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Biomedical subjects

S Kamakura

Publications and source records attributed to S Kamakura.

At least 73 records · Page 4Linked to original sources
PubMed1997

Multinucleated giant cells recruited by implantation of octacalcium phosphate (OCP) in rat bone marrow share ultrastructural characteristics with osteoclasts.

The ultrastructural characteristics of multinucleated giant cells (MNGCs) on octacalcium phosphate (OCP) and hydroxyapatite (HA) were investigated in comparison with those of osteoclasts, when the synthetic OCP and HA were implanted in rat bone marrow. The morphological difference in the MNGCs were shown between OCP and HA implants in 2 weeks after implantation. The MNGC on the implanted OCP (i-OCP) developed the ruffled border-like structure and the clear zone-like structure. The i-OCP was frayed where it was in contact with the ruffled border-like structure. The MNGC on the implanted HA (i-HA) developed the clear zone-like structure, whereas no ruffled border was seen. The surface of i-HA associated with the MNGC was smooth and not frayed. Bone formed directly on the OCP or HA implants. The interface between the i-OCP and bone matrix interdigitated, whereas that between the i-HA and bone matrix was comparatively smooth. The present study suggested that the i-OCP could be resorbed by the MNGCs which share some ultrastructural characteristics with osteoclasts.

Animals↗
PubMed1997

Iatrogenically induced intractable atrioventricular reentrant tachycardia after verapamil and catheter ablation in a patient with Wolff-Parkinson-White syndrome and idiopathic dilated cardiomyopathy.

In a patient with WPW syndrome and idiopathic dilated cardiomyopathy, intractable atrioventricular reentrant tachycardia (AVRT) was iatrogenically induced. QRS without preexcitation, caused by junctional escape beats after verapamil or unidirectional antegrade block of accessory pathway after catheter ablation, established frequent AVRT attack.

Adult↗
PubMed1997

Early afterdepolarizationlike activity in patients with class IA induced long QT syndrome and torsades de pointes.

Early afterdepolarizations (EADs) have been linked to the mechanism of torsades de pointes in long QT syndrome. The purpose of this study was to investigate the role of EADs in Class IA induced torsades de pointes. We studied nine patients with Class IA induced torsades de pointes at the time this arrhythmia was present (acute period, n = 7) and after Class IA therapy was discontinued (chronic period, n = 6). ECGs and monophasic action potentials were recorded in both periods. In the chronic period, electrophysiological studies were performed before and after disopyramide infusion. In the acute period, QTc interval was markedly prolonged (655 +/- 32 ms1/2), and EAD-like activity was recorded in all patients. QTc interval returned to normal (428 +/- 45 ms1/2) and EAD-like activity disappeared after discontinuation of IA drug. Although, in the chronic period, disopyramide infusion prolonged QTc interval from 428 +/- 48 ms1/2 to 479 +/- 31 ms1/2 and induced EAD in three of six patients, the degree was not as marked as observed in the acute period. EADs may play an important role in the genesis of long QT and torsades de pointes. Disopyramide infusion in the chronic period could not reproduce marked repolarization abnormalities and torsades de pointes.

Action Potentials↗
PubMed1997

Influence of epinephrine, propranolol, and atrial pacing on spatial distribution of recovery time measured by body surface mapping in congenital long QT syndrome.

