ELEMENTS OF CARDIAC FUNCTION BERNE Flashcards
What are the 2 main types of Action Potential in the heart?
Fast response
Slow response
The fast response AP of the heart occurs in which tissues?
Artia
Ventricles
Purkinje Fibers (Specialized Conducting fibers)
The slow response of AP of the heart occurs in which regions?
Sinoatrial node
Atrioventricular node
What are the phases of Fast response AP?
Phase 0, 1, 2, 3, 4
The slow-response cells lack which phase of the cardiac AP?
Phase 1 or early repolarization phase
Which of the following is incorrect?
A. The slow-response cells lack the early repolarization phase (phase 1)
B. The resting membrane potential (phase 4) of the fast-response cells is considerably more negative than that of the slow-response cells
C. The slope of the upstroke (phase 0), the amplitude of the action potential, and the overshoot are greater in the slow-response cells than in the fast-response cells.
D. The action potential is propagated more slowly and conduction
is more likely to be blocked in slow-response cells than in fast-response cardiac tissue
C. The slope of the upstroke (phase 0), the amplitude of the action potential, and the overshoot are greater in the fast-response cells than in the slow-response cells.
What is the equilibrium potential of K+ in Cardiac Muscle cell? A. -93mV B. -71mV C. -129mV D. +71mV
A. -93mV for K+
Note:
+71mV for Na+
+129mV for Ca++
Any diffusion of K+ that occurs at the resting membrane potential (phase 4) takes place mainly through specific potassium channels. Opening and closing of these channels are regulated by:
Membrane voltage changes and Chemical signals (eg. ACh concentration)
The specific potassium channel through which K+ passes during phase 4 is a voltage-regulated channel that conducts the _______
Inward rectifying K+ current
What is the consequence of hypokalemia in a resting cardiac cell? A. Depolarization B. Overshoot C. Hyperpolarization D. No effect
C. Hyperpolarization
Note:
- A. Depolarization occurs with Hypokalemia
- D. Changes in extracellular Na+ do not significantly affect Vm because Na+ conductance is so small in the resting cardiac cell
Myocardial ischemia results to which of the following?
A. K+ in the interstitial fluid that surrounds the affected muscle cells rises
B. Fast responses of cardiac muscle change to slow responses
C. K+ is lost from the ischemic cells
D. AOTA
D
How long does the phase 2 of fast response AP lasts?
0.1 - 0.2 second
The fast-response action potential amplitude (the membrane potential change during phase 0) is dependent on extracellular _______.
A. K+
B. Na+
C. Ca++
B. Na+
Note:
when extracellular Na+ is reduced from its normal value of approximately 140mEq/L to approximately 20mEq/L, the cell is no longer excitable.
What is the threshold level of cardiac myocytes? A. -90mV B. -65mV C. 140mV D. -93mV
B. -65mV
Note:
RMP of cardiac myocyte is approximately -90mV
The properties of the fast voltage-activated sodium channel are the basis of the refractory period of the action potential in cardiomyocytes. In what state of these channels result in absolute or effective refractory period wherein another action potential cannot be generated? A. Active state B. Open state C. Closed state D. Inactive state
D. Inactive state of fast Na+ channels = Absolute Refractory Period
Note:
Transition to closed state (phase 3: repolarization) = Relative refractory period (larger-than-normal depolarization of Vm to generate AP)
All channels are in Closed state (phase 4: resting level) = May be reopened by another depolarization of Vm to threshold
In the patch clamp technique demonstrating the ionic current through sodium channels, the starting current of -85mV was suddenly changed to _____ and was held constant for the remainder of the record.
-45mV
Sequence of results:
(1) one sodium channel opened (1.5 pA in amplitude), and then a second sodium channel opened (3 pA total current from both channels)
(2) both closed upon opening of the second channel
(3) both channels remained closed for approximately 4 or 5 msec, and then both channels opened at the same time
(4) one channel closed and then the second rapidly closed.
(5) after several seconds, one channel opened and then closed.
