New developments in ultrasound systems for contrast echocardiography

Safety of ultrasound contrast agents in patients with known or suspected cardiac shunts

Contrast-enhanced ultrasound imaging is a radiation-free diagnostic tool that uses biocompatible ultrasound contrast agents (UCAs) to improve image clarity. UCAs, which do not contain dye, often salvage "technically difficult" ultrasound scans, increasing the accuracy and reliability of a front-line ultrasound diagnosis, reducing unnecessary downstream testing, lowering overall health care costs, changing therapy, and improving patient care. Two UCAs currently are approved and regulated by the US Food and Drug Administration. They have favorable safety profiles and risk/benefit ratios in adult and pediatric populations, including compromised patients with severe cardiovascular diseases. Nevertheless, these UCAs are contraindicated in patients with known or suspected right-to-left, bidirectional, or transient right-to-left cardiac shunts. These patients, who constitute 10% to 35% of the general population, typically receive no UCAs when they undergo echocardiography. If their echocardiographic images are suboptimal, they may receive inappropriate diagnosis and treatment, or they may be referred for additional diagnostic testing, including radiation-based procedures that increase their lifetime risk for cancer or procedures that use contrast agents containing dye, which may increase the risk for kidney damage. An exhaustive review of current peer-reviewed research demonstrated no scientific basis for the UCA contraindication in patients with known or suspected cardiac shunts. Initial safety concerns were based on limited rodent data and speculation related to macroaggregated albumin microspheres, a radioactive nuclear imaging agent with different physical and chemical properties and no relation to UCAs. Radioactive macroaggregated albumin is not contraindicated in adult or pediatric patients with cardiac shunts and is routinely used in these populations. In conclusion, the International Contrast Ultrasound Society Board recommends removal of the contraindication to further the public interest in safe, reliable, radiation-free diagnostic imaging options for patients with known or suspected cardiac shunts and to reduce their need for unnecessary downstream testing.

Prevalence and development of additional cardiac abnormalities in 1448 patients with congenital ventricular septal defects

OBJECTIVE

To determine by modern echocardiographic techniques the prevalence and development of cardiac abnormalities associated with ventricular septal defect (VSD).

METHODS

Consecutive patients referred to a tertiary centre for paediatric cardiology and attenders at an adult congenital heart disease clinic had details of clinical outcome prospectively recorded. Patients with VSD in association with conotruncal abnormalities, atrioventricular septal defects, and univentricular heart were not included in the study.

RESULTS

1448 patients with VSD were assessed between 1991 and 1998. 1127 (78%) patients had isolated defects; of these 862 (76%) were perimembranous and 265 (24%) were muscular. Of the remainder, 284 (19.6% of the total population) patients had VSD associated with one other significant cardiac abnormality: 35 (2.4%) with two and two (0.1%) with three other abnormalities. The most common associated cardiac abnormalities were infundibular pulmonary stenosis (5.8%), aortic valve prolapse (3.6%), pulmonary valvar stenosis (2.7%), osteum secundum atrial septal defect (2.2%), persistent ductus arteriosus (1.9%), and coarctation of the aorta (1.5%). In the cohort of 743 patients followed up from birth, cumulative mortality was 4% by the age of 8 years and most deaths occurred within the first year of life in infants with associated genetic abnormalities such as trisomy 13 or 18. Of the 594 patients attending the adult congenital clinic with VSD, aortic regurgitation due to aortic root prolapse developed in 45 (7.6%) patients. Most of these cases were detected before the patient was 30 years old.

CONCLUSIONS

In 22% of patients with congenital VSD there were significant associated cardiac abnormalities. Some of these abnormalities, such as aortic prolapse and regurgitation or infundibular pulmonary stenosis, may develop or progress subsequently and therefore should be sought during the initial assessment and monitored during follow up. Follow up to the age of 30 years allows the detection of most cases of aortic regurgitation. The prognosis from VSD is excellent and the risk of endocarditis in a population informed of the need for antibiotic prophylaxis is small.

