Cardiology Flashcards
Depolarization
The discharge of energy that accompanies the transfer of electrical charges across the cell membrane.
Differs from contraction in that depolarization is an electrical phenomenon, whereas contraction is mechanical and is expected to follow depolarization.
Polarization
When the electrical charges are balanced and ready for discharge.
Repolarization
The return of electrical charges to their original state of readiness.
Arrhythmias
Graphic representations of electrical activity.
Two types of heart cells:
- Electrical cells, which stimulate (initiate and conduct impules).
- Mechanical cells, which contract in response to stimulation.
Electrical activity precedes mechanical activity.
Electrical activity can occur without mechanical response (pulse).
If the electrical impulse stimulates the mechanical cells to contract, the heart is expected to contract and pump blood, thus producing a pulse.
Electrical flow in the normal heart:
Originates in the SA node, then travels via the intraatrial and intranodal pathways to the AV node , then through the Bundle of His to the Left and Right Bundle Branches, and finally to the Purkinje Fibers, where mechanical cells are stimulated.
Inherent rate of the SA Node
60-100 BPM
Inherent rate of the AV Junction
40-60 BPM
Inherent rate of the Ventricles
20-40 BPM
Sinoatrial Node (SA Node)
Impulse-generating (pacemaker) tissue located in the right atrium of the heart. Generator of normal sinus rhythm. The SA Node initiates impulses at the fastest rates and is the NORMAL pacemaker of the heart.
Irritability
When a site speeds up and takes over as the pacemaker.
Rule regarding the pacemaker function of the heart:
The site that initiates impulses at the fastest rate will usually become the pacemaker.
eg.: if the SA node failed as pacemaker, or if its rate dropped below the normal range, the AV Junction would probably take over as pacemaker. This is known as ESCAPE
Escape
When the normal pacemaker of the heart slows down or fails and a lower site assumes pacemaking responsibility.
Sympathetic response causes:
Increased heart rate (chronotropic)
Increased AV conduction/Increased irritability (dromotropic)
Increased contractility (inotropic)
The sympathetic branch influences both the atria (SA node, the intraatrial and intranodal pathways, and AV junction) and ventricles.
Parasympathetic response causes:
Decreased heart rate
Decreased AV conduction
Decreased irritability
The parasympathetic branch influences only the atria.
Areas of conduction system in the order in which the impulses travel through the heart:
- SA Node
- Intraatrial and Internodal Pathways
- AV Node
- Bundle of His
- Left and Right Bundle Branches
- Purkinje Fibers
Normal pacemaking site of the heart, and why?
The SA Node. It has the fastest inherent rate at 60-100/min.
The process responsible for a site speeding up and overriding a higher site, thus taking over as pacemaker?
Irritability
Mechanism in play if a lower site takes over responsibility for the pacemaking function following a failure of a higher site?
Escape
The discharge of electrical energy that accompanies the transfer of electrical charges across the cell membrane?
Depolarization
The return of the electrical charges to their original state of readiness?
Repolarization
Nervous system that controls the activities of the heart?
Autonomic
What part of the heart does the sympathetic branch innervate?
The atria and ventricles.
What part of the heart does the parasympathetic branch innervate?
Only the atria
What happens if the sympathetic branch of the heart is blocked, or vice versa?
If the sympathetic branch of the heart is blocked, the influence of the parasympathetic branch will control the heart.
If the parasympathetic branch of the heart is blocked, the influence of the sympathetic branch will control the heart.
Which rhythms originate from the SA Node?
Normal Sinus Rhythm
Sinus Bradycardia
Sinus Tachycardia
Sinus Arrhythmia
Rules for Normal Sinus Rhythm (NSR)?
Regularity: Regular
Rate: 60-100 BPM
P Wave: Uniform, upright; one P wave in front of every QRS complex
PRI: measures b/n 0.12-0.20 second and is constant across the strip
QRS: measures less than 0.12 second
Rules for Sinus Bradycardia?
Regularity: Regular
Rate: less than 60 BPM
P Wave: uniform, upright; one P wave in front of every QRS complex
PRI: measures b/n 0.12-0.20 second and constant across the strip
QRS: measures less than 0.12 second
Rules for Sinus Tachycardia?
Regularity: Regular
Rate: Greater than 100 BPM (usually 100-160 BPM)
P Wave: uniform, upright; one P wave in front of every QRS complex
PRI: measures b/n 0.12-0.20 second and constant across the strip
QRS: measures less than 0.12 second
Rules for Sinus Arrhythmia?
Regularity: Irregular
Rate: 60-100 BPM (usually)
P Wave: uniform, upright; one P wave in front of every QRS complex
PRI: measures b/n 0.12-0.20 second and is constant across the strip
QRS: measures less than 0.12 second