Kazuya Fujino

Endothelin blocks ATP-sensitive K+ channels and depolarizes smooth muscle cells of porcine coronary artery.

ATP-sensitive K+ channels with a conductance of 30 pS in smooth muscle cells of porcine coronary artery were found to be highly active in the intact cell-attached patch configuration when the pipette contained a physiological concentration of Ca2+ (greater than 10(-4) M). In the inside-out configuration, these channels were activated by extracellular Ca2+ and blocked by cytosolic ATP and glibenclamide. Endothelin applied to the pipette specifically blocked these channels in a concentration-dependent manner in the cell-attached configuration (half-maximal inhibition, 1.3 x 10(-9) M). A K+ channel opener, nicorandil, activated these channels even in the presence of 10(-8) M endothelin. In the whole-cell current-clamp method, the cell membrane was depolarized by endothelin and then repolarized by nicorandil. The membrane depolarization is closely related to contraction of smooth muscle cells. These results suggest that the ATP-sensitive K+ channels are important in controlling the vascular tone of the coronary artery and that endothelin can increase vascular tone by blocking these channels.

Magnetocardiograms of patients with left ventricular overloading recorded with a second-derivative SQUID gradiometer

Magnetocardiograms (MCGs) were recorded by means of a second-derivative SQUID (superconducting quantum interference device) magnetometer in 60 normal subjects and 95 patients with left ventricular overloading to determine the clinical value of the MCG. In patients with left ventricular overloading, the Q or S wave was increased in the upper anterior part of the thorax, and the R wave was increased in the left lower part of the thorax, indicating increased leftward force due to left ventricular overloading. For detection of left ventricular hypertrophy or dilatation from echocardiographic measurements, the sensitivity and specificity of the MCG were similar to those of the standard ECG, or slightly better. In patients with left ventricular systolic overloading, the Q wave was decreased in the lower anterior part of the thorax, indicating a decreased septal vector. Inversion of the T wave was seen more frequently in the MCGs than in the ECGs of patients with left ventricular overloading, suggesting that the MCG is useful for detecting early abnormalities of repolarization. These results suggest that the MCG may provide information that is difficult to obtain from the standard 12-lead ECG.

Analysis of the T wave of the magnetocardiogram in patients with essential hypertension by means of isomagnetic and vector arrow maps

Magnetocardiograms (MCGs) of 50 normal subjects and 40 patients with essential hypertension were recorded to determine the value of the MCG for detecting abnormal repolarization. Among the patients with essential hypertension, there were nine cases (22.5%) in whom isopotential maps did not show rightward repolarization vectors but isomagnetic and vector arrow maps showed a rightward repolarization vector in some areas in addition to the normal repolarization vector. Departure maps of the ECG showed an increased repolarization vector directed anteriorly in some of these cases. The repolarization abnormality was recognized in only the MCG departure map in four cases, while no case showed abnormality in only the ECG departure map. With the progress of hypertension, the repolarization abnormality was seen more frequently and its detection using the MCG was higher than that using the ECG. Furthermore, multiple dipoles were detected more frequently from the MCG than from the ECG. Thus the MCG seems more useful than the ECG in the analysis of repolarization abnormalities in essential hypertension.

Effects of lidocaine and quinidine on post-repolarization refractoriness after the basic and premature action potentials: Consideration of aim of antiarrhythmic drug therapy

Antiarrhythmic drugs are often more effective in suppressing ventricular tachycardias than are background premature extrasystoles. The mechanism of action of these agents was examined by studies on the effects of lidocaine and quinidine on post-repolarization refractoriness of both basic and premature action potentials. In the absence of antiarrhythmic drugs, the excitability threshold was relatively constant after the end of repolarization of both basic and premature action potentials. In the presence of lidocaine or quinidine, the strength-interval curves were shifted to the right and superiorly, and the two drugs had different effects on the course of the strength-interval curve and Vmax recovery, presumably due to use-dependent V max block. Moreover, depressions of Vmax and excitability were more marked after the premature action potential than after the basic action potential. These results suggest that lidocaine and quinidine cause more depression of the excitability of second premature contractions than of first premature contractions, and also indicate that for protection against sustained ventricular tachycardias, it may not be necessary to suppress chronic premature ventricular contractions.

