Electrical Conduction ECG Flashcards
What are the cardiac cells
Pacemaker cells
Electrical conduction cells
myocardial cells
what are pacemaker cells
electrical conduction point
SA node (60-100bpm)
AV node (40-60bpm)
what are electrical conduction cells
wiring of the heart
Bundle branches and perkinje fibers
where does the SA node receive blood from
the sinoatrial nodal artery off of the RCA
What stimulates the left atrium to contract
Bachman’s bundle
What affects the rate control of the heart?
Sympathetic stimulation increases rate (epi and norepinepherine)
parasympathetic lowers to normal (acetylcholine)
where does sinus rhythm originate
from the SA node
what does the fibrous skeleton act as
electrical insulator between the atria and ventricles
what is teh automaticity rate of AV node
40-60bpm
what is the normal length of PR segment
120-200ms (0.12-0.2sec)
less than 3 small boxes
what is the automaticity rate of the bundle branches
20-40bpm
What is the normal length of QRS complex
should be narrow (<100ms; 0.12 sec)
less than 3 small boxes
what occurs during the QRS complex
ventricular depolarization and contraction
what is R-prime
2nd upward deflection
with right bundle branch block
what is afib
irregularly irregular
What is resting membrane potential
difference in electrical charge across cellular membrane. transmembrane potential for cardiac myocytes is -90mV
- at baseline, there is a net negative charge within the cell
what is action potential
rapid shift of cellular voltage
what does the depolarization affect within the myocardial cell
affect the sarcolemma and spread to one another via the intercalated disks
what is phase 4 during action potential
resting membrane portential is -90mV in cardiac myocyte with K+ predominantly intracellular
Na+ and Ca+ gates are closed
What is phase 0 during action potential
stimulus
indicates that pacer cell has depolarized and transmits action potential to the myocytes beginning the action potential - transmitted via gap junctions
positive depolarization stimuli will cause Na+ channels to open
What is phase 1 during action potential
early repolarization
begins when the fast Na+ gates close - only stay open for a few thousandths of a second
intracellular charge becomes positive
K+ flows out of the cell causing transmembrane potential to go back to 0
what is phase 2 during action potential
the plateau phase
balance maintained near 0 by K+ going out, Ca2+ going into the cell
calcium initiates muscle contraction
What is phase 3 during action potential
repolarization
transmembrane potential goes back to the resting state of -90mV with K+ flowing out and cessation of Ca2+ flowing in
Na+ and Ca2+ flow out of the cell
what is the pacemaker action potential
Na+ will have slow, constant flow until transmembrane potential is -60mV - “funny current”
when do the calcium channels open during pacemaker action potential
-55mV
what is lacking in pacemaker action potential
no phase 2 or pause
what is positive inotrope drugs
increases muscular contraction
what are positive chronotropic drugs
increase HR (sympathetic - norepinepherine)
what are negative chronotrop
decreases HR (parasympathetic - acetylcholine)
what are the Beta receptors
Beta receptors (norepinepherine and epinepherine)
B1 - increase HR, increased contractility
B2 - inhibits smooth muscle contraction
what are the alpha receptors
A1 - increases smooth muscle contraction -> increases BP
A2 - inhibits secretions
What is normokalemia
K 2.5-5.0mM)
-90mV resting potential with higher concentration of K+ in the cell
What is moderate hyperkalemia
K < 8mM
More K+ outside cell making cell partially depolarized.
Na+ channels (stage 0) are activated more quickly so increased excitability. early repolarization occurs causing peaked T waves
What is Hyperkalemia
K > 8mM
Na+ channels can be inactive and K+ goes more into the cell so that cells are refractory (unexcitable) which will cause prolongation
What is hypokalemia
low extracellular K+ will cause increased action potential (hyper-excitability)
ST depression, T wave inversion, U waves
** remember that hypokalemia and hypomagnesemia travel together
