. For oxygenator staining, oxygenator membranes from the in vitro circuit, study animals (n = 4), and control animals (n = 4) were stained for the adherent UCA.

RESULTS

In vitro, with all doses (0.1-4 mL), there was no difference in measured parameters across the oxygenator (P ≥ .09). Contrast agent destruction (3%-14%) across the oxygenator was observed at the first pass with a progressive decline in contrast intensity over time. In vivo, there was no difference in hemodynamic parameters or serum laboratory values (P ≥ .08) with any CEUS examination (n = 17). For oxygenator staining, all oxygenator membranes were negative for UCA with lipid staining.

CONCLUSIONS

The UCA had no detectable effect on the oxygenator or measured parameters in in vitro and in vivo studies, thus providing additional safety data to support the use of CEUS in the setting of extracorporeal support.

Echocardiographic assessment of myocardial function and mechanics during veno-venous extracorporeal membrane oxygenation

BACKGROUND

Transthoracic echocardiography (TTE) plays a fundamental role in the management of patients supported with extra-corporeal membrane oxygenation (ECMO). In light of fluctuating clinical states, serial monitoring of cardiac function is required. Formal quantification of ventricular parameters and myocardial mechanics offer benefit over qualitative assessment. The aim of this research was to compare unenhanced (UE) versus contrast-enhanced (CE) quantification of myocardial function and mechanics during ECMO in a validated ovine model.

METHODS

Twenty-four sheep were commenced on peripheral veno-venous ECMO. Acute smoke-induced lung injury was induced in 21 sheep (3 controls). CE-TTE with Definity using Cadence Pulse Sequencing was performed. Two readers performed image analysis with TomTec Arena. End diastolic area (EDA, cm2), end systolic area (ESA, cm2), fractional area change (FAC, %), endocardial global circumferential strain (EGCS, %), myocardial global circumferential strain (MGCS, %), endocardial rotation (ER, degrees) and global radial strain (GRD, %) were evaluated for UE-TTE and CE-TTE.

RESULTS

Full data sets are available in 22 sheep (92%). Mean CE EDA and ESA were significantly larger than in unenhanced images. Mean FAC was almost identical between the two techniques. There was no significant difference between UE and CE EGCS, MGCS and ER. There was significant difference in GRS between imaging techniques. Unenhanced inter-observer variability was from 0.48-0.70 but significantly improved to 0.71-0.89 for contrast imaging in all echocardiographic parameters.

CONCLUSION

Semi-automated methods of myocardial function and mechanics using CE-TTE during ECMO was feasible and similar to UE-TTE for all parameters except ventricular areas and global radial strain. Addition of contrast significantly decreased inter-observer variability of all measurements.

Contrast Microsphere Destruction by a Continuous Flow Ventricular Assist Device: An In Vitro Evaluation Using a Mock Circulation Loop

OBJECTIVES

Transthoracic echocardiography (TTE) is fundamental in managing patients supported with ventricular assist devices (VAD). However imaging can be difficult in these patients. Contrast improves image quality but they are hydrodynamically fragile agents. The aim was to assess contrast concentration following passage through a VAD utilising a mock circulation loop (MCL).

METHODS

Heartware continuous flow (CF) VAD was incorporated into a MCL. Definity® contrast was infused into the MCL with imaging before and after CF-VAD. 5 mm2 regions of interest were used to obtain signal intensity (decibels), as a surrogate of contrast concentration.

RESULTS

Four pump speeds revealed significant reduction in contrast signal intensity after CF-VAD compared to before CF-VAD (all p < 0.0001). Combined pre- and postpump data at all speeds showed a 22.2% absolute reduction in contrast signal intensity across the CF-VAD (14.8 ± 0.8 dB prepump versus 11.6 ± 1.4 dB postpump; p < 0.0001). Mean signal intensity reduction at each speed showed an inverse relationship between speed and relative reduction in signal intensity.

CONCLUSION

Contrast microsphere transit through a CF-VAD within a MCL resulted in significant reduction in signal intensity, consistent with destruction within the pump. This was evident at all CF-VAD pump speeds but relative signal drop was inversely proportional to pump speed.

