Caffeine and dobutamine challenge induces bidirectional ventricular tachycardia in normal rats

Figure 1. Electrocardiogram traces show examples of occasional premature ventricular contraction (PVC) (Top), bigeminy (Middle), and multiform PVCs (Bottom) induced by caffeine and dobutamine challenge in a rat.

Figure 2. Electrocardiogram (ECG) traces show a typical example of bidirectional ventricular tachycardia (BD-VT) induction (Top), persistence (Middle), and termination (Bottom) after caffeine and dobutamine challenge in a rat. Note that sinus rate is seen in the beginning, followed by the occurrence of premature ventricular contractions (PVCs) and BD-VT (top panel). Middle ECG panel shows sustained BD-VT. The bottom panel shows the termination of BD-VT and return of sinus rate.

Figure 3. Top panel shows an example that the coupling interval (CI) of premature ventricular contraction was only modestly shorter than the spontaneous sinus cycle length (SCL) immediately before the arrhythmia. Middle and bottom panels show the transition from one type of bidirectional ventricular tachycardia to another seen in 2 rats, as indicated by the arrows.

Figure 4. Top panel of electrocardiogram (ECG) trace shows obvious atrioventricular (AV) dissociation (P waves are indicated with triangular symbols) during the occurrence of premature ventricular contraction and bidirectional ventricular tachycardia (BD-VT). Bottom panel shows ECG trace (top) with BD-VT and 2 right atrial electrocardiograms (RA1 and RA2). Note that atrial tachyarrhythmia was induced immediately after the burst atrial pacing. However, the BD-VT was not affected by the atrial burst pacing and the induction of atrial tachyarrhythmia, further indicating AV dissociation during BD-VT.

Figure 5. The activation sequence of left ventricle (LV) vs right ventricle (RV) in both types of QRS complex during bidirectional ventricular tachycardia (BD-VT) was similar to that seen in sinus rate (dashed lines). The traces are surface electrocardiogram (ECG) (top), LV ECG (middle), and RV ECG (bottom). Recordings in sinus rate and BD-VT are shown in top and bottom panels, respectively. Note that there is no obvious RV and LV activation alternation despite the QRS polarity changes during BD-VT.