Robert F. LeVeen

Thrombolytic enhancement with perfluorocarbon-exposed sonicated dextrose albumin microbubbles.

Whereas low-intensity, high-frequency ultrasound (US) alone appears to cause minimal thrombolysis, US combined with air-filled microbubbles does increase the amount of urokinase (UK)-mediated clot lysis (CL). Because this phenomenon may be mediated by cavitation-induced streaming, we hypothesized that perfluorocarbon-exposed sonicated dextrose albumin (PESDA) microbubbles, which are more stable than air-filled microbubbles, may also enhance US-induced thrombolysis. We measured the percentage CL of equally sized thrombi (1.0 +/- 0.1 mg) made from freshly drawn blood incubated for 2 hours and then exposed to 20 kHz US (0.846 MPa peak negative pressure). The thrombi were bathed in 4 ml of saline solution, UK alone (20,000 U), PESDA alone, or a combination of PESDA with UK. The percentage CL achieved with PESDA and therapeutic US was also compared with the percentage CL achieved with room air-filled sonicated dextrose albumin (RASDA) microbubbles. When compared with US alone (24% +/- 13% CL) or UK alone (17% +/- 3% CL), PESDA plus US produced significantly better CL (43% +/- 17%; p< 0.05). PESDA combined with US also produced significantly greater CL than RASDA combined with US (28% +/- 9%; p < 0.05). The optimal CL was achieved with a combination of PESDA with UK with US (60% +/- 14% CL). We conclude that PESDA microbubbles alone may be capable of inducing thrombolysis when insonified with a low-frequency transducer.

Laparoscopic and percutaneous radiofrequency ablation of the kidney: Acute and chronic porcine study

OBJECTIVES The chronic effects of renal radiofrequency ablation are unknown. Herein, we investigate the anatomic and physiologic sequelae of laparoscopic and percutaneous renal radiofrequency ablation in acute and chronic porcine models. METHODS Our study comprised two phases-an acute phase and a chronic phase. In the acute phase, bilateral laparoscopic renal radiofrequency ablation was performed in 6 animals (12 renal units), which were euthanized immediately after surgery. In the chronic study, bilateral percutaneous renal radiofrequency ablation was performed in 5 animals (10 renal units). One animal each was euthanized at postoperative day 3, 7, 14, 30, and 90. RESULTS Ultrasound-monitored laparoscopic (n = 12) and percutaneous (n = 10) radiofrequency ablations of the lower pole of the kidney were technically successful in each instance. No intraoperative complications occurred. In the survival experiments, the radiolesions showed gradual spontaneous resorption and ultimate renal autoamputation, while maintaining pelvocalyceal integrity as confirmed by ex vivo retrograde ureteropyelogram. Serum creatinine and hematocrit remained stable in all survival animals. Postoperative complication occurred in 1 chronic animal with nonobstructive small bowel dilation at autopsy. CONCLUSIONS Laparoscopic and percutaneous renal radiofrequency ablation are technically feasible. The anatomic and physiologic sequelae of renal radiosurgery are favorable. Improved techniques of real-time monitoring of the evolving renal radiolesion are necessary.

Shear Stress in the Performance of Esophageal Dilation: Comparison of Balloon Dilation and Bougienage

While both the balloon catheter and the bougie are effective for esophageal dilation, each has its proponents. From a biomechanical point of view, the two methods should differ significantly, since bougienage depends on advancing a tapered dilator to generate radial force and balloon catheter dilation depends solely on balloon inflation to generate its radial dilating force. In a series of equivalent esophageal stenoses made by suture plication in swine esophageal segments, the authors measured shear force and radial force generated by dilation with a Maloney bougie, a Savary-Gilliard bougie, and an esophageal balloon. The mean radial forces generated were 6.42, 4.46, and 4.04 N, respectively, which did not differ significantly. However, the mean shear forces measured were 16.92, 6.92, and 1.44 N, respectively. The shear force with the Maloney bougie differed significantly from that with the Savary-Gilliard and the balloon and was on the same order of magnitude as the tensile strength of the esophagus (25-27 N). The shear force with the balloon was significantly lower than that with either bougie. In theory, the reduced shear force associated with balloon dilation might reduce the risk of esophageal perforation, but safety will have to be determined in clinical trials.

