原田 将英

Midkine (MK), a heparin-binding growth factor, has been shown to prevent cardiac remodeling after ischemic injury through its anti-apoptotic effect. Cell apoptosis is central to the pathophysiology of cardiac remodeling in congestive heart failure (CHF) of ischemic as well as non-ischemic origin. We hypothesized that MK exerts the anti-apoptotic cardioprotective effect in CHF of non-ischemic etiology. MK protein or vehicle (normal saline) was subcutaneously administered in tachycardia-induced CHF rabbits (right ventricular pacing, 350 beats/min, 4 weeks). The vehicle-treated rabbits (n = 19, control) demonstrated severe CHF and high mortality rate, whereas MK (n = 16) demonstrated a well-compensated state and a lower mortality rate. In echocardiography, left ventricular (LV) end-diastolic dimension decreased in MK versus control, whereas LV systolic function increased. In histological analysis (picrosirius red staining), MK decreased collagen deposition area compared with control. TUNEL staining showed that MK prevented cell apoptosis and minimized myocyte loss in the CHF rabbit ventricle, associated with activation of PI3-K/Akt signaling, producing a parallel decrease of Bax/Bcl-2 ratio. MK prevented progression of cardiac remodeling in the CHF rabbit, likely by activation of anti-apoptotic signaling. Exogenous MK application might be a novel therapeutic strategy for CHF due to non-ischemic origin.

BACKGROUND Cardiac sarcoidosis (CS) generates myocardial scar and arrhythmogenic substrate. CS diagnosis according to the Japanese Ministry of Health and Welfare guidelines relies, among others, on cardiac magnetic resonance imaging with late gadolinium enhancement (CMR-LGE). However, access to CMR-LGE is limited. The electrocardiography-based Selvester QRS score has been validated for identifying myocardial scar in ischemic/nonischemic cardiomyopathy, but its efficacy has not been tested to evaluate CS. OBJECTIVE The purpose of this study was to examine whether the QRS score can be applied to CS. METHODS CS-associated myocardial scar was assessed by both CMR-LGE and QRS scoring in patients with extra-CS (n = 59). RESULTS Of 59 patients, 35 (59%) were diagnosed with CS according to the Japanese Ministry of Health and Welfare guidelines. QRS-estimated scar mass positively correlated with that quantified by CMR-LGE (signal intensity >= 2SD above the reference; r = 0.68; P < .001). Receiver operating characteristic curves demonstrated optimal cutoffs of 9% CMR-LGE scar and 3-point QRS score to identify patients with CS. The areas under the curves of CMR-LGE and the QRS score were not significantly different (0.83 and 0.78, respectively; P =.27); both methods demonstrated similar diagnostic performance. A QRS score of >= 3 led to a higher incidence of CS-associated adverse events (death/fatal arrhythmia/ heart failure hospitalization) than did a QRS score of <3 (35 +/- 21 months of follow-up; P = .01). QRS score was an independent predictor of risk in multivariate analysis (P = .03). CONCLUSION The Selvester QRS scoring estimates CS-associated myocardial damage and identifies patients with CS equally well as CMR-LGE. A higher QRS score is also associated with an increased risk of life-threatening events in CS, indicating its potential use as a risk predictor.

Background Atrial fibrillation (AF) is a significant risk factor for ischemic strokes, and making a robust risk stratification scheme would be important. Few studies have examined whether nonlinear dynamics of the heart rate could predict ischemic strokes in AF. We examined whether a novel complexity measurement of the heart rate variability called multiscale entropy (MSE) was a useful risk stratification measure of ischemic strokes in patients with permanent AF. Methods and Results We examined 173 consecutive patients (age 69 +/- 11 years) with permanent AF who underwent 24-hour Holter electrocardiography from April 2005 to December 2006. We assessed several frequency ranges of the MSE and CHA(2)DS(2)-VASc score (1 point for congestive heart failure, hypertension, diabetes, vascular disease, an age 65 to 74 years, and a female sex and 2 points for an age >= 75 years and a stroke or transient ischemic attack). We found 22 (13%) incident ischemic strokes during a mean follow up of 3.8-years. The average value of the MSE in the very-low frequency subrange (90-300 s, MeanEn(VLF2)) was significantly higher in patients who developed ischemic strokes than in those who did not (0.68 +/- 0.15 vs. 0.60 +/- 0.14, P<0.01). There was no significant difference in the C-statistic between the CHA(2)DS(2)-VASc score and MeanEn(VLF2) (0.56; 95% confidence interval, 0.43-0.69 vs. 0.66; 95% confidence interval, 0.53-0.79). After an adjustment for the age, CHA(2)DS(2)-VASc score, and antithrombotic agent, a Cox hazard regression model revealed that the MeanEn(VLF2) was an independent predictor of an ischemic stroke (hazard ratio per 1-SD increment, 1.80; 95% confidence interval, 1.17-2.07, P<0.01). Conclusion The MeanEn(VLF2) in 24-hour Holter electrocardiography is a useful risk stratification measure of ischemic strokes during the long-term follow-up in patients with permanent AF.

