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Biomedical subjects

K Harumi

Publications and source records attributed to K Harumi.

At least 19 recordsLinked to original sources
PubMed2001

Three-year follow-up of patients with right bundle branch block and ST segment elevation in the right precordial leads: Japanese Registry of Brugada Syndrome. Idiopathic Ventricular Fibrillation Investigators.

OBJECTIVES: We sought to determine the prevalence of right bundle branch block (RBBB) and ST segment elevation in the working Japanese population, as well as the event rate during a three-year prospective follow-up period. BACKGROUND: A poor prognosis of RBBB and ST segment elevation has been reported in Europe and South America, even in asymptomatic patients; however, a large population of asymptomatic patients with sporadic RBBB and ST segment elevation has not been studied. METHODS: Ten thousand 12-lead electrocardiograms (ECGs) were obtained during annual check-ups of working adults in the Tokyo area. This three-year prospective follow-up study consisted of 105 patients, including 20 with ventricular fibrillation, 18 with syncope and 67 who were asymptomatic. They were registered from 46 institutions in Japan. RESULTS: The prevalence of ECG abnormalities in working adults was 0.16%. A coved-type ST segment elevation was related to a history of cardiac events, and 18% of registered patients had PR prolongation and 9.5% had left-axis deviation. The cumulative cardiac event-free rate was 67.6% in the symptomatic group and 93.4% in the asymptomatic group (p = 0.0004) after three years. CONCLUSIONS: The recurrence rate of cardiac events in symptomatic patients was similar to that reported previously, but it was very low in sporadic asymptomatic patients. The ECG findings may help us to select patients for further examination and more accurate evaluation of their prognoses.

Adult↗
PubMed2000

Exercise-induced QTc-interval changes for predicting improvement in regional blood flow in ischemic myocardium and cardiac output after coronary angioplasty in patients with right bundle-branch block.

BACKGROUND: We have previously shown that QT-interval changes are more useful than ST-T changes in evaluating the severity of exercise-induced myocardial ischemia in patients with right bundle-branch block (RBBB). HYPOTHESIS: The purpose of this study was to evaluate whether the improvement in regional myocardial blood flow (RMBF) in ischemic areas and cardiac output after percutaneous transluminal coronary angioplasty (PTCA) can be predicted by exercise-induced QT-interval changes prior to PTCA. METHODS: The RMBF and cardiac output were quantified with nitrogen-13 ammonia positron emission tomography at rest and during exercise in 20 patients with RBBB and ischemic heart disease before and 6 months after PTCA, and in 9 healthy volunteers. RESULTS: Before PTCA, exercise-induced prolongation by < 20 ms or shortening of the Bazett-corrected QT (QTc) interval (454 +/- 38 to 451 +/- 41 ms, p = NS) was observed in 13 patients (Group 1) and prolongation by > or = 20 ms (429 +/- 44 to 466 +/- 50 ms, p < 0.002) was observed in 7 (Group 2). The number of regions of exercise-induced ischemia was significantly greater in Group 2 than in Group 1 (4.0 +/- 1.2 vs. 2.1 +/- 1.2, p < 0.01). The RMBF in regions of exercise-induced ischemia and cardiac output at rest was not significantly different between Groups 1 and 2, whereas during exercise both the parameters were significantly lower in Group 2 than in Group 1 (both p < 0.05). After successful PTCA, RMBF both at rest and during exercise improved significantly in Group 1 (0.67 +/- 0.04 to 0.71 +/- 0.06 ml/min/g, 0.74 +/- 0.05 to 0.84 +/- 0.08 ml/min/g; both p < 0.0001), but did not improve significantly in Group 2 (0.63 +/- 0.05 to 0.65 +/- 0.07 ml/min/g, 0.65 +/- 0.04 to 0.69 +/- 0.11 ml/ min/g; both p = NS). Cardiac output during exercise improved significantly in Group 1 (6.4 +/- 0.7 to 7.4 +/- 0.9 l/min; p < 0.002) but not in Group 2 (5.7 +/- 0.6 to 5.9 +/- 0.6 l/min; p = NS). CONCLUSIONS: Our results suggest that the marked prolongation of the QTc interval induced by pre-PTCA exercise may predict a lack of improvement in RMBF in ischemic areas and cardiac output after PTCA in patients with RBBB and ischemic heart disease.

