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Characterizing Spatial Dynamics of Bifurcation to Alternans in Isolated Whole Rabbit Hearts Based on Alternate Pacing.

Kulkarni K, Visweswaran R, Zhao X, Tolkacheva EG - Biomed Res Int (2015)

Bottom Line: Each heart was paced using an "alternate pacing protocol," where the basic cycle length (BCL) was alternatively perturbed by ±δ.Local onset of alternans in the heart, BCLstart, was measured in the absence of perturbations (δ = 0) and was defined as the BCL at which 10% of LV exhibited alternans.The influences of perturbation size were investigated at two BCLs: one prior to BCLstart (BCLprior = BCLstart + 20 ms) and one preceding BCLprior (BCLfar = BCLstart + 40 ms).

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, University of Minnesota, 312 Church Street SE, Minneapolis, MN 55455, USA.

ABSTRACT
Sudden cardiac death instigated by ventricular fibrillation (VF) is the largest cause of natural death in the USA. Alternans, a beat-to-beat alternation in the action potential duration, has been implicated as being proarrhythmic. The onset of alternans is mediated via a bifurcation, which may occur through either a smooth or a border-collision mechanism. The objective of this study was to characterize the mechanism of bifurcation to alternans based on experiments in isolated whole rabbit hearts. High resolution optical mapping was performed and the electrical activity was recorded from the left ventricle (LV) epicardial surface of the heart. Each heart was paced using an "alternate pacing protocol," where the basic cycle length (BCL) was alternatively perturbed by ±δ. Local onset of alternans in the heart, BCLstart, was measured in the absence of perturbations (δ = 0) and was defined as the BCL at which 10% of LV exhibited alternans. The influences of perturbation size were investigated at two BCLs: one prior to BCLstart (BCLprior = BCLstart + 20 ms) and one preceding BCLprior (BCLfar = BCLstart + 40 ms). Our results demonstrate significant spatial correlation of the region exhibiting alternans with smooth bifurcation characteristics, indicating that transition to alternans in isolated rabbit hearts occurs predominantly through smooth bifurcation.

No MeSH data available.


Related in: MedlinePlus

Spatial correlation of the local onset of SS alternans with bifurcation characteristics. (a) 2D bifurcation map calculated at BCLprior (see Figure 3(c)). (b) 2D SS alternans map calculated at BCLstart (see Figure 2(a)). (c) Correlation between bifurcation and SS alternans maps. Average % of smooth, border-collision, and undetermined bifurcations from all experiments are shown for (d) BCLprior and (e) BCLfar. ∗ indicates P < 0.05.
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fig5: Spatial correlation of the local onset of SS alternans with bifurcation characteristics. (a) 2D bifurcation map calculated at BCLprior (see Figure 3(c)). (b) 2D SS alternans map calculated at BCLstart (see Figure 2(a)). (c) Correlation between bifurcation and SS alternans maps. Average % of smooth, border-collision, and undetermined bifurcations from all experiments are shown for (d) BCLprior and (e) BCLfar. ∗ indicates P < 0.05.

Mentions: First, we studied the spatial correlation between the regions of SS alternans and the bifurcation characteristics. Figures 5(a) and 5(b) show representative examples of 2D bifurcation map generated at BCLprior (see Figure 3(c)) and the SS alternans map generated at BCLstart (see Figure 2(a)), respectively. The spatial superposition of these two maps is shown in Figure 5(c). Therefore, in Figure 5(c) the bifurcation characteristics (calculated at BCLprior) are only shown for spatial regions that exhibited alternans at the next BCL (i.e., BCLstart). The white regions in Figures 5(b) and 5(c) were excluded from the analysis, since no alternans was present there at BCLstart. Figures 5(d) and 5(e) show the average percentage of LV area that developed SS alternans with the bifurcation characteristics calculated across all our experiments at BCLprior and BCLfar, respectively. Since the spatial pattern of alternans developed at BCLstart did not always coincide with the spatial pattern of alternans induced by perturbation, it was difficult to categorize the bifurcation characteristics in relation to spatially concordant or discordant alternans. However, as seen from the figure, the overall regions of SS alternans that coincided with smooth bifurcation characteristics were significantly higher than those coinciding with border-collision bifurcation, both at BCLprior and BCLfar. The data suggests that the regions of the LV that eventually develop alternans at SS show predominantly smooth bifurcation characteristics prior to the onset of alternans.


