Flashcards in cardiac arrhythmias Deck (37)
What is supraventricular tachycardia?
abnormal tachycardia which requires participation of either atrial or AV node tissue
What is ventricular tachycardia?
abnormal tachy originating in ventricle or his-Purkinje system; by definition doesnt requrie involvment of either atrium or av node
What is the normal impulse formation occur?
intrinsic automaticity; pacemaker cells
What is the rate normally for the different pacemaker cells?
AV node (50-60)
What is the static resting membrane potential of normal myocytes?
What is the membrane potential for SV and AV node?
What is the pacemaker current?
If, a slow inward sodium current active only below -50 mV
How does overdrive suppression occur?
If is much smaller than the depolarization from above and leading to net hyperpolarization
What do different threshold portential result in?
more negative the threshold potential the faster the resulting depolarization
what does sympathetic rate do to autonomic regulation?
beta stim leads to increasing the open probablility of pacemeaaker current
secondarily makes the threshold potential more negative
What does parasympathetic autmoaticity of heart rate?
decreases open probability of pacemaker current channel
secondarily makes threshold potential less negative
negative making it easier to trigger
What does parasympathetic tone dominates when?
at rest; therefore wihtout it the SN is about 85-105
How are adjacen myocytes coupled by?
low resistance gap junction
What can lead to cell decoupling?
pathologic fibrosis in the heart; may result in automatcity of pacemaker
What is an escape rythm?
failure of sinus node can result in emergency of normallly suppressed AV node; aka junctional escape in av node
escape rythm in infranodal tissue is a ventricular escape
Junctional escape has what type of QRS?
A ventricular escape has what type of QRS?
What is an early after depolarization
triggered activity, promoted by conditions whichprolong action potential and membrane osscilation
related to inward Ca2+ current or reactivation of fast Na current
What is the clinical mechanism of torsades de pointes VT precipitated by qt prolonging drugs?
What are delayed aferdepolarizations?
membrane oscillations after completion of full repolarization
promoted by conditions which lead to high intracellular calcium
What are the different types of av block?
1st degree delay without failure of conduction
2nd degree: some beats fail to conduct
3rd degree no propogation from atruim to ventricle
What is reentry in unidcirectional block?
abnormal endless loop myocardial progpagation;
What are the requirements for reentry?
two distinct paths for propogation
slowed conduction in one path
unidirectional block; tissue capable of conduction in one but not the opposite direction; often functional
What on EKG is a sign of WPW?
What are the signs of first degree AV block?
PR prolongation; PR>200 ms
1:1 AV relationship
benign and asymptomatic
What are the causes of first degree AV block?
reversible" autonomic, transient AV nodal ischemia, drugs
irreversible: MI, chronic degenerative disease
What is mobitz 1?
2nd degree AV blcok;
PR gradually increases until impulse is blocked
conduction is imparired in AV node
usually benign and asymptomatic
What are the causes of MObitz I?
causes include autonomic tone, acute MI, due to increased vagal tone or ischemia AVN
What is Mobitz II?
suddent intermittent loss of AV conduction without preceding gradual PR length
may progress to 3rd degree without warning
results from scar, myocardial infarct, chornic degenerative disease