Heavy Ion Irradiation Reduces Vulnerability to Atrial Tachyarrhythmias　- Gap Junction and Sympathetic Neural Remodeling.

BACKGROUND: Low-invasive stereotactic body radiation therapy is a novel anti-arrhythmic strategy. The mechanisms underlying its effects against ventricular tachycardia/fibrillation (VT/VF) are gradually becoming clear, whereas those underlying atrial tachycardia/fibrillation (AT/AF) remain unknown. This study investigated the effects of carbon ion beam on gap junction expression and sympathetic innervation.Methods and Results: Atrial and ventricular tachyarrhythmia models was established in 26 hypercholesterolemic (HC) 3-year-old New Zealand white rabbits; 12 rabbits were irradiated with a single 15-Gy carbon ion beam (targeted heavy ion irradiation [THIR]) and 14 were not (HC group). Eight 3-month-old rabbits (Young) were used as a reference group. In vivo induction frequencies in the Young, HC, and HC+THIR groups were 0%, 9.9%, and 1.2%, respectively, for AT/AF and 0%, 7.8%, and 1.2%, respectively, for VT/VF (P<0.01). The conduction velocity of the atria and ventricles on optical mapping was significantly reduced in the HC group; this was reversed in the HC+THIR group. Connexin-40 immunolabelling in the atria was 66.1-78.7% lower in the HC than Young group; this downregulation was less pronounced in the HC+THIR group (by 23.1-44.4%; P<0.01). Similar results were obtained for ventricular connexin-43. Sympathetic nerve densities in the atria and ventricles increased by 41.9-65.3% in the HC vs. Young group; this increase was reversed in the HC+THIR group. CONCLUSIONS: Heavy ion radiation reduced vulnerability to AT/AF and VT/VF in HC elderly rabbits and improved cardiac conductivity. The results suggest involvement of connexin-40/43 upregulation and suppression of sympathetic nerve sprouting.

Validation of Intraoperative Catheter Phase Mapping Using a Simultaneous Optical Measurement System in Rabbit Ventricular Myocardium.

BACKGROUND: Recently, an interoperative catheter electrode mapping system, termed ExTRa Mapping (EXT), was developed for precise diagnosis and effective treatment of non-paroxysmal atrial fibrillations (non-PAF). However, the mapping accuracy of EXT is still unclear.Methods and Results:In this study, the reliability of the EXT in comparison with that of high-resolution optical membrane potential mapping was compared. Spiral wave re-entries (SWRs) were induced in the excised rabbit hearts (n=8, 42 episodes). Electrical signals were measured by electrodes on a transparent silicone plate, with the same arrangement as in the clinical catheter, and fluorescence signals were recorded simultaneously across the plate. Based on the phase maps derived by EXT, activation patterns (one-directed propagations: 26, rotational activities: 16) were identified correctly with 95% accuracy (40/42), and the correlation coefficient of the ratio of the non-passive period was 0.95. In the rotational episodes (15), the mean position error of the centers of gravity of the SWR trajectory (2,000 ms) was 2.0 mm. For the one-directional episodes (25), the correlation coefficient of the directions of one-way propagation was 0.99. CONCLUSIONS: The phase map sequence by EXT is consistent with that by the analyses of high-resolution optical mapping. EXT is reliable for analyzing the activation pattern in the region of interest.

Interaction of phase singularities on the spiral wave tail: reconsideration of capturing the excitable gap.

The action mechanism of stimulation toward spiral waves (SWs) owing to the complex excitation patterns that occur just after point stimulation has not yet been experimentally clarified. This study sought to test our hypothesis that the effect of capturing excitable gap of SWs by stimulation can also be explained as the interaction of original phase singularity (PS) and PSs induced by the stimulation on the wave tail (WT) of the original SW. Phase variance analysis was used to quantitatively analyze the postshock PS trajectories. In a two-dimensional subepicardial layer of Langendorff-perfused rabbit hearts, optical mapping was used to record the excitation pattern during stimulation. After a SW was induced by S1-S2 shock, single biphasic point stimulation S3 was applied. In 70 of the S1-S2-S3 stimulation episodes applied on 6 hearts, the original PS was clearly observed just before the S3 point stimulation in 37 episodes. Pairwise PSs were newly induced by the S3 in 20 episodes. The original PS collided with the newly induced PSs in 16 episodes; otherwise, they did not interact with the original PS. SW shift occurred most efficiently when the S3 shock was applied at the relative refractory period, and PS shifted in the direction of the WT. In conclusion, quantitative tracking of PS clarified that stimulation in desirable conditions induces pairwise PSs on WT and that the collision of PSs causes SW shift along the WT. The results of this study indicate the importance of the interaction of shock-induced excitation with the WT for effective stimulation. NEW & NOTEWORTHY The quantitative analysis of spiral wave dynamics during stimulation clarified the action mechanism of capturing the excitable gap, i.e., the induction of pairwise phase singularities on the wave tail and spiral wave shift along the wave tail as a result of these interactions. The importance of the wave tail for effective stimulation was revealed.