Influence of transducer frequency and imaging modality on the intraoperative assessment of myocardial perfusion with transesophageal echocardiography

OBJECTIVE

To determine factors that improve intraoperative myocardial perfusion assessment with conventional ultrasound imaging and intravenous ultrasound agents.

DESIGN

Prospective cohort study with repeated interventions on each patient.

SETTING

Single university hospital.

PARTICIPANTS

Fourteen patients scheduled for elective coronary artery bypass graft surgery.

INTERVENTIONS

Myocardial perfusion was evaluated with contrast transesophageal echocardiography during conventional imaging after central venous injections of the contrast agent Optison (0.3 mL) before cardiopulmonary bypass. Eight patients received the injection during continuous sampling at each of 4 transducer frequency settings (3.5, 5.0, 6.0, 7.0 MHz). In another 6 patients, injections were administered during continuous and intermittent sampling (electrocardiogram-gated) at 3.5 and 5.0 MHz. Generalized estimating equations were used to compare mean responses, with p < or = 0.05 considered significant.

MEASUREMENTS AND MAIN RESULTS

All recorded images were analyzed with off-line videodensitometry. Background-corrected peak pixel intensity (PPI(corr)) and rate of change in pixel intensity (PPI(corr)/T(PPI)) were determined for each injection. PPI(corr) was greater at 3.5 MHz than at 5.0, 6.0, and 7.0 MHz (p < 0.001). PPI(corr)/T(PPI) was greater at 3.5 MHz than at 5.0 (p < 0.001), 6.0 (p = 0.003), and 7.0 MHz (p < 0.001). PPI(corr) was greater for gated than for nongated sampling conditions at 3.5 (p < 0.05) and 5.0 MHz (p < 0.05).

CONCLUSION

To optimize myocardial contrast opacification, intraoperative transesophageal echocardiography should be performed with intermittent sampling at a transducer frequency close to the intrinsic frequency of the contrast agent.

Contrast echocardiography clarifies uninterpretable wall motion in intensive care unit patients

OBJECTIVES

The study examined the value of contrast echocardiography in the assessment of left ventricular (LV) wall motion in intensive care unit (ICU) patients.

BACKGROUND

Echocardiograms done in the ICU are often suboptimal. The most common indication is the evaluation of LV wall motion and ejection fraction (EF).

METHODS

Transthoracic echocardiograms were done in 70 unselected ICU patients. Wall motion was evaluated on standard echocardiography (SE), harmonic echocardiography (HE), and after intravenous (IV) contrast echocardiography (CE) using a score for each of 16 segments. A confidence score was also given for each segment with each technique (unable to judge; not sure; sure). The EF was estimated visually for each technique, and a confidence score was applied to the EF.

RESULTS

Uninterpretable wall motion was present in 5.4 segments/patient on SE, 4.4 on HE (p = 0.2), and 1.1 on CE (p < 0.0001). An average of 7.8 segments were read with surety on SE, 9.2 on HE (p = 0.1), and 13.7 on CE (p < 0.0001). Ejection fraction was uninterpretable in 23% on SE, 13% on HE (p = 0.14), and 0% on CE (p = 0.002 vs. HE; p < 0.0001 vs. SE). The EF was read with surety in 56% of patients on SE, 62% on HE (p = 0.47), and 91% on CE (p < 0.0001). Thus, wall motion was seen with more confidence on CE. More importantly, the actual readings of segmental wall motion and EF significantly differed using CE.

CONCLUSIONS

CE should be used in all ICU patients with suboptimal transthoracic echocardiograms.

