Figure 6: Myocardial connectivity depends on proper integration of FHF with SHF.

(a–e) Vector polar plots, in which each point represents a vector of the vector field map plotted in respect to its magnitude (velocity) and direction (angle from unit vector), red points show the frequency of angle distribution at 22.5° intervals. (a) Wild type as control reference. Loss of tbx5a (b) results in almost uniform conduction, while loss of pitx2ab (c) and mef2ca (d) partially impairs the coupling gradients as compared to the control (a) hearts. Combined loss of pitx2ab and mef2ca (e) show marked recovery of large velocity vectors. Note the discrete absence of all angles between +160° and+200° in these hearts. (f–j) Frequency angle polar plots averaged from ROIs depicted in (Fig. 5a); majority of the vectors in control (f) hearts of OC/FHF point away from OFT revealing orthogonal mean coupling directions between OC/FHF and IC/SHF. Reduction of tbx5a (g) and pitx2ab (h) levels leads to complete loss of the orthogonal coupling and impairment in mef2ca mutants (i). Combined mef2ca mutants with loss of pitx2ab (j) partially rescues the orthogonal coupling direction. (k) Histogram of angle variability between inner and outer ventricular curvatures plotted as the angle s.d. in degrees. The angle variability is higher in outer curvature of control hearts, but this difference is diminished in the absence of tbx5a, pitx2ab, mef2ca, and combined pitx2ab morphant and mef2ca mutant hearts. Asterisks indicates significance, statistical significance tested with one-way analysis of varinace, with Tukey’s post test, P<0.05. All experiments performed at 54 h.p.f.