Phase III multicenter trial comparing the efficacy of 2% dodecafluoropentane emulsion (EchoGen) and sonicated 5% human albumin (Albunex) as ultrasound contrast agents in patients with suboptimal echocardiograms

Deciphering the Emulsification Process to Create an Albumin-Perfluorocarbon-(o/w) Nanoemulsion with High Shelf Life and Bioresistivity

This work aimed at the development of a stable albumin-perfluorocarbon (o/w) emulsion as an artificial oxygen carrier suitable for clinical application. So far, albumin-perfluorocarbon-(o/w) emulsions have been successfully applied in preclinical trials. Cross-linking a variety of different physical and chemical methods for the characterization of an albumin-perfluorocarbon (PFC)-(o/w) emulsion was necessary to gain a deep understanding of its specific emulsification processes during high-pressure homogenization. High-pressure homogenization is simple but incorporates complex physical reactions, with many factors influencing the formation of PFC droplets and their coating. This work describes and interprets the impact of albumin concentration, homogenization pressure, and repeated microfluidizer passages on PFC-droplet formation; its influence on storage stability; and the overcoming of obstacles in preparing stable nanoemulsions. The applied methods comprise dynamic light scattering, static light scattering, cryo- and non-cryo-scanning and transmission electron microscopies, nuclear magnetic resonance spectroscopy, light microscopy, amperometric oxygen measurements, and biochemical methods. The use of this wide range of methods provided a sufficiently comprehensive picture of this polydisperse emulsion. Optimization of PFC-droplet formation by means of temperature and pressure gradients results in an emulsion with improved storage stability (tested up to 5 months) that possibly qualifies for clinical applications. Adaptations in the manufacturing process strikingly changed the physical properties of the emulsion but did not affect its oxygen capacity.

Acoustic Nanodrops for Biomedical Applications

Acoustic nanodrops are designed to vaporize into ultrasound-responsive microbubbles, which presents certain challenges nonexistent for conventional nano-emulsions. The requirements of biocompatibility, vaporizability and colloidal stability has focused research on perfluorocarbons (PFCs). Shorter PFCs yield better vaporizability via their lower critical temperature, but they also dissolve more easily owing to their higher vapor pressure and solubility. Thus, acoustic nanodrops have required a tradeoff between vaporizability and colloidal stability in vivo. The recent advent of vaporizable endoskeletal droplets, which are both stable and vaporizable, may have solved this problem. The purpose of this review is to justify this premise by pointing out the beneficial properties of acoustic nanodrops, providing an analysis of vaporization and dissolution mechanisms, and reviewing current biomedical applications.

Treatment of Swine Closed Head Injury with Perfluorocarbon NVX-428

Pre-hospital treatment of traumatic brain injury (TBI) with co-existing polytrauma is complicated by requirements for intravenous fluid volume vs. hypotensive resuscitation. A low volume, small particle-size-oxygen-carrier perfluorocarbon emulsion NVX-428 (dodecafluoropentane emulsion; 2% w/v) could improve brain tissue with minimal additional fluid volume. This study examined whether the oxygen-carrier NVX-428 shows safety and efficacy for pre-hospital treatment of TBI. Anesthetized swine underwent fluid percussion injury TBI and received 1 mL/kg IV NVX-428 (TBI-NVX) at 15 min (T15) or normal saline (no-treatment) (TBI-NON). Similarly, uninjured swine received NVX-428 (SHAM-NVX) or normal saline (SHAM-NON). Animals were monitored and measurements were taken for physiological and neurological parameters before euthanasia at the six-hour mark (T360). Histopathological analysis was performed on paraffin embedded tissues. Physiological, biochemical and blood gas parameters were not different, with the exception of a significant but transient increase in mean pulmonary artery pressure observed in the TBI-experimental group immediately after drug administration. There were no initial differences in brain oxygenation at baseline, but over time oxygen decreased ~50% in both TBI groups. Histological brain injury scores were similar between TBI-NVX and TBI-NON, although a number of subcategories (spongiosis-ischemic/dead neurons-hemorrhage-edema) in TBI-NVX had a tendency for lower scores. The cerebellum showed significantly lower spongiosis and ischemic/dead neuron injury scores and a lower number of Fluoro-Jade-B-positive cerebellar-Purkinje-cells after NVX-428 treatment compared to controls. NVX-428 may assist in mitigating secondary cellular brain damage.

Blood-borne and brain-derived microparticles in morphine-induced anti-nociceptive tolerance

We hypothesized that elevations of microparticles (MPs) would occur with morphine administration to mice. Repetitive dosing to induce anti-nociceptive tolerance increases blood-borne MPs by 8-fold, and by 10-fold in deep cervical lymph nodes draining brain glymphatics. MPs express proteins specific to cells including neutrophils, microglia, astrocytes, neurons and oligodendrocytes. Interleukin (IL)-1β content of MPs increases 68-fold. IL-1β antagonist administration diminishes blood-borne and cervical lymph node MPs, and abrogates tolerance induction. Intravenous polyethylene glycol Telomer B, a surfactant that lyses MPs, and intraperitoneal methylnaltrexone also inhibit MPs elevations and tolerance. Critically, neutropenic mice do not develop anti-nociceptive tolerance, elevations of blood-borne or cervical node MPs. Immunohistochemical evidence for microglial activation by morphine does not correlated with the MPs response pattern. Neutrophil-derived MPs appear to be required for morphine-induced anti-nociceptive tolerance. Further, patients entering treatment for opioid use disorder exhibit similar MPs elevations as do tolerant mice.

Ultrasound-responsive lipid microbubbles for drug delivery: A review of preparation techniques to optimise formulation size, stability and drug loading

Lipid-shelled microbubbles have received extensive interest to enhance ultrasound-responsive drug delivery outcomes due to their high biocompatibility. While therapeutic effectiveness of microbubbles is well established, there remain limitations in sample homogeneity, stability profile and drug loading properties which restrict these formulations from seeing widespread use in the clinical setting. In this review, we evaluate and discuss the most encouraging leads in lipid microbubble design and optimisation. We examine current applications in drug delivery for the systems and subsequently detail shell compositions and preparation strategies that improve monodispersity while retaining ultrasound responsiveness. We review how excipients and storage techniques help maximise stability and introduce different characterisation and drug loading techniques and evaluate their impact on formulation performance. The review concludes with current quality control measures in place to ensure lipid microbubbles can be reproducibly used in drug delivery.

Clinical practice of contrast echocardiography: recommendation by the European Association of Cardiovascular Imaging (EACVI) 2017

Contrast echocardiography is widely used in cardiology. It is applied to improve image quality, reader confidence and reproducibility both for assessing left ventricular (LV) structure and function at rest and for assessing global and regional function in stress echocardiography. The use of contrast in echocardiography has now extended beyond cardiac structure and function assessment to evaluation of perfusion both of the myocardium and of the intracardiac structures. Safety of contrast agents have now been addressed in large patient population and these studies clearly established its excellent safety profile. This document, based on clinical trials, randomized and multicentre studies and published clinical experience, has established clear recommendations for the use of contrast in various clinical conditions with evidence-based protocols.

Contrast-enhanced ultrasound of malignant liver lesions

Contrast-enhanced ultrasound (CEUS) is a safe, relatively inexpensive, and widely available imaging technique using dedicated imaging ultrasound sequences and FDA-approved contrast microbubbles that allow detection and characterization of malignant focal liver lesions with high diagnostic accuracy. CEUS provides dynamic real-time imaging with high spatial and temporal capability, allowing for unique contributions to the already established protocols for diagnosing focal liver lesions using CT and MR imaging. In patients with lesions indeterminate on CT and MRI, CEUS is a helpful problem-solving complementary tool that improves patient management. Furthermore, CEUS assists guidance of liver biopsies and local treatment. Variations of CEUS such as DCE-US and ultrasound molecular imaging are emerging for quantitative monitoring of treatment effects and possible earlier detection of cancer. In this review, basic principles of CEUS techniques and ultrasound contrast agents along with a description of the enhancement patterns of malignant liver lesions are summarized. Also, a discussion of the role of CEUS for treatment guidance and monitoring, intraoperative CEUS, and an outlook on emerging applications is provided.

