Exam 4 Lecture 3 Flashcards
What is the Cardiac Refractory Period?
Stimulating an AP before the heart can fully reset
What is the Relative Refractory Period?
*What happens to the AP and heart pumping?
Reset for the most part, but not fully
*Weaker AP and Pumping
What is the Early Premature Contraction Period
Smaller than normal AP and weaker pumping
What is the Later Premature Contraction Period
*Describe the AP
Heart has completely reset itself, but still has an early AP
*Strongest AP out of the refractory issues
What is the Absolute Refractory period
*Describe the AP
Stimulation during an active AP
*Either no AP or very minimal
What is the rate of Action Potentials Per second in the heart?
0.83 AP/sec
Normal HR, including AP per second formula
60 seconds / 0.83 AP = 72 BPM
What is the HR in the SA Node, if it did not include the Vagus Nerves or SNS chain?
110 b/min
What is the HR in the SA Node, if it did not include the SNS chain?
60-62 BPM
What is the HR in the SA Node, if it did not include the Vagus Nerves, but included the SNS chain?
120 BPM
How many beats does the SNS chain add by itself?
10 BPM
Where in the heart is the origin of pacing?
SA Node
What is the conduction system of the heart?
Purkinje Fibers
If the AV Node became the PM of the heart, what would the HR be?
40-60 BPM
If you only had Purkinje Fibers as the PM of the heart, what would be the HR?
15-30 BPM
Which part of the EKG illustrates Atrial Depolarization?
P-Wave
*(+) deflection
What is the duration of a normal P Wave?
0.09 seconds
How long does it take for an action potential to reach the AV node from the SA node?
0.03 seconds
How long does it take to fully depolarize the R atria?
0.07 seconds
How long does it take to fully depolarize the L atria?
0.09 seconds
Name 2 Functions that the AV node performs?
*Prevents ventricles fully contracting before being filled up with blood by the Atria
*Acts as a filter to keep stray AP in the atria and not allowing them to generate down to the ventricles
Why is there a delay in AP in the AV node?
*Main - Not many gap junctions
*2nd - very fat, so poor conductor of electricity
How long is the AV node delay, without the bundle of his?
0.12 sec
How long is the delay in the bundle of his?
0.01 seconds
What is the total AV nodal delay before the AP reaches the interventricular septum and bundle branches?
0.13 seconds
Where is the Bundle of His located?
Inferior to the AV node and Superior to the Bundle Branches in the Ventricles
Where are the Bundle Branches located?
Inferior to the Bundle of His, but Superior to the Interventricular Septum
*1st part of the ventricles
Where are the SA and AV node located?
R Atria
What is the duration of a normal PR interval?
0.16 seconds
At about how many seconds does ventricular depolarization begin?
0.16 seconds
When does the QRS complex begin?
0.16 seconds
What are the 3 connecting parts of the SA to the AV node called?
*Name all 3 Parts
*Where are these located in the heart?
Internodal Pathways: R Atria
*Anterior
*Middle
*Posterior
What branches off of the Anterior Internodal Pathway?
The Interatrial Bundle [Bachman’s Bundle]
What is another name for the Interatrial Bundle?
Bachman’s Bundle
What is the importance of the Interatrial Bundle?
Branches AP from the R atria to the L atria, resulting in propagation of electrical signal to fully depolarize the L atria
Per Lecture, what structures are considered in the top of the heart?
SA, AV, Atria’s
How long does it take to fully depolarize the ventricles at the end of a cardiac AP?
0.22 seconds
If you place a lead on the R shoulder (-) and L foot (+), what is the angle of current?
* What kind of deflection is this depolarization?
59 degrees
* (+) deflection
What is the angle of current of a typical heartbeat?
59 degrees
What does a normal EKG represent?
The result of all the AP happening around the heart
What is the magnitude of an individual AP in a Ventricular Myocyte?
100 mV
If I put electrodes closer to the heart, how would the QRS complex look?
Larger amplitude, as < tissue to go through
*Around 3-4 mV high
Leads V1-V6, compared to a 3-Lead EKG, register what type of QRS complex?
Larger deflection/more voltage, as closer to the heart and less tissue to go through
Why is the Amplitude of the QRS complex in a 3-Lead EKG shorter than leads V1-V6?
Shrunk b/c of air in the lungs and increased tissue/fat to go through
Per Lecture, how is the QT interval described in terms of AP?
Length of the Endocardium AP or Full Ventricular Depolarization
In an EKG, what is represented by a SA node AP?
The start of the P wave
In boxes, how long/tall should a P wave be
2.5 boxes
If the P wave originated in the AV node, traveled retrograde to the SA node, what would the EKG look like?
