Describe the path of "electrical" signals through the intrinsic conduction system
SA node > AV node > Bundle of His > Left and right bundle branches > Purkinje Fibers
T/F: The "electricity" of the heart is created by electron flow.
False
What are the contractions of the heart initiated by?
Ion currents
Where in the intrinsic pathway does the signal pause?
AV node
Why does the signal pause at the AV node?
To allow the ventricles to fill
AP in the heart is spread by ______________. This is possible because of special low-resistance gap jxns
Cell-to-cell conduction
Cell-to-cell conduction in the heart results in___________________
Functional syncytium
Where is the SA node found?
RA (right of SVC orifice)
T/F: The SA node is enriched only with Sympatheic nerve fibers
False
The SA node sets the heart rate. This is known as ________________
Sinus rhythm
What is the size of the SA node?
~1.5 cm long and 2-3 mm wide
Where is the AV node located?
Beneath the endocardium in the inferoposterior region of the interarterial septum
Which node is the "gateway" into the ventricles
AV node
The SA node is connected to the AV node by how many pathways?
3
What class of drug slows the AV conduction pathway?
Beta-blockers
Which part of the intrinsic pathway has the fastest conduction velocity?
Purkinje Fibers
Which part of the intrinsic pathway has the slowest conduction velocity?
SA node
Which part of the intrinsic pathway has the fastest pacemaker rate?
SA node
List extrinsic factors that would increase conduction velocity
- Sympathetic stimulation
- M antagonists
- Beta agonist
- Circulating catecholamines
- Hyperthyroidism
List extrinsic factors that would decrease conduction velocity
- Parasympatheitic stimulation
- M agonists
- Beta blockers
- Ischemia/hypoxia
- Na and Ca blockers
What are the primary factors involved with abnormal impulse formation?
- Altered automaticity
- Abnormal automaticity w/in atria/ventricles
- Triggered activity
Occurs when a conducting pathway is prematurely stimulated via a previously conducted AP
Reentry
Impulses are transmitted back into the atria. If this persists, tachycardia may be generated
Retrograde conduction
T/F: Reentry arrhythmias may be paroxysmal due to the ANS
True
What drugs are used to prevent and/or eliminate reentry?
Antiarrhythmic drugs
Where can local reentry sites be located?
Atria or ventricles
Describe an example of global reentry
Pathway via the bundle of Kent that flows into the RV w/o going through the AV node. Impulse is transmitted to LV and then in a retrograde motion returns to the atria via the AV node
What is happening in the heart in Wolff-Parkinson-White Syndrome?
Global and local reentry is causing depolarization to occur earlier than normal
Which wave corresponds with atrial contraction?
P wave
T/F: The p wave preceeds the mechanical contraction
True
Which part of the ECG is the signal for the ventricles to contract?
QRS complex
A wave of depolarization moving toward a positive electrode is defined as:
Positive deflection in the ECG
A wave of depolarization moving toward a negative electrode is defined as:
Negative deflection in the ECG
A wave of depolarization moving perpendicular to a positive/negative electrode is defined as:
No overall deflection in the ECG
T/F: The voltage amplitude of an ECG is indirectly related to the mass of the tissue experiencing either depolarization/repolarization
False
T/F: The instantaneous amplitudes in the ECG trace are a function of the orientation of the positive electrode relative to the mean electrical vector in the ECG
True
Define normal sinus rhythm
SA node is leading pace
Define bradycardia
Slowed HR (<60 BPM)
Define tachycardia
Fast HR (>100 BPM)
Happens when ventricles beat at a very fast rate
Ventricular tachycardia
Aka "Rhythm of Death"
Ventricular fibrillation
Sudden blow to the chest during this phase in the cardiac cycle can lead to ventricular fibrillation and death.
Commotio cordis
Summation of the individual instantaneous electrical vectors of depolarization at a given instant of time
Mean electrical vector