Cardio Electrophysiology 2 Flashcards
Where is the SA node located?
The Endocardial surface of the RA, in the junction of the Superior Vena Cava and RA appendage.
What are the dimensions of the SA node?
15 mm x 5 mm x 2 mm thick
What are the terms for UNSTABLE resting membrane potential?
Prepotential
Pacemaker potential
Diastolic depolarization
What is the resting membrane potential of a SA node?
-70 mV
What is the maximum membrane potential of a Ventricular Muscle cell?
+20 mV, (at which point where Fast Na+ channels close)
What is the maximum membrane potential of the SA node?
0 mV
Sinoatrial (SA node) -
The pacemaker cell; it gives the greatest rhythmicity.
Has UNSTABLE resting membrane potentials, which makes it the “pacemaker”
IT DOES NOT HAVE Fast Na+ Channels
What are the 3 factors that act together to produce SA nodal Prepotential (pacemaker potential)?
1) Increased Na+ conductance/permeability at REST
2) Decreasing K+ conductance/permeability
3) Slow Ca2+ influx
Verapamil -
It inhibits Prepotential of the SA node by blocking Ca2+ channels, and inhibiting spontaneous pacemaker activity
Do AV nodes have Fast Na+ channels?
No, neither does the SA node
What are the 3 natural pacemakers of the human heart?
SA node
AV node
Purkinje Fiber (idioventricular pacemaker)
What are the firing rates of:
SA node
AV node
Purkinje Fiber
SA node: 60-100 times/ min
AV node: 40-55 times/min
Purkinje Fiber: 25-40 times/min
What are the major difference btw the 3 pacemakers of the human heart?
The rate of decay of K+ conductance during PHASE 4
What are the 3 ways you can change the firing rate of pacemaker cells?
1) change rate of Diastolic depolarization
2) change resting membrane potential
3) change threshold potential
What are the 3 ways to SLOW down the rate of firing of a Pacemaker cell?
1) lower the rate of depolarization
2) Hyperpolarize the cell
3) Change the threshold potential
How does the Sympathetic Nervous system change the slope of Pacemaker cells action potential?
It INCREASES the slope of the Prepotential, increasing HR
How does the Parasympathetic Nervous system change the slope of Pacemaker cell action potential?
It DECREASES the slope, decreasing the HR
Which system is used more, the Sympathetic nervous system or the Parasympathetic nervous system?
The Parasympathetic System.
The SA node is usually 100 beats/min, but the Parasympathetic system is always active, decreasing the SA node to 60-100 beats/min.
List the order of the Conduction System of the Heart.
- Start at SA node
- Atrial Internodal Pathways
- AV node
- Bundle of His or AV bundle
- Bundle Branches
- Purkinje System
- Ventricular (heart) muscle
What is the Conduction Velocity of the Atrial Internodal Pathway?
1 meter/sec
What is the Conduction Velocity of the AV node?
0.02 meter/sec
What is the Conduction Velocity of the Bundle of His/ AV bundle?
1-2 meter/sec
What is the Conduction Velocity of the R/L Bundle Branches?
2-4 meter/sec
What is the Conduction Velocity of the Purkinje System?
2-4 meter/sec
What is the Conduction Velocity of the Ventricular (heart) Muscle?
0.3 meter/sec
What controls the Conduction Velocity?
Fast Na+ Channels
AN zone -
It is the transitional zone; cell types in this region are a mixture of Atrial and Nodal fibers interspersed w/ connective tissue
N zone -
It is the Middle Portion of the AV node
N-H zone -
It is the transitional zone; nodal fibers gradually merge w/ fibers from the Bundle of His.
What controls the opening and closing of the Connexion gap channels?
pH and Ca2+ Concentration
In order for Re-entry to occur, what 2 things must happen?
1) There must be a unidirectional block
2) The Refractory Period must be slower than propagation time around the loop
An ECG/EKG is based off of what 3 suppositions?
1) The body is a conduction medium w/ the heart at the center
2) Heart depolarization generates a flow of ions throughout the extra cellular space of the body
3) Electrodes put on the body can detect ion flow
What is the QRS complex?
It is when the Ventricular muscle depolarized, causing systolic contraction
What is the T wave?
When the ventricle repolarizes and relaxes
What is the P wave?
Atrial Depolarization, when the Atria undergoes systolic contraction
