Lecture 4 Test 4 Flashcards
Anatomy of the heart layers
*Fibrous pericardium (leathery)
*Serous pericardium (parietal layer attached to fibrous pericardium)
*Serous pericardium (visceral layer/stretchy)
*Epicardium
T/F: Purkinjie system has tons of fast sodium channels. The more fast sodium channels there are, the straight up the APs are.
True
What kind of ions work best with gap junctions of the heart?
- Fast NA+ will cause a faster AP
- Ca++ is too big and will most likely cause a slower AP
Downside of using gap junctions
Since it’s not a chemical synapse, it’s a bi directional synapse. Ectopic signals can cause unwanted APs to the heart cells that are not fully reset for another AP leading to problems.
What can prevent unwanted APs or premature APs in our heart cells?
Our heart has guards in place such as Refractory period. (ex. If we’re in absolute refractory period, it won’t fire another AP).
What happens if we have an AP while in relative refractory period?
Odd AP, it won’t look right and force generation won’t look right either.
What is a frontal “coronal” plane EKG system
3-lead EKG setup ( + L arm. - R arm, + L foot)
What does th aVR lead mean?
Augmented right lead
What is the Mean electrical axis of the heart?
59 degrees towards the left foot
What is the “eyeball” sensor?
The (+) electrode
If the current is going towards the “eyeball”, what will you see?
a positive deflection
If the current is going away from the “eyeball” you will see
big current moving away?
small current moving away from?
Negative deflection
Big negative deflection
Small negative deflection
Which lead will show the best picture for the depolarization wave?
Lead II because the wave is heading directly towards it
(3 lead EKG) Lead II
Eyeball (+) electrodes on the Left foot is looking at (-) electrode on right arm
(3 led EKG) Lead III
Eyeball (+) electrode left foot is looking at (-) electrodes on left arm
(3 lead EKG) Lead I
If the current is moving towards it? If it’s moving away?
Eyeball of left arm (+) lead is looking at the right arm (-) lead
Positive deflection, Negative deflection
What is the name for 3 lead EKG?
Einthoven’s triangle
What is the main depolarization wave?
towards left foot
What is the purpose of the orientation of the 3 lead EKG?
To look at 60 degree angles of a unilateral triangle
Who is Einthoven?
Deutsch scientist
What is left axis deviation?
< 0 degrees, Depolarization is heading towards the left arm.
Lead I is in horizontal position
(heart rotated counter clockwise)
What is right axis deviation?
> 90 degrees, Depolarization is heading towards the right side of the body
(heart rotated clockwise)
Reasons that may cause heart deviations
Bundle branch block (may cause L or R deviations), COPD d/t big lungs full of air may cause the heart to be straight up and down. Breathing in and out may change the orientation of the heart. Pathophysiology of the heart may deviate d/t unilateral size.
For our class, what is considered Left or Right axis deviation?
Anything off of 59 degrees, L (anything less than 59 degrees), Right (anything more than 59 degrees).
Are the walls of the heart the same size?
No, the left wall is thicker due to pumping pressures more than the right.
How is depolarization spread throughout the heart?
Endocardium to epicardium
How does the repolarization of the atrium look in the EKG?
Since it’s going the opposite direction, it would be a neg deflection but since the walls are thin compared to the left ventricle, you don’t see it behind the QRS complex.
Einthoven’s law: deflection magnitude.
Lead I + Lead III = Lead II
First remove the negative from the positive.
How can you check how much smaller is the positive deflection of Lead I is compared to Lead II?
You’d have to figure out how much current is moving from the Pts right to the left by putting a perpendicular line from the lead II arrow and up to the lead I horizontal line. Side A < side H (voltage is 1.5mV) = Ex. 0.6mV
The amount of right to left current we have dictates ….
how much current we have in Lead I
What happens if our Mean Axis is 90 degrees (straight up and down), what is the current for Lead I? Lead II?
It would be 0, no current running.
Large positive net deflection
What if we have a Mean axis pointed towards the right side of the body/foot?
We would have a net negative on Lead I
What can you diagnose with a 3 lead EKG?
Any electrical problem, depending on the angle of deflection and may need more chest leads (eyeballs)
What happens when there’s 50% depolarized and 50% repolarized?
Larger magnitude of deflection for Lead I, II, III d/t more current flowing
What happens when 75% of ventricle is depolarized?
Slightly smaller magnitude of deflection in leads I, II, III compared to 50% depolarized
What happens when about 90% of ventricles are depolarized?
Negative deflection in Leads II and III. Positive deflection in Lead I (R>L movement).
What happens when 100% of ventricles are depolarized?
No current = Zero deflection in all leads