Relative Ultrasonographic Echogenicity of Standard, Dimpled, and Polymeric-coated Needles

PURPOSE To use quantitative ultrasonographic measurements to compare the effect of a polymeric coating designed to increase needle echogenicity to commercially available needles. MATERIALS AND METHODS Commercially available standard smooth and dimpled echogenic tip 21-gauge needles established reference levels of echogenicity in gelatin-based and turkey breast phantoms. Examples of both types of needles were coated with a thin polymeric film that utilizes entrapped microbubbles of air on its surface to increase echogenicity. Samples of each type in both coated and noncoated versions were placed in phantoms in matched positions and imaged with clinical ultrasound machines. Similar numbers of each category were evaluated at various angles of insonation for a total of 109 images. Similar numbers of each category were imaged at 5-minute intervals for up to 38 minutes for a total of 226 images. Images were recorded, digitized, and evaluated for relative echo strength in arbitrary echogenic brightness units. RESULTS Coating increased peak echogenicity over the entire needle to a level that closely approximates the peak echogenicity of dimpled needle tips (means: dimpled = 834, coated smooth = 803, coated dimpled = 823; P = .54). Smooth is lower than this group at 468 (P = .0001). Representative area echogenicity increased with coating or dimpling (smooth = 377 vs coated smooth = 778, coated dimpled = 690, dimpled = 775; P = .0001). Coating increased peak values 74% and area values 95% compared to smooth. Decreased angles of insonation moderately reduced echogenicity on coated smooth, coated dimpled, and dimpled, while it decreased to below good visibility threshold on standard smooth needles. The echogenicity of the coated needles fades in saline with time (1%/min). CONCLUSION Objective measurements show that this coating significantly increases echogenicity of entire needles to match that obtained with a dimpled tip.

New Rabbit Atherosclerosis Model for the Investigation of Transluminal Angioplasty

In order to investigate the long-term and short-term effects of transluminal angioplasty, an animal model was developed that closely simulates human disease. Using the Flemish Giant rabbit, lesions were created by air-drying an isolated segment of femoral artery and feeding the rabbits a diet of 2% cholesterol, 6% peanut oil for one month. The lesions were studied with serial angiography for up to three months and with correlative histology. The results showed focal, stenotic lesions that appeared stable over time and had histologic similarity to human lesions. the artery adjacent to the lesions appeared normal. Since the femoral arteries in this rabbit strain are sufficiently large to undergo angioplasty, and it is possible to perform serial angiograms, it is believed that this model is suitable for use in the investigation of angioplasty, and the preliminary work confirms its feasibility.

ULTRASOUND-ASSISTED THROMBOLYSIS

RATIONALE AND OBJECTIVES.Current use of thrombolytic agents to lyse thrombus, though safe, is complicated by stroke, bleeding, and clot embolization. Therapy may be protracted, resulting in further ischemia and possible tissue loss. Peripheral arterial and graft occlusions often require several hours of thrombolytic therapy, which may occasionally exceed 48 hours and may also require expensive intensive care monitoring. It is desirable to accelerate clot lysis and to thereby reduce the risks and costs associated with the procedure and minimize morbidity. In this article, the authors propose the use of intravascular ultrasound in conjunction with thrombolytic agents to increase the rate of thrombolysis. METHODS AND RESULTS.In-vitro thrombolysis of fresh human blood clots was studied with and without urokinase by using continuous wave, 20-KHz ultrasound at the power levels 1-2 watts. Loss in weight of each clot was used to measure the extent of thrombolysis. Clot lysis was observed when ultrasound and thrombolytic agents were used alone. At modest power levels of 1.0 to 1.5 watts of ultrasonic energy a significant increase in lysis was observed in conjunction with 5,000 units of urokinase. CONCLUSIONS.In the short treatment duration of this invitro study, 5,000 units of urokinase combined with 20-KHz ultrasound energy at 1.0 and 1.5 watts was associated with a greater percentage thrombolysis by weight than either urokinase or ultrasound alone.

Permanent percutaneous antegrade ureteral stent placement without transurethral assistance

A simple, one-step, permanent, percutaneous, antegrade insertion of a ureteral stent is described, utilizing a double, pigtail catheter. No transurethral assistance is necessary. The advantages of this simplified technique are presented, and the necessary prerequisites for its application are discussed.

