Understanding EKGs - Ch 4
What 3 regions does the AV node include?
1. AV junctional tissue between the atria and node 2. Nodal area 3. AV junctional tissue between the node and the bundle of HIS
What are the 3 internodal atrial pathways?
1. Anterior 2. Posterior 3. Middle
Describe the right bundle branch. (Hint: 3 items)
1. Long, thin structure lying beneath the endocardium 2. Runs down the right side of the interventricular septum 3. Terminates at the papillary muscles in the right ventricle.
The Bundle of His is divided into two main branches at the top of the interventricular septum. What are these branches called?
1. Right bundle branch 2. Left bundle branch :)
What is the function of the Purkinje network?
1. Spreads impulse throughout the ventricles 2. Intrinsic firing rate of 20 - 40 beats per minute (bpm)
The intrinsic firing rate of the Purkinje network is _________ bpm.
20 - 40
Where does the remainder of the population receive their blood supply?
30% - 40% of the population receives their blood supply from the circumflex artery
The intrinsic firing rate of the AV junction is __________ bpm.
40 - 60
What is the firing rate of the SA Node?
60 - 100 beats per minute
What is the SA artery?
A branch of the right coronary artery in about 60% - 70% of the population.
What does the SA node consist of?
A cluster of hundreds of cells: a KNOT of modified heart muscle.
What is essential to learning and understanding an EKG strip?
A thorough understanding of the electrical conduction system of the heart
What is located on the floor of the right atrium near the opening of the coronary sinus, just above the tricuspid valve?
AV (Atrioventricular) node
The region where the AV node joins the bundle of HIS is called?
AV junction
What is similar to the SA node and contains fibers that can depolarize spontaneously, forming an electrical impulse that can spread to the heart chambers?
AV junction
In the normal heart, where is the ONLY pathway for conduction of atrial electrical impulses to the ventricles?
AV node
How large is the Bundle of His and where is it?
About 15 millimeters long and lies at the top of the interventricular septum.
What happens if the SA node is damaged?
Another group of specialized tissues (such as the atrioventricular tissue or Purkinje network of fibers) will assume the duties of the pacemaker.
What carries electrical impulses to the anterior wall of the left septum?
Anterior fascicle
Where is the electrical activity which is delayed by about .05 seconds?
At the level of the AV node
What is the specialized group of cardiac fibers conducting electrical activity from the SA node to the left atrium?
Bachman's bundle
What conducts electrical activity from the SA node to the left atrium?
Bachmann's bundle
What is a group of interatrial fibers contained in the left atrium?
Bachmann's bundle
What is the subdivision of the anterior internodal tract?
Bachmann's bundle
What is the conduction pathway (aka AV bundle or commond bundle) that leads out of the AV node and is also traditionally referred to as the common bundle?
Bundle of His
The primary functions of the myocardial working cells include:
Contraction and relaxation
What happens to the impulse after leaving the SA node and travels down the path of electrical conduction system?
Depolarization and resultant myocardial contraction occur.
Describe the left bundle branch.
Divides into pathways that spread from the left side of the interventricular septum and through the left ventricule.
The electrocardiogram is used to:
Evaluate electrical activity of the heart
What are the two main divisions of the left bundle branch?
Fascicles
How do these pacemakers work?
From top to bottom. In other words, from the SA node to the AV node to the Purkinje fibers.
Where to the fibers that connect with Purkinje's fibers start?
In the atrioventricular node in the right atrium of the heart.
The major blood vessel that receives blood from the systemic circulation is the:
Inferior vena cava
Which bundle branch is shorter?
Left bundle branch
What is the firing rate of the Purkinje pacemaker fibers?
Normally range from 20 - 40 beats per minute.
How can the Purkinje's network be identified?
ONLY through a microscope
The bundle branches continue to divide until they finally terminate in the _________ __________.
Purkinje fibers
What bundle branches lead to a network of small conduction fibers that spread throughout the ventricles?
Purkinje's network
What network of fibers carries electrical impulses directly to ventricular muscle cells?
Purkinje's network
Which fibers are smaller in diameter than ordinary cardiac muscle fibers?
Purkinje's network
Which fibers can be identified only with the aid of a microscope?
Purkinje's network
The interventricular septum is the wall between the:
Right and left ventricle
The AV node is located in the:
Right atrium
The sinoatrial node is located in the:
Right atrium
The SA node receives its blood supply primarily from the:
SA artery
Where does the SA node receive its blood supply from?
SA artery
What is the normal conduction pattern of the heart?
SA node, internodal pathways, AV node, Bundle of His, Bundle branches, Purkinje fibers
What is the function of the AV junction, AV node, and Bundle?
Slows impulse intrinsic firing rate of 40 - 60 beats per minute
What is the posterior fascicle?
Spreads impulses to the posterior ventricle wall.
What is responsible for the electrical activity that controls each normal heartbeat?
The heart's pacing or conduction system
What is responsible for electrical activity that controls each normal heartbeat?
The hearts pacing (conduction) system
What is the main function of the SA node?
The primary pacemaker of the heart because it normally depolarizes more rapidly than any other part of the conduction system.
What is the SA node?
The primary pacemaker of the heart, located in the upper posterior portion of the right atrial wall of the heart - near the superior vena cava.
How can a clinician determine whether an EKG strip is "abnormal"?
The student must first understand the normal parameters for the graphic representation of the electrical activity of the heart.
What is the interventricular septum?
The wall between the right and left ventricles.
What does the Bundle of His capable of?
This bundle of specialized cells contains pacemaker cells that have the ability to self-initiate electrical activity at an intrinsic firing rate of 40 - 60 beats per minute.
Specifically, what does the SA node or cluster of cells do?
This cluster generates impulses that travel throughout the muscle fibers of both atria, resulting in depolarization.
Why is electrical activity delay at the level of the AV node?
This delay allows for atrial contraction and a more complete filling of the ventricles.
________________ internodal tracts or pathways receive the electrical impulse as it leaves the SA node. These tracts distribute the electrical impulse throughout the atria and transmit the impulse from the SA node to the AV node.
Three
What is the primary function of the right bundle branch?
To carry electrical impulses to the right ventricle.
What is the primary function of the bundle branches?
To conduct electrical activity from the Bundle of His down to the Purkinje network.
What are internodal pathways?
Transfer impulses from the SA node throughout the atria to the AV junction
What is the function of the bundle branches?
Two main branches (left & right) transmit impulse to ventricles
What is facilitated by the rapid spread of the electrical impulse through the left and right bundle branches and Purkinje fibers into the ventricular musle?
Ventricular contraction
A clinician CANNOT determine the ___________________ of a patient's heart by looking at an EKG strip.
mechanical activity
What is small and is located beneath the endocardium (innermost lining of the heart chambers)?
nodes or bundles
What is the unique system in the heart which consists of specialized cells & fibers?
nodes or bundles
