Mechanism of Arrhythmia Flashcards
Two types of triggered activity
Early After Depol
Delay after depol
sign and underlying pathology of WPW
detla waves
extra connection between atria and ventricles, muscle bridge allowing for reentry
DADs
oscillation after completion of rull repol (phase 4)
promoted by high Ca, catecholamines
clinical mechanism category of Torsades de pointes VT
EAD
because of gap junctions, automaticity will be ___- in pacemaker cells coupled to adjacent working myocardium
decreased
escape rhythm arrsing in AV node (=_____)
QRS -
P wave -
Rate -
junctional escape rhthm
narrow QRS
no P wave
rate 50-60
mechanism category of Iodpathic VT in normal heart, Digitalis Toxicity
DAD
EADs
oscillations within plateu (phase 2) or repol (phase 3)
promoted by prolonged AP (QT elongation)
related to inward Ca current (phase 2) or reactivation of Fast Na current (phase 3)
Over drive suppression
faster sites transiently suprress rate of subsidiary pacemakers (I-f smaller in subsidary cells, leading to slow recover after ovredrive of pacemaker cells)
all disordered rhythms originate from (2)
alterations in impulse formation
alteration in impulse conduct - propagation
slow inward sodium current only active at negative potentials below -50, primary current determining normal automaticity
Pacemaker current (If)
relatively high resting potential of ___ and ___ cells keeps most fast na channels in the inactivated stight riquireing dependence on the slower Ca current to mediate depolarization and a slower AP upstroke
AV noded and sinus node
sympathetic effects on automaticity
SN rate increased by sympathetic tone
decreases open probability of I-f channel
makes threshold potential more negative, makng triggering easier
parasympathetic effects on automaticity
SN rate depressed by parasymp
decreases open probabilty of I-f pacemaker channel
makes threshold less negative,
also increases I-KAch channels to be open leading to more negative diastolic potential
normal gradient of automaticity
sinus node - 60-100
AV node 50 - 60
HIs purkinje system - 30-40
requirements for reentry
two distinct paths
area of slowed conduction
functional or permanet unidirectional block
3 factors determity normal automaticity
rate of diastoic depol (I-f)
maximum negative diastolic potential
threshold potential (more neg = faster rate)
degrees of AV or His bundle block
1 - delay without failure of conduction
- some but not all beats fail to conduct
3 no propogation from atrium to ventricle (complete heart block)
escape rhytm arising in franodal tissue =
QRS -
ventricular escape rhythm
wide QRS
parasympathetic or sympathetic tone dominates at rest
parasympathetic
