Dubin's Week 1: pgs 1-93 Flashcards
1970 Luigi Galvani
made a dead frog’s legs move by connecting opposite charges to stimulate an electrical current
1855 Kollicker + Mueller
found that when a motor nerve to a frog’s leg was laid over it’s isolated beating heart, the leg kicked
mid 1880’s Lugwig + Waller
discovered that the heart’s rhythmic electrical stimuli could be omintored from a person’s skin
Dr. William Einthoven
found that electrodes on skin connected to the ends of a silvered wire ran between poles of a magnet twitched with the person’s heartbeat
-wire movements were recorded as waves (P, QRS, T)
EKG
records electrical activity of contraction of the heart muscle
-provides information regarding function and structure
Resting state, myocytes are ____ and ____ charged
polarized and negatively charged
When depolarized, myocytes become ____ and ____
positive and contract
Depolarization begins in the ____ and spreads to…
right atrium and spreads to left atrium then interventricular septum and ventricles
stimulates atria to contract
During repolarization, myocytes regain their ____ charge
negative
As the positive wave of depolarization flows towards a positive electrode, there is a ____ deflection on the EKG
positive
by Na+ ions
SA node
dominant pacemaker with automaticity
-located in upper posterior wall of right atrium
Automaticity foci
focal areas of the heart that also have automaticity
P Wave
represents atrial depolarization emitted by SA node (and contraction)
AV Valves
prevent backflow and electrically insulate the ventricles from the atria
-except for AV node
mitral and tricuspid
Wave of depolarization entering AV node
pause / flat baseline following P wave
allows time for blood in atria to enter ventricles (carried by Ca2+ ions)
SLOW
Depolarization is rapid through …
Bundle of HIS and L + R bundle branches (purkinje fibers)
Fast Na+ ions
QRS Complex
rapid ventricular depolarization (and contraction)
fast moving Na+ ions for conduction
Q wave
often absent on EKG
ST segment
represents initial ventricular repolarization
-ST elevation or depression = pathology
T wave
represent final rapid phase of ventricular repolarization
Repolarization (ST seg + T wave) is accomplished by
K+ ions leaving the myocytes
re-establish negative charge to prepare for depolarization
Ventricular systole on EKG
begins with QRS and spans until the end of the T wave
QT interval
represents ventricular systole
-good indicator of repolarization
-long QT interval = rapid ventricular rhythms
-normal = when QRS is less than half of R to R interval at normal rates
Measure of voltage
height and depth (amplitude) of a wave measured from baseline in millimeters
Deflection of wave
direction which it records on EKG (up or down)
Amount of time represented by 2 heavy black lines
0.2 of a second
Amount of time represented by each small sqaure division
0.04 of a second
Four small squares = ____ of a second
0.16 of a second
0.04 x 4 = 0.16
Limb leads
“bipolar”
1, 2, 3, AVR, AVL, AVF
-each consists of one positive and one negative electrode
frontal plane
Chest leads
V1, V2, V3, V4, V5, V6
oriented through AV node and project through pt’s back (negative)
horizontal plane
Lead 1
Limb leads
left arm electrode = positive
right arm electrode = negative
horizontal
Lead 3
Limb leads
left arm electrode = negative
left leg electrode = positive
Einthoven’s triangle
bipolar limb lead configuration
AVF lead
Limb leads
combination of leads 2 + 3
-left foot electrode = positive
-both arm electrodes = negative
Augmented Voltage (left) Foot
AVR lead
Limb leads
R = R arm positive
-right arm electrode = positive
-remaining 2 electrodes = negative
AVL lead
Limb leads
L = L arm positive
-left arm electrode = positive
-remaining 2 electrodes = negative
Augmented “unipolar” limb leads
AVR, AVF, AVL
-intersect at 60 degree angles + split the angles formed by leads 1, 2, 3
Positive arm electrode is used to record
Limb leads
lateral leads 1 + AVL
Positive foot electrode is used to record
Limb leads
inferior leads 2, 3 + AVF
Electrodes for chest leads are always
positive
In V1, the QRS complex is mainly ___
negative
in V6 the QRS complex is mainly ____
positive
-produced by ventricular depolarization moving towards positive chest electrode V6
ANS function
main concern in autonomic control of the heart + systemic arteries (BP)
-regulates vital functions of all organs by reflex and CNS
Sympathetic NS
ANS
secretes N.E. + delivers to B1 adrenergic receptors
-stimulates SA node to pace faster
-improves AV node conduction
-accelerates conduction through atrial/ventricular myocardium
-increases force of myocardial contraction
-increases irritability of atrial and junctional automaticity foci
-epinephrine secreted into blood by adrenal glands
-constricts arteries = increased BP and flow of blood (by N.E.)
stimulation
Parasympathetic NS
ANS
vagal nerve stimulation; secretes ACH + acts upon cholinergic receptors (mostly within atria)
-inhibts SA node (decr. HR)
-decreases speed of contraction
-depresses AV node
-depresses irritability of automaticity on atria and AV junctional foci
-dilates arteries = reduces BP and flow of blood
inhibitory BUT stimulates G.I. tract
Syncope
reflex parasympathetic response resulting in LOC
-slows SA node pacing (bradycardia)
-same response causes hypotension
-reduces brain’s blood supply
Sympathetic response to standing
pressure baroreceptors initiate symp reflex - constriction of peripheral arteries to prevent distal blood pooling
-stimulates sinus pacing
-conserve blood flow to the brain
-sympathetic vasoconstriction to maintain adequate circulation
Orthostatic hypotension
abrupt fall in BP due to failure of compensatory sympathetic mechanism upon standing
Neurocardiogenic syncope
paradoxical parasympathetic response often in elderly causes vasodilation and slowing of the pulse due to prolonged standing
-results in LOC
-head up tilt (HUT) test confirms diagnosis
Proper interpretation of EKG includes consideration of
rate, rhythm, axis, hypertrophy, infarction
Sinus rhythm
produced by SA node 60-100 bpm
Automaticity foci
potential pacemakers in event that the SA node stops functioning
-normally silent unless emergency
-only one will assume pacemaking
atrial, junctional, ventricular foci
Atrial automaticity foci
inherent rate = at 60-80 bpm
paces if SA node fails
Junctional automaticity foci
inherent rate = 40-60 bpm
paces if Sa node + Atrial foci fails
Ventricular automaticity foci
inherent rate = 20-40 bpm
paces if SA node, atrial + junctional foci fail
Overdrive suppression
rapid automaticity pacing that suppresses slower automaticity
-characteristic of all foci
-eliminates competition from lower foci
Calculation of rate
(normal or tachy)
- look at R wave peaking on heavy black line (=start)
- count off 300, 150, 100, 75, 60, 50
- find the next R wave
- where it falls = rate
Calculation of rate
(bradycardia or irregular rhythms)
- look for small black line trace at top of EKG paper
- two of those 3 second intervals = 6 seconds
- count the number of cycles (R wave to R wave) within the 6 seconds
- multiply number of cycles by 10
