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Biomedical subjects

M B Leon

Publications and source records attributed to M B Leon.

At least 289 records · Page 16Linked to original sources
PubMed1992

Results of coronary angioplasty using the transluminal extraction catheter.

To assess the procedural results after coronary angioplasty using the transluminal extraction catheter (TEC) in patients with complex lesion anatomy, experience with 51 patients undergoing this procedure was reviewed. One or more adverse lesion morphologic features were present in 45 patients (88%) and > or = 2 adverse features were present in 38 (74%). Procedural success (< 50% final diameter stenosis and the absence of major complications) was obtained in 42 patients (82%); major complications occurred in 7 patients (death, 3; Q-wave myocardial infarction, 4; emergency bypass operation, 2). Distal embolization was noted in 5 patients with thrombus-containing saphenous vein graft stenoses. Only lesion thrombus correlated with an unsuccessful outcome. After TEC use, diameter stenosis was reduced from 76 +/- 13 to 50 +/- 22% (p < 0.001). Adjunct balloon angioplasty was used in 44 procedures (86%), further reducing the diameter stenosis to 32 +/- 22% (p < 0.001 compared with post-TEC). High-frequency intracoronary ultrasound was performed in 11 patients after TEC use. Plaque fissuring was present in all lesions and intraluminal dissection was noted in 4 (36%). Residual plaque after TEC use was found in virtually all lesions. During the 5.2 +/- 2.8-month follow-up period, 17 patients (40%) developed recurrent symptoms. Coronary bypass surgery was performed in 4 patients and repeat coronary angioplasty was required in 3. In addition, 3 patients died from cardiac causes. It is concluded that coronary angioplasty using the TEC may be a useful alternative to balloon angioplasty in patients with complex coronary anatomy, although distal embolization may still occur in thrombus-containing saphenous vein graft lesions.

Angioplasty, Balloon, Coronary↗
PubMed1992

Target lesion calcification in coronary artery disease: an intravascular ultrasound study.

OBJECTIVES: The purpose of this study was to evaluate the frequency, amount and distribution of target lesion calcification in patients undergoing transcatheter therapy for symptomatic coronary artery disease. BACKGROUND: Coronary artery target lesion calcification may be an important determinant of response to transcatheter therapy: balloon angioplasty causes dissections in calcified lesions, directional atherectomy cuts calcium poorly, rotational atherectomy causes preferential ablation of calcium and laser irradiation effect may vary. Intravascular ultrasound imaging is a highly sensitive technique for detection of plaque calcification in vivo. METHODS: We performed intravascular ultrasound imaging before or after, or both, various transcatheter therapies in 110 patients. These 84 men and 26 women had a mean age of 60 years and a duration of angina of 22 +/- 34 months. Forty-nine patients had one-vessel, 29 had two-vessel, 25 had three-vessel and 7 had left main coronary disease. Vessels treated and imaged were the left main (n = 7), left anterior descending (n = 47), left circumflex (n = 18) and right (n = 38) coronary arteries. RESULTS: Eighty-four patients (76%) had target lesion calcification; 29 patients had one-quadrant, 25 had two-quadrant, 17 had three-quadrant and 13 had four-quadrant calcification. The calcification was superficial in 42 patients, deep in 13 and both superficial and deep in 31. The axial length of calcium could be measured in 29 patients; it was < or = 5 mm in 11 and > or = 6 mm in 18. Fluoroscopy detected calcification in 50 patients (48%, p < 0.001 vs. detection by ultrasound); this proportion increased to 74% in patients with calcification of two or more quadrants and to 86% in patients with calcification > or = 6 mm in length of two or more quadrants. Calcification was more common in patients who smoked and tended to be more common in patients with multivessel disease or previous coronary artery bypass graft surgery. CONCLUSIONS: We conclude that target lesion calcification occurs in 75% of patients with symptomatic coronary artery disease requiring angioplasty. Target lesion calcification is best detected, localized and quantified by intravascular ultrasound. These observations may be important in selecting devices for transcatheter therapy.