Adult↗
PubMed2000

Exercise-induced ST-segment depression: imbalance between myocardial oxygen demand and myocardial blood flow.

OBJECTIVE: ST-segment depression is believed as a common electrocardiographic sign of myocardial ischemia during exercise testing. Ischemia is generally defined as oxygen deprivation due to reduced perfusion. However, the exact relationship of the ischemic definition to ST-segment depression remains unclear. This study was conducted to evaluate the correlation between myocardial oxygen demand and myocardial blood flow (MBF) when ischemic (horizontal or downsloping) ST-segment depression of > or = 0.1 mV 80 ms after the J point developed during low-level exercise. METHODS AND RESULTS: Seventy-two patients with angiographically proven coronary artery disease (CAD) and 9 healthy volunteers underwent exercise positron emission tomography (PET). Myocardial oxygen demand was defined as a rate-pressure product (RPP, heart rate x systolic blood pressure) during exercise and MBF was quantified by nitrogen-13 ammonia perfusion PET. The myocardial demand-supply balance (MDSB) index was calculated from the MBF ratio (values during exercise/values at rest) against the RPP ratio (values during exercise/values at rest). The MDSB index was significantly lower in patients with ischemic ST-segment depression than in patients with non-ischemic ST depression and healthy volunteers (0.82 +/- 0.16 vs. 1.02 +/- 0.17, p < 0.0001 and vs. 0.99 +/- 0.14, p = 0.0109). Further, the presence of inadequate increase in MBF of < or = 10% (2 SD below the mean % value of healthy volunteers) during exercise in regional myocardium perfused by stenotic CAD significantly correlated with exercise-induced ischemic ST-segment depression (p = 0.0105). CONCLUSIONS: Our study could demonstrate that exercise-induced ischemic ST-segment depression is associated with myocardial ischemia due to exercise-induced imbalance between myocardial oxygen demand and global and regional MBF supply in patients with proven CAD.

Adult↗
PubMed1999

Brady-tachycardia syndrome after radiotherapy for lung cancer. Assessment by computed tomography and carbon-11 methionine positron emission tomography.

A 74-year-old male who had received radiotherapy (total 54 Gy) for right lung cancer 7 months earlier developed a symptomatic brady-tachycardia syndrome requiring the implantation of a permanent pacemaker. Chest CT showed a pulmonary tumor of 2-cm diameter in the right lower lobe with direct extension into the surrounding tissue, suggesting the possibility of cardiac invasion. Carbon-11 methionine positron emission tomography (PET) indicated the absence of visible invasion of the heart with lung cancer. The bradytachycardia syndrome, therefore, was considered to be associated with sinus node injury due to radiation. Carbon-11 methionine PET metabolic imaging might play an important role in evaluating noninvasively the cause of the arrhythmia in this patient.

Aged↗
PubMed1998

Relation between exercise-induced myocardial ischemia as assessed by nitrogen-13 ammonia positron emission tomography and QT interval behavior in patients with right bundle branch block.

