Ann Thorac Surg 2004;77:243-246
© 2004 The Society of Thoracic Surgeons
Original article: cardiovascular
An experimental study of surgical ultrasonic angioplasty: its effect on atherosclerosis and normal arteries
Masahide Chikada, MDa*
a Division of Cardiovascular Surgery, National Center for Child Health and Development, Tokyo, Japan
Accepted for publication July 1, 2003.
* Address reprint requests to Dr Chikada, Division of Cardiovascular Surgery, National Center for Child Health and Development, 2-10-1 Ookura, Setagaya-ku, Tokyo 157-8535, Japan
e-mail: chikada-m{at}ncchd.go.jp
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Abstract
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BACKGROUND: We have developed a new hand-held probe for surgically open ultrasonic angioplasty. Two experimental studies were conducted to determine the optimal power range for carrying out ultrasonic angioplasty.
METHODS: The probe measured 2.5 mm in diameter and 5 cm in length. The amplitude was 210 µm at 100% power. One of the studies was designed to determine the power range that is effective for removal of atherosclerotic lesions. Human cadaveric arteries were used in the study. The other study was designed to investigate the long-term adverse effect on normal arteries. Canine arteries were used in this study.
RESULTS: In the study using cadaveric arteries, the amplitude ranging from 90 to 110 µm was effective for soft atheroma, the range from 110 to 130 µm was effective for mild arteriosclerosis, and 150 µm was effective for calcified lesions. The other study of the long-term effect on canine normal arteries indicated that each incidence of stenosis and occlusion was 0% at amplitude ranging from 90 to 110 µm, 13% at 130 µm, and 25% at 150 µm.
CONCLUSIONS: The surgically open ultrasonic angioplasty with a new hand-held probe was effective for various kinds of atherosclerotic lesions, whereas the angioplasty at high amplitude had a problem with the long-term effect on normal arteries.
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Introduction
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Ultrasonic aspiration devices have recently been developed and applied in many fields. The application of these devices to angioplasty was first performed by Trubestein and associates [1]. Since then, Rosenschein and associates [2] and Siegel and associates [3] have applied ultrasound to angioplasty for arteriosclerosis. We have developed a new hand-held probe. The probe was developed for surgically open use, not for transluminal use. We performed two experimental studies to determine the optimal power range for carrying out ultrasonic surgically open angioplasty using the new probe.
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Material and methods
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The ultrasonic generator used in this study was Sumisonic ME2210 (Sumitomo Bakelite Co, Ltd, Tokyo, Japan). The new probe measured 2.5 mm in diameter and 5 cm in length. This probe was hollow and was made of titanium. The ultrasonic frequency of the body was 24 KHz. The ultrasonic power varied from 40% to 100%, and the power at 100% was 100 W. The amplitude of the probe tip was proportional to the amount of ultrasonic power. The amplitude was 210 µm at 100% power and 90 µm at 40% power. Atherosclerotic and calcified lesions were disrupted with the tip of probe, and the debris was aspirated through the hollow of the probe during angioplasty. Thin silicon rubber 3.3 mm in diameter covered the probe for water irrigation. During the procedure, a 500-mL bag of normal saline water at 4°C was used as the irrigation fluid to avoid overheating of the probe and to help aspiration of the debris. The rate of water irrigation was 10 to 20 ml/min.
The effect of ultrasonic angioplasty on atherosclerosis
We used human cadaveric common iliac arteries for this study. Atherosclerotic common iliac arteries were obtained from 5 adult cadavers aged 57 to 91 years (mean age, 75 years). The effect of different amplitude setting on various kinds of atherosclerotic lesions was investigated. The effect was thought to vary with atherosclerotic lesions. Atherosclerotic lesions of the human cadaveric arteries were divided into three groups (soft atheroma, mild arteriosclerosis, and calcified lesion). Ten specimens of each lesion, cut 8 cm in length, were used. The probe was inserted into each cadaveric artery and angioplasty was performed on the lumen for 30 seconds. Five different amplitudes (90, 110, 130, 150, and 170 µm) were employed. After the angioplasty, cadaveric arteries were fixed in 2.0% formaldehyde and 0.2% glutaraldehyde. Then, the cadaveric arteries were treated with Elastica Van Gieson's staining. The arteries were cut longitudinally. Twenty sections were investigated at each amplitude under light microscopic observation (Fig 1).
The percentage depths of atherosclerotic lesions removed were investigated by microscopic findings. The removal percentages were based on division of the maximum removal depth by the depth of atherosclerotic lesion in each section. Two examiners, who were not informed of the amplitudes used, measured the removal percentages. The optimal power range for each lesion was revealed to show a higher removal percentage (> 50%) and no perforation.
