In vivo radiofrequency thermal balloon angioplasty of porcine coronary arteries: histologic effects and safety

The factors influencing the efficiency of drug-coated balloons

The drug-coated balloon (DCB) is an emerging percutaneous coronary intervention (PCI) device that delivers drugs to diseased vessels to decrease the rate of vascular stenosis. Recent clinical studies have demonstrated that DCBs tend to have both good safety and efficacy profiles, leading to extended application indications in the clinic, including in-stent restenosis (ISR) for metal stents such as drug-eluting stents (DESs), small vascular disease, bifurcation disease, large vascular disease, acute coronary syndrome (ACS), and high bleeding risk. However, some previous clinical data have suggested that DCBs performed less effectively than DESs. No studies or reviews have systematically discussed the improvement strategies for better DCB performance until now. Drug loss during the process of delivery to the target lesion and inefficient delivery of the coating drug to the diseased vascular wall are two key mechanisms that weaken the efficiency of DCBs. This review is the first to summarize the key influencing factors of DCB efficiency in terms of balloon structure and principles, and then it analyzes how these factors cause outcomes in practice based on current clinical trial studies of DCBs in the treatment of different types of lesions. We also provide some recommendations for improving DCBs to contribute to better DCB performance by improving the design of DCBs and combining other factors in clinical practice.

A new radiofrequency balloon angioplasty device for atherosclerosis treatment

Background

Restenosis remains a challenge in the treatment of atherosclerosis due to damage to the endothelial layer and induced proliferation of smooth muscle cells. A novel radiofrequency (RF) heating strategy was proposed to selectively ablate atherosclerosis plaque and to thermally inhibit the proliferation of smooth muscle cells while keeping the endothelial cells intact.

Methods

To realize the proposed strategy, a new radiofrequency balloon catheter, consisting of three ports, a three-channel tube, a balloon and an electrode patch, was designed. To evaluate the feasibility of this new design, a phantom experiment with thermocouples measuring temperatures with different voltages applied to the electrodes was conducted. A numerical model was established to obtain the 3D temperature distribution. The heating ability was also evaluated in ex vivo diseased artery samples.

Results

The experimental results showed that the highest temperature could be achieved in a distance from the surface of the balloon as designed. The temperature differences between the highest temperature at 0.78 mm and those of the surface reached 9.87 °C, 12.55 °C and 16.00 °C under applied 15 V, 17.5 V and 20 V heating, respectively. In the circumferential direction, the heating region (above 50 °C) spread from the middle of the two electrodes. The numerical results showed that the cooling effect counteracted the electrical energy deposition in the region close to the electrodes. The thermal lesion could be directed to cover the diseased media away from the catheter surface. The ex vivo heating experiment also confirmed the selective heating ability of the device. The temperature at the targeted site quickly reached the set value. The temperature of the external surface was higher than the inner wall surface temperature of the diseased artery lumen.

Conclusion

Both the experimental and numerical results demonstrated the feasibility of the newly designed RF balloon catheter. The proposed RF microelectrodes heating together with the cooling water convection can realize the desired heating in the deeper site of the blood vessel wall while sparing the thin layer of the endothelium.

A new endovascular radiofrequency device for dilatation of vascular stenosis in a rabbit model

PURPOSE

To investigate the use of a new endovascular radiofrequency (RF) device, the Habib™ VesCoag™ Catheter, to induce vascular remodeling and dilatation of arterial stenosis in a rabbit model.

MATERIALS AND METHODS

RF was used to induce arterial stenosis in 10 rabbits and this was confirmed by angiography and color Doppler ultrasound. Two groups of five animals were then subjected to (1) balloon dilatation of the stenosis (intervention group), (2) no intervention (control group). Two rabbits from each group were sacrificed following the procedures to investigate vessel histopathology. At six weeks, the remaining six rabbits underwent follow-up angiogram and color Doppler ultrasound to assess vessel patency. They were then sacrificed and the vessels prepared for histopathological analysis. Three-dimensional images with confocal microscopy of the arterial lumen were also acquired.

RESULTS

In the intervention group, stenosis was reversed and patency confirmed by angiography and color Doppler ultrasound six weeks later in all surviving rabbits. Histopathology revealed degenerative changes of elastic fibers, focal losses of elastica lamella, disorganization of myocytes and extensive hyalinization of the tunica adventitia. Focal elastin changes of the arterial elastic lamella were also shown by three-dimensional confocal microscopy images.

CONCLUSION

We have developed a novel endovascular RF catheter that can be safely and effectively used to induce vascular remodeling and dilatation of arterial stenosis in an experimental rabbit model.

Experimental animal study of a novel radiofrequency endovascular occlusion device

BACKGROUND

The purpose of this study was to present a radiofrequency (RF) endovascular occlusion device (ie, Habib VesCoag Catheter; EMcision Ltd, London, UK) and to evaluate safety and efficacy of the device for complete occlusion of normal porcine vessels.

METHODS

The study included 20 pigs. In each pig, a segmental branch of the right hepatic artery, a branch of the splenic artery, and a branch of one of the renal arteries were catheterized. A single or multiple applications of RF energy were performed until vessel occlusion was achieved. Fifteen days later, angiography was repeated to assess vessel patency. The vessels were then excised for pathological analysis.

RESULTS

Vessels 2.5 to 6 mm in diameter were treated. Complete occlusion with a single attempt was achieved using a mean amount of energy of 110.67 J in vessels 2.5 to 3 mm, 111.67 J in vessels 3.5 to 4 mm, and 116.63 J in vessels 5 to 6 mm in diameter and was confirmed by angiography at the 15-day follow-up.

CONCLUSIONS

Vascular occlusion can be effectively and safely achieved by endovascular application of RF energy to normal porcine arteries using the Habib VesCoag catheter.

