Fig. 4. ECG analysis of Gja1^Jrt/+ x FVB mutants by radio-telemetry. Gja1^Jrt/+ mutant mice crossed with FVB wild-type mice resulted in mice large enough to carry radio-telemetry implants for awake ECG analysis (A). Ultrasound (conducted at 7 weeks) and histopathology (conducted 10-12 weeks) analyses revealed no difference in Gja1^Jrt/+ x FVB mice relative to controls (not shown). However, conscious ambulatory ECGs (11-13 weeks) revealed a prolongation of the PQ interval indicative of mild first degree atrioventricular block (A). The PQ intervals were variable, occasionally increasing up to 43 mseconds in length. In addition, P wave width was increased and the heart rate (HR) in Gja1^Jrt/+ x FVB mutants was lower than controls. (B) Several sporadic events were noted in Gja1^Jrt/+ x FVB mutants: 5/9 had bradycardia (HR<300 minute^-1, with the lowest HR at 134 minute^-1), 4/9 had sinus arrest, 2/9 had widened QRS complex, 1/9 had AV block and 1/9 had AV dissociation and junctional escape. In the control group, only one mouse had notable events, namely bradycardia and 2nd degree AV block (not shown). ^*P<0.05, ^**P0.005.