Complications and Technical Limitations of Hepatic Arterial Infusion Catheter Placement for Chemotherapy

PURPOSE To determine the rate of complications associated with hepatic arterial infusion (HAI) catheter placement, as well as technical success related to liver perfusion. MATERIALS AND METHODS The authors reviewed 44 patients who underwent 106 HAI catheter placements, including 15 men and 29 women with an average age of 55 years (range, 32-82 years). One to nine placements were performed per patient with 61 (58%) via the left brachial artery, 40 (38%) via the right femoral artery, and five (4%) via the left femoral artery. Chemoinfusion lasted 4 days, with initial catheter placement assessed on technetium-99m macroaggregated albumin (MAA) perfusion scans, as well as daily abdominal radiographs. RESULTS One hundred attempted hepatic arterial catheter placements were completed. Liver perfusion was global in 66 (66%) cases, in the right lobe only in 28 (28%) cases, and in the left lobe only in six (6%) cases. Eight (8%) had gastrointestinal (GI) tract perfusion; this was eliminated in seven cases (7%) after catheter repositioning. Forty-six (43%) placement attempts required embolization of 62 GI vessels to preclude GI chemoinfusion. Complications included one cerebrovascular accident (related to removal of a left brachial catheter), eight brachial artery thromboses (four that required emergent thrombectomy), six hepatic arterial dissections, four hepatic arterial thromboses, and four catheter malfunctions. CONCLUSIONS HAI catheter placement via the left brachial artery has increased complications. Nearly one-half of placements required embolization of GI vessels to preclude GI perfusion. Global perfusion is possible in two-thirds of cases.

Restenosis and successful angioplasty: histologic-radiologic correlation.

Histologic analysis was undertaken on 24 perfusion-fixed arteries from New Zealand White rabbits that had undergone percutaneous transluminal angioplasty (PTA) of a focal arteriosclerotic lesion in the femoral artery 1 month earlier. Experiments representative of occlusion, restenosis (greater than or equal to 50% stenosis), a good result (less than 50% stenosis), or aneurysm (as defined angiographically) were randomly selected for histologic analysis. Histologic findings were compared with those in untreated control lesions in the contralateral femoral artery. All good results (n = 11) but only four of seven restenoses had histologic evidence of a tear into the tunica media or the tunica adventitia (P = .017). Cases of tears to the adventitia were more likely to have a good result. New myointimal proliferation was more severe with restenosis (P less than .05). Occlusions and aneurysms appeared to be more severe expressions of the histologic findings observed in restenoses and good results, respectively. An arterial tear is necessary but not sufficient to obtain a good result after PTA; outcome is ultimately dependent on the degree of intimal hyperplasia.

Effects of angioplasty balloon inflation time on arterial contractions and mechanics.

The purpose of this study was to characterize and compare the immediate effects of short and long angioplasty inflation times on arterial contractions and passive mechanics and thereby determine if there is a potential advantage obtained by increasing the duration of balloon inflation. In each of 10 nonatherosclerotic New Zealand rabbits, one external iliac artery was dilated for 20 seconds, and the contralateral artery was dilated for 2 minutes. Although angioplasty stretched the arteries 27% and 30% for the short and long dilations respectively, the pre- and post-angioplasty arteriographic diameters were not different. Both short and long dilations had equal effects on passive biomechanics: circumferential wall stress was increased (P less than .01); wall thickness was decreased (P less than .01); the incremental elastic modulus was increased (P less than .01). In vitro studies of arterial rings demonstrated that maximal active contractile force in response to KCl (70 mM) was significantly (P less than .05) less for dilated arteries than for undilated arteries. More importantly, maximal active force after the 2-minute dilations was significantly (P less than .05) less than after the 20-second dilations. These results suggest that, when dilating normal arteries, increasing angioplasty balloon inflation time from 20 seconds to 2 minutes offers no mechanical advantage but produces more smooth muscle cell dysfunction, which may reduce vasospasm and restenosis after angioplasty.Consigny PM, LeVeen RF. Effects of angioplasty balloon inflation time on arterial contractions and mechanics. Invest Radiol 1988;23:271–276. The purpose of this study was to characterize and compare the immediate effects of short and long angioplasty inflation times on arterial contractions and passive mechanics and thereby determine if there is a potential advantage obtained by increasing the duration of balloon inflation. In each of 10 nonatherosclerotic New Zealand rabbits, one external iliac artery was dilated for 20 seconds, and the contralateral artery was dilated for 2 minutes. Although angioplasty stretched the arteries 27% and 30% for the short and long dilations respectively, the pre- and post-angioplasty arteriographic diameters were not different. Both short and long dilations had equal effects on passive biomechanics: circumferential wall stress was increased (P < .01); wall thickness was decreased (P < .01); the incremental elastic modulus was increased (P < .01). In vitro studies of arterial rings demonstrated that maximal active contractile force in response to KCl (70 mM) was significantly (P < .05) less for dilated arteries than for undilated arteries. More importantly, maximal active force after the 2-minute dilations was significantly (P < .05) less than after the 20-second dilations. These results suggest that, when dilating normal arteries, increasing angioplasty balloon inflation time from 20 seconds to 2 minutes offers no mechanical advantage but produces more smooth muscle cell dysfunction, which may reduce vasospasm and restenosis after angioplasty.