ECG analyses of urethane anaesthetized Ts65Dn adult mice revealed cardiac conduction anomalies.

Peripheral (A) and precordial (B) leads are presented for the wt and the Ts65Dn mice in the left and right columns respectively. Wt ECG showed a smooth tracing in all leads. P wave, QRS complex and J wave are clearly distinguishable. Ts65Dn ECG showed notching of the S wave in most leads. In V1, QRS amplitude was reduced with a fragmented RSR'S' complex. A slurr was found in the Vms lead. Notice the prolonged PR interval. Representation of Vms lead from wt (C) and Ts65Dn (D) showed measurements performed on wave amplitudes and durations. The isoelectric line (zero) was taken as the mean potential just preceding the R wave and J and T waves were labeled. The T wave was always positive in this lead while it could be elusive in other leads. ECG features (E) were classified according to the presence of fragmented QRS (RSR'S'), slurr and S wave absence (Vx>0) in the precordial leads. 62% of the Ts65Dn mice showed 3 anomalies while 61% of the wt was free of such features. Frontal QRS electrical axis distribution (F) was evenly distributed in Ts65Dn while that of wt animals showed a leftward preferential orientation. Measurement of wave amplitudes in precordial leads (G) showed a large decrease of S and J waves on V1 and limited changes in V4 whereas R waves were found normal in both V1 and V4 (n = 31 and 29 for wt and Ts65Dn respectively) (Student t-test p-values: **: P<0.01; ***: P<0.001).