Ranolazine Facilitates Termination of Ventricular Tachyarrhythmia Associated With Acute Myocardial Ischemia Through Suppression of Late INa-Mediated Focal Activity.

BACKGROUND: Ventricular tachycardia/fibrillation (VT/VF) associated with acute myocardial ischemia is the most common cause of sudden cardiac death, but its underlying mechanisms are incompletely understood. It is hypothesized that late Na+current (INa) contributes to arrhythmogenic activity in ischemic myocardium.Methods and Results:Langendorff-perfused rabbit hearts with regional ischemia in ventricles were optically mapped. Perfusion with ranolazine (10 µmol/L), a selective inhibitor of lateINa, significantly reduced excitation frequency and facilitated termination of VT/VF induced after occlusion of the left main coronary trunk. The activation pattern during ischemic VT/VF was characterized by breakthrough-type excitations (BEs) from multiple origins, predominantly in the ischemic border zone (BZ) and occasional short-lived rotors. Ranolazine perfusion significantly reduced the incidence of BEs in the BZ. Rotors tended to decrease with progression of ischemia and disappeared after ranolazine perfusion. During constant pacing, ranolazine attenuated ischemia-induced shortening of action potentials in the BZ without affecting conduction velocity, probably due toIKrinhibition. In intact hearts without coronary occlusion, ranolazine (10 µmol/L) terminated aconitine-induced VT by inhibiting focal arrhythmogenic activity in the injection site. CONCLUSIONS: LateINa-mediated focal arrhythmogenic activity plays important roles in the maintenance of ischemic VT/VF in isolated rabbit hearts. Suppression of lateINaby ranolazine may be a promising therapeutic strategy to reduce arrhythmic death during the acute phase of myocardial infarction.

Partial IK1 blockade destabilizes spiral wave rotation center without inducing wave breakup and facilitates termination of reentrant arrhythmias in ventricles.

It has been reported that blockade of the inward rectifier K(+) current (IK1) facilitates termination of ventricular fibrillation. We hypothesized that partial IK1 blockade destabilizes spiral wave (SW) re-entry, leading to its termination. Optical action potential (AP) signals were recorded from left ventricles of Langendorff-perfused rabbit hearts with endocardial cryoablation. The dynamics of SW re-entry were analyzed during ventricular tachycardia (VT), induced by cross-field stimulation. Intercellular electrical coupling in the myocardial tissue was evaluated by the space constant. In separate experiments, AP recordings were made using the microelectrode technique from right ventricular papillary muscles of rabbit hearts. Ba(2+) (10-50 µM) caused a dose-dependent prolongation of VT cycle length and facilitated termination of VT in perfused hearts. Baseline VT was maintained by a stable rotor, where an SW rotated around an I-shaped functional block line (FBL). Ba(2+) at 10 µM prolonged I-shaped FBL and phase-singularity trajectory, whereas Ba(2+) at 50 µM transformed the SW rotation dynamics from a stable linear pattern to unstable circular/cycloidal meandering. The SW destabilization was not accompanied by SW breakup. Under constant pacing, Ba(2+) caused a dose-dependent prolongation of APs, and Ba(2+) at 50 µM decreased conduction velocity. In papillary muscles, Ba(2+) at 50 µM depolarized the resting membrane potential. The space constant was increased by 50 µM Ba(2+) Partial IK1 blockade destabilizes SW rotation dynamics through a combination of prolongation of the wave length, reduction of excitability, and enhancement of electrotonic interactions, which facilitates termination of ventricular tachyarrhythmias.

Mechanisms of torsades de pointes: an update.

