EKG Intervals and Response to Autonomic Stimuli

 Heart rate, bpm634±45473±21*
 P-wave duration, ms7.61±0.349.35±0.53*
 PR, ms33.5±1.636.9±1.2
 QRS, ms9.57±0.8811.59±0.99
 Baseline HR649±21559±35
 Isoproterenol HR (% change)728±14* (12.1)649±26 (16.3)
 Atropine HR (% change)742±6* (14.2)676±16 (21.1)
 Carbachol HR (% change)230±25§ (64.6)227±13§ (59.4)
  • ANOVA indicates analysis of variance; HR, heart rate; and iNICD, inducible Notch intracellular domain.

  • A. Controls are littermate tetO_NICD mice (n=4 males) and iNICD are αMHC-rtTA; tetO_NICD mice (n=4 females, n=4 males). Both genotypes were fed doxycycline chow at 8 wk of age for 3 wk with no washout. EKGs were performed on mice during isoflurane sedation. Statistics was performed using unpaired t tests with Welch’s correction.

  • * P<0.05, data are expressed as mean±SEM.

  • B. Controls are littermate αMHC-rtTA mice on dox (n=3 females, n=8 males), and iNICD are experimental αMHC-rtTA; tetO_NICD on dox group (n=8 females, n=6 males). All mice were fed doxycycline chow starting between 2 and 3 mo of age for 3 wk, followed by a washout period of 2 wk. EKGs were performed on conscious mice. Adrenergic stimulation with isoproterenol was done by intraperitoneal injection of isoproterenol (0.2 mg/kg) and inhibition of parasympathetic activity with atropine (1 mg/kg), and carbachol injection was given intraperitoneally (0.3 mg/kg) to simulate increased vagal nerve activity. With repeated measures 2-way ANOVA, there is a statistically significant genotype effect F(1,23)=10.6, P=0.0039. There is also a statistically significant drug effect across both genotypes F(3,69)=233.2, P<0.001. However, there is not a significant interaction between drug and genotype F(3,69)=1.739, P=0.17.

  • * P<0.05, †P<0.01, ‡P<0.001, §P<0.0001, data are expressed as mean±SEM.