- Email: [email protected]
Scientific Session 9 Revascularization Investigations
Sunday, March 3, 1996 Scientific Session 9 Rev:ascularization Investigations Moderator: Gary I Becker, MD, Miami, FL Room 608
3. Implanted coil technology is a novel technique to investigate atherosclerosis and restenosis. 50-3:45 pm
49-3i:30 pm Visualization of Arterial Wall Changes with MR Microscopy in an Animal Model of Atherosclerosis RD. Sblansky-Goldberg, MD, Pbiladelpbia, PA· M.A. Golden, MD· IC Ford, PbD PURPOSE: To use an implanted radio-frequency (RF) coil to obtain very high resolution in vivo MR images of the aortic wall, thus enabling evaluation of the effect of intimal hyperplasia on wall thickness and luminal diameter. MA TERJALS AND METHODS: Silicone-covered, implanted RF coils (16 X 7 mm) were surgically implanted around the infrarenal abdominal aorta in four New Zealand white rabbits. After coil implantation, atherosclerosis was induced in the region of the coil by means of balloon denudation and high-cholesterol chow. Serial, cardiac-gated, SE images were obtained in the 31-cm bore, 1.9-T magnet by using a 3cm Held of view with an in-plane resolution of 115 lJ.m. In addition, angiographic and histologic findings were obtained. MR images were analyzed for lumen diameter and wall thickness . RESULTS: In injured rabbits (n = 3), MR images showed a mean increase in wall thickness of 55%, and the control showed no increase. MR exhibited a mean decrease in lumen diameter of only 10% of preinjury values; this result was influenced by aneurysm formation in one animal. T2 values increased in the injured wall from <20 to about 50 msec, thus increasing wall conspicuity. CONCLUSION Implanted coil technology affords the ability to serially follow induction of atherosclerosis, which causes luminal narrowing. Future work will use this model to investigate secondary arterial wall injury after balloon angioplasty to study restenosis. Takf~
Home Points: 1. Arterial wall changes due to atherosclerosis and restenosis can be temporally studied noninvasively with MR imaging.
2. High-resolution MR images can be obtained with an implanted coil.
In Vitro Model of Arterial Stenosis: Correlation of MR Signal Dephasing and Transstenotic Pressure Gradients B.R. Mustert, BS, Ann Arbor, MI· M.D. Dumas, MD· D.M. Williams, MD· M.R. Prince, MD, PbD PURPOSE: To correlate MR angiography signal loss from dephasing with transstenotic pressure gradients in an in vitro model of arterial stenosis. MATERIALS AND METHODS: Three-dimensional (3D) phase-contrast (PC), 2D TOF, and 3D TOF imaging with and without gadolinium were performed under physiologic conditions in an in vitro simulation of the cornmon iliac artery. A perfusion pump regulated flow rate and pulsatility. An in-line gate valve provided peripheral resistance. A silk noose provided variable stenosis in a 12-mm-diameter Silastic vessel. Length and diameter of regions of dephasing (flow-void jets) were measured, and their volumes were calculated. RESULTS: With all three pulse sequences, the dephasing occurred at pressure gradients ~ 4 rnm Hg. The region of dephasing length, width, and volume increased with increasing pressure gradients. The dephasing was greatest with 3D Pc. At a flow rate of 600 mL/rnin and a transstenotic pressure gradient of 24 rnm Hg, the dephasing volumes were 3,772.8 rnm3 (3D PC), 490.5 mm3 (2D TOF), and 151.1 rnm3 (3D TOP). Addition of gadolinium diminished the size of the dephasing jets. CONCLUSION MR angiographic signal loss from dephasing in a stenosis correlates directly with pressure gradients. This may provide a noninvasive means for determining the hemodynamic significance of arterial stenoses.
Take Home Points: 1. Dephasing at MR angiography is proportional to pressure gradient. 2. The most sensitive sequence for detection of dephasing is 3D Pc. 3. Use of gadolinium decreases the dephasing in a stenosis.
