Lecture 3: EP Flashcards
What is the P wave:
atrial depolarization
-happens immediately following SA node firing
PR interval
PR segment:
initial depol of ventricle/excitation
PR segment: delay at AV node
PR interval varies with conduction velocity via:
AV node
AV node conduction velocity and PR interval relationships
indirectly proportional
if AV node conduction decreases (heart block), PR invterval increases
by stimulating parasympathetic system: PR interval is inc/dec? HOW ABOUT THE AV CONDUCTION VELOCITY?
PR invterval is INCREASED (dec conduction velocity of AV node)
sympathetic stimulation dec/inc PR? AV node velocity conduction?
PR is decreased (increases conduction velocity of AV node)
QRS interval:
depolarization of ventricles
QT invterval
- begining of Q, end of T
- entire period of depol & repolarization of ventricles–> ventricular AP
ST segment
-end of S to begining of T
-isoelectric
- ventricles are depolarized
- -ventricles are contracting & emptying ~corresponds to plateau phase of ventricular AP
T-wave
ventricular repolarization
Cardiac action potential, the RMP is determined by:
conductance of K+ & approaches to K+ equilibrium
inward current
brings positive charges INTO CELL and depolarizes
outward current:
takes positive charges out of the cell & hyperpolarizes
what maintains ionic gradients across the membrane?
Na+,K+-adenosine triphosphatase (ATPase) maintains ionic gradients
across cell membranes
the image is ventricular (non-pacemaker/rapid!!) action potential, what is phase 0?
**is the upstroke of the action potential
-** increase in Na+ conductance–>inward current–>depolarizes the membrane**
the image is ventricular action potential, what is phase 1?
is a brief period of initial repolarization.“transiently outward K+”
- caused by an outward current of K+ions out of the cell & a decrease in Na+ conductance (inactivation of Na)
the image is ventricular action potential, what is phase 2?
is the plateau of the action potential.
■ is caused by a transient increase in Ca2+ conductance via L-type long lasting channels–>inward Ca2+current & by an increase in K+ conductance
■* During phase 2, outward and inward currents are approximately equal/balanced, so the
membrane potential is stable at the plateau level.*
- IKs- voltage stays close to 0 (Ca influx countering K outlfux)
the image is ventricular action potential, what is phase 3?
is repolarization.
■** Ca2+ conductance decreases (close), and K+ conductance increases**
■ The high K+ conductance results in a large outward K+ current (IK)–>hyperpolarizes
the membrane back toward the K+ equilibrium potential.
**
the image is ventricular action potential, what is phase 4:
is the resting membrane potential.
- is a period during which **inward and outward currents (IK1) are equal **and the mem-
brane potential approaches the K+ equilibrium potential.
-the small fluxes of Na+ (influx) & K+ (outflux)maintain the resting potential - this entire graph is a RAPID DEPOLARIZATION OF THE non-pacemaker cell AP (ventricular AP)–> bc rapid~ referred to as a FAST RESPONSE
Sinoatrial (SA) node
(slow response)
- normally the pacemaker of the heart
- unstable resting potential
- -has phase 4 depolarization/automacity
Sinoatrial (SA) node
phase 0:
-
upstroke of the action potential.
■ is caused by an increase in **Ca2+ conductance. **–> inward Ca2+
current that drives the membrane potential toward the Ca2+ equilibrium potential.
how is phase 0 different in the ventricles,
atria, and Purkinje fibers vs. SA node?
The ionic basis for phase 0 in the SA node is different from that in the ventricles,
atria, and Purkinje fibers (where it is the result of an inward Na+ current in the non-pacemaker).
in the SA node: there is Ca+ inward current
SA node phase 3:
- repolarization.
■ is caused by an increase in K+ conductance. –>results in an outward K+
current –> repolarization of the membrane potential.
~60mV
SA node phase 4:
- slow depolarization.
- * accounts for the pacemaker activity of the SA node (automaticity).*
-caused by an **increase in Na+ conductance, **–> inward Na+ current
called If.