INTRODUCTION: Sympathetic stimulation plays an important role in the genesis of QT(U) prolongation and ventricular arrhythmias in congenital long QT syndrome (LQTS). Permanent pacemaker as well as beta blockers are reported to be effective in the management of this syndrome. The purpose of this study was to examine influence of epinephrine (alpha- and beta-adrenergic stimulation), propranolol (beta blocker), and atrial pacing on the spatial distribution of repolarization using body surface recovery time (RT) in congenital LQTS. METHODS AND RESULTS: Body surface mapping was recorded in 16 patients with congenital LQTS and 20 control patients before and after epinephrine infusion (0.1 microg/kg per min), oral propranolol (1 to 2 mg/kg per day), addition of epinephrine during oral propranolol, atrial pacing at a cycle length of 600 or 750 msec, and addition of epinephrine during atrial pacing. The RT, that is, the interval between the QRS onset and the maximum dV/dt point in the ST-T segment, was measured automatically by a computer from each of the 87 mapping leads, and the corrected RT (RTc) was calculated using Bazett's method. In patients with congenital LQTS, epinephrine markedly changed the T(U) wave morphology and spatial distribution of RT, especially the distribution of maximum RT of the left anterior chest and back. Epinephrine prolonged the maximum RTc and the minimum RTc in 87 leads and increased the RTc dispersion (difference between maximum and minimum RTc in each patient). Neither propranolol nor atrial pacing changed the T(U) wave morphology, spatial distribution of RT, or any RTc parameters at rest. Propranolol prevented the influences of epinephrine on the T(U) wave morphology, spatial distribution of RT, and RTc parameters, whereas atrial pacing did not. In control patients, marked changes of the T(U) wave morphology and RTc parameters were not recognized during the entire protocol. CONCLUSIONS: Our results indicate that epinephrine markedly changes the spatial distribution of repolarization and increases the dispersion of repolarization, which probably are linked to arrhythmogenesis in congenital LQTS. The data suggest that propranolol but not atrial pacing are effective to suppress repolarization abnormalities during sympathetic stimulation.

Adolescent↗
PubMed1997

Electrophysiologic changes in arrhythmogenic substrate following the maze procedure in patients with lone and paroxysmal atrial fibrillation.

Although the Maze procedure is highly successful in restoring sinus rhythm in patients with atrial fibrillation (AF), the electrophysiologic changes that occur after the Maze procedure and its mechanism of action are still unclear. The aims of the present study were to examine the electrophysiologic changes that occur in the arrhythmogenic substrate after the Maze procedure and to evaluate the mechanism by which it prevents lone and paroxysmal AF. The modified Maze procedure was performed in 6 patients (6 men, mean age 47 +/- 7 years) with lone and paroxysmal AF. Electrophysiologic studies were performed before and 35 +/- 8 days after the Maze procedure. Atrial mapping during sinus rhythm revealed that atrial activation propagated smoothly in a concentric circle from the sinus node to other regions in the right atrium and into the coronary sinus before the Maze procedure. Following the Maze procedure, atrial activation propagated selectively through routes produced by incisions or cryoablations in all 6 patients. In addition, double and triple potentials were recorded in regions where conduction blocks were created by the Maze procedure. Neither sinus node function nor AV conduction was changed following the Maze procedure. The Maze procedure did not affect the atrial effective refractory period or the zone of fragmented atrial activity, although the conduction delay zone was increased significantly (p < 0.05). AF was inducible in all 6 patients before the Maze procedure, whereas it was not inducible in any patients after the Maze procedure. The Maze procedure is effective in preventing AF without affecting sinus node function and AV conduction. Intra-atrial conduction block produced by incisions or cryoablations contributes to the prevention of AF.

Adult↗
PubMed1996

Frequency-dependent electrophysiologic properties of ventricular repolarization in patients with congenital long QT syndrome.

OBJECTIVES: This study was performed to evaluate the frequency dependency of ventricular repolarization and the effect of epinephrine in patients with congenital long QT syndrome (LQTS). BACKGROUND: The efficacy of pacemakers in addition to antiadrenergic therapy in the treatment of congenital LQTS has been reported. METHODS: Monophasic action potentials were recorded from right and left ventricular endocardium during atrial pacing at heart rates from 70 to 140 beats/min at baseline and from 100 to 140 beats/min during epinephrine infusion (0.1 microgram/kg body weight per min) in 11 patients with congenital LQTS and 10 control patients. The response of monophasic action potential duration at 90% repolarization (MAPD90) and the dispersion of MAPD90 were examined. RESULTS: At baseline, both the MAPD90 and the dispersion of MAPD90 were significantly (p < 0.001) longer in the congenital LQTS group than the control group. The differences in these variables between the two groups significantly decreased (MAPD90: from 105 to 31 ms; dispersion of MAPD90: from 55 to 13 ms, p < 0.001) at heart rate was increased. Epinephrine prolonged the MAPD90 and increased the dispersion of MAPD90 significantly (p < 0.001) at all paced heart rates in the congenital LQTS group without frequency dependency but did not change in the control group. Thus, epinephrine increased the differences in these variables between the two groups. CONCLUSIONS: The repolarization abnormalities in congenital LQTS were attenuated by increasing the heart rate, which supported the efficacy of pacemaker therapy. However, during sympathetic stimulation, the effects of increased heart rate on these repolarization abnormalities were limited.

