Clinical application of transpulmonary contrast-enhanced Doppler technique in the assessment of severity of aortic stenosis

Multimodality imaging in aortic stenosis

Aortic stenosis (AS) is the most common cardiac valve lesion in the adult population, with an incidence increasing as the population ages. Accurate assessment of AS severity is necessary for clinical decision-making. Echocardiography is currently the diagnostic method of choice for assessing and managing AS. Transthoracic echocardiography is usually sufficient in most situations. Transesophageal echocardiography and stress echocardiography may also be utilized when there is inadequate image quality and/or discordance in the results and the clinical presentation. There is a role for other imaging modalities such as cardiac computed tomography, magnetic resonance imaging, and catheterization in selected cases. The following describes in some detail the role of these modalities in the diagnosis and assessment of AS.

Recommendations on the echocardiographic assessment of aortic valve stenosis: a focused update from the European Association of Cardiovascular Imaging and the American Society of Echocardiography

Echocardiography is the key tool for the diagnosis and evaluation of aortic stenosis. Because clinical decision-making is based on the echocardiographic assessment of its severity, it is essential that standards are adopted to maintain accuracy and consistency across echocardiographic laboratories. Detailed recommendations for the echocardiographic assessment of valve stenosis were published by the European Association of Echocardiography and the American Society of Echocardiography in 2009. In the meantime, numerous new studies on aortic stenosis have been published with particular new insights into the difficult subgroup of low gradient aortic stenosis making an update of recommendations necessary. The document focuses in particular on the optimization of left ventricular outflow tract assessment, low flow, low gradient aortic stenosis with preserved ejection fraction, a new classification of aortic stenosis by gradient, flow and ejection fraction, and a grading algorithm for an integrated and stepwise approach of artic stenosis assessment in clinical practice.

Contrast microsphere enhancement of the tricuspid regurgitant spectral Doppler signal - Is it still necessary with contemporary scanners?

BACKGROUND

Accurate evaluation of the tricuspid regurgitant (TR) spectral Doppler signal is important during transthoracic echocardiographic (TTE) evaluation for pulmonary hypertension (PHT). Contrast enhancement improves Doppler backscatter. However, its incremental benefit with contemporary scanners is less well established. The aim of this study was to assess whether the TR spectral Doppler signal using contemporary scanners was improved using a second generation contrast agent, Definity® (CE), compared to unenhanced TTE (UE).

METHODS

Analysis of patients who underwent UE then CE TR interrogation was performed. TR signal was evaluated by an experienced reader and graded 1 (clear-high level of confidence of interpretation and complete spectral Doppler envelope), 2 (suboptimal with medium-low level of confidence of interpretation and incomplete envelope), 3 (poor-absent and no measurable spectral Doppler signal). Maximal TR velocity (TRV) was defined as peak velocity that could be clearly identified. An inexperienced sonographer read 30 randomly selected studies.

RESULTS

176 TTE were performed in 173 patients (mean age 57 ± 14.8 years). Wilcoxon signed rank test demonstrated significant improvement (p < 0.0001) in TR spectral Doppler signal quality with CE TTE. Mean score CE TTE vs. TTE = 2.32 ± 0.85 vs. 2.56 ± 0.75 respectively (p < 0.0001). Mean maximal TRV CE TTE vs. UE TTE = 2.61 ± 0.44 m/s vs. 2.54 ± 0.49 m/s respectively (p < 0.0001). The inexperienced reader had a greater improvement in scoring CE TTE signals vs. UE TTE (p < 0.0001).

CONCLUSION

In the era of contemporary scanners, CE improved the ability to detect and measure TRV, except in those with clear unenhanced TR spectral Doppler signals or greater than mild tricuspid regurgitation.

Impact of Contrast Echocardiography on Assessment of Ventricular Function and Clinical Diagnosis in Routine Clinical Echocardiography: Korean Multicenter Study

Background

Fundamental echocardiography has some drawbacks in patients with difficult-to-image echocardiograms. The aim of this study is to evaluate impact of contrast echocardiography (CE) on ventricular function assessment and clinical diagnosis in routine clinical echocardiography.

Methods

Two hundred sixty patients were prospectively enrolled over 3 years in 12 medical centers in Korea. General image quality, the number of distinguishable segments, ability to assess regional wall motion, left ventricular (LV) apex and right ventricle (RV) visualization, LV ejection fraction, changes in diagnostic or treatment plan were documented after echocardiography with and without ultrasound contrast agent.