Recent advances in ultrasound-based diagnosis and therapy with micro- and nanometer-sized formulations

Ultrasound (US) is one of the most frequently used imaging methods in the clinic. The broad spectrum of its applications can be increased by the use of gas-filled microbubbles (MB) as ultrasound contrast agents (UCA). In recent years, also nanoscale UCA like nanobubbles (NB), echogenic liposomes (ELIP) and nanodroplets have been developed, which in contrast to MB, are able to extravasate from the vessels into the tissue. New disease-specific UCA have been designed for the assessment of tissue biomarkers and advanced US to a molecular imaging modality. For this purpose, specific binding moieties were coupled to the UCA surface. The vascular endothelial growth factor receptor-2 (VEGFR-2) and P-/E-selectin are prominent examples of molecular US targets to visualize tumor blood vessels and inflammatory diseases, respectively. Besides their application in contrast-enhanced imaging, MB can also be employed for drug delivery to tumors and across the blood-brain barrier (BBB). This review summarizes the development of micro- and nanoscaled UCA and highlights recent advances in diagnostic and therapeutic applications, which are ready for translation into the clinic.

Evolution of contrast agents for ultrasound imaging and ultrasound-mediated drug delivery

Ultrasound (US) is one of the most frequently used diagnostic methods. It is a non-invasive, comparably inexpensive imaging method with a broad spectrum of applications, which can be increased even more by using bubbles as contrast agents (CAs). There are various different types of bubbles: filled with different gases, composed of soft- or hard-shell materials, and ranging in size from nano- to micrometers. These intravascular CAs enable functional analyses, e.g., to acquire organ perfusion in real-time. Molecular analyses are achieved by coupling specific ligands to the bubbles' shell, which bind to marker molecules in the area of interest. Bubbles can also be loaded with or attached to drugs, peptides or genes and can be destroyed by US pulses to locally release the entrapped agent. Recent studies show that US CAs are also valuable tools in hyperthermia-induced ablation therapy of tumors, or can increase cellular uptake of locally released drugs by enhancing membrane permeability. This review summarizes important steps in the development of US CAs and introduces the current clinical applications of contrast-enhanced US. Additionally, an overview of the recent developments in US probe design for functional and molecular diagnosis as well as for drug delivery is given.

Microparticles Impair Hypotensive Cerebrovasodilation and Cause Hippocampal Neuronal Cell Injury after Traumatic Brain Injury

Endothelin-1 (ET-1), tissue plasminogen activator (tPA), and extracellular signal-regulated kinases-mitogen activated protein kinase (ERK-MAPK) are mediators of impaired cerebral hemodynamics after fluid percussion brain injury (FPI) in piglets. Microparticles (MPs) are released into the circulation from a variety of cells during stress, are pro-thrombotic and pro-inflammatory, and may be lysed with polyethylene glycol telomere B (PEG-TB). We hypothesized that MPs released after traumatic brain injury impair hypotensive cerebrovasodilation and that PEG-TB protects the vascular response via MP lysis, and we investigated the relationship between MPs, tPA, ET-1, and ERK-MAPK in that process. FPI was induced in piglets equipped with a closed cranial window. Animals received PEG-TB or saline (vehicle) 30-minutes post-injury. Serum and cerebrospinal fluid (CSF) were sampled and pial arteries were measured pre- and post-injury. MPs were quantified by flow cytometry. CSF samples were analyzed with enzyme-linked immunosorbent assay. MP levels, vasodilatory responses, and CSF signaling assays were similar in all animals prior to injury and treatment. After injury, MP levels were elevated in the serum of vehicle but not in PEG-TB-treated animals. Pial artery dilation in response to hypotension was impaired after injury but protected in PEG-TB-treated animals. After injury, CSF levels of tPA, ET-1, and ERK-MAPK were all elevated, but not in PEG-TB-treated animals. PEG-TB-treated animals also showed reduction in neuronal injury in CA1 and CA3 hippocampus, compared with control animals. These results show that serum MP levels are elevated after FPI and lead to impaired hypotensive cerebrovasodilation via over-expression of tPA, ET-1, and ERK-MAPK. Treatment with PEG-TB after injury reduces MP levels and protects hypotensive cerebrovasodilation and limits hippocampal neuronal cell injury.

Radiosensitization of Hs-766T Pancreatic Tumor Xenografts in Mice Dosed with Dodecafluoropentane Nano-Emulsion-Preliminary Findings

Tumor hypoxia is an important mediator of radiation therapy resistance. We conducted a study to investigate whether an oxygen therapeutic based upon dodecafluoropentane (DDFP) nano-emulsion (NVX-108) could increase tumor PO2 in hypoxic tumors and improve radiation response. Pancreatic (Hs-766T) tumor xenografts were grown in the flanks of 29 SCID mice. Direct tumor PO2 measurements were performed in 9 mice treated with 0.3, 0.45 and 0.6 cc/kg NVX-108 (2% w/vol DDFP) in order to assess the dose dependent increase in tumor PO2. Twenty mice were randomized into 3 groups including control (no treatment), carbogen breathing treated with 12 Gy radiation, and carbogen breathing treated with 12 Gy radiation and NVX-108 (0.6 cc/kg NVX-108 administered as 30 minute IV infusion at time of radiation). Tumor volume was monitored to assess treatment efficacy. Results showed that tumor PO2 increased in NVX-108 treated mice up to 400% with the greatest effect seen at the highest dose of 0.6 cc/kg. Tumor growth was significantly reduced in both treatment groups relative to controls (p < 0.0001). The combination of carbogen, radiation, and NVX-108 demonstrated a 2-fold reduction in average tumor volume compared to carbogen plus radiation treatment (p = 0.01). Further study of NVX-108 as a radiation sensitizer is warranted.

Cardiovascular drug delivery with ultrasound and microbubbles

Microbubbles lower the threshold for cavitation of ultrasound and have multiple potential therapeutic applications in the cardiovascular system. One of the first therapeutic applications to enter into clinical trials has been microbubble-enhanced sonothrombolysis. Trials were conducted in acute ischemic stroke and clinical trials are currently underway for sonothrombolysis in treatment of acute myocardial infarction. Microbubbles can be targeted to epitopes expressed on endothelial cells and thrombi by incorporating targeting ligands onto the surface of the microbubbles. Targeted microbubbles have applications as molecular imaging contrast agents and also for drug and gene delivery. A number of groups have shown that ultrasound with microbubbles can be used for gene delivery yielding robust gene expression in the target tissue. Work has progressed to primate studies showing delivery of therapeutic genes to generate islet cells in the pancreas to potentially cure diabetes. Microbubbles also hold potential as oxygen therapeutics and have shown promising results as a neuroprotectant in an ischemic stroke model. Regulatory considerations impact the successful clinical development of therapeutic applications of microbubbles with ultrasound. This paper briefly reviews the field and suggests avenues for further development.

Acoustic droplet vaporization in biology and medicine

This paper reviews the literature regarding the use of acoustic droplet vaporization (ADV) in clinical applications of imaging, embolic therapy, and therapeutic delivery. ADV is a physical process in which the pressure waves of ultrasound induce a phase transition that causes superheated liquid nanodroplets to form gas bubbles. The bubbles provide ultrasonic imaging contrast and other functions. ADV of perfluoropentane was used extensively in imaging for preclinical trials in the 1990s, but its use declined rapidly with the advent of other imaging agents. In the last decade, ADV was proposed and explored for embolic occlusion therapy, drug delivery, aberration correction, and high intensity focused ultrasound (HIFU) sensitization. Vessel occlusion via ADV has been explored in rodents and dogs and may be approaching clinical use. ADV for drug delivery is still in preclinical stages with initial applications to treat tumors in mice. Other techniques are still in preclinical studies but have potential for clinical use in specialty applications. Overall, ADV has a bright future in clinical application because the small size of nanodroplets greatly reduces the rate of clearance compared to larger contrast agent bubbles and yet provides the advantages of ultrasonographic contrast, acoustic cavitation, and nontoxicity of conventional perfluorocarbon contrast agent bubbles.