Torsades de Pointes (TdP) refers to a polymorphic ventricular tachycardia (VT) with undulating QRS axis that occurs in long QT syndrome (LQTS), although the term has been used to describe polymorphic ventricular tachyarrhythmias in which QT intervals are not prolonged, such as short-coupled variant of TdP currently known as short-coupled ventricular fibrillation (VF) and Brugada syndrome. Extensive works on LQTS-related TdP over more than 50 years since it was first recognized by Dessertennes who coined the French term meaning "twisting of the points", have led to current understanding of the electrophysiological mechanism that TdP is initiated by triggered activity due to early afterdepolarization (EAD) and maintained by reentry within a substrate of inhomogeneous repolarization. While a recently emerging notion that steep voltage gradients rather than EADs are crucial to generate premature ventricular contractions provides additions to the initiation mode, the research to elucidate the maintenance mechanism hasn't made much progress. The reentrant activity that produces the specific form of VT is not well characterized. We have conducted optical mapping in a rabbit model of electrical storm by electrical remodeling (QT prolongation) due to chronic complete atrioventricular block and demonstrated that a tissue-island with prolonged refractoriness due to enhanced late Na+ current (INa-L) contributes to the generation of drifting rotors in a unique manner, which may explain the ECG characteristic of TdP. Moreover, we have proposed that the neural Na+ channel NaV1.8-mediated INa-L may be a new player to form the substrate for TdP. Here we discuss TdP mechanisms by comparing the findings in electrical storm rabbits with recently published studies by others in simulation models and human and animal models of LQTS.

Inhibition of intercellular coupling stabilizes spiral-wave reentry, whereas enhancement of the coupling destabilizes the reentry in favor of early termination.

Spiral-wave (SW) reentry is a major organizing principle of ventricular tachycardia/fibrillation (VT/VF). We tested a hypothesis that pharmacological modification of gap junction (GJ) conductance affects the stability of SW reentry in a two-dimensional (2D) epicardial ventricular muscle layer prepared by endocardial cryoablation of Langendorff-perfused rabbit hearts. Action potential signals were recorded and analyzed by high-resolution optical mapping. Carbenoxolone (CBX; 30 µM) and rotigaptide (RG, 0.1 µM) were used to inhibit and enhance GJ coupling, respectively. CBX decreased the space constant (λ) by 36%, whereas RG increased it by 22-24% (n = 5; P < 0.01). During centrifugal propagation, there was a linear relationship between the wavefront curvature (κ) and local conduction velocity (LCV): LCV = LCV(0) - D·κ (D, diffusion coefficient; LCV(0), LCV at κ = 0). CBX decreased LCV(0) and D by 27 ± 3 and 57 ± 3%, respectively (n = 5; P < 0.01). RG increased LCV(0) and D by 18 ± 3 and 54 ± 5%, respectively (n = 5, P < 0.01). The regression lines with and without RG crossed, resulting in a paradoxical decrease of LCV with RG at κ > ~60 cm(-1). SW reentry induced after CBX was stable, and the incidence of sustained VTs (>30 s) increased from 38 ± 4 to 85 ± 4% after CBX (n = 18; P < 0.01). SW reentry induced after RG was characterized by decremental conduction near the rotation center, prominent drift and self-termination by collision with the anatomical boundaries, and the incidence of sustained VTs decreased from 40 ± 5 to 17 ± 6% after RG (n = 13; P < 0.05). These results suggest that decreased intercellular coupling stabilizes SW reentry in 2D cardiac muscle, whereas increased coupling facilitates its early self-termination.

Origins of oxygen atoms in a marine ladder-frame polyether: evidence of monooxygenation by 18O-labeling and using tandem mass spectrometry.

Yessotoxin is a ladder-frame polyether produced by the dinoflagellate Protoceratium reticulatum. Previous labeling experiments using (13)C-acetate established the unique assembly of the carbon chain from intact and cleaved acetate units. The origins of ether and hydroxy oxygens in the molecule, which would yield further information regarding the assembly of the ladder-frame structure, have yet to be established. In this study, we describe the incorporation of (18)O in one experiment where the dinoflagellate was cultured under (18)O(2) atmosphere and in a second where the culture media was supplemented with [(18)O(2)]acetate. Labeled yessotoxin obtained from these experiments was subjected to collision-induced dissociation tandem mass spectrometry to determine the positions of (18)O-incorporation pattern in the molecule. Detailed analyses of product ions from the fragmentation processes led to the identification of (18)O-labeled positions and the incorporation ratios. The data revealed that the ether oxygens were labeled from (18)O(2) and the hydroxy oxygen on C32 was derived from [(18)O(2)]acetate. These results support a proposed biosynthetic mechanism of marine ladder-frame polyethers that a polyene precursor was oxidized by a monooxygenase after acetate condensation.