BACKGROUND Atrial fibrillation (AF) is associated with metabolic stress, which activates adenosine monophosphate-regulated protein kinase (AMPK). OBJECTIVES This study sought to examine AMPK response to AF and associated metabolic stress, along with consequences for atrial cardiomyocyte Ca2+ handling. METHODS Calcium ion (Ca2+) transients (CaTs) and cell shortening (CS) were measured in dog and human atrial cardiomyocytes. AMPK phosphorylation and AMPK association with Ca2+-handling proteins were evaluated by immunoblotting and immunoprecipitation. RESULTS CaT amplitude and CS decreased at 4-min glycolysis inhibition (GI) but returned to baseline at 8 min, suggesting cellular adaptation to metabolic stress, potentially due to AMPK activation. GI increased AMPK-activating phosphorylation, and an AMPK inhibitor, compound C (CompC), abolished the adaptation of CaT and CS to GI. The AMPK activator 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) increased CaT amplitude and CS, restoring CompC-induced CaT and CS decreases. CompC decreased L-type calcium channel current (I-Ca,I-L), along with I-Ca,I-L-triggered CaT amplitude and sarcoplasmic reticulum (SR) Ca2+ content under voltage clamp conditions in dog cells and suppressed CaT and ICa, L in human cardiomyocytes. Small interfering ribonucleic acid-based AMPK knockdown decreased CaT amplitude in neonatal rat cardiomyocytes. L-type Ca2+ channel a subunits coimmunoprecipitated with AMPKa. Atrial AMPK-activating phosphorylation was enhanced by 1 week of electrically maintained AF in dogs; fractional AMPK phosphorylation was increased in paroxysmal AF and reduced in longstanding persistent AF patients. CONCLUSIONS AMPK is activated by metabolic stress and AF, and helps maintain the intactness of atrial I-Ca,I-L, Ca2+ handling, and cell contractility. AMPK contributes to the atrial compensatory response to AF-related metabolic stress; AF-related metabolic responses may be an interesting new therapeutic target. (C) 2015 by the American College of Cardiology Foundation.

Rationale: Fibroblasts are involved in cardiac arrhythmogenesis and contribute to the atrial fibrillation substrate in congestive heart failure (CHF) by generating tissue fibrosis. Fibroblasts display robust ion currents, but their functional importance is poorly understood. Objective: To characterize atrial fibroblast inward-rectifier K+ current (I-K1) remodeling in CHF and its effects on fibroblast properties. Methods and Results: Freshly isolated left atrial fibroblasts were obtained from controls and dogs with CHF (ventricular tachypacing). Patch clamp was used to record resting membrane potential (RMP) and I-K1. RMP was significantly increased by CHF (from -43.20.8 mV, control, to -55.5 +/- 0.9 mV). CHF upregulated I-K1 (eg, at -90 mV from -1.1 +/- 0.2 to -2.7 +/- 0.5 pA/pF) and increased the expression of KCNJ2 mRNA (by 52%) and protein (by 80%). Ba2+ (300 mol/L) decreased the RMP and suppressed the RMP difference between controls and dogs with CHF. Store-operated Ca2+ entry (Fura-2-acetoxymethyl ester) and fibroblast proliferation (flow cytometry) were enhanced by CHF. Lentivirus-mediated overexpression of KCNJ2 enhanced I-K1 and hyperpolarized fibroblasts. Functional KCNJ2 suppression by lentivirus-mediated expression of a dominant negative KCNJ2 construct suppressed I-K1 and depolarized RMP. Overexpression of KCNJ2 increased Ca2+ entry and fibroblast proliferation, whereas the dominant negative KCNJ2 construct had opposite effects. Fibroblast hyperpolarization to mimic CHF effects on RMP enhanced the Ca2+ entry. MicroRNA-26a, which targets KCNJ2, was downregulated in CHF fibroblasts. Knockdown of endogenous microRNA-26 to mimic CHF effects unregulated I-K1. Conclusions: CHF upregulates fibroblast KCNJ2 expression and currents, thereby hyperpolarizing RMP, increasing Ca2+ entry, and enhancing atrial fibroblast proliferation. These effects are likely mediated by microRNA-26a downregulation. Remodeling-induced fibroblast KCNJ2 expression changes may play a role in atrial fibrillation promoting fibroblast remodeling and structural/arrhythmic consequences.