149
Sunday, March 3, 1996 4. MR angiography can be used to determine the hemodynamic significance of arterial stenoses.
51-4:00 pm Venous versus Arterial Endothelial Cell Modulation of Smooth Muscle Cell Proliferation in Vitro P.N. Waybill, MD, Hershey, PA· V.M. Chincilli, PhD· BJ. Ballermann, MD PURPOSE: The critical role of endothelial cells (ECs) in arterial disease has been well established, but little is known of their role in venous disease. Previous studies suggest inherent differences between arteries and veins: arterial stenoses demonstrate a large lipid component, whereas hemodialysis-related venous stenoses are characterized by marked smooth muscle cell (SMC) proliferation. This study compares effects of venous versus arterial ECs on SMC proliferation in coculture. MATERIALS AND METHODS: Human saphenous vein (HSV) ECs or human aortic (HA) ECs were cultured on the underside of 13-lJ.m porous polycarbonate membranes. On day 0, HA SMCs were cultured opposite confluent ECs. On days 0, 1, 2, 4, 6, and 8, membranes were harvested (3 per day) and stained with Hoechst dye, and HA SMCs were counted under fluorescent microscopy. Controls were HA SMCs cultured alone. Two-way multivariate analysis of variance was used. RESULTS: Over the entire 8-day period, there was significant induction of HA SMC proliferation by both HSV ECs (P = .0003) and HA ECs (P = .0012). Maximal inductions were 88% ± 11 with HSV ECs (P = .0015) and 24% ± 6 with HA ECs (p = .0015). HSV ECs exhibited a 3-9-fold greater induction than HA ECs (P = .0003).
CONCLUSION: HSV ECs induce adjacent HA SMC proliferation in a paracrine manner to a significantly greater extent than HA ECs.
Take Home Points: 1. ECs can modulate adjacent SMC proliferation. 2. Significant differences exist between venous and arterial EC modulation of adjacent SMC proliferation. 3. These findings may in part explain differences between arterial and venous stenoses.
150
52--4:15 pm Inhibition of Smooth Muscle Cell Migration: Greater with Hydrogel-based Delivery of a cRGD Peptide than with Direct Short-Term Peptide Exposnre M]. Slepian, MD~ Tucson, AZ· S.P. Massia, PhD* PURPOSE: Sustained local intravascular drug delivery is being examined as a means of modulating the arterial wall response to interventional injury to prevent restenosis. Current local drug delivery devices provide short-term drug exposure with limited sustained delivery. Polymer-based drug delivery systems potentially may provide sustained local delivery. To assess a model of local in vivo delivery, we compared the effect of hydrogen polymer-based versus direct short-term delivery of an antimigratory peptide on smooth muscle cell (SMC) migration following injury in vitro. MATERIALS AND METHODS: SMC monolayers (rat Ao, n = 16) were scrape wounded. In four of 16 monolayers, thin layers of hydrogel (PEGlactide) + cRGD peptide (l mmo1) were applied to the monolayer surface. In 4 other monolayers, 1 mmol of cRGD in media (MEM) was directly applied without gel. Drug-free hydrogel alone (four of 16) and media alone (four of 16) were applied as controls. After 10 minute of incubation, the media covering all monolayers were discarded, cultures washed and further incubated in drug-free media. At 48 hours the area of SMCs migrating from the wound line for both the gel and direct treatment groups was measured and the extent of migration for each drug treated group reported as a mean percentage migration relative to drug-free controls. RESULTS: Migration for cRGD hydrogel-treated monolayers was 27% ± 9 versus 93% ± 8 for direct 10-minute cRGD exposure (P < .01). Gel-based delivery led to a 66% reduction in the degree of SMC migration compared to direct 10-minute peptide exposure. There was no difference in migration between media-alone and gel-alone controls, with drug-free gel having no effect on underlying SMC migration. CONCLUSION: Hydrogel-based delivery of cRGD peptide led to enhanced local efficacy, with greater reduction in SMC migration compared with direct short-term peptide exposure alone. Delivery of promising antirestenosis
Sunday, March 3, 1996 agents via polymer-based drug delivery vehicles may enhance their efficacy beyond that achievable with direct short-tenn exposure methods alone. Take Home Points: 1. Drug-delivery catheters and coated stents provide short-tenn drug exposure. 2. Polymer-based drug delivery systems offer the potential for sustained local drug deliv~~ry.
