Experimental evaluation of a modified Amplatzer duct occluder.

The purpose of this study was to evaluate a new device specifically designed for patent ductus arteriosus (PDA) occlusion based on PDA anatomy. Percutaneous closure of aortopulmonary shunts was attempted in 10 dogs. Shunts were surgically created in the location and orientation of PDA. The occlusion prosthesis consisted of a cylindrical frame filled with polyester and a 32 degree angled retention disk. The delivery system of the device included a 6 Fr thin-walled Teflon introducing sheath, an antirotating delivery catheter, and cable. Complete occlusion of the shunt was obtained in nine animals. One animal died before device placement. Temporary hemolysis occurred in one dog after device placement. The disk of device was completely covered by smooth glistening neoendothelium at 1-3 months postmortem examination. None of the devices protruded into the lumen of the aorta. The device is an improvement over the standard Amplatzer duct occluder. The angled retention disk lies flatly against the aortic wall, avoiding turbulence or an aortic pressure gradient.

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.

Transcatheter closure of membranous ventricular septal defects with a new nitinol prosthesis in a natural swine model.

Transcatheter closure of a membranous ventricular septal defect (MVSD) is much more difficult than closure of other intracardiac defects because of the proximity to the aortic and tricuspid valves and their relatively large size in small children. In this report, transcatheter closure of naturally occurring membranous VSDs was attempted in 12 Yucatan minipigs. The prosthesis is constructed from fine Nitinol wires in the shape of two buttons and a connecting waist filled with polyester fiber. Two kinds of prosthesis were used in this study: concentric and eccentric left-sided retention disks. A 6 or 7 Fr delivery sheath was advanced across the membranous VSD over a wire from femoral vein. The prosthesis was inserted through the sheath by pushing the delivery cable to deploy a button into left ventricle and the second button was then deployed into right ventricle by withdrawing the sheath. Successful implantation of the device was achieved in all animals except one. Complete closure rate was 58.3% immediately after placement, 100% at 1 week, 90.9% at 1 month and 3 months, and 100% at 6 months. An associated aneurysm of the membranous septum increased significantly in size in two of three animals using the concentric device, and in none of the animals using the eccentric device. A trace to mild aortic regurgitation was present in two of the three animals using the concentric device, and only in one of the eight animals using the eccentric device. Five animals developed a trace to mild tricuspid regurgitation. Pathologic examination showed all devices to be covered by smooth neoendothelium at 3 months. This report presents the first experimental study where closure of membranous ventricular septal defects in a swine model was attempted by specially constructed devices. Procedural success and occlusion rates are very encouraging but overall results cannot equal surgery. Further experimentation is needed with devices that are redesigned according to the experience gained from this study.

Tracheobronchial metal stents: effects of covering a bronchial ostium in pigs.

RATIONALE AND OBJECTIVES: The purpose of this study was to examine the effects of placing a metal stent across a bronchial orifice. MATERIALS AND METHODS: Nine pigs were used as test subjects, because the right upper lobe bronchus comes directly off the trachea in these animals. One of three types of metal stents was placed into the trachea of each pig and covered the orifice of the right upper lobe bronchus. Follow-up studies were performed at 1 and 3 months to evaluate the right upper lobe for signs of bronchial obstruction, infection, and atelectasis. The animals were sacrificed at 3 months to study the histopathologic changes of the trachea and lungs. RESULTS: Two upper lobe bronchi remained patent; seven were obstructed by granulation tissue or plugs of mucus and inflammatory cells. Right upper lobe infiltration and atelectasis were seen in eight animals. Interestingly, radiographic opacities were also common in other lung segments. There was a tendency toward fewer and less extensive lung opacities at 3 months compared with that at 1 month. At histopathologic examination, areas of both acute and chronic pneumonia were found in the right upper lobe of all animals. The segment of trachea covered by the stent was lined with a thin layer of granulation tissue containing neutrophils, monocytes, and lymphocytes. The stent luminal surface was covered with columnar, cuboidal, and stratified squamous epithelium. Tracheal stenosis was seen in three animals because of excessive granulation tissue in two and a collapsed stent in one. CONCLUSION: Placement of metal stents in pig trachea covering the orifice of the right upper lobe bronchus resulted in retention of secretions and secondary infection in the right upper lobe and other distant lung segments.

