Electrophysiology Flashcards
Electrical activity of the heart
An action potential is initiated in the SA node (via In funny sodium channels), Action potentials are conducted from the SA node thru the atrial muscle, Action potentials spread thru the atria to the AV node where conduction slows down, AP travels thru the conduction system to the apex of the heart, the AP spreads thru theventricular muscle upwards, heart will return to resting statte
AV node
AV node delays transmission of electrical signal into the ventricles, Allows time for atria to empty as much blood as possible into the ventricles before the ventricular contraction begins
From the bundle branches, it takes .06 s for the electrical signal to reach the ventricular muscle
EKG parts
P wave: atrial depolarization (initiated by the SA node)
PR interval: time of Atrial depolarization to start of ventricular depolarization
PR segment: the AV node delay, end of atrial depolarization to start of ventricular depolarization
ST segment: measures end of ventricular depolarization to start of ventricular repolarization
QT interval: time from begining of ventricular depolarization to start of ventricular repolarization
QRS: ventricular depolarization begins at apex (atrial repolarization occurs
RR interval: time between beats
ionic equilibrium
the process of ions diffusing and changing the membrane voltage will continue until the membrane potential is at a value sufficient to just balance the ion concentration gradient
equilibrium potential when electrical forces= chemical forces no NET flux
Nernst potential
Resting membrane potential
At rest K ions are most permeable (will efflux out of the cell), the cells interior becomes negative, efflux continues until the electrical force opposes the chemical force with equal force
Electrical voltage that is equal to magnitude to the chemical force= equilibrium potential for that ion
K=-90 mV (sodium makes it slightly more positive)
NA k pump maintains the Na K ionic gradient
NA/K ATPase : 2 k in for 3 NA out
NCX: Ca out with 3 Na in or vice versa
Ca ATPase: Ca pump out with ATP
SERCA: ATP CA into SR
Phases of AP myocytes
Phase 0: Na comes into cell upstroke (Na channels open)
Phase 1: I to (initial repolarization inactivation of NA channels, Voltage gated K channels open
Phase 2: (plateau phase), mainly Ca influx (voltage gated Ca), balances K efflux, Ca influx triggers CA release of SR and myocyte contraction)
Phase 3: Repolarization rapid, massive K efflux due to opening of voltage gated slow K channels and closure of volage gated Ca channels
Phase 4 resting (high K and low Na permeability
Pacemaker AP
Occurs in SA and AV nodes
Phase 0: upstroke- opening of voltage gated Ca channels (voltage set up by funny channels), fast Na channels are permanently inactivated (less negative resting potential , slow conduction velocity thats used by the AV node to prolong transmission from atria to ventricles
Phase 1 and 2 absent
Phase 3: repolarization due to inactivation of Ca channels, and increased K channels (k efflux)
Phase 4 slow spontaneous IF current depolarization- gives automacity
Phase 4 of SA node determines heart rate (Ach/adenosine decrease diastolic depolarization rate and decreases HR, catecholamines increase HR and depolarization rate
funny current is carried by hyperpolarization-activated HCN channels (thru Na channels and a little K), gated by voltage and regulated by cAMP (cAMP activates HCN channel) HCN 4 is the type in cardiac sa node
Channelopathies: Long QT syndrome
Block or dysfunction of K channels can delay repolarization of the cardiac AP
Incrreases of sudden cardiac death due to torsades de points (polymorphic ventricular tachycardia–> V fib)
Na channel mutations –> can cause hyperkalemic periodic paralysis, long QT syndrome, incomplete inactivation of gate
