The Hyperpolarization-Activated Cyclic-Nucleotide-Gated Channel Blocker Ivabradine Does Not Prevent Arrhythmias in Catecholaminergic Polymorphic Ventricular Tachycardia

Figures

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  Figure 1. Ivabradine does not prevent the occurrence of delayed-afterdepolarizations (DADs) in human induced pluripotent stem cells derived cardiomyocytes (hiPSC-CMs) derived from CPVT2 (CASQ2-D307H) patients. (A) Representative traces of spontaneous action potential (AP) recorded in CASQ2 D307H hiPSC-CMs are shown from the same cell in the absence of any drug (black trace, control), then in the presence of 3 μM ivabradine (orange trace), 100 nM of isoproterenol (red trace), and both isoproterenol + ivabradine (purple trace). (B) Data summary for each treatment of the numbers of DADs, which were normalized to those obtained in the same cell before the addition of any drug. Isoproterenol (100 nM) increased DADs by 3.56 ± 0.96-fold [n = 19, P = 0.0147, one-way ANOVA (F = 3.402; P = 0.0147); Dunnett’s multiple comparisons test, P = 0.0406]; ivabradine (3 µM) + isoproterenol (100 nM) increased DADs by 5.67 ± 3.47-fold, n = 4, one-way ANOVA (F = 3.402; P = 0.0147); Dunnett’s multiple comparisons test, P = 0.0239; TRAM-34 (1 µM) + isoproterenol (100 nM) increased DADs by only 1.45 ± 0.41–fold, which is not significant (NS) compared to control; n = 15, one-way ANOVA (F = 3.402; P = 0.0147);…

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  Figure 2. Ivabradine does not reduce the arrhythmic phenotype of calcium transients in sinoatrial node (SAN) from CASQ2-D307H KI mice. (A) Representative traces of calcium transients obtained from the same SAN of knock-in (KI) CASQ2 D307H mice under control (black trace), 100 nM isoproterenol (red trace), and isoproterenol + ivabradine (purple trace). (B) Data summary of the aberrant calcium transients observed in SAN from KI CASQ2 D307H mice under the described conditions (n = 5). (C) Data summary of the aberrant calcium transients observed in SAN from KI CASQ2 D307H mice under the described conditions (n = 10).

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  Figure 3. In contrast to TRAM-34, ivabradine does not prevent the ventricular arrhythmias recorded in ECG from CASQ2-D307H KI mice at rest. (A) Representative ECG recording following intraperitoneal (IP) injection of vehicle (saline, upper) and 6 mg/kg ivabradine (lower), in WT mice at rest. Sequential vehicle and ivabradine injections were performed on the same animal. (B) Data summary of heart rate (paired t test, P = 0.0003, n = 4) and PR interval (paired t test, P = 0.0045, n = 4) after IP injection of ivabradine. (C) Representative ECG recordings following IP injection of vehicle (saline, upper) and 6 mg/kg ivabradine (lower) in CASQ2 D307H knock-in (KI) mice at rest. (D) Data summary of the heart rate (paired t test, P = 0.0192, n = 4) and PR interval [not significant (NS), n = 4] after IP injection of ivabradine. (E) Representative ECG recording following IP injection of vehicle (peanut oil, upper) and 20 mg/kg TRAM-34 (lower) in CASQ2 D307H KI mice at rest. (F) Data summary of heart rate (paired t-test; P < 0.0001, n = 12) and PR interval (paired t-test; P < 0.0001, n = 12) in CASQ2 D307H KI mice at rest.

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  Figure 4. In contrast to TRAM-34, ivabradine does not prevent the ventricular arrhythmias recorded in ECG from CASQ2 D307H KI mice following treadmill exercise. (A) Representative ECG recording following intraperitoneal (IP) injection of vehicle (saline, upper) and 6 mg/kg ivabradine (lower), in WT mice following treadmill exercise. (B) Data summary of heart rate (paired t test, n = 4, P = 0.0068) and PR interval (paired t test, n = 4, P = 0.0217) in WT mice after treadmill exercise and IP injection of ivabradine. (C) Representative ECG recording following IP injection of vehicle (saline, upper) and 6 mg/kg ivabradine (lower) in CASQ2 D307H knock-in (KI) mice following treadmill exercise. (D) Data summary of heart rate [not significant (NS), n = 4] and PR interval [not significant (NS), n = 4] after IP injection of ivabradine. (E) Representative ECG recording following IP injection of vehicle (peanut oil, upper) and 20 mg/kg TRAM-34 (lower) in CASQ2 D307H KI mice following treadmill exercise. (F) Data summary of heart rate (paired t-test; P = 0.0004, n = 11) and PR interval (paired t-test; P = 0.0099, n = 11) in CASQ2 D307H KI mice following treadmill exercise.