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Biomedical subjects

H Mitamura

Publications and source records attributed to H Mitamura.

At least 19 recordsLinked to original sources
PubMed1999

Neurohumoral activations in congestive heart failure: correlations with cardiac function, heart rate variability, and baroreceptor sensitivity.

BACKGROUND: The clinical significance of the determination of heart rate variability and baroreceptor sensitivity relating to cardiac function and neurohumoral factors remains to be established. METHODS AND RESULTS: We investigated the relation between conventional clinical variables and frequency domain analysis of heart rate variability and baroreceptor sensitivity in 146 patients with heart failure. Cardiac function including left ventricular ejection fraction, left ventricular dimensions, and left atrial size was different by the plasma atrial natriuretic peptide level but not by the norepinephrine level. The total power and low-frequency power were correlated with plasma norepinephrine, whereas baroreceptor sensitivity was correlated with plasma atrial natriuretic peptide. None of the frequency domain variables and baroreceptor sensitivity was correlated with cardiac function. There was a positive correlation between the low-frequency power and baroreceptor sensitivity. CONCLUSIONS: Heart rate variability and baroreceptor sensitivity, which reflect autonomic regulation, may be an indicator independent from cardiac function in patients with heart failure.

Atrial Natriuretic Factor↗
PubMed1999

Profiles of aprindine, cibenzoline, pilsicainide and pirmenol in the framework of the Sicilian Gambit. The Guideline Committee for Clinical Use of Antiarrhythmic Drugs in Japan (Working Group of Arrhythmias of the Japanese Society of Electrocardiology).

The Vaughan Williams classification has been used widely by clinicians, cardiologists and researchers engaged in antiarrhythmic drug development and testing in many countries throughout the world since its initial proposal in the early 1970s. However, a major criticism of the Vaughan Williams system arose from the extent to which the categorization of drugs into classes I-IV led to oversimplified views of both shared and divergent actions. The Sicilian Gambit proposed a two-dimensional tabular framework for display of drug actions to solve these problems. From April to December 1996, members of the Guideline Committee met to discuss pharmacologic profiles of 4 antiarrhythmic drugs (aprindine, cibenzoline, pilsicainide, and pirmenol) that were not included in the original spreadsheet but are used widely in clinical practice in Japan. The discussion aimed to fit the drug profiles into the Gambit framework based on all the important literature published to date regarding the actions of the 4 drugs. This report is a summary of that deliberation.

Animals↗
PubMed1999

Ventricular fibrillation and shortening, alternans and after-depolarizations of epicardial monophasic action potentials during coronary occlusion and reperfusion: effect of repetition of ischemia.

The relationship between the occurrence of ventricular fibrillation (VF) and repolarization abnormalities of the ischemic and reperfused myocardium is poorly understood. The present study examined the temporal relationship between ischemia- and reperfusion-induced changes in monophasic action potential (MAP) configurations and the occurrence of VF, and assessed the effects of repetition of ischemia. The left anterior descending coronary artery of 32 anesthetized dogs was occluded twice for 5 min, 30 min apart, during constant atrial pacing while recording MAPs from the epicardial ischemic zone. During the first occlusion, shortening of the MAP duration at 90% repolarization (APD90) and an increase in MAP alternans, defined as the maximal difference in APD90 between 2 consecutive beats, were observed. Afterdepolarizations also occurred transiently in 35% of the animals during occlusion and in 29% upon reperfusion. VF occurred in 28% (9/32 of the dogs) during the first sequence, and the incidence was higher in the subgroups with maximal alternans > or =20 ms (p<0.05), maximal shortening rate > or =30%, and afterdepolarizations. During the second sequence, the incidence of VF was reduced to 9% (3/32, p<0.05), associated with a significant reduction in the MAP changes. Thus, repolarization abnormalities of the ischemic and reperfused myocardium appear to be related to the occurrence of VF. The amelioration of the repolarization abnormalities by repetition of ischemia may be involved in its antifibrillatory effect.

Action Potentials↗
PubMed1999

Influence of age on ambulatory electrocardiogram-derived heart rate variability.

