Carbon nanotube facilitation of myocardial ablation with radiofrequency energy

Ablation of cells in mice using antibody-functionalized multiwalled carbon nanotubes (Ab-MWCNTs) in combination with microwaves

This is a proof-of-principle study on the combination of microwaves and multiwalled carbon nanotubes to induce in vivo, localized hyperthermic ablation of cells as a potential methodology for the treatment of localized tumors. Compared to conventional methods, the proposed approach can create higher temperatures in a rapid and localized fashion, under low radiation levels, eliminating some of the unwanted side effects. Following successful ablation of cancer cells in cell culture and zebrafish tumor-xenograft models, it is hypothesized that a cancer treatment can be developed using safe microwave irradiation for selective ablation of tumor cells in vivo using carbon nanotube-Antibody (CNT-Ab) conjugates as a targeting agent. In this study, mice were used as an animal model for the optimization of the proposed microwave treatment strategy. The safe dose of CNT-Ab and microwave radiation levels for mice were determined. Further, CNT-Ab distribution and toxicology in mice were qualitatively determined for a time span of two weeks following microwave hyperthermia. The results indicate no toxicity associated with the CNT-Ab in the absence of microwaves. CNTs are only found in the proximity of the site of injection and have been shown to effectively cause hyperthermia induced necrosis upon exposure to microwaves with no noticeable damage to other tissues that are not in direct contact with the CNT-Ab. To understand the cellular immune response towards CNT-Abs, transgenic zebrafish with fluorescently labeled macrophages and neutrophils were used to assay for their ability to phagocytize CNT-Ab. Our results indicate that macrophages and neutrophils were able to actively phagocytose CNT-Abs shortly after injection. Taken together, this is the first study to show that CNTs can be used in combination with microwaves to cause targeted ablation of cells in mice without any side effects, which would be ideal for cancer therapies.

Tailor-Made Nanomaterials for Diagnosis and Therapy of Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest cancers worldwide due to its aggressiveness and the challenge to early diagnosis and treatment. In recent decades, nanomaterials have received increasing attention for diagnosis and therapy of PDAC. However, these designs are mainly focused on the macroscopic tumor therapeutic effect, while the crucial nano-bio interactions in the heterogeneous microenvironment of PDAC remain poorly understood. As a result, the majority of potent nanomedicines show limited performance in ameliorating PDAC in clinical translation. Therefore, exploiting the unique nature of the PDAC by detecting potential biomarkers together with a deep understanding of nano-bio interactions that occur in the tumor microenvironment is pivotal to the design of PDAC-tailored effective nanomedicine. This review will introduce tailor-made nanomaterials-enabled laboratory tests and advanced noninvasive imaging technologies for early and accurate diagnosis of PDAC. Moreover, the fabrication of a myriad of tailor-made nanomaterials for various PDAC therapeutic modalities will be reviewed. Furthermore, much preferred theranostic multifunctional nanomaterials for imaging-guided therapies of PDAC will be elaborated. Lastly, the prospects of these nanomaterials in terms of clinical translation and potential breakthroughs will be briefly discussed.

Continuous ablation improves lesion maturation compared with intermittent ablation strategies

BACKGROUND

Interrupted ablation is increasingly proposed as part of high-power short-duration radiofrequency ablation (RFA) strategies and may also result from loss of contact from respiratory patterns or cardiac motion. To study the extent that ablation interruption affects lesions.

METHODS

In ex vivo and in vivo experiments, lesion characteristics and tissue temperatures were compared between continuous (group 1) and interrupted (groups 2 and 3) RFA with equal total ablation duration and contact force. Extended duration ablation lesions were also characterized from 1 to 5 minutes.

RESULTS

In the ex vivo study, continuous RFA (group 1) produced larger total lesion volumes compared with each interrupted ablation lesion group (273.8 ± 36.5 vs 205.1 ± 34.2 vs 174.3 ± 32.3 mm³ , all P < .001). Peak temperatures for group 1 were higher at 3 and 5 mm than groups 2 and 3. In vivo, continuous ablation resulted in larger lesions, greater lesion depths, and higher tissue temperatures. Longer ablation durations created larger lesion volumes and increased lesion depths. However, after 3 minutes of ablation, the rate of lesion volume, and depth formation decreased.

