An in vivo comparison of radiofrequency cardiac lesions formed by standard and magnetically steered 4 mm tip catheters

Background. In vivo comparison of cardiac radiofrequency ablation lesions between standard and magnetically steered 4 mm tip catheters has never been reported. Methods. High and low right atrium (RA) free wall, isthmus, right ventricle (RV) free wall and outflow tract lesions were studied macroscopically and microscopically five days after lesion formation in seven pigs. Shape, size, thrombus formation, and ablation parameters were compared. The effect of minimal, medium and high wall contact was assessed by a contact measurement utility for magnetic catheters. Results. All 14 RA free wall lesions were transmural with a similar epicardial and endocardial surface area. In the RV, the epicardial area usually appeared to be smaller than the endocardial area with standard catheters. Isthmus lesions were difficult to assess transmurality. There was no difference in endocardial area: standard 39 mm² (range 16 to 82 mm²) vs. magnetic 36 mm² (range 23 to 111 mm²). If the catheter tip was perpendicular to the tissue, magnetic lesions were more often round or oval, while standard lesions were more often elongated (p<0.05). When the catheter tip was parallel to tissue, lesions always tended to be elongated. Microscopic characteristics were similar. The contact utility was not useful. Average impedance (p<0.0001) and energy delivered (p<0.05) were less with magnetic catheters. Conclusion. Lesions from magnetically steered catheters are transmural of similar size, but with less variability than standard catheter lesions when the tip is perpendicular to the tissue. Magnetic lesions are associated with lower impedance and energy delivery. This suggests a more stable tip-to-tissue contact. (Neth Heart J 2010;18:66–71.)     

Characterization of performance of multihole nozzle in cryospray

Present study deals with improvement in conventional technique of spraying liquid nitrogen on cancerous lesions to improve its efficacy. It is an attempt to demarcate the variation in outcome when cryogen is sprayed through customised multi-hole nozzle (MHN). Influence of mass flow rate on cryoablation while varying the number of holes in MHNs is analysed experimentally. Another section of study focuses on the impact of the rate of evaporation of cryogen when margin among the holes is changed. Total 6 MHNs are fabricated while changing their geometrical parameters. Single freeze-thaw cycle is carried out to spray liquid nitrogen on tissue mimicking gel with a spraying distance of 18 mm. Temperature profile captured through infrared images advocates that lethal area formed through the application of MHNs with 5 holes is larger than MHNs with 4 holes on the surface of gel. It reflects the influence of central hole on necrosis. In order to necrotize lesion through freezing, the most desired cooling rate (CR) varies from 50^∘C/min to 200^∘C/min. It is achieved up to a depth of 2 mm below the gel surface and in a radius of 10 mm from the centre of spray (CS) for all MHNs, except 4C. Most optimised margin in terms of cryoablation is also estimated in the study. MHN with 1.5 mm margin provides the most optimised results in terms of cryoablation when MHNs with the central hole are considered while MHN with 1 mm margin provides most optimised result when MHNs without central hole are considered. On the basis of observations made through thermal images it can be said that multiple freezing fronts are not observed on the gel surface which aids in the formation of lone giant ice ball. This provides an extra edge to the treatment methodology because alteration in the dimensions of necrotic zone can be made by changing the duration of spray. Larger lateral spread of necrotic zone will also reduce the number of sittings required for the treatment of larger lesions.     

Cryoablation used in fertility-sparing treatment for early endometrial cancer: A pig model experiment using a new designed balloon cryoprobe

Young patients with early endometrial cancer have a strong desire to retain reproductive function, which require us to develop a therapeutic method that can not only assure the complete resection of tumor but also retain the uterine integrity. In the present study, we proposed a fertility-sparing surgery option that combined hysteroscopic resection with cryoablation to achieve this goal. To verify the safety and effectiveness of cryoablation for local uterine wall, we designed the experiment in pig model using a novel cryoablation balloon probe. In the process of freezing and thawing, the temperature of different parts of the uterus was measured in real time. The uterus was harvested immediately, three weeks after cryotherapy for histological evaluation. The results demonstrated cryoablation using the new cryoprobe is safe and effective. The effective freezing range can cover a range of 2 cm in diameter at least. This study provided us evidence before cryoablation could be applied in clinical practice of fertility-sparing treatment for young women with early endometrial cancer.     

