General Information

Imagent (previously known as Imavist) injectable suspension has been approved by the FDA for use in patients with suboptimal echocardiograms. It is indicated for improving visualization of (opacifying) the left ventricular chamber of the heart, as well as improving the delineation of the endocardial borders (walls).

Imagent is a synthetic product packaged as a dry powder in a ready-to-use kit. The powder is first reconstituted with water to form a suspension of microscopic spheres, or "microspheres." The solution is then injected intravenously into a patient undergoing echocardiography (ultrasound of the heart). The use of Imagent in combination with an ultrasound may better differentiate normal and abnormal heart structure and function.

Clinical Results

Imagent was evaluated in two randomized, controlled, multicenter trials in subjects with suboptimal echocardiograms. The two studies included a total of 409 adults with a mean age of 58.9 years. A suboptimal echocardiogram was defined as two to nine non-visualized segments (out of 12 segments) in the apical four- and two-chamber views of the baseline continuous fundamental, two-dimensional echocardiogram.

In the trials, all Imagent-treated subjects received a single intravenous bolus injection of 0.125 mg/kg. Two-dimensional echocardiography was performed both before and after Imagent administration.

The trials were designed to evaluate Imagent's ability to improve endocardial border delineation, ejection fraction, and wall motion scores/measurements. Independent blinded readers (three per study) scored 16 left ventricular endocardial border segments on a four-point ordinal scale for delineation and on a six-point scale for wall motion, in addition to measuring ejection fraction. The 16 segments were in three views: apical four-chamber, apical two-chamber, and apical long-axis.

In comparing Imagent to baseline, the mean change in endocardial border delineation score was statistically significant for all readers for all three views. For ejection fraction, no improvement over non-contrast studies was observed when ejection fractions derived from echocardiography were compared to radionuclide ventriculography.

Wall motion was analyzed in a subset of subjects with at least two adjacent segments non-evaluable in at least two of the three views on non-contrast imaging. Results showed that treatment with Imagent converted a baseline non-evaluable image to an evaluable image in 43 to 79% of the subjects, depending on the reader. In the converted images, the ability to interpret wall motion (normal vs. abnormal) improved in 10 to 46% of the subjects, also depending on the reader; however, improvement in the specific diagnostic assessments was not established.

Mechanism of Action

The active moiety, the microsphere, consists of two critical components: perflexane, the gaseous component, and DMPC, the lipid membrane component. Perflexane is chemically characterized as n-perfluorohexane, and DMPC is a semi-synthetic (not of animal origin) phospholipid. After reconstitution and intravenous injection, Imagent increases the ultrasound reflectivity of blood in the left ventricle, thereby enhancing the ultrasound signal. (from Revised Proposed Package Insert)