Harmonic imaging: echocardiographic enhanced contrast intensity and duration

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.

Prognostic value of cardiac power output to left ventricular mass in patients with left ventricular dysfunction and dobutamine stress echo negative by wall motion criteria

AIMS

Cardiac power output to left ventricular mass (power/mass) is an index of myocardial efficiency reflecting the rate at which cardiac work is delivered with respect to the potential energy stored in the left ventricular mass. In the present study, we sought to investigate the capability of power/mass assessed at peak of dobutamine stress echocardiography to predict mortality in patients with ischaemic cardiomyopathy and no inducible ischaemia.

METHODS AND RESULTS

One-hundred eleven patients (95 males; age 68 ± 10 years) with 35 ± 7% mean left ventricular ejection fraction and a dobutamine stress echocardiography (up to 40 µg/kg/min) negative by wall motion criteria formed the study population. Power/mass at peak stress was obtained as the product of a constant (K = 2.22 × 10^-1) with cardiac output and the mean arterial pressure divided by left ventricular mass to convert the units to W/100 g. Patients were followed up for a median of 29 months (inter-quartile range 16-72 months). All-cause mortality was the only accepted clinical end point. Mean peak-stress power/mass was 0.70 ± 0.31 W/100 g. During follow-up, 29 deaths (26%) were registered. With a receiver operating characteristic analysis, a peak-stress power/mass ≤0.50 W/100 g [area under curve 0.72 (95% CI 0.63; 0.80), sensitivity 59%, specificity 80%] was the best value for predicting mortality. Univariate prognostic indicators were age, male sex, peak-stress ejection fraction, peak-stress stroke volume, peak-stress cardiac output, peak-stress cardiac power output ≤1.48 W, and peak-stress power/mass ≤0.50 W/100 g. At multivariate analysis, age (HR 1.08, 95% CI 1.04; 1.14; P = 0.004) and peak-stress power/mass ≤0.50 W/100 g (HR 4.05, 95% CI 1.36; 12.00; P = 0.01) provided independent prognostic information. Three-year mortality was 14% in patients with peak-stress power/mass >0.50 W/100 g and 47% in those with peak-stress power/mass ≤0.50 W/100 g (log-rank 20.4; P < 0.0001).

CONCLUSION

Power/mass assessed at peak of dobutamine stress echocardiography allows effective prognostication in patients with ischaemic cardiomyopathy and test result negative by wall motion criteria. In particular, a peak-stress power/mass ≤50 W/100 g is a strong and multivariable predictor of mortality.

Clinical application and laboratory protocols for performing contrast echocardiography

Technically difficult echocardiographic studies with suboptimal images remain a significant challenge in clinical practice despite advances in imaging technologies over the past decades. Use of microbubble ultrasound contrast for left ventricular opacification and enhancement of endocardial border detection during rest or stress echocardiography has become an essential component of the operation of the modern echocardiography laboratory. Contrast echocardiography has been demonstrated to improve diagnostic accuracy and confidence across a range of indications including quantitative assessment of left ventricular systolic function, wall motion analysis, and left ventricular structural abnormalities. Enhancement of Doppler signals and myocardial contrast echocardiography for perfusion remain off-label uses. Implementation of a contrast protocol is feasible for most laboratories and both physicians and sonographers will require training in contrast specific imaging techniques for optimal use. Previous concerns regarding the safety of contrast agents have since been addressed by more recent data supporting its excellent safety profile and overall cost-effectiveness.

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.

Pretest score for predicting microbubble contrast agent use in stress echocardiography: a method to increase efficiency in the echo laboratory

Background. In stress echocardiography, contrast agents are used selectively to improve endocardial border definition. Early identification of candidates may facilitate use of these agents in small and medium volume laboratories where resources are limited. Methods. We studied 15232 patients who underwent stress echocardiography. Contrast agent was used if 2 or more ventricular segments were not adequately visualized without contrast. Logistic regression models were used to evaluate the association between individual characteristics and contrast use. An 11-point score was derived from the significant characteristics. Results. Variables associated with microbubble use were age, sex, smoking, presence of multiple risk factors, bodymass index (BMI), referral for dobutamine stress echocardiography, history of coronary artery disease, and abnormal baseline electrocardiogram. All variables except BMI were given a score of 1 if present and 0 if absent; BMI was given a score of 0 to 4 according to its value. An increased score was directly proportional to increased likelihood of contrast use. The score cutoff value to optimize sensitivity and specificity was 5. Conclusions. A pretest score can be computed from information available before imaging. It may facilitate contrast agent use through early identification of patients who are likely to benefit from improved endocardial border definition.

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.

