Cardiac AP Flashcards
How is cardiac muscle like skeletal muscle? (3)
contains actin and myosin myofilaments
capable of contraction
T-tubule system and the SR work to maintain Ca++ homeostasis for contraction and relaxation
How is cardiac muscle NOT like skeletal muscle? (2)
Tight junctions serve as low resistance pathways that help spread the cardiac action potential throughout the myocardium.
(Tight junctions are also called gap junctions or nexi)
cardiac myocytes contain more mitochondria than skeletal muscle cells.
How is cardiac muscle like neural tissue? (3)
It generates resting membrane potential
It can initiate an action potential.
It can propagate an action potential
What is automaticity?
The ability to spontaneously generate an action potential
What is excitability?
The ability to respond to an electrical stimulus by depolarizing and firing an action potential.
What is conductance?
Ions require an open channel to cross from one side of the membrane to the other. An open ion channel increases the conductance of that ion, while a closed channel reduces conductance of that ion.
What equation can be used to predict an ion’s equilibrium potential?
Nernst equation
When is equilibrium of the cardiac cells reached?
Equilibrium is achieved when there is no concentration gradient and therefore no net flow of ion across the cell membrane. The charge inside the membrane balance the charges on the outside of the membrane.
What is the Nernst equation?
E Ion = -61.5 log ( [Ion] inside / [Ion] outside )
What is RMP?
The difference in electrical potential between the inside and outside of the cell. The inside of the cell is negative relative to the outside.
RMP is established by three mechanisms?
chemical force
electrostatic counterforce
sodium/potassium ATPase
Is the inside or outside of the cardiac cell relatively negative?
Inside
What is threshold potential?
The initial voltage at which the cell depolarizes.
Can depolarization be stopped?
Depolarization is an all or none phenomenon - once it begins, it cannot be stopped.
When is the cell easier to depolarize?
When RMP is closer to threshold potential.
When is the cell harder to depolarize?
When RMP is further from threshold potential.
When does depolarization take place?
When there is a reduced polarity across the membrane. This means there is less of a charge difference between the inside and outside of the cell.
In excitable tissue, depolarization results in what?
action potential
Negative to positive is known as?
depolarization
Positive to negative is known as?
repolarization
What is hyperpolarization?
Hyperpolarization takes place when there is an increased polarity across a membrane, there is a large charge difference between the inside and the outside of the cell.
What is repolarization?
The restoration of membrane potential towards resting membrane potential following depolarization.
Why is the cardiac cell relatively positive on the outside and negative on the inside?
The cell continuously leaks potassium, thus losing positive charge from the inside of the cell.
What electrolyte is the MYOCYTE permeable to?
potassium
What electrolyte is the primary determinant of resting membrane potential in the MYOCYTE?
potassium
When the serum potassium decreases (HYPOKALEMIA) what happens to the RMP?
RMP becomes more negative, and the myocyte becomes more resistant to depolarization.
When the serum potassium increases (HYPERKALEMIA) what happens to the RMP?
RMP becomes more positive and myocyte depolarize more easily
When the cell is at rest what is the sodium to potassium permeability of the cardiac cell?
The cell is very permeable to potassium and very low permeability to sodium
What ultimately depolarizes the cell?
When RMP approaches threshold potential, voltage-gated sodium channels open and sodium conductance increases, this depolarizes the cell.
(depolarizing is becoming more positive)
What two purposes does the sodium potassium pump serve?
- removes sodium that enters the cell - during depolarization.
- Returns potassium that has left the cell - during repolarization.
Na/K-ATPase has another name, what is it?
Na/K pump
What is the exchange rate of sodium and potassium by the Na/K pump?
3 sodium ions are removed from the cell and 2 potassium ions go into the cell.
True or False
The sodium potassium pump turns on and off depending on the resting membrane potential?
False, the sodium potassium pump is ALWAYS on
Does the sodium potassium pump require energy?
Yes, the sodium potassium pump is an active transport mechanism that requires energy in the form of ATP?
Cardiac / Ventricular myocytes normal RMP value?