Noninvasive assessment of local myocardium repolarization changes using high resolution surface ECG mapping

A method using body surface potential maps for assessment of myocardium lesions with changed repolarization is presented and suitable mapping system is introduced. Differences between normal and altered QRST integral maps together with torso volume conductor model were used to determine the equivalent dipole representing the lesion. Performance of the method was studied on simulated data. Changed repolarization was modeled by shortening of myocyte action potentials in regions typical for stenosis of the main coronary arteries. The equivalent dipole estimated the positions of small lesions with a mean error of 9+/-4 mm (17+/-14 mm for larger transmural lesions). The subepicardial or subendocardial character of the lesions was reflected in the dipole orientation. Tests of the method on patients after myocardial infarction that underwent coronary intervention on a single coronary vessel showed that in 7 of 8 successfully treated patients the dipole position matched well with the treated vessel. A small dipole moment in another patient indicated unsuccessful treatment. The method was implemented in a new 128-channel mapping system. Its active electrodes, battery powered measuring unit and optical computer interface help to minimize noise in ECG and guarantee patient's safety. The results suggest that the method and mapping system offer useful tools for noninvasive identification of local repolarization changes in the myocardium.     

Percutaneous cryoablation of the kidney in a porcine model

Several reports have documented that renal cryoablation when used either via open or laparoscopic surgical techniques can be well tolerated in animal models. We sought to examine the feasibility of performing renal cryoablation percutaneously, under ultrasound guidance, in a porcine model. A total of 13 juvenile swine was treated. In each animal the lower pole of the left kidney was used as the target. Each animal had serum drawn for Hct, Wbc, CK, BUN, creatinine, and myoglobin pre- and postcryoablation and again at the time of sacrifice. Animals were sacrificed at 0-42 days postoperatively, and the treated renal units were harvested and submitted for histologic examination. The procedures were divided into three groups based on the extent of the freeze time. Group 1 (n = 4) was treated for 3-4 min, single freeze; Group 2 (n = 3), 6-7 min, single freeze; and Group 3 (n = 6), a double freeze-thaw cycle, each for 10 min. None of the animals in this experiment died or experienced significant clinical deteriorations at any time post-treatment. No significant differences in any of the measured serum markers were noted between pre- and post-treatment values. For animals in Groups 1 and 2 discrete cryolesions were created with sharp 1-mm borders and no perirenal reaction/damage to surrounding structures. For animals in Group 3 large areas of renal infarction/cryolesions were produced, with significant perirenal reaction in 5/6 animals and gross hydronephrosis/total renal loss in 2/6. Percutaneous renal cryoablation appears to be well tolerated in the porcine model which we used. Associated morbidity appears to be related to the extent of freezing, with a safety tolerance in the present study limited to target areas of approximately 3-5 cm3. These findings suggest that a pilot study of percutaneous renal cryoablation for patients with 3-4-cm exophytic lesions may be warranted.     

Optical measurements reveal nature of intercellular coupling across ventricular wall

Previously, we showed that intercellular uncoupling through gap junctions is an important mechanism for maintaining transmural heterogeneities of repolarization that are responsible for ventricular arrhythmias in disease states such as heart failure. However, rotational anisotropy between transmural muscle layers also may influence coupling. To determine the effect of rotational anisotropy on transmural coupling, we developed a numerical three-dimensional model of passive cardiac tissue in which rotational anisotropy was varied in a controlled fashion. Simulations of optical mapping demonstrated that spatial averaging produced a voltage decay in space best fit by a single decaying exponential compared with the theoretically predicted decay. As fiber orientation varied by 90 degrees with respect to the transmural surface, the effective transmural space constant (lambda(TM)) changed by only 0.31% in simulations. In contrast, reducing intercellular conductivity by 24% decreased lambda(TM) by 7.7%. In the canine wedge preparation (n = 5), lambda measured by optical mapping of the epicardial and subepicardial surface was similar transverse (lambda(TV) = 0.73 +/- 0.10 mm) and transmural (lambda(TM) = 0.70 +/- 0.08 mm) to subepicardial fibers. We confirmed previous findings that lambda(TM) in subepicardial layers was significantly reduced by 14 +/- 2% compared with deeper layers of myocardium, providing evidence for transmural uncoupling in the epicardial-midmyocardial interface. These data establish the theoretical and experimental basis for measuring intercellular coupling between muscle layers spanning the ventricular wall with optical mapping techniques. Furthermore, this study demonstrates that transmural uncoupling at the epicardial-midmyocardial interface may be attributable to heterogeneous expression of cardiac gap junctions and not rotational anisotropy.     