Action Potentials↗
PubMed1996

Usefulness of electron-beam computed tomography in arrhythmogenic right ventricular dysplasia. Relationship to electrophysiological abnormalities and left ventricular involvement.

BACKGROUND: Electron-beam computed tomography (CT) may be useful for detecting myocardial fat infiltration and diagnosing arrhythmogenic right ventricular dysplasia (ARVD). There are several characteristic electron-beam CT findings of ARVD. However, the incidence, their relation to electrophysiological abnormalities, and the usefulness of electron-beam CT for evaluating left ventricular involvement are unknown. This study aimed to clarify these issues. METHODS AND RESULTS: Electron-beam CT was performed in 14 patients with ARVD (ARVD group), 16 age- and sex-matched patients with right ventricular enlargement and/or dysfunction without ARVD (RV enlargement group), and 13 control subjects (control group). The incidences of abnormal electron-beam CT findings in the three groups were examined. Furthermore, we examined the endocardial fat-infiltrated areas detected by electron-beam CT (CT-A) and electrophysiologically abnormal areas detected in the mapping electrophysiology study (EPS-A) and compared the relationship between them in the ARVD group. (1) The frequencies of abundant epicardial adipose tissue, low-attenuation trabeculations, scalloping of the right ventricular free wall, and intramyocardial fat deposits were 86%, 71%, 79%, and 50%, respectively, in the ARVD group, whereas these findings were not observed in the RV enlargement and control groups. (2) Three ARVD patients (21%) had adipose tissue involvement of the left ventricle. (3) The relationship between CT-A and EPS-A was as follows: CT-A > EPS-A, 71%; CT-A = EPS-A, 14%; and EPS-A only, 14%. CONCLUSIONS: Characteristic electron-beam CT findings are frequently observed only in patients with ARVD. Electron-beam CT is useful for evaluating for left ventricular involvement and can estimate EPS-A.

Adult↗
PubMed1996

Initiation of alveolar ridge augmentation in the rat mandible by subperiosteal implantation of octacalcium phosphate.

The study was designed to investigate the process of bone formation caused by implantation of octacalcium phosphate as well as stability of the bone formed at the alveolar ridge. Synthetic octacalcium phosphate was implanted into a subperiosteal pocket in the rat mandible. Bone formation at the alveolar ridge was examined radiographically and histologically between 1 and 48 week(s) after implantation. Radiopacity of the octacalcium phosphate implant became obvious in week 2. Osteogenesis was initiated from the bone surface near the implantation site and multinucleated giant cells appeared on the implanted octacalcium phosphate in week 1. More apposition of new bone was observed on the implanted octacalcium phosphate in week 2 or later. Some implants were directly enclosed by newly formed bone and no cellular component was seen between the implant and the bone matrix. Many octacalcium phosphate implants were enclosed by bone, whereas the augmented ridge was not seen radiographically in week 24 or later. If its persistence can be improved, octacalcium phosphate could be used to augment atrophic alveolar ridges.

Alveolar Process↗
PubMed1996

Full-thickness reconstruction of cheek defect involving oral commissure with forearm tendinocutaneous flap.

An 82-year-old man underwent full-thickness reconstruction of the cheek for a defect of the oral commissure resulting from a T3N1M0 squamous cell carcinoma. He had previously had both radiotherapy and chemotherapy. A tendinocutaneous flap from the forearm incorporating palmaris longus was used for static reconstruction. The vermilion was then reconstructed with rotation flaps from the contralateral vermilion. Oral function was restored, and he had no problems with drooling or speech.

Aged↗
PubMed1996

T wave alternans in idiopathic long-QT syndrome: insight from body surface mapping.

