EKG Week 1

Cardiac
Electrophysiology
• Cardiac action potential
• Depolarization cycle
• Refractory periods
• Conduction system
Properties of Cardiac Cells
Automaticity (electrical event)
• Ability to spontaneously initiate an electrical
impulse
Excitability (electrical event)
• Ability to respond to an electrical stimulus
Conductivity (electrical event)
• Ability to receive & conduct an electrical
stimulus
Contractility (mechanical event)
• Ability to shorten or contract
Cardiac Action Potential
• Electrical impulses are a result of rapid flow of
ions back & forth across cell membrane
• Ion exchange/movement (K, Na, Ca) in heart
cells creates electrical activity that appears on
the EKG as waveforms
• Major electrolytes (ions) affecting cardiac
function:
– Potassium (K), Sodium (Na), Calcium (Ca)
• Ü K, Ca = Û automaticity
• Û K, Ca = Ü automaticity
Refractory Periods
Absolute Refractory Period (ARP)
• From onset of QRS to approximate
peak of T wave
• Cells are depolarized & can’t be stimulated to conduct
an impulse no matter how strong the stimulus
Relative Refractory Period (RRP)
• Known as the “Vulnerable Period”
• Corresponds with the downslope of T wave
• Cells can be stimulated if stimulus is strong enough
• Can result in ventricular chaos (VT, VF)