Constrained neighboring-sarcomere phase topology shapes mean HSO amplitude in living cardiomyocytes

How neighboring sarcomeres redistribute timing while a cardiomyocyte continues to beat, and how that coordination shapes mean HSO amplitude in the segment-average trace, remain unresolved. We reanalyzed sarcomere-length recordings from five consecutive sarcomeres in each of seven living neonatal rat cardiomyocytes and represented each valid time point by the four neighboring-pair phase relations that define a 16-state local phase network. During warming-induced hyperthermal sarcomeric oscillations (HSOs), the fraction of time with trackable local phase relations increased from 0.298 before warming to 0.956 (paired Wilcoxon P = 0.0156), enabling direct analysis of local reconfiguration. Successive local states were almost always connected by Hamming-1 edges, meaning that only one neighboring-pair relation changed at a time (34/35, 97.1%, before warming; 216/230, 93.9%, during HSOs). HSOs also increased occupancy of anti-phase-rich states with three or more anti-phase neighboring pairs (0.254 to 0.509, P = 0.0156). In a complementary cycle-level analysis of the same HSO window, Yvalid, the HSO amplitude of the valid-sarcomere mean trace, was closely approximated by the product of mean local HSO amplitude (A) and weighted synchrony across valid sarcomeres (Rw; pooled r = 0.992, normalized mean squared error = 0.015, {beta}1 = 0.948, {beta}0 {approx} 0). To link the binary local-state description to this continuous synchrony term, we derived a simple state-based synchrony factor from the local phase patterns; cycles with higher values showed higher Rw (cell-adjusted {beta} = 0.197, P = 0.0165). Blocked cross-validation showed that the A x Rw model markedly outperformed an additive alternative (pooled normalized mean squared error 0.0138 vs 0.1006), whereas simple history terms changed error only marginally. HSOs therefore do not reflect unstructured local disorder. Rather, they are characterized by a constrained neighboring-sarcomere phase topology, and mean HSO amplitude in the same segment is largely captured by a cycle-level relation between local amplitude and synchrony.