Mechanics of the single left ventricle - A study in ventricuiar-ventricular interaction II

Background-Left ventricular (LV) effects an right ventricular (RV) function are well known. Less is understood about the effect of the RV on systemic LV mechanics. To determine this interaction, we compared systemic LVs with and without an RV mechanically coupled to them. Methods and Results-MR myocardial tagging was used to examine 18 subjects with systemic LVs: 10 with functional single LVs (SLV) and 8 normal subjects (NL). Tracking the systolic motion of the intersecting stripes were used to determine regional twist and radial motion. Finite strain analysis was applied to derive principal strains at the atrioventricular valve (AVV) and apical short-axis levels and in 4 anatomic wall regions. Similar E-1 (circumferential shortening) strain and heterogeneity of strain were noted between SLV and NL except in the septal wall. At the septal wall, NL displayed greater absolute strain(AVV=-0.16+/-0.02, apex=-0.17+/-0.02) and less heterogeneity of strain than SLV (AVV=-0,12+/-0.02, apex=-0.13+/-0.02). Similar E-2 (wall thickening) strain and heterogeneity of strain were also noted between SLV and NL except again at the septal wall. At the septal wall, SLV displayed greater absolute E-2 strain (AVV=0.17+/-0.08, apex=0.19+/-0.09) and less heterogeneity of strain than NL (AVV=0.07+/-0.07, apex=0.05+/-0.05). SLV twisted significantly less counterclockwise than NL in 6 of 8 wall regions and actually twisted clockwise at the AVV lateral wall. Although there was no significant difference between groups in radial wall motion, the septal and inferior walls of SLV demonstrated significantly less radial motion compared with other SLV walls. Conclusions-A major influence of the RV on systemic LV strain and radial motion occurs in the septal wall, whereas absence of the RV causes marked differences in LV twist. These findings may yield clues to the long-term functioning.