Fast responses may change to slow responses under certain pathological conditions, for example, in coronary artery disease A B C 0 mV K=3 mM K+=7 K+=10 50 msec E H 20 mV 0 mV St K+=14 K+=16 K+=3 FIGURE 16-3. Effect of changes in external [K+] on the transmembrane action potentials recorded from a Pur- kinje fiber The stimulus artifact (St)appears as a bipha- sic spike to the left of the upstroFast responses may change to slow responses under certain pathological conditions, for example, in coronary artery disease