<原著>心室性期外収縮の非協同性心筋収縮に関する実験的研究
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Asynergic myocardial contraction of ventricular premature beat evoked by epicardial electrical stimulation was assessed with small ultrasonic crystals implanted in the subendocardium of 15 open chest anesthetized dogs. The time (t_<S-Q>) from stimulation to onset of electrical activation was more prolonged at the base of the heart than at the apex, depending upon regional left ventricular (LV) wall thickness. t_<S-Q> was prolonged inversely to the decrease of coupling time (CT) and this finding was considered to be related to the relative refractory period of action potential in the stimulation site. Calculated propagation velocity of excitation throughout ventricular wall was 43.7 cm/sec. Excitation conduction time in the subendocardium between the apex and the base was not influenced by both stimulation site and CT, i.e. conduction velocity was ranged 1.53〜1.58 m/sec, which was comparable to that of the peripheral Purkinje fibers. There was a significantly negative correlation between the time (t_<S-Sh>) from stimulation to onset of shortening of segment length (SL) and CT. Excitation-contraction coupling time (t_<Q-Sh>) was greater at the apex than at the base. At the apex, there was a significantly negative correlation between t_<Q-Sh> and CT. Also, a significantly positive correlation was found between shortening time (t_<Sh-L>) and CT. t_<Sh-L> was greater at the apex than at the base in the early activated area. The time from stimulation to onset of LV pressure elevation was smaller at the apex than at the base. LV pressure was greater at the apex than at the base. There was a significantly positive correlation between LV pressure and CT. The time from onset of LV pressure elevation to that of SL lengthening and LV pressure of onset of SL lengthening at stimulation site were greater at the apex than at the base. In conclusion, the basic mechanism of asynergic contraction of ventricular premature beat was earlier shortening and earlier lengthening compared to LV pressure elevation at stimulation site, and the variations of the pattern of asynergic contraction were influenced by stimulation site and CT. Several factors such as a dispersion of electrical and mechanical activation due to different regional wall thickness, diastolic volume changes, timing of papillary muscle contraction against mitral valve closure, regional wall stress and LV pressure elevation may affect the asynergic contraction of LV premature beat.
- 近畿大学の論文
- 1986-09-25
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