OBJECTIVE: To evaluate the quantitative change in heart rate variability with age by using 24 h Holter ambulatory monitoring of electrocardiogram and to set the lower limit of heart rate variability depending on age. PARTICIPANTS: Eighty healthy subjects without any medication (male to female ratio 40:40, 45.6 +/- 14.1 years of age, range 16 to 68 years). METHODS: Holter monitoring was performed, and frequency and time domain heart rate variability was obtained. RESULTS: A significant inverse relationship was found between age and heart rate variability, especially in the frequency domain, and, in the time domain analysis, in the root mean square of the difference in the RR intervals of sinus rhythm (NN) between successive beats and in the portion of NN cycles greater than 50 ms apart. Except for the standard deviation of the mean of RR intervals taken every 5 mins and averaged over 24 h and the ratio of low frequency high frequency power spectra, all parameters decreased to a certain age and did not change thereafter, and the rate of decrease differed among the parameters of heart rate variability. Because age had a strong influence on heart rate variability, the lower limit of heart rate variability for a certain age was determined by using the polynomial curve fitting of the moving average minus 2 SD of 10 consecutive subjects. By using these equations, it could be determined whether heart rate variability was normal or abnormal depending on age.

Adult↗
PubMed1998

Association between preinfarction angina and a lower risk of right ventricular infarction.

BACKGROUND: Right ventricular infarction occurs in conjunction with inferior myocardial infarction caused by proximal occlusion of the right coronary artery. However, right ventricular infarction occurs infrequently, and the reasons for this are uncertain. METHODS: We retrospectively assessed the association between preinfarction angina and right ventricular infarction, as well as the short-term outcome, in 113 patients with a first acute inferior myocardial infarction caused by right-coronary-artery occlusion. The association between the timing of angina during the week before infarction and the clinical outcome was also assessed. RESULTS: The absence of preinfarction angina predicted the development of right ventricular infarction (odds ratio, 6.3; 95 percent confidence interval, 2.7 to 15.1; P<0.001), complete atrioventricular block (odds ratio, 3.6; 95 percent confidence interval, 1.4 to 10.3; P=0.01), and combined hypotension and shock (odds ratio, 12.4; 95 percent confidence interval, 4.5 to 40.6; P<0.001). Angina 24 to 72 hours before infarction was most strongly associated with reductions in the rates of right ventricular infarction (adjusted odds ratio, 0.2; 95 percent confidence interval, 0 to 0.8; P=0.02) and combined hypotension and shock (adjusted odds ratio, 0.1; 95 percent confidence interval, 0 to 0.5; P=0.02). CONCLUSIONS: Preinfarction angina was an independent predictor of the absence of right ventricular infarction in patients with acute inferior myocardial infarction. The patients with preinfarction angina also had better short-term outcomes than those without preinfarction angina.

Angina Pectoris↗
PubMed1998

Successful predilation of a resistant, heavily calcified lesion with cutting balloon for coronary stenting: a case report.

A 65-year-old man with a restenotic lesion of the mid LAD was scheduled for Wiktor stent placement. The IVUS revealed circumferential severe calcification. Two conventional, non-compliant angioplasty balloons inflated to high pressures failed to achieved sufficient dilatation and both ruptured. At this point, we selected high pressure inflation of the Cutting Balloon. The Cutting Balloon achieved adequate dilation for stenting and proved to be useful in predilating a circumferential, heavily calcified lesion.

Aged↗
PubMed1998

Absent myocardial accumulation of two different radioiodinated pentadecanoic acids.

This article presents two cases with preserved myocardial 201Tl uptake and absent uptake of two kinds of radioiodinated fatty acids: iodine-123-labeled 15-(p-iodophenyl)-3-(R,S)-methylpentadecanoic acid (BMIPP) and iodine-123-labeled 15-(p-iodophenyl)-9-(R,S)-methylpentadecanoic acid (9MPA). Although coronary angiography showed no stenotic lesion and left ventriculography revealed no wall motion abnormality, no myocardial uptake of BMIPP and 9MPA was observed in the first case. In the second case, no myocardial accumulation was recognized even in the initial phase of dynamic SPECT acquired soon after the injection of 9MPA. The results suggest that the non-visualized myocardium was not specific for BMIPP imaging and that rather than the early back diffusion of the tracers from the myocardium, abnormality of the myocardial cell membrane was a possible mechanism accounting for the phenomenon.

