Serum lipid pattern in ischemic heart disease--study on fatty acid composition and pre-beta-lipoprotein

Abstract

With respect to the mechanism of formation of ST-T wave in the electrocardiogram, various hypotheses have been proposed by many investigators. However, it cannot be said that any of these has been entirely accepted. The author assumed that the formation of ST-T wave would be attributable to temporal and spacial difference in the electrical current occur-red in various parts of the ventricle. Such a differ-ence may be observed between the epicardial and endocardial sites. From this point of view, the following investigations on the repolarization phase of transmembrane action potentials of the endocardial and epicardial sites were performed. Method Ventricular muscle of the rabbit was subjected to the experiment. The preparation was perfused constantly flowing with oxygenated Tyrode solution at a constant temperature (37°C). The transmembrane action potential (AP) is recorded through a microelectrode of Ling-Gerad type filled with 3M KCl (resistance 20-30 MΩ). The driving stimuli were delivered through a monopolar silver wire electrode attached to the ven-tricular surface. In some experiments, two microelectrodes were concurrently inserted into the epicardium and endocardium. Monopolar surface electrogram was also simultaneously recorded. Results 1. Comparison of action potential configurations between the endocardial and epicardial sites As indicated in Fig. 1 and Table I, no significant difference was recognized in action potential amplitude as well as resting potential between the epicardial and endocardial sites, while significant difference was observed in duration of AP between the epicardial and endocardial sites (Table II). The mean value of the maximum rate of rise recorded from the epicardial and endocardial sites were 217.6 ± 60.4 volt/sec and 508.5 ± 86.1 volt/sec, respectively, the latter being significantly greater than the former (Fig. 2. Table III). 2. Effects of stimulus frequency on the epicardial and endocardial APs Effect of change in frequency of electrical stimulation on the AP of the endocardial and epicardial sites was observed (Fig. 3). At a higher rate of stimulation, the duration of the AP was markedly reduced and the amplitude of resting and action potentials slightly decreased. At a lower rate, the duration was prolonged while the amplitude of resting and action potentials was slightly decreased. A linear relationship was observed between the duration of the AP and stimulus frequency, the frequency ranging from 0.2 cps to 6 cps. The patterns of change in the AP by frequency change were virtually identical between the endocardial and epicardial sites.