Efficacy of a Surgical Cardiac Ablation Clamp using Nanosecond Pulsed Electric Fields: An Acute Porcine Model.

OBJECTIVE: This study examined the effectiveness of a recently developed non-thermal technology, nanosecond pulse field ablation (nsPFA), for surgical ablation of the atria in a beating heart porcine model. METHODS: Six pigs underwent sternotomy and ablation using an nsPFA parallel clamp. The ablation electrodes (53 mm long) were embedded in the jaws of the clamp. Nine lesions per pig were created in locations chosen to be representative of the Cox-Maze procedure. Four lesions were intended to electrically isolate parts of the atrium: the right atrial appendage, left atrial appendage, right pulmonary veins, and left pulmonary veins. For these lesions, exit block testing was performed both after ablation and before euthanasia; the time between the two tests was 3.3±0.5 hours (range 2 to 4 hours). Using purse string sutures, five more lesions were created up to the superior vena cava, down to the inferior vena cava, across the right atrial free wall, and at two distinct locations on the left atrial free wall. The clamp delivered a train of nanosecond duration pulses, with a total duration of 2.5 s, independent of tissue thickness. The heart tissue was stained with 1% triphenyltetrazolium chloride (TTC) after a dwelling period of two hours. Subsequently, each lesion was cross sectioned at 5 mm intervals to assess the ablation depth and transmurality. In some sections, transmurality could not be established on the basis of TTC staining alone; for these lesions, Gomori-trichrome stains were used, and the histological sections were evaluated for transmurality. RESULTS: The ablation time was 2.5 seconds per lesion, for a total of only 22.5 seconds ablation time to create 9 lesions. A total of 53 lesions were created, resulting in 388 separate histological sections. Transmurality was established in 386 sections (99.5%). Mean tissue thickness was 3.1±1.5 mm (range of 0.2 mm to 8.6 mm). Exit block was confirmed in 23 of the 24 lesions (96%) post-ablation and 23/24 (96%) pre-euthanasia. Over the course of the procedure, neither pulse-induced arrhythmias nor any other complications were noted. CONCLUSIONS: The novel nsPFA clamp device was effective in creating acute conduction block and transmural lesions in both the right and left atria in an acute porcine model. This non-thermal energy source has great potential to both shorten procedural time and enable effective ablation in the beating heart.

Optical Coherence Tomography Angiography of Diabetic Retinopathy in Human Subjects.

BACKGROUND AND OBJECTIVE: Optical coherence tomography angiography (OCTA) is a novel, non-invasive OCT technique capable of imaging the retinal vasculature. This study aims to evaluate the retinal microvasculature in diabetic human subjects with OCTA and assess potential clinical applications. PATIENTS AND METHODS: Cross-sectional study of 33 subjects with diabetic retinopathy. OCTA was performed on 3 mm × 3 mm sections using a swept-source OCTA prototype and a phase- and intensity-based contrasting algorithm. OCT angiograms were studied with corresponding clinical examination and fluorescein angiograms, when available, to assess accuracy and clinical utility. RESULTS: OCTA was able to demonstrate most clinically relevant vascular changes in subjects with diabetic retinopathy, including microaneurysms, impaired vascular perfusion, some forms of intraretinal fluid, vascular loops, intraretinal microvascular abnormalities, neovascularization, and cotton-wool spots that were largely consistent with fluorescein angiography. CONCLUSION: OCTA generates high-resolution angiograms that illustrate many of the clinically relevant findings in diabetic retinopathy and offers a novel complement or alternative to fluorescein angiography. Although currently an investigational technique, OCTA in combination with standard OCT imaging is at least as good as fluorescein angiography in the evaluation of the macular complications of diabetic retinopathy.

MULTIMODAL IMAGING OF GEOGRAPHIC AREAS OF RETINAL DARKENING.

PURPOSE: To describe the clinical and multimodal imaging characteristics of a patient with unilateral asymptomatic dark retinal lesions corresponding to ellipsoid zone hyporeflectivity on optical coherence tomography (OCT). METHODS: The authors report a case of a 35-year-old man with HIV who presents with asymptomatic dark geographic retinal lesions corresponding to ellipsoid zone hyporeflectivity on OCT. Multimodal imaging techniques, including fundus color and widefield photographs, autofluorescence, spectral domain OCT (Spectralis, Heidelberg, Germany), prototype spectral domain OCT (Carl Zeiss Meditec, Dublin, CA) with OCT angiography, and en face images, were performed to evaluate and characterize the morphology of these lesions. RESULTS: Clinical examination and multimodal imaging reveal geographic darkening of the retina. Optical coherence tomography conveys hyporeflectivity of the ellipsoid zone band, which occurs abruptly and is present only in the areas of geographic retinal darkening. Optical coherence tomographic angiography shows a qualitatively similar appearance of the vasculature from the superficial retina through the avascular retina and the choriocapillaris, on both sides of the demarcation of retinal darkening, and also as compared to the unaffected eye. En face images from spectral domain OCT reveal an abrupt darkening of the tissue that localizes and is limited to the ellipsoid zone, with similar topographic appearance across the demarcation line. CONCLUSION: Geographic areas of darkening with photoreceptor hyporeflectivity have been described previously as "dark without pressure." In this case, the authors demonstrate photoreceptor hyporeflectivity that localizes to the clinically darkened areas, without topographic qualitative differences on en face spectral domain OCT images. The authors term these dark areas as geographic areas of retinal darkening because of ellipsoid nonreflectivity (GARDEN) spots.

OCT angiography in healthy human subjects.

BACKGROUND AND OBJECTIVE: To noninvasively evaluate the retinal microvasculature in healthy human subjects with optical coherence tomography angiography (OCTA). PATIENTS AND METHODS: Cross-sectional, observational study of five healthy subjects. OCTA was performed on 3 × 3 mm(2) sections centered on the fovea, nasal macula, and temporal macula. Retinal vasculature was assessed within three horizontal slabs consisting of the inner, middle, and outer retina. The vasculature within each retinal slab was reconstructed using phase-based and intensity contrast-based algorithms and visualized as separate en face images. RESULTS: OCTA in healthy subjects demonstrates capillary networks consistent with previous histological studies. No retinal vessels were found in the outer retina. OCT angiography of the inner and middle retinal layers showed region-specific vascular patterns that consistently corroborated qualitative findings from past histological studies. CONCLUSION: OCTA generates high-resolution, noninvasive angiograms qualitatively similar to conventional fluorescein angiography. OCTA may serve as a bridge to assess some features of the retinal microvasculature between conventionally performed angiograms.