Fig. 5.

Misalignment with environmental LD cycles disrupts cardiac rate and leads to long QT interval. a Incomparison to matched 24 h LD cycle housed mice, mean heart rate (HR) was significantly reduced in mice maintained in 22.5 and 27 h LD cycles, which was accompanied by a significant reduction in the amplitude of HR rhythms in the 27 h LD mice. b HR remained significantly reduced in non-24 h LD housed mice even when analyses were limited to periods of inactive (no recorded movement for 20 min preceding HR measure). c Murine ECG beat waveform with defining features labelled. d–h Diurnal profiles and mean interval durations for RR (d), PR (e), QRS (f), QT (g) and RR-adjusted QT (QTc; h) of mice maintained under 24 h, 22.5 h or 27 h LD conditions. All parameters were significantly lengthened under non-24 h LD cycles. i, j A 2 h light pulse (LP, red) from ZT14-16 caused a significant reduction in night-time HR when compared with the average HR profile recorded over three preceding cycles (blue, NLP). k–m Complete autonomic blockade (AB) increased HR at ZT2 (~2 h after lights on; k) and ZT14 (~2 h after lights off; l) in 22.5 h LD housed mice, and normalised it to 24 h LD conditions. m Change in HR (vs. baseline) during autonomic blockade at ZT2 and ZT14. Diurnal profiles depict mean ± 95%CI. ^∗ p < 0.05, ^{∗ ∗} p < 0.01. a–h One-way ANOVA with Dunnett’s post hoc test (vs. 24 h control group); j paired t-test; k–m repeated measures two-way ANOVA with Tukey’s post hoc test