Atrial fibrillation (AF) is the most common clinically relevant arrhythmia, but the methods available for treating AF and its complications (of which the most important is thrombogenesis), as well as for assessing AF risk and underlying pathophysiology, are largely limited. Emerging evidence suggests a significant role of inflammation in the pathogenesis of AF. That evidence includes elevated serum levels of inflammatory biomarkers in AF subjects, the expression of inflammatory markers in cardiac tissues of AF patients and animal models of AF, and beneficial effects of anti-inflammatory drugs in experimental AF paradigms. Inflammation is suggested to be linked to various pathological processes, such as oxidative stress, apoptosis, and fibrosis, that promote AF substrate formation. Inflammation has also been associated with endothelial dysfunction, platelet activation, and coagulation cascade activation, leading to thrombogenesis. Thus, inflammation may contribute to both the occurrence/maintenance of AF and its thromboembolic complications. Here, we review the evidence for a role of inflammation and inflammatory biomarkers in the risk management and treatment of AF. We also summarize the current knowledge of inflammationdependent cellular and molecular mechanisms in AF pathophysiology and their potential as therapeutic targets.

Atrial fibrillation (AF) is the most common sustained arrhythmia in clinical practice. AF and its complications are responsible for important population morbidity and mortality. Presently available therapeutic approaches have limited efficacy and nontrivial potential to cause adverse effects. Thus, new mechanistic knowledge is essential for therapeutic innovation. Atrial arrhythmogenic remodeling, defined as any change in atrial structure or function that promotes atrial arrhythmias, is central to AF. Remodeling can be due to underlying cardiac conditions, systemic processes and conditions such as aging, or AF itself. Recent work has underlined the importance of remodeling in AF, provided new insights into basic mechanisms, and identified new biomarker/ imaging approaches to follow remodeling processes. The importance of intracellular Ca2+ handling abnormalities has been highlighted, both for the induction of triggered ectopic activity and for the activation of Ca2+ -related cell signaling that mediates profibrillatory remodeling. The importance of microRNAs, which are a new class of small noncoding sequences that regulate gene expression, has emerged in both electrical and structural remodeling. Remodeling related to aging, cardiac disease, and AF itself is believed to underlie the progressive nature of the arrhythmia, which contributes to the complexities of long- term management. New tools that are being developed to quantify remodeling processes and monitor their progression include novel biomarkers, imaging modalities to quantify/ localize fibrosis, and noninvasive monitoring/ mapping to better characterize the burden of AF and identify arrhythmic sources. This report reviews recent advances in the understanding of the basic pathophysiology of atrial remodeling and potential therapeutic implications. (C) 2014 by the American College of Cardiology Foundation

MicroRNAs (miRNAs) are emerging as key control molecules in the regulation of gene expression, and their role in heart disease is becoming increasingly evident. Given the critical role of Ca2+ handling and signaling proteins in the maintenance of cardiac function, the targeting of such proteins by miRNAs would be expected to have important consequences. miRNAs have indeed been shown to control the expression of genes encoding important Ca2+ handling and signaling proteins, and are themselves regulated by Ca2+-dependent processes. Ca2+-related miRNAs have been found to be significant pathophysiological contributors in conditions like myocardial ischemic injury, cardiac hypertrophy, heart failure, ventricular arrhythmogenesis, and atrial fibrillation. This review is a comprehensive analysis of the present knowledge concerning miRNA regulation of Ca2+ handling processes, the participation of Ca2+-regulating miRNAs in the evolution of heart disease, the mutual relationship between Ca2+ signaling and miRNAs in the control of cardiac function, and the potential value of miRNA-control of Ca2+ handling as a therapeutic target.

