The difference between apical and peripheral pulse rates that results from decreased cardiac output when the atria fail to contract is known? as:

The answer to this question is pulse deficit. Pulse deficit is a term wherein it shows the difference between the count of the heart beat and the pulse. Pulse deficit is also known as pulse apex deficit. Pulse deficit is also caused by a irregular heart beat of the patient. 

yes, it is pretty much the same thing, which is cool. : )