3. Hydrogel-based delivery of an antimigratory peptide led to enhanced local efficacy, with greater reduction in SMC migration, compared with direct short-tenn peptide exposure alone. 4. Endoluminal paving with drug-laden hydrogels holds promise for endovascular drug delivery.
53-4:30 pm Suppression of Platelet Aggregation by Balloon-directed Local Intraarterial Delivery of Iloprost S. Nakatsuka, MD, Boston, MA • K. Kandarpa, MD~ PhD' S.M. Bravo, MD' ].M. Santos, MD' R.5. Harapanhalli, PhD' ] J. Barry, phD' PURPOSE: To detennine if aggregation of platelets after PTA can be suppressed with local delivery of Iloprost. MATERIALS AND METHODS: Three anesthetized Yorkshire pigs were subjected to PTA at two experimental and two control sites per animal. Experimental sites were treated with hydrogel-coated balloons loaded with approximately 2.25 f.!g of Iloprost. Control sites were treated similarly with unloaded hydrogel-coated balloons. Immediately before PTA, autogenous indium-labeled platelets were injected 00.2 MBq on average). One hour after PTA, the animals were killed, the treated sites were harvested, and local platelet aggregation was quantified with a gamma counter. RESULTS: The mean rate of the uptake of platelets at the Iloprost-treated sites divided by the activity of injected indium-labeled platelets was 221 cpm/MBq ± 59, and that at untreated sites was 358 cpm/MBq ± 158 (p < .025). The mean reduction rate of platelet aggregation was 37.7%.
CONCLUSION Local delivery of Iloprost loaded on a hydrogel-coated balloon resulted in a significant suppression of platelet aggregation at PTA sites. The effect of this suppression on intimal hyperplasia must be assessed. (This work was made possible by a grant from Boston Scientific Corp.)
Take Home Points: Quantified local drug delivery with hydrogelcoated balloons during PTA is feasible. Local delivery of Iloprost results in significant suppression of platelet aggregation. The mean reduction rate of platelet aggregation for this experiment was 37.7%.
54-4:45 pm Local Delivery of Heparin with Balloon Angioplasty: Results of a Prospective Randomized Trial R.C. Sheley, MD~ Portland, OR' B.S. Schuman, MD • B.A. Standage, MD' J W Ragsdale, MD' S.P. Quinn, MD PURPOSE: To evaluate the effectiveness of local delivery of heparin via hydrogel-coated, treated balloons in the treatment of vascular stenoses associated with hemodialysis access. MATERIALS AND METHODS: In this randomized prospective trial, treatment with heparinsoaked hydrogel balloon catheters (n = 32) was compared with treatment with hydrogel balloon catheters without heparin. All patients were undergoing hemodialysis, and all stenoses involved either the venous anastomosis of a dialysis graft or a native vein. Before the procedures, the heparin-coated balloons were soaked in concentrated heparin and delivered in a protected manner with a sheath to help prevent washout of the heparin on the balloon. RESULTS: The median primary patencies were as follows: heparin coated, 144 days; non-heparin coated, 202 days (P = .128). The median assisted primary patencies were: heparin coated, 165 days; non-heparin coated, 184 days (p = .3002). The media secondary patencies were: heparin coated, 351 days; non-heparin coated; 373 days (P = .92). CONCLUSION In this population, local delivery of heparin via a hydrogel-coated balloon is no better than use of a hydrogel-coated balloon without heparin.
