Blake_Physio_07_Heart Rhythmicity Flashcards
SA node: definition, loccation and connections
Sinoatrial Node
Special Cardiac Muscle Fibers
SA fibers connect directly to atrial fibers
AV node: definition
Receives signal ______ sec after origin
Signal is delayed in AV node for ________ sec
final delay of ____ sec in penetrating bundles
=> there is a ____sec delay from the initial origin of the isgnal until the onset of ventricular contraction
Atrioventricular Node
- 03
- 09
- 04
- 16
Why is signal delayed in the AV node for 0.09 sec?
Due to the small size of cells, low amplitude of AP, and slow rate of depolarization during excitation.
CONDUCTIVE SYSTEM OF THE HEART:
Slow conduction is caused mainly by diminished numbers of _____________ along the pathway resulting in an _____________ in the __________ to ___________
Gap junctions
increase
resisitance
conduction
Resting membrane potential of SA node fiber:
-55 to -60mV (threshhold~-40mV)
At resting potential, the Fast sodium channels in the SA node are____________
inactivated
Inactivation gates close when the membrane potential of the SA node is __________________.
As a result, only ______ ______-_____ channels can open.
THEREFORE: (2 things)
less than -55mV
slow sodium-calcium
- atrial nodal AP is slower to develop
- repolarization is slower
What causes the SA node to reach threshold on its own?
slow leak of sodium Ions back into cells
Sodium-calcium channels in the SA node are inactivated within _____ to _______ msec after opening
100-150
Resting membrane potential of SA node fiber:
Large numbers of _________ channels open at the time the __________-________ channels become ________
Nodal cells become ____________
Potassium channels remain __________ for a few tenths of a second
potasium, sodium-calcium, inactivated
repolarized
open
Ventricular fiber resting potential:
=85 to -90mV
Sinus Rhythm
AP originating in the SA node
Action potentials that originate anywhere other than the SA node are said to be from an ________ or ________
ectopic focus or pacemaker
What parasympathetic nerve can modulate heart rate?
What result does parasympathetic innervation have on the heart?
Vagus nerve
Decreased heart rate
What receptors does acetylcholine affect on the heart?
- Muscarinic receptors on the SA and AV nodes
What effect does acetylcholine have on the SA node?
decreases rate of rhythm (negative chronotropic effect)
What effect does acetylcholine have on the AV node?
Decreases excitability of the AV junctional fibers, slowing transmission of the cardiac impulse into the ventricles.
How does acytlycholine generally accomplish it’s functions in cardiac tissues? (2 things)
- Increases permeability of fiber membranes to potassium ions
- Hyperpolarization: -65 to -70mV
How does sympathetic innervation by norepiniphrine effect cardiac tissue? (3 things)
- stimulates beta-1 adrenergic receptors
- increases depolarization rate (positive chronotropic effect)
- may increase permeability of fiber membranes to sodium and calcium ions
Where is norepinephrine distributed to the heart by sympathetic nerves?
All parts of the heart, mainly the ventricles.
In an ECG Depolarization is represented by the_ _ _
P and QRS waves
ECG: P wave represents
QRS wave represents
T wave represents
Atrial depolarization
Ventricular depolarization
Ventricular repolarization
In an ECG, why is there no wave representing Atrial repolarization?
because it is obscured by the QRS wave
An ECG measures ______________
Extracellular potential
Deflection from 0 occurs only when there is __________ between regions of the heart. Current flows between ________ of different _____________.
current flow
regions
membrane potentials
Because atrial musculature and ventricular musculature are _________ _________, current flow does not occur when only the ________ and the _______ have different _______.
electrically isolated
atria
ventricals
potentials
Monophasic action potential of the ventricular muscle:
Depolarization and Repolarization both register as positive.
in an ECG, no potential is recorded when the ventrical is:
completely polarized
completely depolarized
Normal ECG: P wave occurs at the beginning of the contraction of the ______. QRS complex occurs at the beginning of the contraction of the __________. Repolarization of the _______ occurs after the end of the _______.
atria
ventricals
ventricals
T-wave
how long is the P-Q interval?
