Nitaro Shibata

Statistical Guideline of Threshold Determination for Cardiac Spiral Wave Center Detection Using Phase Variance Analysis

Spiral wave (SW) plays a key role in generation and termination of fatal tachyarrhythmia. In our previous study, we proposed a novel objective tracking method of SW center trajectories by using phase variance (PV) analysis. This method evaluates local variance of phase values around each point to detect the position of SW center as the peak of PV map. PV analysis improved the detection accuracy of meandering SW centers and complex multiple SW centers significantly. However, the algorithm still includes some hyperparameters, the window size for the evaluation of phase variance and the binarization threshold for the peak detection. Thus, some guideline for proper determination of those parameters has been required. In this study, we hypothesized that the appropriate binarization threshold depends on the window size, and it can be determined as the level of PV value with specific p-value on Rayleigh’s test. We compared the detection results with various window sizes (3, 6, 9, 12 pixels) and various thresholds (from 0.4 to 0.9). Optical mapping measurement data with single SW center and four SW centers were evaluated. As a result, proper numbers of SW centers were detected with the thresholds corresponding to the p-value of 0.05, even with the smallest window size (3 pixels). From these results, it was indicated that the suggested method based on Rayleigh’s test is valuable for proper determination of PV analysis parameters.

Fluctuation of the blood pressure during head-up tilt test in neurally mediated syncope patients

Maintaining the blood pressure is crucial to perfuse the blood to the vital organs in order to preserve the life. In neurally mediated syncope (NMS), the failure of blood pressure control causes the ischemia of the brain, which induces syncope. We tested whether the failure of the compensation of the blood pressure predisposes the syncope in NMS. Six healthy volunteers (Group H), 5 syncope patients with HUT negative (Group N), and 6 syncope patients with HUT positive (Group P) were included in the study. The changes, as well as the fluctuation of the systolic blood pressure (SBP), were compared among the three groups. The time domain analysis of the SBP was evaluated using mean and standard deviation. The frequency domain of SBP was evaluated using frequency analysis. In Group P slight decrease in SBP (106 [mmHg]) starts between 4 and 2 minutes before syncope. Then, significant decrease (88 [mmHg]) follows at 2minutes later. These changes in BP indicate that deterioration of the BP homeostasis may starts around 2 to 4 minutes and accelerate around 1 minute before syncope. The SBP-SD at 4 to 1 minutes before syncope is smaller (3.9~4.8 [mmHg]) than in Group H and N (4.0~6.5 [mmHg]). Low component of the frequency domain power during 6 to 2 minutes before syncope in Group P (2200~3400 [mmHg2]) is rather lower than Group H and N (3000~13000 [mmHg2]). The failure of maintaining BP might be the etiology of syncope episode. Decreased LF power of fSBP might have some relationship to the mechanism of SBP homeostasis failure.

Role of Ca^ Release from Sarcoplasmic Reticulum in Pacemaker Activity of the Sinoatrial Node

Recent studies using confocal microscopy combined with patch clamping on single sinoatrial (SA) node pacemaker cells suggest that Ca 2 + release from the sarcoplasmic reticulum (SR) during diastole may play a prominent role in the late phase of pacemaker depolarization. The present study was designed to test this hypothesis in the intact SA node. We investigated the effects of a high concentration of ryanodine, which is known to disable SR Ca 2 + release, on spontaneous activity of isolated rabbit right atrium including the whole SA node by using an extracellular potential mapping technique. Inhibition of SR Ca 2 + release by 30 μM ryanodine caused only a moderate reduction of the spontaneous firing rate (by 20.0′2.8 %, n=4) of the intact SA node. This observation is inconsistent with previous data obtained from single pacemaker cells. Physiological significance of SR Ca 2 + release in the regulation of SA node pacemaker activity is still unsettled.

High-speed digital video imaging system to record cardiac action potentials

A new digital video imaging system was developed and its performance was evaluated to analyze the spiral wave dynamics during polymorphic ventricular tachycardia (PVT) with high spatio-temporal resolution (1 ms, 0.1 mm). The epicardial surface of isolated rabbit heart stained with di- 4-ANEPPS was illuminated by 72 high-power bluish-green light emitting diodes (BGLED: (lambda) 0 500 nm, 10mw). The emitted fluorescence image (256x256 pixels) passing through a long-pass filter ((lambda) c 660nm) was monitored by a high-speed digital video camera recorder (FASTCAM-Ultima- UV3, Photron) at 1125 fps. The data stored in DRAM were processed by PC for background subtraction. 2D images of excitation wave and single-pixel action potentials at target sites during PVT induced by DC shocks (S2: 10 ms, 20 V) were displayed for 4.5 s. The wave form quality is high enough to observe phase 0 upstroke and to identify repolarization timing. Membrane potentials at the center of spiral were characterized by double-peak or oscillatory depolarization. Singular points during PVT were obtained from isophase mapping. Our new digital video-BGLED system has an advantage over previous ones for more accurate and longer time action potential analysis during spiral wave reentry.