-90 mV
Cardiac / Ventricular myocytes normal TP value?
-70 mV
Does hypocalcemia or hypercalcemia decreased TP?
hypocalcemia decreases TP
Does hypocalcemia or hypercalcemia increase TP?
hypercalcemia raises TP
What is the intrinsic firing rate of the SA node, AV node, and the Purkinje fibers?
SA node = 70-80
AV node = 40-60
Purkinje Fibers = 15-40
which node of the heart provides the P wave?
SA node, thus if the SA node is diseased or impaired you will lack a P wave
At rest which part of the autonomic nervous system modulates the heart rate?
PNS tone exceeds SNS tone at rest
PNS tone includes which nerve to innervate the heart? (SA node and AV node)
Vagus nerve ( CN X)
the right Vagus innervates the SA node and the left Vagus innervates the AV node
SNS tone is innervated / regulated by what?
Cardiac accelerator fibers (T1-T4)
How many phases are there to a cardiac myocyte?
4,0,1,2,3
How many phases are there to the SA node? (could also be AV node)
4,0,3
no phase 1 or 2
Phase 4 in the nodal cells is known as?
spontaneous depolarization
The membrane of the nodal cells is leaky to which electrolyte?
Na+
RMP for the nodal cells is what?
around -60
TP for the nodal cells is what?
-45
What is “funny” about the funny sodium channels?
they are activated by hyperpolarization and not depolarization
(funny current or funny sodium channels)
In the nodal cell what happens at -50 mV?
transient calcium channels (T-type) open to further depolarize the cell.
What is the equation for 02 carrying capacity?
(Hgb x Sa02 x 1.34) + (Pa02 x 0.003)
What is the equation for D02?
CO x [(Ca02)] x 10
Ca02 = (Hgb x Sa02 x 1.34) + (Pa02 x 0.003)
What is oxygen carrying capacity: Ca02?
What is the normal reference value?
How much 02 is carried in the arterial blood.
20mL/dL
What is Oxygen delivery: DO2?
What is the normal reference value?
How much 02 is carried in the blood and how fast it is being delivered to the tissues.
1000 mL/min
What is oxygen extraction ratio: E02?
what is the normal reference value?
How much 02 is extracted by the tissues.
25% for the whole body
What is oxygen consumption: VO2?
what is the normal reference value?
Ho much oxygen is consumed by the tissues.
250mL/min (this value is at rest)
What is Venous oxygen content: Cv02?
what is the normal reference value?
How much 02 is carried in the venous blood.
15mL/dL
Hemodynamic term for flow, pressure gradient, and resistance?
flow = cardiac output
pressure gradient = MAP-CVP
resistance = SVR
Formula for MAP?
MAP = (CO X SVR) = CVP /80
What is the formula for Poiseuille’s law?
Q = pie x R^4 x change P / 8 X n x l
which means: Blood flow = pie times Radius to the fourth power times arteriovenous pressure gradient (Pa -Pv) divided by 8, times viscosity times length of tube
Reynolds number (Re) can be used to predict if flow will be laminar or turbulent. Tell me the three ranges for Re number?
Re < 2000 predicts flow will be mostly laminar
Re > 4000 predicts flow that will be mostly turbulent
Re = 2000-4000 suggests transitional flow
Tell me what laminar, turbulent, and transitional flow are?
Laminar = molecules travel in a parallel path through the tube.
Turbulent flow = molecules travel in a non linear path and will create eddies
Transitional flow = laminar flow along the vessel walls and turbulent flow in the center.
What determines blood viscosity?
hematocrit and body temperature
When flow is turbulent what does that cause?
A greater amount of energy is lost via heat and vibration. The pressure gradient will be larger than what is predicted by Poiseuille’s law.
If a murmur or bruit is produced from blood flow what type of blood flow would it be considered?
turbulent flow
the vibrations that occur with turbulent flow produce the murmur or bruit
What is viscosity a result of?
friction from intermolecular forces as a fluid passes through a tube
What is blood viscosity inversely proportional to?
temperature
Does a cooler or warmer temperature increase the viscosity of blood?
a cooler temperature increases viscosity of blood and thus increases resistance
During Cardiopulmonary Bypass the patient is hypothermic, what can be done to decrease the viscosity of the blood that is not rewarming?
reducing the hematocrit will help counteract the increased viscosity from being hypothermic.
