Graphs Flashcards
1
Q
Draw a cardiac action potential for contractile cells
How to antiarrhythmic drugs alter the myocardial action potential
A
X axis - time (ms)
Y axis - membrane potential (mV)
Correct shape with phases 0-4
Height -90 to +30
Duration - 300ms
0-2 = absolute refractory period
3 = relative refractory period (supramaximal stimulus here will result in AP with slower rate of depolarisation, smaller amplitude, weaker contraction
VW classification class 1 (Na+ channel blockers) reduce the slope of phase 0 and the magnitude of depolarisation, and also prolong the refractory periods by delaying reactivation of Na channels
VW class 3 (K+ channel blockers) delay phase 3 repolarisation, lengthening the duration of the AP and refractory periods
