Fig. 3

Pseudo-ECG traces during normal sinus rhythm (top), during HB-pacing with capture (middle), during VM-pacing and captured (bottom). In the top trace, the time interval between two QRS peaks (R–R interval) is 270 ms. When the HB was paced slightly faster than the intrinsic R–R interval with a current amplitude above the threshold, the shape of QRS around the peaks in the middle trace remained very similar to the shape of QRS around the peaks in the top trace. However, the R–R interval in the middle trace now adjusted to the rate of pacing. The stimulation artifacts in the pseudo-ECG in the middle trace are separated by 230 ms (shown). The time lag between the QRS peak and the stimulation artifacts also becomes constant so that t1 = t2 (shown). Similarly, when the VM was paced and captured, t1 = t2. However, unlike the top two traces, the shape of QRS is longer and different