Inverted P wave
What heart issue is associated with a longer duration in the P wave?
Conduction problem in the L atria; L atria is more stretched, resulting in longer P wave
If I started my AP in the SA node, in what angle direction should I head to reach the AV node?
59 degrees
What heart issue is most likely associated with a higher P wave >2.5 boxes?
Problem with the R atria [hypertrophy]; more tissue = more amplitude
What could be indicated by a “double” hump in the P Wave
Electrical Block in the L atria
How does the Q wave look on the EKG?
*Does everyone have a Q wave?
Negative deflection before the R wave
*Not everyone has a Q wave, hence why it is a PR interval, not PQ interval
What does the S Wave represent in the EKG?
Negative deflection after the R wave
How long is a typical QRS complex?
0.06 seconds
What 2 things can indicate a larger deflection in the QRS complex?
Increased ventricular tissue or the electrodes are placed closer to the heart
What disease process can prolong the QRS without increasing the amplitude?
Dilated Cardiomyopathy
What does the R wave represent in the EKG?
Beginning of ventricular depolarization
When does the QRS complex End?
When all of the ventricular muscle mass has been depolarized
Around what part of the EKG represents Atrial Repolarization?
*Why can’t you see it?
Around the S-Wave
*Overshadowed by Ventricular Depolarization
Why is the end of the S-Wave important?
*What are 2 names for this spot
Point where we can determine current of injury
*J-Point or Isoelectric Point
Why is the end of the T-Wave important?
All healthy ventricular tissue will be repolarized, but unhealthy tissue will be still depolarized
What is the QT interval?
*Duration?
Start of Interventricular Septum depolarization to end of ventricles depolarizing
*0.25-0.35 seconds
What does a faster HR do to the ST-segment?
*QT interval?
Shorts ST segment/QT interval, which makes the ventricle repolarize faster than normal, leading to a firing of an AP Faster
What is the RR interval?
*Formula?
Time between adjacent QRS complexes
*60 sec/ 0.83 [RR] = 72 BPM
In terms of Heart Tissue AP, how can we describe the QT interval?
Endocardial Fast AP duration
What is Chronotropy?
Heart Rate
What is Inotropy?
Stronger contraction via more Ca++ coming in from the SR
What is Dromotropy?
Speed of conduction of electrical impulses
What is Lusitropy?
*+ agent
*- agent
Resetting of the ventricle
*+ = repolarize the ventricle faster than normal = increased HR
* - = repolarize the ventricle slower than normal = decreased HR
What is dromotropy dependent on?
Entirely dependent of Na+ currents and how much ionic Na+ flow we have
Y Axis Big Box
0.5 mV
Y Axis Small Box
0.1 mV
Big Box Time
0.2 sec
Small Box Time
0.04 sec
What was the units on the Paper EKG fed thru the machine?
25 mm/sec
If I have + electrode in the L arm and a - electrode in the R shoulder, what deflection would depolarization be from R shoulder to L arm?
+ deflection
If I have + electrode in the L arm and a - electrode in the R shoulder, what deflection would repolarization be from R shoulder to L arm?
- deflection
If I have + electrode in the L arm and a - electrode in the R shoulder, what deflection would repolarization be from L arm to R shoulder?
+ deflection; T Wave
Describe a Fast Ventricular Myocyte AP Phase 4 slope
*Can it fire an AP on its’ own?
Shallow slope from leaky Na+ channels
*Can fire AP on own if given enough time
Another name for P4 in the SA Node Slow AP
Diastolic Depolarization
Why is Phase 0 in a SA nodal cell slower than Phase 0 in a ventricular myocyte?
L-Type Ca++ channels are slower to open and slower to close [longer AP duration]
If the heart has a steep Phase 0, what happens?
*Why
Faster AP spread thru the heart b/c increased Ca++ leads to increased Na+ spreading throughout the ventricular muscle
If you have a shallow Phase 0, what happens?
Slower AP spread throughout the heart
What happens in Phase 3 of a SA nodal myocyte?
K channels opening and slow Ca++ channels closing
What Phases do a SA nodal cell have?
Phase 4, 0, 3 [maybe 2]
Why is the AV node Vrm more negative than SA node?
Less leaky to Na+ and Ca++ than the SA node; longer time to reach threshold
Where are HCN channels located?
Mostly SA node
Some AV node
Sparse in Ventricular Myocytes
Where are the deeper, longer AP most likely found?
Subendocardium
Would an Epicardial AP be deeper/longer than a subendocardium?
Epicardium repolarizes before the endocardial tissue, so starts a little later, so no
Describe an Atrial AP
Mix between fast and slow
*only contract short period of time and dont have high resistance to push against