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.

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.

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.

Urokinase-mediated thrombolysis: a dose-response relationship in cats. Work in progress.

A cat model was developed to study thrombolytic agents. The infrarenal aorta was surgically exposed, all side branches were ligated, and both ends of the segment were occluded. After preformed clot was injected into the segment, proximal flow was restored and a distal stenosis was created. Urokinase was infused at rates varying from 4,000 to 250,000 U/h. Amount of remaining clot was quantified every 15 minutes with cine angiography. Pre- and postinfusion measurements of prothrombin time, partial thromboplastin time, thrombin time, and levels of fibrinogen and fibrin degradation products were obtained. A graph of thrombolysis rate versus infusion rate was obtained yielding maximal thrombolytic activity at 126,000 U/h and 90% of maximal activity at an infusion rate of 70,000 U/h. Levels of fibrin degradation products did not change. Prothrombin, partial thromboplastin, and thrombin times increased with increasing infusion rates, leveling off at 100,000 U/h, while fibrinogen levels decreased, with a plateau at 50,000 U/h.

Nonselective and semiselective catheters for renal artery evaluation: experimental study.

Abdominal aortography is widely used for evaluation of potential renal donors and for patients with renal failure or hypertension in whom a renal artery ostial or polar branch stenosis is suspected. It would be desirable to use a catheter that consistently enables good bilateral renal artery and polar branch visualization without opacification of overlying mesenteric vessels. Existing and newly designed catheters were compared to determine the optimal design necessary for these studies. An in vitro model of the abdominal aorta and its branches was made, and dye dilution densitometry was employed for quantitative evaluation. Semiselective catheters demonstrated significantly increased renal artery opacification with decreased mesenteric opacification in this in vitro model.

Thrombogenicity of hydrophilically coated guide wires and catheters.

The thrombogenicities of stainless steel spring guide wires and two hydrophilically coated guide wires were compared. The guide wires were placed in canine femoral arteries for 30 minutes. The guide wires were removed, the thrombi were stripped off, and the clots were weighed. Clot weights obtained with the two hydrophilically coated guide wires were significantly less than those obtained with the stainless steel spring guide wires. The thrombogenicities of hydrophilically coated catheters and noncoated nylon catheters were compared with and without the use of heparin. Carotid arteries, jugular veins, femoral arteries, and femoral veins were used. Catheters were left in place for 45 minutes. The animals were heparinized and killed. The vessels were then removed en bloc with the catheter clamped in place. The vessels were incised, and the clot was removed and weighed. In arterial and venous catheterization, no significant difference in clot deposition was shown between the hydrophilically coated catheters and the noncoated nylon catheters. A striking reduction of thrombogenicity was achieved with heparinization of the catheters in both arteries and veins.

Retrograde left atrial catheterization.

Catheterization of the left atrium can provide valuable information about both congenital and acquired heart disease. The traditional approach to examination of the left atrium has been the transseptal route, which has occasionally been associated with serious complications. A method of retrograde left atrial catheterization has been developed that is performed with a modified standard catheter. The technique was tested in five dogs and was easy and safe to perform.

Prostatic urethra: experimental dilation in dogs.

An animal study was undertaken to develop a balloon dilation technique that could be used in humans to treat the common ailment of benign prostatic hypertrophy. Dogs were used as a model because of the similarities in the prostate between the two species and the ready availability of the canines. A retrograde transurethral approach was used for dilation. Balloon catheters, 8-20 mm in diameter, were used. Significant, long-lasting dilatation of the prostatic urethra was not accomplished until 20-mm balloons (or two 10-mm ones) inflated for 10 minutes were used. The animals were followed for up to 14 months. No deleterious histologic effects of dilation were identified within the urethra or prostate that could lead to stenosis of the prostatic urethra in later stages.