Microparticles initiate decompression-induced neutrophil activation and subsequent vascular injuries

Progressive elevations in circulating annexin V-coated microparticles (MPs) derived from leukocytes, erythrocytes, platelets, and endothelial cells are found in mice subjected to increasing decompression stresses. Individual MPs exhibit surface markers from multiple cells. MPs expressing platelet surface markers, in particular, interact with circulating neutrophils, causing them to degranulate and leading to further MP production. MPs can be lysed by incubation with polyethylene glycol (PEG) telomere B surfactant, and the number of circulating MPs is reduced by infusion of mice with PEG or antibody to annexin V. Myeloperoxidase deposition and neutrophil sequestration in tissues occur in response to decompression, and the pattern differs among brain, omentum, psoas, and leg skeletal muscle. Both MP abatement strategies reduce decompression-induced intravascular neutrophil activation, neutrophil sequestration, and tissue injury documented as elevations of vascular permeability and activated caspase-3. We conclude that MPs generated by decompression stresses precipitate neutrophil activation and vascular damage.

Diagnostic value of parametric imaging of left ventricular wall motion from contrast-enhanced echocardiograms in patients with poor acoustic windows

BACKGROUND

Analysis of left ventricular (LV) regional wall motion (RWM) is subjective and may be challenging in patients with suboptimal images, even with contrast enhancement. It was hypothesized that the amplitude and timing of RWM obtained from contrast-enhanced echocardiograms can be accurately represented in still-frame parametric images. This study was designed to (1) test this hypothesis, (2) establish the diagnostic value of these images as an aid for inexperienced readers, and (3) test the feasibility of automated quantitative analysis of RWM.

METHODS

Contrast-enhanced apical 4-chamber, 2-chamber, and 3-chamber LV views were acquired in 45 patients with poor acoustic windows. The interpretation of dynamic images by an experienced reader who classified RWM as normal or abnormal was used as a reference for comparisons against (1) visual interpretation of parametric images, (2) interpretation of dynamic images by two inexperienced readers (American Society of Echocardiography level I) without and subsequently with parametric images, and (3) automated quantification of RWM.

RESULTS

Expert readers detected abnormal RWM in 30 patients (437 of 945 segments). Visual interpretation of parametric images showed good agreement with the reference (sensitivity, 85%; specificity, 82%; accuracy, 84%). The interpretations by inexperienced readers improved with the addition of parametric images, with increases in specificity (from 58% to 79%) and accuracy (from 74% to 84%), despite a slight decrease in sensitivity (from 92% to 91%). Automated classification was feasible and accurate (sensitivity, 82%; specificity, 78%; accuracy, 80%).

CONCLUSION

Parametric images derived from contrast-enhanced echocardiograms of patients with poor acoustic windows accurately depicted RWM, improved the diagnostic accuracy of inexperienced readers, and allowed the objective detection of RWM abnormalities.

Heart failure and chronic obstructive pulmonary disease: diagnostic pitfalls and epidemiology

Heart failure (HF) and chronic obstructive pulmonary disease (COPD) are global epidemics incurring significant morbidity and mortality. The combination presents many diagnostic challenges. Clinical symptoms and signs frequently overlap. Evaluation of cardiac and pulmonary function is often problematic and occasionally misleading. Echocardiography and pulmonary function tests should be performed in every patient. Careful interpretation is required to avoid misdiagnosis and inappropriate treatment. Airflow obstruction, in particular, must be demonstrated when clinically euvolaemic. Very high and very low concentrations of natriuretic peptides have high positive and negative predictive values for diagnosing HF in those with both conditions. Intermediate values are less informative. Both conditions are systemic disorders with overlapping pathophysiological processes. In patients with HF, COPD is consistently an independent predictor of death and hospitalization. However, the impact on ischaemic and arrhythmic events is unknown. Greater collaboration is required between cardiologists and pulmonologists to better identify and manage concurrent HF and COPD. The resulting symptomatic and prognostic benefits outweigh those attainable by treating either condition alone.

Contrast-enhanced versus non-enhanced three-dimensional echocardiography of left ventricular volumes

BACKGROUND

In three-dimensional echocardiography (3DE), individual endocardial trabeculae are not clearly visible necessitating left ventricular (LV) volumes to be measured by tracing the innermost endocardial contour. Ultrasound contrast agents aim to improve endocardial definition, but may delineate the outermost endocardial contour by filling up intertrabecular space. Although measurement reproducibility may benefit, there may be a significant influence on absolute LV volume measurements.

METHODS

Twenty patients with a recent myocardial infarction and good ultrasound image quality underwent 3DE using the TomTec Freehand method before and during continuous intravenous contrast infusion. LV volumes were measured offline using TomTec Echo-Scan software.

RESULTS

The use of contrast enhancement increased end-diastolic (110+/-35 vs. 144+/-53 ml; p<0.01) and end-systolic volume measurements (68+/-31 vs. 87+/-45 ml; p<0.01) significantly compared with non-contrast; the ejection fraction remained unchanged (40+/-13 vs. 41+/-14%, p=NS). Measurement reproducibility did not improve significantly, however.

CONCLUSION

Volumes measured by 3DE are significantly larger when ultrasound contrast is used. Possibly, intertrabecular space comprises a substantial part of the LV cavity. In the presence of an adequate apical acoustic window, ultrasound contrast does not improve LV volume measurement reproducibility. (Neth Heart J 2008;16:47-52.).

Parametric harmonic-to-fundamental ratio contrast echocardiography: a novel approach to identification and accurate measurement of left ventricular area under variable levels of ultrasound signal attenuation

OBJECTIVES

We introduced a harmonic-to-fundamental ratio (HFR) of the radiofrequency (RF) signals that reduces confounding effects of attenuation. We studied whether HFR analysis of RF signals received from contrast microbubbles allows accurate measurement of the left ventricular (LV) cavity area under varying levels of attenuation.

BACKGROUND

Attenuation is a fundamental problem in ultrasound imaging and limits the use of clinical echocardiography.

METHODS

RF data from short axis systolic and diastolic scans were obtained from 14 open-chest dogs following left-atrial bolus of Optison. Attenuation was induced by interposed silicone pads calibrated to induce 7dB or 14dB reductions of the backscattered RF signal. RF images were reconstructed from the RF signals, HFR values calculated for each image pixel for 0dB, 7dB and 14dB attenuation conditions, and LV area obtained by summation of "LV cavity pixels". A reference LV cavity area was obtained from endocardial border tracings in enhanced scans by experts.

RESULTS

Correlation of the HFR-defined and reference areas at systole was R=0.95, R=0.94, and R=0.91 for 0dB, 7dB and 14dB levels of attenuation, respectively, and at diastole was R=0.95 for 0dB, 7dB and 14dB levels of attenuation. The mean difference from both systolic and diastolic values was <1.45 cm(2) (i.e. negligible) in all attenuation settings.

CONCLUSION

Our novel HFR method supports precise measurement of the LV cavity area in contrast images with simulated high attenuation of ultrasound signals.

Pulmonary Hemodynamic Effects of Dipyridamole Infusion in Patients with Normal and Elevated Pulmonary Artery Systolic Pressure Receiving PB127

BACKGROUND

Intravenous administration of microspheres used as ultrasound contrast agents may potentially alter pulmonary hemodynamics. PB127 (POINT Biomedical Corp., San Carlos, CA) is an investigational ultrasound perfusion-imaging agent used in conjunction with dipyridamole to diagnose coronary artery disease. The effects of PB127 alone or in combination with dipyridamole on pulmonary hemodynamics have not been described.