0.16 sec
How long is the Q-T interval?
0.35 sec
Three bipolar limb leads:
I
II
III
I - neg to R-arm; pos to L-arm; Left to Right
II - neg to R-arm; pos to L-leg; upper right to lower left
III - neg to L-arm; pos to L-leg; upper left to lower left
Two arms and left leg form ________ triangle
Einthoven’s
Einthoven’s law:
If the electrical potentials of any two of the three bipolar limb leads are known at any givan instant, the third can be determined by summing the first two.
Normally, in the ventricals, current flows from ______ to the ________ in the direction of the _______ of the heart to the _________ for most of the heart cycle until the very end.
negative to positive
base to apex
Axis for ECG bipolar limb leads:
I
II
III
I - 0
II - 60
III - 120
The QRS vector: name and angle
mean electrical axis
59 degrees
T-Wave:
Greatest portion of ventricular mass to repolarize first is the entire_____________ of the _________, especially near the _________.
outer surface
ventricles
apex
T-Wave:
Endo cardial areas normally repolarize ________
last
T-wave:
Ventricular vector during repolarization is toward the ______ of the _________
apex of the heart
T-wave:
Normal T-wave in all three bipolar leads is ________
positive
P-wave:
Atrial depolarization begins in the ________
Sinus Node
P-wave:
Vector direction is generally in the ________of the axes of the three standard bipolar limb leads.
same direction
P-wave:
ECG of P-wave is normally _______ in all three leads
positive
Atrial T-wave:
Spread of depolarization through atrial muscle is ________ than in ____________
slower than in ventricles
Atrial T-wave:
Musculature around the sinus node becomes __________ a long time _______ the musculature in the distal parts of the atria.
depolarized
before
Atrial T-wave:
The ___________ area is the first part to become repolarized.
sinus node
Atrial T-wave:
At the beginning of repolarization, the sinus node is ___________ with respect to the rest of the atria.
positive
Atrial T-wave:
Atrial T-wave is almost always ________ by the QRS wave.
obscured
A typical ECG may utilize ___ leads.
Each lead provides a _______ _______ on the _____ _________ between areas of the heart.
In addition to the three bipolar (conventional leads) there are:
12
different perspective
voltage difference
6 standard leads (V1-V6)
Three augmented Leads (aVR, aVL, aVF)
The mean electrical axis is the direction of _________________ from the __________ to the _______
electrical potential
base of the ventricals to the apex
5 abnormal ventricular conditions that cause axis deviation:
- Change in position of the heart in the chest
- hypertrophy of one ventrical
- bundle branch block
- fluid in pericardium
- pulmonary emphysema
Abnormal Voltages of QRS complex:
In creased voltage in the standard bipolar leads: (2 things)
(1 measurement, 1 cause)
- High-voltage ECG is said to occur when the sum of the voltages of all QRS complexes of the three standard leads is greater than 4mV.
- Most common cause is hypertrophy of the ventricle.
Abnormal Voltages of QRS complex:
Decreased Voltage: (2 causes)
cardiac myopathies
conditions surrounding the heart
Hypertrophy or dilation of the left or right ventricle, QRS may be prolonged to _____ to _____ sec
0.09 to 0.12 sec
Conditions causing bizarre QRS complexes:
- Destruction of cardiac muscle and replacement by scar tissue.
- Multiple small local blocks in the conduction impulses at many points in the Purkinje system.
Currents of injury:
Different cardiac abnormalities cause part of the heart to remain ________ or _______ ______ all the time
partially or totally depolarized
_______ of ______ flows between the pathologically depolarized and the normally polarized areas, even between heart beats.
current of injury
Abnormalities causing current of injury: (3)
Mechanical Trauma
Infectious Processes
Ischemia (most common)
Effect of current of injury on QRS complex:
Abnormal negative current flows from infarcted area and spreads toward the rest of the ventricles.
J point =
reference point on ECG for analyzing current of injury.
