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Radiofrequency ablation (RFA) is an important standard therapy for cardiac arrhythmias, but direct monitoring of tissue treatment is currently lacking. We demonstrate an RFA catheter integrated with polarization sensitive optical coherence tomography (PSOCT) for directly monitoring the RFA process in real time. The integrated RFA/OCT catheter was modified from a standard clinical RFA catheter and includes a miniature forward-viewing cone-scanning OCT probe. The PSOCT system was validated with a quarter-wave plate while the RFA function of the integrated catheter was validated by comparing lesion sizes with those made with an unmodified RFA catheter. Additionally, the integrated catheter guided catheter-tissue apposition and monitored RFA lesion formation in cardiac tissue in real time. The results show that catheter-tissue contact can be characterized by observing the features of the blood and tissue in the acquired OCT images and that RFA lesion formation can be confirmed by monitoring the change in phase retardance in the acquired PSOCT images. This system demonstrates the feasibility of an integrated RFA/OCT catheter to deliver RF energy and image the cardiac wall simultaneously and justifies further research into use of this technology to aid RFA therapy for cardiac arrhythmias.

Succinate accumulates during ischemia, and its oxidation at reperfusion drives injury. The mechanism of ischemic succinate accumulation is controversial and is proposed to involve reversal of mitochondrial complex II. Herein, using stable-isotope-resolved metabolomics, we demonstrate that complex II reversal is possible in hypoxic mitochondria but is not the primary succinate source in hypoxic cardiomyocytes or ischemic hearts. Rather, in these intact systems succinate primarily originates from canonical Krebs cycle activity, partly supported by aminotransferase anaplerosis and glycolysis from glycogen. Augmentation of canonical Krebs cycle activity with dimethyl-α-ketoglutarate both increases ischemic succinate accumulation and drives substrate-level phosphorylation by succinyl-CoA synthetase, improving ischemic energetics. Although two-thirds of ischemic succinate accumulation is extracellular, the remaining one-third is metabolized during early reperfusion, wherein acute complex II inhibition is protective. These results highlight a bifunctional role for succinate: its complex-II-independent accumulation being beneficial in ischemia and its complex-II-dependent oxidation being detrimental at reperfusion.

The relationship between changes in endocardial cushion and resultant congenital heart diseases (CHD) has yet to be established. It has been shown that increased regurgitant flow early in embryonic heart development leads to endocardial cushion defects, but it remains unclear how abnormal endocardial cushions during the looping stages might affect the fully septated heart. The goal of this study was to reproducibly alter blood flow in vivo and then quantify the resultant effects on morphology of endocardial cushions in the looping heart and on CHDs in the septated heart. Optical pacing was applied to create regurgitant flow in embryonic hearts, and optical coherence tomography (OCT) was utilized to quantify regurgitation and morphology. Embryonic quail hearts were optically paced at 3 Hz (180 bpm, well above intrinsic rate 60–110 bpm) at stage 13 of development (3–4 weeks human) for 5 min. Pacing fatigued the heart and led to at least 1 h of increased regurgitant flow. Resultant morphological changes were quantified with OCT imaging at stage 19 (cardiac looping—4–5 weeks human) or stage 35 (4 chambered heart—8 weeks human). All paced embryos imaged at stage 19 displayed structural changes in cardiac cushions. The amount of regurgitant flow immediately after pacing was inversely correlated with cardiac cushion size 24‐h post pacing (Pvalue < .01). The embryos with the most regurgitant flow and smallest cushions after pacing had a decreased survival rate at 8 days (P <.05), indicating that those most severe endocardial cushion defects were lethal. Of the embryos that survived to stage 35, 17/18 exhibited CHDs including valve defects, ventricular septal defects, hypoplastic ventricles, and common AV canal. The data illustrate a strong inverse relationship in which regurgitant flow precedes abnormal and smaller cardiac cushions, resulting in the development of CHDs.