Exercise-induced myocardial ischemia is difficult to detect with ST-T changes in patients with right bundle branch block (RBBB). We sought to predict exercise-induced myocardial ischemia with QT interval behavior during exercise in patients with RBBB. Twenty-two patients with angiographically proven coronary artery disease and RBBB and 9 healthy volunteers underwent nitrogen-13 ammonia positron emission tomography with bicycle ergometer exercise at a fixed workload of 25 W. Regional myocardial blood flow (RMBF) and electrocardiographic changes were measured both at rest and after 5 minutes of exercise. The QT interval was measured from the onset of the QRS complex to the offset of the T wave in lead V5. The deltaQT and deltaRMBF, which indicated values after 5 minutes of exercise minus values at rest, were negatively correlated (r = -0.74, p <0.001). Exercise-induced shortening of the QT interval (422 +/- 27 to 381 +/- 38 ms, p = 0.0020) was observed in 15 patients (group 1) and no change or prolongation (411 +/- 45 to 420 +/- 37 ms, p = NS) was observed in 7 patients (group 2). Multivessel disease was significantly more frequent but collateral circulation was significantly less in group 2 than in group 1 (p <0.01, p <0.05, respectively). Cardiac output at rest was significantly lower in groups 1 and 2 than in healthy volunteers (4.52 +/- 0.83 and 4.51 +/- 0.84 vs 6.20 +/- 0.83 L/min; p = 0.0014, p = 0.0003). Although RMBF at rest did not differ significantly among groups 1 and 2 and healthy volunteers (0.63 +/- 0.20 vs 0.69 +/- 0.13 and vs 0.77 +/- 0.14 ml/min/g), RMBF after 5 minutes of exercise was significantly lower in group 2 than in group 1 and healthy volunteers (0.78 +/- 0.11 vs 0.96 +/- 0.20 and vs 1.20 +/- 0.18 ml/min/g; p = 0.0289, p <0.0001). The number of regions of critical coronary artery disease was significantly greater in group 2 than in group 1 (4.0 +/- 1.2 vs 2.1 +/- 1.3, p = 0.0039). Our results suggest that the absence of QT interval shortening during exercise may indicate severe myocardial ischemia induced by exercise in patients with RBBB and coronary artery disease.

Ammonia↗
PubMed1998

Correlation between exercise-induced ischemic ST-segment depression and myocardial blood flow quantified by positron emission tomography.

BACKGROUND: Ischemic ST-segment depression (horizontal or downsloping) is the most common manifestation of exercise-induced myocardial ischemia. The mechanisms responsible for these types of ST-segment depression are largely unknown. We investigated the relation of these 2 types of exercise-induced ST-segment depression to changes in regional myocardial blood flow (RMBF) by using exercise positron emission tomography (PET). METHODS AND RESULTS: The RMBF was measured with nitrogen-13 ammonia PET both at rest and during low-level supine bicycle exercise in 27 patients with angiographically proven coronary artery disease and in 6 healthy volunteers. ST-segment depression was measured from the isoelectric PR segment 80 ms after the J point. Exercise-induced horizontal ST-segment depression > or =0.1 mV was observed in 9 patients and downsloping depression > or =0.1 mV was observed in 18 patients. Multivessel disease was more frequent and areas of exercise-induced ischemia were larger in patients with downsloping depression than in patients with horizontal depression (P < .02, P < .05). In patients with horizontal ST-segment depression, RMBF in ischemic areas and in surrounding areas increased by a similar amount (31%+/-29% and 32%+/-16%) with exercise. In patients with downsloping ST-segment depression, RMBF was unchanged or decreased in ischemic areas (10%+/-24%) but increased in surrounding areas (46%+/-27%) with exercise. In healthy volunteers, RMBF increased in all areas (56%+/-30%) with exercise. CONCLUSIONS: Compared with horizontal changes in ST-segment morphology, downsloping changes may better indicate severe ischemia and greater differences in the increase of blood flow with exercise in the ischemic myocardium and in the surrounding areas.

Adult↗
PubMed1998

Possible mechanism of ECG features in patients with idiopathic ventricular fibrillation studied by heart model and computer simulation.

