Dual intraventricular response after cardiac resynchronization

Figure 1 A: Baseline electrocardiogram (ECG) during biventricular pacing at 60 beats per minute showing an underlying left atrial flutter and bigeminy. The premature ventricular complexes have the same morphology and a coupling interval of 630 ms, indicated by the blue rectangle. B: Baseline ECG, after reprograming the lower pacing rate at 30 beats per minute, showing poor residual atrioventricular conduction with narrow QRS complexes and 2 different morphologies of premature ventricular complexes (PVCs) with the same coupling interval (580 ms). The red line corresponds to the beginning of the narrow QRS complexes. The blue rectangles indicate a longer PVC coupling interval (630 ms) during biventricular pacing at 60 beats per minute. C: Biventricular pacing at 80 beats per minute showing bigeminywith the same 2 different PVCmorphologies. PVCs alternate and have a similar coupling interval compared with biventricular pacing at 60 beats per minute (blue rectangle).