Renal artery embolization with diluted hot contrast medium: an experimental study.

PURPOSE: To evaluate the safety and efficacy of diluted hot contrast medium to embolize the renal arteries in a canine model. MATERIALS AND METHODS: Transcatheter embolization was performed in 15 dogs (five dogs in each phase: I, II, and control). The diluted hot contrast medium was heated to 90 degrees C--100 degrees C and 30--60 mL were injected into a renal artery of each dog in phase I (optimization studies) and II (efficacy studies). In the control group, balloon inflation was performed without injection of diluted hot contrast medium. The temperature measurement was performed on one dog in phase I by temperature probe. Follow-up angiography was performed immediately (n = 15), at 1 week (n = 9), at 1 month (n = 9), and after 3 months (n = 5). All dogs were killed and kidneys were removed for histologic examination. RESULTS: The procedure was performed successfully in all dogs. Follow-up angiography showed complete obstruction of the injected renal arteries in phases I and II. The microscopic findings showed acute full-thickness necrosis of the renal cortex and renal artery in phase I, and complete coagulative necrosis of the cortex, medulla, and intrarenal blood vessels in phase II. There were no histologic changes of renal veins, inferior vena cava (IVC), and aorta. There were nonspecific findings in the control group. CONCLUSION: This preliminary experimental study suggests that diluted hot contrast medium may be a safe agent for renal ablation without thrombus formation in the renal vein or IVC.

New device for closure of muscular ventricular septal defects in a canine model.

BACKGROUND: Repair of muscular ventricular septal defects (MVSDs) has always been challenging to the surgeon. Long-term morbidity and mortality are significantly increased if the defects are closed via left ventriculotomy or if they are associated with other complex congenital anomalies. The purpose of this study was to close MVSDs with the Amplatz ventricular septal defect device. This device is constructed from 0.004-in nitinol wire mesh filled with polyester fibers. It is retrievable, repositionable, self-centering, and of low profile. METHODS AND RESULTS: MVSDs were created with the help of a sharp punch in 10 dogs. The location of the defects was anterior muscular (n=3), midmuscular (n=3), apical (n=3), and inlet muscular (n=1). The diameter of the defects ranged from 6 to 14 mm. All defects were closed in the catheterization laboratory. The device was placed with the help of transesophageal echocardiography and fluoroscopy. A 7F sheath was used to deploy the device from the right ventricular side in 8 and the left ventricular side in 2 dogs. Placement was successful in all animals. The complete closure rate was 30% (3/10) immediately after placement and 100% at 1-week follow-up. Pathological examination of the heart revealed complete endothelialization of the device in dogs killed after 3 months. CONCLUSIONS: The Amplatz ventricular septal defect device appears highly efficacious in closing MVSDs. The advantages include a small delivery sheath, complete retrievability before release, and the fact that it is self-centering and self-expanding, thereby making it an attractive option in smaller children.

New self-expanding patent foramen ovale occlusion device.

Our purpose was to evaluate a new self-expanding device for closure of the patent foramen ovale (PFO). A transeptal catheter passage through the flap of the fossa ovalis was performed with a transeptal needle inside a catheter, creating a PFO in two minipigs. In an additional five animals, a naturally occurring PFO was found. The device is made from 0.005 inch nitinol wire mesh with polyester fabric inside, similar in construction to the Amplatzer atrial septal occluder. However, the left atrial disc is smaller (18 mm) than the right atrial disc (26 mm). Both discs are connected by a very short flexible waist (3 mm) that allows free movement of both retention discs. Pulmonary and right atrial angiography were performed after placement, at 1 month, and at 3 months follow-up. Placement of the device was technically successful in six animals. One animal died from ventricular fibrillation during placement. Pulmonary angiography and echocardiography showed complete occlusion of the PFO in six animals. Two animals were sacrificed after 1 month and four animals after 3 months. In the animals sacrificed at 1 month, histopathological examination showed partial (n = 2) endothelialization, and in the 3 months follow-up group (n = 4) endothelialization was complete. The device appears to be highly effective for occlusion of PFOs. This procedure may be performed as an outpatient procedure due to the small 7 Fr delivery system sheath. Cathet. Cardiovasc. Intervent. 47:370-376, 1999.

