What is the function of the AV node?
- Acts as a gate to slow the impulses to the ventricles and prevent premature atrial impulses from influencing ventricular rate
What do the following portions of EKG wave correspond with in terms of the heart?
- P wave
- Q wave
- R wave
- S wave
- T wave
- P = atrial activation
- Q = His, BB, septal activation
- R = ventricular activation (left)
- S = late ventricular activation (right)
- T = ventricular repolarization
S1 and S2 correspond to what?
S1 - closure of tricuspid and mitral valves
S2 - closure of aortic and pulmonic valves
What factors affect the threshold of a cardiac cell?
1) resting potential (availability of potassium)
2) excitability (availability of sodium and channels)
3) cell size (hypertrophy, edema)
What factors affect the refractory period of a cardiac cell?
1) action potential duration (especially plateau phase, proportional to QT interval)
2) excitability (sodium current, potassium current)
Describe phase 0 for the
a) fast response AP
b) slow response AP
- upstroke
a) fast - sodium current activation, occurs in atrium, ventricle, and His-Purkinje system
b) slow - calcium current activation, occurs in SA node and AV node
Describe phase 1 for the fast response AP
- early repolarization, AP notch
- inactivation of INa
- activation of transient outward K+ current (Ito)
- occurs in atrium, His-Purkinje, ventricular epicardium
Describe phase 2 for the fast response AP
- plateau
- inactivation of outward K+ current (Ito)
- activation of L-type Ca current (ICa,L)
- activation of ultra-rapid K current (IKur)
- ICa,L and IKur oppose each other, causing plateau
Describe phase 3 for fast and slow response AP
- final repolarization
- slow inactivation of ICa,L
- activation of delayed rectifier K currents (IKr, IKs)
Describe phase 4 for pacemaker cells
- inactivation of IKr, IKs
- inward K current provided by funny channel (If); ICa,T; INCX; ICa,L
Describe phase 4 for non pacemaker cells
- background K current from IK1 (inward rectifier Kir 2.x channel proteins)
- balance of inward and outward current
What is the cardiomyocyte resting membrane potential?
- 90 mV
use Goldman-Hodgkin-Katz to determine, due to multiple ion conductances in cell membrane
What are the end effects of hypokalemia on the heart?
- decrease in conduction velocity
- shortens effective refractive period
- prolongs relative refractive period
- increases automaticity
- early afterdepolarizations (reentrant arrhythmias)
- increased excitability!
What are the end effects of hyperkalemia on the heart?
- initially increases and then decreases membrane excitability
- decreases action potential duration
What are the 3 different junctions for cell-cell adhesion or communication in cardiac cells?
1) desmosome - for mechanical stability
2) fascia adherens - anchoring of thin actin filaments
3) gap junction - site of electrical communication
I think these are all in the intercalated disc? Or together make up the intercalated disc?
What are the primary, secondary, and tertiary pacemakers in the heart?
- primary: SA node
- secondary: AV node
- tertiary: His-Purkinje