Adult↗
PubMed1992

Prolonged intravenous urokinase infusion: an alternative pharmacologic approach in the treatment of thrombus-containing saphenous vein graft stenoses.

A subtotally occlusive saphenous vein graft stenosis resolved after rapid intracoronary and prolonged intravenous urokinase infusion. Additional therapy was unnecessary, avoiding the attendant risks of saphenous vein graft angioplasty. Combined intracoronary and intravenous urokinase infusion should be considered prior to coronary angioplasty of saphenous vein graft stenoses, particularly when diffuse degeneration is present or the risk of underlying thrombus is high.

Angioplasty, Balloon, Coronary↗
PubMed1992

Failure or success of complex catheter-based interventional procedures assessed by intravascular ultrasound.

Intravascular ultrasound provides high resolution cross-sectional images of vessel walls and may help to characterize atherosclerotic plaque morphology subtypes. This new imaging modality may have an important role in assessing the results of standard and investigational interventional therapeutic procedures. Four case histories of patients with coronary artery disease treated with different catheter-based therapies are presented. In each case, intravascular ultrasound added diagnostic information unobtainable from standard radiographic imaging techniques. These cases, involving PTCA (balloon dilatation), directional coronary atherectomy, high-speed rotational ablation, and balloon-expandable stent implantation, each represent an interesting example of procedure success or failure that could not be fully discerned without the use of intravascular ultrasound. Specifically, the distribution of intramural dissection, the presence and magnitude of intracoronary calcification, and morphologic patterns of intimal hyperplasia leading to restenosis, were accurately identified by ultrasound images. Thus intracoronary ultrasound imaging significantly enhances the understanding of failure modes, success, and complications after therapeutic interventions in patients with complex coronary disease.

Aged↗
PubMed1992

Atherosclerotic saphenous vein grafts treated with different interventional procedures assessed by intravascular ultrasound.

Intravascular ultrasound imaging of saphenous vein grafts may enhance the angiographic interpretation of results following transcatheter interventions. We used intravascular ultrasound to study 18 patients with stenotic vein grafts following balloon angioplasty, atherectomy, or stent placement. In real-time imaging the three-layer appearance was rarely seen, calcification was infrequent (11% of patients), and atheroma were usually mildly echogenic ("soft"). Despite excellent angiographic results (reduction in percent diameter stenosis from 90 +/- 8% to 17 +/- 8%) and concordant improvement in lumen area by ultrasound regardless of the intervention, there was usually significant retained atheroma at the treatment site. Following balloon angioplasty, ultrasound showed multiple superficial fissures and fractures without discrete dissections. Atherectomy caused a smooth lumen surface without deep dissections or resections, but significant retained atheroma was observed with each one of the atherectomy procedures. Endovascular stents were concentric in the vein with reflective struts above compressed atheroma and an outer echogenic adventitia. Stent expansion was asymmetric axially and longitudinally and evidence of stent recoil was present. Thus intravascular ultrasound may be an important adjunct to angiography in characterizing postintervention results in saphenous vein grafts.

Aged↗
PubMed1992

Arterial responses to balloon coronary angioplasty: an intravascular ultrasound study.

OBJECTIVES: The purpose of this study was to examine the coronary artery response to percutaneous transluminal coronary angioplasty by using intravascular ultrasound. BACKGROUND: The immediate effects of coronary angioplasty on arterial wall geometry and surface appearance are understood poorly. Most of the available data are derived from small necropsy series, inferred from animal models or extrapolated from in vitro studies. High frequency intravascular ultrasound provides transmural images of coronary arteries in vivo. METHODS: We used intravascular ultrasound to study 29 patients before or after, or both, successful coronary angioplasty. RESULTS: The angiographic diameter narrowing was 72 +/- 13% before and improved to 19 +/- 11% after angioplasty. Calcium was visualized in 7 (24%) of the 29 angioplasty sites by fluoroscopy versus 15 (52%) of sites by intravascular ultrasound (p = 0.022). Arterial dissection after angioplasty was observed in 8 (27%) of cases by contrast angiography versus 24 (83%) by intravascular ultrasound (p less than 0.001). Intravascular ultrasound detected extensive dissection at the angioplasty site in 11 (73%) of the 15 calcified plaques and in only 3 (21%) of the 14 noncalcified plaques (p = 0.024). Arterial expansion (defined as the area within the external elastic membrane at the angioplasty site greater than that of the proximal reference segment) occurred in 29% of calcified plaques compared with 86% of noncalcified plaques (p = 0.007). CONCLUSIONS: Intravascular ultrasound is more sensitive than angiography for identifying arterial calcium and dissection at the site of angioplasty. At the site of angioplasty, arterial dissection occurred more frequently in calcified plaques whereas arterial expansion occurred more frequently in noncalcified plaques. Successful angioplasty causes a continuum of arterial responses that vary importantly with plaque composition.

