Structured local mismatch placement and internal packaging in cardiomyocytes during hyperthermal sarcomeric oscillations

Abstract Neighboring sarcomeres during hyperthermal sarcomeric oscillations (HSOs) are not perfectly synchronous, yet their local nonuniformity is organized rather than random. Earlier reanalyses of the same continuous five-sarcomere recordings showed that local reconfiguration is dominated by minimal Hamming-1/one-link updates and that fast cycles can be aligned onto a shared rephasing compass whose clearest physiological translation is mismatch-pocket placement along the observed chain. Here we integrate those results with reduced-geometry analysis that asks how the same minimal update is internally distributed within the chain. Using seven living neonatal rat cardiomyocytes recorded at 500 frames/s, we converted each fast HSO cycle into one local coordination summary, extracted event-centered internal pre-to-post sarcomere-length change patterns after subtraction of the instantaneous five-sarcomere mean, and retained exact directed one-link transitions together with mismatch-pocket context. Continuous reduced-plane trajectories were geometrically complex, and total event displacement was not identical to redistribution span. Cross-cell alignment again revealed a common rephasing order, and aligned position most strongly predicted edge-biased mismatch placement. Reduced geometry added a distinct mesoscale layer: route classes formed an ordered redistribution-span axis from compact to broad internal redistribution, and even when exact one-link transition and pocket context were matched, events still separated into compact and extended redistribution profiles. Across common matched groups, the extended family showed broader span in 8 of 9 groups (median span difference +0.423; paired Wilcoxon P = 0.027). These findings support a structured-mismatch view of HSOs: the observed five-sarcomere chain reuses the same minimal local reconfiguration through more than one internal redistribution route. Significance statement Cardiac contraction must transform noisy local events into a stable beat. This study shows that local nonuniformity in living cardiomyocytes is structured at more than one mesoscale level. A shared rephasing compass organizes where a mismatch pocket tends to sit along an observed five-sarcomere chain, and reduced geometry shows that the same minimal local update can still be internally packaged through more than one redistribution route. Graphical abstract. An observed fast HSO window is condensed into cycle-wise local phase summaries. A topology-based circular coordinate and cross-cell alignment yield a shared rephasing compass. The clearest primary readout of that compass is mismatch-pocket placement along the observed five-sarcomere chain, whereas reduced geometry adds a secondary descriptive layer in which route packaging is ordered from compact to broad redistribution span.