Results

Poor or uninterpretable general image was 31% before contrast use, and decreased to 2% (p<0.05) after contrast use. The average number of visualized LV segments was 9.53 before contrast use, and increased to 14.46 (p<0.001) after contrast use. The percentage of poor or not seen LV regional wall motion was decreased from 28.4% to 3.5% (p<0.001). The percentage of poor or not seen LV apex and RV was decreased from 49.4% to 2.4% (p<0.001), from 30.5% to 10.5% (p<0.001), respectively. Changes in diagnostic procedure and treatment plan after CE were 30% and 29.6%, respectively.

Conclusion

Compared to fundamental echocardiography, CE impacted LV function assessment and clinical decision making in Korean patients who undergo routine echocardiography.

Use of contrast echocardiography in intensive care and at the emergency room

Bedside echocardiography in emergency room (ER) or in intensive care unit (ICU) is an important tool for managing critically ill patients, to obtain a timely accurate diagnosis and to immediately stratify the risk to the patient’s life. It may also render invasive monitoring unnecessary. In these patients, contrast echocardiography may improve quality of imaging and also may provide additional information, especially regarding myocardial perfusion in those with suspected coronary artery disease. This article focuses on the principle of contrast echocardiography and the clinical information that can be obtained according to the most frequent presentations in ER and ICU.

Morbid obesity: obscuring the diagnosis of aortic stenosis in a patient with cardiogenic wheezing

We report the case of a morbidly obese 65-year-old female who presented with repeated hypotensive episodes following dialysis. She was misdiagnosed as suffering from asthma, and eventually was found to have severe aortic stenosis. Obesity has become a common and formidable obstacle to gathering important diagnostic information in patients. Modern diagnostic lab tests and imaging modalities such as transthoracic echocardiography (TTE) can provide spurious data in the morbidly obese population, which can ultimately lead to misdiagnosis. In this clinical vignette, we discuss the relationship between the basic pathophysiologic mechanisms underlying aortic stenosis and patient clinical presentation. We also review the relevant literature and discuss the impact of obesity on the diagnosis of this condition.

Advanced echocardiographic techniques

Echocardiography has advanced significantly since its first clinical use. The move towards more accurate imaging and quantification has driven this advancement. In this review, we will briefly focus on three distinct but important recent advances, three‐dimensional (3D) echocardiography, contrast echocardiography and myocardial tissue imaging. The basic principles of these techniques will be discussed as well as current and future clinical applications.

Echocardiography for the clinician: a practical update

Echocardiography is the mainstay of cardiovascular diagnostics, and is the most performed test for the evaluation of cardiac function. Critical and costly management decisions are based on quantification of left ventricular volumes and ejection fraction. Recent advances in echocardiography, such as microsphere contrast echocardiography for left ventricular opacification and perfusion imaging, three-dimensional transthoracic and trans-oesophageal imaging, strain and tissue Doppler imaging, all contribute to improving accuracy and reproducibility of these important measurements. Such techniques are now routinely available on standard echocardiography equipment in Australian centres for daily use. Hand-carried ultrasound devices have been developed, which are portable, are affordable and offer increased availability of echocardiography to the wider community. Clinicians should be actively encouraged to adopt these technologies to improve the diagnostic quality and reproducability of echocardiography for our patients. This article provides an overview of important recent advances in echocardiographic imaging with an emphasis on their role in clinical practice today.

American Society of Echocardiography Consensus Statement on the Clinical Applications of Ultrasonic Contrast Agents in Echocardiography

ACCREDITATION STATEMENT: The American Society of Echocardiography (ASE) is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians. The ASE designates this educational activity for a maximum of 1 AMA PRA Category 1 Credit.trade mark Physicians should only claim credit commensurate with the extent of their participation in the activity. The American Registry of Diagnostic Medical Sonographers and Cardiovascular Credentialing International recognize the ASE's certificates and have agreed to honor the credit hours toward their registry requirements for sonographers. The ASE is committed to resolving all conflict-of-interest issues, and its mandate is to retain only those speakers with financial interests that can be reconciled with the goals and educational integrity of the educational program. Disclosure of faculty and commercial support sponsor relationships, if any, have been indicated.

TARGET AUDIENCE

This activity is designed for all cardiovascular physicians, cardiac sonographers, and nurses with a primary interest and knowledge base in the field of echocardiography; in addition, residents, researchers, clinicians, sonographers, and other medical professionals having a specific interest in contrast echocardiography may be included.