(6) both channels remained closed for the rest of the recording
What causes the phase 1 of fast-response AP? A. inward rectifier K+ current B. transient outward K+ current C. funny sodium channels D. slow Ca++ channels
B. Transient outward K+ current
Phase 1 is the Early repolarization phase cause by transient efflux of K+ from the cell
The phase 1 notch is prominent in the following location except: A. Epicardial region of LV wall B. Myocardial region of LV wall C. Endocardial region of LV wall D. Ventricular Purkinje fibers
C. The notch is negligible in myocytes from the Endocardial region of the left ventricle because the density of transient outward K+ channels is less in these cells.
Which drug blocks the potassium channels that carry transient outward K+ currents?
4-aminopyridine
Fampridine used in LEMS and MS
What are the three outward K+ currents that contribute to the final repolarization (phase 3) of the cardiac cell?
Transient K channels
Inward rectifier
Ik (specifically-activated K channels)
In _______ myocytes, in which the duration of the action potential is least, the magnitude of Ik is greatest.
endocardial
The converse applies to the midmyocardial myocytes. The magnitude of iK and the duration of the
action potential are intermediate for epicardial myocytes.
The ________ current does not participate in the initiation of repolarization because the conductance of these channels is very small over the range of Vm values that prevail during the plateau.
iK1 - inward rectifier
However, the ______ channels contribute substantially to the rate of repolarization once phase 3 has been initiated.
iK1 - inward rectifier
The steady inward leak of Na+ that enters the cell rapidly
during phase 0 and more slowly throughout the cardiac
cycle would gradually depolarize the resting membrane
voltage were it not for __________, which is located
in the cell membrane
Na+,K+-ATPase
Most of the excess Ca++ ions that had entered the cell mainly during phase 2 are eliminated principally by a ________
3Na+-Ca++ antiporter
which exchanges three Na+ ions for one Ca++ ion. However, some of the Ca++ ions are eliminated by an ATP-driven Ca++ pump.
Colocalization of these two channels therefore exerts a powerful effect on excitability and its regulation under normal and pathological conditions (arrhythmias)
Na v1.5 channels and inward-rectifying K (Kir2.1) channels
- these can be connected in a complex, or channelosome, with SAP97.
_______ is the most important process for transcapillary
exchange, and ________ is the least important.
Diffusion
Pinocytosis
(the other one is Filtration)
Fick’s law
for diffusion
J = −DA (ΔC/Δx)
where
J = quantity of a substance moved per unit time
D = free diffusion coefficient for a particular molecule
A = cross-sectional area of the diffusion pathway
ΔC = concentration gradient of the solute
Δx = distance over which diffusion occurs
For diffusion across a capillary wall, Fick’s law:
J = −PS(Co −Ci )
where
P = capillary permeability by the substance
S = capillary surface area
Co = concentration of the substance outside the capillary
Ci = concentration of the substance inside the capillary
(The PS product provides a convenient expression of available capillary surface area because the intrinsic permeability of the capillary is rarely altered much under physiological conditions.)
Limiting factor for movement of molecules across capillary wall:
Small molecules - ________
Large molecules - _________
Small is flow limited
Large is diffusion limited
CO2 loading and the resulting intravascular shifts in the
oxyhemoglobin dissociation curve occur in the _______
vessels.
precapillary
The ___________ represents a diffusional shunting of gas away from the capillaries; this shunting may limit the supply of O2 to the tissue at low blood flow rates.
Countercurrent exchange
Venous ends are more permeable than the arterial ends
(True or False), and permeability is greatest in the ___________, a property attributed to the greater number of pores in these regions.
True
venules
Pores are absent in ______ capillaries, where the blood-brain
barrier blocks the entry of many small molecules.
cerebral
________ is the principal force in capillary filtration.
Hydrostatic pressure
A given change in Pv produces a greater effect on
capillary hydrostatic pressure than does the same change in
Pa. (T/F)
True
__________, or, more specifically, _________ outside the capillaries, opposes capillary filtration.
Tissue pressure, interstitial fluid pressure (Pi)
The key factor that restrains fluid loss from capillaries is the ________ of plasma proteins (such as albumin).