Superficial contact cryoablation attenuates experimentally created lung air leakage

Previously, we, and others found that cryoablation on normal lung produced localized pulmonary hemorrhage and edema, causing obliteration of air space. Therefore, we hypothesized that lung air leakage may be diminished by this procedure. In the present study, we examined if cryoablation can attenuate experimentally created lung air leakage. Male domestic pigs (n = 4) underwent a thoracotomy. The lung was resected approximately 5 mm in diameter and 1 mm in depth to create air leakage lesions. An argon gas cryoprobe with a copper plate attached to its tip was used to cryoablate the lesions superficially. After cryoablation, the positive airway pressure that produced macroscopic bubbles from each lesion site was compared between cryoablated and untreated lesions. Also, cryoablation of the lung surface was carried out in male Donryu rats (n = 20) which were sequentially sacrificed to observe the histological changes over a time course. In the pigs, the air leakage pressure was significantly increased with cryoablation (40 cmH₂O <) compared to no treatment (19 ± 5 cmH₂O) (p = 0.021, Mann–Whitney U test). Histologically, cryoablation produced acute pulmonary hemorrhage and edema. In the rats, the region with extensive hemorrhage progressed to fibrosis in 1 month, and the areas with edema recovered. This study provides supportive evidence that cryoablation has the potential to stop air leakage from surface pulmonary injury. This procedure may provide a useful adjunct to surgical resection for spontaneous pneumothorax, and the control of air leakage from dissected raw lung surfaces during lung resection.     

Studying the thermal effects of a clinically-extracted vascular tissue during cryo-freezing

Cryosurgery is known to be a suitable treatment for unresectable tumors by employing extremely low temperature to induce cryo-lesion. However, large blood vessels in the tissue may induce insufficient freezing at the targeted area. In this work, we have developed a cryo-freezing model specifically dedicated to tumors with a complex blood vessel network taken from CT-scanned images. The model was validated with in-vitro experimental data. Adopting an appropriate mesh size, the simulated results achieved an excellent agreement with the experimental data at a maximum error of 3.4%. The validated model was applied to study an optimal cryotherapy in the treatment of a human liver. The movement of 265 K isotherm and the thermal influence of blood flow were investigated. Key results indicated that large neighboring vessels could significantly influence the shape of the ice fronts, but they exerted less impact on the development of the lethal temperature boundary. The freezing duration, distance to the vessel, blood flow rate and blood vessel size were observed to be key parameters in determining the optimal cryoablation. A case study further demonstrated that by precisely controlling the cryo-freezing process, up to 44.6% of the unintended tissue freezing could be achieved. Pragmatically, this work provides surgeons with essential information on how to precisely tune key parameters to promote greater surgical success.     

Influence of left-ventricular shape on passive filling properties and end-diastolic fiber stress and strain

Passive filling is a major determinant for the pump performance of the left ventricle and is determined by the filling pressure and the ventricular compliance. In the quantification of the passive mechanical behaviour of the left ventricle and its compliance, focus has been mainly on fiber orientation and constitutive parameters. Although it has been shown that the left-ventricular shape plays an important role in cardiac (patho-)physiology, the dependency on left-ventricular shape has never been studied in detail. Therefore, we have quantified the influence of left-ventricular shape on the overall compliance and the intramyocardial distribution of passive fiber stress and strain during the passive filling period. Hereto, fiber stress and strain were calculated in a finite element analysis of passive inflation of left ventricles with different shapes, ranging from an elongated ellipsoid to a sphere, but keeping the initial cavity volume constant. For each shape, the wall volume was varied to obtain ventricles with different wall thickness. The passive myocardium was described by an incompressible hyperelastic material law with transverse isotropic symmetry along the muscle fiber directions. A realistic transmural distribution in fiber orientation was assumed. We found that compliance was not altered substantially, but the transmural distribution of both passive fiber stress and strain was highly dependent on regional wall curvature and thickness. A low curvature wall was characterized by a maximum in the transmural fiber stress and strain in the mid-wall region, while a steep subendocardial transmural gradient was present in a high curvature wall. The transmural fiber stress and strain gradients in a low and high curvature wall were, respectively, flattened and steepened by an increase in wall thickness.     

