Hiroshi Nakagawa

Semiquantitative grading of severity of mitral regurgitation by real-time two-dimensional Doppler flow imaging technique

An attempt was made to determine whether mitral regurgitation could be detected and its severity evaluated semiquantitatively by newly developed real-time two-dimensional Doppler flow imaging in 109 patients who underwent left ventriculography. In the Doppler flow imaging technique, Doppler signals due to blood flow in the cardiac chambers are processed using a high speed autocorrelation technique, so that the direction, velocity and turbulence of the intracardiac blood flow are displayed in the color-coded mode on the monochrome B-mode echocardiogram in real time. Mitral regurgitant flow was imaged as a jet spurting out from the mitral valve orifice into the left atrial cavity. It was noted that the regurgitant jet in the left atrial cavity had a variety of orientations and dynamic features when studied by the present technique. The sensitivity of the technique in the detection of mitral regurgitation was 86% as compared with that of left ventriculography. Mitral regurgitation in the false negative cases was mostly mild. On the basis of the farthest distance reached by the regurgitant flow signal from the mitral valve orifice, the severity of regurgitation was graded on a four point scale and these results were compared with those of angiography. A significant correlation (r = 0.87) was found between Doppler imaging and angiography in the evaluation of the severity of mitral regurgitation. A similar result was obtained for the evaluation based on the area covered by the regurgitant signals in the left atrial cavity. Thus, noninvasive semiquantitative evaluation by real-time two-dimensional Doppler flow imaging appears to be a promising clinical technique.

Chapter 59 – Electrophysiologic Characteristics of Atrioventricular Nodal Reentrant Tachycardia: Implications for the Reentrant Circuits

Atrioventricular nodal reentrant tachycardia (AVNRT), the most common form of paroxysmal supraventricular tachycardia, 1 is a fascinating complex of arrhythmias. AVNRT was originally proposed to result from reentry totally confined within the compact atrioventricular (AV) node. 2 3 However, the typical form of AVNRT (slow/fast) is now thought to involve the AV node, a component of atrial myocardium, and at least two atrionodal connections. 4 5 6 7 8 9 10 11 12 13 14 15 16 Much of the current understanding about the components of the reentrant circuit has evolved from the development of ablation procedures, in which one of the atrionodal connections, remote from the compact AV node, is destroyed, eliminating AVNRT without producing AV block. 4 5 6 7 8 9 10 11 12 16 17 18

Early Afterdepolarizations in a Patient with Idiopathic Monomorphic Right Ventricular Tachycardia

To identify the role of afterdepolarizations in the induction of idiopathic monomorphic right ventricular tachycardia (VT), monophasic action potentials (MAPs) were recorded in a patient with this type of VT. The VT had a left bundle branch block configuration and inferior axis, and originated in the right ventricular outflow tract (RVOT). MAPs were recorded with a contact electrode at the origin of the VT, as well as other ventricular sites. The VT was induced by the intravenous administration of isoproterenol and/or rapid ventricular pacing and was preceded by short‐long‐short sequences of RR intervals. Early afterdepolarizations (EADs) in MAPs were recorded at the origin of VT (RVOT), but not recorded at other ventricular sites. These data suggest that catecholamine sensitive triggered activity seems to be the mechanism of idiopathic monomorphic right VT and EADs can be recorded in association with the occurrence of this type of VT.

Characterization of Interfacial Oxide Layers in Heterostructures of Hafnium Oxides Formed on NH3-Nitrided Si(100)

In the stack structures fabricated by NH3 nitridation of Si(100) at 650–700°C and subsequent electron-beam evaporation of HfO2, the blocking properties of ultrathin SiNx (x=~1.3) upon oxidation in dry O2 ambient in the temperature range of 300–600°C have been studied by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared attenuated total reflection (FT-IR-ATR). Although the oxidation of Si(100) during O2 anneal is retarded using a ~1-nm-thick SiNx layer grown by 700°C nitridation in NH3 ambient prior to the HfO2 evaporation, the surface oxidation of the ultrathin SiNx layer proceeds, accompanied by the movement of nitrogen atoms from the oxidized SiNx surface to the Si surface. As a result, the interfacial layer thickness is increased with no significant changes in nitrogen bonding features at the interface. From the temperature dependence of the interfacial oxide formation in the stack structure of HfO2 on thermally nitrided Si(100), we suggest that the control of O2 partial pressure is practically inevitable in suppressing completely the interfacial oxide growth at a thermal budget higher than 350°C.

Surgical repair of Wolff-Parkinson-White syndrome complicated with myocardial bridging

Myocardial bridging causes myocardial ischemia during supraventricular tachycardia. We present a case of Wolff-Parkinson-White syndrome combined with myocardial bridging. The patient complained of angina pectoris during paroxysmal supraventricular tachycardia because of severe constriction of the left anterior descending coronary artery during systole. A myocardial scintigram revealed myocardial ischemia in the anteroseptal wall during paroxysmal supraventricular tachycardia. Myotomy to prevent myocardial bridging and interruption of the accessory conduction pathway was successfully accomplished in a one-stage operation.