The possible contribution of localized conduction delay and abnormal action potentials to ventricular fibrillation (VF) was studied by applying an anisotropic cardiac computer model to clinical cases of the Brugada-type electrocardiogram (ECG), which shows right bundle branch block (RBBB), a normal QT interval, ST-segment elevation, and late r' in leads V1 and V2. The anisotropic heart model was composed of 50,000 discrete units with a spatial resolution of 1.5 mm and was mounted in a human torso model. The longitudinal/transverse conduction velocity ratio was 3:1. For the normal ECG, a conduction velocity of 0.75 m/s was required. In the abnormal area of the right anterior epicardial wall, the conduction velocity was set at 0.2 m/s, with decreasing action potential amplitude and 10% prolonged action potential duration. The ECG features of ST-segment elevation and Brugada-type right bundle branch block pattern were simulated. The action potential duration was able to change dynamically with coupling interval of stimulation, with a ratio of 9% for normal ventricular muscle and 50% for Purkinje fibers. Five successive stimuli were applied to the left lateral epicardium 300 ms after the first sinus excitation, and sustained VF was induced with the transmural conduction delay at the right anterior ventricle as a block increasing the vulnerability. At the initiation of VF, reentry circuits were shown around the border zone of the right epicardium and were very heterogeneous around the conduction delayed area and septal area. In an area with the characteristics of nontransmural conduction delay, sustained VF was prevented, and the pattern of transient right bundle branch block appeared on the simulated ECG and body surface potential maps. The late r' wave was calculated in the precordial leads and right anterior site on the body surface potential maps. These results suggest that increased multipolarity in the border zone between the Purkinje fibers and delayed conduction area in the right ventricle might play an important role as a functional block for the persistence of VF.

Action Potentials↗
PubMed1998

A simulation study of Torsade de Pointes with M cells.

Recent studies have reported the relation between Torsade de Pointes (TdP) and midmyocardial (M) cell function associated with long QT syndrome. To investigate this relation, we conducted a simulation study with a three-dimensional (3D) heart model incorporating M cells in the anterolateral areas of the model. Parameters of premature cycle-length dependent shortening of action potential duration (APD) and conduction velocity for the M cells were adjusted to induce tachyarrhythmias of TdP type. Under a basic pacing cycle length of 1,000 msec at the sinus node, four successive premature beats of 160-ms interval were generated 300 ms after the first sinus pacing. Setting lower conduction velocity and longer APD to M cells induced sustained TdP-like tachyarrhythmia resembling ECG findings. TdP could not be induced without the presence of M cells. This study suggests that TdP might be caused by reentry around M cells and dispersive refractory areas due to prolonged APD and slow conduction velocity.

Action Potentials↗
PubMed1998

Correlation between myocardial blood flow and fasting glucose metabolism in ischemic heart disease. Quantitative assessment by nitrogen-13 ammonia and fluorine-18 fluorodeoxyglucose positron emission tomography.

Ischemic myocardium avidly incorporates fluorine-18 fluorodeoxyglucose (F-18 FDG) in the fasting state, in contrast to the relative absence of F-18 FDG uptake in normal myocardium with sufficient blood flow in the fasting state. Although many studies have attempted to use F-18 FDG uptake to discriminate ischemic but viable myocardium from scarred myocardium, little is known clinically about the correlation between blood flow and F-18 FDG uptake in ischemic myocardium. We studied the critical level of blood flow that causes avid F-18 FDG uptake in myocardium in 9 patients. All patients had angiographically proven ischemic heart disease but no diabetes. Regional myocardial blood flow (RMBF) was measured quantitatively by positron emission tomography (PET) using nitrogen-13 ammonia in the resting state, in which the normal value was 80.2 +/- 13.0 ml/min/100 cm3. The F-18 FDG uptake in myocardium was assessed with the differential uptake ratio (DUR) scale. We constructed circumferential profiles of radioactivity uptake in myocardium for each study, and chose 780 sections of myocardium in which the relation between the two factors could be analyzed. In moderately ischemic to normal myocardium with RMBF of 50 to 90 ml/min/100 cm3, RMBF and F-18 FDG uptake were negatively correlated (r = -0.44, p < 0.01). When RMBF was 50 to 60 ml/min/100 cm3 (n = 121), the peak DUR value of F-18 FDG uptake was 4.0 +/- 2.0. The two factors were not correlated when RMBF was less than 50 ml/min/100 cm3 or 90 ml/min/100 cm3 or higher. Our results suggest that RMBF and F-18 FDG uptake values as measured with PET may provide valuable information on the possible benefit of intervention in ischemic heart disease.

Aged↗
PubMed1997

Correlations between resting regional wall motion and regional myocardial blood flow (at rest and during exercise) in infarct-related myocardium--a study with [13N]ammonia positron emission tomography.

