Cardio - FA Phys/Patho p290 - 304 Flashcards
(100 cards)
Explain briefly what happens in each phase during myocardial action potential ?
Phase 0 - opening of voltage gated Na channels open, rapid upstroke and depol
Phase 1 - inactivation of voltage gated Na channels, voltage gated K+ channels begin to open
Phase 2 - plateau, Ca2+ influx, K+ efflux,
Phase 3 - repol by K+ efflux
Phase 4 - resting potential by high K+ perm
How is cardiac muscle action potential compare to skeletal muscle action potential?
Cardiac muscle action potential has a plateau, which is due to Ca2+ influx and K+ efflux.
Cardiac muscle contraction requires Ca2+ influx from ECF to induce Ca2+ release from sarcoplasmic reticulum (Ca2+-induced Ca2+ release).
Cardiac myocytes are electrically coupled to each other by gap junctions
Which phases of AP are not present in SA/AV node action potential?
There’s no phase 1 or 2
Which channel is responsible for phase 0 of SA node AP? What is phase 0?
opening of voltage gated Ca channels; upstroke
What are Na channels’ role in phase 0 of SA node?
None, Fast voltage gated channels are permanently inactivated here bc of the resting voltage of these cells is closer to zero than in ventricular myocytes
What part of the AP determines HR?
The slope of phase 4 in the SA node determines HR.
How does SNS activation increase HR?
Sympathetic stimulation inc the chance that If channels are open and thus inc HR.
Normal duration of PR interval?
<200 msec
List the following in order of speed of conduction: atria, ventricles, AV, bundle of his, purkinje fibers
Purkinje > atria > ventricles >Bundle of His> AV node
Normal duration of QRS?
<120 msec
U wave caused by?
hypokalemia, bradycardia
Which drugs cause long QT?
AntiArrythmics (Class Ia, III) Antibiotics (Macrolides - and not an antibiotic but also the HIV anti viral rx Protease inhbitors and anti- malaria Chloroquine) Anti”C”ychotics (haloperidol, Risperidone)\ AntiDepressants - TCAs Anti-Emetics - Odansetron
Other than drugs, what else can cause long QT?
dec K+, dec Mg2+, dec Ca2+, congenital abnormalities.
Long QT leads to? How to treat it?
Torsades de pointes; Tx = MgSO4
Which congenital long QT is more common?
Jervell and Lange-Nielsen (AR)
Which congenital long QT syndrome is associated with deafness?
Jervell and Lange-Nielsen
ECG pattern of Brugada syndrome?
ECG pattern of RBBB (wide QRS, slurred S, T irreg) + ST elevation esp in V1-V3
Brugada syndrome lead to a an inc risk of?
Vtach and SCD
What is underlying patho mech of WPW syndrome?
Abnormally fast conduction from atria –> ventricle, bypassing the AV node
ECG signs of WPW?
delta wave + wide QRS + short PR
ECG signs of 1st degree AV block?
prolonged PR (>200msec)
ECG signs of 2nd degree AV block, Mobitz I?
progressive lengthening of PR interval until a beat is dropped
ECG signs of 2nd degree AV block, Mobitz II?
Dropped beats not preceeded by progressively longer PR internals - can be 2 or more P waves to one QRS
How does one know that 2nd degree AV block has progressed to 3rd degree?
When atria and ventricle beat independent of one another - P waves and QRS not associated with each other.