Background-Fibroblast proliferation and differentiation are central in atrial fibrillation (AF)-promoting remodeling. Here, we investigated fibroblast regulation by Ca2+-permeable transient receptor potential canonical-3 (TRPC3) channels. Methods and Results-Freshly isolated rat cardiac fibroblasts abundantly expressed TRPC3 and had appreciable nonselective cation currents (INSC) sensitive to a selective TPRC3 channel blocker, pyrazole-3 (3 mu mol/L). Pyrazole-3 suppressed angiotensin II-induced Ca2+ influx, proliferation, and alpha-smooth muscle actin protein expression in fibroblasts. Ca2+ removal and TRPC3 blockade suppressed extracellular signal-regulated kinase phosphorylation, and extracellular signal-regulated kinase phosphorylation inhibition reduced fibroblast proliferation. TRPC3 expression was upregulated in atria from AF patients, goats with electrically maintained AF, and dogs with tachypacing-induced heart failure. TRPC3 knockdown (based on short hairpin RNA [shRNA]) decreased canine atrial fibroblast proliferation. In left atrial fibroblasts freshly isolated from dogs kept in AF for 1 week by atrial tachypacing, TRPC3 protein expression, currents, extracellular signal-regulated kinase phosphorylation, and extracellular matrix gene expression were all significantly increased. In cultured left atrial fibroblasts from AF dogs, proliferation rates, alpha-smooth muscle actin expression, and extracellular signal-regulated kinase phosphorylation were increased and were suppressed by pyrazole-3. MicroRNA-26 was downregulated in canine AF atria; experimental microRNA-26 knockdown reproduced AF-induced TRPC3 upregulation and fibroblast activation. MicroRNA-26 has NFAT (nuclear factor of activated T cells) binding sites in the 5' promoter region. NFAT activation increased in AF fibroblasts, and NFAT negatively regulated microRNA-26 transcription. In vivo pyrazole-3 administration suppressed AF while decreasing fibroblast proliferation and extracellular matrix gene expression. Conclusions-TRPC3 channels regulate cardiac fibroblast proliferation and differentiation, likely by controlling the Ca2+ influx that activates extracellular signal-regulated kinase signaling. AF increases TRPC3 channel expression by causing NFAT-mediated downregulation of microRNA-26 and causes TRPC3-dependent enhancement of fibroblast proliferation and differentiation. In vivo, TRPC3 blockade prevents AF substrate development in a dog model of electrically maintained AF. TRPC3 likely plays an important role in AF by promoting fibroblast pathophysiology and is a novel potential therapeutic target. (Circulation. 2012;126:2051-2064.)

Takemoto Y, Takanari H, Honjo H, Ueda N, Harada M, Kato S, Yamazaki M, Sakuma I, Opthof T, Kodama I, Kamiya K. Inhibition of intercellular coupling stabilizes spiral-wave reentry, whereas enhancement of the coupling destabilizes the reentry in favor of early termination. Am J Physiol Heart Circ Physiol 303: H578-H586, 2012. First published June 15, 2012; doi:10.1152/ajpheart.00355.2012.-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 mu M) and rotigaptide (RG, 0.1 mu M) were used to inhibit and enhance GJ coupling, respectively. CBX decreased the space constant (lambda) 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 (kappa) and local conduction velocity (LCV): LCV = LCV0 - D . kappa (D, diffusion coefficient; LCV0, LCV at kappa = 0). CBX decreased LCV0 and D by 27 +/- 3 and 57 +/- 3%, respectively (n = 5; P < 0.01). RG increased LCV0 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 kappa > similar to 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.

