Preclinical evaluation of a rheolytic catheter for percutaneous coronary artery/saphenous vein graft thrombectomy

The presence of thrombus increases the rate of acute complications and restenosis in percutaneous revascularization of native coronary arteries and saphenous vein grafts. Rheolytic thrombectomy uses high velocity saline jets to create a Bernoulli effect for thrombus entrainment, dissociation, and evacuation of debris, providing a novel approach to the treatment of thrombotic lesions. The study objective was to determine the preclinical safety and effectiveness of a 5 French rheolytic thrombectomy catheter designed for use in coronary arteries and saphenous vein grafts. In vitro testing was performed to evaluate catheter effectiveness (clot removal rate) and safety (particle generation and hemolysis). This was followed by acute (n = 6) and chronic (n = 6) canine studies to determine hemodynamic, angiographic, and histopathologic effects of the catheter. The results showed effective clot removal with minimal embolization: 99.4% of the total clot volume was removed with only 0.1% proximal embolization and 0.5% distal embolization. 98.4% of the embolic particles were less than 10 microm. Canine studies revealed no significant angiographic, hemodynamic, histopathologic, or electrocardiographic abnormalities with the exception of transient heart block in one animal. There was transient hemolysis which normalized within 24 hours with no adverse effects. These results demonstrate the effectiveness and safety of coronary rheolytic thrombectomy and provided the basis for clinical trials to further evaluate this promising new approach for coronary thrombectomy.

Rheolytic thrombectomy with use of the AngioJet-F105 catheter: preclinical evaluation of safety

PURPOSE

A preclinical evaluation of the safety of the AngioJet-F105 rheolytic thrombectomy catheter.

MATERIALS AND METHODS

The AngioJet-F105 catheter uses multiple retrograde high-speed fluid jets impinging on a primary aspiration lumen to create a hydrodynamic recirculation vortex that traps and fragments adjacent thrombus, with simultaneous evacuation of the resulting debris through the aspiration lumen. The effect of the AngioJet on treated vessels was evaluated in 10 canines. Vascular integrity on histopathologic examination and endothelial coverage on scanning electron microscopic study were examined in 15 vessel segments treated with the AngioJet-F105 catheter, compared with four vessel segments subjected to the Fogarty balloon maneuver, and 10 untreated vessel segments. The size distribution of particulate debris, upstream and downstream, after thrombectomy was determined in a flow-circuit model simulating the superficial femoral artery. Aliquots from the downstream effluent were then injected into the renal arteries of two healthy canines.

RESULTS

The device caused only minimal focal endothelial denudation and no significant deep injury. No significant difference in endothelial coverage occurred in AngioJet-treated vessel segments compared to untreated control vessels (mean +/- standard deviation: 88.0% +/- 7.9% vs 89.7% +/- 11.6%, P = .77). Vessels treated with the Fogarty balloon pullback maneuver had significantly less residual endothelial coverage (58.0% +/- 8.0%, P < .03). Particulate microemboli in the effluent of the flow model accounted for 12% of the initial thrombus volume (0% > 100 microm, 99.83% < or = 10 microm). Histopathologic evaluation of the four renal beds injected with the resulting debris demonstrated no signs of necrosis. A moderate transient increase in plasma-free hemoglobin occurred, with a mild corresponding decrease in hematocrit.

CONCLUSIONS

The AngioJet-F105 catheter resulted in only mild and focal injury to the treated vessels. The vast majority of resulting particulate debris consist of microscopic particles, without significant ischemic effect.

A spun elastomeric graft for dialysis access

A new composite vascular graft was developed using electrostatic spinning technology. The graft is primarily microfibrous polydimethylsiloxane spun onto a mandrel; a small diameter polyester yarn provides additional strength while minimizing wall thickness, and a helical bead provides crush and kink resistance. Eighteen grafts were implanted in a mongrel canine arteriovenous shunt model for 12 months. The grafts were implanted in femoral artery to femoral vein loops and were cannulated using three pairs of 16 gauge dialysis needles per week. Grafts were evaluated during each puncture session, and also followed using angiography. Histologic study of explanted grafts, regional lymph nodes, and lungs was performed. The grafts provided excellent handling and puncture characteristics, with no bleeding through the graft wall at puncture sites. Cumulative patency of these punctured grafts was 88% at 6 months and 80% at 1 year. Histologic study showed external fibroconnective tissue encapsulation of the grafts, with tissue growth through the interstices of the graft consisting of a microvascular network surrounded predominantly by histiocytes, many multinucleated foreign body giant cells, with some fibroblasts and collagen formation also present. Little luminal thrombus was seen at puncture sites in the patent grafts, and there was no evidence of pulmonary thromboemboli. This new elastomeric graft shows excellent promise for dialysis access; similar grafts under development may also find application for small diameter peripheral vascular reconstruction.