Angioplasty, Balloon, Coronary↗
PubMed1992

Pulsed laser and thermal ablation of atherosclerotic plaque: morphometrically defined surface thrombogenicity in studies using an annular perfusion chamber.

Although clinical trials using laser and thermal angioplasty devices have been underway, the effects of pulsed laser and thermal ablation of atherosclerotic plaque on surface thrombogenicity are poorly understood. This study examined the changes in platelet adherence and thrombus formation on freshly harvested atherosclerotic aorta segments from Watanabe-heritable hyperlipidemic rabbits after ablation by two pulsed laser sources (308-nm xenon chloride excimer and 2,940-nm erbium:yttrium-aluminum-garnet [YAG] lasers) and a prototype catalytic hot-tip catheter. Specimens were placed in a modified Baumgartner annular chamber and perfused with citrated whole human blood, followed by quantitative morphometric analysis to determine the percent surface coverage by adherent platelets and thrombi in the treated and contiguous control areas. Pulsed excimer laser ablation of plaque did not change platelet adherence or thrombus formation in the treated versus control zones. However, photothermal plaque ablation with a pulsed erbium:YAG laser resulted in a 67% reduction in platelet adherence, compared with levels in control areas (from 16.7 +/- 2.2% to 5.5 +/- 1.8%; p less than 0.005). Similarly, after plaque ablation using a catalytic thermal angioplasty device, there was a 74% reduction in platelet adherence (from 29.2 +/- 5.1% to 7.7 +/- 1.6%; p less than 0.005) and a virtual absence of platelet thrombi (from 8.6 +/- 2.3% to 0.03 +/- 0.03%; p less than 0.005). This reduced surface thrombogenicity after plaque ablation with either an erbium:YAG laser or a catalytic hot-tip catheter suggests that thermal modifications in the arterial surface ultrastructure or thermal denaturation of surface proteins, or both, may be responsible for reduced platelet adherence. These in vitro findings indicate that controlled thermal plaque ablation by catheter-based techniques may elicit endovascular responses that can reduce early thrombus formation during angioplasty procedures.

Angioplasty, Laser↗
PubMed1992

In vitro and in vivo intravascular ultrasound imaging.

This paper presents our experience with intravascular ultrasound imaging of animal and human arteries in vitro and in vivo using a high-frequency (20 M Hz) ultrasound transducer. In vitro, 32 human coronary artery segments were imaged with intravascular ultrasound and compared with corresponding histological sections. Ultrasound and histology measurements correlated significantly (P less than 0.0001) for coronary artery cross-sectional area (r = 0.94), lumen cross-sectional area (r = 0.85) and wall thickness (r = 0.92). In vivo, 19 sheep and eight human common femoral arteries were imaged and the angiographic lumen diameter of 14 animal and six human arteries was compared to the diameter of the corresponding ultrasound images. Significant correlations were found for lumen diameter in animals and humans (P less than 0.001, r = 0.91 and P less than 0.0001, r = 0.96, respectively). These studies demonstrate that this technique can provide high resolution images of arterial vessels and may have unique advantages in diagnosing atherosclerotic vascular disease and in catheter based therapies.

Adult↗
PubMed1992

Emergent use of balloon-expandable coronary artery stenting for failed percutaneous transluminal coronary angioplasty.

