Pulse deficit or pulse apex deficit is the difference between the simultaneously counted heart rate and the pulse rate. This usually occurs in atrial fibrillation. When heart beats very fast and irregularly as in atrial fibrillation, some of the beats are not strong enough to open the aortic valve so that a pulse is not felt. This occurs usually when there is a short cardiac cycle with little time for diastolic filling of the ventricle. Highly premature ectopic beats can also produce pulse deficit for the same reason. A pulse deficit of more than 10 per minute is more likely in atrial fibrillation. The pulse deficit will become lesser as the rate is controlled by medicines in atrial fibrillation.
Documenting the pulse deficit used to be a tough job earlier because one is supposed to count the heart rate using a stethoscope and the pulse using fingers simultaneously to get the pulse deficit. But now with cardiac monitors displaying pulse waveform (pulse oximetry) and ECG (electrocardiogram) simultaneously, both pulse rate (from pulse oximetry) and heart rate (from ECG) are displayed on the bed side monitor and it is very easy to calculate the pulse deficit!