OBJECTIVES

Upon completing this activity, participants will be able to: 1. Demonstrate an increased knowledge of the applications for contrast echocardiography and their impact on cardiac diagnosis. 2. Differentiate the available ultrasound contrast agents and ultrasound equipment imaging features to optimize their use. 3. Recognize the indications, benefits, and safety of ultrasound contrast agents, acknowledging the recent labeling changes by the US Food and Drug Administration (FDA) regarding contrast agent use and safety information. 4. Identify specific patient populations that represent potential candidates for the use of contrast agents, to enable cost-effective clinical diagnosis. 5. Incorporate effective teamwork strategies for the implementation of contrast agents in the echocardiography laboratory and establish guidelines for contrast use. 6. Use contrast enhancement for endocardial border delineation and left ventricular opacification in rest and stress echocardiography and unique patient care environments in which echocardiographic image acquisition is frequently challenging, including intensive care units (ICUs) and emergency departments. 7. Effectively use contrast echocardiography for the diagnosis of intracardiac and extracardiac abnormalities, including the identification of complications of acute myocardial infarction. 8. Assess the common pitfalls in contrast imaging and use stepwise, guideline-based contrast equipment setup and contrast agent administration techniques to optimize image acquisition.

Current role of contrast echocardiography in the diagnosis of cardiovascular diseases

The use of contrast echocardiography (CE) in cardiovascular medicine has grown significantly over the last 15 years. Depending on the site of injection, contrast enhancement of the right- or left-sided cardiac chambers or myocardium now can be achieved. Contrast echocardiography can improve the evaluation of patients with valvular heart disease by enhancing the Doppler signal; CE also improves detection of intracardiac or intrapulmonary shunts. In patients with coronary artery disease, enhancement of the endocardial blood-tissue boundary allows for improved visualization of endocardial wall motion, assessment of wall thickening, and calculation of ejection fraction. Contrast echocardiography promises to delineate myocardial perfusion and has the potential for quantitating coronary flow and assessing myocardial viability. These applications may add important physiologic information to the anatomic information readily available from noncontrast echocardiography. Because it can be rapidly performed at the bedside, CE may be a valuable tool for use with inpatients with acute myocardial ischemia. When CE has been used after recanalization of occluded coronary arteries, the assessment of myocardial salvage conveys information concerning reflow, stunning, and prognosis, and in the case of an angioplasty it provides immediate information regarding the success of the procedure. Contrast echocardiography can also assess myocardial areas at risk of irreversible damage and the presence or absence of collateral flow. When performed with transesophageal or epicardial echocardiography in the operating room, CE is emerging as a valuable tool in the assessment of cardioplegia distribution and graft patency as well as in the delineation of the regional supply of each graft. With the continued development of newer contrast agents and refinement of ultrasound imaging equipment, the applications of CE will continue to grow.

Contrast Echocardiography Can Save Nondiagnostic Exams in Mechanically Ventilated Patients

Patients in an intensive care unit (ICU) under mechanical ventilation (MV) are very difficult to image by transthoracic echocardiography, diminishing the beneficial information that could be obtained by this noninvasive approach. The objective of this study is to assess whether the addition of a contrast agent to fundamental imaging (FI) can improve or change the initial diagnosis in cardiac postoperative patients under mechanical ventilation by enhancing endocardial border delineation and Doppler flow signal. Thirty mechanically ventilated post-cardiac surgery patients (20 men, mean age 61 +/- 13 years) were evaluated with FI before and after intravenous injection of contrast. Left ventricular endocardial border delineation score index (EBDSI), estimated left ventricular ejection fraction (LVEF), and color and spectral Doppler were analyzed. The use of contrast resulted in a significant increase in the number of well-delineated segments, with a salvage rate of 77% of nondiagnostic studies. EBDSI was 1.62 +/- 0.61, before contrast, increasing to 2.05 +/- 0.53 after it (P < 0.001). There was a change in the LVEF estimation in 5 exams, and a new wall motion abnormality was detected in other 4 exams, after the use of contrast. Moreover, a significant change was observed in the quantification of mitral regurgitation in 5 patients, in the aortic transvalvular peak gradient in 1 patient, and measurement of tricuspid regurgitation peak flow velocity in 8 patients. It is concluded that in cardiac postoperative patients under mechanical ventilation, intravenous injection of a contrast agent using FI resulted in a high salvage rate of studies and changed the initial diagnosis in a significant number of patients.

