Cardiac Electrophysiology Flashcards
What are the elements of an action potential?
- Resting cell
- Depolarization
- Repolarization
What happens during resting cell phase?
Inside of cell is negative relative to the outside. K+ is inside the cell, Na+ is outside kept in balance by NaK pump
What happens during depolarization?
Resting cell becomes positive / excited.
Stimulus from SA node makes membrane increase semi-permeability which cases Na to rush in to cell making it more ++
What happens during repolarization?
Cell interior slowly becomes negative again.
Cl- passively follows Na+ into cell while NaCa channels open allowing Ca++ to enter. K starts leaving cell just as NaCa channels close and cell becomes more negative again. NaK pump restores cell to resting state.
What is refractoriness?
Extent to which a cell is able to respond to a stimulus
What is the relative refractory period?
Cardiac cells are repolarizing but strong enough stimulus will cause depolarization again. Cells are “relatively still excited”.
Comprises 2nd half of the T-wave, ectopic beats going through may cause R-on-T
What are the electrophys properties of pacemaker cells?
Resting membrane potential is not fixed/stable (approx -60mv)
NaCa channels remain open all the time allowing Na to slowly drift into cell until it reaches threshold at -40mV. Depolarization occurs (automaticity)
What are Class 1 anti-arrhythmic drugs?
Slows Na+ influx by blocking Na channels
Decrease HR by slowing depolarization
E.g. Lidocaine, procainamide
What are Class 2 anti-arrhythmic drugs?
Blocks beta receptors, makes RMP more negative therefore harder to reach threshold potential
Decrease HR
E.g. Metoprolol
What are Class 3 anti-arrhythmic drugs?
Blocks K+ channels, prolonging action potential
Decrease HR by increasing refractory time (**May cause arrythmia!)
E.g. Amiodarone, ibutilide
What are Class 4 anti-arrhythmic drugs?
Blocks Ca++ channels, decreases APs in SA node and prolongs AP in the ventricles
Decrease HR, contractility, BP
E.g. Diltiazem, Verapamil
What are Class 5 anti-arrhythmic drugs?
Works magically.
E.g. Adenosine, MgSO4
What is the sarcoplasmic reticulum?
Storage space for Ca++
What are transverse tubules?
Passageways for Ca++
What is actin and myosin?
Filaments in sarcomere (muscle cell) that combine during muscle contraction with help from troponin and tropomyosin
What happens during cardiac contraction?
1) Ca+ binds to troponin using ATP
2) Troponin tells tropomyosin to change binding sites allowing
3) Actin and myosin filaments slide together
What happens during cardiac relaxation?
Actin and myosin disengage when Ca++ removed / unbinds from troponin
What is the role of troponin and tropomyosin?
1) Attached to actin filaments, binds with Ca++ to trigger contraction
2) Prevents actin and myosin from creating cross bridges (inhibits constant contraction)