Cardiac conduction maturation is an important and integral component of heart development. Optical mapping with voltage-sensitive dyes allows sensitive measurements of electrophysiological signals over the entire heart. However, accurate measurements of conduction velocity during early cardiac development is typically hindered by low signal-to-noise ratio (SNR) measurements of action potentials. Here, we present a novel image processing approach based on least squares optimizations, which enables high-resolution, low-noise conduction velocity mapping of smaller tubular hearts. First, the action potential trace measured at each pixel is fit to a curve consisting of two cumulative normal distribution functions. Then, the activation time at each pixel is determined based on the fit, and the spatial gradient of activation time is determined with a two-dimensional (2D) linear fit over a square-shaped window. The size of the window is adaptively enlarged until the gradients can be determined within a preset precision. Finally, the conduction velocity is calculated based on the activation time gradient, and further corrected for three-dimensional (3D) geometry that can be obtained by optical coherence tomography (OCT). We validated the approach using published activation potential traces based on computer simulations. We further validated the method by adding artificially generated noise to the signal to simulate various SNR conditions using a curved simulated image (digital phantom) that resembles a tubular heart. This method proved to be robust, even at very low SNR conditions (SNR = 2-5). We also established an empirical equation to estimate the maximum conduction velocity that can be accurately measured under different conditions (e.g. sampling rate, SNR, and pixel size). Finally, we demonstrated high-resolution conduction velocity maps of the quail embryonic heart at a looping stage of development.

Background:Hypertension (HT) is highly prevalent and associated with significant mortality and morbidity among older individuals. Aging is associated with structural and functional remodeling of the vasculature, similar to blood vessel alterations observed in HT. We previously demonstrated that young adult global Rsk2KO mice had more dilated mesenteric arteries (MAs), with reduced vessel tone, stiffness and RLC20phosphorylation, and significantly lower basal blood pressure compared to WT. However, it is unknown whether RSK2 plays a role in age-related HT.Hypothesis:Loss of RSK2 signaling in aged mice inhibits age-related- and L-NAME-induced HT, arterial stiffness, and vascular remodeling.Methods:Systolic blood pressure (SBP) measurements of >24-month-old global Rsk2KO and WT males were performed daily for 2 weeks after 2 weeks of daily training using tail cuff manometry. Baseline echocardiographic (echo) parameters were measured. N(G)-Nitro-L-arginine-methyl ester (L-NAME) was administered (20 mg/kg/day) via drinking water to induce HT. Pressure myography studies assessed vascular reactivity and arterial stiffness in MAs isolated from Rsk2KO and WT mice. Aorta and MAs were sectioned and stained to examine structural changes.Results:WT mice had a significantly higher mortality rate (63.6%) compared to Rsk2KO (12.5%). Baseline SBP was also significantly higher in WT compared to KOs (123±10 vs. 99±12 mmHg, p < 0.001, n = 9/7). L-NAME elevated SBP in WT but not in KO mice (137±2 vs. 97±8 mmHg, p < 0.00001, n = 4/7). Although there were no differences in echo parameters, we observed a negative correlation between ejection fraction (EF) and SBP in WT (-0.94 %/mmHg, p = 0.046, R2= 0.59, n = 6), but not in Rsk2KO mice (p = 0.15, n = 7). Functional and histological studies in aged KO mice are ongoing to examine age-related changes in vascular reactivity and remodeling.Conclusion:Loss of RSK2 reduces BP levels in aged mice akin to young adult mice. Additionally, the hypertensive effects of L-NAME are absent in aged Rsk2KO mice. Aged Rsk2KO mice appear to be protected from cardiovascular effects associated with age-related HT. Therapeutic targeting of RSK2 could prove beneficial for reducing risk of cardiovascular diseases associated with HT in the elderly.

