Simultaneous Morphological and Functional Assessment of a Renal Artery Stent Intervention With Intravascular Ultrasound
A 73-year-old woman with a history of high blood pressure and hypercholesterolemia developed medically uncontrolled hypertension (200/100 mm Hg). Serum creatinine level was 145 μmol/L, and creatinine clearance was 34 mL/min. Renal ultrasound demonstrated a small right kidney (80 mm long) compared with the left one (92 mm long). Left ventricular hypertrophy was present on the ECG and was confirmed by echocardiography. On isotope radiography with 99mTc-mercaptoacetyltriglycine after oral intake of 25 mg captopril, the right kidney was small, with delayed excretion and impaired function (36%). Renal arteriography showed subocclusive ostial stenosis of the right renal artery.
The lesion was related to a calcified plaque extending from the aortic wall into the renal artery ostium (angiogram I in Figure 1⇓, arrow). After an unsuccessful angioplasty attempt in the interventional radiology department (failure to cross the stenosis), the patient was investigated in the cardiac catheterization laboratory. The lesion was crossed with a hydrophilic guidewire and predilated. A short (9-mm) stent was then implanted by use of a 4.5-mm balloon inflated up to 18 atm for postdilatation (angiogram II).
The immediate result of the intervention was assessed by both biplane angiography (angiogram III, anteroposterior projection) and intravascular ultrasound (IVUS). Distal to the stent, IVUS shows a normal arterial wall (panel 1 in Figure 1⇓). A cross section within the stent (panel 2) demonstrates good expansion and apposition of the struts (arrows). The lumen area measured at this level was 18.9 mm2. The arrows in panel 3 demonstrate the highly calcified plaque at the junction with the aorta.
The top of Figure 2⇓ shows images obtained with a newly developed method to quantify the blood flow with an IVUS imaging catheter. They were recorded distally to the stent at different times (a through e) during the cardiac cycle. This blood flow measurement method has recently been validated and calibrated in vitro against electromagnetic flowmeter data and in vivo in porcine carotid arteries.1 The principle is based on the analysis of decorrelation of the IVUS radiofrequency (RF) signals. Red blood cells flowing in the ultrasound beam result in a decorrelation of successively received RF signals. The rate of decorrelation is proportional to the local blood flow velocity.2 3 These are then converted into color maps representing local instantaneous blood flow velocity in the arterial cross section. The color scheme used goes from dark red (10 cm/s) to yellow (100 cm/s). Flow velocities are measured at 100 angular positions, with a depth resolution of 160 μm. Cross sections with color flow data can be recorded during a 4-second period at 16 frames per second.
The moment of each IVUS image with flow information in the cardiac cycle is indicated at the bottom right of Figure 2⇓, showing flow traces recorded simultaneously with the ECG. The instantaneous flow calculated with the IVUS method is represented in green and the flow derived from an intravascular Doppler wire in blue. In panel a, very low blood flow velocities at end diastole are not encoded, because they fall below the sensitivity threshold level, which is ≈10 cm/s. With increasing flow in early systole (b), the color map shows homogeneous blood flow velocities encoded in red. Maximal velocities are reached at peak systole (c). The decrease in blood flow in diastole is seen in panels d and e. Integration of the velocities over the lumen area allows the computation of instantaneous volumetric blood flow (green curve) during a 4-second period. The measurements are in agreement with the blood flow simultaneously measured with the Doppler wire (in blue: Doppler instantaneous peak velocity times the cross-sectional vessel area at Doppler wire tip). The mean IVUS flow was 238 mL/min, whereas the flow derived from the Doppler wire measurements was 208 mL/min. This demonstrates the feasibility of simultaneous assessment of morphological and physiological parameters during interventional procedures with an intravascular imaging catheter. The method is presently being evaluated in coronary arteries.
This patient was discharged 2 days after the procedure and is doing well. Good early and long-term results of stenting ostial renal lesions have been reported recently,4 with a restenosis rate of 10%, making this procedure the best current therapy for renovascular disease related to critical ostial stenoses.
The excellent technical support of J. Honkoop and F. Mastik was of paramount importance for the realization of this work.
The editor of Images in Cardiovascular Medicine is Hugh A. McAllister, Jr, MD, Chief, Department of Pathology, St Luke’s Episcopal Hospital and Texas Heart Institute, and Clinical Professor of Pathology, University of Texas Medical School and Baylor College of Medicine.
Circulation encourages readers to submit cardiovascular images to Dr Hugh A. McAllister, Jr, St Luke’s Episcopal Hospital and Texas Heart Institute, 6720 Bertner Ave, MC1-267, Houston, TX 77030.
- Copyright © 1998 by American Heart Association
Carlier S, Li W, Mastik F, Honkoop J, van der Steen AFW, Lancée CT, de Zeeuw S, van Bremen R, Céspedes EI, Serruys PW, Bom K. New intracoronary volumetric blood flow measurement method with intravascular ultrasound: in-vitro assessment and first in vivo results. Eur Heart J. 1997;18:376. Abstract.
Li W, van der Steen AFW, Lancée CT, Céspedes EI, Gussenhoven EJ, Bom N. Estimation of local blood velocity and volume flow with intravascular ultrasound. Ultrasound Med Biol. In press.
Li W. Image and Signal Processing in Intravascular Ultrasound [PhD thesis]. Rotterdam, Netherlands: Erasmus University; 1997.