ric ular ▁f ibr ill ation , ▁waves ▁of ▁elect rical ▁activation ▁spir al ▁through ▁the ▁card iac ▁mus cle ▁cha ot ically ▁in ▁a ▁mass ▁of ▁dis organ ised , ▁broken ▁wave lets . ▁The ▁consequence ▁of ▁f ibr ill ation ▁is ▁that ▁the ▁ch amb ers ▁of ▁the ▁heart ▁affected ▁by ▁the ▁dis organ ised ▁elect rical ▁activation ▁lose ▁their ▁p ump ing ▁ability   – ▁f ibr ill ation ▁of ▁the ▁card iac ▁at ria ▁in ▁at rial ▁f ibr ill ation ▁leads ▁to ▁an ▁irregular ▁pul se , ▁and ▁f ibr ill ation ▁of ▁the ▁card iac ▁vent ric les ▁in ▁vent ric ular ▁f ibr ill ation ▁rend ers ▁the ▁heart ▁unable ▁to ▁p ump ▁blood ▁at ▁all . ▁ ▁There ▁are ▁several ▁possible ▁mechan isms ▁by ▁which ▁short ▁action ▁potential s ▁might ▁promote ▁f ibr ill ation . ▁The ▁link ▁between ▁these ▁mechan isms ▁is ▁how ▁the ▁duration ▁of ▁the ▁action ▁potential ▁influ ences ▁how ▁frequently ▁a ▁heart ▁mus cle ▁cell ▁can ▁be ▁excited . ▁A ▁shorter ▁action ▁potential ▁generally ▁allow ▁a ▁heart ▁mus cle ▁cell ▁to ▁be ▁excited ▁more ▁frequently   – ▁the ▁ref ract ory ▁period ▁is ▁shorter . ▁ ▁The ▁first ▁mechanism , ▁referred ▁to ▁as ▁the ▁disp ersion ▁of ▁rep olar isation , ▁occurs ▁because ▁the ▁action ▁potential ▁short ening ▁seen ▁in ▁this ▁condition ▁occurs ▁to ▁a ▁greater ▁extent ▁in ▁some ▁layers ▁of ▁the ▁heart ▁wall ▁than ▁in ▁others . ▁This ▁means ▁that ▁at ▁certain ▁points ▁in ▁the ▁card iac ▁cycle , ▁some