Lecture 7 Starting at Vectors Flashcards
A ________ is an arrow that points in the directionof the electrical potential generated by the _______ flow, with the arrowhead in the _______ direction
Vector
Current
Positive
Axis for lead I (both arms), what do the following equal?
R-arm = ?
L-arm = ?
Direction of Lead = ?
R = negative
L = positive
Direction of lead = 0 degrees
Axis for lead II (r-arm and l-leg), what do the following equal?
Arm = ?
Leg = ?
Direction of Lead = ?
Arm = negative
Leg = positive
Direction of Lead = 60 degrees
Axis for lead III (l-arm and l-leg), what do the following equal?
Arm = ?
Leg = ?
Direction of Lead = ?
Arm = negative
Leg = positive
Direction of Lead = 120 degrees
When is the voltage recorded in the ECG very low?
when the vector in the heart is in a direction almost perpendicular to the axis of the lead
What happens when the heart vector has almost the same axis as the axis of the lead?
The entire voltage of the vector will be recorded
What do we call the summated vector of the generated potential at a particular instant?
Instantaneous mean vector
With respect to the base of the heart, the apex of the heart remains ______ as a result of the depolarization wave through the ventricles
Positive
What is the mean electrical axis of the heart?
59 degrees
The direction of the electrical potential (- to +) from the base of the ventricles toward the apex
In T-waves, what is the greatest portion of ventricular mass to repolarize first?
The entire ouster surface, especially near the apex
In T-waves, what areas normally repolarize last?
Endocardial
In T-waves, where is the ventricular vector during repolarization?
Towards the apex of the heart
Is the normal T-wave in all three bipolar leads positive or negative?
Positive
In the P-wave, where does atrial depolarization begin?
Sinus node
In the P-wave, what direction is the atrial vector generally in?
In the direction of the axes of the three standard bipolar limb leads
P-wave ECG is normally _____ in all three leads
positive
In atrial T-wave, is the spread of depolarization through the atrial muscle faster or slower than in the ventricles?
Slower
In the atrial T-wave, what is the first part to become repolarized?
Sinus node
What is different about each lead?
Each lead provides a different perspective on the voltage differences between areas of the heart
Name abnormal ventricular conditions that cause axis deviation (5):
Change in position of heart in the chest Hypertrophy of one ventricle Bundle branch block Fluid in pericardium Pulmonary emphysema
High-voltage ECG is said to occur when the sum of the voltages of all the QRS complexes of the three standard leads is greater than ____
4 mV
What is the most common cause of High-Voltage ECG?
Hypertrophy of the ventricle
What causes decreased voltage in the standard bipolar leads?
Cardiac myopathies
Conditions surrounding the heart
How long does a normal QRS last?
0.06 to 0.08 seconds