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Fig 1. The microscopic findings of ultrasonic angioplasty on the atherosclerotic lesions of human cadaveric arteries. Elastica van Gieson stain was used (original magnification, x40). (A) Ultrasonic angioplasty for soft atheroma. Angioplasty with an amplitude of 90 µm was performed (arrow). (B) Ultrasonic angioplasty for mild arteriosclerosis. Angioplasty with an amplitude of 130 µm was performed (arrow). (C) Ultrasonic angioplasty for calcified lesion. Angioplasty with an amplitude of 150 µm was performed (arrow).
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The adverse effect of ultrasonic angioplasty on normal arteries
During the procedure, the tip of the probe also contacted the normal portion of arteries. Another study was conducted to investigate the long-term adverse effect of ultrasonic angioplasty on normal arteries. Twelve dogs, weighing 12 to 17 kg (mean weight, 15 kg) were used for this study. After sedation with pentobarbital (20 mg/kg), the dogs were intubated and anesthetized with 1% to 2% isoflurane. Both carotid arteries and femoral arteries were isolated, and each artery was clamped proximally and distally. Then, the probe was inserted into an artery through a small transverse incision, and ultrasonic angioplasty was performed for 30 seconds at four different amplitudes (90, 110, 130, and 150 µm). The small incision of the artery was closed by using 7-0 polypropylene sutures. After ensuring adequate hemostasis, the wound was closed in layers. One week, 1 month, and 1 year after surgery, the arteries were removed under general anesthesia. Eight specimens were collected in each group. They were fixed and stained by the same method as that for atherosclerotic lesions, and observed microscopically. The incidence of stenosis or occlusion was determined. Neointimal hyperplasia of more than 25% of an intimal layer was considered to be stenotic.
The local committee on human and animal research approved the animal study protocols, which were performed according to the institutional guidelines.
Statistical analysis
All data are expressed as the means ± standard deviation. The removal percentages were compared by Student's t test. The 
2 test was used for analysis of long-term results from normal arteries. A value of p less than 0.01 was considered to be statistically significant.
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Results
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The effective power range for atherosclerotic lesions
Soft atheroma.
When the amplitude was 130 µm or above, a perforation occurred. The incidence of perforation was 10% at 130 µm, 50% at 150 µm, and 60% at 170 µm. The removal percentages were 58% ± 16% and 67% ± 13% at 90 and 110 µm, respectively (Fig 2).
These results suggested that amplitudes ranging from 90 to 110 µm were effective.
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Fig 2. The removal percentages of four different amplitudes in three kinds of athereosclerotic lesions of human cadaveric arteries. The amplitude of 170 µm had no data because it caused a perforation in every atherosclerotic lesion in humans. In mild arteriosclerosis, the removal percentages of 110 µm and 130 µm were significantly higher than those of 90 µm (*p < 0.01 versus other groups). The removal percentages of 150 µm were significantly higher than those of 90, 110, and 130 µm (**p < 0.01 versus other groups). Open bars = 90 µm; black bars = 110 µm; dark gray bars = 130 µm; light gray bar = 150 µm.
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Mild atherosclerosis.
The removal percentages for atherosclerotic lesions were 33% ± 13%, 58% ± 5%, and 61% ± 1% at 90, 110, and 130 µm, respectively (Fig 2). When the amplitude was 150 µm or above, the arteries were perforated. The incidence of perforation was 25% at 150 µm and 60% at 170 µm. An amplitude ranging from 110 to 130 µm was effective for mild arteriosclerosis.
Calcified lesion.
The removal percentages were 23% ± 9%, 31% ± 11%, 35% ± 8%, and 63% ± 12% at 90, 110, 130, and 150 µm, respectively (Fig 2). An amplitude of 150 µm was effective for calcified lesions. The incidence of perforation at 170 µm was 15%.
Long-term adverse effect on canine normal arteries
Incidence of stenosis and occlusion 1 week after surgery was 0% at 90 µm, 25% at 110 µm, 25% at 130 µm, and 38% at 150 µm. One month after surgery, the incidence was 0% at amplitudes ranging from 90 to 110 µm, 13% at 130 µm, and 25% at 150 µm. One year after surgery, the incidence was 0% at 90 to 110 µm, 13% at 130 µm, and 25% at 150 µm. No significant difference was found in any group. The microscopic findings showed no thermal injury or inflammatory response in the intima and media. The findings also showed that one of the main causes of restenosis was neointimal hyperplasia and that the arteries were occluded primarily by thrombus formation.