CONCLUSIONS

Continuous RFA delivery resulted in larger and deeper lesions with higher tissue temperatures compared with interrupted ablation. This study may have implications for high-power short duration ablation strategies, motivates strategies to reduce variations in ablation delivery, and provides an upper limit for ablation duration beyond which power delivery has diminishing returns.

Impact of epicardial adipose tissue and catheter ablation strategy on biophysical parameters and ablation lesion characteristics

BACKGROUND

Epicardial adipose (EA) tissue may limit effective radiofrequency ablation (RFA).

OBJECTIVES

We sought to evaluate the lesion formation of different ablation strategies on ventricular myocardium with overlying EA.

METHODS

Bovine myocardium with EA was placed in a circulating saline bath in an ex vivo model. Open-irrigated (OI) RFA was performed, parallel to the myocardium, over fat at 50 W for variable RF durations, variable contact force, catheter configurations (unipolar RF vs bipolar RF), and catheter irrigants (normal saline vs half-normal saline). Ablation was also performed with a needle-tipped ablation catheter (NTAC), perpendicular to the myocardium.

RESULTS

Increasingly thick EA attenuated lesion size regardless of ablation strategy. RF applied with longer durations and increasing CF produced larger lesion volumes and deeper lesions with ablation over EA more than 3 mm but was unable to produce measurable lesions when EA less than 3 mm. Similarly, ablation with half normal saline irrigant created slightly deeper lesions than bipolar RF and unipolar RF with normal saline as EA thickness increased, but was unable to produce measurable lesions when EA more than 3 mm. Of all ablation strategies, only NTAC produced effective lesion volumes when ablating over thick (>3 mm) EA.

CONCLUSIONS

While EA attenuates lesion depth and size, relatively larger, and deeper lesions can be achieved with longer RFA duration, higher CF, half normal saline irrigant, and, to a greater extent, by utilizing bipolar RF or NTAC, but only over thin adipose (<3 mm). Of those catheters/strategies tested, only NTAC was able to effectively deliver RF over thick (>3 mm) EA with this model.

Longer Duration Versus Increasing Power During Radiofrequency Ablation Yields Different Ablation Lesion Characteristics

OBJECTIVES

The goal of this study was to characterize differences in ablation lesions with varying radiofrequency ablation (RFA) power and time.

BACKGROUND

Increasing power delivery or prolonging duration can improve the efficacy of RFA. However, the extent to which ablation lesion characteristics change, based on varying degrees of power and duration, is unknown.

METHODS

An ex vivo model consisting of viable bovine myocardium in a circulating warmed saline bath was used. An open irrigated RFA catheter was positioned with 10 g of force in the perpendicular position, and RFA was delivered at powers of 20, 30, 40, and 50 W and for various time intervals, up to a total of 90 s, at each power. An in vivo porcine thigh preparation model was used to perform RFA at 50 W for 5 s and 20 W for 30 s. Lesion volumes were analyzed.

RESULTS

Greater power delivery and longer radiofrequency time increased ablation lesion size. However, compared with a proportional change in radiofrequency duration, the same proportional increase in power produced a significantly larger lesion volume (p < 0.01). For in vivo models, 50 W/5 s ablation lesions yielded similar volumes but significantly less depth than 20 W/30 s ablation lesions. Peak temperatures were not significantly different at 2 and 4 mm with 50 W/5 s versus 20 W/30 s.

CONCLUSIONS

Varying power and duration will confer different ablation lesion characteristics that can be tailored according to the substrate/anatomy that is being ablated. This phenomenon has important implications during catheter ablation.

Radiofrequency Ablation Using an Open Irrigated Electrode Cooled With Half-Normal Saline

OBJECTIVES

This study evaluated the use of half-normal saline (HNS) as the radiofrequency ablation (RFA) cooling irrigant.

BACKGROUND

Some instances of ventricular arrhythmia may originate deep within myocardium and can be refractory to standard ablation using open irrigated RFA. Recent data suggest that deeper ablation lesions can be created by decreasing the irrigant ionic concentration delivered through open irrigated RFA than by using normal saline (NS).

METHODS

Bovine myocardium was placed in a circulating saline bath. Two RFA catheters were oriented across from each other, with myocardium in between. Sequential unipolar HNS-irrigated RFA was performed and compared to bipolar ablation by using NS or HNS. Unipolar HNS ablation of the ventricles in a porcine model was performed and compared to ablation using NS.