METHODS

We studied 20 patients, including 10 with elevated screening pulmonary artery systolic pressure (>35 mm Hg). Doppler-derived pulmonary hemodynamics were determined before and after continuous infusion of PB127 (0.175 mg/kg diluted in 5% dextrose) or 5% dextrose. Patients then received dipyridamole (0.56 mg/kg) and hemodynamics were again assessed.

RESULTS

During PB127/dextrose infusion, there were no significant changes in pulmonary hemodynamics compared with baseline. After dipyridamole, there were small increases in pulmonary artery systolic pressure and in pulmonary flow and a reduction in pulmonary vascular resistance. These changes occurred in patients with normal and elevated pulmonary artery systolic pressure.

CONCLUSION

PB127 infusion does not alter pulmonary hemodynamics. Mild alterations of pulmonary hemodynamics occur after dipyridamole administration.

Automated border detection on contrast enhanced echocardiographic images

BACKGROUND

Accurate determination of left ventricular ejection fraction (LV EF) is of paramount importance in the evaluation of patients with cardiovascular disease. Quantitative techniques for the automated calculation of EF exist however, the robustness of these techniques is dependent on adequate endocardial border definition and therefore are difficult to use in patients with limited images. We sought to combine the endocardial border enhancing effects of contrast echocardiography with an automated border detection technique to provide quantitative and accurate determination of LV EF.

METHODS

Thirty-nine consecutive patients referred to nuclear cardiology for EF determination underwent radionuclide angiography followed by echocardiographic imaging using prototype software that allowed automated border detection during contrast infusion.

RESULTS

Adequate LV cavity opacification with contrast was possible in 38/39 patients. The mean radionuclide EF was 50+/-16% (range 19-73). There was no statistically significant difference between the mean nuclear EF and averaged echocardiographically determined EF (51+/-18%). The mean bias was 0.6 with limits of agreement that were +15 and -14.

CONCLUSION

This study demonstrated that prototype software successfully tracked the contrast enhanced endocardial border allowing accurate calculation of LV EF.

Assessment of systolic left ventricular function: a multi-centre comparison of cineventriculography, cardiac magnetic resonance imaging, unenhanced and contrast-enhanced echocardiography

AIMS

To assess the agreement of left ventricular ejection fraction (LVEF) determinations from unenhanced echocardiography, contrast-enhanced echocardiography, magnetic resonance imaging (MRI), and cineventriculography as well as the inter-observer agreement for each method.

METHODS AND RESULTS

In 120 patients, with evenly distributed EF-groups (> 55, 35-55, < 35%), cineventriculography, unenhanced echocardiography with second harmonic imaging, and contrast echocardiography at low mechanical index with iv administration of SonoVue were performed. In addition, cardiac MRI at 1.5 T using a steady-state free precession sequence was performed in a subset of 55 patients. On-site, and two blinded off-site assessments were performed for unenhanced and contrast echocardiography, cineventriculography, and MRI according to pre-defined standards. Intra-class correlation coefficients (ICCs) were determined to assess inter-observer reliability between all three readers (i.e. one on-site and two off-site). EF was 56.2 +/- 18.3% by cineventriculography, 54.1 +/- 12.9% by MRI, 50.9 +/- 15.3% by unenhanced echocardiography, and 54.6 +/- 16.8% by contrast echocardiography. Correlation on EF between cineventriculography and echocardiography increased from 0.72 with unenhanced echocardiography to 0.83 with contrast echocardiography (P < 0.05). Similarly, correlation on EF between MRI and echocardiography increased from 0.60 with unenhanced echocardiography to 0.77 with contrast echocardiography (P < 0.05). The inter-observer reliability ICC was 0.91 (95% CI 0.88-0.94) in contrast echocardiography, followed by cardiac MRI (0.86; 95% CI 0.80-0.92), cineventriculography (0.80; 95% CI 0.74-0.85), and unenhanced echocardiography (0.79; 95% CI 0.74-0.85).

CONCLUSIONS

Unenhanced echocardiography resulted in slight underestimation of EF and only moderate correlation compared with cineventriculography and MRI. Contrast echocardiography resulted in more accurate EF and significantly improved correlation with cineventriculography and MRI. Contrast echocardiography significantly improved inter-observer agreement on EF compared with unenhanced echocardiography. Inter-observer reliability on EF using contrast echocardiography reaches a level comparable to MRI and is better than those obtained by cineventriculography.

Incremental Benefit of Myocardial Contrast to Combined Dipyridamole-Exercise Stress Echocardiography for the Assessment of Coronary Artery Disease

Background— Although assessment of myocardial perfusion by myocardial contrast echocardiography (MCE) is feasible, its incremental benefit to stress echocardiography is not well defined. We examined whether the addition of MCE to combined dipyridamole-exercise echocardiography (DExE) provides incremental benefit for evaluation of coronary artery disease (CAD).

Methods and Results— MCE was combined with DExE in 85 patients, 70 of whom were undergoing quantitative coronary angiography and 15 patients with a low probability of CAD. MCE was acquired by low-mechanical-index imaging in 3 apical views after acquisition of standard resting and poststress images. Wall motion, left ventricular opacification, and MCE components of the study were interpreted sequentially, blinded to other data. Significant (>50%) stenoses were present in 43 patients and involved 69 coronary territories. The addition of qualitative MCE improved sensitivity for the detection of CAD (91% versus 74%, P =0.02) and accurate recognition of disease extent (87% versus 65% of territories, P =0.003), with a nonsignificant reduction in specificity.

Conclusions— The addition of low-mechanical-index MCE to standard imaging during DExE improves detection of CAD and enables a more accurate determination of disease extent.

Combination of contrast with stress echocardiography: a practical guide to methods and interpretation

Contrast echocardiography has an established role for enhancement of the right heart Doppler signals, the detection of intra-cardiac shunts, and most recently for left ventricular cavity opacification (LVO). The use of intravenously administered micro-bubbles to traverse the myocardial microcirculation in order to outline myocardial viability and perfusion has been the source of research studies for a number of years. Despite the enthusiasm of investigators, myocardial contrast echocardiography (MCE) has not attained routine clinical use and LV opacification during stress has been less widely adopted than the data would support. The purpose of this review is to facilitate an understanding of the involved imaging technologies that have made this technique more feasible for clinical practice, and to guide its introduction into the practice of the non-expert user.

Effect of tissue harmonic imaging and contrast upon between observer and test-retest reproducibility of left ventricular ejection fraction measurement in patients with heart failure

AIMS

To investigate the effects of tissue harmonic imaging (THI) and contrast chamber opacification (LVO) upon measurement variability and reproducibility of echocardiographic left ventricular (LV) volume and ejection fraction (EF) measurements in patients with heart failure (HF).

BACKGROUND

Echocardiography is often used in HF patients to determine LV volumes and EF. However, current echo methods are variable and may not be applicable for repeat testing in individual patients. THI and LVO have both been shown to improve endocardial visualisation, but it remains to be determined whether this results in better measurement reproducibility.

METHODS

Thirty-one HF patients and 30 control subjects underwent echocardiography on two separate days. LV volumes were measured under four different imaging conditions: fundamental, THI, LVO and LVO with ECG-triggered Power Doppler. Chamber opacification, pulmonary transit time (PTT), endocardial enhancement, reproducibility and bias were assessed.

RESULTS

Chamber opacification was inferior and the PTT longer in the HF patients. PTT was related to LV volumes, EF, jugular venous pressure and mitral filling pattern. THI improved endocardial visualisation, and although LVO improved endocardial visualisation in the controls, it offered no benefit over THI in the HF patients. LV volumes and EF were different for each method and THI was the least variable method for repeat measurements.

CONCLUSIONS

THI improved endocardial visualisation and was the least variable of the techniques. LVO offered no further advantage in patients with HF and thus cannot be routinely advocated and since LV volumes and EF were different for each, these methods are neither comparable nor interchangeable for follow-up assessments.