Detection of Accessory Pathway in Patients with WPW Syndrome by Means of The Isomagnetic Map and MRI

The current source is expected to be localized more exactly with a magnetocardiogram (MCG) than with an electrocardiogram (ECG). In the present study, the isomagnetic map at the time of the delta wave and a gated magnetic resonance imaging (MRI) were compared to assess the usefulness of the magnetocardiogram (McG) in localizing a position of the accessory pathway (Kent bundle). Spach and Benson reported that the analysis of the T wave was as useful as that of the QRS wave in predicton of the pre-excited sites of the ventricle. 1,2 Therefore, we examined the repolarization wave in order to localize the site of an accessory pathway in WPW syndrome, because the repolarization abnormality might be detected more precisely by the MCG. 3 Our results showed that the analysis of the repolarization wave’s of the MCG was as useful as the delta wave to detect the site of an accessory pathway.

Vector U loop in normal and hypertensive subjects

The U loops of vectorcardiograms (VCG) were recorded in 100 normal subjects and 123 subjects with hypertension, using a direct-writing vectorcardiograph with memory function. These U loops were examined qualitatively and quantitatively. Subjects with hypertension were classified into four groups on the basis of electrocardiographic findings, and the correlation between findings on the U loop and the severity of hypertension was studied. The U loop of normal subjects was directed similarly to the T loop, showing either an arc or semilunar shape in the horizontal plane. In hypertensive subjects the U loop tended to be displaced anteroinferiorly and to the right with an increase in severity of hypertension. In these subjects the U loop was of slightly greater amplitude than in normal subjects, and was long and slender in shape. Anterior and rightward displacement of the U loop was also observed in hypertensive cases who showed no abnormality in the T wave of standard lead ECGs or in the T loop of the VCG. These findings seem useful as clinical parameters of the hemodynamic state in the early stage of hypertension. Based on these results, it was hypothesized that mechanical factors, such as stretch of the ventricular muscles induced by pressure loading of the left ventricle, may contribute greatly to genesis of the U loop.

Vector U loop in patients with right ventricular overloading

The U loop of the vectorcardiogram (VCG) was examined qualitatively and quantitatively in 126 normal subjects, 15 subjects with complete right bundle branch block (CRBBB group) and 58 patients with right ventricular overloading (RVO group), using a direct-writing vectorcardiograph with memory function. In normal subjects the U loop was directed similarly to the T loop, i.e., to the left, anteriorly and inferiorly. In the CRBBB group, maximum U vector was smaller, but its direction was not significantly different from that in normal subjects. In the RVO group, the U loop tended to be displaced posteriorly and to the left and was significantly greater in magnitude than that in normal subjects in the horizontal (P less than 0.01) and frontal (P less than 0.001) planes. In the RVO group, a good correlation was found between the direction of maximum U vector and right ventricular systolic pressure. In some cases of the RVO group, the U loop was the only abnormality suggesting right ventricular overloading. These findings suggest that abnormality of the U loop is a good indicator in a diagnosis of right ventricular overloading.

The Magnetocardiogram in Patients with Systolic and Diastolic Overload of the Right Ventricle

The second derivative gradiometer is expected to detect the current source from the right ventricle more specifically, where it is located close to the anterior chest wall because of its unique system. Therefore, we investigated the magnetocardiogram (MCG) in patients with right ventricular overload (RVO), and correlated the MCG findings with hemodynamic parameters. This study was also aimed to diagnose RVO in the presence of right bundle branch block (RBBB), which so far has been considered to be difficult to diagnose by the conventional electrocardiogram (ECG).

Detection of the Abnormal Repolarization Vector in Diabetes Mellitus by Means of the Isomagnetic Map

The magnetocardiogram (MCG) recorded with the second-derivative SQUID gradiometer may be more useful to detect the current source parallel to the anterior chest wall and multiple current dioples than the electrocardiogram (ECG). We have already reported that the abnormal repolarization vector could be detected more frequently by the MCG than ECG in patient with left ventricular overloading and myocardial infarction. 1,2 In the present study, we investigated the clinical usefulness of the isomagnetic map analysis for the diagnosis of repolarization abnormality in diabetic patients.