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Biomedical subjects

M Yashima

Publications and source records attributed to M Yashima.

At least 37 records · Page 2Linked to original sources
PubMed1999

Nicotine Increases Spatiotemporal Complexity of Ventricular Fibrillation Wavefront on the Epicardial Border Zone of Healed Canine Infarcts.

BACKGROUND: The influence of a pharmacologic agent on wavefront dynamics during ventricular fibrillation (VF) in a setting of remodeled and healed myocardial infarction (MI) remains poor explored. We hypothesized that nicotine, by virtue of its complex direct and indirect cardiovascular effects, increases wavefront complexity during VF. Specifically, we sought to determine whether nicotine increases the number and complexity (approximate entropy) of wavelets during stage II VF in hearts with healed MI. METHODS AND RESULTS: The left anterior descending coronary artery was permanently occluded in five mongrel dogs and wavefront dynamics during VF studied 5 to 6 weeks after occlusion in the open-chest anesthetized state. VF was induced by rapid pacing and the activation pattern mapped on the surviving epicardial border zone (EBZ) of the left ventricle with a plaque (3.2 x 3.8 cm) having 477 bipolar electrodes 1.6 mm apart. VF was mapped before and 20 minutes after 5 µg/kg/min nicotine infusion. Nicotine with a mean arterial plasma concentration of 127 +/- 76 ng/mL (range 57 to 240 ng/mL) significantly (P <.01) increased the number of wavelents from 3.8 +/- 0.4 to 5 +/- 0.41. The increased number of wavelets was caused by an increase (P <.01) in the spontaneous breakup of wavefronts from 4.1 +/- 0.9 times/s to 6.9 +/- 1.1 times/s. Wavebreak over the EBZ was functional in nature as no breakup occurred during normal sinus rhythm. Approximate entropy, a measure of complexity, significantly (P <.01) increased after nicotine administration from 0.23 +/- 0.02 to 0.28 +/- 0.01. CONCLUSIONS: Nicotine increases the number of wavelets and their complexity during VF by promoting spontaneous wavebreak over the EBZ of healed MI.

Journal Article↗
PubMed1999

[Emergency CABG for patients with LMT lesion treated by mechanical cardiac support].

We retrospectively analysed the perioperative course of 22 patients who underwent emergency CABG for severe left main trunk lesion. The causes of LMT lesion were spontaneous acute myocardial infarction in 14 patients and failed coronary intervention and coronary angiography in 8 patients. IABP was used preoperatively in all patients and additional coronary perfusion catheter were induced for two patients and PCPS was for one patient. Overall incidence in-hospital operative mortality was 22.7% (5/22), four of them were due to cardiac related causes and one of them was due to acute renal failure. Postoperative level of max CPK enzyme was significantly higher in death cases compared to survivors, 6,330 +/- 3,649 versus 1,299 +/- 1,417 IU/dl. We considered that the most important factors in surgical strategy for acute coronary syndrome with LMT lesion were as follows: improvement of hemodynamics with mechanical cardiac support by IABP or/and PCPS, protection of broad myocardial ischemia using coronary perfusion catheter and urgent surgical revascularization by emergency CABG.

Adult↗
PubMed1998

Role of pectinate muscle bundles in the generation and maintenance of intra-atrial reentry: potential implications for the mechanism of conversion between atrial fibrillation and atrial flutter.

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). Computer simulation studies were used to investigate the importance of regional myocardial thickness in reentry formation. A total of 40 episodes of reentry were induced; 28 episodes were stationary, and the remaining 12 were nonstationary. The stationary reentry was induced either immediately after the S2 stimuli (n=9) or after an initial period of irregular activations that lasted 1460+/-1077 ms (n= 19). Of 28 episodes, 20 were initiated by conduction block along large PM ridges, leading to wave break and the initiation of reentry. The reentrant wave fronts remained stationary and rotated around these ridges as anchoring sites. During the transition from the initial irregular activations to stationary reentry, the electrogram morphology converted from "fibrillation-like" to "flutter-like" activity. In 8 episodes, initially stationary reentry converted to irregular activations because of interference with outside wave fronts (n=5) or spontaneous separation of waves from the ridges (n=3). Compared with stationary reentry, nonstationary reentry always occurred over an area without large PMs, and the mean life span was much shorter (102+/-151 versus 3.8+/-1.1 rotations, P<0.001). Computer simulation studies showed that a critical ridge thickness is needed for reentry to anchor, thereby converting fibrillation to flutter. We conclude that PM ridge forms an area where wave break occurs, allowing the initiation of reentry. It also provides a natural anchor to the reentrant wave front, lengthening the life span of reentry. The attachment and detachment of the reentrant wave front to and from the ridge determine "flutter-like" or "fibrillation-like" activity.

