Fig. 2.
Arrhythmogenic changes in guinea pigs upon acute isoproterenol (ISO) exposure. A: representative images of cardiac rhythms from young and adult guinea pigs exposed to ISO demonstrating premature ventricular contractions (PVCs) leading to polymorphic ventricular tachycardia/ventricular fibrillation. These episodes were associated with collapse of the animal and sudden death. B: quantification of PVCs in young and adult guinea pigs for 14 min of recording within 30 min of pump implantation. Both young and adult guinea pigs had significantly more PVCs than age-matched control guinea pigs when exposed to ISO (young: P = 0.002 and adult: P < 0.01). Adult guinea pigs treated with ISO had more PVCs than young guinea pigs treated with ISO (P < 0.01). Statistical analysis of data was by Kruskal-Wallis test with Dunn’s multiple comparisons. Young control group: n = 15, young ISO-treated group: n = 29, adult control group: n = 9, and adult ISO-treated group: n = 7. C: heart rate (HR) averaged over first 10 min after pump implantation. Within the first 10 min of ISO exposure, young guinea pigs had a significantly higher HR (P = 0.03). There was a significant difference between young and adult guinea pig HRs with exposure to ISO (P = 0.003). Statistical analysis of transformed data was done using one-way ANOVA with Bonferroni’s multiple-comparisons analysis. Young control group: n = 6, young ISO-treated group: n = 5, adult control group: n = 5, and adult ISO-treated group: n = 6. D: ISO exposure for 10 min significantly increased the time from the peak to the end of the T wave (Tp-e) in adult guinea pigs (P = 0.03). Adult guinea pigs exposed to ISO had longer duration of Tp-e than young guinea pigs treated with ISO (P = 0.06). Statistical analysis of transformed data was done using one-way ANOVA with Bonferroni’s multiple-comparisons analysis. Young control group: n = 6, young ISO-treated group: n = 5, adult control group: n = 5, and adult ISO-treated group: n = 6. E: time from Tp-e over corrected QT interval (Tp-e/QTc) increased in adult guinea pigs treated with ISO (P = 0.02). Adult guinea pigs treated with ISO had a significantly higher Tp-e/QTc than young guinea pigs treated with ISO (P = 0.04). Statistical analysis of transformed data was done using one-way ANOVA with Bonferroni’s multiple-comparisons analysis. Young control group: n = 6, young ISO-treated group: n = 5, adult control group: n = 5, and adult ISO-treated group: n = 6.