Biomedical subjects

J M Isner

Publications and source records attributed to J M Isner.

At least 235 records · Page 13Linked to original sources

PubMed1991

Three-dimensional reconstruction of human coronary and peripheral arteries from images recorded during two-dimensional intravascular ultrasound examination.

BACKGROUND: Intravascular ultrasound provides high-resolution images of vascular lumen, plaque, and subjacent structures in the vessel wall; current instrumentation, however, limits the operator to viewing a single, tomographic, two-dimensional image at any one time. Comparative analysis of serial two-dimensional images requires repeated review of the video playback recorded during the two-dimensional examination, followed by a "mind's eye" type of imagined reconstruction. METHODS AND RESULTS: Computer-based, automated three-dimensional reconstruction was used to generate a tangible format with which to assess and compare a "stacked" series of two-dimensional images. Three-dimensional representations were prepared from sequential images obtained during intravascular ultrasound examination in 52 patients, 50 of whom were studied before and/or after percutaneous revascularization. Conventional two-dimensional ultrasound images were acquired by means of a systematic, timed pullback of the ultrasound catheter through the respective vascular segments. Images were then assembled in automated fashion to create a three-dimensional depiction of the vessel lumen and wall. Computer-enhanced three-dimensional reconstructions were generated in both sagittal and cylindrical formats. The sagittal format resulted in a longitudinal profile similar to that obtained during angiographic examination; in contrast to angiography, however, the sagittal reconstruction offered 360 degrees of limitless orthogonal views of the plaque and arterial wall as well as the vascular lumen. The cylindrical format yielded a composite view of a given vascular segment, and a hemisected version of the cylindrical reconstruction enabled en face inspection of the reconstructed luminal surface. Sagittal reconstructions facilitated analysis of dissections and plaque fractures resulting from percutaneous revascularization, and the hemisected cylindrical reconstructions enhanced analysis of endovascular prostheses. CONCLUSIONS: This preliminary experience demonstrates that computer-based three-dimensional reconstruction may further augment the use of intravascular ultrasound in assessing vascular pathology and guiding interventional therapy.

Aged↗

PubMed1991

Cocaine-induced myocardial infarction: clinical observations and pathogenetic considerations.

Clinical and experimental data published to date suggest several possible mechanisms by which cocaine may result in acute myocardial infarction. In individuals with preexisting, high-grade coronary arterial narrowing, acute myocardial infarction may result from an increase in myocardial oxygen demand associated with cocaine-induced increase in rate-pressure product. In other individuals with no underlying atherosclerotic obstruction, coronary occlusion may be due to spasm, thrombus, or both. With regard to spasm, the clinical findings are largely circumstantial, and the locus of cocaine-induced vasoconstriction remains speculative. Although certain clinical and experimental findings support the hypothesis that spasm involves the epicardial, medium-size vessels, other data suggest intramural vasoconstriction. Diffuse intramural vasoconstriction is not consistent with reports of segmental, discrete infarction. Whereas certain in vivo data suggest that these effects are alpha-mediated, other in vitro data suggest the opposite. The finding of cocaine-induced vasoconstriction in segments of (noninnervated) human umbilical artery suggests that the presence or absence of intact innervation is not sufficient to explain the discrepant data involving the possibility of alpha-mediated effects. Finally, the contribution of a primary, thrombotic effect of cocaine has not been excluded.

Animals↗

PubMed1990

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.

Aorta, Abdominal↗

PubMed1990

Contrasting histoarchitecture of calcified leaflets from stenotic bicuspid versus stenotic tricuspid aortic valves.

Preliminary findings from clinical trials of percutaneous balloon aortic valvuloplasty and intraoperative debridement of calcific deposits in patients with aortic stenosis have suggested that calcified, congenitally bicuspid aortic valves may be less amenable to these techniques than are calcified tricuspid aortic valves. Accordingly, we evaluated the histoarchitecture of calcific deposits in 30 operatively excised aortic valves. Light microscopic sections taken through the calcified aortic valve leaflets disclosed two principal types of histoarchitecture. In 11 aortic valves nodular calcific deposits were superimposed on an underlying fibrotic aortic valve leaflet (type A); in 17 valves calcific deposits were diffusely distributed throughout the body (spongiosa) of the aortic valve leaflets (type B). Two aortic valves could not be classified histologically. These histologic subtypes were not randomly distributed with regard to gross valvular morphology. All 14 bicuspid valves (100%) were type B; in contrast, 11 (69%) of 16 tricuspid aortic valves were type A, and only 3 (19%) of 16 tricuspid valves were type B (p less than 0.01). Both valves with nonclassifiable histologic features were tricuspid on the basis of gross examination. Thus, the histoarchitectural distribution of calcific deposits is different for bicuspid than for tricuspid stenotic aortic valves. The more diffuse distribution of calcium throughout the body of calcified bicuspid aortic valve leaflets may render these valves less amenable to operative and percutaneous valvuloplasty than are calcified tricuspid aortic valve leaflets on which calcific deposits are typically superimposed in nodular form.

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PubMed1990

Atherosclerotic Yucatan microswine: an animal model with high-grade, fibrocalcific, nonfatty lesions suitable for testing catheter-based interventions.