A new technique for sizing of atrial septal defects.

This article evaluates a new compliant balloon catheter for sizing of Atrial Septal Defects (ASDs) in vitro and in vivo using X-ray and echo measurements. A phantom consisting of a plastic plate with 17 circular holes varying from 8 to 30 mm was used to determine the accuracy of the measurements. The catheter has a 7 Fr shaft with a double lumen. The balloon is made from a 0.002" plastic membrane. Four platinum marker bands on the shaft of the catheter allow radiographic measurements. The balloon catheter was placed through various holes of the phantom and inflated with 38% contrast medium. X-ray measurement by video and cine recording were performed and compared with the true measurement of the model. The study was carried out in a double blind fashion. For echo measurements, the plastic model was immersed in a water bath. The balloon was inflated with water and measured in a long-axis view. The actual diameters were compared with the measurements obtained by video, cine, and echo recordings. One young pig with a surgically created ASD was used for in vivo measurement. The balloon catheter was passed through the ASD over an exchange wire, inflated with diluted contrast medium until a waist was observed, which was measured by video and cine techniques. The animal was euthanized, and the defect was measured by a tapered measuring probe. The difference between the actual size and measurements obtained by video recordings was 0.54 +/- 0.30 mm, by cine 0.62 +/- 0.20 mm, and by echo measurements 0.60 +/- 0.43 mm. All measurements were less than 1 mm in error except for four measurements (<1.5 mm). A strong correlation was present between each two groups (r = 0.99, P < 0.0001). In the in vivo study, the size of the video and cine recordings (14.2 and 13.9 mm, respectively) were very closer to the actual size (14 mm) as measured by a probe in the postmortem specimen. The new balloon catheter provides a more rapid and precise determination of the stretched diameter of atrial septal defects. It eliminates the error of pulling a catheter through the communication. This new technique should be of benefit to all investigators using septal occlusion devices and will facilitate the selection of the properly sized Amplatzer septal occluder.

The nitinol vascular occlusion plug: preliminary experimental evaluation in peripheral veins.

PURPOSE: To compare the nitinol occlusion plug with standard stainless steel coils for the occlusion of moderate-size peripheral veins. MATERIALS AND METHODS: The nitinol plug is a braided multilayered vascular occlusion device filled with thrombogenic polyester fibers. It is self-expanding and can be recaptured into its 6-F introducing sheath for repositioning prior to detachment. Ten occlusion procedures were performed in five dogs from a retrograde transjugular venous approach. Five nitinol plugs (diameter: 7.4 mm +/- 0.5) were deployed in five femoropopliteal veins (diameter: 6.5 mm +/- 0.7; mean oversizing 14.6%). Two sequential Gianturco coils (diameter: 7.4 mm +/- 0.9) were deployed in the corresponding contralateral veins (diameter: 6.2 mm +/- 0.8; mean oversizing 19.6%). Follow-up venography was performed at 1 month, following which the animals were killed and the vessels were explanted. RESULTS: Time-to-occlusion was significantly shorter with the nitinol plug as compared to two Gianturco coils (4.2 minutes +/- 3.4 vs 25.6 minutes +/- 14.1, respectively [P < .03]). At 1 month all but one coil-doublet (80%) had recanalized or migrated, compared to only one nitinol occluder (20%, P < .04). Histopathologic examination of plug-occluded veins showed a uniform organized matrix and underlying intimal proliferative response. CONCLUSION: A single nitinol occluder resulted in significantly faster occlusion time and significantly lower recanalization or migration rate than two Gianturco coils, in moderate-size peripheral veins.

Injury potential to venous valves from the Amplatz thrombectomy device.