Clinical potential of nonhemoglobin oxygen therapeutics in cardiac and general surgery

Significant efforts have been made over the past 70 years to find a solution that could substitute for blood. Over the years, the focus has shifted to developing a solution capable of delivering oxygen to the tissues. Fluorocarbons (FC) are highly inert solutions with a high solubility for all gases, making them a prime candidate to become such an oxygen delivery agent. Although clinical research efforts into the use of these agents as substitutes for blood transfusions continue at present, the rapid disappearance of emulsified FCs from the vascular space and accumulation in the liver and spleen may well limit their usefulness as transfusion substitutes. Because of their ability to dissolve significant quantities of oxygen and carbon dioxide, these agents may be more attractive as oxygen delivery agents during periods of local or global organ ischemia, including preservation of organs for transplantation. FCs have also been tested in animal models of cardiopulmonary bypass, and may be efficacious in adsorbing the gases present in air emboli. Recently a second class of oxygen therapeutics (allosteric modifiers) has been developed, and these agents enhance oxygen delivery by shifting the oxygen dissociation curve to the right, thus increasing tissue PO(2). Allosteric modifiers have been shown to effectively shift the p50 of hemoglobin 10mm Hg at clinically relevant dosages, and have been shown (in animal models) to reduce cerebral infarct size following carotid ligation and to improve myocardial performance following myocardial ischemia. Despite significant research efforts, however, none of the solutions under development are currently approved for clinical use by the Food and Drug Administration, with the exception of myocardial contrast imaging agents.

Clinical potential of blood substitutes or oxygen therapeutics during cardiac surgery

Several complications and unforeseen adverse side effects have colluded to keep commercially available blood substitutes or oxygen therapeutic agents tantalizingly "just out of reach." Because the three classes of agents under development have different oxygen-delivery mechanisms and side-effect profiles, each can be expected to have its own unique clinical applications, particularly in the cardiac surgery population. The fact that South Africa recently approved one HBOC for use as a transfusion alternative in patients with chronic anemia indicates that initial clinical use is near for a number of these agents. It is to be hoped that they will be used for several applications rather than just for a "transfusion alternative." Despite some frustrating limitations, all of these agents are antigen and pathogen free, have an acceptable side-effect profile, and have a long shelf life. Increasing volunteer-blood-donor shortages, coupled with increasing blood-transfusion needs, and expanding human immunodeficiency virus and hepatitis B and C epidemics, continue to fuel the demand for further development of these products. Transfusion alternatives will eventually become commercially available--the question is "when," not "if." Equally important, these agents' potential for serving as effective oxygen-delivery agents to ischemic tissues heralds an entirely new field of clinical investigation.

Impact of myocardial contrast echocardiography on vascular permeability: an in vivo dose response study of delivery mode, pressure amplitude and contrast dose

An in vivo rat model of myocardial contrast echocardiography (MCE) was defined and used to examine the dose range response of microvascular permeabilization and premature ventricular contractions (PVCs) with respect to method of imaging, peak rarefactional pressure amplitude (PRPA) and agent dose. A left ventricular short axis view was obtained on anesthetized rats at 1.7 MHz using a diagnostic ultrasound system with simultaneous ECG recording. Evans blue dye, a marker for microvascular leakage, and a bolus of Optison were injected i.v. Counts of PVCs were made from video tape during the 3 min of MCE. Hearts were excised 5 min after imaging and petechial hemorrhages, Evans blue colored area and Evans blue content were determined. No PVCs or microvascular leakage were seen in rats imaged without contrast agent followed by contrast agent injection without imaging. When PVCs were detected during MCE, petechial hemorrhages and Evans blue leakage were also found in the myocardium. Triggering 1:4 at end-systole produced the most PVCs per frame and most microvascular leakage, followed by end-systole 1:1, continuous scanning and end-diastole triggering 1:1. All effects increased with increasing Optison dosage in the range 25 to 500 microL kg(-1). Ultrasound PRPA was important, with apparent thresholds for PVCs at 1.0 MPa and for petechiae at 0.54 MPa. PVCs, petechial hemorrhages and microvascular leakage in the myocardium occur as a result of MCE in rats.

Influence of contrast ultrasonography with perflutren lipid microspheres on microvessel injury

Microbubbles have been reported to enhance ultrasound (US)-related side effects in animal systems. The present study investigated the influence of contrast ultrasonography (US) with perflutren lipid microspheres, a recently developed second-generation contrast agent, on microvessels. Rat mesentery was exposed to 1.8-MHz pulsed US with intravenous injection of perflutren (0.1 or 1.0 ml/kg) or Levovist (300 mg/kg), and the microvessel bleeding and endothelial cell injury was examined. Impaired endothelial cells were identified by the fluorescence of propidium iodide. Microvessel bleeding was examined also in the rat myocardium. The interaction between 0.1 ml/kg of perflutren and US exposure did not cause microvessel bleeding, and did not increase endothelial cell injury compared with the sham operation, unless frequent, strong US exposure occurred. When the dose was increased to 1.0 ml/kg, the combination of perflutren and US exposure resulted in capillary bleeding and increased endothelial cell injury in capillaries and venules (p<0.01). However, the incidence of microvessel bleeding and endothelial cell injury did not exceed that with Levovist microbubbles. In the myocardium, microvessel bleeding was not observed under any conditions. In conclusion, perflutren lipid microspheres enhanced US-related microvessel injury as with other contrast agents at the dose of 1.0 ml/kg, but not with 0.1 ml/kg and the appropriate US setting.

Left ventricular opacification at rest and during stress

Although echocardiography is the most widely used cardiac imaging modality in the world, it is often limited by poor endocardial border definition. The development of contrast agents that opacify the cardiac chambers after intravenous injection now makes it possible to acquire high-quality images, even in technically difficult cases. Several studies have now shown that contrast echocardiography improves assessment of global and regional wall motion, enhances observer agreement, and salvages technically difficult studies. In addition, contrast echocardiography is valuable in specific settings, such as the intensive care unit or emergency department, where high-quality images are often most difficult to acquire. Finally, obstacles to the penetration of contrast echocardiography into routine clinical practice (such as cost/reimbursement, logistics, and education) are discussed.

Myocardial contrast echocardiography in acute coronary syndromes

Myocardial contrast echocardiography (MCE) is an emerging technique in which microbubble contrast agents are visualized in the coronary microvasculature. MCE is an ideal modality for the noninvasive evaluation of acute coronary syndromes because it provides portable, simultaneous assessment of regional wall motion and myocardial perfusion. Recent advances in microbubble contrast agents and ultrasound imaging technology have allowed new clinical applications of MCE in acute coronary syndromes. Studies suggest a promising role for MCE in the evaluation of chest pain, the diagnosis and prognosis in acute myocardial infarction, the assessment of the success of reperfusion, and the differentiation of myocardial stunning from myocardial necrosis. Potential future applications of MCE in acute coronary syndromes include the detection of inflammation and ultrasound induced thrombolysis. The following serves as a review of the current status of myocardial contrast echocardiography in acute coronary syndromes.

Automated endocardial border detection and evaluation of left ventricular function from contrast-enhanced images using modified acoustic quantification

Automated border detection (ABD) techniques have been used for the quantitative assessment of left ventricular (LV) performance but require adequate visualization of the endocardial border to accurately track the blood-tissue interface. We sought to evaluate whether ABD could be used in conjunction with an infusion of echocardiographic contrast to objectively quantify LV systolic performance. Twenty-one subjects had LV volume and ejection fraction (EF) assessed by hand-tracing and prototype ABD software during contrast infusion. The mean hand-traced EF was 45% +/- 16%. Automatic tracking of contrast-enhanced endocardial borders with prototype ABD software was possible in all subjects. This allowed generation of signal averaged LV volume waveforms, from which quantitative LV ejection fraction was obtained. There were no significant differences in LV volumes or EF between contrast-enhanced acoustic quantification and manually traced borders. This technique has the potential of providing objective quantitation of LV volume and function in patients with technically limited echocardiograms.