Osmotic pressure
The _________ is the relative impediment to the passage of a substance (solute) through the capillary membrane.
reflection coefficient (σ)
actual oncotic pressure of the plasma (πp) is defined by the equation:
πp = σRTCp where σ = reflection coefficient R = gas constant T = temperature in degrees Kelvin Cp = plasma solute concentration
____ is a name for the behavior of charged particles near a semi-permeable membrane that sometimes fail to distribute evenly across the two sides of the membrane.
Gibbs-Donnan effect
Charge of albumin at normal blood pH (positive or negative)
negative
Resistance to flow formula
Poiseuille’s law
R=8η/πr^4
where
R = resistance, η = gas viscosity, I = length of airway, r = radius of airway
Threshold for Fast- and slow-response cardiomyocytes
Fast = -65mV Slow = -40mV
The phase 1 notch is negligible in myocytes from the _________ region of the left ventricle because the density of transient potassium channels is less in these cells.
Endocardial
Size of Phase 1 notch is prominent in myocytes in the epicardial and midmyocardial regions of the left ventricular wall (Fig. 16.5) and in ventricular Purkinje fibers. However, the notch is negligible in myocytes from the endocardial region of the left ventricle (see Fig. 16.5) because the density of ito channels is less in these cells.
What are the 3 ionic currents that mediate the slow diastolic depolarization in SA node?
Outward K+ current (Ik)
Hyperpolarization-induced inward current (If);
Inward Ca++ currents (ICa)
Funny Na+ current is activated at end repolarization in phase 3 as membrane becomes hyperpolarized beyond ___mV
-50mV
Mutations in ________ gene can cause greater hyperpolarization needed to open the funny sodium channels which may underlie sinus bradycardia and sick sinus syndrome.
HCN4
The idioventricular pacemakers in the Purkinje fiber network initiate the ventricular contractions, but at a frequency of only ________ beats per minute.
30 to 40
Overdrive suppression results from the activity of membrane ________ because when the overdrive suddenly ceases, the activity of this transporter does not slow instantaneously but temporarily remains overactive.
Na-K ATPase
A special pathway, the anterior interatrial myocardial band (or ____________), conducts the SA node impulse directly to the left atrium.
Bachmann’s bundle
Most common clinical disorder of accessory AV pathway
Wolff-Parkinson-White syndrome - bypass tract of myocardial fibers becomes an accessory pathway between the atria and ventricles.
Reentry loops in presence of accessory AV pathways causes continuous circling thus very rapid rhythm called ____________
Supraventricular Tachycardia
The presence of an __________ in atrial myocytes, but not in ventricular myocytes, contributes to greater K+ efflux and shorter action potentials in atrial myocytes.
ultrarapid K+ current (IKur)
Conduction times through which regions account for the delay between the start of the P wave and the QRS complex?
Atrionodal and Nodal regions
the other less delayed is the Nodal-His region
Abnormal prolongation of the AV conduction time is called a _______
first-degree AV block
The conduction pattern in which only a fraction of the atrial impulses are conducted to the ventricles is called a ____________
second-degree AV block
The conduction pattern in which none of the atrial impulses reaches the ventricles is called a __________
third degree, or complete, AV block
Which division of LBBB is thicker?
Posterior
What are the broadest cells, thus with the fastest conduction velocity, in the Heart?
Purkinje fibers
The last portions of the ventricles to be excited are the ________ regions and a small zone in the __________
posterior basal epicardial regions and a small zone in the
basal portion of the interventricular septum.
A necessary condition for reentry is that at some point
in the loop the impulse can pass in one direction but not
in the other. This phenomenon is called ____________
unidirectional block
When does Early After-depolarization occurs?
end of AP plateau (phase 2) or
midway through repolarization (phase 3)
When does delayed after-depolarization occurs?
Very end of repolarization or
just after full end of repolarization (phase 4)
EADs can be induced more readily in myocytes from the ___________ region of the ventricular walls
Midmyocardial region
Which gene underlies the development of atrial fibrillation?
The connexin 40 gene (GJA5)
As the action potential lengthens, EADs occur and cause triggered automaticity. In the electrocardiogram, this problem is manifested as __________, also called _________.
polymorphic ventricular tachycardia
or torsades de pointes
What are the clinical hallmarks of torsades de pointes?