Biological Transport, Active↗
PubMed1998

Application of transmission scan-based attenuation compensation to scatter-corrected thallium-201 myocardial single-photon emission tomographic images.

A practical method for scatter and attenuation compensation was employed in thallium-201 myocardial single-photon emission tomography (SPET or ECT) with the triple-energy-window (TEW) technique and an iterative attenuation correction method by using a measured attenuation map. The map was reconstructed from technetium-99m transmission CT (TCT) data. A dual-headed SPET gamma camera system equipped with parallel-hole collimators was used for ECT/TCT data acquisition and a new type of external source named "sheet line source" was designed for TCT data acquisition. This sheet line source was composed of a narrow long fluoroplastic tube embedded in a rectangular acrylic board. After injection of 99mTc solution into the tube by an automatic injector, the board was attached in front of the collimator surface of one of the two detectors. After acquiring emission and transmission data separately or simultaneously, we eliminated scattered photons in the transmission and emission data with the TEW method, and reconstructed both images. Then, the effect of attenuation in the scatter-corrected ECT images was compensated with Chang's iterative method by using measured attenuation maps. Our method was validated by several phantom studies and clinical cardiac studies. The method offered improved homogeneity in distribution of myocardial activity and accurate measurements of myocardial tracer uptake. We conclude that the above correction method is feasible because a new type of 99mTc external source may not produce truncation in TCT images and is cost-effective and easy to prepare in clinical situations.

Adult↗
PubMed1998

Postrepolarization refractoriness as a potential anti-atrial fibrillation mechanism of pilsicainide, a pure sodium channel blocker with slow recovery kinetics.

The antifibrillatory effect of pilsicainide, a sodium channel blocker with slow recovery kinetics, was investigated in a canine model of atrial fibrillation. Prolonging the atrial effective refractory period is an important mechanism for pharmacological termination of atrial fibrillation. However, the effectiveness of potassium channel blockers has been questioned because of their reverse-use-dependent property. In eight open-chest dogs, the duration of the atrial endocardial monophasic action potential and the atrial effective refractory period were determined using a Franz catheter. Conduction velocity was obtained from a 96-channel mapping electrode at multiple cycle lengths. Inducibility of sustained atrial fibrillation (> 30 minutes) was confirmed by atrial burst pacing during bilateral vagal stimulation, and local fibrillation cycle lengths were measured. Five minutes after restarting fibrillation, pilsicainide (0.6 mg/kg + 0.04 mg/kg/min) was administered. After fibrillation was terminated, measurements were repeated. Pilsicainide successfully terminated atrial fibrillation in 7 of 8 dogs after the median time of 5.1 minutes. The conduction velocity decreased significantly. Although pilsicainide did not affect monophasic action potential duration, it caused use-dependent prolongation of the atrial effective refractory period (P < 0.05), creating postrepolarization refractoriness. Accordingly, pilsicainide prolonged the atrial fibrillation cycle length from 80.6 to 113.8 ms (P < 0.05) before termination of fibrillation. Sodium channel blockers with slow recovery kinetics can prolong the atrial effective refractory period without affecting monophasic action potential duration. Unlike potassium channel blockers, these sodium channel blockers maintain postrepolarization refractoriness, even at rapid stimulation rates, thus exerting a salutary antifibrillatory effect.

Action Potentials↗
PubMed1998

Catheter ablation of accessory atrioventricular connection between right atrial appendage to right ventricle: a case report.

A 24-year-old woman had experienced frequent attacks of orthodromic AV reciprocating tachycardia. The polarity of the delta waves suggested a right anterior or anterolateral accessory pathway. After ablation at the tricuspid annulus was unsuccessful, earliest retrograde atrial activation was recorded on the floor of the right atrial appendage, 2 cm above the tricuspid ring. Application of radiofrequency energy at this site abolished accessory pathway conduction. This unusual accessory pathway, located between the floor of the right atrial appendage and the right ventricle, was amenable to radiofrequency catheter ablation from within the right atrial appendage.

Adult↗
PubMed1998

Discordant prolongation of the refractory period and repolarization time by a class III agent, E4031, in the healing phase of myocardial infarction.

