Cardiac Conduction Flashcards
Where does cardiac contraction originate?
specialized cardiac pacemakers
Where does the cardiac contraction spread through?
through myocardium via myocardial conduction system
What is the SA node also called?
pacemaker
SA node: bpm
60-100 bpm
flow of cardiac contraction
- SA node
- Internodal atrial pathways
- AV node
- Bundle of His
- Purkinje system
- Intrinsic ventricular rate
AV node: bpm
40-60 bpm
intrinsic ventricular rate: bpm
<40 bpm
what happens after the pacemakers discharge?
the membrane potential returns to resting potential prior to discharging again
The ______ pacemaker conducting to the ventricles always sets the ventricular rate!
The fastest pacemaker conducting to the ventricles always sets the ventricular rate!
normal pacemaker sequence of rates
SA>AV>ventricular
areas of the heart which may serve as potential pacemakers
automaticity foci
_____ _______ determined by where pacing originates
Heart rhythm determined by where pacing originates
_______ foci of automaticity (originating outside of SA or AV nodes) can result in _________
Ectopic foci of automaticity (originating outside of SA or AV nodes) can result in arrhythmia
SA node origin = _____ rhythm
SA node origin = sinus rhythm
AV node origin = ____ rhythm
AV node origin = junctional rhythm
ventricle node origin = ____ rhythm
ventricle node origin = ventricular rhythm
Which nerves arise from spinal T2-4 segments?
postganglionic sympathetic nerves
What is the neurotransmitter for postganglionic sympathetic nerves?
norepinephrine
Where do the postganglionic nerves pass?
into the cardiac plexus to the SA node (right) and AV node (left)
What is in response to SNS stimulation?
adrenal epinephrine
effects of the Sympathetic NS
- Increase SA node pacing
- Increased AV node transmission
- Increase myocardial contractility
What nerve provides parasympathetic control?
vagus nerve
What is the neurotransmitter for the vagus nerve?
acetylcholine
effect of the Parasympathetic NS
- decreased SA node pacing
- delayed signal transmission through AV node
That does delayed signal transmission through the AV node cause?
increased refractory period
speeds depolarization and increases discharge rate and force of contraction
norepinephrine stimulation in SNS
hyperpolarizes and decreases rate of firing (no effect on contractility)
Ach stimulation in PNS
_________ firing rate is also influenced by _____________ and _____.
Pacemaker firing rate is also influenced by temperature and drugs.
What drug inhibits the PNS? Stimulates PNS?
- atropine inhibits
- digitalis stimulates
Which node normal sets the pace?
SA node
AV node _____ transmission to bundle of _____
AV node SLOWS transmission to bundle of His
What does slowing transmission to bundle of His do?
coordinates atrial and ventricular firing
What wave is generated by activation of both atria?
P wave
The interventricular ______ is activated first, from ____ to right, generating the __-wave
The interventricular septum is activated first, from left to right, generating the Q-wave
What generates the R wave?
left and right ventricular wall activation
What generates the S wave?
A few small areas of the ventricles are activated at a late stage
What generates the T wave?
ventricular repolarization
size of wave deflection that is either positive or negative
voltage
Where is voltage greater?
in areas where there is more CONDUCTING muscle
Is voltage greater in the ventricles or atria?
ventricles
Is voltage greater in the right ventricles or left ventricle?
left ventricle
Is voltage greater in areas of hypertrophy or normal mass of cardiac tissue?
areas of hypertrophy
Does ischemic or dead tissue conduct voltage?
NO
average direction of the combined electrical activity within the ventricles, affected by tissue mass, tissue conductivity
frontal axis/QRS axis
causes of left axis deviation
- Left ventricular hypertrophy
- Left bundle branch block (LBBB)
- Left anterior fasicular block (LAHB)
- High diaphragm (ascites, pregnancy, abdominal mass)
- Normal variants (especially elderly, obese)
- Wolf-Parkinson-White syndrome (WPW)
LVH - ___% of cases present with LAD
LVH - 50% of cases present with LAD
Causes of right axis deviation
- Right ventricular hypertrophy
- Right bundle branch block (RBBB)
- Left posterior fascicular block (LPHB)
- Flat diaphragm (COPD)
- Normal variants (especially young, thin)
RVH - ____% cases present with RAD
RVH - 100% cases present with RAD
indicated by the equiphasic precordial lead being either V3 or V4
normal horizontal axis
indicated if equiphasic lead is V1 or V2
right axis rotation
indicated if equiphasic lead is V5 or V6
left axis rotation
Axis deviation (_____ plane) and rotation (_______ plane) is always ____ from infarction and ______ hypertrophy
Axis deviation (vertical plane) and rotation (horizontal plane) is always away from infarction and towards hypertrophy
