Biomedical subjects

T Kohya

Publications and source records attributed to T Kohya.

43 records · Page 3Linked to original sources

PubMed1987

Regional effects of verapamil on recovery of excitability and conduction time in experimental ischemia.

This study was designed to test the hypothesis that verapamil has an effect on ischemia-initiated arrhythmias related to its regional influences on recovery of excitability and conduction time. Using a coronary perfused preparation of cat left ventricle that allows simultaneous electrophysiologic monitoring of both endocardium and epicardium, we studied the effect of verapamil on ischemia-induced changes in transmembrane action potentials, conduction properties, and refractory periods of endocardial and epicardial muscle cells. Oxygenated Tyrode's solution was perfused through the left anterior descending coronary artery, while the preparation was superfused with Tyrode's solution gassed with 95% N2 and 5% CO2. "Ischemia" was produced by stopping coronary perfusion. During 30 min of ischemia, resting potential, action potential amplitude (APA), and action potential duration (APD) were reduced, and conduction time was prolonged in both endocardial and epicardial cells, but the changes were greater in the epicardial cells. Endocardial refractory periods shortened in parallel with APD shortening throughout 30 min of ischemia, whereas epicardial refractory periods shortened for the first 10 min and then increased due to development of longer postrepolarization refractoriness. As a result, there were significant differences in refractory periods between endocardial and epicardial cells at 10 and 30 min of ischemia, and rapid ventricular activity could be induced at these times. Exposure to verapamil (1 mg/liter) before cessation of coronary perfusion significantly limited the reduction of APA and the prolongation of conduction time during the first 10 min of ischemia in epicardial cells, but did not influence endocardial cells. During the remaining 20 min of ischemia, verapamil enhanced the reduction of APD of both epicardial and endocardial cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

PubMed1986

Simultaneous recording of action potentials from endocardium and epicardium during ischemia in the isolated cat ventricle: relation of temporal electrophysiologic heterogeneities to arrhythmias.

We studied the effects of ischemia on transmembrane action potentials, conduction time, and refractory periods of both endocardial and epicardial muscle cells of coronary-perfused cat left ventricles. Oxygenated Tyrode's solution was perfused through the left anterior descending coronary artery, while the preparation was superfused with Tyrode's solution gassed with 95% N2 and 5% CO2. Transmembrane action potentials recorded simultaneously from endocardial and epicardial cells were normal during coronary perfusion. When perfusion was discontinued ("ischemia"), rapid deterioration of action potentials and prolongation of conduction time were observed in both endocardial and epicardial cells. The magnitude of the reduction of action potential amplitude and action potential duration (APD), and of prolongation of conduction time, was greater in epicardial cells than in endocardial cells, although the change in resting membrane potential was almost the same. However, APD of endocardial cells decreased progressively during 30 min of ischemia, whereas APD of epicardial cells was reduced maximally at 10 min and then partially recovered. Shortening of refractory periods of endocardial cells paralleled APD shortening, whereas refractory periods of epicardial cells decreased for the first 10 min and then increased. At 10 min of ischemia, APD and refractory periods of epicardial cells were significantly shorter than those of endocardial cells. At 30 min of ischemia, refractory periods of epicardial cells exceeded those of endocardial cells because of development of greater postrepolarization refractoriness in epicardial cells. Accompanying these different changes in APD and refractory periods of endocardial and epicardial cells, spontaneous extrasystolic impulses increased and rapid runs of extrasystolic impulses could be induced by extrastimuli.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

PubMed1985

[Right ventricular dysplasia: clinical features compared with dilated cardiomyopathy].

Five patients with right ventricular dysplasia (RVD) and 28 patients with predominantly left sided dilated cardiomyopathy (DCM) were studied. RVD was characterised by syncope, recurrent sustained ventricular tachycardia, which typically had a left bundle branch block pattern on the surface electrocardiogram, right heart failure, and faint or absence of the right ventricular free wall on the myocardial scintigraphy. Two-dimensional echocardiographic, radionuclide angiographic, and contrast ventriculographic studies were typical of the right ventricular abnormalities in both Uhl's anomaly and arrhythmogenic right ventricular dysplasia. Two of them were died suddenly. Pathologic examinations showed "parchment-like" thinning of portions of the right ventricular free wall and its replacement by adipose tissue, although such degenerations were not found in the septum and the left ventricle. By contrast, DCM was characterised by exertional dyspnea and short run ventricular tachycardia, most of which had a right bundle branch block pattern. Ten of them had left ventricular myocardial defects on the scintigraphy, of whom five died suddenly. Hemodynamic data showed that left ventricular dysfunction was predominant more than right ventricle. Thus we postulate that these two syndromes are manifestations of a congenital, pathophysiologic process - the "involved right or left ventricle" syndrome.

Adult↗

PubMed1983