Figure 2.

Analysis of the rhythm and QT intervals of ECGs obtained from LQT and control mice. (a) The relationships between the observed QT interval and the RR intervals in the conscious LQT mice (⧫, •, and ▴, n = 10) and control mice (▵, ◊, ×, +, n = 10). Each point represents an average of 72 measurements of the QT and RR intervals (every 20 min) per 24 hr. Each measurement is an average of a 4-sec screen. Each mouse was monitored continuously for 3 days and is therefore represented by three points. (b) The ECG of an anesthetized 3-month-old control mouse (50 mg/kg ketamine and 10 mg/kg xylazine) recorded by the transmitter. The observed heart rate was 180 beats per minute (bpm), and the observed QT interval was 101 ms. (c) The ECG of an anesthetized matched LQT mouse (50 mg/kg ketamine and 10 mg/kg xylazine) recorded by the transmitter. The observed heart rate was 180 bpm, and the observed QT interval was 179 ms. (d) Sensitivity of the QTc interval of LQT mice to ketamine. The average QTc interval of anesthetized and conscious LQT and control mice (average of 2 hr after 50 mg/kg ketamine administration). The ketamine-induced prolongation of the QTc interval in LQT mice was significantly greater than that of control. (e) Surface ECG recording of an 11-beat run of ventricular tachycardia in a conscious freely moving LQT mouse. Note the atrio-ventricular dissociation. The enlarged QRS complexes demonstrate that the individual QRS complexes in the nonsustained ventricular tachycardia differ substantially from the sinus QRS complexes. The sinus heart rate is about 530 bpm (RR interval of 113 ms). The rate of the ventricular tachycardia is 570 bpm (RR interval of 105 ms).