An Easily Implemented Method to Improve Detection of Ultrasound Contrast in Body Tissues

The recent commercial availability of ultrasound contrast agents poses new challenges to ultrasound lprofessionals. There is a need to identify the most:relevant clinical applications for which the agents are indicated, as well as ways jin which to use existing ultrasound technology with contrast. Herein is described la new imaging tehnique frame-one maging that: imp rovsthe detection of contrast in bo0d:tissues. Frame-one imaging was attempted in six examin attons of suspected renal abnormalities performed as part of the FDA Phase IcliIcIal trials of the contrast agent Definity® (DuPont Pharmaceuticals, N. Billerica,: M, A). Conventional and harmonic gray-scale imaging was perfrmed at baseline and postcntrat addm inistration. US imaging results were compared to surgical findings. U1, sing gray-scalle harm: o:nicimagg, improved depiction: of:contrast enhancement was achieved in all:cases where FOI was employed. Contrast enhancement was better demonstrated using the FOI tchnique than with continuous real-time imaging. FOI improved the display of contrast enhancement from within normal tissues and vessels as wel as:frombi tumor vessels and tumor tissue. FOI may permit improved tumor characterization using contrasenhanced sonogphy. Additiol vestigations are neede to determine if FOL can imp0rovethe diagnostic potential of contrast-enhanced sonography.

Evaluation of myocardial, hepatic, and renal perfusion in a variety of clinical conditions using an intravenous ultrasound contrast agent (Optison) and second harmonic imaging

OBJECTIVE

To assess the potential of intravenous Optison, a second generation ultrasound contrast agent, and various ultrasound imaging modes to determine myocardial, kidney, and liver perfusion in normal subjects and patients with left ventricular dysfunction or chronic pulmonary disease together with renal or hepatic dysfunction.

METHODS

Five normal subjects and 20 patients underwent grey scale echocardiographic imaging of myocardium, kidney, and liver during 505 intravenous injections of Optison. Images were assessed qualitatively by two independent observers and quantitatively using video densitometry to determine the peak contrast enhancement effect.

RESULTS

Qualitative analysis showed that intermittent harmonic imaging was superior to either conventional fundamental or continuous harmonic imaging for all organs. Quantitative analysis showed that the peak change in echocardiographic intensity v baseline during continuous harmonic imaging was 11 units for myocardium (p < 0.03), 7 units for kidney (NS), and 14 units for liver (p < 0.05). During intermittent harmonic imaging the peak change was significantly greater, being 33 units for myocardium (p < 0.0001), 24 units for kidney (p < 0.0002), and 16 units for liver (p < 0.001).

CONCLUSIONS

Organ tissue perfusion can be demonstrated following intravenous injection of Optison, particularly when used in combination with intermittent harmonic imaging techniques. This contrast agent is effective in a variety of clinical conditions.

Ambulatory blood pressure monitoring and echocardiography--noninvasive techniques for evaluation of the hypertensive patient

Clinic blood pressure measurements have only limited ability to determine which hypertensive patients are at greatest risk of cardiovascular events. Ambulatory blood pressure monitoring allows for noninvasive measurement of blood pressure throughout the 24-hour period. This may help to clarify discrepancies between blood pressure values obtained in and out of the clinic and confirm the presence of white-coat hypertension, broadly defined as an elevated clinic blood pressure but a normal ambulatory blood pressure. Ambulatory blood pressure values have been shown to have a better relationship to cardiovascular morbidity and mortality and end-organ damage than clinic blood pressure values. Further, patients with white-coat hypertension appear to be at greater risk of cardiovascular morbidity and end-organ damage than a normotensive population, although they are at less overall risk than a hypertensive population. Hypertensive heart disease is characterized by diastolic dysfunction, increased left ventricular mass, and coronary flow abnormalities. Left ventricular hypertrophy increases the risk of coronary heart disease, congestive heart failure, stroke, ventricular arrhythmias, and sudden death. A variety of invasive and noninvasive techniques are described herein that measure left ventricular mass, diastolic function, and coronary blood flow abnormalities. Most antihypertensive treatments promote regression of left ventricular hypertrophy and reversal of diastolic dysfunction, which may decrease symptoms of congestive heart failure and improve survival.