BACKGROUND Moderate global cooling of myocardial tissue was shown to destabilize 2-dimensional (2-D) reentry and facilitate its termination. OBJECTIVE This study sought to test the hypothesis that regional cooling destabilizes rotors and facilitates termination of spontaneous and DC shock-induced subepicardial reentry in isolated, endocardially ablated rabbit hearts. METHODS Fluorescent action potential signals were recorded from 2-D subepicardial ventricular myocardium of Langendorff-perfused rabbit hearts. Regional cooling (by 5.9 degrees C +/- 1.3 degrees C) was applied to the left ventricular anterior wall using a transparent cooling device (10 mm in diameter). RESULTS Regional cooling during constant stimulation (2.5 Hz) prolonged the action potential duration (by 36% +/- 9%) and slightly reduced conduction velocity (by 4% +/- 4%) in the cooled region. Ventricular tachycardias (VTs) induced during regional cooling terminated earlier than those without cooling (control): VTs lasting &gt;30 seconds were reduced from 17 of 39 to 1 of 61. When regional cooling was applied during sustained VTs (&gt;120 seconds), 16 of 33 (48%) sustained VTs self-terminated in 12.5 +/- 5.1 seconds. VT termination was the result of rotor destabilization, which was characterized by unpinning, drift toward the periphery of the cooled region, and subsequent collision with boundaries. The DC shock intensity required for cardioversion of the sustained VTs decreased significantly by regional cooling (22.8 +/- 4.1 V, n = 16, vs 40.5 +/- 17.6 V, n = 21). The major mode of reentry termination by DC shocks was phase resetting in the absence of cooling, whereas it was unpinning in the presence of cooling. CONCLUSION Regional cooling facilitates termination of 2-D reentry through unpinning of rotors.

Rationale: Atrial fibrillation (AF) causes atrial-tachycardia remodeling (ATR), with enhanced constitutive acetylcholine-regulated K(+) current (I(KAChC)) contributing to action potential duration shortening and AF promotion. The underlying mechanisms are unknown. Objective: To evaluate the role of protein-kinase C (PKC) isoforms in ATR-induced I(KAChC) activation. Methods and Results: Cells from ATR-dogs (400-bpm atrial pacing for 1 week) were compared to control dog cells. In vitro tachypaced (TP; 3 Hz) canine atrial cardiomyocytes were compared to parallel 1-Hz paced cells. I(KAChC) single-channel activity was assessed in cell-attached and cell-free (inside-out) patches. Protein expression was assessed by immunoblot. In vitro TP activated I(KAChC), mimicking effects of in vivo ATR. Discrepant effects of PKC activation and inhibition between control and ATR cells suggested isoform-selective effects and altered PKC isoform distribution. Conventional PKC isoforms (cPKC; including PKC alpha) inhibited, whereas novel isoforms (including PKC epsilon) enhanced, acetylcholine-regulated K(+) current (I(KACh)) in inside-out patches. TP and ATR downregulated PKC alpha (by 33% and 37%, respectively) and caused membrane translocation of PKC epsilon, switching PKC predominance to the stimulatory novel isoform. TP increased [Ca(2+)](i) at 2 hours by 30%, with return to baseline at 24 hours. Buffering [Ca(2+)](i) during TP with the cell-permeable Ca(2+) chelator BAPTA-AM (1 mu mol/L) or inhibiting the Ca(2+)-dependent protease calpain with PD150606 (20 mu mol/L) prevented PKC alpha downregulation and TP enhancement of I(KAChC). PKC epsilon inhibition with a cell-permeable peptide inhibitor suppressed TP/ATR-induced I(KAChC) activation, whereas cPKC inhibition enhanced I(KAChC) activity in 1-Hz cells. Conclusions: PKC isoforms differentially modulate I(KACh), with conventional Ca(2+)-dependent isoforms inhibiting and novel isoforms enhancing activity. ATR causes a rate-dependent PKC isoform switch, with Ca(2+)/calpain-dependent downregulation of inhibitory PKC alpha and membrane translocation of stimulatory PKC epsilon, enhancing I(KAChC). These findings provide novel insights into mechanisms underlying I(KAChC) dysregulation in AF. (Circ Res. 2011;109:1031-1043.)

