Cardiac Lecture 2 Flashcards
exam 4
The action potential of ______ tissue is considered a “Fast AP” because phase 0 slope is steep
Ventricular
Normal healthy heart rate
72bpm
Why is the SA node considered the pacemaker of the heart
It reaches threshold faster than anywhere else in the heart.
What is the magnitude of deflection of an EKG?
1.5mV
The mV between the lowest point and peak of R wave
What is the Vrm in the SA node?
-55mV
What is the threshold mV in SA node
-40mV
Which channel is responsible for the steep phase 4 in SA node action potential?
HCN
When do HCN channels open
Opens at Vrm or by cAMP
What ions can diffuse through HCN channel
Non-specific to + charged ions (cations). Primarily Na+ and Ca++ enter cell. (K+ can technically leave through, but usually leaves elsewhere)
What is an HCN channel
Hyperpolarization cyclic nucleotide channel
EKG is the sum of all _____ of cardiac electrical activity
current
Vrm in ventricular myocyte
-80mV
Peak of AP in ventricular myocyte
+20mV
1 big box on EKG is _____ mV
0.5mV
1 big box on EKG is ____ sec/msec
0.2 seconds/ 200ms
what is occuring at the P wave?
atrial depolarization
what is occuring at the QRS
ventricular depolarization and atrial repolarization (can’t see atrial repolarization because of ventricular depol)
What is occuring at the T wave
ventricular repolarization
Electrons moving _______ the positive lead results in a positive deflection
towards
Electrons moving _______ the positive lead results in a negative deflection
away
Electrons moving ______ the negative leads results in a negative deflection
towards
Electrons moving _______ the negative lead results in a positive deflection
away
Depolarization occurs first in the ________ and spreads _______ towards the ________
endocardium, superficially, epicardium
Repolarization occurs first in the _______ and spread _______ towards the _______
epicardium, deep, endocardium
One large box on EKG contains how many small boxes?
5 wide and 5 tall for 25 total
Why is the T wave a positive deflection
Because repolarization starts in epicardium and travels deep towards the endocardium. Repolarization occurs in the opposite direction, resulting in a + deflection on EKG.
Ischemia prevents electrical ______ of tissue
resetting/repolarization
Ischemic tissue is _______ constantly
depolarized
Current of injury where there should not be any
Ischemic tissue depolarization
Why is EKG current lower mV than actual AP
Voltage lost due to high resistance of tissue/fat/air between myocyte and superficial leads; air - COPD
muscle layer that is very deep in the wall of heart (only in left ventricle)
subendocardium
usual location of an MI because pressures are the highest, and furthest from blood supply
subendocardium
inner, stretchy layer of pericardium
parietal pericardium
outer, fibrous layer of pericardium (thick leathery, similar to dura layer)
fibrous pericardium
The myocardium is ________ muscle meaning it’s a network of cells that function as a single unit
unitary
Vrm of purkinje fibers
-90mV
what is five and dime reflex?
the stimulation of the ophthalmic branch of the trigeminal nerve (CN V) that triggers brainstem to stimulate the vagus nerve (CN X) causing bradycardia/asystole
Phase 0 of AP occurs because of
opening of VG-Na+ channels once threshold is reached
Phase 1 of AP occurs because of
VG-Na+ channels close, K+ channels close, fast T-type Ca++ channels open.
Phase 2 of AP occurs because of
slow L-type Ca++ channels open causing plateau
Phase 3 of AP occurs because of
K+ channels open back up until Vrm reached
Ohm’s law
V= I x R
V= voltage, I= current, R= resistance
Majority of vagus nerve affects what area of the heart
nodal areas (SA/AV nodes)
Parasympathetic effects are more _______ and sympathetic effects are more ________ in the heart
focal, widespread
Primary catecholamine in heart
norepi
increase of cAMP would do what to HR
increase
What is blood Ca++ levels effect on threshold
inc. Ca++ = inc. threshold (more +) = dec. HR
dec. Ca++ = dec threshold (more negative) = inc. HR
How does mACh-R affect HR?
binding of ACh on mACh-R causes them to open and increases K+ permeability, making Vrm more negative and decreasing HR.
How is the anatomy of the gap junctions in the heart different from other muscles?