Non-homogeneous analysis of three-dimensional transmural finite deformation in canine ventricular myocardium

A new method has been developed for analyzing transmural distributions of finite deformation in canine ventricular myocardium without the need to assume that the strain in a finite volume of the wall is homogeneous. The three-dimensional nodal geometric parameters of bilinear-cubic or bilinear-quadratic finite elements are fitted by least squares to the measured coordinates of 12-18 radiopaque markers implanted in the left ventricular free wall. For six dog hearts, root-mean-squared errors in the fitted in-plane coordinates ranged from 0.079-0.556 mm in the end-diastolic reference state and 0.142-0.622 mm at end-systole. The corresponding error ranges in the radial coordinate were 0.042-0.264 mm at end-diastole and 0.106-0.279 mm at end-systole. Smoothly continuous transmural profiles of wall strain computed as the element deformed during the cardiac cycle from end-diastole to end-systole showed good agreement with the discrete results of conventional homogeneous analysis. Using the kinematics of a thick-walled incompressible cylinder, overall absolute errors due to the non-homogeneity of myocardial deformation were found to be reduced in the new analysis by 30-35% for typical experimental parameters. Overall relative errors were also reduced (from 23 to 20%). Since measurement errors in the reconstructed marker coordinates were spatially smoothed by the fitting procedure, noise in the computed deformations was also substantially attenuated, and transmural gradients of three-dimensional strain components could be obtained with improved accuracy. Hence physiological factors affected by transmural stress and strain distributions, such as myocardial blood flow, ischemia and hypertrophy, may be better understood.     

The effects of squatting while pregnant on pelvic dimensions: A computational simulation to understand childbirth

Biomechanical complications of childbirth, such as obstructed labor, are a major cause of maternal and newborn morbidity and mortality. The impact of birthing position and mobility on pelvic alignment during labor has not been adequately explored. Our objective was to use a previously developed computational model of the female pelvis to determine the effects of maternal positioning and pregnancy on pelvic alignment. We hypothesized that loading conditions during squatting and increased ligament laxity during pregnancy would expand the pelvis. We simulated dynamic joint moments experienced during a squat movement under pregnant and non-pregnant conditions while tracking relevant anatomical landmarks on the innominate bones, sacrum, and coccyx; anteroposterior and transverse diameters, pubic symphysis width and angle, pelvic areas at the inlet, mid-plane, and outlet, were calculated. Pregnant simulation conditions resulted in greater increases in most pelvic measurements – and predominantly at the outlet – than for the non-pregnant simulation. Pelvic outlet diameters in anterior-posterior and transverse directions in the final squat posture increased by 6.1 mm and 11.0 mm, respectively, for the pregnant simulation compared with only 4.1 mm and 2.6 mm for the non-pregnant; these differences were considered to be clinically meaningful. Peak increases in diameter were demonstrated during the dynamic portion of the movement, rather than the final resting position. Outcomes from our computational simulation suggest that maternal joint loading in an upright birthing position, such as squatting, could open the outlet of the birth canal and dynamic activities may generate greater pelvic mobility than the comparable static posture.     