What effect does increased temp have on viscosity and flow?
increased temp = decreased viscosity and increased flow
temp and flow are directly proportional, viscosity is inversely proportional to temp.
What effect does decreased temp have on viscosity and flow of blood?
decreased temp = increased viscosity and decreased flow
temp is directly proportional to flow and inverse to viscosity
How do changes in hematocrit change viscosity and flow of blood?
increased hct increases viscosity and decreases flow
decreased hct decreases viscosity and increases flow
(hct is directly proportional to viscosity)
What is the formula for Cardiac Output?
HR X SV
Normal value for CO?
5-6 L/min
Formula for Cardiac Index?
CO/BSA
normal value for Cardiac index?
2.8-4.2 L/min per m^2
What are the TWO formulas for Stroke Volume?
EDV X ESV
CO X (1000/HR)
normal value for Stroke volume?
50-110 mL/beat
What is SV index?
SV/BSA
What is normal SV index?
30-65 mL/ beat per m^2
2 Formulas for ejection fraction?
EDV-ESV/EDV X 100
or
SV/EDV X 100
Normal value for EF?
60-70%
2 Formulas for calculating MAP?
SBP + 2XDBP /3
or
(CO x SVR) /80 + CVP
Normal value for MAP?
70-105 mmHg
2 Formulas for calculating Pulse Pressure?
SBP -DBP
or
Stroke volume output / arterial compliance
normal value for pulse pressure?
40 mmHg
Formula for SVR?
MAP-CVP / CO X 80
Normal value for SVR?
800 - 1500 dynes per sec per cm^-5
Formula for SVR index?
MAP-CVP / CI X 80
Normal value for SVR index?
1,500 -2400 dynes per sec per cm^-5 per m^2
Formula for PVR?
MPAP-PAOP / CO X80
Normal value for PVR?
150-250 dynes per sec per cm^-5
PVR index formula?
MPAP-PAOP / CI X 80
Normal value for PVR index?
250-400 dynes per sec per cm^-5 per m^2
What three conditions can set the afterload proximal to the systemic circulation?
aortic stenosis
hypertrophic cardiomyopathy
coarctation of the aorta
Wall stress is reduced by what three factors?
decreased intraventricular pressure
decreased radius
increased wall thickness
Blood from the Aorta during diastole supplies the coronary circulation, what two arteries branch from the aorta?
R coronary artery and L coronary artery
The R coronary artery branches into what two artery?
Posterior descending artery and marginal artery
The L coronary artery branches into what two artery?
circumflex artery and anterior interventricular artery (often called the LAD or widow maker)
PDA, marginal artery, LAD, and CxA all drain into what?
MYOCADIUM
After supplying the myocardium with oxygenated blood what veins are supplied with de-oxygenated blood?
Small cardiac vein (from marginal)
Middle cardiac vein (from the PDA)
Great cardiac vein (from the LAD)
Not included on Apex:
Posterior vein of the L ventricle (from the L circumflex artery)
All of the veins drain into what large vein?
They all drain into the coronary sinus
The SA nodal artery perfuses the SA node, where does this originate from?
RCA in 50-60% of the population
CxA in 40-50% of the population
The coronary artery that feeds the PDA determines dominance, what artery(s) supply the PDA?
In general the RCA supplies the PDA in 80% of the population, meaning R dominance.
CxA can supply the PDA also which would mean left dominance
You can also have co-dominance with the RCA and CxA supplying the PDA
What arteries of the hearts circulation are called the epicardial vessels?
RCA
LAD
LCx
(CxA and LCx are the same thing)
What structures are responsible for providing the majority of coronary vascular resistance?
The coronary arterioles (not the epicardial veins)
Which leads tell you about an inferior wall infarct?
Which artery supplies this area?
I, III, avf
supplied by the RCA
Which leads tell you about a R ventricular wall infarct?
