Cardiac Mechanics and EKG Flashcards
pacemaker cells
initiate depolarization, autorhythmic
SA node, AV node, purkinje fibers
contractile cells
forceful contraction
myocardium
what helps the heart to function as one unit?
gap junctions by sending charge on to the next quickly
phase 0 action potential cardiac
depolarization
voltage gated Na channels
phase 1 action potential cardiac
initial repolarization
closing VGNa
phase 2 action potential cardiac
plateau
opening VGCa
phase 3 action potential cardiac
repolarization
opening VGK
phase 4 action potential cardiac
resting membrane potential
K+ leak channels
what changes during action potential in cardiac muscle cells?
permeability
absolute refractory period
0.2-0.25 s
relative refractory period
0.05 s
do skeletal muscles or cardiac muscles have longer refractory periods?
cardiac muscles
what is the mechanism of cardioplegic solution?
increases extracellular K+
depolarizes and then cannot repolarize
two ways to alter contraction
augmenting force
decreasing force
two ways to augment force of contraction
increase calcium (beta agonist) sensitizing contractile machinery
how does the beta agonist increase calcium?
activates PKA that phosphorylates VGCC and makes them more likely to be open
way to decrease force of contraction
decrease calcium
beta blocker
what is special about pacemaker cells
contain fewer contractile fibers
no organized sarcomeres
faster conducting rate
If- funny current other name
hyperpolarization activated cyclic nucleotide gated
funny current mechanism
resting potential is unhill curve and is caused by leaky sodium current
which action potential phase is absent in SA and AV nodes compared to cardiac muscle cells
phase 2
intrinsic depolarization rate SA node
60-80bpm
intrinsic depolarization rate AV node
40-55bpm
intrinisic depolarization rate purkinje fibers
15-35bpm
what type of cells have funny current?
pacemaker
chronotropic
increase heartrate
lusitropic
increase rate of relaxation
phospholambin
inhibits SERCA
beta 1 agonist
increases HR by increasing cAMP
what nerve is the parasympathetic mediated through?
vagus nerve
2 ways that parasym works to decrease HR
increases K+ current (hyperpolarize)
inhibits AC and decreases cAMP and PKA
conduction velocity SA node
1m/s
conduction velocity AV node
0.05 m/s
total time from SA node to bundle branch
0.16
conduction velocity purkinje fibers
1.5-4.0m/s
conduction velocity muscle cells
0.3-0.5 m/s
4 common inotropic agents used for short term HF
digitalis(digoxin)
dobutamine
milrinone
levosimendan
What is digoxin mechanism of action
inhibits NaK pump increases Ca slows conduction of AV node depresses SA node does NOT increase HR
dobutamine mechanism of action
beta 1 agonist
increases Ca
increases HR
milrinone mechanism of action
phophodiesterase 3 inhibitor
increases cAMP
increases Ca
increases HR
levosimendan mechanism of action
increases Ca sensitization of troponin C
does not increase HR
does NOT cause arrhythmias
1 large box ECG = __ mV?
0.5mV
1 large box ECG= __ sec?
0.2 sec
how many large boxes = 1sec?
5 large boxes
normal P-R interval length
<0.2 sec (< 1 large box)
normal QRS complex width?
<3 small boxes
what does the height of the QRS complex indicate?
muscle mass
What can cause a wide QRS?
bundle branch block
normal QT interval
0.35-0.42s
QTc
corrected QT interval
hypocalcemia effect on QT interval
long
hyercalcemia effect on QT interval
short
what is the ion channel involved in prolonged QT interval due to genetics?
K+
What usually causes ST segment changes?
MI
STEMI
what do ECGs measure
the potential difference between two leads
(outside the cardiomyocytes)
this is why it is positive
what does an ECG read when the heart is at rest?
0
what does the lead two measure
QRS complex
why is the QRS complex positive?
the negative lead has more neg charges around it and positive lead has more pos charges around it
during repolarization of the ventricles what repolarizes first?
last area to depolarize is the first to repolarize
epi to endo
t wave
repolarization of the ventricle
why would the t wave be inverted
if the first area to depolarize is the first area to repolarize
what are the causes of inverted t wave
coronary ischemia
hypertrophy
bundle branch block
bradycardia speed/ causes
<60bpm
vagal nerve stimulation, athlete, cold temp
SA block
missed beat
AV block causes
vagal stimulation
ischemia
calcification
inflammation
wenckebach
AV block 2nd degree type 1 (longer and longer)
tachycardia
> 100bpm
tachycardia causes
sympathetic nerve stimulation epi drugs increased temp hyperthyroidism blood loss fever
supraventricular tachycardia rate
100-250 bpm
How to help reduce SVT?
adenosine
vagal maneuvers
torsade de pointes
looks like a ribbon
twisting of the QRS
prolonged QT syndrome
moves to Vfib
causes of premature contractions
ischemia
calcification
chemicals
genetic
causes of premature ventricular contractions
MI/ ischemia
drugs that cause excitability
treatment for afib
antiarrhythmics
anticoagulants
ablation
electrical cardioversion
mean QRS axis deviation
right or left BBB
hypertrophy
