Doc,
In Western medicine it would be referred to as a disturbance of the cardiac cycle during something known as the "Relative Refractory Period". The refractory period has two stages, the Absolute and Relative refractory periods. Think of it like a toilet when you push the handle (the impulse),the water floods the bowl and changes the pressure. The same thing happens in the heart, only faster. Now try to flush it again before the upper chamber fills and nothing will happen. This is similar to the "Absolute" refractory period. The heart has contracted and is now beginning to repolorize or re-charge itself, so any stimulus you send to it will not affect it, (like when you try to flush the bowl immediately after the initial flush).
Think of the Relative refractory period as when the upper chamber of the toilet is about half full, it'll flush but the flush will be weak. The same goes for the cells of the heart, they are not fully charged but they will still attempt to contract if they receive a signal. This is important to remember because an impulse during the relative refractory period can cause premature contractions leading to compromised filling and poor ejection of blood from the heart. This can also lead to life threatening dysrhythmias that severly compromise the hearts ability to pump resulting in rapid death of the patient. It is generally referred to as R on T Phenomenon.