We evaluated quantitatively the correlations between resting wall motion and regional myocardial blood flow (RMBF; at rest and during exercise) in infarct-related myocardium. The study was performed in 28 subjects: 21 patients who had previously suffered myocardial infarction of the anteroseptal wall, and 7 normal individuals. Positron emission tomography (PET) with [13N]ammonia was performed at rest and during low-grade exercise (bicycle ergometer fixed at 25 W for 6.5 min), and RMBF was measured quantitatively from the radioactivity in myocardial tissue and arterial blood. Resting regional wall motion was calculated using the centerline method on left ventriculographic findings. Resting regional wall motion was correlated with RMBF both at rest and during exercise in the infarct areas (anterior walls; y = 2.74 +/- 4.25 x 10(-2)x, r = 0.43, at rest; and y = -2.48 + 3.04 x 10(-2)x, r = 0.48, during exercise, p < 0.05; septal walls; y = -3.61 + 5.64 x 10(-2)x, r = 0.62, at rest; and y = -3.46 + 4.31 x 10(-2)x, r = 0.62, during exercise, p < 0.01). In each infarct-related wall, the coefficient (the slope) during exercise was smaller than that at rest (3.04 vs 4.25 and 4.31 vs 5.64 in each), and the infarct areas with preserved wall motion showed higher RMBF during exercise than those with reduced wall motion. Our results may show that wall motion depends on viable but ischemic myocardium in infarct-related walls.

Adult↗
PubMed1997

Significance of downsloping ST-segment depression induced by low-level exercise in severe coronary artery disease. Assessment with myocardial ischemia and collateral perfusion.

Exercise-induced downsloping ST-segment depression is a common manifestation of severe myocardial ischemia. Although greater downsloping ST-segment depression is suspected to indicate more severe ischemia, its exact relationship to regional myocardial blood flow (RMBF) has not yet been clarified. We investigated the relationship between the magnitude of downsloping ST-segment depression and exercise-induced changes in RMBF and collateral perfusion. Nitrogen-13 ammonia positron emission tomography was performed in 6 healthy volunteers and 72 patients with angiographically proven coronary artery disease. The left ventricle was divided into 11 regions of interest, and RMBF in each region was measured at rest and during low-level supine bicycle exercise. Downsloping ST-segment depression of 0.1 mV or more at 80 milliseconds after the J point was accepted as significant. Low-level exercise induced downsloping depression of 0.1 to 0.2 mV in 10 patients (group D1) and downsloping depression of 0.2 mV or more in 8 patients (group D2). Multivessel disease was common in both group D1 (80% of patients) and group D2 (88% of patients). Collateral circulation was significantly more frequent in group D1 (90%) than in group D2 (13%, p < 0.01). Ischemic areas were larger and cardiac function was worse in group D2 than in group D1. The RMBF increased sufficiently in all regions (56 +/- 30%) with exercise in the healthy group. In group D1, RMBF was unchanged or decreased in ischemic areas (10 +/- 23%) but increased sufficiently in surrounding areas (50 +/- 32%). In group D2, RMBF was unchanged in ischemic areas (17 +/- 24%) and increased insufficiently in surrounding areas (41 +/- 21%). Therefore, exercise-induced downsloping ST-segment depression of 0.1 to 0.2 mV may reflect an underlying change in blood flow in viable myocardium with collateral perfusion, and downsloping depression of 0.2 mV or more may reflect more severely impaired myocardium without collateral perfusion.

Adult↗
PubMed1996

Characteristics of patients with right bundle branch block and ST-segment elevation in right precordial leads. Idiopathic Ventricular Fibrillation Investigators.

To elucidate the clinical characteristics of patients with right bundle branch block and ST elevation in the right precordial leads, a prospective follow-up study was made in 63 registered patients, including 17 with a history of ventricular fibrillation (VF) and 14 with a history of syncope. The prevalence of coved type ST elevation was significantly higher in patients who had had cardiac events, and during the initial 15-month follow-up, 2 patients in the VF group died suddenly.

Adult↗
PubMed1995

Functional role of coronary collaterals with exercise in infarct-related myocardium.