Which artery supplies this area?
avR, V1, V2
supplied by the LAD
Which leads tell you about a lateral wall of the L ventricle infact?
Which artery supplies this area?
I, avL, V5, V6
supplied by the Left circumflex artery (CxA)
Which leads tell you about an anterioseptal infarct?
Which artery supplies this area?
V1-V4
supplied by the LAD
Which vein runs along side the LAD?
Great cardiac vein
Which vein runs along side the PDA?
Middle cardiac vein
Which vein runs along side the RCA?
Anterior cardiac vein
Most of the blood returning from the left ventricle drains into what?
Coronary sinus
Where is the coronary sinus located?
posterior aspect of the right atrium just superior to the tricuspid valve.
Most of the blood returning from the Right ventricle is carried by which vein?
anterior cardiac veins
This vein bypasses the coronary sinus and empties directly into the right atrium?
anterior cardiac veins
Coronary blood flow is autoregulated between a MAP of what?
60-140 mmHg
When MAP falls below the range of autoregulation then coronary perfusion becomes dependent on what?
coronary perfusion pressure
True or False:
cardiac relaxation requires ATP?
True
Both cardiac contraction and relaxation requires ATP
What is normal coronary blood flow?
225-250 mL/min or 4-7 percent of cardiac output
at rest how much oxygen does the myocardium consume?
8-10 mL/min/100g
What inactivates Nitric oxide?
hemoglobin
what is the half life of nitric oxide?
5 sec.
Does NO cause hypotension?
No, it is inactivated before it enters the systemic circulation thus it can not cause hypotension. But it does reduce right ventricular afterload with it’s vasodilation effects.
Normal valve orifice diameter for the aortic valve?
2.5 -3.5 cm ^2
Aortic stenosis is considered sever when the valve orifice is?
less than 0.8 cm ^2
Most common causes of AS?
Bicuspid aortic valve
calcification of the valve leaflets
rheumatic fever
infective endocarditis
Before performing a subarachnoid block (in anyone but especially the elderly) what should you listen for and why?
murmur of aortic stenosis
These individuals can not handle a decrease in preload as a subarachnoid block is known to decrease. If preload is decreased these people risk having an MI.
If potassium conductance is increased by PNS stimulation what will happen to the myocyte?
more potassium (a positive ion) exits the myocyte, the interior becomes more negative. This increases the distance between RMP and TP, so it takes longer for the cell to reach TP and this slows the HR
Normal Ca02 values?
20 mL 02/dL blood
Normal CV02 value?
15mL O2/dL/ blood
Ca-v difference?
5 mL 02/dL blood
How to calculate Ca-v difference?
(1.34 x Hgb x Sp02) - (1.34 x Hgb x Sv02)
Is contractility dependent on preload or afterload?
neither, contractility is the ability of the sarcomeres to shorten and perform work, this is independent of preload and afterload.
A greater ventricular output for a given LVEDV reflects what?
increased contractility
A lower ventricular output for a given LVEDV reflects what?
decreased contractility
Saying to remember what affects contractility?
Chemicals affect Contractility - particularly Calcium
Contractility of the heart is known as inotropy, is this the same as Frank-Starling mechanism?
No
The cardiac cycle is divided into 6 phases, how many belong to systole and how many belong to diastole?
2= systole 4= diastole
Isovolumetric contraction belongs to diastole or systole?
Isovolumetric contraction belongs to systole
Isovolumetric relaxation belongs to diastole or systole?
Isovolumetric relaxation belongs to diastole
Which Coronary artery supplies the apex of the heart?
LAD
Which coronary artery supplies (perfuses) the LBB?
LAD
Why does IV calcium stabilize the myocardium in the patient with hyperkalemia?
More calcium raises the threshold potential and if the patient is already hyperkalemic then the RMP has already moved closer to TP and now TP needs to be moved away from RMP so that depolarization at a faster rate does not occur
Why are patients with hypocalcemia prone to muscle spasm and tetany?
The TP has been lowered in patients with low calcium thus it is closer to RMP and the cell is more likely to depolarize