BACKGROUND: The balloon-expandable intracoronary stent developed by Palmaz and Schatz is undergoing clinical evaluation for use in unfavorable anatomic situations and in the prevention of restenosis. Because the stent's mechanism of action would suggest effectiveness in salvaging certain percutaneous transluminal coronary angioplasty (PTCA) failures, we retrospectively examined the results of emergency unplanned coronary artery stenting for failed PTCA procedures, including acute occlusion. METHODS AND RESULTS: The study population consisted of all US patients receiving emergency unplanned stent implantation in a nonrandomized fashion at seven centers over a 2 1/2-year period (n = 56). All available medical records and angiograms were reviewed to determine retrospectively the reason for stenting: Group 1 consisted of 23 patients with a suboptimal angioplasty result; group 2 included patients with evidence of impending vessel closure after PTCA (n = 15); and group 3 were patients with frank acute occlusion after PTCA (n = 18). The immediate and final (30-day) results of stenting were examined with respect to major complications, which included death, need for coronary artery bypass graft surgery, and occurrence of myocardial infarction. Finally, restenosis rates (greater than or equal to 50% stenosis) based on follow-up angiography were calculated. Baseline characteristics of the study population included a mean +/- SD age of 58 +/- 11 years and a large prevalence of angiographic characteristics generally considered unfavorable for PTCA, which include lesion eccentricity (49%), intimal dissection (9%), or angiographically visible thrombus (6%). After conventional balloon angioplasty, there was an increased incidence of intimal dissection (74%) and thrombus formation (38%), and overall stenosis severity was unchanged (75 +/- 12% versus 70 +/- 27%, p = NS). Successful stent deployment was achieved in 55 (98%) of 56 patients with initial success (freedom from death, surgery, and infarction) in 52 (93%) of 56 patients. The success rate at 1 month fell to 71% primarily because of the occurrence of subacute stent thrombosis (16%) and its associated complications. Overall, major complications occurred in 16 (29%) of 56 patients within 30 days. The only predictor of subacute stent thrombosis in multiple stepwise logistic regression analysis was the presence of angiographically visible thrombus after stenting (p = 0.03). Angiographic restenosis was documented in eight (23%) of 35 eligible patients. CONCLUSIONS: Emergency stenting may be a useful and effective treatment for failed angioplasty. High initial success rates (greater than 90%) can be achieved, but subsequent complications, often related to subacute thrombosis, occur in a substantial portion of patients. Patients who receive stents on an emergency basis, particularly those with previous acute occlusion, should be considered to be at greater than usual risk for complications and receive more careful anticoagulation and follow-up.

Aged↗
PubMed1992

Dose-dependent smooth muscle cell proliferation induced by thermal injury with pulsed infrared lasers.

BACKGROUND: Recently, laser-heated and radio frequency-heated balloon angioplasty techniques have been proposed as a means to treat or minimize dissection and elastic recoil but have been associated with a high rate of clinical restenosis. Similarly, pulsed laser angioplasty techniques proposed to minimize thermal injury while ablating obstructing atheroma have failed to reduce clinical restenosis. Because "hot balloon" and pulsed laser angioplasty create both mechanical and thermal injury, it has been difficult to discern the cause of the smooth muscle cell (SMC) proliferation resulting in restenosis and whether such magnitude of proliferation is predictable and dose related. This study was undertaken to explore these issues. METHODS AND RESULTS: Localized thermal lesions accompanying efficient ablation were created with a pulsed Tm:YAG laser in nine rabbit aortas, which consistently led to a focal proliferation of SMC that filled the ablated region by 4 weeks. Transcutaneous Ho:YAG pulsed laser irradiation at multiple independent sites of 24 central rabbit ear arteries without ablation led to brief approximately 30 degrees C thermal transients and thermal damage to the artery wall resulting in significant neointimal proliferation by 3 weeks and a mean cross-sectional narrowing of 59 +/- 17% at a dose of 390 mJ/mm2. Acute and chronic responses to varying total energy deposition were studied by histology after the rabbits were killed at 2 hours to 4 weeks. Arterial segments midway between laser injuries were unaffected and served as internal controls. Neointimal proliferation at 3 weeks after laser injury exhibited a clear dose dependence. Mean cross-sectional narrowing increased from 34 +/- 10% to 85 +/- 15% as laser fluence increased from 240 mJ/cm2 to 640 mJ/cm2 (r = 0.84). Similarly, cross-sectional narrowing caused by SMC neointimal proliferation increased from 20 +/- 10% to 77 +/- 17% for a fixed surface irradiation as the depth of the most superficial arterial media decreased from 600 microns to 330 microns (r = 0.94). CONCLUSIONS: Thermal injury to the arterial wall is a potent stimulus for SMC proliferation and may necessitate reduction in laser or thermal energy used for angioplasty. Moreover, a dose-response relation exists between the degree of thermal injury and SMC proliferative response. Hence, this technique could be used as a practical model of restenosis suitable for screening therapies for inhibition of SMC proliferation.