Reduction of arterial graft smooth muscle mass by moderate heat therapy

Radial artery (RA) graft spasm is a major cause of early graft failure in coronary artery bypass grafting surgeries. We explored the feasibility of thermal reduction of smooth muscle mass to attenuate vasoconstriction. Rat and rabbit femoral arteries were treated thermally in situ (45°C to 65°C; 0 s to 120 s) and then excised at various time points for histological and physiological study (pressure-diameter relationships). Human radial arteries were treated in vitro and studied in similar fashion. Weeks after thermal treatment, no overt indication was noted of vasospasm, thrombosis, or scarring in the arterial wall; however, this intervention led to a thermal dose-dependent reduction of vasoconstriction (to phenylephrine or potassium chloride) and to a conspicuous loss of smooth muscle. Pressure-diameter relationships showed no aneurismal dilation of these demuscularized arteries up to 200 mmHg. Qualitatively identical results were obtained in human radial arteries. Thermal ablation of RAs may provide a simple, safe, and effective solution to postsurgical vasospasm.

Radiofrequency thermal balloon angioplasty in an experimental model of peripheral arterial stenosis

RATIONALE

To assess the effect of thermal balloon angioplasty on surgically created peripheral arterial stenoses.

METHODS

Unilateral femoral arterial stenoses were created in 17 neonatal lambs (Dorset X Suffolk/Mule), using absorbable sutures. Six to 8 weeks later, the stenoses were dilated using either a standard (N=5), or thermal balloon angioplasty (N=9). Immediate angiography, flow and pressure gradient measurements were made to assess the acute result following either procedure. The survivors were followed up for a further period of 4 to 6 weeks, and a terminal angiographic study performed. The thermally treated segments of vessels were removed for qualitative histologic analysis.

RESULTS

Thermal angioplasty appeared to be acutely successful in eight of nine animals, compared with one of five successful procedures following standard angioplasty. Higher therapeutic temperatures (> or = 80 degrees C) were associated with vascular complications. At the terminal study, stenoses had recurred in four of six survivors successfully treated with thermal angioplasty. Histologic studies demonstrated non-uniform effects of thermal dilation on the vessel wall, with variable changes ranging from partial or full-thickness tears, fibroblastic or myocyte proliferation, and disorganization of the vessel wall layers.

CONCLUSION

Thermal angioplasty appears to be acutely more beneficial compared with standard angioplasty. However there is a significant recurrence of stenoses, and non-uniform changes in the vessel wall.

First in-vivo trials of a fiber Bragg grating based temperature profiling system

We describe the results of in-vivo trials of a portable fiber Bragg grating based temperature profile monitoring system. The probe incorporates five Bragg gratings along a single fiber and prevents the gratings from being strained. Illumination is provided by a superluminescent diode, and a miniature CCD based spectrometer is used for demultiplexing. The CCD signal is read into a portable computer through a small A/D interface; the computer then calculates the positions of the center wavelengths of the Bragg gratings, providing a resolution of 0.2 degree C. Tests were carried out on rabbits undergoing hyperthermia treatment of the kidney and liver via inductive heating of metallic implants and comparison was made with a commercial Fluoroptic thermometry system.

Effect of low grade radiofrequency heating on arterial vasospasm in the porcine model

Nineteen pigs were studied in order to assess the effect of low grade, radiofrequency-powered, thermal balloon angioplasty on the vasoconstrictor response of peripheral arteries. A mechanical stimulus was used to induce vasospasm. Thermal angioplasty reduced the extent of inducible vasospasm from 79% to 6% compared to nonthermal control inflations, which reduced the vasoconstrictor response from 75% to 60% (P < 0.001). Histologic studies demonstrated that the extent of myocyte necrosis was significantly greater in the thermally treated arteries than in the control vessels (P < 0.01). Thermal balloon angioplasty at 60 degrees C significantly attenuates peripheral arterial vasospasm induced by mechanical trauma in the porcine model. This paralytic effect may be related to the loss of myocytes secondary to thermal necrosis.

Effect of low-grade conductive heating on vascular compliance during in vitro balloon angioplasty

Radiofrequency-powered, thermal balloon angioplasty is a new technique that enhances luminal dilatation with less dissection than conventional angioplasty. The purpose of this study was to assess the effect of radiofrequency heating of balloon fluid on the pressure-volume mechanics of in vitro balloon angioplasty and to determine the histologic basis for thermal-induced compliance changes. In vitro, radiofrequency-powered, thermal balloon angioplasty was performed on 46 paired iliac segments freshly harvested from 23 nonatherosclerotic pigs. Balloon inflations at 60 degrees C were compared to room temperature inflations in paired arterial segments. Intraballoon pressure and volume were recorded during each inflation as volume infusion increased pressure over a 0 to 10 atm range. Pressure-volume compliance curves were plotted for all dilatations. Six segments were stained to assess the histologic abnormalities associated with thermal compliance changes. Radiofrequency heating acutely shifted the pressure-volume curves rightward in 20 of 23 iliac segments compared to nonheated controls. This increase in compliance persisted after heating and exceeded the maximum compliance shift caused by multiple nonheated inflations in a subset of arterial segments. Histologically, heated segments showed increased thinning and compression of the arterial wall, increased medial cell necrosis and altered elastic tissue fibers compared to nonheated specimens. In conclusion, radiofrequency heating of intraballoon fluid to 60 degrees C acutely increases vascular compliance during in vitro balloon angioplasty of nonatherosclerotic iliac arteries. The increased compliance persists after heating and can be greater than the compliance shifts induced by multiple conventional dilatations. Arterial wall thinning and irreversible alteration of elastic tissue fibers probably account for thermal compliance changes.