Rapid Interpretation of EKG's reading Dubin Book flashies Flashcards
how does electrical current travel in the heart.
at rest what is the charge of mycocytes
what is repolarization
at rest myocytes are negatively charged
wave of depolarization is a wave of positive charge within the heart’s myocytes
the cell to cell conduction of depolarization through the myocardium is carried by fast-moving sodium (Na ions)
repolarization is the myocytes returning to a negative charge
how does the EKG collect electrical activity of the heart
as the positive wave of depolarization within the myocytes flows toward a positive electrode, there is a positive upward deflection recorded on EKG
what is the hearts dominant pacemaker
SA node
creates sinus rhythm
each depolarization wave of + charges (Na+ ions) proceeds outward from the SA node and stimulates both atria to contract producing a P wave
the P wave represnts the depolarization and contraction of both atria
what are the 2 atrioventricular valves
what node is in between them
tricuspid and mitral valves
AV node
tricuspid valve
b/w right atrium and right ventricle
mitral valve
b/w left atrium and left ventricle
what occurs when the wave of atrial depolarization enters the AV node?
depolarization slows, producing a brief pause
this allows time for the blood in the atria to enter the ventricles and b/c there is a delay there is a flat baseline after each P wave
slow conduction through the AV node is carried by calcium ions
after the AV node, what happens with depolarization conduction
depolarization conducts slowly through AV node and upon reaching ventricular conduction system, depolarization rapidly shoots through the His Bundle and Left and Right Bundle Branches
so depolarization rapidly distributes to the ventricles
what are the His bundle and bundle branches made up of?
purkinje fibers
these are use fast moving Na ions for the conduction of depolarization
the terminal filaments of the purikinje fibers spread just beneath the endocardium that lines both ventricular cavities and therefore ventricular depolarization begins at the lining and proceeds toward the outside surface (epicardium) of the ventricles
these fibers don’t penetrate into the myocardium
what does the QRS complex on the EKG represent
represents depolarization of the entire ventricular myocardium
so ventricular contraction
NOTE- ventricular contraction actually lasts longer than the QRS complex
what is the Q wve
the first downward wave of the QRS
it is followed by the upward R wave
often absent on EKG
what is the R wave
the first upward wave of the QRS complex
followed by the S wave
what is a QS wave
it is just a downward deflection. since there is no upward wave we cannot determine whether number 4 is a Q wave or an S wave
what is the ST segment
a segment of horizontal baseline that is FLAT and most importantly level with other areas of the baseline
can be elevated or depressed and this represents pathology
represents the initial phase of ventricular repolarization
after this a broad T wave occurs
what does the T wave represent
the final “rapid” phase of ventricular repolarization (even though the the t wave is low, broad hump)
what is the length on the EKG of ventricular repolarization
begins immediately after the QRS and persists until the end of the T wave
how is repolarization accomplished?
potassium K ions leaving the myocytes
when does ventricular systole begin and end?
begins with the QRS and persists until the end of the T wave (QT interval)
what is long QT interval signficant for ?
the QT interval is a good indicator of repolarization
since repolarization compromises most of the QT interval, patients with Long QT interval are vulnerable to dangerous (or even deadly ) rapid ventricular rhythms.
QT interval should be less than half of the R-R interval
what ion causes myocyte contraction
Ca
what ion causes repolarization of myocytes
K
what ion produces cell-to-cell conduction of depolarization in the heart
what is the exception to this?
Na
exception–> AV node depends on slow movement of Ca ions
how long is each large box on the EKG paper
5 mm
each small square is 1 mm by 1 mm
0.2 sec = 1 big box
when a wave of stimulation (depolarization) travels toward a positive skin electrode, what does it produce on an EKG reading?
produces a positive upward deflection
how many seconds is each small box …
0.4 seconds
how many seconds is 4 small squares
0.16 sec
what are the bipolar limb leads?
each limb lead consists of a pair of electrodes
one is positive and one is negative
so these leads are called bipolar limb leads
there are 3 (I, II, III)
lead I
horizontal
left arm is positive
right arm is negative
lead III
left arm electrode is negative
left leg is positive
AVF (an augmented/unipolar lead)
uses left foot electrode as positive and both arm electrodes as common ground (negative)
AVR (unipolar)
right arm is electrode positive
the left arm is negative
left foot is negative
AVL (unipolar)
left arm is positive
left foot is negative
right arm is negative
what are the inferior leads?