Transmural Intestinal Wall Permeability in Severe Ischemia after Enteral Protease Inhibition

In intestinal ischemia, inflammatory mediators in the small intestine''s lumen such as food byproducts, bacteria, and digestive enzymes leak into the peritoneal space, lymph, and circulation, but the mechanisms by which the intestinal wall permeability initially increases are not well defined. We hypothesize that wall protease activity (independent of luminal proteases) and apoptosis contribute to the increased transmural permeability of the intestine''s wall in an acutely ischemic small intestine. To model intestinal ischemia, the proximal jejunum to the distal ileum in the rat was excised, the lumen was rapidly flushed with saline to remove luminal contents, sectioned into equal length segments, and filled with a tracer (fluorescein) in saline, glucose, or protease inhibitors. The transmural fluorescein transport was determined over 2 hours. Villi structure and epithelial junctional proteins were analyzed. After ischemia, there was increased transmural permeability, loss of villi structure, and destruction of epithelial proteins. Supplementation with luminal glucose preserved the epithelium and significantly attenuated permeability and villi damage. Matrix metalloproteinase (MMP) inhibitors (doxycycline, GM 6001), and serine protease inhibitor (tranexamic acid) in the lumen, significantly reduced the fluorescein transport compared to saline for 90 min of ischemia. Based on these results, we tested in an in-vivo model of hemorrhagic shock (90 min 30 mmHg, 3 hours observation) for intestinal lesion formation. Single enteral interventions (saline, glucose, tranexamic acid) did not prevent intestinal lesions, while the combination of enteral glucose and tranexamic acid prevented lesion formation after hemorrhagic shock. The results suggest that apoptotic and protease mediated breakdown cause increased permeability and damage to the intestinal wall. Metabolic support in the lumen of an ischemic intestine with glucose reduces the transport from the lumen across the wall and enteral proteolytic inhibition attenuates tissue breakdown. These combined interventions ameliorate lesion formation in the small intestine after hemorrhagic shock.     

Feasibility and safety of cryoablation on the porcine ureter using a new balloon cryoprobe

Cryoablation, as a well-characterized technology, has multifarious clinical applications. But few are reported on ureteral endometriosis. Thus, we examined the feasibility and safety of cryotherapy with a novel balloon cryoprobe on ureter in a live porcine model. During the freezing and thawing cycle, temperature was recorded in different parts of the ureter in real-time. Two-minute cryoablation could induce necrosis within range in 1 cm diameter on serosa layer. The temperature respectively dropped to −136.5 °C, −96.1 °C and −17.5 °C at the cryotherapy center, 1 cm and 1.5 cm from center on serosal side. The ureters were harvested immediately, 2 weeks or 3 months after cryotherapy. No perforation, stricture, adhesions, or hydronephrosis was observed. Histopathologic representations of ureters after cryoablation indicated that full thickness necroses of ureters were seen in all samples. The results demonstrated ureteral cryoablation using a novel balloon probe was feasible, safe, and effective. These findings provided us reference before cryoablation could be applied in clinical practice in treating ureteral endometriosis.     

Heterogeneity in distribution of cardiac glycogen following isoproterenol infusions in the dog

Synopsis A combined biochemical, histochemical and cytochemical study was made of cardiac glycogen distribution following intravenous infusions of varying doses of isoproterenol in anaesthetized, open-chested dogs. There was a dose-dependent decrease in glycogen levels in biopsies of the posterolateral wall of the left ventricle which also exhibited a transmural gradient with the endocardial third the most severely affected. Periodic acid-Schiff (PAS) histochemical studies also suggested a transmural gradient. There was, however, a marked variability within each layer, particularly the large amounts in the conduction system fibres. The ultrastructural studies exhibited a marked variation in glycogen content from one cell to the next. This was particularly evident in the complete absence of granules in the contraction band lesions of isoproterenol cardiotoxicity yet substantial amounts were retained in neighbouring cells. Isoproterenol, therefore, produces a heterogenous depletion of cardiac glycogen related to the scattered catecholamine-induced myocardial cellular lesions. These relationships have not previously been documented or emphasized.     

Turbulence detection in a stenosed artery bifurcation by numerical simulation of pulsatile blood flow using the low-Reynolds number turbulence model