Endothelial cell injury in venule and capillary induced by contrast ultrasonography

The aim of the present study was to test the hypothesis that microvascular endothelial cells (EC) are subject to the bioeffects induced by contrast ultrasound (US) because of their proximity to the circulating microbubbles. We examined EC injury in each microvessel section (arteriole, capillary or venule) in rat mesenteries among the following five groups: three controls (sham operation, microbubble injection alone, US exposure with saline injection), and two contrast-US groups (US exposure at a 1-Hz or 30-Hz frame rate with microbubble injection). Propidium iodide (PI), a fluorescent indicator of cell injury, was employed to visualize impaired EC. PI-positive nuclei were equally few among the three controls. Contrast-US increased PI-positive cells in capillaries (1-Hz frame rate, 2.4 +/- 2.2 cells per 0.1-mm vessel length, p = 0.09; 30-Hz frame rate, 4.3 +/- 1.8 cells, p < 0.01) and in venules (1-Hz frame rate, 4.1 +/- 2.5 cells, p < 0.05; 30-Hz frame rate, 13.8 +/- 3.6 cells, p < 0.01) compared with sham operation (0.10 +/- 0.22 cells). The finding indicates that diagnostic contrast US potentially causes EC injury, particularly in venules and capillaries.

Enhancement of contrast echocardiography by image variability analysis

BACKGROUND

Although there have been recent advances in echocardiography, many studies remain suboptimal due to poor image quality and unclear blood-myocardium border. We developed a novel image processing technique, cardiac variability imaging (CVI), based on the variance of pixel intensity values during passage of ultrasound microbubble contrast into the left ventricle chamber, with the aim of enhancing endocardial border delineation and image quality.

METHODS AND RESULTS

CVI analysis was performed on simulated data to test and verify the mechanism of image enhancement. Then CVI analysis was applied to echocardiographic images obtained in two different clinical studies, and still images were interpreted by expert reviewers. In the first study (N = 15), using contrast agent EchoGen, the number of observable wall segments in end-diastolic images, for example, was significantly increased by CVI (4.93) as compared to precontrast (3.28) and contrast images (3.36), P < 0.001 for both comparisons to CVI. In the second study (N = 8), using contrast agent Optison, interobserver variability of manually traced end-diastolic volumes was significantly decreased using CVI (22.3 ml) as compared to precontrast (63.4) and contrast images (49.0), P < 0.01 for both comparisons to CVI.

CONCLUSION

CVI can substantially enhance endocardial border delineation and improve echocardiographic image quality and image interpretation.

Contrast microbubbles improve diagnostic yield in ICU patients with poor echocardiographic windows

OBJECTIVE

To determine the value of contrast echocardiographic studies in patients admitted to ICUs who have poor echocardiographic windows secondary to COPD, ventilator use, or inability to obtain optimal positioning for the echocardiogram.

DESIGN

A prospective comparison study of technically difficult patients in the ICU.

OUTCOME MEASURE

The total scores for the left ventricle (LV) in the two-chamber and four-chamber views were calculated at baseline and following injection of 1 to 2 mL of a contrast agent. The mean numbers of segments visualized in all patients at baseline and after injection of contrast agent were compared to assess the effect on improved visualization.

RESULTS

Forty consecutive patients underwent echocardiography in the ICU for evaluation of LV function. Of these, 25 patients (63%) had poor visualization of the endocardium and required IV contrast agent. In these 25 patients, the average baseline segmental score was 4.5, compared to 11.6 in patients who received an IV contrast agent. Nineteen patients had an average baseline segmental score of 3.9 and were deemed to have a nondiagnostic study. After administration of IV contrast, all patients converted to a diagnostic study, with an average score of 11.6 segments visualized.

CONCLUSIONS

Use of echocardiographic contrast agents in selected patients with poor baseline echocardiographic windows in the ICU setting significantly enhances segmental LV visualization and yielded 100% conversion from nondiagnostic to diagnostic studies.

Echocardiographic imaging of technically difficult patients in the intensive care unit: use of optison in combination with fundamental and harmonic imaging

Previous studies of intravenous contrast agents have excluded patients in the intensive care unit. These patients remain among the most technically difficult to image with ultrasound. We studied the effect of different imaging modalities with and without intravenous contrast (Optison) on endocardial border visualization during echocardiography. Fifty patients in the intensive care unit (32 men, 24 on mechanical ventilator, 10 with chest bandages; mean age, 59 years; mean weight, 91.7 kg; mean height, 67.6 inches) were considered to have technically difficult images when the endocardium could not be visualized in at least 2 of the 6 segments in either apical view. Each patient was studied with the use of fundamental (F), harmonic (H), fundamental + Optison (F + O), and H + O techniques, with standard long-axis, short-axis, and apical 4- and 2-chamber views. Intravenous Optison (0.5 to 1.5 mL) was given before F + O and H + O imaging. There were no contrast-related side effects noted. All images were stored digitally in a quad-screen format. For each set of images, segments (n = 22) were given an endocardial border visualization score of 0 if not visualized, 1 if visualized in either systole or diastole, and 2 if visualized in both. There was stepwise improvement in endocardial border visualization, with mean endocardial border visualization score of 1.09 +/- 0.83 (F), 1.33 +/- 0.81 (H), 1.64 +/- 0.62 (F + O), and 1.90 +/- 0.35 (H + O). There was a statistically significant difference between each group (P <.001). The incremental benefit of Optison was greater with harmonic imaging than with fundamental (P <.001). The use of Optison is safe and effective in the intensive care unit. In combination with harmonic imaging, contrast provides maximal endocardial border delineation during echocardiographic imaging of technically difficult patients in the intensive care unit.

Detection and quantification of coronary stenosis severity with myocardial contrast echocardiography

The development of microbubble contrast agents and new imaging modalities now allows the assessment of myocardial perfusion during echocardiography. These microbubbles are excellent tracers of red blood cell kinetics. Apart from providing a spatial assessment of myocardial perfusion, myocardial contrast echocardiography (MCE) can also be used to quantify the 2 specific components of myocardial blood flow-flow velocity and myocardial blood volume. The method to quantify myocardial blood flow velocity is based on rapid destruction of microbubbles by ultrasound, and subsequent assessment of the rate of replenishment of microbubbles into the myocardial microcirculation within the ultrasound beam elevation. Assessment of steady state myocardial video intensity (VI) provides a measure of myocardial or capillary blood volume. Perfusion defects that develop distal to a stenosis during hyperemia are therefore due to capillary derecruitment. We have shown that the degree of derecruitment (and therefore the severity of a perfusion defect) is proportional to stenosis severity. Because the capillary bed also provides the greatest resistance to hyperemic flow, decreases in capillary blood volume distal to a stenosis during hyperemia result in increases in microvascular resistance, which is the mechanism underlying the progressive decrease in flow reserve in the presence of a stenosis. Consequently, both the severity of a perfusion defect and quantification of abnormal myocardial blood flow reserve on MCE can be used to determine stenosis severity. As imaging methods with MCE continue to be refined, the optimal imaging algorithms for clinical practice still need to be determined. MCE, however, holds promise as a noninvasive, instantaneous, on-line method for the detection and quantification of coronary artery disease.

Myocardial contrast agents: recent advances and future directions

The assessment of perfusion by myocardial contrast echocardiography has evolved from the early contrast agents, including agitated saline solutions and hydrogen peroxide, to the current second-generation contrast agents. Unlike the first-generation contrast agents, which are composed of air, the newer, second-generation agents contain gases with a higher molecular weight and less solubility and diffusivity, improving microbubble persistence. The newer contrast agents are capable of transpulmonary passage and opacification of the left-heart chambers and the myocardial microcirculation after intravenous administration. Also, innovative imaging techniques using harmonics and triggered imaging have minimized tissue signal and improved signal-to-noise ratio, making the assessment of myocardial perfusion possible. Currently, microbubbles are being designed for specific research or clinical use by exploiting certain characteristics of the microbubble such as the shell, surface characteristics, and/or gas content. Some novel applications of microbubble technology include tissue-targeted gene therapy, drug delivery, ultrasound-enhanced thrombolysis, and the assessment of endothelial function and integrity. This review focuses on the composition, physical properties, and acoustic characteristics of the currently available myocardial contrast agents and those under clinical investigation. In addition, the clinical trials involving these agents will also be discussed.