■ If is turned on by repolarization of the membrane potential during the preceding
action potential.
- dec outward K (Ik) & gradual influx of Ca+ as threshold is approached
which phases does SA node not have?
phase 1 & 2
which pacemaker fires 60-100 depols per min?
SA node
what is the secondary pacemaker that takes over regulation of the heart if the primary pacemaker of the heart is damaged?
AV node
which pacemaker fires 40-50 depols/min?
AV node
this pacemaker takes over only if the primary AND secondary pacemakers are damaged:
bundle of His/Purkinje fibers
this pacemaker fires 20 depolarizations per minute:
bundle of His/Purkinje fibers
the heart receives sympathetic innervation from the ________
thoracic spinal cord (cardiac plexus)
the heart receives parasympathetic innervation from the ________
vagus nerve
which type of innervation releases acetyl choline to SA node?
parasympathetic
voltage gated K+ channels closing more slowly - hyperpolarizes resting potential, is an effect of _________ innervation on the heart
parasympathetic
decreased If (funny)– reduces slope of phase 4 depolarization, is an effect of _________ innervation on the heart
parasympathetic
NT of the para & sympathetics?
Ach (para) & NE (symp)
HR in
para & symp?
para: dec HR
symp: inc HR
increased If (funny) in nodes and ICa in all myocardial cells, is an effect of _________ innervation on the heart
sympathetic
the lowering of the threshold is an effect of _________ innervation on the heart
sympathetic ASK*
what causes a stronger and faster contraction in the heart?
increasing intracellular Ca++
what is the “resting potential” of pacemaker cells?
what is the resting potential of non-pacemaker cells?
pacemakers: -60mV
non-pacemakers: -90mV
the absolute refractory period for non-pacemaker cells includes what phases?
0-3
during absolute refractory period for non-pacemaker cells, what channels are inactivated?
Na+ channels
what is the significance of the absolute refractory period?
-allows time for ventricular filling between beats
-prevents the heart from summing twitches or tetanizing
In atrial and ventricular myocardium it is primarily by cell-cell contact through _________
gap junctions
from the SA node, what is the order of the spread of impulse?
SA node–>septum–>apex –> base/endocardium –> epicardium
the only conducting pathway from the atria into the ventricle comes from the _______
AV node
where does the AP begin?
SA node
SA conduction pathway
SA node–>atrial muscles–>AV node–>bundle of HIS–>left & right bundle branches–>purkinjie fibers
conduction arriving in the L& R purkinjie branches allows:
stimulation to ramify down the endocardial surfaces of the septum spreading laterally
how does the heart conduction system spread the impulses into the ventricular myocardium to individual myocytes?
Purkinje fibers
ventricular repolarization spreads “_________” over the pathway of depolarization
backwards
though the _________ are the last to depolarize, and the first to repolarize
subepicardial myocytes
the _________ are the last to repolarize
left and right bundle branches
When a dipole vector indicating depolarization points toward the** + electrode**, the signal is ________
positive
When a dipole vector indicating depolarization points away the + electrode, the signal is ________
NEG
When a dipole vector indicating repolarization points toward the + electrode, the signal is __________
positive
Electrodes placed perpendicularly to a dipole vector show __________
no deflection
Electrodes placed perpendicularly to a dipole vector show __________
no deflection
the largest + and - signals occur when the mean electrical vector is ________ to the electrodes
parallel
No signal can be detected when the vectors are _____________ to the electrodes
perpendicular
to achieve Einthoven’s triangle, where are leads placed on the body?
left arm, right arm, left leg
Einthoven’s triangle
This arrangement of electrodes allows measurement of cardiac depolarizations along three electrical axes:
Because the limb leads are assumed to form an equilateral triangle, they can form an axial coordinate system with lead I at what degree ___
0°
Because the limb leads are assumed to form an equilateral triangle, they can form an axial coordinate system with** lead II** at ___
60°
Because the limb leads are assumed to form an equilateral triangle, they can form an axial coordinate system with lead III at ___
120°
where does AP begin?
SA node
