Ultrasound Angioplasty (Developments in Cardiovascular Medicine)

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One criticism of this model is that foam cells are rare in human restenotic neointima. However, balloon angioplasty in this model does cause histopathologic injury comparable to that seen with human angioplasty, with medial dissection and plaque fracture. Platelet deposition occurs rapidly at sites of a balloon-induced plaque fracture. Thus, antiplatelet agents, as a potential anti-restenosis therapy, were studied early in the history of this model 29, 30 and showed efficacy in reducing neointimal thickness.

Catheterization and Stent procedure at Mercy's Oklahoma Heart Hospital

The coronary arteries of domestic pigs after injury respond in similar fashion as human coronary arteries 31, Furthermore, when porcine coronary arteries are injured, thick neointima will be seen within 28 days and is identical to human restenotic neointima. When a balloon-only injury is performed, a typical medial laceration occurs and is filled at 28 days by neointima.

In addition, the amount of neointimal thickening is directly proportional to injury thereby permitting the creation of an injury-response regression relationship that can further quantify the response to potential treatment therapies 33, Experience suggests that the coronary arteries in domestic swine and iliac arteries of rabbits are suitable in that their size, access, and injury response are similar to human vessels, and therefore allow assessment of devices that might be used in clinical evaluation Although armed with fewer collateral vessels, there are pertinent similarities between the pig and human cardiovascular system, including the distribution of epicardial coronary arteries.

Porcine coronary models using vascular injury methods are now accepted standards by which potential restenosis therapies are studied These vessels are of similar diameter to those in the human 2. Cardiac catheterization techniques in the pig are similar in many ways to the techniques used in humans. Procedures are often performed under general anesthesia. Intubation can be achieved using human endotracheal tubes, although the pig's longer pharynx may make this more technically challenging. Arterial access can be achieved via the carotid or femoral arteries, using a cut-down approach or by direct percutaneous puncture using a modified Seldinger technique, respectively.

Standard human diagnostic and interventional equipment may be used, with catheter choice dependent on the approach. In general, via the carotid approach, our group has usually used a Judkins left 3. Via the femoral approach, the hockey stick guide catheter may be used for both left main and RCA ostia 8 , or Judkins right 4.

Antiplatelet therapy is recommended, using aspirin mg started the day before the procedure and continuing until sacrifice 6,8. Clopidogrel 75 mg has also been used in addition to aspirin 36, Only one stent should be implanted per artery except when issues of stent overlap or multiple stent dosing are considered.

Stent overlap frequently occurs during clinical implant and overlapping DES present the possibility of a combined effect from drug released from the 2 stents.

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A rigorous, semi quantitative and defined scale for device evaluation should be presented as well:. When possible, cell density in tissue compartments should be recorded as number of cells per area 32, A subjective description should also be rendered for adjacent tissue, including medial thinning, loss of cellularity, and hyalinization. Measurements at all sections should include medial area, IEL area area within the internal elastic lamina , EEL area area within the external elastic lamina , lumen area, and stent area area within the stent itself. Neointimal measurement is important for efficacy assessment and should include thickness at each stent strut site and total neointimal area 9.

Ultrasound Angioplasty

From numerous studies, considerable data exist on how sirolimus and paclitaxel differ in terms of their effects on the arterial wall 43, Endothelialization after stent implantation should be recorded as absent, partial, or complete in all sections and the time of re-endothelialization should be estimated. In the porcine coronary stent model, a thick neointima was reliably induced by 28 days Fig. However, enthusiasm for this technology has recently dampened by concerns of late stent thrombosis. A major criticism of earlier preclinical studies leading to the United States Food and Drug Administration FDA approval of both stents was their failure to detect significant differences in the healing response of the arterial wall when compared with BMS at 28 days while human angioscopic and autopsy data clearly demonstrated significant differences in healing 50, Most preclinical studies have failed to show any significant differences between DES and BMS in the extent of endothelial coverage when a 1.

It was not until the results of a study using overlapping commercially available SES and PES stents in the rabbit iliac artery model showed incomplete endothelialization compared with matched BMS controls that these differences were recongnized Recently, Nakazawa et al. Accompanying these findings were more increases in fibrin and inflammatory cells in SES than in either ZES or BMS, which persisted out to 90 days after stent implantation Two time points should be used for the evaluation of stent performance, the first at 28 days to observe for neointimal hyperplasia, and at least one later time point to examine long term effects.

The later time point 3 or 6 months depends on when "healing" and drug release are both complete. Of note, the FDA has typically recommended 6 months follow up as the interval to acquire preclinical stent data. The porcine coronary stent restenosis model is a well-accepted standard. However, the fundamental drawback of this model is that there is no stenosis lesion in coronary arteries and that the stent itself is foreign material.

As a result, this model may not be suitable to evaluate the performance of bifurcation or bioabsorbable stents due to lack of a true stenosis lesion. Also, results of coronary artery imaging such as computed tomography CT , magnetic resonance imaging MRI , intravascular ultrasound IVUS , and optical coherence tomography OCT may be hampered as the stent can produce artifact. Radiofrequency thermal balloon angioplasty was introduced as a new technique for percutaneous arterial dilatation in the 's , yet due to increased restenosis rates observed in patients receiving this therapy 57 , it was soon abandoned as a percutaneous interventional treatment option.

Using this system, Staab et al. In our study using 22 swine with a total of 54 coronary arteries, coronary artery stenoses were consistently developed at 4 weeks after heat-injury Fig. In light of these results, this porcine coronary restenosis model might be useful for the evaluation of bifurcation stents and bioabsorbable stents, coronary imaging studies such as MRI, CT, IVUS, and OCT, and for the technical training of complex percutaneous coronary interventions such as bifurcation stenting and atherectomy Experimental animal model for chronic total occlusion CTO.

