Difference between action potential of sa node and contractile myocytes​

Different groups of cells depolarize at different rates. The rate of depolarization of SA node cells is faster than the rate of depolarization of AV node cells. ... If both the SA node and AV node fail, the Purkinje fibers have a modest level of automaticity (20 beats/minute) that may still reach threshold

answer:

it could come from a variety of sources.

explanation:

..although it was most likely developed through zoonotic transmission, where an infectious disease which usually afflicts when animals jump to humans.