Body surface mapping was recorded during T wave alternans in two patients with idiopathic long QT syndrome. Eighty-seven lead ECGs of two consecutive beats during T wave alternans demonstrated that alternating changes in the morphology and polarity of the T wave existed mainly in the left frontal chest. The QRST isointegral maps of the same two consecutive beats showed alternation of a large negative area appearing mainly in the left frontal chest. These results indicate that T wave alternans in the two patients were related to alternate heterogeneous prolongation of the action potential duration in this region.

Action Potentials↗
PubMed1996

Sudden death in a patient with apparent idiopathic ventricular tachycardia.

Idiopathic ventricular tachycardia is widely believed to carry a favorable prognosis, although there have also been reports of sudden cardiac deaths. We present a case of sudden death in a patient with apparent idiopathic right ventricular tachycardia. This patient had long-standing and exercise-related symptoms, an essentially negative non-invasive cardiac evaluation, and spontaneous and inducible ventricular tachycardia of left bundle branch block and inferior axis morphology, that was treated with propranolol. After an uneventful 5-year course, the patient died suddenly. Postmortem examination revealed a severely dilated right ventricle and significant replacement of the right ventricular wall with adipose tissue. Interstitial fibrosis was also seen, but only to a very slight degree.

Bundle-Branch Block↗
PubMed1996

QRS alteration-induced torsade de pointes in a patient with an artificial pacemaker and hypokalemia.

The present patient demonstrated torsade de pointes (TdP) after a pacemaker implantation without a decrease in heart rate or pacemaker malfunction. Marked QT prolongation and TdP were closely related to alteration of the depolarization pattern (appearance of junctional rhythm). Resetting the pacemaker to a rate that inhibited spontaneous rhythm was effective in preventing TdP.

Electrocardiography↗
PubMed1996

[Class III antiarrhythmic drugs].

Class III antiarrhythmic drugs prolong action potential duration by blocking cardiac potassium channels. Amiodarone and d-1 sotalol are representative class III drugs commonly used for drug resistant arrhythmias. Amiodarone has miscellaneous properties including potassium, sodium, calcium, and nonspecific sympathetic blocking effects when it is given orally. It mainly blocks sodium channels when it's given intraveneously. Amiodarone requires careful follow up because of its important side effects. Some randomised studies are still ongoing to confirm whether amiodarone can improve mortality in patients with refractoly ventricular arrhythmias.

Amiodarone↗
PubMed1995

Effects of verapamil and propranolol on early afterdepolarizations and ventricular arrhythmias induced by epinephrine in congenital long QT syndrome.

OBJECTIVES: This study used monophasic action potentials to investigate the effects of verapamil and propranolol on epinephrine-induced repolarization abnormalities in congenital long QT syndrome. BACKGROUND: Early afterdepolarizations have been suggested to play a significant role in QT prolongation and ventricular arrhythmias in congenital long QT syndrome. Calcium channel blocking as well as beta-adrenergic blocking agents are reported to be effective in the management of this syndrome. METHODS: Monophasic action potentials from 2 to 4 sites were recorded simultaneously in eight patients with the long QT syndrome (22 sites) and in eight control patients (23 sites) and were obtained during constant atrial pacing 1) before epinephrine infusion; 2) during epinephrine infusion (0.1 microgram/kg body weight min); 3) after verapamil injection (0.1 mg/kg) during epinephrine infusion; and 4) after both propranolol (0.1 mg/kg) and verapamil injections. RESULTS: Early afterdepolarizations were recorded in two of the eight patients (2 of 22 sites) during the control state. During epinephrine infusion, early afterdepolarizations were recorded in six patients (six sites), and ventricular premature complexes were induced in three and torsade de pointes in one. Epinephrine prolonged 90% monophasic action potential duration from 348 +/- 48 (mean +/- SD) to 381 +/- 49 ms (22 sites, p < 0.0005) and increased the dispersion of action potential duration (difference between the longest and shortest action potential duration) from 36 +/- 20 to 64 +/- 34 ms (p < 0.005). Verapamil eliminated (two sites) or reduced (four sites) early afterdepolarizations and abolished ventricular premature complexes in two of the three patients as well as suppressing torsade de pointes. Verapamil shortened the action potential duration to 355 +/- 28 ms (p < 0.01 vs. epinephrine) and decreased the dispersion to 44 +/- 19 ms (p < 0.05 vs. epinephrine). Propranolol further eliminated (two sites) or reduced (two sites) early after depolarizations, abolished ventricular premature complexes in the remaining one patient and further shortened the action potential duration to 337 +/- 32 ms (p = 0.09 vs. verapamil). In the control patients, none of the early afterdepolarizations, ventricular arrhythmias or marked prolongations of action potential duration were induced by epinephrine, and neither verapamil nor propranolol changed repolarization variables. CONCLUSIONS: These results indicate that both verapamil and propranolol can improve repolarization abnormalities induced by epinephrine in congenital long QT syndrome.

