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Biomedical subjects

K Ajiki

Publications and source records attributed to K Ajiki.

27 records · Page 2Linked to original sources
PubMed1994

Shock-induced refractory period extension and pharmacologic modulation of defibrillation threshold.

Shock-induced refractory period extension (RPE) has been suggested as a mechanism of electrical defibrillation. We measured RPE caused by localized field stimulation measured before and during infusion of disopyramide (n = 5), flecainide (n = 5), or E-4031 (n = 5) in anesthetized dogs and determined the effect of the drugs on the internal defibrillation threshold (DFT). In the baseline state (n = 15), 16 V/cm S2 field stimulation prolonged the effective RP by 36 +/- 15 ms (22 +/- 12% of RP without S2), whereas 4 and 8 V/cm S2 stimuli did not cause marked RPE. The RPE normalized by the RP without S2 was not significantly influenced by any drug (16 V/cm: disopyramide 30 +/- 11 vs. 27 +/- 11, flecainide 25 +/- 5 vs. 19 +/- 12, and E-4031 18 +/- 13 vs. 22 +/- 14%). Disopyramide did not alter the defibrillation threshold (4.2 +/- 0.6-4.4 +/- 0.6 J). In 2 dogs given flecainide, ventricular fibrillation became refractory to defibrillation. In contrast, E-4031 lowered the threshold from 4.5 +/- 2.4 to 2.2 +/- 1.2 J (p < 0.01). The results suggest that flecainide and E-4031 do not modulate defibrillation efficiency through their effects on RPE.

Animals↗
PubMed1994

Attenuation of antifibrillatory effects of lidocaine by its metabolite, glycylxylidide: application of modulated receptor hypothesis.

Lidocaine, one of the drugs effective in treating ventricular arrhythmias in acute myocardial infarction (AMI), sometimes loses its efficacy after prolonged administration, possibly owing to the counteraction of glycylxylidide, one of the metabolites of lidocaine, through modulation of binding of lidocaine to sodium channels. To determine whether glycylxylidide interferes with the antiarrhythmic action of lidocaine, we compared the antifibrillatory effects of lidocaine, glycylxylidide, and their combination in 14 anesthetized open-chest dogs. Although glycylxylidide alone prolonged intraventricular conduction time (CT) and did not affect ventricular effective refractory period (VERP), it had different effects when added to lidocaine; i.e., it had no effect on intraventricular conduction time but shortened VERP. Although glycylxylidide alone did not change ventricular fibrillation threshold (VFT), the increase in VFT induced by lidocaine was decreased by addition of glycylxylidide, possibly as a result of competition for the same cardiac sodium channels between lidocaine and glycylxylidide with similar onset but different offset kinetics, which may explain, at least in part, the drug-resistance phenomena that ensue from prolonged lidocaine administration.

Animals↗
PubMed1993

Autonomic nervous system activity in idiopathic dilated cardiomyopathy and in hypertrophic cardiomyopathy.

To assess autonomic nervous activity in patients with cardiomyopathies, analysis of heart rate variability was performed using 24-hour ambulatory electrocardiograms in 14 patients with idiopathic dilated cardiomyopathy (IDC), 15 with hypertrophic cardiomyopathy (HC) and 18 healthy subjects. Heart rate variability during the night and daytime was calculated using fast-Fourier transform, and power spectra were quantified in 2 frequency bandwidths: 0.00 to 0.15 Hz (low-frequency power [LF]) and 0.15 to 0.50 Hz (high-frequency power [HF]). Log(HF) was used as an index of parasympathetic nervous activity, and log(LF/HF), of sympathetic nervous activity. Log(HF) was significantly lower and log(LF/HF) was significantly higher in IDC. These changes were related to ejection fraction. In HC, lower log(HF) and higher log(LF/HF) were recognized only during the night, and these changes were independent of the degree of myocardial hypertrophy. Our results indicated attenuation of parasympathetic activity and enhanced sympathetic activity in HC during the night, and also in IDC. Assessment of autonomic imbalance by analysis of heart rate variability may be useful for understanding the pathophysiology of cardiomyopathies.

Autonomic Nervous System↗
PubMed1993

Parasympathetic activity is a major modulator of the circadian variability of heart rate in healthy subjects and in patients with coronary artery disease or diabetes mellitus.

Autonomic heart rate control was assessed by power spectral analysis of heart rate variability in 24-hour ambulatory electrocardiographic recordings from 23 healthy subjects, 14 patients with coronary artery disease without cardiac dysfunction, and 14 patients with diabetes mellitus. The log value of the ratio of the low-frequency component (LF = 0.04 to 0.15 Hz) to the high-frequency component (HF = 0.15 to 0.5 Hz) and logHF were employed as indexes of sympathetic and parasympathetic activity, respectively. Diurnal and nocturnal logLF, logHF, and log(LF/HF) values were calculated for heart rates of 60, 70, and 80 beats/min. Intergroup differences among these three variables were not significant at any heart rate. Although a heart rate-related decrease in logHF was generally observed, the relationship between log(LF/HF) and heart rate was not consistent. The correlation between diurnal and nocturnal logHF values was significant at all three heart rates (r = 0.63, 0.87, and 0.59), whereas the diurnal log(LF/HF) was correlated with the nocturnal value only at 70 beats/min (r = 0.77). These results suggest that the heart rate during normal daily activities is a reliable indicator of parasympathetic tone, if not sympathetic tone, in healthy subjects and patients with coronary artery disease or diabetes mellitus.

Aged↗
PubMed1991

A case of a pseudomalfunction of a DDD pacemaker.

DDD pacemaker pseudomalfunction occurred in a 65-year-old man. This was due to premature ventricular contraction (PVC) response option and cross-talk detection window, which are designed to protect against pacemaker related tachycardia or cross-talk. Pseudomalfunction disappeared by eliminating PVC response option.

Aged↗