Susceptibility to reentrant tachyarrhythmias and the antiarrhythmic efficacy of class III agents are related more to the duration of the refractory period (ERP) than to the repolarization time (RT). We measured both ERP and RT in a canine model of healing myocardial infarction, and evaluated the effect of a class III agent (E4031) on these parameters and on the inducibility of ventricular tachyarrhythmias. ERP and RT on the unipolar electrogram were measured at several cycle lengths in the normal (NZ) and infarct zones (IZ), respectively, in 10 canine myocardial infarction models and extrastimulation was used to induce ventricular arrhythmias. Measurements were repeated after E4031 administration. At baseline, both ERP and RT were significantly longer in IZ than in NZ with ERP/RT ratio also higher in IZ. This ratio tended to increase at longer cycle lengths. E4031 increased ERP and RT both in NZ and IZ at all cycle lengths, but increased the ERP/RT ratio predominantly in IZ. E4031 prevented induction of sustained VT or VF, which was inducible in 3 out of 10 dogs at baseline, although it facilitated induction of VF in 1 dog with no baseline arrhythmia. By increasing the ERP/RT ratio, class III drugs may shorten the relative refractory period in IZ at the expense of a greater ERP difference created between NZ and IZ.

Animals↗
PubMed1997

C-reactive protein as a predictor of infarct expansion and cardiac rupture after a first Q-wave acute myocardial infarction.

BACKGROUND: Pump failure after acute myocardial infarction (AMI) can be predicted by several indices that estimate infarct size. However, there are few indices that predict infarct expansion and cardiac rupture. We focused on the prognostic significance of serum C-reactive protein (CRP) after AMI. METHODS AND RESULTS: Serum CRP levels were measured every 24 hours in 220 patients with a first Q-wave AMI. In-hospital complications, predischarge left ventriculographic findings, and long-term prognosis were assessed in relation to peak CRP levels. Peak levels of both CRP and creatine kinase (CK) were higher in patients with pump failure than in those without pump failure. In patients with cardiac rupture, peak CRP levels were higher than in those without rupture (P=.001); peak CK levels were not predictive. Higher CRP levels were found in patients with left ventricular aneurysm (P=.001 versus those without), aggravated heart failure (P=.03 versus those without), and cardiac death (P<.0001 versus survivors) during the first year after AMI. Multivariate analysis confirmed that an elevation of the peak CRP level > or = 20 mg/dL was an independent predictor of cardiac rupture (relative risk, 4.72; P=.004), left ventricular aneurysmal formation (relative risk, 2.11; P=.03), and 1-year cardiac death (relative risk, 3.44; P<.0001). CONCLUSIONS: Cardiac rupture, left ventricular aneurysmal formation, and 1-year cardiac death were associated with an elevation of serum CRP early after AMI, suggesting that elevation of CRP levels after AMI may predict infarct expansion.

Adult↗
PubMed1997

Increase in heart rate after radiofrequency catheter ablation is mediated by parasympathetic nervous withdrawal and related to site of ablation.

To assess the mechanism for the increased sinus rate after radiofrequency catheter ablation performed for atrioventricular nodal reentrant tachycardia (AVNRT), we studied heart rate variability before and after radiofrequency catheter ablation in 17 patients with AVNRT and in 38 patients with an accessory pathway. The accessory pathway was located at the left ventricular free wall, the right ventricular free wall, or the posterior interventricular septum. An increased sinus rate was observed in patients with AVNRT or with the accessory pathway at the posterior septum or left free wall after radiofrequency ablation. In these groups, high-frequency power, root mean square of successive difference and percent of adjacent cycles that were more than 50 ms apart, all of which are indices reflecting parasympathetic nervous activity, were decreased. The ratio of low-frequency to high-frequency power reflecting sympathovagal balance, was increased in patients with AVNRT or with an accessory pathway at the posterior septum or left free wall. Increases in sinus rate were correlated with decreases in high-frequency power, and percent of adjacent cycles more than 50 ms apart that the increase in heart rate was due to parasympathetic nervous withdrawal.

Adolescent↗
PubMed1997

A case of widely split double P waves with marked intra-atrial conduction delay.