Action Potentials↗
PubMed1995

Subperiosteal implantation of octacalcium phosphate (OCP) stimulates both chondrogenesis and osteogenesis in the tibia, but only osteogenesis in the parietal bone of a rat.

BACKGROUND: It is not known whether long bones and calvaria have distinct biological characteristics. Octacalcium phosphate (OCP), which is a precursor phase of the hydroxyapatite, has been reported to stimulate bone formation if implanted in the subperiosteal region of mouse calvaria. The present study was designed to investigate how the long bone and the calvarium respond to OCP implantation and to compare their biological characteristics. METHODS: The synthetic OCP was implanted into the subperiosteal region of rat tibiae and parietal bones being mixed with bovine type I collagen treated by pepsin (Atelocollagen). The biological response was examined histologically and immunohistochemically for collagen matrix phenotypes of types I and II to identify bone and cartilage formation. RESULTS: Both chondrogenesis and osteogenesis were initiated in the tibia 1 week after implantation of OCP and most of the cartilage was replaced by bone at week 2. However, the parietal bone did not show osteogenesis responding to OCP implantation until week 3, and no cartilage formation was associated with the osteogenesis. CONCLUSIONS: The present study demonstrated the distinct characteristics of biological response to OCP implantation between the long bone and the calvarium in terms of whether or not cartilage formation is involved in the stimulated osteogenesis by OCP, and in terms of timing of the stimulated chondrogenesis and/or osteogenesis, i.e., the parietal bone takes more time to respond to OCP implantation than the tibia.

Animals↗
PubMed1995

Percutaneous transvenous mitral commissurotomy immediately restores quick response of VO2 to mild exercise despite insignificant increases in peak VO2.

Percutaneous transvenous mitral commissurotomy (PTMC) increases peak oxygen uptake (VO2) chronically, but not acutely, despite early symptomatic improvements. Analysis of transient VO2 responses to submaximal exercise (an exercise regimen more comparable to the patients' daily activities than that provided by maximal exercise testing), may be sensitive in detecting the acute hemodynamic benefits of PTMC. Since no methods are available to accurately estimate the transient response of VO2, we developed a new technique, using random exercise. In 15 patients who underwent successful PTMC, we repeated the conventional maximal exercise test and the random exercise test before and within a few days after PTMC. For the random exercise test, we intermittently imposed upright bicycle exercise at 50 W, according to a random binary sequence, while measuring breath-by-breath VO2. After determining the transfer function relating workload to VO2, we computed the high resolution VO2 response to a hypothetical step increase in exercise. Despite improvements in resting hemodynamics and New York Heart Association (NYHA) Class, peak VO2 improved insignificantly (952 +/- 271 vs 1,029 +/- 342 ml/min, P = 0.063) shortly after successful PTMC. In contrast, the amplitude of the VO2 step response increased significantly in the early-to-mid portion (28-76s; P < 0.01-0.05). The remaining portion was unchanged. Consequently, the time constant shortened from 64 +/- 26 to 48 +/- 22s (P < 0.05). The maximal Borg scale value during random exercise decreased significantly (13.1 +/- 1.8 vs 11.4 +/- 1.1; P < 0.01). We conclude that the VO2 step response, using the random exercise test, is more sensitive than peak VO2 in detecting the functional improvement that is coupled with the hemodynamic improvement immediately after PTMC.

Adult↗