151
3. Implanted coil technology is a novel technique to investigate atherosclerosis and restenosis. 50-3:45 pm
49-3i:30 pm Visualization of Arterial Wall Changes with MR Microscopy in an Animal Model of Atherosclerosis RD. Sblansky-Goldberg, MD, Pbiladelpbia, PA· M.A. Golden, MD· IC Ford, PbD PURPOSE: To use an implanted radio-frequency (RF) coil to obtain very high resolution in vivo MR images of the aortic wall, thus enabling evaluation of the effect of intimal hyperplasia on wall thickness and luminal diameter. MA TERJALS AND METHODS: Silicone-covered, implanted RF coils (16 X 7 mm) were surgically implanted around the infrarenal abdominal aorta in four New Zealand white rabbits. After coil implantation, atherosclerosis was induced in the region of the coil by means of balloon denudation and high-cholesterol chow. Serial, cardiac-gated, SE images were obtained in the 31-cm bore, 1.9-T magnet by using a 3cm Held of view with an in-plane resolution of 115 lJ.m. In addition, angiographic and histologic findings were obtained. MR images were analyzed for lumen diameter and wall thickness . RESULTS: In injured rabbits (n = 3), MR images showed a mean increase in wall thickness of 55%, and the control showed no increase. MR exhibited a mean decrease in lumen diameter of only 10% of preinjury values; this result was influenced by aneurysm formation in one animal. T2 values increased in the injured wall from <20 to about 50 msec, thus increasing wall conspicuity. CONCLUSION Implanted coil technology affords the ability to serially follow induction of atherosclerosis, which causes luminal narrowing. Future work will use this model to investigate secondary arterial wall injury after balloon angioplasty to study restenosis. Takf~
Home Points: 1. Arterial wall changes due to atherosclerosis and restenosis can be temporally studied noninvasively with MR imaging.
2. High-resolution MR images can be obtained with an implanted coil.
In Vitro Model of Arterial Stenosis: Correlation of MR Signal Dephasing and Transstenotic Pressure Gradients B.R. Mustert, BS, Ann Arbor, MI· M.D. Dumas, MD· D.M. Williams, MD· M.R. Prince, MD, PbD PURPOSE: To correlate MR angiography signal loss from dephasing with transstenotic pressure gradients in an in vitro model of arterial stenosis. MATERIALS AND METHODS: Three-dimensional (3D) phase-contrast (PC), 2D TOF, and 3D TOF imaging with and without gadolinium were performed under physiologic conditions in an in vitro simulation of the cornmon iliac artery. A perfusion pump regulated flow rate and pulsatility. An in-line gate valve provided peripheral resistance. A silk noose provided variable stenosis in a 12-mm-diameter Silastic vessel. Length and diameter of regions of dephasing (flow-void jets) were measured, and their volumes were calculated. RESULTS: With all three pulse sequences, the dephasing occurred at pressure gradients ~ 4 rnm Hg. The region of dephasing length, width, and volume increased with increasing pressure gradients. The dephasing was greatest with 3D Pc. At a flow rate of 600 mL/rnin and a transstenotic pressure gradient of 24 rnm Hg, the dephasing volumes were 3,772.8 rnm3 (3D PC), 490.5 mm3 (2D TOF), and 151.1 rnm3 (3D TOP). Addition of gadolinium diminished the size of the dephasing jets. CONCLUSION MR angiographic signal loss from dephasing in a stenosis correlates directly with pressure gradients. This may provide a noninvasive means for determining the hemodynamic significance of arterial stenoses.
Take Home Points: 1. Dephasing at MR angiography is proportional to pressure gradient. 2. The most sensitive sequence for detection of dephasing is 3D Pc. 3. Use of gadolinium decreases the dephasing in a stenosis.