We report a 78-year-old man as the first documented case of double P waves separated by 400 msec on 12-lead ECG. These P waves had different polarities on lead V1. The first P wave represented activation of the lateral wall of the right atrium, and the latter P wave represented activation of the medial right atrium and the left atrium. Widely spaced double potentials were recorded craniocaudally along the line, presumably corresponding to the crista terminalis during sinus rhythm. For this to occur, conduction disturbance has to be present both in the upper and lower right atrium. Conduction disturbance in the upper right atrium would interrupt excitation from the sinus node to the medial wall, and conduction disturbance in the lower right atrium would interrupt excitation spreading from the lower lateral right atrium to the isthmus area where fragmented potentials were recorded. These multiple discrete lesions appear to constitute a unique electrical atriopathy in this patient.

Aged↗
PubMed1997

[Chest radiographic diagnosis of dissecting thoracic descending aorta].

Widening of the aortic shadow on chest radiography is one of the first indicators of aortic dissection. The degree of widening of the aortic shadow was estimated on two successive chest radiographs (mean [+/-SD] interval 0.8 +/- 0.7 years) before and after aortic dissection in 11 patients (four with DeBakey classification type I, seven with type III dissection). The distance between the center of each thoracic vertebra and the lateral margin of the descending aortic shadow (L) was measured. Since only a supine frontal film is usually available in acute aortic dissection, chest radiographs in both erect and supine positions were compared in 18 patients with hypertension. On supine films, L was larger than that on erect films, but the difference (delta L) was minimal (+2.6 mm) at the level of the tracheal bifurcation. Therefore, the L at the level of tracheal bifurcation (Lb) was best suited for comparing films taken in different positions. On supine films, Lb was significantly longer in patients with aortic dissection than in patients with hypertension (60.5 +/- 8.2 vs 46.0 +/- 7.9 mm, p < 0.001), and none with dissection showed Lb < 50 mm. Serial change of L over the follow-up of 1.4 +/- 0.7 years in patients with hypertension was also examined in erect films and was less than +1 mm. When the index film in a supine position was compared with the previous films in an erect position, delta Lb in patients with aortic dissection was +12.7 +/- 5.6 mm, which was significantly greater than that in patients with hypertension (+2.9 +/- 2.8 mm, p < 0.001). All 11 patients with aortic dissection showed delta Lb > or = +7 mm, but only one patient with hypertension (6%) exhibited this finding. Chest radiography is useful for identifying patients with aortic dissection, who characteristically show Lb > or = 50 mm on presentation and delta Lb > or = +7 mm, compared with previous films.

Aged↗
PubMed1997

[Effect of barnidipine hydrochloride on the autonomic nervous system: difference between short- and long-acting components of calcium antagonist].

Short-acting calcium antagonists have a deleterious effect on the prognosis for patients with myocardial ischemia, possibly caused by overactivation of sympathetic nerves due to vasodilatation, negative inotropism, or coronary steal. However, there is considerable debate about whether long-acting calcium antagonists as well as the short-acting calcium antagonists have the same effect. Barnidipine-HCl is a newly-developed calcium antagonist with 1:2 short- and long-acting particles. This study evaluated the changes of autonomic tone due to barnidipine. Both the short- and long-acting effect of the calcium antagonist was evaluated. Eleven patients with primary hypertension underwent 24-hour ambulatory electrocardiogram and blood pressure monitoring before and after the treatment with barnidipine. Heart rate and blood pressure were compared before and after the medication. Heart rate variability was analyzed with a Marquette 8000/T. High frequency power (HF), as a parameter of vagal tone, and the ratio to low frequency power (LF), as a parameter of sympathetic tone, were obtained. Twenty-four-hour average blood pressure decreased significantly during the day, but nocturnal hypotension was not observed. Heart rate did not increase. HF decreased at the peak of the short- and long-acting components. LF/HF increased at the peak of the short-acting component. Short-acting particles of barnidipine had a deleterious effect on the autonomic tone, that is overactivation of sympathetic tone and suppression of vagal tone. Long-acting particles of barnidipine suppressed the vagal tone. These findings suggest that short-acting calcium antagonists may cause arrhythmia or deterioration of coronary ischemia.

Autonomic Nervous System↗