UCSF Intravascular Ultrasound Laboratory

A. Clinical Trials: This laboratory is the participating facility for many ongoing trials investigating the use of IVUS and intracoronary Doppler utility in coronary intervention.

B. Plaque Morphology: In collaboration with the Lipid Research group headed by Drs. John Kane and Mary Malloy, we are currently examining the coronary circulation of asymptomatic patients with familial hyperlipidemias, using intravascular ultrasound. These patients are at high risk for coronary artery disease, and intravascular ultrasound techniques provide the opportunity of detecting early (angiographically silent) lesions. In approximately 6 months this project will be expanded to study the hyperlipidemic patients already enrolled in the SCOR protocol at UCSF. This effort will be the first to investigate regression by ultrasound in human subjects. Similarly, a recently funded NIH RO1 study designed by Mary Malloy will employ ultrasound to examine coronary risk factors in asymptomatic hypercholesterolemic women.

There is evidence that certain types of atherosclerotic lesions regress over time if lipid profiles are significantly altered. Intravascular ultrasound provides a unique tool to accurately study the degree of plaque progression and/or regression in cholesterol- fed animals. Our studies are presently focused on the atherosclerotic rabbit model. Serial measurements of intimal thickness in the aorta are performed with ultrasound for one series of rabbits being fed a normal diet and another fed a high cholesterol diet over a 16 week period.

C. Coronary Flow: Cross-sectional area computations from ultrasound images combined with Doppler velocities can be used for direct computation of absolute flow measurements. We have recently used an .014 inch guide wire together with the ultrasound catheter to obtain simultaneous imaging and Doppler measurement in the coronary arteries. This has been done in both animals and humans. Flow information may be clinically important with respect to monitoring recanalization techniques such as angioplasty and atherectomy. Areas of flow stasis may be a nidus for thrombus formation, and velocity together with morphologic information may allow lesions at high risk to be identified. In addition, spasm and the response to intracoronary pharmacologic agents can be studied with this combined ultrasound-Doppler technique.

D. Fetal Intracardiac and Transesophageal Echocardiography: In conjunction with the active fetal surgery program here at UCSF, our group has explored the use of these devices as monitoring tools during fetal surgical procedures and potentially as tools to guide interventional catheter-based intrauterine and/or fetal cardiac procedures. Our group has pioneered the use of this microtechnology in imaging via intracardiac (via umbilical access) and transesophageal imaging with amniotic sac intact (similar to a laparoscopic technique).

E. Catheter Design: We have an animal facility to test prototype catheter performance with respect to deliverability and image quality. Recently, efforts have been directed at testing new intracardiac catheters in the 10-20 MHz range. In addition to these catheters being able to provide high-quality images of myocardial structure, they may have an important application interventional procedures.

F. Peripheral Applications: We have a close working relationship with the interventional radiology group at UCSF. This provides the environment and expertise to test peripheral ultrasound catheters in a variety of clinical vascular situations. Assessing aneurysm anatomy, graft occlusions, angioplasty success and stent placement are presently active areas of investigation.

G. Vascular Physiology: Intravascular ultrasound provides a convenient tool to study vascular response to pharmacologic agents. Intracoronary ultrasound has been used in animals to study the response of the left anterior descending artery to nitroglycerin, acetyltcholine and other vasoactive compounds by measuring instantaneous cross-sectional area. Using ECG-gated measurements of end-diastolic cross-sectional areas, data on coronary vascular compliance can be obtained. In addition spasm which may be an important co-factor to restenosis is being studied using intracoronary ultrasound imaging in the cath lab.

H. Ischemic Preconditioning: Recent studies have demonstrated that repetitive episodes of coronary artery occlusion confer protection against ischemic injury from a subsequent or prolonged period of coronary artery occlusion, a phenomenon known as "ischemic preconditioning". We will soon begin a randomized blinded study whose purpose is to evaluate the potential for intravenous dipyridamole administration to further preconditioned myocardium prior to coronary angioplasty. Ultrasound imaging and flow velocity determination will be integral in determining the pharmacologic impact to be gained.