Intercalated discs - allows more gap junctions d/t increased surface area, curvy/indentations instead of flat
Each cardiac muscle cell has how many nuclei?
one
The term used to describe the connection between one heart cell and another is ______
intercalated discs - only found in heart
What are the 2 mechanisms heart cells use to replace heart cells that have died?
- Stem cells - slow repair process
- Fibroblasts - lay down scar tissue where stem cells are overwhelmed
Multinucleated cells think _______
skeletal muscle
______ is the condition where fibroblasts are laying down extra scar tissue than normal. _______ are the class of medications used to prevent this
CHF; ACE inhibitors
How do ACE inhibitors prevent unnecessary scar tissue formation in the heart?
ACE inhibitors inhibit growth factor side of angiotensin II
What are the 2 issues with having scar tissue in the heart?
- doesn’t conduct action potential
- doesn’t contract
ACE inhibitors are known to reduce ______
afterload
Conduction tissue is good at transmitting AP because it doesn’t have _______
myofibrils
_______ describes the arrangement of the heart muscle in two distinct ventricular layers that twist in different directions
Syncytial connections
Above the AV node
Top half - atria
Below the AV node
lower half of the heart - ventricles
The vast majority of heart cells are _______
myocytes - muscle tissue, used to produce force via myofibrils
What are the 2 types of tissue in the heart?
- Muscle tissue
- Conduction tissue
The _______ is the one-cell thick layer in the endocardium
endothelial layer
The _______ is the muscle layer that is located between the myocardium and endocardium
Subendocardium
The bulk of the heart muscle wall is in the ______
myocardium
The pericardial space is filled with ______ and _____ to prevent friction in the pericardium
fluid and mucus
Typically all the major blood vessels of the heart are sitting on top of the _______
epicardium
Pain in the pericardium can be caused by what 2 things?
- Inflammation
- Loss of fluid/mucus
- both cause increased friction
The pericardium consists of what 3 layers?
- Pericardial space
- Serous pericardium - parietal
and visceral layers - Fibrous pericardium
The ______ is the outer layer of the pericardium that is stiff and similar to the dura layer
fibrous pericardium
What are the 2 layers of the serous pericardium?
- Visceral layer - thin/elastic layer that sits between parietal layer and the heart tissue
- Parietal layer - connected to the fibrous pericardium
The visceral pericardium is also known as the _______
epicardium
The heart, when relaxed, is not relaxed to an optimum degree. It is _______
under-stretched - no H band, actin and myosin overlapping
The ________ is the conduction system within the ventricular muscles
purkinje fibers - don’t contract, ventricles do contract
Threshold potential for both Purkinje and ventricular cells is _____
-70mV
Sodium permeability in myocytes is not ______, giving phase ____ a slope
constant, phase 4
Sodium permeability ______ as time goes by in myocytes, allowing _______ depolarization
increases, spontaneous or self depolarization
How long does it take for the Purkinje fibers to self-depolarize?
30+ seconds
What is the length or duration of the AP in the heart?
200ms
Phase ___ indicates length of contraction
2
_____ is the primary neurotransmitter of the PANS that affects the heart. What receptors does it interact with?
ACh, mACh-R
_____ is the primary neurotransmitter of the SANS that affects the heart. What receptors does it interact with?
Norepinephrine - interacts with beta receptors
The PANS primarily innervates what tissue in the heart? What about the SANS?
PANS - nodal tissue
SANS - ventricular tissue
The total change in electrical activity of a ventricular myocyte from it’s resting state to its activated state is ______ mV
100
If the normal HR is 72 bpm, how often is an AP fired?
every 0.83 seconds
By itself, the SA node will beat at ____ bpm
110
SANS activity without vagal input would cause the heart to beat at _____ bpm
120
PANS or vagal input w/o SANS input would cause the heart to beat at ____ bpm
60-62
What effect would beta antagonists have on the heart? Why?
Beta-blockers will decrease cAMP and therefore cause less activation of HCN channels, decreasing the slope of phase 4 in the nodal tissue action potentials, and decreasing HR
What would the HR be if just the AV node if firing?
40-60 bpm if no SA node AP
What would the HR be if just the purkinje fibers were firing?
15-30bpm
Which layer of the heart would have the longest AP?
Endocardium
What effect would beta-agonists have on the heart? Why?
Beta-agonists will increase cAMP and therefore cause more activation of HCN channels, increasing the slope of phase 4 in the nodal tissue action potentials, and increasing HR
Hypocalcemia causes ____ in the heart by _____. Hypercalcemia causes ____ in the heart by _____.
