Experimental Studies on the Manner of Ventricular Contraction : Relationship between the Excitation Process and the Sequence of Contraction in the Ventricular Wall

As for the ventricular excitation process, much has been studied by many investigators and the systematic theory has been almost established by MIZUNO, SCHER, etc. The reconstruction method based on this ventricular excitation process brought the merits to the theoretical interpretation of the clinical electrocardiography and vectorcardiography. On the other hand, as for the onset of contraction in the ventricular wall, several reports have pointed out merely its asynchronism. No systematic investigation has been performed in the mechanism of contraction of the whole ventricle. The aims of the present report are to investigate the sequence of onset of contraction in the ventricle in situ, to compare it with the ventricular excitation process simultaneously obtained, and to observe the time relationship between excitation and contraction in the ventricle in situ. Methods. Twenty-seven mongrel adult dogs weighing 8.5 to 24.5kg, 15.1 kg on the average, were anesthetized with pentobarbital sodium, 30 mg/kg through peritoneum. The sternum was transected, and the thorax was opened at the level of the fifth intercostal space. Then the pericardium was incised, and thus the heart was exposed. In order to determine the onset times of contraction in various local places in the ventricular wall, small-sized strain gauge arches (the distance between two legs: 10 mm) using negative typed Ge 111 semiconductor as a transducing element, were firmly sutured along or/and across the superficial muscle bundle in various areas on the ventricular surface, enough resting tension given to the cardiac muscle between its legs, and the myocardial tension tracing was obtained by each area. The relatively rapid rising point of the myocardial tension tracing was regarded as the onset time of contraction in each arch-sutured area. On the other hand, in order to investigate the arrival time of excitation in each arch-sutured area, the epicardial or/and endocardial surface electrograms were sirnultaneously reqorded with the unipolar electrodes placed close to the arch on the epicardial or/and endocardial surface, respectively. The initial point of the intrinsic deflection of each unipolar electrogram was regarded as the arrival time of excitation at the electrode. For the purpose of observing the onset time of rise of left ventricular pressure and watching the change of condition of the animal during the experiment, the left ventricular pressure was recorded with a catheter tip micromanometer, which was inserted into the left ventricular cavity.