PURPOSE: To evaluate the acute effects of the Amplatz thrombectomy device (ATD) on peripheral venous valves in a canine model. MATERIALS AND METHODS: ATD thrombectomy was performed in 17 veins, and control experiments with use of an 8-F sheath-dilator were performed in four veins. Prethrombectomy ascending venography was performed, followed by device passage across the vein segment. Post-thrombectomy ascending venography was then performed, followed by heparinization and euthanasia. The treated veins were carefully explanted and stored in formaldehyde for histopathologic examination. Severity of valve injury was graded on a scale of 0 to 4. RESULTS: In ATD-treated veins: 10 veins sustained no injury [grade 0] (diameter, 6.7 mm +/- 1.7; antegrade/retrograde approach, 5/5), five veins sustained mild injury [grade 1-2] (diameter, 5.2 mm +/- 0.8; antegrade/retrograde, 3/2), while the remaining two veins sustained moderate-to-severe injury [grade 3-4] (diameter, 5 and 6 mm; antegrade/retrograde, 1/1). In sheath-dilator treated veins: no injury [grade 0] in any of the four treated veins (mean diameter, 5.5 mm +/- 0.6; all retrograde). In ATD-treated veins, valve injury (of any grade) was significantly more frequent in veins 6 mm or less in diameter than in veins at least 7 mm in diameter (seven of 12 vs zero of five; P < .03). There was no significant association between thrombectomy approach and injury grade. CONCLUSION: Veins 7 mm or greater in diameter were associated with no significant valve injury during ATD thrombectomy. However, long-term and short-term effects on valvular function will need to be assessed.

[Percutaneous closure of an interatrial communication with the Amplatzer device. The first case in Mexico]. / Cierre percutáneo de comunicación interatrial con el dispositivo Amplatzer. Primer caso en México.

The Amplatzer septal occluder is a new device intended for the percutaneous closure of secundum atrial septal defects that has distinctive characteristics and important advantages over other available devices. We present the first successful closure of an atrial septal defect with this device in Mexico in a 19 year old man with a 16 mm secundum type septal defect.

Acute and delayed outcomes of mechanical thrombectomy with use of the steerable Amplatz thrombectomy device in a model of subacute inferior vena cava thrombosis.

PURPOSE: To study the efficacy and delayed outcome of mechanical thrombectomy with the Amplatz thrombectomy device (ATD) in an experimental model of subacute inferior vena cava (IVC) thrombosis. MATERIALS AND METHODS: Mechanical thrombectomy was performed in 23 dogs with subacute infrarenal IVC thrombosis (6-15 days old). Heparin was administered during thrombectomy in all procedures (activated clotting time > or = 300 sec). Thirteen animals were killed immediately after thrombectomy, and the remaining 10 were allowed to survive for up to 1 month with no anticoagulation therapy. RESULTS: Venographic patency of the IVC was restored in all animals, although residual mural thrombus remained in nine dogs (< 20% narrowing in seven, 20%-30% narrowing in two). No histopathologic evidence of mechanical wall disruption attributed to mechanical thrombectomy was seen. However, foci of organizing residual thrombus with associated transmural phlebitic changes with round-cellular infiltration were present in all acute specimens, including those appearing clear at venography. Venography at 1 week or 1 month after thrombectomy showed IVC rethrombosis in eight dogs (80%) who were not receiving anticoagulants. During mechanical thrombectomy, a small increase in mean pulmonary artery pressure occurred, with a corresponding decrease in systemic arterial oxygen saturation. No acute emboli were noted on the post-thrombectomy pulmonary angiograms. However, histopathologic examination of acutely explanted lungs in 11 animals showed arteriolar microemboli (100-500 microm) in four. CONCLUSION: Mechanical thrombectomy with use of the ATD can effectively clear subacute IVC thrombus. However, rethrombosis is common and may be due to the high prevalence of phlebitis and residual thrombus. Anticoagulation may need to be continued after successful thrombectomy to prevent progression of residual thrombus and allow mural phlebitic changes to subside.

Transvenous closure of secundum atrial septal defects: preliminary results with a new self-expanding nitinol prosthesis in a swine model.