Characterizing Spatial Dynamics of Bifurcation to Alternans in Isolated Whole Rabbit Hearts Based on Alternate Pacing.

Kulkarni K, Visweswaran R, Zhao X, Tolkacheva EG - Biomed Res Int (2015)

Spatial correlation of the local onset of SS alternans with bifurcation characteristics. (a) 2D bifurcation map calculated at BCLprior (see Figure 3(c)). (b) 2D SS alternans map calculated at BCLstart (see Figure 2(a)). (c) Correlation between bifurcation and SS alternans maps. Average % of smooth, border-collision, and undetermined bifurcations from all experiments are shown for (d) BCLprior and (e) BCLfar. ∗ indicates P < 0.05.
© Copyright Policy - open-access
Related In: Results  -  Collection

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fig5: Spatial correlation of the local onset of SS alternans with bifurcation characteristics. (a) 2D bifurcation map calculated at BCLprior (see Figure 3(c)). (b) 2D SS alternans map calculated at BCLstart (see Figure 2(a)). (c) Correlation between bifurcation and SS alternans maps. Average % of smooth, border-collision, and undetermined bifurcations from all experiments are shown for (d) BCLprior and (e) BCLfar. ∗ indicates P < 0.05.
Mentions: First, we studied the spatial correlation between the regions of SS alternans and the bifurcation characteristics. Figures 5(a) and 5(b) show representative examples of 2D bifurcation map generated at BCLprior (see Figure 3(c)) and the SS alternans map generated at BCLstart (see Figure 2(a)), respectively. The spatial superposition of these two maps is shown in Figure 5(c). Therefore, in Figure 5(c) the bifurcation characteristics (calculated at BCLprior) are only shown for spatial regions that exhibited alternans at the next BCL (i.e., BCLstart). The white regions in Figures 5(b) and 5(c) were excluded from the analysis, since no alternans was present there at BCLstart. Figures 5(d) and 5(e) show the average percentage of LV area that developed SS alternans with the bifurcation characteristics calculated across all our experiments at BCLprior and BCLfar, respectively. Since the spatial pattern of alternans developed at BCLstart did not always coincide with the spatial pattern of alternans induced by perturbation, it was difficult to categorize the bifurcation characteristics in relation to spatially concordant or discordant alternans. However, as seen from the figure, the overall regions of SS alternans that coincided with smooth bifurcation characteristics were significantly higher than those coinciding with border-collision bifurcation, both at BCLprior and BCLfar. The data suggests that the regions of the LV that eventually develop alternans at SS show predominantly smooth bifurcation characteristics prior to the onset of alternans.

Bottom Line: Each heart was paced using an "alternate pacing protocol," where the basic cycle length (BCL) was alternatively perturbed by ±δ.Local onset of alternans in the heart, BCLstart, was measured in the absence of perturbations (δ = 0) and was defined as the BCL at which 10% of LV exhibited alternans.The influences of perturbation size were investigated at two BCLs: one prior to BCLstart (BCLprior = BCLstart + 20 ms) and one preceding BCLprior (BCLfar = BCLstart + 40 ms).

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, University of Minnesota, 312 Church Street SE, Minneapolis, MN 55455, USA.

ABSTRACT
Sudden cardiac death instigated by ventricular fibrillation (VF) is the largest cause of natural death in the USA. Alternans, a beat-to-beat alternation in the action potential duration, has been implicated as being proarrhythmic. The onset of alternans is mediated via a bifurcation, which may occur through either a smooth or a border-collision mechanism. The objective of this study was to characterize the mechanism of bifurcation to alternans based on experiments in isolated whole rabbit hearts. High resolution optical mapping was performed and the electrical activity was recorded from the left ventricle (LV) epicardial surface of the heart. Each heart was paced using an "alternate pacing protocol," where the basic cycle length (BCL) was alternatively perturbed by ±δ. Local onset of alternans in the heart, BCLstart, was measured in the absence of perturbations (δ = 0) and was defined as the BCL at which 10% of LV exhibited alternans. The influences of perturbation size were investigated at two BCLs: one prior to BCLstart (BCLprior = BCLstart + 20 ms) and one preceding BCLprior (BCLfar = BCLstart + 40 ms). Our results demonstrate significant spatial correlation of the region exhibiting alternans with smooth bifurcation characteristics, indicating that transition to alternans in isolated rabbit hearts occurs predominantly through smooth bifurcation.

No MeSH data available.


Related in: MedlinePlus