II, III, AVF
positive electrode on the left foot
what are the lateral leads
I and AVL
positive electrode on the left arm
what is the center/intersection point for the chest leads>
AV node
V2 lead
describes as straight line directly from the front to the back of the patient
what is the most positive chest lead>
V5 >V6 > V4> V3 >V2 >V1
what are leads V3 and V4 over
oriented over the interventricular septum
V3 - more near right
V4 - more left
what does sympathetic stimulation of the heart result in
increased rate of SA node pacing
increased rate of conduction
increased force of contraction
increased irritability of foci
what are the effects of the parasympathetic nervous system on the heart?
decreases SA node pacing, depresses AV node, decreases rate of conduction, force of contraction and decreases irritability of atrial and junctional foci
what can occur with a devastating injury….
parasym response that lowers BP and slows the heart
what are vagal maneuvers
induced gagging
carotid sinus massage
used to produce a parasympathetic response for both diagnostic and therapeutic purposes
can inhibit irritable focus (atrial or AV junctional)
-supraventricular tachy converts to sinus rhythm
or inhibit AV node (increases refractoriness)
-diagnostic aid with 2:1 AV block or atrial flutter
what are the 5 genearl areas of routine EKG interpretation
rate rhythm Axis hypertrophy infarction
what is hearts pacemaker.what is the pace?
SA node
60-100 bpm
located in upper-posterior wall of right atrium
generates the sinus rhythm
the SA node overdrive/suppresses the slower inherent pacemaking activity of all the automaticity foci below it
sinus bradycardia
sinus rhythm less than 60 bpm that originates in the SA node
most often results from parasympathetic excess as we see in conditioned athletes at rest
sinus tachy
greater than 100
most common cause is exercise sympathetic stimulation
what are automaticity foci
focal areas of automaticity in the heart
potential pacemakers that are capable of pacing in emergency situations
if the SA node fails, then one of these potential pacemakers will assume pacemaking activity at is inherent rate
where are junctional automaticyt foci?
middle and distal regions of the AV node (AV junction)
the proximal end of the AV node has no automaticity foci
where are ventricular automaticity foci?
in the purkinje fibers that have automaticity–> His Bundle and Bundle Branches
what are the inherent rates of atrial, AV junction and ventricle automaticity foci?
Atrial- 60-80
AV junction - 40-60
Ventricles 20-40
what is idioventricular rate
beat of 20-40 bpm
it is a ventricular focus that forms if all pacemaking centers above have failed or if there is a complete block of conduction below the AV node (including AV junction) that prevents any pacing stimulus above it
rule for counting rate?
300, 150, 100
75, 60, 50
sinus arrhythmia
normal
extremely minimal increase in heart rate during inspiration and extremely minimal decrease in heart rate during expiration
increases during inspiration b/c of inspiration activated sympathetic stimulation of theSA node and decrease b/c of expiration- parasympathetic inhibition of SA node
what makes up the atrial conduction system?
internodal tracts including anterior, middle, and posterior and one conduction tract (Bachmann’s bundle) to the left atrium
are there terminal filaments of the right bundle branch in the septum?
no
so left-to-right depolarization of the septum occurs immediately before the rest of the ventricular myocardium depolarizes
what is a U wave
this is a wave that represents the final phase of purkinje fiber repolarization . it is a wave after the T wave
what are the 3 irregular rhythms (atrial)
wandering pacemaker
multifocal atrial tachycardia
atrial fibrillation
what is an irregular rhythm
rhythm that lacks a constant duration b/w paced cycles
what does parasystolic mean
when an automaticity focus has entrance block it is said to be parasystolic
wandering pacemaker
P wave shape varies–> represents different automaticity foci in the atria (each has a different shape)
wanders from SA node to atrial foci
atrial rate less than 100–> if it
irregular ventricular rhythm
multifocal atrial tachy
irregular rhythm
P wave shape varies
atrial rate exceeds 100
irregular ventricular rhythm
disease of patients with COPD
can be sometimes associated with digitalis toxicity in patients with heart disease
atrial fibrillation
irregular
continuous chaotic atrial spikes
irregular ventricular rhythm
no single impulse depolarizes the atria completely, so no p waves
it is the result of many irritable atrial foci suffering from entrance block pacing rapidly
these multiple foci are all parasystolic so they’re all insensitive to overdrive suppression and they all pace at once
Escape rhythm
atrial
junctional
ventricular
p. 112
sinus arrest leads to what…
p 113
Junctional automaticity focus can cause retrograde atrial depolarizaiton. what is this and how does it show up on EKG
Each P wave is inverted in leads with an upright QRS
Stokes adams syndrome
this occurs with ventricular escape rhythm which has a rate of 20-40 bpm
it is idioventricular rhythm
the pacing is so slow that blood flow to the brain is signficantly reduced to the point of unconsciousness
monitor airway!
ventricular escape beat on EKG
enormous ventricular QRS complex
this can happen often b/c parasympathetic innervation inhibits the SA node and also inhibits the atrial and junctional foci but NOT the ventricular foci
