Physiology: Principles of Electrophysiology

electrical communication in the heart begins with an ___ __in an__ ___

action potential in an autorhythmic cell

autorhythymic cells have the unique ability to generate action potential ___ __in the absence of the nervous system__ ___

spontaneously in the absence of the nervous system input

the depolarization spreads rapidly to adjacent cells through _____ in the intercalated disks

gap junctions

the depolarization wave is followed by a _____ that passes across the atria, then moves into the ventricles

wave of contraction

depolarization begins in the autorhythmic cells in the ___ ___ near the junction of the superior vena cava and the right atrium

sinoatrial node (SA node)

autorhythmic cells serve as the main _____ of the heart

pacemaker

the depolarizing wave spreads rapidly though the specialized conducting system of _________

non-contractile autorhythmic fibers

a branched _____ connects the SA node to the AV node

internodal pathway

the AV node is a group of _____ near the floor of the right atrium

autorhythmic cells

between the left and right atria, you can find interatrial tracts aka _____

bachmann’s bundle

from the AV node, the depolarization moves into the _____

ventricles

what is another name for the atrioventricular bundle (AV bundle)?

bundle of His

where is the AV bundle/bundle of His located?

ventricular septum

a short way down the septum, the AV bundle fibers divide into left and right _____

bundle branches

the bundle branch fibers continue downward, and they divide into _____

purkinje fibers

purkinje fibers are specialized conducting cells of the _____

ventricles

electrical signals coordinate _____

contraction

the electrical signal for _____ begins when the SA node fires an action potential and the _____ spreads to adjacent cells through gap junctions

contraction; depolarization

electrical conduction is rapid through the _____

internodal conducting pathways

electrical conduction is slower through the _____ of the atria

contractile cells

as action potentials spread across the atria, they encounter the _____ at the junction of the atria and ventricles

heart fibrous tissue

the AV node is the _____ through which action potentials can reach the contractile fibers of the ventricles

only pathway

the AV node delay is accomplished by the _____ of signals through nodal cells

slower conduction

the electrical signal passes form the AV node through the AV bundle and the bundle branches to the ______

apex of the heart

the purkinje fibers transmit impulses very rapidly with speeds up to 4m/s, so that all contractile cells in the apex _____

contract nearly simultaneously

steps in the conduction system of the heart:

1. cardiac impulse originates at SA node


1. action potential spreads through the right and left atria
2. SA node depolarizes


2. impulse passes from atria intro ventricles through the AV node (the only point of electrical contact between chambers)


1. electrical activity goes rapidly to AV node via internodal pathways
3. action potentials briefly delayed at AV node (ensures atrial contraction precedes ventricular contraction to allow complete ventricular filling)


1. depolarization spreads more slowly across atria
2. conduction slows through AV nodes
4. impulse travels rapidly disperses throughout the myocardium using Purkinje fibers


1. depolarization moves rapidly through the ventricular conducting system to the apex of the heart
5. the rest of the ventricular cells are activated by the cell-to-cell spread of impulse through gap junction


1. depolarization wave spreads upward form the apex

why is it necessary to direct the electrical signals through the AV node instead of allowing them to spread downward from the atria?

* b/c the blood is pumped out of the ventricles through openings at the top of the chambers, if electrical signals from the atria were conducted directly into the ventricles, the ventricles would start contracting at the top
* the apex-to-base contraction squeezes blood toward the arterial openings at the base of the heart

the cells of the _____ set the pace of the heartbeat

SA node

the cells in the SA node fire the _____ of any spontaneously active cell under normal conditions

fastest

cells in other parts of the specialized conduction system (AV node/bundle of His/purkinje fibes) have _____ and act as latent pacemakers in some conditions

unstable resting potentials

latent pacemakers aka _____

secondary or escape pacemakers

is the rhythm of latent pacemakers slower/faster than the SA node

slower

the Purkinje fibers can spontaneously fie action potentials, but their _____ is very slow between 25-40 beats per minute

firing rate

ventricular or atrial muscle cells normally do NOT _____

exhibit pacemaker activity

if the SA node is damaged and can’t function, one of the _____ takes over; the heart rate then matches the rate of the new pacemaker

slower pacemakers

electrocardiography abbreviation

ECG

an electrocardiogram (ECG/EKG) is a graphic record of the _____ by the heart

electrical activity generated

ECG/EKG is not the same as an _____

action potential

_____ generate electrical signals and these signals are conducted through the body to the surface where they can be recorded with appropriate equipment

excitable cells

using surface electrodes, it is possible to record ______ b/c salt solutions (like our NaCl- based extracellular fluid) is a good conductor of electricity

internal electrical activity

electrocardiogram (ECG/EKG) recordings show the _____ generated by all the cells of the heart

summed electrical activity

the EKG enables physicians to get valuable insight into:

1. anatomical orientation of the heart
2. relative sizes of its chambers
3. various disturbances in rhythm and conduction
4. extent of ischemic damage to the myocardium

the method where the sides of the triangle are number to correspond with 3 leads; or pairs of electrodes used for a recording