Animals↗
PubMed1998

Delayed diagnosis of anomalous origin of the left coronary artery 16 years after mitral valve replacement.

Mitral insufficiency caused by ischemia is frequently found in anomalous origin of the left coronary artery from the pulmonary artery. We report a case of a 25-year-old woman who was diagnosed to have anomalous origin of the left coronary artery from the pulmonary artery and had successful left internal mammary artery bypass grafting 16 years after mitral valve replacement for mitral insufficiency of an unknown cause in her childhood.

Adult↗
PubMed1998

Transmembrane potential properties of atrial cells at different sites of a spiral wave reentry: cellular evidence for an excitable but nonexcited core.

Transmembrane action potentials (TAPs) were recorded during simultaneous mapping of a reentrant wavefront induced in canine isolated atria. The activation pattern was visualized dynamically using a high resolution electrode catheter mapping system. During functional reentry (spiral wave), cells in the core of the spiral wave remained quiescent near their resting membrane potential. Cells away from the core progressively gained TAP amplitude and duration, and at the periphery of the spiral wave the cells generated TAPs with full height and duration. During anatomical reentry, when the tip of the wavefront remained attached to the obstacle (a condition of high source-to-sink ratio), the TAP near the obstacle had normal amplitude and duration. However, when the tip of the wavefront detached from the obstacle (condition of lowered source-to-sink ratio) the TAP lost amplitude and duration. These results are consistent with the theory that the source-to-sink ratio determines the safety factor for wave propagation and wave block near the core. With decreasing source-to-sink ratio, TAP progressively decreases in amplitude and duration. In the center of the core, the cells, while excitable, remain quiescent near their resting potential. This decrease reflects a progressive decrease in the source-to-sink ratio. TAP vanishes in the core where cells remain quiescent near their resting potential. Functional and meandering reentrant wavefronts are compatible with the spiral mechanism of reentry where block at the rotating point is provided by the steep curvature of the wave tip.

Animals↗
PubMed1997

Time course of endothelin-1 and nitrate anion levels after cardiopulmonary bypass in congenital heart defects.

BACKGROUND: The endothelium-derived vasoconstrictor endothelin-1 (ET-1) may be involved in pulmonary hypertension (PH), but production of the endothelium-derived vasodilator nitric oxide (NO) after cardiopulmonary bypass (CPB) in congenital heart disease is unclear. METHODS: Twenty patients (age, 4 months to 12 years) were divided into three groups: severe PH (mean pulmonary-to-systemic arterial pressure ratio > 0.5) and high pulmonary flow (n = 8), mild PH (mean pulmonary-to-systemic arterial pressure ratio < 0.35) and high pulmonary flow (n = 6), and no PH and low pulmonary flow (n = 6). The mean pulmonary-to-systemic arterial pressure ratio was calculated and blood samples were taken, and NO3-, an NO metabolite, was measured. RESULTS: Levels of ET-1 in the group with severe PH and high pulmonary flow were higher than in the other groups until 6 hours after CPB, and NO3- was not changed significantly in the group with severe PH and high pulmonary flow and or the group with mild PH and high pulmonary flow during CPB. Endothelin-1 in the group with no PH and low pulmonary flow was higher than in the group with mild PH and high pulmonary flow after CPB, and NO3- in the group with no PH and low pulmonary flow significantly decreased after CPB. A positive correlation was obtained between mean pulmonary-to-systemic arterial pressure ratio and ET-1 (r = 0.742 before CPB; r = 0.689 after CPB). CONCLUSIONS: Imbalance between increased ET-1 and constant NO after CPB in the group with severe PH and high pulmonary flow could contribute to dominant effects of ET-1, which may injure the lung. The increased ET-1 and the decreased NO after CPB in the group with no PH and low pulmonary flow may induce a mechanism of protective vasoconstriction against an acute increase in pulmonary flow.

