Masaaki Yashima

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BACKGROUND Ventricular fibrillation (VF) is maintained by 2 mechanisms: first by reentry formation and second by spontaneous wave break or wave splitting. We hypothesized that spontaneous wave break results from a critical shortening of the action potential duration (APD) during VF and that its prevention by procainamide eliminates spontaneous wave break.(More)
To determine the role of pectinate muscle (PM) bundles in the formation of intra-atrial reentry, 10 isolated canine right atrial tissues were perfused with Tyrode's solution containing 1 to 2.5 micromol/L acetylcholine (ACh). The endocardium was mapped using 477 bipolar electrodes with 1.6-mm resolution. Reentry was induced by a premature stimulus (S2).(More)
BACKGROUND The effect of effective refractory period (ERP) shortening on the vulnerability and characteristics of induced functional reentry in the ventricle remain poorly defined. We hypothesized that ERP shortening increases ventricular vulnerability to reentry and accelerates its rate, as is the case in the atrium. METHODS AND RESULTS The epicardial(More)
OBJECTIVES To elucidate pharmacokinetics and pharmacodynamics of landiolol hydrochloride, newer developed ultra-short-acting beta-blocker, in patients with various cardiac tachyarrhythmias. BACKGROUND The short duration of action and titratability of landiolol hydrochloride make it ideal for use in patients with a clinical need for beta-blockers. (More)
BACKGROUND In dogs, chronic rapid pacing may result in sustained atrial fibrillation (AF). However, activation patterns in pacing-induced sustained AF are unclear. METHODS AND RESULTS We induced sustained AF (>48 hours) in 6 dogs by rapid pacing for 139+/-84 days. We then performed computerized atrial epicardial mappings and recorded the activations in(More)
BACKGROUND The role of papillary muscle (PM) in the generation and maintenance of reentry is unclear. METHODS AND RESULTS Computerized mapping (477 bipolar electrodes, 1.6-mm resolution) was performed in fibrillating right ventricles (RVs) of swine in vitro. During ventricular fibrillation (VF), reentrant wave fronts often transiently anchored to the PM.(More)
Acetylcholine chloride (ACh) induces nonstationary meandering reentrant wave fronts in the atrium. We hypothesized that an anatomic obstacle of a suitable size prevents meandering by causing attachment of the reentrant wave front tip to the obstacle. Eight isolated canine right atrial tissues (area, 3.8 x 3.2 cm) were mounted in a tissue bath and superfused(More)
OBJECTIVES The study was done to test the hypothesis that an artificial anatomical obstacle prevents the maintenance of ventricular fibrillation (VF) by stabilizing reentrant wavefronts (RWF) and increases the critical mass (CM) of myocardium required to sustain VF. BACKGROUND Artificial obstacles can anchor RWF in simulated models of VF. Whether an(More)
We report 29Si NMR study on a single crystal of the heavy-fermion superconductor CeIrSi3 without an inversion symmetry along the c axis. The 29Si Knight-shift measurements under pressure have revealed that the spin susceptibility for the ab plane decreases slightly below T(c), whereas along the c axis it does not change at all. The result can be accounted(More)
We report 75As nuclear quadrupole resonance studies on (Ca4Al2O(6-y))(Fe2As2) with T(c) = 27  K. Measurement of nuclear-spin-relaxation rate 1/T1 has revealed a significant development of two-dimensional antiferromagnetic spin fluctuations down to T(c) in association with the smallest As-Fe-As bond angle. Below T(c), the temperature dependence of 1/T1(More)