BACKGROUND: Our purpose was to evaluate a new prosthesis for percutaneous closure of secundum atrial septal defects (ASDs). METHODS AND RESULTS: Percutaneous closure of surgically created fossa ovalis ASD was attempted in 15 minipigs. The mean balloon-stretched ASD diameter was 12.3+/-2.3 mm (range, 10 to 16 mm). The self-expanding prosthesis was braided from 0.005-in Nitinol wires in the shape of two flat buttons with a short connecting waist with a diameter corresponding to that of the defect to be closed. Polyester filling was added to enhance thrombogenicity. Pulmonary arteriography with levo-phase was obtained before placement; immediately after placement; and at 1-week, 1-month, and 3-month follow-ups. Four animals were killed at 1 week, 1 month, and 3 months for histopathological correlation. Three deaths resulted from ventricular fibrillation (one during anesthesia and two during the placement procedure). Successful placement of the prosthesis was achieved in the remaining 12 animals. Overall immediate ASD closure on angiography occurred in 7 of 12 animals (all polyester-filled prostheses). Absent or trace shunt by angiography was present in 11 of 12 devices at 1 week, with the remaining one demonstrating a small shunt. All septal defects were completely closed at 1 month with the exception of one case in which delayed partial dislodgment of an undersized prosthesis into the right atrium had developed. Closure rate at 3 months was 100%. Neoendothelialization and fibrous incorporation of the prosthesis were completed within 1 to 3 months. CONCLUSIONS: Effective and permanent occlusion of secundum ASDs is feasible with a device that offers the advantages of easy placement, self-centering, and repositionability.

Dialysis grafts arterial plug: retrieval using the tulip sheath device in vitro.

The "arterial plug" is a resistant thrombus that frequently persists at the arterial anastomosis of clotted hemodialysis grafts following thrombolytic therapy. We studied the physical and morphological characteristics of the plug and determined the feasibility of transcatheter removal in vitro using the tulip compression thrombectomy system. Sixteen thrombus plugs were recovered during surgical thrombectomy of clotted human dialysis grafts. The physical and gross physical characteristics of all plugs were analyzed. Eight specimens were evaluated microscopically. Transcatheter compression thrombectomy of eight plugs was attempted in vitro. Each plug was embedded in a polyvinyl tube filled with newly clotted blood and connected to a flow circuit. First, balloon-assisted aspiration thrombectomy (BAT) of soft thrombus was performed, while sparing the distal-most segment containing the plug. The tulip sheath was then introduced facing the "arterial end" of the tube. The thrombus segment containing the plug was pulled back into the tulip mesh using either a 3 Fr Fogarty balloon catheter or a self-expanding rake. The tulip was closed to compress and remove the trapped plug. Near-complete thrombectomy of soft clot was achieved in all tested tubes. Compression and retrieval of the entire arterial plug was successful in all except one, where only partial compression of the plug occurred, presumably due to fibrotic changes. No fragmentation or embolization occurred in the remaining procedures. Spongy consistency was noted in 94% of the specimens. Microscopic evaluation showed organized layered thrombus with compaction in five plugs. Transcatheter removal of a thrombus plug is feasible in vitro using the tulip compression-thrombectomy system.

Experimental evaluation of a new self-expanding patent ductus arteriosus occluder in a canine model.

PURPOSE: A new self-expanding patent ductus arteriosus (PDA) occluder was designed. MATERIALS AND METHODS: Percutaneous closure of surgically created aortopulmonary shunts was attempted in 19 dogs. The occlusion device consisted of a nitinol wire frame tightly woven into a cylinder with a flat retention disc. A polyester-filled frame was used in the last six procedures. A 6-F introducing sheath was advanced across the aortopulmonary conduit into the descending thoracic aorta. The prosthesis (attached on a stiff delivery cable) was advanced through the introducing sheath. The retention disc was first released in the descending thoracic aorta, then the cylindrical device frame was expanded within the conduit by withdrawing the sheath. RESULTS: Subtotal misplacement into the descending aorta occurred in one procedure (overall technical success rate, 95%), and one animal died before the 1-week follow-up. Complete angiographic shunt closure was achieved in seven of 18 (39%) animals at 30 minutes, 12 of 17 (71%) animals at 1 week, 14 of 17 (82%) animals at 1 month, and 11 of 12 (92%) animals at 3 months. Significantly higher 30-minute closure rates occurred with polyester-filled occluders compared with nonfilled occluders (five of five [100%] vs one of 13 [15%]; P = .002). Persistent shunt at 3 months occurred in only one nonfilled device (6%). In the remaining 16 animals, both orifices of the shunt were covered by a smooth glistening neoendothelium at postmortem examination. CONCLUSION: This device combines the advantages of small delivery system, easy placement, self-centering, and repositionability. Immediate shunt closure can be reliably accomplished with the polyester-filled prosthesis.

