Damage to the conduction system at any location can block (or delay) conduction impulses or stimulate contraction at inappropriate times. In addition, because the ventricles may be stimulated to contract before being completely filled, the stroke volume may be periodically diminished which will be reflected in the pulse intensity. This is the case during atrial fibrillation when the stimulation of the AV node is erratic and ventricular filling is often diminished due to an irregularly changing stroke volume and irregular pulse pressure. These rapid atrial contractions cannot usually be detected by auscultation, however, the pulse rate from the ventricular contractions is rapid.
Premature ventricular contractions (PVC's) are extra systolic/ventricular beats and do not necessarily indicate serious heart disease. A PVC occurs when the ventricle contracts and has only partially completed its refractory period when a second contraction occurs. The result is a normal beat, followed by a weaker beat due to inadequate stroke volume, then a pause for a prolonged refractory period. The pulse beat immediately following is usually stronger due to the increased filling during the prolonged pause.The resulting pulse is referred to as a bigeminal pulse or coupled rhythm.