The pulsatile blood flow in a partially blocked artery is significantly altered as the flow regime changes through the cardiac cycle. This paper reports on the application of a low-Reynolds turbulence model for computation of physiological pulsatile flow in a healthy and stenosed carotid artery bifurcation. The human carotid artery was chosen since it has received much attention because atherosclerotic lesions are frequently observed. The Wilcox low-Re k-omega turbulence model was used for the simulation since it has proven to be more accurate in describing transition from laminar to turbulent flow. Using the FIDAP finite element code a validation showed very good agreement between experimental and numerical results for a steady laminar to turbulent flow transition as reported in a previous publication by the same authors. Since no experimental or numerical results were available in the literature for a pulsatile and turbulent flow regime, a comparison between laminar and low-Re turbulent calculations was made to further validate the turbulence model. The results of this study showed a very good agreement for velocity profiles and wall shear stress values for this imposed pulsatile laminar flow regime. To explore further the medical aspect, the calculations showed that even in a healthy or non-stenosed artery, small instabilities could be found at least for a portion of the pulse cycle and in different sections. The 40% and 55% diameter reduction stenoses did not significantly change the turbulence characteristics. Further results showed that the presence of 75% stenoses changed the flow properties from laminar to turbulent flow for a good portion of the cardiac pulse. A full 3D simulation with this low-Re-turbulence model, coupled with Doppler ultrasound, can play a significant role in assessing the degree of stenosis for cardiac patients with mild conditions.     

In vivo destruction of tumor tissue by cryoablation can induce inhibition of secondary tumor growth: an experimental study

BACKGROUND: Cryoablation has been used successfully for the local treatment of several cancers. Besides local destruction, a systemic antitumor response has been postulated after cryoablation of tumor tissue. In this study we evaluate the possible systemic antitumor response induced by cryodestruction of tumor tissue in two mouse tumor models. METHODS: Mice received two subcutaneously placed tumor implants (thigh and flank) of the nonimmunogenic mouse colon tumor cell line, colon 26-B. After 7 days, the thigh implant was treated by cryoablation or excision and the effect on secondary tumor growth was determined by volume measurement of the nontreated flank tumor. Cytokine (IL-1alpha and TNF-alpha) levels in plasma were measured after treatment. Similar experiments were performed in nude mice using a human melanoma cell line (MV3). Moreover, in this model the effect of cryoablation on development of spontaneous lung metastases was evaluated. RESULTS: In the colon 26-B tumor model treatment of primary tumor implants by cryoablation resulted in a significant inhibition of secondary tumor growth compared to animals treated by surgical excision (P < 0.01). Six hours after treatment, plasma levels of IL-1alpha and TNF-alpha were higher after cryoablation than after excision (P < 0.01). Also in the nude mice model cryoablation resulted in inhibition of secondary tumor growth, though not significant. Mice treated by cryoablation showed significantly less lung metastases compared to those treated by excision (P = 0.03). CONCLUSIONS: Cryoablation of tumor tissue can result in inhibition of secondary and metastatic tumor growth. A cytokine response induced by cryoablation of tumor tissue may attribute to this feature.     

Epicardial Ablation on the Beating Heart: Limited Efficacy of a Novel, Cooled Radiofrequency Ablation Device

OBJECTIVE: To perform a minimally invasive procedure for atrial fibrillation without cardiopulmonary bypass, it is necessary to create transmural lesions on the beating heart. Although bipolar radiofrequency clamps can isolate the pulmonary veins, they have difficulty in performing any other left atrial lesions, particularly those of the traditional Cox-Maze procedure. This study examined the performance of an internally cooled, bipolar radiofrequency device designed for such an application. METHODS: Eleven domestic pigs underwent median sternotomy. Five animals had eight atrial lesions created with the radiofrequency device at times of 20, 30, 40, and 50 seconds. In six other pigs, the device was compared with another technology that has been used clinically for epicardial, beating heart ablation, the Guidant Flex 4 microwave device. The tissue was stained with 2,3,5-triphenyl-tetrazoluim chloride, and the lesions were sectioned at 5-mm intervals. Lesion width, depth, and transmurality were evaluated. RESULTS: The radiofrequency device had a linear dose-response relationship. Lesions were wider and deeper with increasing ablation times. A total of 40%, 45%, 60%, and 67% of lesions were transmural at times of 20, 30, 40, and 50 seconds, respectively. Ninety-one percent of lesions in tissue up to 4-mm thick were transmural after 50 seconds. However, performance in thicker tissue was poor. Lesions created by the device were deeper and more likely to be transmural than the Flex 4. CONCLUSIONS: This internally cooled, bipolar radiofrequency device can reliably create transmural lesions on tissue up to 4-mm thick and performs better than a microwave device.     