Contrast agent increases doppler velocities and improves reproducibility of aortic valve area measurements in patients with aortic stenosis

Observer variability may limit assessment of aortic stenosis by Doppler echocardiography. This study aimed to assess whether echocardiographic contrast agent improves reproducibility of aortic valve area (AVA) measurements for patients with aortic stenosis. In all, 20 patients with aortic stenosis (67 +/- 10 years old) underwent noncontrast and contrast Doppler echocardiography on 2 occasions, 3 weeks apart. Intraobserver and interobserver coefficients of reproducibility were 0.36 and 0.20 cm for left ventricular outflow tract (LVOT) diameter, and 0.38 and 0.24 cm(2) for AVA, respectively. Although intraobserver reproducibility was unaffected, contrast improved interobserver reproducibility for LVOT diameter (mean of differences -0.02 +/- 0.07 cm vs 0.01 +/- 0.10 cm, P <.05) and AVA (mean of differences 0.02 +/- 0.10 cm(2) vs 0.07 +/- 0.12 cm(2), P <.05). Prevalve and postvalve velocities were increased with contrast compared with noncontrast imaging (prevalve, 1.07 +/- 0.20 vs 0.94 +/- 0.19 m/s, P <.01; postvalve, 3.76 +/- 0.87 vs 3.47 +/- 0.78 m/s, P <.01). We conclude that contrast significantly increases Doppler velocities and produces modest improvements in reproducibility of LVOT diameter and AVA. We suggest that, when assessing patients with aortic stenosis, contrast agents should be considered in patients who are difficult to image with poor baseline LVOT images or Doppler studies, or where there is poor interobserver reproducibility.

The effect of echo contrast agent on Doppler velocity measurements

The purpose of this investigation was to determine the effect of echo contrast agents on spectral Doppler velocity measurements. SH U 508A was administered by IV injection in 15 patients. The transmitral flow velocity was measured at the E- and A-wave peaks before the start and at the peak of the contrast effect. The Doppler velocity was determined from the Doppler video spectral display and from power spectral analysis of the audio Doppler signal. The Doppler signal intensity was also measured. The Doppler signal intensity increased 17.4 +/- 3.5 dB (p < 0.0001) following echo contrast injection. This was associated with a significant increase in the spectral peak velocity as determined from either the video display or audio analysis. (p < 0.0001). The velocity corresponding to the audio power peak frequency (the modal velocity) did not change significantly (p = NS) and was independent of Doppler signal strength.

Echo contrast-enhanced diagnosis of atrial septal defect

Pulsed wave, continuous wave, and color flow Doppler imaging as well as intravenously administered agitated saline solution can detect intracardiac shunts during transthoracic echocardiography. Ultrasonographic contrast agents have greatly improved the visualization of left heart chambers and can enhance signals from blood flow within chambers and across valves, increasing the sensitivity of Doppler techniques. We describe a patient in whom the use of echo contrast media during transthoracic echocardiography allowed the detection of a previously unseen atrial septal defect. Combining such modalities may help to increase the sensitivity of transthoracic echocardiography and may eliminate the need for transesophageal echocardiography in selected patients.

Clinical usefulness of intravenous albunex for the Doppler assessment of aortic stenosis

Optimal Doppler recordings of stenotic aortic flow are not always easy to obtain. Therefore, the present study investigated how useful intravenous Albunex injections were for improving the Doppler assessment of pressure gradients for aortic stenosis in 20 consecutive patients who underwent Doppler and left-heart catheterization studies within a 1-week period. Continuous-wave Doppler echocardiography was performed using both a 2.5 MHz duplex and a 1.9MHz independent transducer before and after Albunex injections. The maximum and mean pressure gradients were calculated from the highest Doppler velocity tracings using the simplified Bernoulli equation. Pullback catheterization pressure tracings from the left ventricle to the ascending aorta were superimposed for determination of the maximum instantaneous and mean pressure gradients. The Doppler-derived peak and mean pressure gradients showed significant underestimation compared with the catheterization gradients (23+/-17 mmHg and 11+/-7 mmHg, respectively). However, this underestimation disappeared with Albunex injection (-2+/-7 mmHg and -1+/-4mmHg, respectively). Although the Doppler-derived instantaneous and mean pressure gradients correlated well with the catheterization gradients (r=0.909 and r=0.879, respectively), they became much closer with Albunex (r=0.987 and r=0.963, respectively). The improvements in the Doppler-derived peak pressure gradients were significant from an apical window (n=12, 84-120mmHg, p<0.001). but less so from non-apical windows (n=8, 84-91 mmHg, p=0.0146). Accordingly, Albunex is most useful for Doppler recordings of stenotic aortic flow available from the apical window, but not less so from other acoustic windows.

