Andreas Kreis

Ultrasound angioscopy: Real-time, two-dimensional, intraluminal ultrasound imaging of blood vessels

The assessment of the presence and severity of disease in the peripheral and coronary arteries currently requires contrast angiography. Although computed tomography, noninvasive ultrasound imaging and fiberoptic angioscopy may allow visualization of certain portions of the arteries, these techniques have limitations.1–3 Contrast angiography, which yields only long-axis images of the blood vessel lumen, continues to be the major diagnostic modality for assessing vascular anatomy. In this report we describe the in vitro and in vivo evaluation of ultrasound angioscopy, a new technique capable of providing dynamic, circumferential images of blood vessels.

Simultaneous transesophageal atrial pacing and transesophageal two-dimensional echocardiography: A new method of stress echocardiography

The diagnostic use of exercise echocardiography has been widely reported. However, transthoracic exercise echocardiography is inadequate in up to 20% of patients because of poor image quality related to exercise. In an attempt to overcome these limitations, a system was developed in which transesophageal echocardiography is combined with simultaneous transesophageal atrial pacing by means of the same probe. In a prospective study, transesophageal echocardiography was performed before, during and immediately after maximal atrial pacing in 50 patients with suspected coronary artery disease. Results of transesophageal stress echocardiography were considered abnormal when new pacing-induced regional wall motion abnormalities were observed. Correlative routine bicycle exercise testing was carried out in 44 patients. Cardiac catheterization was performed in all patients. The success rate in obtaining high quality diagnostic images was 100% by transesophageal echocardiography. All nine patients without angiographic evidence of coronary artery disease had a normal result on the transesophageal stress echocardiogram (100% specificity). Thirty-eight of 41 patients with coronary artery disease (defined as greater than or equal to 50% luminal diameter narrowing of at least one major vessel) had an abnormal result on the transesophageal stress echocardiogram (93% sensitivity). The sensitivity of the technique for one, two or three vessel disease was 85%, 100% and 100%, respectively, compared with 44%, 50% and 83%, respectively, for bicycle exercise testing; the 12 lead electrocardiogram (ECG) during rapid atrial pacing showed a sensitivity of 25%, 64% and 86%, respectively. Thus, rapid atrial pacing combined with simultaneous transesophageal echocardiography is a highly specific and sensitive technique for the detection of coronary artery disease. Ischemia-induced wall motion abnormalities were detected earlier than observed ECG changes. The technique appears to be particularly suited to patients who are unable to perform an active stress test or those with poor quality transthoracic echocardiograms.

Intracardiac, intravascular, two-dimensional, high-frequency ultrasound imaging of pulmonary artery and its branches in humans and animals

Intravascular ultrasound imaging is a promising new method for assessing vascular morphology. We evaluated the capability of intravascular ultrasound to quantify pulmonary artery (PA) morphology in vitro and explored the feasibility of in vivo PA imaging in animals and humans. In the in vitro study of 15 PA segments, we used a 20-MHz prototype ultrasound catheter. Intravascular ultrasound (y) provided crisp images of PA segments and demonstrated excellent correlations with anatomic measurements (x) in the estimation of luminal area (y = 0.89x + 2.95, r = 0.99, p less than 0.001), luminal diameter (n = 30, y = 0.79x + 0.96, r = 0.92, p less than 0.001), and vessel wall thickness (n = 60, y = 0.65x + 0.33, r = 0.85, p less than 0.001). We subsequently introduced the probe into the PA of 10 dogs and were able to obtain real-time, two-dimensional images of the main PA, its major branches, and farther smaller branches as far as the wedge level. To evaluate the in vivo feasibility of PA imaging in conscious humans, we used a commercially available, 20-MHz intravascular ultrasound (IVUS) catheter in 22 subjects through a femoral or jugular venous sheath at the end of standard diagnostic cardiac catheterization. In 20 subjects, we acquired dynamic, high-resolution, cross-sectional images of the proximal and distal PA. Changes in shape and decreasing luminal area could be clearly recognized as the IVUS catheter reached branching points and as it passed more distally. There were no complications.(ABSTRACT TRUNCATED AT 250 WORDS)

Real-time intravascular ultrasound imaging in humans

The capability of obtaining cross-sectional, high resolution images of arteries with the use of ultrasound catheters has recently been demonstrated in animal studies. In this study the in vivo feasibility of intravascular ultrasound imaging in humans was evaluated. In 26 patients who had undergone diagnostic cardiac catheterization or iliofemoral arteriography, 1 of 3 different models of 20-MHz ultrasound catheters was advanced retrograde, into the iliac arteries and aorta or anterograde into the femoral arteries and real-time cross-sectional images of the arteries were obtained in all. In 10, the iliac arteries were normal and appeared circular and pulsatile with a 3-layered wall and crisply defined lumens. In 7 patients with nonobstructive plaques, the plaque was easily identified in the ultrasound image as a linear, bright, adynamic echo-dense structure. In 4 with obstructive disease in the iliac artery, the arterial lumen appeared irregular, bordered by a thickened, nonpulsatile wall. Variable grades of atheromatous abnormalities in the wall could be visualized. In all 5 patients with arteriographic evidence of obstructive disease of the femoral artery, intravascular ultrasound displayed reduced lumens and irregular borders with protruding high-intensity echoes in the wall. In all patients, the arterial lumen and the normal or abnormal wall were well visualized in the ultrasound images. There were no complications. This study thus demonstrates the feasibility of intravascular ultrasound imaging of arterial circulation in humans. With further improvements in catheter design and image quality, this imaging approach is likely to have a number of potential applications in the assessment of peripheral and coronary arterial diseases and in guiding interventional therapeutic procedures.