Rotors anchored by refractory islands drive torsades de pointes in an experimental model of electrical storm.

BACKGROUND: Electrical storm (ES) is a life-threatening emergency in patients at high risk of ventricular tachycardia/ventricular fibrillation (VF), but the pathophysiology and molecular basis are poorly understood. OBJECTIVE: The purpose of this study was to explore the electrophysiological substrate for experimental ES. METHODS: A model was created by inducing chronic complete atrioventricular block in defibrillator-implanted rabbits, which recapitulates QT prolongation, torsades des pointes (TdP), and VF episodes. RESULTS: Optical mapping revealed island-like regions with action potential duration (APD) prolongation in the left ventricle, leading to increased spatial APD dispersion, in rabbits with ES (defined as ≥3 VF episodes/24 h). The maximum APD and its dispersion correlated with the total number of VF episodes in vivo. TdP was initiated by an ectopic beat that failed to enter the island and formed a reentrant wave and perpetuated by rotors whose centers swirled in the periphery of the island. Epinephrine exacerbated the island by prolonging APD and enhancing APD dispersion, which was less evident after late Na+ current blockade with 10 µM ranolazine. Nonsustained ventricular tachycardia in a non-ES rabbit heart with homogeneous APD prolongation resulted from multiple foci with an electrocardiographic morphology different from TdP driven by drifting rotors in ES rabbit hearts. The neuronal Na+-channel subunit NaV1.8 was upregulated in ES rabbit left ventricular tissues and expressed within the myocardium corresponding to the island location in optically mapped ES rabbit hearts. The NaV1.8 blocker A-803467 (10 mg/kg, intravenously) attenuated QT prolongation and suppressed epinephrine-evoked TdP. CONCLUSION: A tissue island with enhanced refractoriness contributes to the generation of drifting rotors that underlies ES in this model. NaV1.8-mediated late Na+ current merits further investigation as a contributor to the substrate for ES.

Anti-oxidant effects of kiwi fruit in vitro and in vivo.

We previously reported that kiwi fruit is rich in polyphenols and has immunostimulatory activity. Polyphenols are widely known for having anti-oxidant effects. We also revealed potential anti-oxidant effects of kiwi fruit in vivo by oral administration to mice. Here, we compared the anti-oxidant effects of kiwi fruit with those of other fruits in vitro. Then, we examined the inhibitory effects of kiwi fruit on oxidation in the human body. There are two varieties of kiwi fruit, green kiwi and gold kiwi. We also examined variation between these varieties. Comparison of the anti-oxidant effects in vitro demonstrated that kiwi fruit had stronger anti-oxidant effects than orange and grapefruit, which are rich in vitamin C; gold kiwi had the strongest anti-oxidant effects. Kiwi fruit inhibited oxidation of biological substances in the human body. In particular, kiwi fruit may inhibit early lipid oxidation. In this study, kiwi fruit had strong anti-oxidant effects and may prevent the development and deterioration of diseases caused by oxidative stress.

Spatial phase discontinuity at the center of moving cardiac spiral waves.

BACKGROUND: Precise analysis of cardiac spiral wave (SW) dynamics is essential for effective arrhythmia treatment. Although the phase singularity (PS) point in the spatial phase map has been used to determine the cardiac SW center for decades, quantitative detection algorithms that assume PS as a point fail to trace complex and rapid PS dynamics. Through a detailed analysis of numerical simulations, we examined our hypothesis that a boundary of spatial phase discontinuity induced by a focal conduction block exists around the moving SW center in the phase map. METHOD: In a numerical simulation model of a 2D cardiac sheet, three different types of SWs (short wavelength; long wavelength; and low excitability) were induced by regulating ion channels. Discontinuities of all boundaries among adjacent cells at each instance were evaluated by calculating the phase bipolarity (PB). The total amount of phase transition (PTA) in each cell during the study period was evaluated. RESULTS: Pivoting, drifting, and shifting SWs were observed in the short-wavelength, low-excitability, and long-wavelength models, respectively. For both the drifting and shifting cases, long high-PB edges were observed on the SW trajectories. In all cases, the conduction block (CB) was observed at the same boundaries. These were also identical to the boundaries in the PTA maps. CONCLUSIONS: The analysis of the simulations revealed that the conduction block at the center of a moving SW induces discontinuous boundaries in spatial phase maps that represent a more appropriate model of the SW center than the PS point.