Contrast Echocardiography in Clinical Practice

After FDA approval of the new-generation contrast agent Optison (Mallinckrodt Medical, St. Louis, MO) January 1998, the use of contrast in echocardiograhy has become an invaluable tool. A review of 100 patients revealed contrast to be useful for endocardial border definition and wall segment analysis, enhancement of pulsed Doppler, and chamber opacification for the detection of thrombi. Evaluation of wall segments by two observers before and after injection of the contrast agent revealed an increase in the number of wall segments visualized by 4.8. Postinjection readings were consistent between the two observers. Routine contrast echocardiography may provide a more diagnostic study.

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.

Intravenous Optison (FS069) enhances pulmonary vein flow velocity signals: a multicenter study

BACKGROUND

Pulmonary vein spectral Doppler signals to characterize ventricular diastolic and systolic function, though often difficult to obtain, can be enhanced using contrast agents.

HYPOTHESIS

The objective of this study was to determine the efficacy of the intravenous contrast agent Optison for enhancement of Doppler signals in patients with poor signals on two-dimensional echocardiographic examinations.

METHODS

Enhancement of pulmonary venous flow was evaluated in 191 patients at 0.2, 0.5, 3.0, and 5.0 ml per injection.

RESULTS

Greatest contrast enhancement for right and left pulmonary veins was observed at the highest doses. At 0.5 ml, conversion from inadequate to adequate was observed in right and left pulmonary veins in 48.0 and 79.3% of patients, respectively, while any degree of improvement was 54.4 and 65.8%, respectively. The adverse event rate (6.5%) was similar to a first-generation agent.

CONCLUSION

The results demonstrate that Optison is a safe and effective contrast agent for improving visualization of pulmonary Doppler signals, especially the left pulmonary vein.

Clinical applications of transpulmonary contrast echocardiography

BACKGROUND

The recent development of new fluorocarbon-based echocardiographic contrast agents that are capable of opacification of the left-sided cardiac chambers after intravenous injection is a major new advance in diagnostic cardiac imaging.

METHODS AND RESULTS

This is a review article focusing on these novel contrast agents, new echocardiographic imaging techniques to optimize their efficacy, and their clinical applications. Specific clinical applications of these agents are (1) enhancement of endocardial border definition to improve assessment of regional and global left ventricular function, (2) myocardial perfusion imaging by intravenous contrast echocardiography, (3) augmentation of spectral and color flow Doppler images, and (4) tissue-specific targeting of microbubbles for delivery of therapeutic agents.

CONCLUSIONS

New intravenous contrast agents offer the possibility to assess myocardial perfusion echocardiographically. It is also possible to use these agents for delivery of therapeutic agents, including gene therapy.

Contrast echocardiography: review and future directions

Recent developments and advances in contrast echocardiography have been made to improve the diagnosis and evaluation of cardiac structures and function. By coupling new developments in acoustic instrumentation with new contrast agents, information that was previously difficult or impossible to gather by standard 2-dimensional echocardiography can now be obtained. Numerous studies have been published confirming the advantages of using contrast during echocardiographic studies, particularly with stress testing and myocardial perfusion. This review aims to summarize (1) the various contrast agents that are available or being developed; (2) factors that have been found to affect the strength of enhanced signals; (3) the new developments in instrumentation that improve the ability of scanners to differentiate echo contrast from cardiac tissue; and (4) the documented and possible future uses of contrast echocardiography.

[Applications of contrast media in echocardiography]

The development of contrast media in ultrasound has been slow and sporadic, and there are no fully satisfactory agents for clinical imaging to date. Most contrast agents consist of air filled microbubbles which generate scattered echoes and enhance the ultrasound information. In this article we review the different phases of contrast echocardiography their potentials and clinical applications. First, right-sided echocontrast which is mainly used for the assessment of intracardiac shunts. Second, left-sided contrast agents with smaller and more stable microbubbles, that allow the visualization of the left ventricle after intravenous injection. With these agents, one it is now possible to study myocardial perfusion which is one of the most attractive potentials of these types of agents.

Preload and incident angle independent index of left ventricular contractility determined by continuous wave Doppler echocardiography

Although left ventricular dP/dtmax can be accurately assessed using Doppler echocardiography, the fact that Doppler-derived dP/dtmax depends both on preload and Doppler incident angle limits its clinical value. We investigated the clinical usefulness of Doppler-derived (dP/dtmax)/IP (IP, isovolumic pressure), which is known to be relatively insensitive to preload and theoretically independent of the incident angle in 9 subjects. We conclude that Doppler-derived (dP/dtmax)/IP is relatively insensitive to both the incident angle and preload. In addition to its noninvasiveness, these unique features makes it very attractive as a clinical index of ventricular contractility.