Intravascular high frequency two-dimensional ultrasound detection of arterial dissection and intimal flaps

Abstract The anatomy of an arterial lesion has important prognostic and therapeutic implications. Current advances in interventional therapy for coronary and peripheral arterial disease have emphasized the need for more detailed morphologic information on the arterial anatomy than that derived from contrast angiography. Contrast arteriography can display dimensional narrowing of an artery. Other abnormalities such as atheromas, thrombi and dissections are not demonstrated in sufficient detail by arteriography. With fiberoptic angioscopy, some of these abnormalities can be visualized but this technique is cumbersome, requiring intermittent arterial occlusions and injections of clear fluid. Further, arterial wall architecture cannot be evaluated by fiberoptic angioscopy. Among alternate means of imaging an artery, intravascular high frequency ultrasound imaging appears promising. In vitro and in vivo studies from our laboratory and others have shown that catheter-based high frequency intravascular ultrasound imaging can provide information on the arterial wall and luminal size, and detect atheroma. 1–6 Whether this approach can identify arterial abnormalities such as small dissections and intimal flaps, commonly associated with arterial diseases, is not known. In this study we evaluated the potential of intravascular ultrasound imaging in the detection of arterial dissection and delineation of flaps from the arterial wall.

Intravascular ultrasound estimation of arterial stenosis.

The evaluation of the degree of reduction in the cross-sectional area of an artery has important pathophysiologic and therapeutic implications. Currently, no technique can easily provide this information. In this in vitro study we evaluated the potential of a new imaging technique, intravascular high frequency ultrasound angioscopy, in the estimation of percentage of cross-sectional area stenosis of an artery. To do this, we compared intravascular high frequency ultrasound to previously-validated external high frequency ultrasound and to anatomic estimation of arterial stenosis. Using a prototype intraluminal imaging catheter with a 20 MHz ultrasound transducer at its tip, we imaged 20 arterial segments of various size (15 to 90 mm2 lumen area by anatomy) in the control state and after experimental stenosis. These arterial segments were also imaged by external high frequency ultrasound. Lumen areas were measured from calibrated ultrasound images in the control state and after stenosis, and percentage of cross-sectional area stenosis was calculated. These data were compared to the percentage of area stenosis derived from calibrated anatomic photographs of the arteries taken in the control state and after stenosis. Both intravascular ultrasound angioscopy and external high frequency ultrasound yielded high-resolution, two-dimensional, circumferential images of the arteries. Alterations in vessel area and shape were apparent after creation of stenosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental Observations on Intracavitary Imaging of Cardiac Structures with 20‐MHz Ultrasound Catheters

Recently catheter‐based ultrasound devices have become available for obtaining high‐resolution images of blood vessels. In this study we evaluated the feasibility of imaging cardiac structures using 20‐MHz ultrasound catheters. In 25 dogs, the ultrasound catheter was advanced into the right and left heart chambers percutaneously. The intravascular devices yielded images of the right atrial wall, right and left ventricular myocardia, tricuspid, pulmonic, and aortic valves, and the great vessels. Although the small depth of field inherent to the frequency range of 20 MHz limited the visualization to only portions of the cardiac chambers, the images obtained were of high resolution and allowed easy identification of the various cardiac structures. Intracardiac echocardiography was easy to perform and did not result in damage to the cardiac structures. We conclude that intracardiac echocardiography using ultrasound catheters provides a new approach to cardiac imaging and that the development of lower frequency catheters could aid in extending the potential utility of intracardiac echocardiography. (ECHOCARDIOGRAPHY, Volume 8, January 1991)

Effects of atrial cardioplegia on the ischemic right ventricle after acute coronary artery occlusion and reperfusion

Right atrial cardioplegia has been advocated as a simple method of delivering retrograde cardioplegia. Passive distention of the right heart inherent with right atrial cardioplegia has been shown to impair right ventricular function in a canine model of global ischemia. This study was designed to compare right ventricular performance after right atrial cardioplegia administered intermittently (n = 5) and continuously (n = 5) with coronary sinus retrograde cardioplegia (n = 5) and aortic root cardioplegia (n = 8) in a canine model of acute right ventricular ischemia and reperfusion. Right ventricular performance was assessed using the load-independent relationship of end-systolic pressure versus dimension (myocardial fiber length). Right ventricular performance was well preserved after reperfusion in those dogs protected with intermittent right atrial cardioplegia (95% of control). Results with continuous right atrial cardioplegia (66% of control) and coronary sinus retrograde cardioplegia (40% of control) demonstrated diminished postreperfusion right ventricular performance. Right ventricular performance in the group protected with aortic root cardioplegia was significantly impaired after reperfusion when compared with all retrograde groups (34% of control, p less than 0.05). In this model, postreperfusion right ventricular performance was preserved in the right atrial cardioplegia groups despite passive ventricular distention. All methods of retrograde cardioplegia resulted in superior preservation of right ventricular performance when compared with standard aortic root cardioplegia.