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Figure 4 Time course of developing pre-excitation in mutant transgenic mice. (A) The PR intervals from a cohort of 16 mice pups are plotted over 12 weeks. At birth (week 0), all pups have normal PR intervals without pre-excitation. By week 1, two of eight transgene positive mice (solid circles) develop short PR intervals and pre-excitation, increasing to seven mice by week 4. No transgene-negative mice (open circles) had short PR intervals or pre-excitation. (B) The top portion shows electrocardiogram (ECG) leads I, II (LI and LII), and aVF from a TGWT mouse. The PR interval remains distinct and unchanged from birth through four weeks. The bottom portion displays the same ECG leads from a TGN488I mouse. At week 0, the PR interval is similar to that of the TGWT mouse. By week 1, a short PR and wide QRS complex develop, suggestive of ventricular pre-excitation. At week 4, the PR interval remains short, with a wide QRS complex, sinus bradycardia, and sinus arrhythmia.
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