Improved transvalvular continuous-wave Doppler signal intensity after intravenous Albunex injection in patients with prosthetic aortic valves

A lung-crossing contrast agent, sonicated albumin (Albunex), has been reported to enhance left-sided Doppler signals in patients with native valvular diseases. The purpose of this study was to clarify the ability of Albunex to enhance transvalvular Doppler signals in patients with prosthetic aortic valves. Forty-five consecutive patients were studied after they underwent aortic valve replacement. Transvalvular flow signals were recorded from the apical long-axis view with the use of continuous-wave Doppler echocardiography before and after intravenous injection of Albunex (0.04 to 0.08 ml/kg). Continuous-wave Doppler signal quality was graded as follows: 1, none; 2, poor; 3, suboptimal; and 4, optimal.

RESULTS

Grade 4 continuous-wave Doppler signal could be detected in 64% of the cases (29 of 45). After contrast injection, continuous-wave Doppler signal quality improved in all, and grade 4 continuous-wave Doppler signal could be detected in 93% (0.04 ml/kg) and 100% (0.08 ml/kg), respectively. The transvalvular maximal velocities derived from contrast-enhanced, continuous-wave Doppler signals were well correlated with the highest available unenhanced. Doppler maximal velocities (y = 0.90x + 0.27, r = 0.93, p < 0.01, standard error of estimate = 0.08 m/sec).

CONCLUSION

Intravenous Albunex injection improves transvalvular continuous-wave Doppler signal intensity in patients with prosthetic aortic valves.

Improved Doppler echocardiographic assessment of the left atrial appendage by peripheral vein injection of sonicated albumin microbubbles

We evaluated the usefulness of peripherally injected sonicated albumin microbubbles in transesophageal echo-Doppler cardiographic assessment of the left atrial appendage in 19 patients (age 61 +/- 19 [range 21 to 86] years; 12 [63%] women). Multiplane transesophageal echocardiography was performed before and after intravenous injection of sonicated albumin, and the left atrial appendage image and Doppler flow signal quality were assessed by a grading system of 0 to 3+ (0 = poor, 1 + = adequate, 2+ = good, and 3+ = excellent). Microbubbles appeared in the left atrium in 15 (79%) of 19 patients and completely opacified the left atrial appendage in 7 (37%) of 19 patients. Left atrial appendage maximal and minimal areas by planimetry were similar before and after contrast injection, although image quality improved in 13 (68%) of 19 patients (echocardiographic grade 1.8 +/- 0.6 vs 2.6 +/- 0.5, p< 0.001). Similarly, left atrial appendage peak emptying and peak filling Doppler flow velocities did not change before and after contrast injection, although Doppler flow signal quality improved in 12 (63%) of 19 patients (Doppler grade 1.6 +/- 0.5 vs 2.1 +/- 0.8, p < 0.05). Overall, contrast injection improved left atrial appendage echocardiographic or Doppler quality in 16 (84%) of 19 patients. Thus peripheral vein injection of sonicated albumin microbubbles can improve the assessment of left atrial appendage structure and function by transesophageal echocardiography.

Transthoracic echocardiographic assessment of periprosthetic mitral regurgitation using intravenous injection of sonicated albumin

Mechanical prostheses induce artifacts that decrease the accuracy of conventional transthoracic echocardiographic imaging for the detection and quantitation of periprosthetic mitral regurgitation. In 15 patients undergoing transthoracic echocardiography, injection of sonicated albumin significantly enhanced the assessment of periprosthetic mitral regurgitation with an accuracy similar to that of transesophageal echocardiography.

Contrast echocardiography: influence of ultrasonic machine settings, mixing conditions, and pressurization on pixel intensity and microsphere size of Albunex solutions in vitro

To use Albunex as a blood-flow tracer, the stability and consistency of microspheres under mixing conditions must be known. This study examined the effects of mixing conditions and machine settings on the size and echogenicity of Albunex solutions in vitro. Acoustic power, log compression, time-gain compensation, and transducer frequency were varied as Albunex solutions were imaged after mixing with magnetic stirring and pressurized. Higher acoustic power and lower transducer frequency decreased mean pixel intensity of Albunex solution images over time. Intensity, size, and number of Albunex microspheres were not significantly different between stirring speeds. The echogenicity of the Albunex solutions decreased with pressurization, and the critical pressure necessary to reduce the intensity to half its initial value increased with the logarithm of concentration (r = 0.91; p < 0.001). The microsphere size decreased with pressurization and remained smaller after pressure release (3.66 +/- 2.13 versus 1.47 +/- 0.95 microns; p < 0.01). These data indicate that acoustic power and transducer frequency may affect the physical properties of Albunex microspheres, decreasing mean videointensity. Pressure sensitivity of Albunex caused the decrease of videointensity and microsphere size.

