cardiovascular system
• homozygotes exhibit significantly delayed atrioventricular and intraventricular conduction as well as uncoordinated ventricular excitation despite normal heart rates and normal sinus rhythms
• no histological evidence of ventricular hypertrophy or dilation, and no signs of abnormal cardiac orientation are observed
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• three-lead ECGs indicate that mutant PR intervals are at least 21% longer than wild-type PR intervals, indicating delayed atrioventricular conduction
• prolonged PR intervals associated with a normal sinus rhythm indicate presence of a first-degree atrioventricular block
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• homozygotes exhibit spatially altered propagation of electrical activity in the ventricles i.e. a significantly wider distribution of frontal plane axes relative to wild-type mice (-130 to + 180 vs -80 to +90), as measured by vectorially summing the QRS amplitudes in limb leads
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• ECGs indicate that mutant P waves are, on average, ~9% longer than wild-type P waves
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• mutant ECGs show split QRS complexes in lead II, rSR' morphology in lead III and wide S waves in lead I, indicating uncoordinated ventricular activation
• 90% of homozygotes show either a split QRS complex in lead II or rSR' morphology in lead III compared with 13% of wild-type and 20% of heterozygous mutant mice
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• mutant ECGs indicate prolonged QT intervals compared with wild-type ECGs
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• presence of broad, split or notched QRS complexes associated with frontal plane axis deviation indicate a bundle branch block
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• mutant three-lead ECGs that mutant QRS complexes are on average 34% longer than wild-type QRS complexes, indicating delayed intraventricular conduction
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