Clinical applications of contrast echocardiography

BACKGROUND

Contrast media, used in conjunction with newly developed echocardiographic techniques, can currently be used in several clinical settings: (1) the study of myocardial perfusion, (2) delineation of the endocardial border in technically difficult echocardiographic examinations, and (3) enhancement of low-intensity blood flow, especially coronary blood flow, to study coronary flow reserve.

METHODS

Published studies were reviewed to identify the advantages of associating contrast perfusion with classic or new echocardiographic and ultrasonographic imaging techniques in the study of myocardial perfusion and coronary artery flow.

RESULTS

Several studies demonstrated the usefulness of contrast echocardiography, even in patients with a bad acoustic window, in evaluating opacification of the left ventricle or in enhancing echocardiographic color Doppler studies of coronary flow and coronary flow reserve. Preliminary results of transthoracic echocardiographic studies of myocardial perfusion are described.

CONCLUSIONS

The clinical applications of contrast echocardiography are effective in exploiting examinations that provide poor diagnostic information (ventricular cavity opacification) or in obtaining new physiopathologic data (microvascular opacification/perfusion and coronary flow reserve). The evaluation of coronary flow reserve by contrast-enhanced transthoracic Doppler ultrasonography is an attractive new diagnostic modality that points the way toward important new clinical applications of contrast echocardiography. This technique is useful in evaluating the severity of coronary artery disease of the left anterior descending coronary artery and in all clinical conditions in which the effects of therapeutic interventions aimed at improving coronary flow reserve need to be monitored.

Efficacy and safety of the novel ultrasound contrast agent perflutren (definity) in patients with suboptimal baseline left ventricular echocardiographic images

Suboptimal left ventricular (LV) cavity visualization and endocardial border delineation often compromise the clinical utility of echocardiography. This study examines the safety and efficacy of perflutren, a novel ultrasound contrast agent, for LV cavity opacification and endocardial border delineation in patients with suboptimal baseline echocardiograms. In a multicenter, randomized, placebo-controlled, double-blind trial, 211 patients with suspected cardiac disease and suboptimal baseline echocardiograms were enrolled at 17 sites. Two intravenous injections of either placebo (saline) or perflutren (5 or 10 microl/kg) were given approximately 30 minutes apart. Images of the apical 4- and 2-chamber views were acquired and scored. Perflutren opacified the LV cavity after both dosages (5 and 10 microl/kg dosages). Clinically useful contrast was observed in 89% of patients who received perflutren and in 0% of patients who received placebo (p < 0.01). Quantitative assessment of LV opacification with videodensitometry showed similar results. The mean duration of clinically useful contrast was 90 seconds. Improvement in endocardial border delineation was demonstrated in 91% of patients who received perflutren and in 12% of those who received placebo (p < 0.001). Following perflutren, an average of 4 more segments per patient were evaluable compared with baseline. Salvage of nondiagnostic baseline examinations by perflutren was demonstrated in 48% of eligible subjects. The safety profile of perflutren was similar to placebo. These data indicate that administration of perflutren to patients with suboptimal baseline images is well tolerated and provides substantial LV cavity opacification and improvement in endocardial border delineation.

Preliminary clinical experience in cardiology with sonazoid

Sonazoid (formerly NC100100) is a new ultrasound contrast agent for intravenous injection developed by Nycomed-Amersham. It consists of perfluorocarbon microbubbles that are stabilized with a surfactant and are within a well-defined size range (median diameter approximately 3 microm). Due to the low diffusibility and blood solubility of the gas, the controlled size distribution of the microbubbles, and the flexibility of the shell, Sonazoid is a free-flowing tracer capable of crossing the pulmonary capillary bed after peripheral intravenous injection. It is stable enough for the duration of the ultrasound examination and provides echo enhancement useful for clinical requirements. The preliminary clinical experience in cardiology indications, including its use in reducing the frequency of inadequate echocardiographic studies in patients with suboptimal echocardiograms, and its use as a myocardial perfusion agent in the setting of acute myocardial ischemia is briefly discussed.

Contrast echocardiography is superior to tissue harmonics for assessment of left ventricular function in mechanically ventilated patients

BACKGROUND

Assessment of left ventricular function by echocardiography is frequently challenging in mechanically ventilated patients. We evaluated the potential value of contrast-enhanced imaging and tissue harmonic imaging over standard fundamental imaging for endocardial border detection (EBD) in these patients.

METHODS AND RESULTS

Fifty patients underwent standard transthoracic 2D echocardiography and were imaged in fundamental and tissue harmonic modes and subsequently with intravenous contrast (Optison). Two echocardiographers reviewed all studies for ease of visualization of endocardial border segments and scoring of wall motion. EBD for each wall segment was graded from 1 to 4 (1 = excellent EBD). Wall motion was scored by a standard 16-segment model and 1 to 5 scale. Studies were categorized as nondiagnostic if 4 of 6 segments in the apical 4-chamber view were either poorly seen or not seen (EBD score 3 or 4). Quantification of ejection fraction was independently performed offline. Visualization of 68% of all segments improved with contrast echocardiography versus 17% improvement with tissue harmonics compared with fundamental mode. Significant improvement (poor/not seen to good/excellent) occurred in 60% of segments with contrast echocardiography versus 18% with tissue harmonics. A total of 850 segments were deemed poor/not seen, 78% of which improved to good/excellent with contrast echocardiography versus 23% with tissue harmonics. Interobserver agreement on EBD was 64% to 70%. Conversion of nondiagnostic to diagnostic studies occurred in 85% of patients with contrast echocardiography versus 15% of patients with tissue harmonics. Scoring of wall motion with fundamental mode, tissue harmonics, and contrast echocardiography was possible in 61%, 74%, and 95% of individual segments, respectively (P <.001). Wall motion scoring was altered in 17% of segments with contrast echocardiography and in 8% with tissue harmonics. Interobserver agreement on wall motion scoring was 84% to 88%. Contrast echocardiography permitted measurement of ejection fraction 45% (P =.003) more often over fundamental mode versus a 27% (P =.09) increase with tissue harmonics.

CONCLUSIONS

Contrast echocardiography is superior to tissue harmonic imaging for EBD, wall motion scoring, and quantification of ejection fraction in mechanically ventilated patients.

Measurement of left ventricular volumes and ejection fraction after intravenous contrast agent administration using standard echocardiographic equipment

The enhancement of endocardial border delineation using second harmonic imaging and contrast administration improves the measurement of ventricular volumes. In the majority of existing echocardiographic equipment, however, harmonic imaging is not yet available. The aim of this study was to assess the feasibility of the measurement of left ventricular volumes and ejection fraction after intravenous administration of the contrast agent Levovist using standard echocardiographic equipment and fundamental imaging modality. In 10 patients with good-quality two-dimensional echo imaging, 4 g (400 mg/mL concentration) of Levovist was injected intravenously. Hewlett-Packard Sonos 2000 ultrasound equipment without second harmonic imaging capability was used. To avoid the destruction of microbubbles, the echo machine was set to produce only one end-systolic and one end-diastolic frame in each cardiac cycle (dual triggering). Native and contrast imaging measurements of left ventricular volumes and ejection fractions calculated by modified Simpson's rule were compared in the fundamental mode. Intraobserver and interobserver variability values were assessed. End-diastolic volumes in native continuous and triggered mode and by contrast echo were 126 +/- 48, 121 +/- 46, and 130 +/- 50 mL, respectively (NS), whereas end-systolic volumes were 79 +/- 48, 76 +/- 45, and 79 +/- 46 mL, respectively (NS). Calculated ejection fraction using the three different imaging modalities were 0.41 +/- 0.16, 0.41 +/- 0.16, and 0.42 +/- 0.16 (NS). The intraobserver and interobserver reproducibility values were excellent in triggered mode. Standard echocardiographic equipment with fundamental imaging modality in the triggered mode is suitable for the measurement of left ventricular volumes after intravenous Levovist administration. In clinically difficult patients, contrast echocardiography in triggered mode may be applied even if echocardiographic equipment does not have harmonic imaging possibility.