Fabrication of multiply-stacked structures of Si quantum-dots embedded in SiO/sub 2/ by combination of low-pressure CVD and remote plasma treatments

Silicon nanocrystals embedded in Si02 network have attracted a great deal of interest as quantum dots with discrete charged states and their application to the floating gate of MOS memories [l]. For the multivalued capability of the Si dots floating gate MOS devices, the growth control of Si quantum dots (Si-QDs) with an areal density as high as 10l2 cmm2 on an ultrathin Si02 layer is a crucial factor. In our previous work, we demonstrated the self-assembling formation of Si-QDs on ultrathin S O 2 layers by controlling the early stages of low-pressure chemical vapor deposition (LPCVD) using a SiH4 gas [2]. Also, we reported that the Si02 surface treatment with a dilute HF sohtion is quite efficient to form dots with high areal density and high size uniformity because Si-OH bonds created on the Si02 surface act as reactive sites to precursors such as SiHz during LPCVD. In addition, by spatially controlling OH termination of the Si02 surface before LPCVD, the selective growth of Si dots has been demonstrated [3]. More recently, we have also reported that, by exposing as-grown Si02 surface to a remote Ar plasma and subsequently to a remote H2 plasma, OH bonds are efficiently created on the Si02 surface and results in the Si dot formation with fairly uniform size distribtution and high areal dot density as in the case of wet-chemical treatment using a dilute HF solution [4]. In this work, we extended our research work to fabricate multiply-stacked structures consisting of Si-QDs and ultrathin Si02 by alternately repeating the Si dot formation by SiH4-LPCVD and the dot surface modification by remote plasma treatments in which surface oxidation and subsequent OH termination are preformed by exposing to remote O2 plasma and remote Ar/H2 plasma, respectively. And electron charging and discharging characteristics of Si-QDs stacked structure as a floating gate in MOS capacitors has been studied. For the first formation of Si-QDs, a 4 nm-thick Si02 layer was grown on n-Si(lOOj at 1000°C in dry O2 and the Si02 surface was exposed to pure Ar remote plasma and subsequently to pure I32 remote plasma at 560 C for lmin in each plasma treatment. The remote plasma was generated in a quartz tube with a size of 10 cm in diameter by inductively-coupling with an external single-tum antenna connected to a 60 MHz generator through a matching box. The sample was placed on the susceptor at a distance of 32 cm away from the position of the antenna to eliminate ion damage. The VHF power and the gas pressure for the remote Ar plasma pretreatment were maintained at 100 W and 0.1 Torr, respectively, and for the remote H2 plasma treatment at 200 W and 0.2 Torr, respectively. After remote plasma treatments, the formation of Si dots was carried out on plasma-treated Si02 in the same reaction chamber at 560°C by LPCVD using pure monosilane under 0.5 Torr. And subsequently the surface oxidation of Si dots was performed at the same temperature by a remote VHF plasma of 1% 0 2 diluted with He generated at 50 W and 0.1Torr. When HF-last nc-Si(100j was exposed to the remote 0 2 plasma, 2.4nm-thick SiOz was formed uniformly by 10 min exposure. For the fabrication of the stacked structures of Si-QDs, the above-mentioned process steps of remote Ar/Hz plasma treatments, LPCVD and remote plasma oxidation were repeated at 560°C. In the floating gate application, to form a 7.5nm-thick control oxide conformally on the dot layer, amorphous Si layer was grown on formed Si dots by LPCVD of 10% Si2H6 diluted with He at 440 O C , then the a-Si layer was hlly oxidized in dry O2 at 1000 C. From the analysis of the Si2p spectra for the thermally-grown Si02 layer before and after remote Ar plasma and subsequent H2 plasma treatments, the formation of surface OH bonds is suggested with no Finally, A1 gates were evaporated to form MOS capacitors.

The spectrum of “Mahaim-like” accessory connections and their associated ablation techniques

A discussion of the spectrum of “Mahaim-like” accessory connections must begin with a definition. As our understanding of these connections has improved, it has become clear that the literature contains several subtle misnomers and misconceptions concerning these pathways. Interestingly, Mahaim’s frequently cited manuscripts are not concerned with preexcitation or arrhythmia; rather, they discuss the normal atrioventricular conduction system and the relationship between histology and electrocardiographic patterns of bundle branch block. One describes a 21-year-old male who died of severe myocarditis and bundle branch block; 6,320 sections of this heart were studied in effort to understand the patient’s electrocardiographic pattern. A connection from the superior posterior portion of the proximal left bundle branch to the interventricular septum was identified, which Mahaim felt could account for AV condition [1]. A second describes a 22-year-old male who had a normal heart, and died from a skull fracture; neither an arrhythmia nor an EKG was described. A connection was found between the anterior bundle of His and the septal myocardium [2]. A third is a rebuttal of Kent’s description of AV conduction via small myocardial fasciculi joining the atria to the ventricles laterally [3]. Interestingly, connections between the AV node and right ventricle or right bundle branch, which have been attributed to Mahaim, were not described by Mahaim either in his English language manuscripts, nor in the several manuscripts that we have had translated from the French and Italian [1–5].