149
Sunday, March 3, 1996 4. MR angiography can be used to determine the hemodynamic significance of arterial stenoses.
51-4:00 pm Venous versus Arterial Endothelial Cell Modulation of Smooth Muscle Cell Proliferation in Vitro P.N. Waybill, MD, Hershey, PA· V.M. Chincilli, PhD· BJ. Ballermann, MD PURPOSE: The critical role of endothelial cells (ECs) in arterial disease has been well established, but little is known of their role in venous disease. Previous studies suggest inherent differences between arteries and veins: arterial stenoses demonstrate a large lipid component, whereas hemodialysis-related venous stenoses are characterized by marked smooth muscle cell (SMC) proliferation. This study compares effects of venous versus arterial ECs on SMC proliferation in coculture. MATERIALS AND METHODS: Human saphenous vein (HSV) ECs or human aortic (HA) ECs were cultured on the underside of 13-lJ.m porous polycarbonate membranes. On day 0, HA SMCs were cultured opposite confluent ECs. On days 0, 1, 2, 4, 6, and 8, membranes were harvested (3 per day) and stained with Hoechst dye, and HA SMCs were counted under fluorescent microscopy. Controls were HA SMCs cultured alone. Two-way multivariate analysis of variance was used. RESULTS: Over the entire 8-day period, there was significant induction of HA SMC proliferation by both HSV ECs (P = .0003) and HA ECs (P = .0012). Maximal inductions were 88% ± 11 with HSV ECs (P = .0015) and 24% ± 6 with HA ECs (p = .0015). HSV ECs exhibited a 3-9-fold greater induction than HA ECs (P = .0003).
CONCLUSION: HSV ECs induce adjacent HA SMC proliferation in a paracrine manner to a significantly greater extent than HA ECs.
Take Home Points: 1. ECs can modulate adjacent SMC proliferation. 2. Significant differences exist between venous and arterial EC modulation of adjacent SMC proliferation. 3. These findings may in part explain differences between arterial and venous stenoses.
150
52--4:15 pm Inhibition of Smooth Muscle Cell Migration: Greater with Hydrogel-based Delivery of a cRGD Peptide than with Direct Short-Term Peptide Exposnre M]. Slepian, MD~ Tucson, AZ· S.P. Massia, PhD* PURPOSE: Sustained local intravascular drug delivery is being examined as a means of modulating the arterial wall response to interventional injury to prevent restenosis. Current local drug delivery devices provide short-term drug exposure with limited sustained delivery. Polymer-based drug delivery systems potentially may provide sustained local delivery. To assess a model of local in vivo delivery, we compared the effect of hydrogen polymer-based versus direct short-term delivery of an antimigratory peptide on smooth muscle cell (SMC) migration following injury in vitro. MATERIALS AND METHODS: SMC monolayers (rat Ao, n = 16) were scrape wounded. In four of 16 monolayers, thin layers of hydrogel (PEGlactide) + cRGD peptide (l mmo1) were applied to the monolayer surface. In 4 other monolayers, 1 mmol of cRGD in media (MEM) was directly applied without gel. Drug-free hydrogel alone (four of 16) and media alone (four of 16) were applied as controls. After 10 minute of incubation, the media covering all monolayers were discarded, cultures washed and further incubated in drug-free media. At 48 hours the area of SMCs migrating from the wound line for both the gel and direct treatment groups was measured and the extent of migration for each drug treated group reported as a mean percentage migration relative to drug-free controls. RESULTS: Migration for cRGD hydrogel-treated monolayers was 27% ± 9 versus 93% ± 8 for direct 10-minute cRGD exposure (P < .01). Gel-based delivery led to a 66% reduction in the degree of SMC migration compared to direct 10-minute peptide exposure. There was no difference in migration between media-alone and gel-alone controls, with drug-free gel having no effect on underlying SMC migration. CONCLUSION: Hydrogel-based delivery of cRGD peptide led to enhanced local efficacy, with greater reduction in SMC migration compared with direct short-term peptide exposure alone. Delivery of promising antirestenosis
Sunday, March 3, 1996 agents via polymer-based drug delivery vehicles may enhance their efficacy beyond that achievable with direct short-tenn exposure methods alone. Take Home Points: 1. Drug-delivery catheters and coated stents provide short-tenn drug exposure. 2. Polymer-based drug delivery systems offer the potential for sustained local drug deliv~~ry.