Cardiac macrophages prevent sudden death during heart stress.

Cardiac arrhythmias are a primary contributor to sudden cardiac death, a major unmet medical need. Because right ventricular (RV) dysfunction increases the risk for sudden cardiac death, we examined responses to RV stress in mice. Among immune cells accumulated in the RV after pressure overload-induced by pulmonary artery banding, interfering with macrophages caused sudden death from severe arrhythmias. We show that cardiac macrophages crucially maintain cardiac impulse conduction by facilitating myocardial intercellular communication through gap junctions. Amphiregulin (AREG) produced by cardiac macrophages is a key mediator that controls connexin 43 phosphorylation and translocation in cardiomyocytes. Deletion of Areg from macrophages led to disorganization of gap junctions and, in turn, lethal arrhythmias during acute stresses, including RV pressure overload and ß-adrenergic receptor stimulation. These results suggest that AREG from cardiac resident macrophages is a critical regulator of cardiac impulse conduction and may be a useful therapeutic target for the prevention of sudden death.

Acute amiodarone promotes drift and early termination of spiral wave re-entry.

Intravenous application of amiodarone is commonly used in the treatment of life-threatening arrhythmias, but the underlying mechanism is not fully understood. The purpose of the present study is to investigate the acute effects of amiodarone on spiral wave (SW) re-entry, the primary organization machinery of ventricular tachycardia/fibrillation (VT/VF), in comparison with lidocaine. A two-dimensional ventricular myocardial layer was obtained from 24 Langendorff-perfused rabbit hearts, and epicardial excitations were analyzed by high-resolution optical mapping. During basic stimulation, amiodarone (5 microM) caused prolongation of action potential duration (APD) by 5.6%-9.1%, whereas lidocaine (15 microM) caused APD shortening by 5.0%-6.4%. Amiodarone and lidocaine reduced conduction velocity similarly. Ventricular tachycardias induced by DC stimulation in the presence of amiodarone were of shorter duration (sustained-VTs >30 s/total VTs: 2/58, amiodarone vs 13/52, control), whereas those with lidocaine were of longer duration (22/73, lidocaine vs 14/58, control). Amiodarone caused prolongation of VT cycle length and destabilization of SW re-entry, which is characterized by marked prolongation of functional block lines, frequent wavefront-tail interactions near the rotation center, and considerable drift, leading to its early annihilation via collision with anatomical boundaries. Spiral wave re-entry in the presence of lidocaine was more stabilized than in control. In the anisotropic ventricular myocardium, amiodarone destabilizes SW re-entry facilitating its early termination. Lidocaine, in contrast, stabilizes SW re-entry resulting in its persistence.

Spatial distribution of fibrosis governs fibrillation wave dynamics in the posterior left atrium during heart failure.

Heart failure (HF) commonly results in atrial fibrillation (AF) and fibrosis, but how the distribution of fibrosis impacts AF dynamics has not been studied. HF was induced in sheep by ventricular tachypacing (220 bpm, 6 to 7 weeks). Optical mapping (Di-4-ANEPPS, 300 frames/sec) of the posterior left atrial (PLA) endocardium was performed during sustained AF (burst pacing) in Langendorff-perfused HF (n=7, 4 micromol/L acetylcholine; n=3, no acetylcholine) and control (n=6) hearts. PLA breakthroughs were the most frequent activation pattern in both groups (72.0+/-4.6 and 90.2+/-2.7%, HF and control, respectively). However, unlike control, HF breakthroughs preferentially occurred at the PLAs periphery near the pulmonary vein ostia, and their beat-to-beat variability was greater than control (1.93+/-0.14 versus 1.47+/-0.07 changes/[beats/sec], respectively, P<0.05). On histological analysis (picrosirius red), the area of diffuse fibrosis was larger in HF (23.4+/-0.4%) than control (14.1+/-0.6%; P<0.001, n=4). Also the number and size of fibrous patches were significantly larger and their location was more peripheral in HF than control. Computer simulations using 2-dimensional human atrial models with structural and ionic remodeling as in HF demonstrated that changes in AF activation frequency and dynamics were controlled by the interaction of electrical waves with clusters of fibrotic patches of various sizes and individual pulmonary vein ostia. During AF in failing hearts, heterogeneous spatial distribution of fibrosis at the PLA governs AF dynamics and fractionation.