Quantification of perflutren microsphere contrast destruction during transit through an ex vivo extracorporeal membrane oxygenation circuit

BACKGROUND

Echocardiography is a key investigation in the management of patients on extracorporeal membrane oxygenation (ECMO). However, echocardiographic images are often non-diagnostic in this patient population. Contrast-enhanced echocardiography may overcome many of these limitations but contrast microspheres are hydrodynamically labile structures prone to destruction from shear forces and turbulent flow, which may exist within an ECMO circuit. This study sought to evaluate microsphere destruction (utilising signal intensity as a marker of contrast concentration) during transit through an ECMO circuit.

METHODS

Activated Definity® contrast was diluted to 50 ml with normal saline and infused into a crystalloid primed ex vivo ECMO with a Quadrox oxygenator at 150 ml/h. Imaging was performed on pre- and post-pump head/oxygenator sections of the circuit using a Philips iE33 scanner and S5-1 transducer. Five-millimetre regions of interest were placed in the centre of the ultrasound field. Average signal intensity (decibels) was calculated at speeds of 1000, 2000, 3000 and 4000 rpm and then repeated with an infusion rate of 300 ml/h. The oxygenator was then spliced out of the circuit and the measures repeated.

RESULTS

There was a significant reduction in contrast concentration during passage through the ECMO circuit at all speeds (with higher pump head speeds resulting in greater microsphere destruction). In a circuit with an oxygenator, relative decrease in signal intensity was 21.4 versus 5.2 % without an oxygenator. There was significant destruction of contrast microspheres during passage through the ECMO circuit at all pump head speeds. An oxygenator contributed to microsphere destruction at a significantly greater level than the pump head alone. There was no significant difference in mean signal intensity reduction in the circuit between an infusion of 150 or 300 ml/h (3.5 ± 3.2 versus 3.6 ± 2.5 dB, respectively, p = 0.79).

CONCLUSIONS

Flow of contrast through an ECMO circuit results in significant destruction of microspheres. Circuits with an oxygenator result in significantly greater levels of contrast destruction than by the pump head alone. Clinicians should be cognisant of the relationship between ECMO circuit configurations, pump head speed and contrast destruction when performing a contrast-enhanced echocardiogram in patients supported with ECMO.

The Complex Relationship of Extracorporeal Membrane Oxygenation and Acute Kidney Injury: Causation or Association?

Extracorporeal membrane oxygenation (ECMO) is a modified cardiopulmonary bypass (CPB) circuit capable of providing prolonged cardiorespiratory support. Recent advancement in ECMO technology has resulted in increased utilisation and clinical application. It can be used as a bridge-to-recovery, bridge-to-bridge, bridge-to-transplant, or bridge-to-decision. ECMO can restitute physiology in critically ill patients, which may minimise the risk of progressive multiorgan dysfunction. Alternatively, iatrogenic complications of ECMO clearly contribute to worse outcomes. These factors affect the risk : benefit ratio of ECMO which ultimately influence commencement/timing of ECMO. The complex interplay of pre-ECMO, ECMO, and post-ECMO pathophysiological processes are responsible for the substantial increased incidence of ECMO-associated acute kidney injury (EAKI). The development of EAKI significantly contributes to morbidity and mortality; however, there is a lack of evidence defining a potential benefit or causative link between ECMO and AKI. This area warrants investigation as further research will delineate the mechanisms involved and subsequent strategies to minimise the risk of EAKI. This review summarizes the current literature of ECMO and AKI, considers the possible benefits and risks of ECMO on renal function, outlines the related pathophysiology, highlights relevant investigative tools, and ultimately suggests an approach for future research into this under investigated area of critical care.

CRITICAL CARE ECHO ROUNDS: Extracorporeal membrane oxygenation

Extracorporeal membrane oxygenation (ECMO) is an advanced form of organ support indicated in selected cases of severe cardiovascular and respiratory failure. Echocardiography is an invaluable diagnostic and monitoring tool in all aspects of ECMO support. The unique nature of ECMO, and its distinct effects upon cardio-respiratory physiology, requires the echocardiographer to have a sound understanding of the technology and its interaction with the patient. In this article, we introduce the key concepts underpinning commonly used modes of ECMO and discuss the role of echocardiography.