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Figure 2 Resynchronizing effects of biventricular pacing. Phase images acquired in four patients with DCM and varying patterns of IVCD. Contraction sequence, from early to late: green, azure, navy, violet, orange, yellow. Histograms illustrate dispersion of phase angles during ventricular ejection, plotted as phase angle (x axis) versus number of pixels (y axis). Vertical bars represent the arithmetic mean phase angle, Ø, computed for RV and LV blood pools. (A) Patient with DCM and LBBB. (Left) Abnormal phase pattern in sinus rhythm with right to left (azure to navy) ventricular contraction sequence. Left ventricular apex and septum contract with extreme delay, in phase with atrial systole (orange segment at top of figure). Histogram illustrates abnormal dispersion of phase angles spanning the cardiac cycle, with  Ø of 75°. (Right) Characteristic apex to base contraction sequence during BiV. Phase pattern is more symmetrical across interventricular septum. Despite close proximity to pacing stimulus sites (green), the LV apex (yellow) fails to contract in sequence. A decrease in phase angle occurs with pacing. (B) Patient with DCM and LBBB. (Left) Dyssynchronous RV and LV phase pattern in sinus rhythm. The bulk of the RV (green) contracts before onset of LV contraction (azure). Histogram illustrates bimodal distribution of phase angles for the RV and LV, with Ø of 28°. (Right) During BiV, ventricular activation originates simultaneously at the LV and RV apices (green), followed by RV outflow tract (azure) and LV base (azure, navy). A more symmetrical RV and LV phase pattern is observed with restoration of early septal contraction (green). Histogram illustrates a decrease in Ø to 0°, representing a 28° correction of baseline interventricular dyssynchrony. (C) Patient with DCM and RBBB. (Left) Dyssynchronous RV and LV phase pattern in sinus rhythm. Ventricular activation originates at LV septum and base (azure), followed by bulk of RV (navy) and LV lateral wall (navy). Histogram illustrates disparity in RV and LV phase during sinus rhythm with Ø of 28°. (Right) During BiV, ventricular contraction originates at the RV apex and LV apical-septum (azure) in proximity to pacing stimulus sites. The RV and LV basal and midsegments (navy) contract in sequence with minimal delay. A more symmetrical phase pattern is observed across the interventricular septum. Ventricular contraction proceeds from apex to base, representing a 26° correction of baseline interventricular dyssynchrony. (D) Patient with DCM and IVCD. (Left) Diffuse and inhomogeneous contraction pattern in sinus rhythm. Ventricular activation originates at LV base and RV apex (green); eccentric contraction pattern, culminating at LV apex and RV base (azure/navy). Histogram illustrates gross dispersion of RV and LV phase angles with Ø of 15°. (Right) During BiV, intraventricular contraction abnormalities persist. The LV base and RV apex remain early (azure); the LV free wall and RV base contract with delay (navy/violet). Histograms demonstrate an 8° correction of interventricular dyssynchrony. BiV = atrial sensed biventricular pacing; DCM = dilated cardiomyopathy; IVCD = nonspecific intraventricular conduction delay; LBBB = left bundle branch block; LV = left ventricular; RBBB = right bundle branch block; RV = right ventricular.
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