Safety assessment of perflenapent emulsion for echocardiographic contrast enhancement in patients with congestive heart failure or chronic obstructive pulmonary disease

BACKGROUND

Perflenapent injectable emulsion is a newer echocardiographic contrast agent that provides chamber opacification and improved endocardial border delineation. In >1000 patients tested, adverse effects have been minimal. However, previous studies have included few patients with congestive heart failure (CHF) or severe chronic obstructive pulmonary disease (COPD). Because of their reduced cardiopulmonary reserve, these patients might be at greater risk for adverse events.

METHODS AND RESULTS

The safety of perflenapent emulsion was evaluated in ambulatory patients with New York Heart Association class III to IV congestive heart failure (CHF) or severe obstructive pulmonary disease (COPD). In 2 separate multicenter, phase II, randomized, double-blind, placebo-controlled, single-administration clinical trials, 146 patients in the CHF study and 134 patients in the COPD study received either perflenapent emulsion or saline placebo during an echocardiographic examination. Perflenapent emulsion was well tolerated in patients with CHF or COPD. The adverse event rates with perflenapent emulsion (15%) were similar to those with saline (11%; P =.43) in the combined groups, and similar findings were seen when analyzed by CHF or COPD groups separately. All adverse events were rated as mild, required no treatment, resolved spontaneously, and left no sequelae. Changes from baseline in vital signs, pulse oximetry, electrocardiography, and laboratory tests were similar between treatment groups.

CONCLUSIONS

These data support the safety of perflenapent emulsion for contrast echocardiography in stable ambulatory patients with CHF or COPD.

Contrast echocardiography: current and future applications

Recent updates in the field of echocardiography have resulted in improvements in image quality, especially in those patients whose ultrasonographic (ultrasound) evaluation was previously suboptimal. Intravenous contrast agents are now available in the United States and Europe for the indication of left ventricular opacification and enhanced endocardial border delineation. The use of contrast enables acquisition of ultrasound images of improved quality. The technique is especially useful in obese patients and those with lung disease. Patients in these categories comprise approximately 10% to 20% of routine echocardiographic examinations. Stress echocardiography examinations can be even more challenging, as the image acquisition time factor is critically important for accurate detection of coronary disease. Improvements in image quality with intravenous contrast agents can facilitate image acquisition and enhance delineation of regional wall motion abnormalities at the peak level of exercise. Recent phase III clinical trial data on the use of Optison and several other agents (currently under evaluation) have revealed that for approximately half of patients, image quality substantively improves, which enables the examination to be salvaged and/or increases diagnostic accuracy. For the "difficult-to-image" patient, this added information results in (1) enhanced laboratory efficiency, (2) a reduction in downstream testing, and (3) possible improvements in patient outcome. In addition, substantial research efforts are underway to use ultrasound contrast agents for assessment of myocardial perfusion. The detection of myocardial perfusion during echocardiographic examinations will permit the simultaneous assessment of global and regional myocardial structure, function, and perfusion-all of the indicators necessary to enable the optimal noninvasive assessment of coronary artery disease. Despite the added benefit in improved efficacy of testing, few data exist regarding the long-term effectiveness of these agents. Currently under evaluation are the clinical and economic outcome implications of intravenous contrast agent use for daily clinical decision making in a variety of patient subsets. Until these data are known, this document offers a preliminary synthesis of available evidence on the value of intravenous contrast agents for use in rest and stress echocardiography. At present, it is the position of this guideline committee that intravenous contrast agents demonstrate substantial value in the difficult-to-image patient with comorbid conditions limiting an ultrasound evaluation of the heart. For such patients, the use of intravenous contrast agents should be encouraged as a means to provide added diagnostic information and to streamline early detection and treatment of underlying cardiac pathophysiology. As with all new technology, this document will require updates and revisions as additional data become available.

Clinical impact of second harmonic imaging and left heart contrast in echocardiographic stress testing

Second harmonic imaging and left heart contrast agents are recent echocardiographic advancements that enhance the assessment of wall motion. Because little information exists concerning their clinical impact on echocardiographic stress testing in daily practice, this was determined for 9-month periods before (1997) and after (1998) their introduction. Harmonic imaging was used in all patients after its introduction. A second generation intravenous left heart contrast agent (Optison) was used at the discretion of the sonographer and physician team. Both exercise and dobutamine stress tests were included. At the time of study interpretation, diagnostic confidence was assigned as high, medium, or low. For all patients who underwent coronary angiography < or = 6 months after stress testing, the diagnostic accuracy was determined (true positive plus true negative/total studies). There were 574 studies before and 746 studies after implementation. Optison was used in 28% of the harmonic imaging studies. Study cancellations due to uninterpretable images fell from 6.4% to 1.2% (p <0.001) despite a more obese population completing testing (body mass index: 29 +/- 7 to 31 +/- 8 kg/m2, p = 0.02), whereas high diagnostic confidence increased from 55% to 64% (p <0.001). For the 7% of patients who underwent cardiac catheterization, the diagnostic accuracy remained unchanged (74 vs 73%) although a prior negative stress test was less common (40% to 20% p = 0.04). Thus, these new technologies had a favorable clinical impact.

Infusion versus bolus contrast echocardiography: a multicenter, open-label, crossover trial

BACKGROUND

In current practice, contrast echocardiography is performed with single or multiple bolus injections, which often result in an uncontrolled period of attenuation followed by transient left ventricular opacification (LVO). Because a "slow bolus" appears to reduce attenuation and prolong LVO, we hypothesized that a controlled infusion of contrast might provide a more uniform contrast effect with less attenuation and longer contrast duration.

METHODS AND RESULTS

We sought to test the hypothesis by using an infusion of contrast (DEFINITY [perflutren], The DuPont Pharmaceuticals Co, Medical Imaging, North Billerica, Mass) that is stable when diluted in saline in a randomized, multicenter, controlled, crossover trial. Sixty-four patients with poor noncontrast images were recruited at 3 centers and randomly assigned to 2 single "slow" bolus injections of contrast (10 microL/kg each over a period of 30 to 60 seconds) or an infusion (1. 3 mL in 50 mL normal saline initially at 4.0 mL/min) of contrast. Patients then returned within 24 to 72 hours for the alternative form of contrast delivery. Three independent experienced echocardiographers viewed 30 seconds of videotape for all optimal baseline and optimal contrast images to score LVO and qualitatively assessed endocardial border evaluability. The duration of adequate LVO then was independently assessed by review of the entire videotape. Three independent sonographers traced single-frame, digitally captured images to measure the length of the contiguous endocardial border visualized. Both bolus and infusion administration demonstrated improved LVO (>90% by all blinded readers, P <.01) and endocardial border visualized (mean increase of 1.8 to 4.7 cm at both end-diastole and end-systole, all P <.05) as compared with baseline images. However, contrast infusion resulted in a longer duration of LVO (range of mean durations for each reader, 158 to 174 seconds longer, P <.05) and a shorter duration of attenuation (18 to 54 seconds, P <.05) compared with either bolus injection. There were no severe adverse events with contrast infusion.

CONCLUSIONS

Contrast echocardiography delivered as an infusion optimizes the contrast effect by decreasing the attenuation period, extending the LVO duration, and providing a uniform contrast effect that may be useful in obtaining multiple echocardiographic views, stress echocardiography, myocardial perfusion imaging, and applications in which blood flow must be quantified.