Harada M, Tsuji Y, Ishiguro YS, Takanari H, Okuno Y, Inden Y, Honjo H, Lee JK, Murohara T, Sakuma I, Kamiya K, Kodama I. Rate-dependent shortening of action potential duration increases ventricular vulnerability in failing rabbit heart. Am J Physiol Heart Circ Physiol 300: H565-H573, 2011. First published December 10, 2010; doi: 10.1152/ajpheart.00209.2010.-Congestive heart failure (CHF) predisposes to ventricular fibrillation (VF) in association with electrical remodeling of the ventricle. However, much remains unknown about the rate-dependent electrophysiological properties in a failing heart. Action potential properties in the left ventricular subepicardial muscles during dynamic pacing were examined with optical mapping in pacing-induced CHF (n = 18) and control (n = 17) rabbit hearts perfused in vitro. Action potential durations (APDs) in CHF were significantly longer than those observed for controls at basic cycle lengths (BCLs) &gt; 1,000 ms but significantly shorter at BCLs &lt; 400 ms. Spatial APD dispersions were significantly increased in CHF versus control (by 17-81%), and conduction velocity was significantly decreased in CHF (by 6-20%). In both groups, high-frequency stimulation (BCLs &lt; 150 ms) always caused spatial APD alternans; spatially concordant alternans and spatially discordant alternans (SDA) were induced at 60% and 40% in control, respectively, whereas 18% and 82% in CHF. SDA in CHF caused wavebreaks followed by reentrant excitations, giving rise to VF. Incidence of ventricular tachycardia/VFs elicited by high-frequency dynamic pacing (BCLs &lt; 150 ms) was significantly higher in CHF versus control (93% vs. 20%). In CHF, left ventricular subepicardial muscles show significant APD shortenings at short BCLs favoring reentry formations following wavebreaks in association with SDA. High-frequency excitation itself may increase the vulnerability to VF in CHF.

Bepridil is effective for conversion of atrial fibrillation to sinus rhythm and in the treatment of drug-refractory ventricular tachyarrhythmias. We investigated the effects of bepridil on electrophysiological properties and spiral-wave (SW) reentry in a 2-dimensional ventricular muscle layer of isolated rabbit hearts by optical mapping. Ventricular tachycardia (VT) induced in the presence of bepridil (1 mu M) terminated earlier than in the control. Bepridil increased action potential duration (APD) by 5% - 8% under constant pacing and significantly increased the space constant. There was a linear relationship between the wavefront curvature (kappa) and local conduction velocity: LCV = LCV(0) D.kappa (D, diffusion coefficient; LCV(0), LCV at kappa = 0). Bepridil significantly increased D and LCV(0). The regression lines with and without bepridil crossed at kappa = 20 - 40 cm(-1), resulting in a paradoxical decrease of LCV at kappa &gt; 40 cm(-1). Dye transfer assay in cultured rat cardiomyocytes confirmed that bepridil increased intercellular coupling. SW reentry in the presence of bepridil was characterized by decremental conduction near the rotation center, prominent drift, and self-termination by collision with boundaries. These results indicate that bepridil causes an increase of intercellular coupling and a moderate APD prolongation, and this combination compromises wavefront propagation near the rotation center of SW reentry, leading to its drift and early termination. [Supplementary Figures: available only at http://dx.doi.org/10.1254/jphs.10233FP]

Background-Coronary artery disease predisposes to atrial fibrillation (AF), but the effects of chronic atrial ischemia/infarction on AF-related substrates are unknown. Methods and Results-Regional right atrial myocardial infarction (MI) was created in 40 dogs by ligating an artery that supplies the right atrial free wall and not the ventricles; 35 sham dogs with the same artery isolated but not ligated were controls. Dogs were observed 8 days after MI and subjected to open-chest study, in vitro optical mapping, and/or cell isolation for patch-clamp and Ca(2+) imaging on day 8. Holter ECGs showed more spontaneous atrial ectopy in MI dogs (eg, 662+/-281 on day 7 versus 34+/-25 ectopic complexes per day at baseline; 52+/-21 versus 1+/-1 atrial tachycardia episodes per day). Triggered activity was increased in MI border zone cells, which had faster decay of caffeine-evoked Ca(2+) transients and enhanced (by approximate to 73%) Na(+)-Ca(2+) exchange current. Spontaneous Ca(2+) sparks (confocal microscopy) occurred under beta-adrenergic stimulation in more MI dog cells (66+/-9%) than in control cells (29+/-4%; P&lt;0.01). Burst pacing induced long-lasting AF in MI dogs (1146+/-259 versus 30+/-14 seconds in shams). Increased border zone conduction heterogeneity was confirmed by both bipolar electrode mapping in vivo and optical mapping. Optical mapping demonstrated stable border zone reentry in all 9 MI preparations but in none of 6 shams. Border zone tissue showed increased fibrous tissue content. Conclusions-Chronic atrial ischemia/infarction creates substrates for both spontaneous ectopy (Ca(2+)-release events, increased Na(+)-Ca(2+) exchange current) and sustained reentry (conduction abnormalities that anchor reentry). Thus, chronic atrial infarction in dogs promotes both AF triggers and the substrate for AF maintenance. These results provide novel insights into potential AF mechanisms in patients with coronary artery disease. (Circulation. 2011;123:137-146.)