We evaluated the regional myocardial blood flow in collateral dependent infarct-related areas to examine the functional role of coronary collaterals. Regional myocardial blood flow was measured by positron emission tomography with 13N-ammonia at rest and during low-grade exercise (bicycle ergometer fixed at 25 W for 6.5 min). The study was performed in 24 subjects, consisting of 19 patients with prior myocardial infarction, and five normal individuals. Regional myocardial blood flow was calculated using the radioactivity in myocardial tissue measured by positron emission tomography and the radioactivity in arterial blood. Concerning the infarct related area, the exercise caused myocardial blood flow to decrease by 18.4% (P < 0.01) in the collateral-dependent areas (n = 8) of angiographically positive collaterals, and to increase by 14.4% (P = not significant) in the areas (n = 10) of negative collaterals. Four patients in whom the myocardial blood flow in all walls, including the normal areas, decreased with exercise were excluded from this evaluation. Myocardial blood flow in collateral-dependent infarct-related areas appeared to decrease transiently by low-grade exercise. Our results suggest that collaterals increase the incidence of exercise-induced ischemia, but may protect the infarct related but viable myocardium from necrosis.

Adult↗
PubMed1995

Comparison of body surface potential maps simulated with isotropic and anisotropic computer heart models.

Simulated body surface potential maps (SBSPM) with isotropic and anisotropic heart models were compared to investigate the effect of myocardial anisotropy on body surface electrocardiograms at a whole heart level. Rotative fiber orientations of total 90 degrees was incorporated into an isotropic heart model. The anisotropy of conduction velocity and intracellular electric conductivity was included in the simulation. SBSPM based on epicardial, intramural, and endocardial stimulation show high correlation with fiber orientations. On the other hand, the anisotropy cannot be distinguished from the SBSPM in the simulation of normal heart model.

Anisotropy↗
PubMed1995

Comparative simulation of excitation and body surface electrocardiogram with isotropic and anisotropic computer heart models.

Comparative simulations between isotropic and anisotropic computer heart models were conducted to study the effects of myocardial anisotropy on the excitation process of the heart and on body surface electrocardiogram. The isotropic heart model includes atria, ventricles, and a special conduction system, and is electrophysiologically specified by parameters relative to action potential, conduction velocity, automaticity, and pacing. The anisotropic heart model was created by incorporating rotating fiber directions into the ventricles of the isotropic heart model. The orientation of the myocardial fibers in the ventricles of the model was gradually rotated counterclockwise from the epicardial layer to the endocardial layer for a total rotation of 90 degrees. The anisotropy of conduction velocity and intracellular electric conductivity was included in the simulation. Comparative simulations of the normal heart, LBBB, and RBBB showed no significant differences between the two models in the excitation processes of the whole heart or in the body surface electrocardiograms. However, it was easier to induce ventricular fibrillation in the anisotropic model than in the isotropic model. The comparative simulation is useful for investigating the effects of myocardial anisotropy at the whole heart level and for evaluating limitations of the isotropic heart model.

Action Potentials↗
PubMed1995

Relation between cardiac index and regional myocardial blood flow in the non-infarcted wall using PET with 13NH3 in healed myocardial infarction.

It is not clear whether there is any relationship between cardiac output and myocardial blood flow in the infarcted heart. We measured regional myocardial blood flow (RMBF) quantitatively by positron emission tomography (PET) with 13N-ammonia at rest in 18 patients with prior myocardial infarction. RMBF was calculated using the radioactivity in myocardial tissue measured by PET and the radioactivity of arterial blood. Cardiac output was determined by the dilution method using 13NH3 as an indicator, and the relation between cardiac output and RMBF was evaluated at the same time during PET study. There was a good linear correlation between cardiac index (C.I.) and mean RMBF in non-infarcted myocardium (r = 0.45, p < 0.05), and non-infarcted size (r = 0.74, p < 0.01). There was an even better linear correlation between C.I. and sigma RMBF (representing the product of mean RMBF and non-infarcted size) as follows: y = 0.016x + 1.94, r = 0.76 (p < 0.001). It was indicated that the value of C.I. may be related to RMBF of non-infarcted myocardium and its size.

Aged↗