The mechanism and clinical implication of improved left ventricular videointensity following intravenous injection of multi-fold dilutions of albumin with dextrose

The left ventricular ultrasound videointensity of an intravenous injection of sonicated albumin is improved if the agent is diluted with dextrose prior to sonication. The objective of this study was to determine the mechanism for improved left ventricular ultrasound contrast with intravenous sonicated multi-fold dilutions of albumin with dextrose compared to sonicated albumin alone. Epicardial short axis images of the left ventricle were obtained in 11 mongrel dogs and incremental one part sonicated dilutions (up to 10-fold) of albumin with 5 or 50% dextrose were given intravenously to determine which dilution and dextrose concentration produced optimal left ventricular videointensity. Microbubble size and concentration of these dilutions were measured. The one to seven-fold sonicated dilutions resulted in a slight, but significantly larger microbubble size when compared to sonicated albumin alone (SA), but no difference in concentration. All dilutions produced significantly higher end-diastolic peak videointensity (PVI) in the left ventricle than SA (range 160-569% of SA PVI; p < 0.001) with the three to five-fold dilution producing maximal PVI. Five percent dextrose dilutions produced the same videointensity as 50% dilutions. End-systolic videointensity of both 5 and 50% dextrose dilutions were also over 250% higher than SA (p < 0.001). This resulted in good or excellent end-systolic endocardial border definition in the majority of injections. Therefore, the mechanism for improved left ventricular chamber opacification with multifold sonicated dilutions of albumin with dextrose appears to be due to a small increase in microbubble size and not increased viscosity or microbubble concentration.

Clinical evaluation of left heart Doppler contrast enhancement by a saccharide-based transpulmonary contrast agent. The Levovist Cardiac Working Group

OBJECTIVES

A multicenter study was carried out to evaluate the efficacy with which SHU 508A enhances left heart Doppler signals and improves the clinical quantification of valve disease.

BACKGROUND

Poor signal-to-noise ratio often limits the Doppler interrogation of left heart flows. This problem may be resolved by the enhancement of Doppler signals by an ultrasound contrast agent capable of pulmonary transmission, such as the recently developed SHU 508A.

METHODS

Left heart contrast enhancement was tested for 1) continuous wave Doppler evaluation in 51 patients with aortic stenosis, 2) pulsed Doppler transthoracic evaluation of pulmonary venous flow in 85 patients, and 3) color Doppler evaluation of mitral regurgitation in 60 patients. Studies were performed immediately before and during the intravenous administration of SHU 508A (16 ml of 200 mg/ml) and compared with unenhanced transesophageal data in representative subsets of patients.

RESULTS

SHU 508A had no serious adverse effects. A significant increase in left heart Doppler signal intensity lasted for 30 to 300 s. The continuous wave Doppler velocity envelope was enhanced for all jets, but Doppler peak velocity was not altered in high quality baseline studies. However, Doppler contrast enhancement resulted in higher measured peak gradients (p < 0.001) in 29 patients with aortic stenosis who had poor quality baseline studies. This improved the overall correlation with invasive pressure measurements (r = 0.73 vs. r = 0.89, p < 0.01). The enhanced pulsed Doppler traces of transthoracic pulmonary venous flow allowed quantitative analysis in 92% patients (vs. 27% at baseline) and correlated well with peak velocities and velocity profiles obtained by transesophageal echocardiography (r = 0.91, p < 0.001). The enhanced color Doppler display of regurgitant jets increased jet area with a high interindividual variability (mean 276%), resulting in almost identical jet areas as unenhanced transesophageal values (r = 0.97, p < 0.001).

CONCLUSIONS

SHU 508A is a safe transpulmonary contrast agent that significantly enhances both spectral and color Doppler signals in the left heart. In specific patient subsets, the increase in signal-to-noise ratio improved the quantitative assessment of aortic stenosis, pulmonary venous flow and mitral regurgitation.