Hypocalcemia - tachycardia, decreasing threshold potential
Hypercalcemia - bradycardia, increasing threshold potential
Mild hyperkalemia would result in _______
tachycardia because the Vrm would be higher (more depolarized) and thus require less time to reach threshold potential.
What ions are nodal tissue most permeable to during phase IV?
Calcium and sodium - via HCN and leak channels
Differentiate between effects of potassium permeability vs beta-adrenergic receptors vs calcium permeability
Potassium - changes the Vrm
Beta-adrenergic - changes the slope
Calcium - changes the threshold potential
How is HR calculated from an ECG?
60 seconds divided by R-R interval (0.83 seconds) = 72 bpm
______ is the speed of electrical conduction
dromotropy
______ is the force of contraction
ionotropy
______ is the frequency at which the heart fires an AP
chronotropy
________ is how fast the ventricles reset or relax during diastole
Lusitropy, length of ST segment
How fast did the ECG paper feed back in the old days?
25mm/sec
What is the average angle in which the heart fires an AP?
59 degrees, towards left foot
Phase IV of SA node depolarization is also called what? What does it determine?
Diastolic depolarization - determines HR
What ion channels determine the decreased slope of phase 0 in SA node depolarization?
L-type Ca++ channels - less permeable to Na+ than in ventricles
SA node depolarization doesn’t have a phase __
1, and doesn’t have a plateau, phases 2 and 3 are combined
The slope of phase 0 in SA node depolarization determines what?
How fast AP travel through the heart
What is the conduction tissue in the R atrium called? What do they connect?
Internodal pathway (3) - anterior, middle, and posterior
Connect SA to AV node
What is the conduction tissue called that is in the L atrium? Where does it come from?
Interatrial (Bachman’s) bundle - comes from the anterior nodal pathway from SA node
How long does it take for an AP to get from the SA to AV node?
0.03 sec
How long does it take for the R atrium to depolarize?
0.07 sec
How long does it take for the L atrium to depolarize? What does it signify on an ECG?
0.09 sec - P wave, both atria depolarized
How long does it take for the entire heart to depolarize?
0.22 sec
How long id the delay at the AV node?
0.12 sec -
Why is there a delay at the AV node?
Gives atria time to contract before ventricles; also functions as a filter for electrical activity/extraneous AP (refractory period)
- caused by fat and less gap junctions in the AV node
How long is the delay in the bundle of His?
0.01 sec
How long does it take for an AP to get from the SA node to the interventricular branches?
0.16 sec - length of time before QRS interval starts
The length of the QT interval corresponds to the AP of ________ tissue
endocardial ventricular tissue - start of depolarization of ventricles to repolarization
The P wave is ____ boxes long by ___ boxes tall
2.5 x 2.5
If the AP originated in the AV node instead of the SA node, what would change on the ECG?
The P wave would be inverted (negative deflection)
How would hypertrophy of the R atrium change an ECG?
P wave taller
How would hypertrophy of the L atrium change an ECG?
P wave longer
A double hump of the P wave on an ECG would indicate an ______ block between the ______
electrical, atria
How long is the QT interval?
0.25-0.35 sec
How long is the PR interval?
0.16 sec
How long is the QRS interval?
0.06 sec
A longer and taller QRS interval would be caused by what?
extra ventricular tissue
What would cause the QRS interval to be longer without it being taller?
Dilated cardiomyopathy
_____ is the point at the end of the QRS complex that indicates that all of the ventricular tissue is depolarized
J point or isoelectric point
You can compare the ____ to the point after the ___ wave to determine if there is an injury to the heart
J point to the point just after the T wave - ST segment
An action potential that is transmitted in the relative refractory period will be _____
abnormal/weaker than normal AP
A premature contraction affects what in the heart in terms of cardiac output
Decreased filling time (EDV) and therefore decreased Stroke volume. (overall decreased cardiac output)
An impulse that is passed to the heart while it is in the absolute refractory period will result in ______
No contraction; no response from the cells that are in the absolute refractory period
An early premature contraction begins in the ______ period
relative refractory period
An early action potential that occurs after the refractory period is called ______ contraction. What will the effect be in the force of contraction?
later premature contraction
normal force of contraction