3. Hydrogel-based delivery of an antimigratory peptide led to enhanced local efficacy, with greater reduction in SMC migration, compared with direct short-tenn peptide exposure alone. 4. Endoluminal paving with drug-laden hydrogels holds promise for endovascular drug delivery.
53-4:30 pm Suppression of Platelet Aggregation by Balloon-directed Local Intraarterial Delivery of Iloprost S. Nakatsuka, MD, Boston, MA • K. Kandarpa, MD~ PhD' S.M. Bravo, MD' ].M. Santos, MD' R.5. Harapanhalli, PhD' ] J. Barry, phD' PURPOSE: To detennine if aggregation of platelets after PTA can be suppressed with local delivery of Iloprost. MATERIALS AND METHODS: Three anesthetized Yorkshire pigs were subjected to PTA at two experimental and two control sites per animal. Experimental sites were treated with hydrogel-coated balloons loaded with approximately 2.25 f.!g of Iloprost. Control sites were treated similarly with unloaded hydrogel-coated balloons. Immediately before PTA, autogenous indium-labeled platelets were injected 00.2 MBq on average). One hour after PTA, the animals were killed, the treated sites were harvested, and local platelet aggregation was quantified with a gamma counter. RESULTS: The mean rate of the uptake of platelets at the Iloprost-treated sites divided by the activity of injected indium-labeled platelets was 221 cpm/MBq ± 59, and that at untreated sites was 358 cpm/MBq ± 158 (p < .025). The mean reduction rate of platelet aggregation was 37.7%.
CONCLUSION Local delivery of Iloprost loaded on a hydrogel-coated balloon resulted in a significant suppression of platelet aggregation at PTA sites. The effect of this suppression on intimal hyperplasia must be assessed. (This work was made possible by a grant from Boston Scientific Corp.)
Take Home Points: Quantified local drug delivery with hydrogelcoated balloons during PTA is feasible. Local delivery of Iloprost results in significant suppression of platelet aggregation. The mean reduction rate of platelet aggregation for this experiment was 37.7%.
54-4:45 pm Local Delivery of Heparin with Balloon Angioplasty: Results of a Prospective Randomized Trial R.C. Sheley, MD~ Portland, OR' B.S. Schuman, MD • B.A. Standage, MD' J W Ragsdale, MD' S.P. Quinn, MD PURPOSE: To evaluate the effectiveness of local delivery of heparin via hydrogel-coated, treated balloons in the treatment of vascular stenoses associated with hemodialysis access. MATERIALS AND METHODS: In this randomized prospective trial, treatment with heparinsoaked hydrogel balloon catheters (n = 32) was compared with treatment with hydrogel balloon catheters without heparin. All patients were undergoing hemodialysis, and all stenoses involved either the venous anastomosis of a dialysis graft or a native vein. Before the procedures, the heparin-coated balloons were soaked in concentrated heparin and delivered in a protected manner with a sheath to help prevent washout of the heparin on the balloon. RESULTS: The median primary patencies were as follows: heparin coated, 144 days; non-heparin coated, 202 days (P = .128). The median assisted primary patencies were: heparin coated, 165 days; non-heparin coated, 184 days (p = .3002). The media secondary patencies were: heparin coated, 351 days; non-heparin coated; 373 days (P = .92). CONCLUSION In this population, local delivery of heparin via a hydrogel-coated balloon is no better than use of a hydrogel-coated balloon without heparin.
151