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 AM) caused prolongation of action potential duration (APD) by 5.6%-9.1%, whereas lidocaine (15 mu M) 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 &gt;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.

Electrical storm(ES)家兎モデルを用いて心室細動に伴うCa2+ハンドリングシグナルの変化について解析した。その結果、重篤なESに伴い心室筋組織のCaMK IIやPKCαといったCa2+活性化シグナルが亢進し、RyR2が過リン酸化、PLBが脱リン酸化されることが確認された。今回作製した家兎モデルでは左室短縮率の有意な低下が認められたが、心不全徴候はみられなかった。これまでの臨床報告と今回の実験結果から、ESの病態・転帰にもCaMK II活性亢進による催不整脈リモデリングの進展が深く寄与することが示唆され、CaMK II系シグナルの遮断がESの抑制ならびにESに伴う催不整脈リモデリングの進展阻止に有効である可能性が考えられた。

BACKGROUND Modification of spiral wave (SW) reentry by antiarrhythmic drugs is a central issue to be challenged for better understanding of their benefits and risks. OBJECTIVE We investigated the effects of pilsicainide and/or verapamil, which block sodium and L-type calcium currents (I-Na and I-Ca,I- L), respectively, on SW reentry. METHODS A two-dimensional epicardial ventricular muscle Layer was created in rabbit hearts by cryoablation (n = 32), and action potential signals were analyzed by high-resolution optical mapping. RESULTS During constant stimulation, pilsicainide (3-5 mu M) caused a frequency-dependent decrease of conduction velocity (CV; by 20%-54% at 5 Hz) without affecting action potential duration (APD). Verapamil (3 mu M) caused APD shortening (by 16% at 5 Hz) without affecting CV. Ventricular tachycardias (VTs) that were induced were more sustained in the presence of either pilsicainide or verapamil. The incidence of sustained VTs (&gt;30 s)/all VTs per heart was 58% +/- 9% for 5 mu M pilsicainide vs. 22% +/- 9% for controls and 62% +/- 10% for 3 mu M verapamil vs. 22% +/- 8% for controls. The SWs with pilsicainide were characterized by slower rotation around Longer functional block lines (FBLs), whereas those with verapamil were characterized by faster rotation around shorter FBLs. Combined application of 3 mu M pilsicainide and 3 mu M verapamil resulted in early termination of VTs (sustained VTs/all VTs per heart: 2% +/- 2% vs. 29% +/- 9% for controls); SWs showed extensive drift and decremental conduction, leading to their spontaneous annihilation. CONCLUSION Blockade of either I-Na, or I-Ca,I- (L) stabilizes SWs in a two-dimensional epicardial Layer of rabbit ventricular myocardium to help their persistence, whereas blockade of both currents destabilizes SWs to facilitate their termination.

Background. A functional line of conduction block is often observed in the sinus venosa (SV) during typical atrial flutter (AFL). Little information, however, is available as to the action potential characteristics in the SV with respect to the functional block. Methods and Results: Monophasic action potentials (MAPs) from the SV and lateral wall of the right atrium were recorded in 7 patients with paroxysmal AFL and 11 control patients. For both the control and AFL patients, the MAP duration at 90% repolarization (MAPD(90)) in the SV was longer, and the MAPD(90) restitution slope was less steep than in the lateral wall. The MAPD(90) in the SV in the AFL patients was slightly longer than that in the controls at the shortest cycle length (CL) tested (300 ms). However, the MAPD(90S) at longer CLs (350-700 ms), as well as the MAPD(90) restitution slopes in the SV were comparable between the 2 groups. Conclusions: The MAPs in the SV are characterized by a long duration and flat restitution kinetics in humans. MAP properties to facilitate the development of conduction block in the SV are not appreciable in patients with paroxysmal typical AFL. (Circ J 2009;73:647-653)

