PMC5775439_01
The decrease in pacing output was accompanied by QRS complex prolongation, suggestive of loss of His bundle capture. However, there was no corresponding prolongation of the ventriculoatrial (VA) interval, indicating an extranodal response. CS1 to CS5 represent proximal to distal coronary sinus electrodes.
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The decrease in pacing output resulted in a sudden QRS complex prolongation, but there was no corresponding change in the retrograde atrial activation sequence or in the VA interval of 85 ms (Figure 1).