Steroidal glycosides from Agave utahensis and their cytotoxic activity.

Eight new spirostanol saponins (1-8) and three new furostanol saponins (9-11) were isolated from the whole plants of Agave utahensis. The structures of 1-11 were determined by analysis of extensive spectroscopic data. The saponins were evaluated for their cytotoxic activity against HL-60 human promyelocytic leukemia cells. Compound 1 showed cytotoxicity against HL-60 cells with an IC(50) value of 4.9 microg/mL, induced apoptosis in HL-60 cells, and markedly activated caspase-3.

Cathepsin G, a neutrophil protease, induces compact cell-cell adhesion in MCF-7 human breast cancer cells.

Cathepsin G is a serine protease secreted by activated neutrophils that play a role in the inflammatory response. Because neutrophils are known to be invading leukocytes in various tumors, their products may influence the characteristics of tumor cells such as the growth state, motility, and the adhesiveness between cells or the extracellular matrix. Here, we demonstrate that cathepsin G induces cell-cell adhesion of MCF-7 human breast cancer cells resulting from the contact inhibition of cell movement on fibronectin but not on type IV collagen. Cathepsin G subsequently induced cell condensation, a very compact cell colony, resulting due to the increased strength of E-cadherin-mediated cell-cell adhesion. Cathepsin G action is protease activity-dependent and was inhibited by the presence of serine protease inhibitors. Cathepsin G promotes E-cadherin/catenin complex formation and Rap1 activation in MCF-7 cells, which reportedly regulates E-cadherin-based cell-cell junctions. Cathepsin G also promotes E-cadherin/protein kinase D1 (PKD1) complex formation, and Go6976, the selective PKD1 inhibitor, suppressed the cathepsin G-induced cell condensation. Our findings provide the first evidence that cathepsin G regulates E-cadherin function, suggesting that cathepsin G has a novel modulatory role against tumor cell-cell adhesion.

Structural characterisation and biological activities of a unique type beta-D-glucan obtained from Aureobasidium pullulans.

A beta-D-glucan obtained from Aureobasidium pullulans (AP-FBG) exhibits various biological activities: it exhibits antitumour and antiosteoporotic effects and prevents food allergies. An unambiguous structural characterisation of AP-FBG is still awaited. The biological effects of beta-D-glucan are known to depend on its primary structures, conformation, and molecular weight. Here, we elucidate the primary structure of AP-FBG by NMR spectroscopy, and evaluate its biological activities. Its structure was shown to comprise a mixture of a 1-3-beta-D-glucan backbone with single 1-6-beta-D-glucopyranosyl side-branching units every two residues (major structure) and a 1-3-beta-D-glucan backbone with single 1-6-beta-D-glucopyranosyl side-branching units every three residues (minor structure). Furthermore, this beta-D-glucan exhibited immunostimulatory effects such as the accumulation of immune cells and priming effects against enterobacterium. To our knowledge, 1-3-beta-glucans like AP-FBG with such a high number of 1-6-beta-glucopyranosyl side branching have a unique structure; nevertheless, many 1-3-beta-glucans were isolated from various sources, e.g. fungi, bacteria, and plants.

Atrial Infarction-Induced Spontaneous Focal Discharges and Atrial Fibrillation in Sheep: Role of Dantrolene-Sensitive Aberrant Ryanodine Receptor Calcium Release.