RESULTS

Sequential ex vivo unipolar RFA with HNS produced larger lesions than sequential unipolar RFA with NS and produced lesions of similar size to those created with bipolar RFA using NS. Ex vivo bipolar RFA using HNS created the largest lesions. In vivo unipolar HNS ablation in porcine endocardium created larger lesion volumes, 152.9 ± 29.2 μl, compared to 94.7 ± 33.4 μl for unipolar ablation using NS.

CONCLUSIONS

By decreasing ionic concentration and charge density in RFA using HNS instead of NS irrigant, larger ablation lesions can be created and are similar in size to lesions created using bipolar ablation. This may be a useful ablation strategy for deep myocardial circuits refractory to standard ablation. Further studies are needed to evaluate this novel RFA strategy.

A Strategy for Precise Treatment of Cardiac Malignant Neoplasms

The prevalence of cardiac malignant neoplasms in the general population has been shown to be significant higher than what was previously estimated, yet their treatment has remained difficult and effective therapies are lacking. In the current study, we developed a novel thermotherapy in which PEG-functionalized carbon nanotubes were injected into the tumor regions to assist in the targeted delivery of infrared radiation energy with minimal hyperthermic damage to the surrounding normal tissues. In a mouse model of cardiac malignant neoplasms, the injected carbon nanotubes could rapidly induce coagulative necrosis of tumor tissues when exposed to infrared irradiation. In accordance, the treatment was also found to result in a restoration of heart functions and a concomitant increase of survival rate in mice. Taken together, our carbon nanotube-based thermotherapy successfully addressed the difficulty facing conventional laser ablation methods with regard to off-target thermal injury, and could pave the way for the development of more effective therapies against cardiac malignant neoplasms.

Protection of Critical Structures During Radiofrequency Ablation of Adjacent Myocardial Tissue Using Catheter Tips Partially Insulated With Thermally Conductive Material

OBJECTIVES

This study sought to determine whether partially insulated focused ablation (PIFA) catheters can minimize risk of injury to critical structures, such as the phrenic nerve and atrioventricular (AV) node, during ablation of adjacent myocardial tissue.

BACKGROUND

PIFA catheters using thermally conductive materials may have differential radiofrequency (RF) heating properties allowing for tailored RF application with more precision.

METHODS

Open-irrigated, 4- and 8-mm RF ablation catheter tips were insulated partially by coating one-half of their surfaces with a layer of vinyl, silicone, vinyl-silicone, polyurethane, or a composite of aluminum oxide/boron nitride (AOBN). These coated catheters or corresponding noninsulated catheters were positioned with 10 g of force on viable bovine myocardial tissue during RF application in an ex vivo setup. Tip temperatures, power, and lesion volumes were compared. The most effective coating, AOBN, was modified further by adding fenestrations to aid in passive cooling. PIFA catheters with fenestrated AOBN coating were then tested in an in vivo porcine model to target myocardial tissue adjacent to the AV node and the phrenic nerve.

RESULTS

PIFA catheters all demonstrated higher tip temperatures, although silicone- and AOBN-catheters demonstrated this to a lesser degree. Significant differences in lesion volumes and temperature-limited powers were noted between control, silicone, and AOBN tips. Steam pops were significantly higher for silicone but not AOBN. In contrast with non-PIFA catheters, injuries to the phrenic nerve and AV node during in vivo ablations with AOBN insulation positioned over these structures were reduced significantly.

CONCLUSIONS

RF ablation using catheter tips partially coated with a thermally conductive insulation material such as AOBN results in larger ablation lesion volumes without temperature limitations. Partial insulation of the catheter tip will protect adjacent critical structures during RF ablation.

Bio-effect of nanoparticles in the cardiovascular system

Nanoparticles (NPs; < 100 nm) are increasingly being applied in various fields due to their unique physicochemical properties. The increase in human exposure to NPs has raised concerns regarding their health and safety profiles. The potential correlation between NP exposure and several cardiovascular (CV) events has been demonstrated. The aim of this review is to provide a comprehensive evaluation of the current knowledge regarding the bio-toxic impacts of titanium oxide, silver, silica, carbon black, carbon nanotube, and zinc oxide NPs exposure on the CV system in terms of in vivo and in vitro experiments, which is not fully understood presently. Moreover, the potential toxic mechanisms of NPs in the CV system that are still being questioned are elaborately discussed, and the underlying capacity of NPs used in medicine for CV events are summarized. It will be an important instrument to extrapolate relevant data for human CV risk evaluation and management. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2881-2897, 2016.