Repositionable vascular occluder: experimental comparison with standard Gianturco coils.

PURPOSE: To evaluate the efficacy and recanalization rates of a newly designed vascular occlusion device. MATERIALS AND METHODS: The self-expanding vascular occluder was braided from fine nitinol wires and filled with polyester fibers. The device was delivered through a 6-F polyethylene introducing sheath with use of a delivery cable with a microscrew adaptor. Comparison was made between one occlusion plug and two Gianturco coils placed in the corresponding contralateral arterial segment in nine dogs and six pigs. The mean diameter of the targeted vessels was 4.8 mm +/- 0.8. Two animals were killed immediately after occlusion, and the remaining 13 animals underwent follow-up angiography at 1 week and/or 1 month, after which the animals were killed and the vessels were explanted for gross and histopathologic examination. RESULTS: Significantly shorter time-to-occlusion was achieved with the nitinol plug compared with two Gianturco coils (1.73 minutes +/- 1.28 vs 5.73 minutes +/- 6.18; P = .021). The recanalization rate at 1 month was also significantly lower (36.4% vs 81.8%, P = .027). The occlusion time was strongly dependent on the target artery diameter with Gianturco coils (R = .79, P = .0007), and not with the nitinol plug. CONCLUSION: The nitinol vascular occluder appears highly effective and reliable, with one plug resulting in significantly faster and longer lasting occlusions compared with two Gianturco coils. The new device can be repositioned prior to release, therefore allowing optimal positioning.

Axial and lateral resolution of rotational intravascular ultrasound: in vitro observations and diagnostic implications.

PURPOSE: To determine the axial and lateral resolution of a rotating intravascular ultrasound system and the diagnostic implications for the diagnosis of early artherosclerosis. METHODS: The resolution of a 20 MHz rotating transducer was tested in a specially designed high-resolution phantom and in five aortic autopsy specimens with varying degrees of early atherosclerosis. RESULTS: The best lateral resolution is at the minimal distance between transducer and object. Measurements in the wire phantom showed this to be better than 0.43 mm. This is less than the axial resolution which is better than 0.13 mm. Decreasing lateral resolution with increasing distance between transducer and object is manifested by arcing and overestimation of the extent of focal atherosclerotic lesions. CONCLUSION: Axial resolution is significantly better than lateral resolution. Rapid deterioration of lateral resolution affects the diagnostic ability to characterize the extent of early atherosclerosis. Eccentric positioning of the transducer tip, particularly in larger vessels, will therefore influence diagnostic accuracy in vivo.

Transcatheter occlusion of patent ductus arteriosus using a newly developed self-expanding device. Evaluation in a canine model.

RATIONALE AND OBJECTIVES: A new occlusion device designed for use in a patent ductus arteriosus was tested in an animal model. METHODS: The device consists of a self-expanding conical-shaped stainless steel mesh, with hooks encircling the expanding end acting to secure the device within the ductus. A screw thread at the apex allows attachment to a stylet, and a 6 F delivery system is used. Placement of the device was attempted in 20 canines that previously had a vascular graft surgically inserted between the descending thoracic aorta and main pulmonary artery, creating the patent ductus model. Angiographic follow-up at regular intervals was performed over a 3-month period. RESULTS: Early cases resulted in device misplacement and migration because of inaccurate assessment of ductus position and size. In 15 canines the device was placed within the ductus and regularly assessed over the 3-month placement period. Ductus occlusion occurred within 1 week in 12 of 13 dogs (92%) when device placement was considered ideal. In two dogs where significant protrusion of the device from the ductus was evident (either into the aorta or main pulmonary artery) ductus closure was delayed but present by 3 months, resulting in a 93% overall closure rate at this time. In one dog, the ductus remained partially opened. CONCLUSIONS: This self-expanding patent ductus arteriosus occlusion device is promising. The 6 F delivery system is advantageous over other devices currently available, making it more suited for use in the pediatric population. Accurate assessment of the ductus is imperative, however, to enable correct device sizing. The screw thread system allows the device to be repositioned if desired prior to deployment.