BACKGROUND: The mechanisms underlying spontaneous atrial fibrillation (AF) associated with atrial ischemia/infarction are incompletely elucidated. Here, we investigate the mechanisms underlying spontaneous AF in an ovine model of left atrial myocardial infarction (LAMI). METHODS AND RESULTS: LAMI was created by ligating the atrial branch of the left anterior descending coronary artery. ECG loop recorders were implanted to monitor AF episodes. In 7 sheep, dantrolene-a ryanodine receptor blocker-was administered in vivo during the 8-day observation period (LAMI-D, 2.5 mg/kg, IV, BID). LAMI animals experienced numerous spontaneous AF episodes during the 8-day monitoring period that were suppressed by dantrolene (LAMI, 26.1±5.1; sham, 4.3±1.1; LAMI-D, 2.8±0.8; mean±SEM episodes per sheep, P<0.01). Optical mapping showed spontaneous focal discharges (SFDs) originating from the ischemic/normal-zone border. SFDs were calcium driven, rate dependent, and enhanced by isoproterenol (0.03 µmol/L, from 210±87 to 3816±1450, SFDs per sheep) but suppressed by dantrolene (to 55.8±32.8, SFDs per sheep, mean±SEM). SFDs initiated AF-maintaining reentrant rotors anchored by marked conduction delays at the ischemic/normal-zone border. NOS1 (NO synthase-1) protein expression decreased in ischemic zone myocytes, whereas NADPH (nicotinamide adenine dinucleotide phosphate, reduced form) oxidase and xanthine oxidase enzyme activities and reactive oxygen species (DCF [6-carboxy-2',7'-dichlorodihydrofluorescein diacetate]-fluorescence) increased. CaM (calmodulin) aberrantly increased [3H]ryanodine binding to cardiac RyR2 (ryanodine receptors) in the ischemic zone. Dantrolene restored the physiological binding of CaM to RyR2. CONCLUSIONS: Atrial ischemia causes spontaneous AF episodes in sheep, caused by SFDs that initiate reentry. Nitroso-redox imbalance in the ischemic zone is associated with intense reactive oxygen species production and altered RyR2 responses to CaM. Dantrolene administration normalizes the CaM response, prevents LAMI-related SFDs, and AF initiation. These findings provide novel insights into the mechanisms underlying ischemia-related atrial arrhythmias.

Biobank-driven genomic discovery yields new insight into atrial fibrillation biology.

To identify genetic variation underlying atrial fibrillation, the most common cardiac arrhythmia, we performed a genome-wide association study of >1,000,000 people, including 60,620 atrial fibrillation cases and 970,216 controls. We identified 142 independent risk variants at 111 loci and prioritized 151 functional candidate genes likely to be involved in atrial fibrillation. Many of the identified risk variants fall near genes where more deleterious mutations have been reported to cause serious heart defects in humans (GATA4, MYH6, NKX2-5, PITX2, TBX5)1, or near genes important for striated muscle function and integrity (for example, CFL2, MYH7, PKP2, RBM20, SGCG, SSPN). Pathway and functional enrichment analyses also suggested that many of the putative atrial fibrillation genes act via cardiac structural remodeling, potentially in the form of an 'atrial cardiomyopathy'2, either during fetal heart development or as a response to stress in the adult heart.

Endoscopic fluorescence mapping of the left atrium: a novel experimental approach for high resolution endocardial mapping in the intact heart.

BACKGROUND: Despite the availability of several mapping technologies for investigating the electrophysiologic mechanisms of atrial fibrillation (AF), an experimental tool enabling high-resolution mapping of electrical impulses on the endocardial surface of the intact left atrium is lacking. OBJECTIVE: The purpose of this report is to present a new optical mapping approach implementing a steerable cardio-endoscope in isolated hearts. METHODS: The system consists of a direct or side-view endoscope coupled to a 532-nm excitation laser for illumination and a CCD camera for imaging of potentiometric dye fluorescence (di-4-ANEPPS, 80 x 80 pixels, 200-800 frames/s). The cardio-endoscope was aimed successively at diverse posterior left atrial locations to obtain high-resolution movies of electrical wave propagation and detailed endocardial anatomic features in the presence and absence of atrial stretch. RESULTS: We present several examples of high-resolution endoscopic posterior left atrial recordings of wave propagation patterns during both sinus rhythm and AF with signal-to-noise ratio similar to conventional optical mapping systems. We demonstrate the endoscope's ability to visualize highly organized AF sources (rotors) at specific locations on the posterior left atrium and posterior left atrium-pulmonary vein junctions. We present video images of waves emanating from such sources as they propagate into pectinate muscles in the left atrial appendage. In particular, we demonstrate this approach is ideally suited for studying the effects of atrial stretch on AF dynamics. CONCLUSION: In isolated hearts, cardio-endoscopic optical mapping of electrical activity should enable comprehensive evaluation of AF activity in the posterior left atrium, the role of local anatomy on AF dynamics, and the efficacy of pharmacologic and ablative interventions.