Animals↗
PubMed1992

Intravascular ultrasound evaluation of the effect of rotational atherectomy in obstructive atherosclerotic coronary artery disease.

BACKGROUND: High-speed rotational atherectomy uses a diamond-coated, elliptical burr to abrade occlusive atherosclerosis, especially noncompliant calcified plaque. METHODS AND RESULTS: Intravascular ultrasound (IVUS) was used to analyze 28 patients after atherectomy. Arteries treated and imaged were left main (three), left anterior descending (12), left circumflex (five), right coronary (seven), and saphenous vein graft (one). Twenty patients had adjunct balloon angioplasty. Twenty-two (79%) target lesions were calcified; the intimal arc of calcium was 160 +/- 126 degrees (range, 0-360 degrees). After atherectomy, the intima-lumen interface was unusually distinct and circular. The lumen was larger than the largest burr used for both stand-alone (1.19 +/- 0.19-fold the largest burr size) and adjunct balloon procedures (1.30 +/- 0.15-fold the largest burr). Three-dimensional reconstruction of the ultrasound images showed a smooth lumen, especially in calcified plaque. Deviations from cylindrical geometry occurred only in areas of soft plaque or superficial tissue disruption of calcified plaque. Five patients were studied before and after rotational atherectomy. IVUS showed an increase in lumen size, a decrease in plaque-plus-media area and in arc of target lesion calcification, and no change in target lesion external elastic membrane cross-sectional area. CONCLUSIONS: Rotational atherectomy causes atheroablation with only moderate evidence of barotrauma in heavily calcified arteries, even after adjunct balloon angioplasty. The lumen is cylindrical, especially in areas of calcified plaque, and somewhat larger than the largest burr tip used.

Angioplasty, Balloon, Coronary↗
PubMed1992

Genetically engineered endothelial cells remain adherent and viable after stent deployment and exposure to flow in vitro.

Intravascular stents, currently in experimental human use for recurrent arterial stenosis, are plagued by subacute thrombosis. As a therapeutic approach to stent-related thrombosis, we and others have suggested coating stents with endothelial cells before implantation. In a previous study we demonstrated the feasibility of coating stents with endothelial cells that were genetically modified to secrete large amounts of human tissue plasminogen activator. In the present study we attempted both to develop a clinically applicable protocol for stent seeding and to test whether seeded cells would remain adherent to stents after exposure to pulsatile flow. Endothelial cells were harvested from the saphenous veins of sheep with survival of the donor animals. Harvested cells were transduced with a retroviral vector containing a marker gene and seeded onto catheter-mounted stents under sterile conditions. Scanning electron microscopy revealed complete coverage of the stent surfaces by seeded cells. Stents were expanded and exposed to pulsatile flow in vitro. Substantial cell retention was observed on the lateral stent surfaces by light microscopy and scanning electron microscopy; fewer cells were seen on the luminal and abluminal surfaces. Removal of seeded cells from flow-exposed stents by trypsin digestion resulted in the recovery of approximately 70% of the seeded cells. These cells were viable and healthy as judged by their ability to proliferate to confluence with the same kinetics as control (non-flow-exposed) cells. Autologous genetically modified endothelial cells can be seeded onto catheter-mounted stents in a sterile manner, and stent deployment under flow conditions results in substantial retention of viable cells.

Animals↗