Comparison of dual- and triple-freeze protocols for pulmonary cryoablation in a Tibet pig model

The purpose of this study was to compare a dual-freeze protocol with a triple-freeze protocol for pulmonary cryoablation in a porcine lung model. Five dual- (10-5-10-5) and five triple-freeze (5-5-5-5-10-5) cryoablations were performed on an exposed operation field in normal porcine lung. Changes in the temperature of the cryoprobes and the diameter of the iceballs were measured during the ablation and pathologic changes in the cryozones (zones of tissue destruction) were reviewed 7 days after the procedure. The diameter of the iceball surface differed between the two protocols. Pathologically, the triple-freeze protocol was associated with a longer complete necrosis zone than the dual-freeze protocol, though the two protocols produced cryolesions and cryozones of similar length, and in both cases there were five areas of tissue destruction. With the same duration of freezing (20 min), the triple-freeze protocol may be better for pulmonary cryoablation than the dual-freeze protocol.     

Dynamics of diffusivity and pressure drop in flow-through and parallel-flow bioreactors during tissue regeneration

In this study, transport characteristics in flow-through and parallel-flow bioreactors used in tissue engineering were simulated using computational fluid dynamics. To study nutrient distribution and consumption by smooth muscle cells colonizing the 100 mm diameter and 2-mm thick scaffold, effective diffusivity of glucose was experimentally determined using a two-chambered setup. Three different concentrations of chitosan-gelatin scaffolds were prepared by freezing at -80°C followed by lyophilization. Experiments were performed in both bioreactors to measure pressure drop at different flow rates. At low flow rates, experimental results were in agreement with the simulation results for both bioreactors. However, increase in flow rate beyond 5 mL/min in flow-through bioreactor showed channeling at the circumference resulting in lower pressure drop relative to simulation results. The Peclet number inside the scaffold indicated nutrient distribution within the flow-through bioreactor to be convection-dependent, whereas the parallel-flow bioreactor was diffusion-dependent. Three alternative design modifications to the parallel-flow were made by (i) introducing an additional inlet and an outlet, (ii) changing channel position, and (iii) changing the hold-up volume. Simulation studies were performed to assess the effect of scaffold thickness, cell densities, and permeability. These new designs improved nutrient distribution for 2 mm scaffolds; however, parallel-flow configuration was found to be unsuitable for scaffolds more than 4-mm thick, especially at low porosities as tissues regenerate. Furthermore, operable flow rate in flow-through bioreactors is constrained by the mechanical strength of the scaffold. In summary, this study showed limitations and differences between flow-through and parallel-flow bioreactors used in tissue engineering.     

Long-Term Outcomes of Percutaneous Cryoablation for Patients with Hepatocellular Carcinoma within Milan Criteria

Background

Accumulating evidences have suggested that percutaneous cryoablation could be a valuable alternative ablation therapy for HCC but there has been no large cohort-based analysis on its long-term outcomes.

Methods

A series of 866 patients with Child-Pugh class A-B cirrhosis and HCC within Milan criteria who underwent percutaneous cryoablation was long-term followed. The safety, efficacy, 5-year survival, and prognostic factors of percutaneous cryoablation in the treatment of HCC were analyzed.

Results

A total of 1197 HCC lesions were ablated with 1401 cryoablation sessions. Complete response (CR) was achieved in 1163 (97.2%) lesions and 832 (96.1%) patients with 34 (2.8%) major complications, but no treatment-related mortality. After a median of 30.9 months follow-up, 502 (60.3%) patients who achieved CR developed different types of recurrence. The cumulative local tumor recurrence rate was 24.2% at 5-years. Multiple tumor lesions, tumor size > 3 cm, and repeated ablation of same lesion were independent risk factors associated with local recurrence. The 5-year overall survival (OS) rates were 59.5%. Age < 36 years, HCC family history, baseline hepatitis B virus DNA >10⁶ copies/ml, and three HCC lesions were independently and significantly negative predictors to the post-cryoablation OS.

Conclusions

Percutaneous cryoablation is an effective therapy for patients with HCC within Milan criteria, with comparable efficacy, safety and long-term survival to the reported outcomes of radiofrequency ablation.