A new breed of swine, the Yucatan microswine, that was derived from repetitive inbreeding of selected, small Yucatan swine, was investigated as an animal model of advanced vascular atherosclerosis. Nineteen animals were fed an atherogenic diet for 9.9 +/- 1.5 (mean +/- SEM) weeks before and 19.9 +/- 1.8 weeks after balloon endothelial denudation of all four iliac arteries. In 18 (94.7%) of the 19 microswine, angiography performed at 33 to 87 weeks of age disclosed some degree of luminal diameter narrowing: six animals (33.3%) had one-vessel, six (33.3%) had two-vessel, four (22.2%) had three-vessel, and two (11.1%) had four-vessel disease. In 38 (50%) of 76 denuded arteries, angiographically apparent luminal diameter narrowing was observed as follows: three arteries (7.9%) were narrowed less than 50%; 10 arteries (26.3%) were narrowed 50% to 75%; seven arteries (18.4%) were narrowed 76% to 99%; and 18 arteries (47.3%) were occluded. Sixty-four arteries were harvested from 16 of the 18 microswine with angiographically apparent luminal narrowing, which yielded 748 histologic sections. Maximum cross-sectional area narrowing from atherosclerotic plaque exceeded 90% in 135 (18%) of the sections examined, while 65 sections (9%) were narrowed 76% to 90%, and 127 sections (17%) were narrowed 51% to 75%. Atherosclerotic plaque in these animals appeared histologically similar to the so-called "complex" lesion that is typical of human atherosclerosis, which consists predominantly of collagen with focal calcific deposits and a minor lipid component. The smaller size and lower weight of these animals, in comparison with full-size farm pigs and "minipigs," facilitated transportation, handling, and instrumentation. These findings establish the Yucatan microswine as a useful, representative, and economical atherosclerotic animal model for the evaluation of novel interventional techniques.

Angiography↗

PubMed1990

Atrial septal defect resulting from mitral balloon valvuloplasty: relation of defect morphology to transseptal balloon catheter delivery.

Percutaneous balloon mitral valvuloplasty has been shown to be an effective means of reducing mitral valve gradient and increasing mitral valve area in patients with mitral stenosis. Most techniques currently employed for performing this procedure involve delivery of one or two balloon valvuloplasty catheters through the interatrial septum en route to the mitral valve orifice. To determine the morphology of the resultant atrial septal defect (ASD), particularly as a function of the technique employed, we performed a series of in vitro experiments designed to simulate a variety of technical approaches. Ninety-eight experiments in total were performed in 19 normal adult hearts obtained in the fresh, nonpreserved state at necropsy. Transseptal delivery and withdrawal of two conventional, elliptical balloon catheters through two, individual septostomy sites was found to produce the largest ASD (combined area of two defects = 21.4 +/- 2.2 mm2). The defect resulting from transseptal delivery and tandem withdrawal of two elliptical balloon catheters through a single septostomy site measured 14.8 +/- 1.1 mm2, significantly (p = 0.0043) smaller than that produced by two septostomies. Transseptal delivery and withdrawal of a single, segmentally inflating (Inoue) balloon catheter produced a defect of intermediate size (17.5 +/- 1.2 mm2). ASD size was exacerbated by improper balloon withdrawal compared with tandem withdrawal of two completely deflated balloon catheters. Simultaneous withdrawal of two completely deflated balloon catheters through the same septostomy site increased ASD size from 14.8 +/- 1.1 mm2 to 23.6 +/- 2.3 mm2 (p = 0.0004). Simultaneous withdrawal of two incompletely deflated balloon catheters further increased ASD size to 45.8 +/- 2.6 mm2 (p less than 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Catheterization↗

PubMed1990

Catheter-based intravascular ultrasound discriminates bicuspid from tricuspid valves in adults with calcific aortic stenosis.

A catheter-based intravascular ultrasound transducer was used to study aortic valve morphology in adults with calcific aortic stenosis. Examination of 14 postmortem specimens disclosed that intravascular ultrasound consistently identified the number of cusps or the presence of a calcified median raphe in the conjoined cusp, or both, and thereby distinguished a calcified bicuspid from a calcified tricuspid aortic valve. These postmortem findings were then employed to identify valvular morphology in 15 patients undergoing diagnostic cardiac catheterization or balloon aortic valvuloplasty, or both. Reproduction of criteria established in vitro allowed discrimination of congenital valvular morphology in all 15 patients, including 7 in whom assessment by intravascular ultrasound was confirmed by subsequent pathologic examination. Identification of aortic valvular morphology by intravascular ultrasound has potential therapeutic implications for patients considered to be candidates for operative or nonoperative aortic valvuloplasty.

Adult↗

PubMed1990

Percutaneous intravascular US as adjunct to catheter-based interventions: preliminary experience in patients with peripheral vascular disease.

Catheter-based ultrasound (US) transducers may be introduced into the vascular system to record high-resolution images of the vessel wall and lumen. The potential advantages and existing liabilities of percutaneous intravascular US as an adjunct to transluminal vascular recanalization were investigated. A 6.6-F braided, polyethylene catheter enclosing a rotary drive shaft with a single-element, 20-MHz transducer at the distal tip was used in 17 patients undergoing percutaneous transluminal (balloon) angioplasty (PTA) alone (10 patients), PTA with implantation of an endovascular stent (two patients), atherectomy alone (two patients), or laser angioplasty with PTA and/or atherectomy (three patients). The arteries treated and examined included the common iliac in five patients, the external iliac in two, the superficial femoral in nine, and a vein graft-arterial anastomosis in one. In 14 cases PTA was employed as sole or adjunctive therapy; plaque cracks were clearly delineated with intravascular US in all 14 (100%) and dissections were observed in 11 (78%). Plaque-arterial wall disruption was less prominent in the arteries treated with mechanical atherectomy. The results of laser angioplasty reflected the adjunctive modality employed. After stent implantation, serial intravascular US documented effacement of PTA-induced plaque cracks and/or dissections. Intravascular US also aided in the quantitative assessment of luminal cross-sectional areas after the procedures (19.0-51.8 mm2). The observations recorded in this preliminary group of 17 patients illustrate the potential utility of intravascular US as an adjunct to conventional angiography in patients undergoing percutaneous revascularization.

Aged↗

PubMed1990