Cardiopulmonary Bypass↗
PubMed1997

Hydroxyapatite ceramics with selected sintering additives.

Several sintering additives for hydroxyapatite (HA) have been tested in order to enhance its sinterability without decomposing the HA and/or decreasing bioactivity and biocompatibility, additionally providing a weak interface for HA ceramics. The ion species of sintering additives were selected from those in the mineral constituents of hard tissues and bioactive glasses. After investigation of phase diagrams in the CaO-P2O5-additive systems, and analysis of physiochemical properties of the additives, several sintering aids for HA have been chosen. Subsequently, densification, phase composition, grain growth and fracture behaviour of HA containing 5 wt% of each additive, sintered at 1000-1100 degrees C, have been studied. H3BO3, CaCl2, KCl, KH2PO4, (KPO3)n and Na2Si2O5 did not enhance densification of HA. K2CO2, Na2CO3, KF and sodium phosphates improved the densification significantly. Expect for KCl and some sodium phosphates, all the additives caused formation of large quantities of undesired beta-tricalcium phosphate or CaO; therefore, they are not appropriate for HA. In the case of sodium phosphate additives, it was possible to avoid formation of CaO or beta-tricalcium phosphate by control of the additive quantity and chemical composition. beta-NaCaPO4 has been found to be an effective sintering agent which causes neither decomposition of HA nor formation of other undesired phases.

Biocompatible Materials↗
PubMed1997

Attachment of meandering reentrant wave fronts to anatomic obstacles in the atrium. Role of the obstacle size.

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 with Tyrode's solution containing 10 to 15 mumol/L ACh. Holes with 2- to 10-mm diameters were sequentially created in the center of the tissue with biopsy punches. Reentry was induced by a premature stimulus after eight regular stimuli at 400-ms cycle length. The endocardial activation maps and the motion of the induced reentry were visualized dynamically before and after each test lesion using 509 bipolar electrodes. In the absence of a lesion (n = 8), the induced single reentrant wave front, in the form of a spiral wave, meandered irregularly from one site to another before terminating at the tissue border. Holes with 2- to 4-mm diameters (n = 6) had no effect on meandering. However, when the hole diameters were increased to 6 mm (n = 8), 8 mm (n = 8), and 10 mm (n = 6), the tip of the spiral wave attached to the holes, and reentry became stationary. Transition from meandering to an attached state converted the irregular and polymorphic electrogram to a periodic and monomorphic activity with longer cycle lengths (101 +/- 11 versus 131 +/- 9 ms for no hole versus 10-mm hole, respectively; P < .001). Regression analysis showed a significant positive linear correlation between the cycle length of the reentry and the hole diameter (r = .89, P < .01) and between the cycle length of the reentry and the excitable gap (r = .89, P < .05). We conclude that a critically sized anatomic obstacle converts a nonstationary meandering reentrant wave front to a stationary one. This transition converts an irregular "fibrillation-like" activity into regular monomorphic activity.

Acetylcholine↗
PubMed1997

Curative percutaneous catheter ablation for various supraventricular and ventricular tachyarrhythmias. Results in 187 consecutive patients during the first five years.

Closed-chest transcatheter electrical ablation (catheter ablation) has been applied to various supraventricular and ventricular tachyarrhythmias as a radical therapeutic technique since its introduction in 1982. Currently, it has become a first line therapy for supraventricular tachyarrhythmias except atrial fibrillation and uncommon types of atrial flutter. We first carried out the ablation procedure in 1991 for the treatment of ventricular tachycardia. Up to February 1997, a total of 187 patients underwent catheter ablation in our institution. The aims of this study are to demonstrate our results of catheter ablation in the early 5 years and to show the usefulness of this new curative method. Successful results were obtained in 168 of 187 patients (overall final success rate: 89.8%). The success rates of each category of tachyarrhythmias were 100/105 patients (95%) with WPW syndrome, 41/46 (89%) with atrioventricular nodal reentrant tachycardia, 7/10 (70%) with atrial flutter, 4/4 (100%) with atrial tachycardia, 2/2 (100%) with medically refractory atrial fibrillation, 13/15 (85%) with idiopathic ventricular tachycardia and 3/7 (43%) with sustained ventricular tachycardia associated with structural heart disease, respectively. Complications that required invasive treatments were observed in 3 patients (2 hemopericardium and 1 complete atrioventricular block). Our results indicate that catheter ablation is highly effective in most categories of tachyarrhythmias and can be applied safely without lethal complications.