What is interventional cardiology?

Recent advances of DES technology has shifted focus within interventional cardiology from restenosis prevention to the treatment of CTO. It is often stated that successful chronic total occlusion CTO recanalization represents the "last frontier" of percutaneous coronary intervention. This interest has stimulated the development of specialized devices such as the Frontrunner Lumend Inc.

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Despite its common occurrence, there is surprisingly little information about the pathophysiology of CTO, and why some CTO can be crossed while in others, crossing is unsuccessful. For the past several years, researchers have developed CTO models to guide therapeutic investigations, including image-guidance intervention and device development.

Spontaneous atherosclerotic plaque rupture and subsequent arterial occlusion do not occur naturally in any animal model, even among those models that have been genetically engineered to have increased atheroma formation. For the past several years, researchers have tried to develop several kinds of animal CTO models.

The initial method of producing a total occlusion utilized external ligature or ameroid constriction 61, However, a fundamental drawback of this method is the inability to facilitate the development of devices to recanalize CTO. Subsequent techniques for endoluminal formation of CTO in coronary and peripheral arteries have differed in their fundamental approach. Murphy et al. Of these, gas-drying with thrombin and a high-cholesterol diet was deemed the most efficacious.

Strauss et al. Several characteristics of human CTO were evident in this model, including mature fibrous tissue, multiple small intraluminal vascular channels, occasional extracellular lipid deposits, and disruption of the internal elastic lamina Fig. Their reports suggested that the microchannels may be a critical determinant of successful CTO guide wire crossing Other CTO models have included stents with occluded outflow and even direct alcohol injection to promote thrombosis Developing an accurate and reproducible human-like coronary CTO model has been a complex undertaking because 1 coronary vessels are less amenable to a direct surgical approach; 2 simulating luminal and medial pathology, including microcalcification, has been difficult; and 3 an inflammatory component must be present to mimic human CTO lesions 67, Balloon angioplasty and stent implantation in animal coronary arteries, both standard methods of denuding the vessel and engendering neointimal proliferation, rarely result in CTO development.

More aggressive measures tried have involved the use of thermal injury and copper stent implantation as described above Polymers have also been used to invoke chronic coronary occlusions. Early polymeric implants were abandoned as stent platforms because they induced severe inflammatory responses and vessel occlusion Prosser et al. The polymer is absorbed by 28 days, resulting in a micro-channeled occlusion histologically similar to a human CTO These animal models may contribute to a deeper understanding of the biology of human CTO and enable new device and pharmacological investigation to improve recanalization success in these challenging lesions.

Percutaneous interventions for the treatment of valvular heart disease. Valve repair and replacement are common surgical procedures and are typically effective in eliminating or significantly reducing valve dysfunction. However, these procedures remain controversial as sole treatments for patients with a low ejection fraction. The challenge in treating patients with congestive heart failure due to valvular disease is deciding the mode of repair to address multiple factors such as alignment of the leaflets, the size of annulus, and geometries of subvalvular apparatus.

Invasive and Interventional Cardiology | Cardiovascular Medicine | Medical College of Wisconsin

Coupled with the risk of morbidity and mortality due to open heart surgery, these reconstructive procedures have proven to be a challenge to the surgeon and a risk to the patient, thereby motivating scientists to design devices that can treat valvular dysfunction in a minimally invasive manner. Based on the experience gained from the development of surgical valve prostheses, the FDA has established detailed guidelines for the assessment of fatigue, flow dynamics, and hydrodynamics of valve implants as well as processes for in vitro and in vivo preclinical testing of heart valve prostheses.

In these preclinical studies, not only device development and durability testing but also optimal imaging and deployment protocols should be established and comprehensive user training should be initiated in the latter stages of the preclinical evaluation This section will focus on the percutaneous treatment of valvular heart disease.

Age-related aortic valve disease contributes to continuously increasing morbidity and mortality worldwide and is associated with an increase in aortic valve replacement procedures over the past decade. Degenerative aortic stenosis, a common adult valvular abnormality 72 , has been the focus of percutaneous treatments since the mid s. To date, 2 percutaneous aortic valve procedures have been introduced in clinical setting 73,74 Fig. The ovine model is preferred for in vivo assessment of percutaneous aortic valve devices. Currently there is no chronic animal model representative of aortic stenosis.

Ultrasound angioplasty

While the healthy ovine model has provided validation of catheter function, prosthesis anchoring, device function post-implantation, and unimpaired coronary blood flow, this model has several limitations:. Newer valve technologies may provide solutions to access issues and other limitations of first generation devices. The mitral valve is a complex anatomic and physiologic structure. Its proper function depends on coordinated interaction of the mitral annulus, leaflets, chordae, papillary muscles, and the left ventricle.

Improved understanding of the mechanisms of mitral valve dysfunction coupled with advances in catheter-based technology has resulted in several potential percutaneous approaches to mitral valve repair Innovations attempt to duplicate techniques of surgical mitral repair. Similar to aortic valve devices, the ovine model is preferred for in vivo assessment of percutaneous mitral valve devices. To date, 2 types of diseased animal models were used in published data One type is the rapid-pacing heart failure model and the other type is the ischemic mitral regurgitation MR model.

One drawback of this model is that after recovery from rapid pacing, LV function return to levels seen in the healthy animals In light of this observation, researchers should pay attention to this fact with regard to evaluation of device efficacy. For researchers Facilities and contacts.


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