What is the name of the condition where no pacemaker cells are active in the heart for a short-time?
If there are no pacemaker cells active, no muscle contraction will occur. This condition is named asystole. It can be a temporary or definitive condition. Some would call it "extreme bradycardia" in temporary cases, but this is just an euphemism.

Edit:

Ok, so let's try to clear up the confusion a bit. Technically, there is no asystole involved here (not even temporary). This rhythm is regularly irregular (irregular, but has a pattern), while asystole has no pattern by its very nature.

What you are seeing here is not the consequence of low frequency firing from pacemaker cells. The supraventricular extrasystoles (every 3rd QRS complex) are a consequence of early ventricular depolarization not triggered by SA node activity. The P wave that would normally trigger the 3rd complex does in fact occur, but it is synchronous with the abnormal QRS complex, which is why you cannot see it. The compensatory pause is due to lengthening of the hyperpolarized state in pacemaker cells, and is a consequence of the addition of the hidden P wave and the extrasystole in a short time.

In conclusion, this pattern is not the result of delayed pacemaker firing, but of early depolarization of cardiomyocytes by an accessory pacemaker.



I have marked on this strip the maximal time interval of SA node hyperpolarization. Depending on when the P wave hidden in the extrasystole occurs, the real time may be shorter than the above interval.