Adult↗
PubMed1996

Processing and mechanical properties of hydroxyapatite reinforced with hydroxyapatite whiskers.

Hydrothermally synthesized HAp fine crystals/HAp whiskers mixtures have been used for the preparation of HAp/0-30% (whiskers) composites. The composites have been fabricated by pressureless sintering and hot-pressing. The best mechanical properties and the highest densities have been achieved for composites hot pressed at 1000 degrees C (2 h, 30 MPa in flowing Ar). Their density was in the range of 90-97% of the theoretical density. Fracture toughness (Klc) of the composites reflected their microstructure and had the value of 1.4 MPa m1/2 (as compared with Klc = 1.0 MPa m1/2 for the non-reinforced HAp matrix). Compressive prestressing of the HAp matrix and crack deflection (both derived from the residual stress field) contributed to the increase of fracture toughness. Other toughening mechanisms have not been observed. HAp/HAp (whiskers) composites exhibited improved toughness without degradation of biocompatibility, because the HAp whiskers acted both as a reinforcement and as a biocompatible phase. Problems related to biocompatibility and mechanical properties of available HAp-based composites were also discussed.

Biocompatible Materials↗
PubMed1996

Use of intravenous dofetilide in atrial flutter with hemodynamic instability.

Paroxysmal atrial flutter is a drug-resistant supraventricular tachyarrhythmia that is often accompanied by hemodynamic instability due to an excessive ventricular response. We report here a case of atrial flutter with 1:1 atrioventricular conduction, in which we were able to rescue the patient from a state of cardiogenic shock by using intravenous dofetilide, a new class III antiarrhythmic agent. Dofetilide was suitable for the treatment because it immediately increased atrioventricular nodal refractoriness without any negative inotropic action.

Adult↗
PubMed1996

[A case report of a successful Redo Bentall operation].

An initial Bentall operation was performed on a patient aged 38 years with annuloaortic ectasia and aortic regurgitation. An echocardiogram and RI angiogram revealed a perigraft aortic aneurysm on the same patient aged 45 years. The aneurysm gradually developed and the maximum diameter reached 90 mm in size. The Redo-Bentall operation (Piehler modification) was successfully done once again on the same patient aged 56 years. The anastmosis between the right coronary orifice and the graft was detached on all sides. The anastmosis between the left coronary orifice and the graft was detached two thirds of all sides.

Aneurysm, False↗
PubMed1995

[Coronary artery bypass grafting without cardiopulmonary bypass in patients with LV dysfunction (EF < or = 30%)--a report of 3 cases].

The purpose of this article is to describe our technique for performing coronary artery bypass grafting without cardiopulmonary bypass and to demonstrate that this operation is safe and useful to the case of LV dysfunction. Between April 1988 and March 1994, 2 men and 1 woman aged 61 to 69 years (mean 65 years) with LV dysfunction (EF < or = 30%) underwent coronary artery bypass grafting without cardiopulmonary bypass. Saphenous vein grafts were placed to the right coronary artery (n = 2), left anterior descending artery (n = 2), and internal thoracic artery grafts were placed to the right coronary artery (n = 1), left anterior descending artery (n = 1). The post operative course were uneventful in all patients and discharged with no complications. All patients underwent coronary angiography, and 5 of 6 (83.3%) grafts placed without cardiopulmonary bypass were patent. In selected patients, coronary artery bypass grafting to the case of LV dysfunction without cardiopulmonary bypass can be performed safe and satisfactory graft patency rates.

Aged↗
PubMed1993

Polymyositis-dermatomyositis and non-Hodgkin's lymphoma.

An association between polymyositis-dermatomyositis (PM/DM) and malignancy has been reported. However, controversy exists regarding a direct causal relationship between the two diseases. We describe a patient who had had PM and subsequently developed non-Hodgkin's lymphoma, and discuss the possibility of their causal relation.

Adult↗