Multifold sonicated dilutions of albumin with fifty percent dextrose improve left ventricular contrast videointensity after intravenous injection in human beings

An intravenous injection of a onefold dilution of sonicated albumin with 50% dextrose improves echocardiographic left ventricular cavitary opacification in dogs compared with sonicated albumin. The objective of this study was to determine whether sonicated dilutions of albumin with dextrose would improve left ventricular videointensity after intravenous injection in humans and to delineate what ratio of albumin with dextrose results in optimal left ventricular cavitary opacification. We gave intravenous injections (randomized) of sonicated albumin and three different dilutions of albumin with 50% dextrose sonicated at different time intervals (onefold, threefold, and sevenfold dilutions sonicated albumin for 40 seconds and threefold and sevenfold dilutions sonicated albumin for 80 to 100 seconds) to 10 healthy human volunteers. End-diastolic and end-systolic videointensity and mean transit time from the mid-left ventricular cavity were compared after an 8.0 ml intravenous injection of all six samples. The threefold and sevenfold dilutions sonicated for 80 to 100 seconds produced microbubble concentrations similar to those of sonicated albumin but with significantly larger (5.6 microns versus 4.7 microns for sonicated albumin) size. These dilutions produced significantly higher end-diastolic and end-systolic videointensity, area under the time-intensity curve, and mean transit time compared with sonicated albumin or any of the dilutions sonicated for 40 seconds (p < or = 0.005). These data suggest that multifold dilutions of albumin with dextrose produce improved ultrasound contrast.

Myocardial contrast enhancement after intravenous injection of sonicated albumin microbubbles: a transesophageal echocardiography dipyridamole study

Myocardial opacification after intravenous injection of an echo-contrast agent is a major end point in contrast echocardiography, but it has not yet been obtained in human beings. We propose transesophageal contrast echocardiography as a clinical tool for the study of myocardial perfusion in human beings. Sonicated albumin microbubbles are bright ultrasound reflectors that cross the pulmonary vasculature after intravenous injection and show physiologic transit times through tissues. Transesophageal echocardiography uses ideal transducer frequency and acoustic window for in vivo detection of sonicated albumin microbubbles. We have studied 11 patients receiving peripheral vein bolus injection of sonicated albumin microbubbles during transesophageal echocardiography at baseline and during dipyridamole infusion. Images were recorded on videotape and digitized off-line. Quantitative measurements were made on 11 normally perfused myocardial segments by tracing a region of interest of greater than 100 pixels on frozen end-systolic frames, at baseline, and during dipyridamole infusion. Transpulmonary passage with full left ventricular cavity opacification was obtained in all injections. In 8 of 22 injections there was also transient left ventricular cavity attenuation. In all patients there was a marked opacification of the left ventricular outflow tract and aortic root. At baseline, mean signal intensity in the myocardium increased from 80 +/- 37 to 117 +/- 49 IU (p < 0.05) and during dipyridamole infusion increased from 84 +/- 28 to 146 +/- 36 IU (p < 0.001). The analysis of background-subtracted data showed that mean pixel intensity increased from baseline to dipyridamole contrast injection (from 37 +/- 15 to 62 +/- 19 IU; p < 0.01). The opacification of normally perfused left ventricular myocardium is feasible during transesophageal echocardiography because there is a significant increase in signal intensity versus background intensity. During dipyridamole infusion there is a further increase in signal intensity that probably reflects pharmacologically induced increase in myocardial blood flow.

Validation of continuous wave Doppler-determined right ventricular peak positive and negative dP/dt: effect of right atrial pressure on measurement

OBJECTIVES

The present study aimed to validate the peak positive and negative values of the first derivative of right ventricular pressure (dP/dt) using Doppler echocardiography and to determine the impact of right atrial pressure on the measurements.

BACKGROUND

A pressure gradient between the right ventricle and the right atrium can be obtained by continuous wave Doppler-derived tricuspid regurgitant velocity using the simplified Bernoulli equation. If right atrial pressure fluctuation during systole and isovolumic diastole were small compared with right ventricular pressure changes, right ventricular pressure could be evaluated, and maximal positive and negative dP/dt could also be determined with Doppler echocardiography.

METHODS

We investigated 11 patients with a wide range of right atrial pressure with tricuspid regurgitation using simultaneous examination by Doppler ultrasound and catheterization. Hemodynamic conditions were altered by the Valsalva maneuver, and a total of 40 beats were analyzed.

RESULTS

There was good correlation between Doppler-derived and catheterization-derived peak positive dP/dt (y = 1.0x - 15.4, r = 0.98, n = 40), irrespective of the level of right atrial pressure. Doppler-derived peak negative dP/dt also showed good correlation with that determined by catheterization (y = 0.9x + 58.2, r = 0.93, n = 40). However, in patients with high right atrial pressure (v wave pressure > or = 10 mm Hg), Doppler-derived peak negative dP/dt tended to show lower values than those from catheterization measurements, except in patients with pulmonary hypertension.

CONCLUSIONS

We conclude that right ventricular dP/dt can be estimated by the Doppler method accurately and noninvasively. However, when right atrial pressure is relatively high compared with corresponding right ventricular pressure changes during isovolumic diastole, Doppler-derived peak negative dP/dt might underestimate catheter-derived measurements.