Einthoven triangle

einthoven EKG discoveries

* noted when people died and did autopsies to explain the unusual EKG
* noted any abnormalities

an EGC is different from a single _____

action potential

an action potential is one electrical event in a single cell recording using an _____ electrode

intracellular

the ECG is an _____ that represents the sum of multiple action potentials taking place in many heart muscle cells

external recording

the _____ of action potentials and ECG recordings are quite different

amplitude

ex: a ventricular action potential has a voltage change of 110 mV, but the ECG signal has an _____ of only 1 mV by the time it reaches the surfaces of the body

amplitude

an upward deflection represents: _____ (change to a more positive resting membrane potential)

depolarization

down deflection represents: _____ (the return of the membrane potential to its resting level)

repolarization

the electric dipole consists of _____ separated by distance (d)

two equal and opposite charges (+q and -q)

a dipole is the _____ caused by the negative and positive electrical charge in proximity

potential force

the cardiac dipole is a ___ __(moving from the heart’s most negative to positive areas) and an__ ___ (voltage)

vector with direction; amplitude

on the body, many electrodes ae placed to look at the _____ from various angles

cardiac dipoles

the production of current by the heart is the production of a _____

sequence of dipoles

as each myocardial cell is depolarized, it produces a _____

dipole

the heart is a large electric dipole; the orientation and strength of the dipole change during _____

each beat of the heart

at any instant, a boundary divides the negative charges of the depolarized cells from the positive charges of cells that have _____ in the heart

not yet depolarized

the dipole _____ and potential generated by the heart extend throughout the body

electric field

the dipole exists because there is a difference in _____ btw different areas of the myocardium

charge

an ECG provides info about the cardiac dipoles ___ __and__ ___ from various angles

direction and size

when the heart is fully depolarized or _____ there is no dipole, and the ECG is flat

repolarized/isoelectric

to record electrical activity at a distance from the source (dipole) the source must be in a _____

conducting medium

the body is a _____ since it is largely made up of a highly conductive material (an aqueous solution of electrolytes) and conducts in 3 dimensions

volume conductor

the sum of all dipole magnitudes and vector directions produces a _____

net vector and net magnitude

vector arrows indicate the ___ __(by the direction of the arrowhead) and__ ___ (by the length of the arrow)

direction and magnitude

the whole of the myocardium as a _____ changes magnitude and direction as the wave of action potential propagates across it

single electric dipole

as depolarization affects different parts of this structure at different times, through a single heartbeat the direction and magnitude of the _____ changes

summed dipole

as this dipole generates an electric field, it also changes its properties as the dipole moves around the _____

cardiac cycle

the changing electric filed forms the basis of the _____

ECG

a potential difference of zero will result from measuring the potential difference between two places on the same _____ (if every point within it has the same potential)

equipotential line

on the other hand, placing electrodes at 2 locations with different electric strengths will result in a potential difference that is not _____

zero

if you connect electrodes to two different points at the body surface, you should be able to measure the potential difference generated by the _____ and then plot its changes over time as the cardiac dipole vector changes during each cardiac cycle; this is the ECG

cardiac electric field

einthoven’s triangle is a hypothetical triangle formed around the heart when electrodes are put on both __ __and the__ ___

both arms and the left leg

the sides of the triangle are numbered to correspond with the _____ or pairs of electrodes used for a recording

3 leads

one electrode acts as the ___ __electrode of a lead, and a second electrode acts as the__ __*electrode of the lead, the third electrode is*__ ______

positive, negative, inactive

an electrode is a _____

sensor

a lead is a combination of _____

two electrodes

a system of recording leads oriented in a given plane detects only the projection of the _____ on that plane

three-dimensional vector

_____ an electrode that senses the electrical field

active/exploring electrode

_____ a reference electrode (not sensing the field), considered to be at 0 mV

passive/indifferent electrode

_____ is a combination of an active and passive electrode; measure the voltage only at the active electrode

unipolar lead

_____ is the combination of 2 active electrodes

bipolar lead

with the bipolar lead, you measure the voltage difference between the _____ (subtract the voltage at the negative electrode from the voltage at the positive electrode)

two electrodes

Einthoven’s triangle _____ is connecting the pateint’s arms

lead 1

if additional electrodes are included in the measurement process, then the direction of the vector can be _____

triangulated

leads 1, 2, and 3 are _____ electrodes

bipolar

the bipolar electrodes in Einthoven’s triangle record the difference between "_____” one positive and one negative, which are in anatomically different locations

two poles

when an electrical wave moving through the heart is directed toward the positive electrode, the ECG wave goes up from the _____

baseline

if net charge movement through the heart is toward the negative electrode, the wave points _____

downward

a vector that is _____ to the axis of the electrode causes no deflection (baseline)

perpendicular

the direction of deflection

1. a wave of depolarization traveling toward a positive electrode results in a positive deflection in the ECG trace
2. a wave of depolarization traveling away from a positive electrode results in a negative deflection
3. a wave of repolarization traveling toward a positive electrode results in a negative deflection
4. a wave of repolarization traveling away from a positive electrode results in a positive deflection
5. a wave of depolarization or repolarization traveling perpendicular to an electrode axis results in no net deflection
6. the voltage amplitude is directly related to the mass of tissue undergoing depolarization or repolarization

the standard _____ is a noninvasive representation of the electrical activity of the heart

12-lead ECG

the thorax is assumed to be a _____ when it comes to lead arrangements, depicted by the difference between electrodes on predetermined body locations (leads)

homogenous conductor

number of leads

* 3 bipolar leads (I, II, III)
* 6 unipolar chest leads (V1-V6)
* 3 augmented unipolar leads (aVR, Avl, and a aVF)

standard limb leads/bipolar limb leads (the original system used by Eithoven); 3 bipolar leads make up the triangle with the heart at the center

standard limb and lead electrode arrangements:

* lead I: RA (-) and LA (+)
* lead II: RA (-) and LL (+)
* lead III: LA (-) and LL (+)

with standard limb leads, what is often used as a ground electrode?

right leg (ankle)

memory tricks for standard limb lead

* the number of L’s in the electrodes corresponds to the Standard Limb Lead number
* Lead 1 has 1 L (RA, **L**A)
* Lead 2 has 2 L’s (RA, **LL**)
* Lead 3 has 3 L’s (**L**A, **LL**)

the electrode with the greatest number of L’s is the positive/negative electrode

positive