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Comment
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Ultrasonic aspiration devices have recently been applied to the cardiovascular surgery in several fields. The application of these devices to angioplasty is recognized as a new field. The first experimental application of ultrasonic energy to angioplasty was performed for removal of thrombus [1]. The frequency of the device was 26.5 KHz, and the probe was hollow, measuring 2 mm in diameter and 25 to 30 µm in amplitude. Aspiration and irrigation were available. It had low power, and it took 3 minutes to remove a thrombus with the probe.
Clinical study of ultrasonic angioplasty was first described in a paper by Rosenschein and associates in 1991 [2]. The probe they developed for surgical angioplasty was a wire 1.6 mm in diameter. It could neither aspirate nor irrigate with water. The frequency was 24 KHz and the amplitude of the probe ranged from 125 to 175 µm. The frequency and amplitude were similar to our probes. Their maximum power was 35 W, which was much less than ours (100 W). Intraoperative ultrasonic angioplasty was performed in totally occluded peripheral arteries. The average lumen patency of the treated arteries was 82.5% and the calcified lesion was an indication for the angioplasty. The problems with their procedure were debris embolism and thermal injuries. The long-term results remained unknown.
Clinical percutaneous ultrasonic coronary angioplasty was first reported by Siegel and associates in 1994 [3]. The probe was made of titanium and had a 1.7-mm ball tip. The frequency was 19.5 KHz and the amplitude was 15 to 30 µm. The power was so low that the procedure was combined with percutaneous transluminal coronary angioplasty. The procedure had no serious complication and allowed balloon dilation at relatively low pressure levels. Percutaneous ultrasonic angioplasty devices have recently been improved and applied to coronary thrombolysis in acute myocardial infarction [4]. Ultrasonic thrombolysis was also performed in thrombus-rich lesions in saphenous vein grafts [5]. On this occasion, the ultrasonic thrombolysis device had a 1.6-mm-long tip and high frequency of 41 KHz. The power was 18 W. The power was so low that it was applied only to thrombolysis. Adjunct percutaneous transluminal coronary angioplasty [6–8] or another angioplasty procedure [9] was needed.
The procedure used in this study was developed for surgically open use, not for percutaneous use. The probes were short and not flexible. The power was high enough to remove the calcified lesion. Aspiration was useful for preventing debris embolism, and water irrigation could reduce thermal injuries. In cadaveric arteries, soft atheroma and calcified lesion could be removed by adjusting the amplitude. The amplitudes were adjustable to treatment of various kinds of atherosclerotic lesions in arteries of various sizes. The ideal probe for percutaneous angioplasty should be long and flexible and have high amplitude and an aspiration hole, but such a probe has not yet been developed. At present, the procedure used in this study is thought to be applicable to clinical angioplasty for occluded or severe stenotic arteries and ostial stenosis of the coronary arteries [10].
The long-term adverse effect of ultrasonic ablation on normal arteries has not been investigated. Several studies of ultrasonic debridement for aortic or mitral valve stenosis have shown high incidences of restenosis [11, 12]. In a present study, higher amplitudes caused higher incidences of restenosis and occlusion. Caution should be taken against the performance of angioplasty at high amplitudes. Because neointimal hyperplasia plays a main role of restenosis, some procedures for gene therapy or drugs to prevent intimal hyperplasia need to be added after the angioplasty. Antiplatelet drugs were not used in this study, but they should be given to prevent thrombus formation after the procedure.
Conclusions
Surgical ultrasonic angioplasty using new hand-held probes could be effective for various kinds of atherosclerotic lesions, whereas angioplasty at high amplitudes had a problem with the long-term effect on normal arteries.
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References
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- Rosenschein U., Rozenszajin L.A., Kraus L., et al. Ultrasonic angioplasty in totally occluded peripheral arteries: initial clinical, histological, and angiographic results. Circulation 1991;83:1976-1986.[Abstract/Free Full Text]
- Siegel R.J., Gunn J., Ahsan A., et al. Use of therapeutic ultrasound in precutaneous coronary angioplasty: experimental in vitro studies and initial clinical experience. Circulation 1994;89:1587-1592.[Abstract/Free Full Text]
- Rosenschein U., Roth A., Rassin T., et al. Analysis of coronary ultrasonic thrombolysis endpoints in acute myocardial infarction (ACUTE trial): results of the feasibility phase. Circulation 1997;95:1411-1416.[Abstract/Free Full Text]
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Abstract
Introduction