Hypokalemia and Bradycardia
Thus, restoring extracellular K+ to normal levels and
increasing heart rate are two approaches used to overcome
the propensity for development of torsades de pointes.
The graphic display of the electrical impulse recorded in an ECG is
called a __________.
tracing
A recording of changes in the difference in potential between two points on the skin surface over time is called a ________.
scalar ECG
In ECG, the __________ is a measure of the time from the onset of atrial activation to the onset of ventricular activation
PR interval (or more precisely, the PQ interval)
Duration of PR interval
0.12 to 0.2 sec
Duration of QRS complex
0.06 to 0.10 seconds
Duration of P wave
0.08 to 0.10 seconds
Which part of the normal ECG is in the isoelectric line since the entire ventricular myocardium is depolarized, and so when ischemia is present, it would also present deviations?
ST interval
Duration of QT interval
0.20 to 0.40 seconds
In the standard ECG lead system, the vector sum of all cardiac electrical activity at any moment is called the ____________.
Resultant cardiac vector
Which lead records the potential difference between the right arm and the left leg?
Lead II
How to compute vector on Lead I?
Vector of LA minus Vector of RA
In normal individuals, the average mean electrical axis is approximately _______ degrees
+60
Hypertrophy of right ventricle will elicit what kind of axis deviation in ECG?
Right axis deviation
What is the negative lead for the augmented lead aVR?
Middle of the heart
What are the angles for the augmented limb leads’ axes?
aVF = +90 degrees aVL = -30 degrees aVR = -150 degrees
The mean electrical axis in ECG tends to shift toward which side in tall, thin persons?
Right,
the axis tends to shift toward the left (more horizontal) in short, stocky individuals and toward the right (more vertical) in tall, thin persons.
Leads can also be applied to the surface of the chest, so-called ________ leads, to determine the projections of the cardiac vector on the sagittal and transverse planes of the body.
precordial
What are the 2 types of premature depolarization?
Coupled Extrasystole
and
Ectopic foci usually producing Parasystole
What type of premature depolarization generally reflect reentry phenomenon?
Coupled extrasystole
If premature depolarization caused by an ectopic focus occurs at a regular interval or at an integral multiple of that interval, the disturbance is called _________.
parasystole
This is characterized by a bizarre, inverted QRS complexes and elevated T waves and is followed by a compensatory pause. (p.328 Berne, Fig 16.32)
Premature ventricular depolarization
This is characterized by an inverted P wave and normal QRS complexes and T waves. (p.328 Berne, Fig 16.32)
Premature atrial depolarization
What type of arrythmia is often a precursor of Ventricular Fibrillation?
Paroxysmal ventricular tachycardia
These abnormal triggered activities in the heart are either caused by prolonged AP or increased intracellular Ca++
After depolarization (early and delayed respectively)
These are irregular type of contraction of the heart that is ineffectual in propelling blood.
Fibrillation
These are waves found in ECG of Atrial fibrillation, in replacement to the normal P wave.
f waves
- continuous, uncoordinated rippling motion
- continuous irregular fluctuations in potential
When patients the atrial reentry loop and the pattern of AV conduction are more regular than they are in atrial fibrillation, the arrythmia is called ___________
Atrial flutter
Medications for patients with atrial fibrillation or flutter
Anticoagulants like Dicumarol to prevent formation of blood clots
What is the condition that shows prolonged the interval between the QRS complex and the T wave?
Long QT syndrome
The free __________ is the factor principally responsible for the contractile state of the myocardium.
intracellular [Ca++]
Does reducing extracellular Na+ or Na+ gradient increase contractile force of the heart?
Yes, because of NCX
reducing extracellular [Na+] causes less Na+ to enter the cell in exchange for Ca++
What protein in the sarcoplasmic reticulum normally inhibits Ca++-ATPase that when phosphorylated by PKA, this inhibitory action stops and uptake of Ca++ into the sarcoplasmic reticulum is enhanced, increasing relaxation of heart thus, increasing heart rate
Phospholamban
_______ is the force that stretches the relaxed muscle fibers, thereby increasing their resting length
Preload
______ is the force added to the muscle against which the contracting muscle must act
Afterload
