Developmental trajectories of electrocardiographic parameters in pediatric patients

Figures

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  Figure 1.. Developmental changes in cardiomyocyte structure and calcium handling genes. A) Relationship between heart and body weight during postnatal development. Neonates: 0–2 days (n=43), juveniles 4–10 days (n=16), adults (n=24). B) Examples of left ventricular heart tissue sections were stained with hematoxylin and eosin. C) Morphometric changes in cardiomyocyte width and length during postnatal development. Inset shows an intercalated disc in adult tissue section. Sample size includes multiple tissue sections for neonatal (N=6 hearts, n=32 sections), juvenile (N=5, n=25), and adult hearts (N=6, n=26). Data reported as the mean ± standard deviation, Welch’s ANOVA with Dunnett’s comparison testing, *p<0.05. D) Cartoon highlighting calcium handling genes. Heatmaps show differentially expressed genes involved in calcium handling (each row) for each animal (column; n=5 hearts per age group). On a per gene basis, the signal intensity was log10 transformed and Z-score normalized (blue: decreased, red: increased expression). Differentially expressed genes were identified by 1-way ANOVA with a 0.1 false discovery rate.

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  Figure 2.. Developmental differences in cardiac electrophysiology and the chronotropic response to milrinone. Pseudo-ECGs were recorded from excised, intact heart preparations from A) neonates (n=22–26), B) juveniles (n=17–18), C) adults (n=21–22). Left: Representative ECG trace from guinea pig heart before and after milrinone treatment (ex vivo, retrograde perfusion). Right: ECG metrics for each age group before and after milrinone treatment. Individual replicates are shown; values are reported as mean ± SD. Comparisons before and after drug exposure by mixed effects analysis with Holm-Sidak multiple comparisons test; *p<0.05.

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  Figure 3.. Milrinone enhances contractility and relaxation. A) Example of biphasic frequency response shown for a neonate, juvenile, and adult heart. LVDP increases with sinus rate acceleration (shorter cycle length), and decreases at increasingly faster pacing rates. B) Positive LVDP vs heart rate slope changes during accelerated sinus rhythm (left), vs negative slope with external pacing (center). Illustration of LVDP, contractility, and lusitropy measurements (right). Effects of milrinone on LVDP (C), contractility (D), lusitropy (E) are shown during sinus rhythm (left) and external pacing (right). Data represented as mean ± SD. Each dot represents an individual animal (n=14–15 neonates, n=13 juveniles, n=10–13 adults). Mixed effects analysis with Holm-Sidak multiple comparisons testing; *p<0.05.

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  Figure 4.. Post-rest potentiation increases with maturation and is reduced after milrinone exposure. S1-S2 pacing protocols were implemented to measure post-rest potentiation with across multiple rest periods (300 ms, 250 ms, 200 ms), and the corresponding change in LVDP is shown for A,B) neonates, C,D) Juveniles, E,F) adult hearts. For each age group the compiled data is shown (left), with representative pressure wave examples (right). Dynamic pacing is shown (S1 carrots, 150 ms), followed by the S2 beat, and the change in LVDP is shown. G,H) Change in LVDP from S1 dynamic pacing (120 ms) to the first spontaneous beat. Data represented as mean ± SD. Each dot represents an individual animal (n=11–16 neonates, n=12–13 juveniles, n=10–11 adults). Mixed effects analysis with Holm-Sidak multiple comparisons testing; *p<0.05.

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  Figure 5.. Effects of milrinone on cardiac action potential duration. Optical action potential duration measurements are plotted relative to pacing cycle lengths at A) baseline, B) after 10 μM milrinone treatment, C) after 100 μM milrinone treatment. Slope of the restitution curve is shown for each age group D) Comparison between baseline and milrinone measurements at APD50 are shown for 200 ms, 160 ms, and 140 ms pacing cycle length. APD30 = action potential duration at 30% repolarization, APD50 = 50% repolarization, APD70 = 70% repolarization. Data represented as mean ± SD (shown as a line in restitution curves and error bar in bar plot). Each dot represents an individual animal (n=5–19 neonates, n=6–7 juveniles, n=8–13 adults). Mixed effects analysis with Holm-Sidak multiple comparisons testing; *p<0.05.

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  Figure 6.. Effects of milrinone on intracellular calcium handling. Optical calcium transient measurements are plotted relative to pacing cycle lengths at A) baseline, B) after 10 μM milrinone treatment, C) after 100 μM milrinone treatment. Slope of the restitution curve is shown for each age group. D) Comparison between baseline and milrinone measurements at CaD50 are shown for 200 ms, 160 ms, and 140 ms pacing cycle length. CaD30 = calcium transient duration at 30% decay, CaD50 = 50% decay, CaD70 = 70% decay. Data represented as mean ± SD (shown as a line in restitution curves and error bar in bar plot). Each dot represents an individual animal (n=5–11 neonates, n=6 juveniles, n=8–10 adults). Mixed effects analysis with Holm-Sidak multiple comparisons testing; *p<0.05.