Rheolytic catheter for percutaneous removal of thrombus

The authors present a percutaneous thrombectomy system (rheolytic thrombectomy catheter [RTC]) in which high-velocity jets of saline solution are used to lyse and remove thrombus. The catheters (4-6 F) direct a 10,000-15,000-psi (0.7-1.05 x 10(5)-kPa) jet of saline solution onto an exhaust port from orifices at the end of the catheter. The jet entrains clot and resulting fragments and brings them into the high-velocity region for lysis and removal. Whole blood clots (10-15 cm) placed in 6-9-mm-diameter tubing were completely dissolved and removed with the RTC in less than 1 minute. In vivo use in a canine model resulted in lysis and removal of clots from a femoral artery, without vessel damage. The small caliber, flexibility, and effective lysis of this system suggest its potential usefulness in large central vessels that are difficult to access surgically and in small-diameter vessels that require more rapid removal of thrombus than can be achieved with thrombolytic therapy.

A rheolytic system for percutaneous coronary and peripheral plaque removal

A method for plaque dissolution has been identified that percutaneously delivers a pulsatile high-velocity stream of saline to the site of an atheromatous lesion within a coronary or peripheral artery. In vitro evaluation and in vivo canine and porcine testing were performed using this 'rheolytic' system to determine its feasibility in ablating calcified plaque and soft thrombotic tissue. A prototype rheolytic guidewire capable of providing 30,000 psi of internal pressure was designed to fit within the guidewire lumen of a standard percutaneous transluminal coronary angioplasty catheter. An additional over-the-wire rheolytic catheter was fabricated to follow a standard .014-inch guidewire. The rheolytic devices were tested in vitro with simulated atheromatous and thrombotic lesions to evaluate the size and quantity of the particulate effluent. The particulate was then sterilized, mixed with saline, and introduced percutaneously into the animal kidney and heart for evaluation. The in vitro studies demonstrated that the rheolytic catheter and guidewire were able to follow both a coronary and femoral arterial model and successfully ablate the simulated lesions. The particle size for osseous, muscular, and cartilagenous tissue ranged from 2 to 6 micrometers; for fresh human plaque the particles ranged from 2 to 15 micrometers. Injection of cartilagenous and plaque particles into the animal model caused very slight regions of necrosis but no clinical sequelae. Applications of the rheolytic devices to the animal femoral artery demonstrated that both devices could ablate and cross calified or soft thrombosed lesions without damage to the vessel wall; the rheolytic catheter provided a debulking of the plaque.(ABSTRACT TRUNCATED AT 250 WORDS)

Venturi grafts for hemodialysis access

Vascular access grafts can produce venous and puncture site stenosis, and excessive shunted flow. A vascular access graft that controls the shunted flow at 500-650 ml/min by venturi flow resistance, and offers the potential for reduced venous stenosis, is presented. Twelve venturi grafts consisting of 6 mm ePTFE, with a thermally formed venturi resistance, were implanted in a canine femoral arterio-venous (A-V) model and cannulated for simulated dialysis for periods up to 6 months. Pressures, bleeding times, and puncture site healing were compared at sites upstream and downstream of the venturi. Nine 6 mm ePTFE grafts were implanted as controls. Venturi and control graft patency rates were similar: 90% for venturi grafts and 89% for control implants at 4 months. Measurements verified pressure dissipation by the venturi from 85 to 15 mmHg, delivering near-normal pressures to the vein; downstream pressures were 22 mmHg higher in controls. Sites downstream of the venturi did not bleed at 4 min, whereas bleeding was often noted after 9 min at other sites. Puncture sites upstream of the venturi had less stenosis and less mural thrombus than sites downstream of the venturi, and compared favorably with puncture sites in the control grafts. This improved healing and low pressure delivery to the vein may offer clinical advantages.

A unique vascular graft concept for coronary and peripheral applications

Synthetic vascular grafts for coronary bypass (3-4 mm inner diameter [ID], 40-100 ml/min) continue to fail despite success in high flow peripheral applications. A unique method is presented that uses a fluid dynamic approach to improve patency. A large diameter graft (5-6 mm ID) is used with an arteriovenous (AV) shunt to create a high flow rate (350-650 ml/min); a Venturi flow resistance controls the AV shunt and provides high pressure to the coronary arteries. The resulting graft can supply as many coronary arteries as required by means of side to side anastomoses upstream from the Venturi resistance. The concept was studied in a mock circulation system to analyze fluid dynamics under pulsatile flow. Mathematical models were used to study laminar and turbulent shear stresses and flow distributions over the physiologic range of Reynolds numbers. In vitro testing demonstrated little bovine red blood cell (RBC) hemolysis (0.249 mg Hb/min) compared with other devices. In vivo testing in sheep showed no significant acute changes in pulse rate or blood pressure in response to the shunt. The fluid and mathematical modeling of this concept has additional application in the study of flow past stenoses.