Mapping and ablation procedures for the treatment of ventricular tachycardia

INTRODUCTION

Ventricular tachycardia (VT) may occur in the presence or absence of structural heart disease. Given that the management of VT hinges on the presence of symptoms and risk of sudden cardiac death (SCD), the main treatment goals are elimination of symptoms (including frequent implantable cardioverter defibrillator [ICD] therapies) and prevention of SCD. Unfortunately, medical management is suboptimal in a significant proportion of patients. As such, ablative therapy plays a prominent role in the treatment of ventricular tachycardia.

AREAS COVERED

In this review, we will discuss various VT disorders that are encountered in patients with and without structural heart disease. Further, we will highlight salient features regarding mapping and ablation of the various VT syndromes. Finally, we will discuss what lies on the horizon for VT ablation. Expert commentary: Meticulous mapping should aim to find the region that is most likely to be successful and least likely to result in a complication. Although recognition of the various mechanisms of VT, familiarity with different methods to mapping and ablation, and awareness of potential limitations of current approaches is critical, a thorough understanding of the fundamental principles and nuances of each facet within EP is required to ensure optimal outcomes for our patients.

Biomimetic Polymers for Cardiac Tissue Engineering

Heart failure is a morbid disorder characterized by progressive cardiomyocyte (CM) dysfunction and death. Interest in cell-based therapies is growing, but sustainability of injected CMs remains a challenge. To mitigate this, we developed an injectable biomimetic Reverse Thermal Gel (RTG) specifically engineered to support long-term CM survival. This RTG biopolymer provided a solution-based delivery vehicle of CMs, which transitioned to a gel-based matrix shortly after reaching body temperature. In this study we tested the suitability of this biopolymer to sustain CM viability. The RTG was biomolecule-functionalized with poly-l-lysine or laminin. Neonatal rat ventricular myocytes (NRVM) and adult rat ventricular myocytes (ARVM) were cultured in plain-RTG and biomolecule-functionalized-RTG both under 3-dimensional (3D) conditions. Traditional 2D biomolecule-coated dishes were used as controls. We found that the RTG-lysine stimulated NRVM to spread and form heart-like functional syncytia. Regarding cell contraction, in both RTG and RTG-lysine, beating cells were recorded after 21 days. Additionally, more than 50% (p value < 0.05; n = 5) viable ARVMs, characterized by a well-defined cardiac phenotype represented by sarcomeric cross-striations, were found in the RTG-laminin after 8 days. These results exhibit the tremendous potential of a minimally invasive CM transplantation through our designed RTG-cell therapy platform.

Enhanced Radiofrequency Ablation With Magnetically Directed Metallic Nanoparticles

Background—

Remote heating of metal located near a radiofrequency ablation source has been previously demonstrated. Therefore, ablation of cardiac tissue treated with metallic nanoparticles may improve local radiofrequency heating and lead to larger ablation lesions. We sought to evaluate the effect of magnetic nanoparticles on tissue sensitivity to radiofrequency energy.

Methods and Results—

Ablation was performed using an ablation catheter positioned with 10 g of force over prepared ex vivo specimens. Tissue temperatures were measured and lesion volumes were acquired. An in vivo porcine thigh model was used to study systemically delivered magnetically guided iron oxide (FeO) nanoparticles during radiofrequency application. Magnetic resonance imaging and histological staining of ablated tissue were subsequently performed as a part of ablation lesion analysis. Ablation of ex vivo myocardial tissue treated with metallic nanoparticles resulted in significantly larger lesions with greater impedance changes and evidence of increased thermal conductivity within the tissue. Magnet-guided localization of FeO nanoparticles within porcine thigh preps was demonstrated by magnetic resonance imaging and iron staining. Irrigated ablation in the regions with greater FeO, after FeO infusion and magnetic guidance, created larger lesions without a greater incidence of steam pops.

Conclusions—

Metal nanoparticle infiltration resulted in significantly larger ablation lesions with altered electric and thermal conductivity. In vivo magnetic guidance of FeO nanoparticles allowed for facilitated radiofrequency ablation without direct infiltration into the targeted tissue. Further research is needed to assess the clinical applicability of this ablation strategy using metallic nanoparticles for the treatment of cardiac arrhythmias.