Contrast ultrasound: general principles and veterinary clinical applications

The concept of contrast enhancement has significantly extended the usefulness of ultrasound imaging in human medicine and medical research over the past decade. The persistence and efficacy of ultrasound contrast agents has been improved and specific imaging sequences have been developed. Contrast ultrasound provides Doppler and grey-scale enhancement. Doppler examinations are improved when studying deep or small vessels and vessels with low flow velocities. Specific contrast imaging sequences allow detection of tissue enhancement with grey-scale ultrasound which enables assessment of tissue perfusion. Major clinical applications of contrast ultrasound in the human medicine field are the heart, the parenchymal organs such as the liver, spleen and kidneys, and vascular applications. Many other interesting applications have been identified and beside their diagnostic value, intensive research is currently investigating the use of ultrasound contrast agents for therapeutic applications such as targeted delivery of drug- or gene-loaded microbubbles. In the last few years, contrast ultrasound has also been introduced in veterinary medicine. Its usefulness has been shown in diseases of the liver, spleen, kidney, pancreas, lymph nodes and superficial tumours. In the present article, an overview of the physical principles, imaging techniques and image analyses is presented. In addition, a literature review details the current use in veterinary medicine and areas of potential utilization are discussed.

Comparison of Echocardiography Using Tissue Harmonics and Contrast Harmonics with Radionuclide Angiography for the Assessment of Left Ventricular Function

Background

Left ventricular ejection fraction (LVEF) is a significant predictor of morbidity and mortality; however, the optimal noninvasive modality for the quantitative determination of LVEF is not apparent.

Hypothesis

We verified the hypothesis that the various echocardiographic methods of assessing LVEF using the Method of Discs with contrast (Optison human albumin microspheres; Amersham Health, Princeton, NJ) and visual assessment of LVEF using tissue harmonics and contrast harmonics compare favorably with radionuclide angiography (RNA).

Methods

In a prospective analysis, 24 consecutive patients scheduled to undergo RNA had an echocardiogram using tissue harmonics and contrast harmonics on the same day. LVEF was assessed by RNA by an experienced, blinded reader using manual determination of the region of interest. LVEF was calculated using the Method of Discs (Simpson's Rule) by a blinded sonographer. LVEF was visually estimated by two blinded readers using echocardiography with tissue harmonics and contrast harmonics on separate occasions.

Results

By linear regression analysis, LVEF determination by echocardiography with contrast using the Method of Discs correlated well with RNA (r = .835, p < .0005). Using Bland-Altman analysis, the second echocardiogram reader had excellent agreement with RNA, whereas the first reader had a mean difference of 5.25% (CI 1.3–9.2; p = .012) with visual assessment using tissue harmonics and a mean difference of 4.67% (CI 0.4–8.8; p = .031) with visual assessment using contrast harmonics compared with RNA. Thus, a small difference in agreement between RNA and echocardiographic visual estimation was noted that appeared to be primarily reader dependent.

Conclusions

LVEF determination with echocardiography with contrast using the Method of Discs correlated well with RNA and provided agreement across a range of cardiac functions. Visual echocardiographic assessment of LVEF with both tissue harmonics and contrast harmonics correlated well with RNA, but contrast harmonics did not appear to offer an advantage over tissue harmonics alone.

Harmonic ultrasound: a review

Harmonic ultrasound is a technique based on the principle of transmitting at frequency f and receiving at frequency 2f (or 1/2f). This technology has become available through the development of wide-bandwidth transducers. Microbubble contrast media produce a large amount of harmonic signal. Contrast harmonic ultrasound provides the opportunity to image patterns of high flow vasculature and overall perfusion. Regions of poor perfusion, including necrosis or infarction, can be identified with contrast harmonic ultrasound. While proportionately lower, tissues also produce harmonic signals. Tissue harmonic ultrasound sequences often improve subjective image quality compared to fundamental ultrasound in echocardiographic and abdominal examinations. This review will discuss the physical principles of harmonic ultrasound signal generation, medical and animal research applications, and an overview of current veterinary experiences.

Contrast dobutamine stress echocardiography: clinical practice assessment in 300 consecutive patients

In this study we compared non-contrast imaging with contrast imaging of the left ventricle during dobutamine stress echocardiography (DSE). Wall segment visualization, image quality, and confidence of interpretation were determined with and without the use of intravenous Optison, a second-generation echocardiographic contrast agent, in 300 consecutive patients undergoing rest and peak DSE. At rest and at peak stress, the percentage of wall segments visualized, image quality, and confidence of interpretation were better with contrast compared with non-contrast imaging. No significant decrease was seen in wall segment visualization, image quality, or confidence of interpretation from rest to peak stress in images obtained with contrast, unlike the images obtained without contrast from rest to peak stress. The use of the intravenous echocardiographic contrast agent Optison during DSE significantly improved wall segment visualization and image quality at rest and at peak stress, resulting in improved confidence of interpretation.

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.