Lecture 8 Flashcards
What is the SA composed of?
special cardiac muscle fibers
What do SA fibers connect directly to?
atrial fibers
The AV node receives signal from SA node ____ seconds after origin
.03
Signal is delayed in AV node for _____ sec
.09
A final delay of _____ sec occurs in the penetrating bundles
.04
There is a _____ sec delay from the initial origin of the signal onset of ventricular contraction
.16
What is the resting membrane potential of SA node fiber
-55 to -60 mV
Fast sodium channels are already ______ at resting membrane potential of SA node. Slow sodium-calcium channels can _____
inactivated (blocked); open
What is ventricular fiber resting potential?
-85 to -90 mV
What is generated by action potentials in the SA node?
sinus rhythm
Action potentials that originate anywhere else are said to from an ______
ectopic focus or pacemaker
Where is the vagus nervous distributed?
SA and AV nodes
What is the neurotransmitter of vagus nerve?
acetylcholine
What does acetylcholine do to heart rate?
decreases rate of rhythm of SA node
Acetylcholine ________ excitability of the AV junctional fibers, _______ transmission of the cardiac impulse into the ventricles
decreases; slowing
What increase permeability of fiber membranes to potassium ions?
acetylcholine
Where is sympathetic innervation distributed to?
all parts fo the heart, mainly the ventricles
What is the neurotransmitter of sympathetic innervation?
norepinephrine
What does norepinephrine do?
stimulates beta 1 adrenergic receptors
increases depolarization rate
may increase permeability of fiber membranes to sodium and calcium ions
What is the P wave?
atrial depolarization
What is the QRS wave?
ventricular depolarization
What is the T wave?
ventricular repolarization
When does the P wave occur?
beginning of the contraction of the atria
When does the QRS complex occur?
at the beginning of the contraction of the ventricles
When does repolarization of the ventricles?
end of the T wave
How long is the P-Q (P-R) interval?
0.16 sec
How long is the Q-T interval?
0.35 sec
The negative terminal of the recording limb lead I is connected to where?
right arm
The positive terminal of the recording limb lead I is connected to where?
let arm
The recording limb lead I looks at what?
heart from left to right
The negative terminal of ECG of the recording limb lead II is connected to where?
right arm
The positive terminal of ECG of the recording limb lead II is connected to where?
left leg
Recording limb lead II looks at what?
heart from upper right to lower left
The negative terminal of recording limb III is connected to where?
left arm
The positive terminal of recording limb III is connected to where?
left leg
The recording limb III looks at what?
heart from upper left to lower leg
What is Einthoven’s triangle?
two arms and left leg form apices of triangle
Normally in the ventricles, current flows from _______ to _____ primarily in the direction from the base of the heart toward the apex for most of the heart cycle until the very end
negative to positive
The electrode nearer the base is ______ and the electrode nearer the apex is _____
negative; positive
In the recording limb lead I where the right arm connects to the Ches is negative with respect to the point where the left arm connects, the ECG records ______
positive
In recording limb lead II when the right arm is negative with respect to the left leg, the ECG records
positive
In recording limb lead III when the left arm is negative with respect to the left leg, the ECG records
positive
What is a vector?
an arrow that points in the direction of the electrical potential generated by the current flow, with the arrowhead in the positive direction
Length of the arrow of a vector is drawn ______ to the voltage of the potential
proportional
Axis for Lead I
two electrodes on two arms
R= negative
L= positive
What is the direction of the axis for lead I?
0 degrees
What is the axis for lead II?
electrodes on right arm and left leg
A: negative
L: positive
What is the direction fo the axis for lead II?
60 degrees
What is the axis for lead III?
electrodes on left arm and left leg
A: negative
L: positive
What is the direction of the lead for lead III?
120 degrees
When the vector in the heart is in a direction almost ______ to the axis of the lead, the voltage recorded in the ECG of this lead is very _____
perpendicular; low
When the heart vector has almost the ____ axis as the axis of the lead, the entire voltage of the vector will be _____
same; recorded
The ______ vector of the generated potential at a particular instant is called the _________ mean vector
summated; instantaneous
The reference vector is ______ and extends toward a person’s ______ side; this reference direction= _____ degrees
horizontal; left; 0
The QRS vector is about _____ degrees in relation to the zero reference point
+59
What is the greatest portion of ventricular mass to repolarize first?
entire outer surface of the ventricles, especially near the apex
What areas of the T wave normally repolarize last?
endocardial areas
Ventricular vector during repolarization is _____ the apex of the heart
toward
Normal T-wave in all three bipolar leads is ____
positive
Where does atrial depolarization begin?
sinus node
Where is vector direction in the p-wave?
in the direction of the axes of the three standard bipolar limb leads
True or false: the ECG is normally negative in all three leads in the p-wave
false, they are usually positive
Spread of depolarization through atrial muscles is _____ than in the ventricles
slower
In the atrial t-wave the ________ area is the first part to become depolarized
sinus node
In the atrial t-wave at the beginning of repolarization the sinus node is _____ with respect to the rest of the atria
postive
Atrial t-wave is almost always obscured by what?
QRS wave
What are abnormal ventricular conditions that cause axis deviation?
change in position of heart in the chest hypertrophy of one ventricle bundle branch block fluid in pericardium pulmonary emphysema
What is the most common cause increased voltage in the standard bipolar leads?
hypertrophy of the ventricle
What decreases voltage in abnormal voltages of the QRS complex?
caused by cardiac myopathies
caused by conditions surrounding the heart
How long does the normal QRS lasts?
0.06 to 0.08 seconds
in hypertrophy or dilation of the left or right ventricle, QRS may be prolonged to _______
0.09 to 0.12 seconds
What are the abnormalities causing current of injury?
mechanical trauma
infectious processes
ischemia
What are the effect of current of injury on the QRS complex?
abnormal negative current flows from infarcted area and spreads toward the rest of the ventricles
What is the J point?
reference point for analyzing current of injury
Where does the J point occur?
at the end of the QRS wave and is the point at which all parts of the ventricle become depolarized (including the injured areas)