Chronic iliac artery occlusions: primary recanalization with endovascular stents.

PURPOSE: The authors describe treatment of chronic iliac artery occlusions with primary stent placement without prior thrombolysis or angioplasty. PATIENTS AND METHODS: Eight patients with chronic iliac artery occlusions (six men and two women) underwent primary stent placement without prior use of thrombolytic agents or angioplasty. Palmaz stents were placed in seven patients and a Wallstent device was placed in one. RESULTS: In all patients, revascularization was successful without residual stenoses or pressure gradients. There was no angiographic evidence of distal embolization. CONCLUSION: Primary stent placement for chronic iliac artery occlusions without prior thrombolysis or angioplasty appears to be safe and efficacious and is potentially cost effective.

In vitro metal fatigue testing of inferior vena cava filters.

RATIONALE AND OBJECTIVES: Inferior vena cava filter fractures have been described in vivo on several occasions. No studies have compared the fatigue life of the different filter types. Four different, frequently used filters (Vena-Tech filters [VTF], stainless-steel Greenfield filters [SSGF], Simon nitinol filters [SNF], and titanium Greenfield filters [TGF]) were, therefore, tested with regard to fatigue life. METHODS: Ten filters of each type were tested by compressing the filter legs repeatedly. A travel distance of 1.5 cm was used, setting minimal and maximal filter leg separations of 1.0 cm and 2.5 cm, respectively. The endpoint was filter fracture or 10,000,000 compressions. The test was then repeated on five of the filters from each group, but on a different filter leg pair. RESULTS: Seven of 10 VTFs fractured during the first part of the study, and all five VTFs fractured during the second part of the study. One SSGF fractured in each part of the study. None of the SNFs or the TGFs fractured. Significant difference in fracture frequency was found. CONCLUSION: The VTFs appear to have the shortest fatigue life. The TGF and the SNF have a fatigue life exceeding the test limits. The consequences of filter fracture are unknown.

Mechanical thrombectomy with the Amplatz device: human experience.

PURPOSE: The authors present their early experience of mechanical arterial and graft thrombectomy with the Amplatz thrombectomy device. PATIENTS AND METHODS: Preliminary data are presented for 14 patients treated with the Amplatz thrombectomy catheter. The procedure was carried out in 10 arterial polytetrafluorethylene grafts, in two native arteries, and in two patients with venous thrombosis. RESULTS: The thrombectomy catheter completely removed the clot in 11 patients and partially removed clot in three patients. Mean thrombectomy time was 2 minutes 45 seconds. Despite distal blood pressure cuff occlusion, two instances of insignificant distal embolization occurred. Mechanical clot dissolution has consistently produced hemolysis without adverse clinical effects. The underlying causative factors such as stenoses were treated by means of angioplasty, atherectomy, or surgical endarterectomy. CONCLUSION: Mechanical thrombectomy with this device is a new, effective technique and can rapidly remove the thrombus. From preliminary results, the device seems most promising in clearing out thrombi in occluded synthetic femoral-to-popliteal bypass grafts. The device could have wider application if it were steerable and if it could be introduced from the contralateral approach.

Relation between changes in severity of coronary artery stenosis and anginal patterns.

Although myocardial ischemia causes angina pectoris, angina and the severity of coronary artery stenosis in individuals do not correlate. However, changes in anginal status over time correlated with changes in the severity of coronary artery stenosis as determined by repeated coronary arteriograms has not been previously studied. Coronary arteriograms, done both at entry into the Program on the Surgical Control of the Hyperlipidemias (POSCH) and 3 years later, were blindly graded for changes in overall severity of coronary artery stenosis according to protocol by the POSCH Arteriography Review Committee. Arteriographic and clinical data from 376 control subjects (347 men, 29 women) were analyzed. There was no statistically significant relation over a long-term (3 year) period between the absence, presence, development, or disappearance of angina pectoris and changes in coronary artery stenosis severity as determined by coronary arteriography.