Figure 4.

Force-Length Curve and Maximal Twitch Force Production in Patient-Specific EHTs

WT Ib-CM and FCM IIb-CM were used to generate patient-specific EHTs. After attaching EHTs to the force transducer, (A) active force per area twitch height was graphed against EHT length (Starling curve). The active force per area increased in a linear fashion over increasing preparation lengths. The slope of the first 25% length change (dotted line) was lower in the FCM EHT compared with the WT EHT (p < 0.0001), indicating impaired contractility in the FCM EHT. (B) Passive force per area was graphed against EHT length. The slope of the first 25% length change (dotted line, Young’s modulus) was unchanged between the 2 groups (p = 0.57). (C) Absolute and (D) normalized twitch force per area traces of WT Ib EHT and FCM IIb EHT measured at 140% length. (E) Maximum (Max) force per area produced. (F) Time to peak contraction (T_peak). (G) T_peak to 50% relaxation (RT₅₀). (H) Time from 50% to 90% relaxation (RT_50–90). All EHTs were paced at 1.5 Hz, and all force values were normalized to cross-sectional area. *p < 0.05 (Student’s t-test). Error bars indicate SEM. Abbreviations as in Figures 1 and 3.