-In five anesthetized open chest dogs, contraction patterns of the left ventricle induced by ventricular pacing were analyzed using cineangiocardiography.Left ventriculography was performed with dogs in the right anterior oblique position. The right atrial appendage (RA) and two ventricular sites (RVO: outflow tract of the right ventricle and LVA: apex of the left ventricle) were stimulated electri cally at a rate of 150 per min. Contraction patterns and cardiodynamics in response to ventricular pacing were compared with those to RA pacing, which represents a normal sequence and extent of ventricular contraction.RVO pacing resulted in asyneresis of anterior wall and normal contraction of posterior wall, while LVA pacing produced a systolic expansion of the apex associated with enhanced contraction of the posterior wall. Ventricular pacing uniformly caused decreases in left ventricular end-diastolic volume (LVEDV), stroke volume (SV) and ejection fraction (EF), with relatively constant left ventricular end-systolic volume (LVESV). Blood pressure was significantly decreased with ventricular pacing. There were only minor differences of these parameters between RVO and LVA pacing.It was considered that a diminution of SV and EF during ventricular pacing resulted from the asynchronous contraction of the ventricle which was not related to decreased myocardial contractility. cineangiocar diography; ventricular pacing; ventricular asynchrony; cardiac performance; pacemaker siteIt has been well known that ectopic ventricular beats are associated with asynchronous contraction of the left ventricle (Herman et al. 1967). Our previous studies (Miyazawa et al. 1976(Miyazawa et al. , 1977a showed that ventricular pacing from various sites caused a diminution of cardiac output and systemic bood pressure as compared with right atrial pacing, and there were no significant differences in these hemodynamic parameters by changing the site of ventricular pacing. However, little information is available concerning the influence of asynchronous activation on the contraction patterns of the left ventricle and the relation with the cardiac pumping action (Ueda et al. 1968;Herman and Gorlin 1969;Eber et al. 1974). In this regard, the present study was undertaken to describe the

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Ten mongrel dogs were used to assess regional myocardial function in response to electrical pacing from the inflow (RVI), outflow tracts (RVO), and apex (RVA) of the right ventricle and apex (LVA) and lateral wall (LVL) of the left ventricle. Straingauge arches were sutured to the epicardial segments of the apical and lateral walls of the left ventricle and their mechanical shortening was measured during right atrial (RA) and during ventricular pacing. The onset of shortening of two segments did not differ significantly in RA and RVI pacing, while the stimulation of RVA and LVA caused the initial contraction of the apical segment, and RVO and LVL pacing caused that of the lateral segment; i.e. RVA and RVO pacing resulted in left ventricular asynchrony of contraction similar to LVA and LVL pacing, respectively.Asynchrony of contraction was not accompanied by a uniform change in peak tension of regional myocardial segments, but preejection tension rose and ejection tension fell at the pacing site. The reduction in mean aortic pressure inversely correlated with the prolongation of the time interval between the onset of shortening of two segments during left ventricular pacing. The decrease in cardiac performance observed during ventricular pacing was related to the severity of asynchrony rather than the direction of the ventricular depolarization or change in regional myocardial tension. regional myocardial contraction; straingauge arch; ventricular pacing; ventricular asynchrony; cardiac performance Decreased cardiac performance during ventricular pacing has been ascribed to the lack of synchrony resulting from altered ventricular activation and contraction (Wiggers 1925;Gilmore et al. 1963;Finney 1965; Miyazawa et al. 1976). This is due to slow passage of the depolarization wave through ventricular muscle, as compared with the relatively rapid activation through the normal conduction system. However, there have been few reports concerning the regional myocardial function under this condition (Osadjan and Randall 1964;Finney 1965;Hood et al. 1969). From this standpoint , two strain gauge arches were stitched to the epicardial surface of the apical and lateral walls of the left ventricle. Tension curves in each of the segments were analyzed in control period during RA pacing

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