Cooling of myocardial tissue destabilizes spiral wave reentry through a prolongation of the action potential and a decrease in conduction velocity. We have recently demonstrated that moderate regional myocardial cooling (by ∼5°C) causes a significant decrease in the intensity of DC shocks required to terminate spiral wave reentry in the rabbit ventricle (Heart Rhythm 2006). In this study, we have investigated its underlying mechanisms in 2-dimensional rabbit ventricular myocardium by using high-resolution optical mapping. Application of high-intensity shocks caused an immediate termination of spiral wave reentry through a phase-resetting mechanism (mode-1 termination) regardless of absence or presence of regional cooling. Moderate-intensity DC shocks created multiple phase singularities and interactions of these shock-induced singularities with the stationary spiral wave (rotor) often resulted in delayed termination of reentry through unpinning of the rotor (mode-2 termination). In the presence of regional cooling, the mode-2 termination of spiral waves occurred with lower-intensity DC shocks. These results suggest that appropriate regional myocardial cooling facilitates DC shock-induced termination of spiral wave reentry through unpinning of rotors in the ventricular myocardium. [J Physiol Sci. 2008;58 Suppl:S178]

Introduction: Cardiac resynchronization therapy (CRT) by simultaneous biventricular pacing is now widely accepted as a new therapeutic option for patients with severe congestive heart failure (CHF). Recent studies have shown comparable hemodynamic benefits of left ventricular (LV) pacing alone. The clinical usefulness of CRT, however, might be compromised by potential exaggeration of arrhythmogenic substrates through a modification of ventricular repolarization. Methods and Results: We compared ECG parameters during sinus rhythm (SR), atrioventricular synchronous pacing at the right ventricular apex (RVendP), at LV epicardium (LVepiP), and at both sites (BiVP) in acute homodynamic studies of 14 CHF patients scheduled for CRT (QRS duration = 144 +/- 23 msec, LVEF = 27 +/- 10%). The maximum rate of increase in LV pressure (LVdp/dt(max)) was decreased significantly during RVendP, whereas it was increased similarly during LVepiP and BiVP compared with SR. QTc was increased during RVendP (by 10.2%) and LVepiP (by 26.1%). QTc dispersion (QTc(max)-QTc(min) in the six precordial leads) was also increased during LVepiP (by 66.5%). These parameters were unaffected during BiVP. JTc was unchanged, and the interval from the peak to the end of the T wave (Tcpeak-end) was increased slightly (by 19.3%) during RVendP. Both JTc and Tcpeak-end were increased dramatically during LVepiP (by 18.2% and 55.4%, respectively), but increased only modestly during BiVP (by 6.6% and 15.8%, respectively). Conclusions: LVepiP causes much greater increase in spatial dispersion of ventricular repolarization than BiVP in CHF patients. BiVP may have a substantial advantage over LVepiP to minimize the proarrhythmic perturbation of ventricular repolarization in association with CRT.

Spiral-wave reentry is a principal mechanism of life-threatening ventricular tachyarrhythmias. We investigated the effects of regional cooling (RC) on the dynamics of spiral-waves. Methods and Results: Optical action potential signals were recorded from 2-dimensional ventricular myocardium (1 mm thick) of Langendorff-perfused rabbit hearts. Ventricular tachycardias (VTs, >2 min) were induced by burst stimulation. RC (by 5-7ºC) was applied to the left ventricular free wall using a transparent cooling device (diameter, 10 mm). RC caused a marked prolongation of action potential (by 25±4%) and a slight reduction of conduction velocity (by 16±5%) in the affected region under constant pacing (2.5Hz, n=10). Spiral-wave dynamics during VTs were transformed by RC from stationary to chaotic meandering types. During RC, the rotors moved irregularly around the cooled region, and often collided with the anatomical boundary (atrioventricular groove) resulting in spontaneous termination. The incidence of termination of VTs within 15 s was increased from 2/18 (11%) without RC to 14/18 (78%) with RC. Conclusion: RC facilitates spontaneous termination of spiral-wave reentry through the unpinning of rotors. [J Physiol Sci. 2006;56 Suppl:S129]

A 24-year-old woman with atopic dermatitis was admitted to our hospital with fever. Echocardiography showed a huge vegetation attached to the posterior mitral commissure without mitral valve dysfunction. Blood culture identified methicillin-sensitive Staphylococcus aureus. The serum level of antiphospholipid antibody was elevated. A splenic infarction occurred on the second hospital day. Surgery to resect the residual mobile vegetation was performed uneventfully on the 6th hospital day. The postoperative course was uneventful, and the patient was discharged after 4 weeks of antibiotic therapy. Preservation of the mitral valve is rare in the face of virulent Staphylococcus infection and the presence of a huge mobile vegetation. These findings were apparently related to the high serum level of infection-related antiphospholipid antibody and atopic dermatitis.