Background:Smooth muscle (SM) contraction is triggered by Ca2+/calmodulin-dependent myosin light chain kinase (MLCK), which phosphorylates the regulatory light chain of myosin (RLC20). However, additional regulatory mechanisms exist. We found that global Rsk2KO mice had more dilated mesenteric arteries (MAs) with reduced myogenic tone and RLC20phosphorylation, and significantly lower blood pressure. Furthermore, RSK2-dependent activation of the Na+/H+exchanger resulted in an increase in pHiand increased Ca2+itransients. However, it is unclear whether our observations were due to developmental abnormalities observed in Rsk2global KO mice.Hypothesis:RSK2 signaling in SM is a significant regulator of myogenic tone, arterial stiffness, and Ca2+signaling.Methods:To study the role of RSK2 signaling in vascular tone, we generated inducible SM-specific RSK2 KO mice. Detection of total and phospho proteins were determined by western blot. Pressure myography studies assessed vascular reactivity in 4th- and 5th-order MAs isolated from MYH11-Cre+Rsk2fl/fl(RSK2SM-/-) and MYH11-Cre-Rsk2fl/fl(RSK2SM+/+) mice. We examined SM-specific Ca2+events in pressurized MAs by confocal fluorescent microscopy.Results:Western blot confirms knock down of RSK2 expression (~70%) in MAs and aorta. Intraluminal pressure-induced constriction of MAs is attenuated in RSK2SM-/-. RSK2SM-/-MAs display a delay in development of myogenic tone at 40 mmHg and decreased vascular stiffness, compared to RSK2SM+/+. Vasodilatory responses to Spermine NONOate (1-100 μM) in preconstricted (L-NNA; 10 μM) RSK2SM-/-vessels were enhanced. RSK2SM-/-MAs display fewer Ca2+events (97±19.6; n = 4) than RSK2SM+/+(400±24.5; n = 4) at 80 mmHg (p= 0.0001). Additionally, Ca2+events are slower and longer-lasting in the RSK2SM-/-. Decreased levels of p-RLC20are observed at 40 mmHg, but not 80 mmHg in RSK2SM-/-vs. RSK2SM+/+mice, consistent with impeding tone development.Conclusion:RSK2 signaling contributes to myogenic tone and vessel stiffness by regulating sensitivity to NO, increasing Ca2+events, and RLC20activity. RSK2 signaling pathway is a potential therapeutic target for hypertension.

An all-fiber optic catheter-based polarization-sensitive optical coherence tomography system is demonstrated. A novel multiplexing method was used to illuminate the sample, splitting the light from a 58.5 kHz Fourier-domain mode-locked laser such that two different polarization states, alternated in time, are generated by two semiconductor optical amplifiers. A 2.3 mm forward-view cone-scanning catheter probe was designed, fabricated, and used to acquire sample scattering intensity and phase retardation images. The system was first verified with a quarter-wave plate and then by obtaining intensity and phase retardation images of high-birefringence plastic, human skin in vivo, and untreated and thermally ablated porcine myocardium ex vivo. The system can potentially in vivo image of the cardiac wall to aid radio-frequency ablation therapy for cardiac arrhythmias.

Cardiac electrophysiology plays a critical role in the development and function of the heart. Studies of early embryonic electrical activity have lacked a viable point stimulation technique to pace in vitro samples. Here, optical pacing by high-precision infrared stimulation is used to pace excised embryonic hearts, allowing electrophysiological parameters to be quantified during pacing at varying rates with optical mapping. Combined optical pacing and optical mapping enables electrophysiological studies in embryos under more physiological conditions and at varying heart rates, allowing detection of abnormal conduction and comparisons between normal and pathological electrical activity during development in various models.

Cardiac remodelling following myocardial infarction (MI) is a complex, dynamic process. There have been few longitudinal studies of these changes.

Background: Collectrin (Tmem27), an ACE2 homologue, is a chaperone of amino acid transporters in the kidney and endothelium. Global collectrin knockout (KO) mice have hypertension, endothelial dysfunction, exaggerated salt sensitivity, and diminished renal blood flow. This phenotype is associated with altered nitric oxide and superoxide balance, and increased proximal tubule NHE3 expression. Collectrin is located on the X chromosome where genome wide association population studies have largely been excluded. Methods: We generated proximal tubule specific collectrin KO (PT KO) mice to determine the precise contribution of proximal tubule collectrin in blood pressure homeostasis. We also examined the association of human TMEM27 single nucleotide polymorphisms (SNPs) with blood pressure traits in 11,926 HCHS/SOL Hispanic/Latino participants, Results: PT KO mice exhibited hypertension, and this was associated with increased baseline NHE3 expression and diminished lithium excretion. However, PT KO mice did not display exaggerated salt sensitivity nor reduction in renal blood flow, compared to control mice. Furthermore, PT KO mice exhibited enhanced endothelium-mediated dilation, suggesting a compensatory response to systemic hypertension induced by deficiency of collectrin in the PT. In HCHS/SOL participants, we observed sex-specific SNP associations with diastolic blood pressure. Conclusion: Loss of collectrin in the PT is sufficient to induce hypertension, at least in part, through activation of NHE3. Importantly, our model supports the notion that altered renal blood flow may be a determining factor for salt sensitivity. Further studies are needed to investigate the role of the TMEM27 locus on BP and salt-sensitivity in humans.