Lecture 7 Cardiac Flashcards
Limb Lead I
Negative terminal is connected to the right arm
positive terminal is connected to the left arm
Looks at the heart form left to right
Limb Lead II
Negative terminal of ECG is connected to the right arm
Positive terminal of ECG is connected to the left leg
Looks at heart form upper right to lower left
Limb lead III
Negative terminal is connected to the left arm
Positive terminal is connected to the left leg
Looks at heart from the upper left to lower left
Einthoven’s triangle
Two arms and left leg form apices of triangle
Einthoven’s law
If the electrical potentials of any two of the three bipolar limb ECG leads are known at any given instant, the third can be determined by summing the first two
Normally in the ventricles current flows?
form negative to positive primarily in the direction form the base of the heart toward the apex for most of the heart cycle until the very end
In recording limb lead I: when the point where the right arm connects to the chest is negative with respect to the point where the left arm connects, the ECG records _______?
Positive
In Limb lead II: when the right arm is negative with respect to the left leg the ECG records _________?
Positive
Limb Lead III: When the left arm is negative with respect to the left leg, the ECG records _____?
Positive
What is the angle for Lead I
0 degrees
what is the angle for Lead II
60 Degrees
what is the angle for Lead III
120 degrees
In term of ECG the a vector is what
an arrow that points in the direction of the electrical potential generated by the current flow, with the arrowhead in the positive direction.
The length is proportional to the voltage of the potential
When the vector in the heart is in a direction almost perpendicular to the axis of the lead, the voltage recorded in the ECG of this lead is very _____
low
When the heart vector has almost the same axis as the axis of the lead, the _____ voltage of the vector is recorded
Entire
What is the instantaneous mean vector
The summated vector of the generated potential at a particular instant
_____ is horizontal and extends towards a person’s left side
Reference vector
What is reference direction
0 degrees
reference vector is horizontal and extends towards a person’s left side
what is the mean electrical axis of the heart
+ 59 degrees
what results in the apex of the heart remaining positive with respect to the base of the heart
The average direction of the vector during spread of the depolarization wave through the ventricles
T-Wave Vectorial Analysis
what repolarizes last
Endocardial areas
T-Wave Vectorial Analysis
Ventricular vector during repolarization is toward ?
The apex of the heart
The normal T-wave in all three bipolar leads is ______
Positive
T-Wave Vectorial Analysis
what is the greatest portion of ventricular mass to repolarize first?
The entire outer surface of the ventricles, especially near the apex
Atrial depolarization begins where
at the Sinus node
The P-wave is normally ____ in all three leads
positive
Vector direction of the P-wave is generally in what direction
direction of the axes of the three standard bipolar limb leads
The spread of depolarization is slower where
In the atria than in the ventricles
The Atrial T-wave is almost always obscured by what
The QRS complex
what is the first area to become repolarized
The sinus node area
At the beginning of repolarization the sinus node is ______ with respect to the rest of the atria
Positive
A typical ECG may utilize how many leads
12 leads
Each lead provides what
A different perspective on the voltage differences between areas of the heart
In addition to the three conventional leads what are the additional leads in a common 12 lead
six standard leads (V1-V6)
three augmented leads (aVR, aVL, aVF)
what is the mean electrical axis
is the direction of the electrical potential (negative to positive) form the base of the ventricles toward the apex
59 degrees
what are some abnormal ventricular conditions that cause mean electrical axis deviation
Change in position of the heart in the chest hypertrophy of one ventricle bundle branch block fluid in pericardium pulmonary emphysema
When is a high-voltage ECG said to occur and what is the most common cause
when the sum of the voltages of all the QRS complexes of the three standard leads is greater than 4 mV
most common cause is hypertrophy of the ventricle
What are the most common causes of decreased voltages in an ECG
cardiac myopathies,
caused by conditions surrounding the heart
The normal QRS lasts how long
0.06 to 0.08 seconds
Hypertrophy or dilation of the left or right ventricle can lead to the QRS?
being prolonged to 0.09 to 0.12 seconds (nl QRS duration is 0.06-0.09 seconds)
what are some conditions that can cause bizarre patterns of the QRS
Destruction of cardiac muscle and replacement by scar tissue
multiple small local blocks in the conduction impulses at many points in the Purkinje system
Different cardiac abnormalities cause part of the heart
To remain partially or totally depolarized all the time
Current of injury flows?
between the pathologically depolarized and the normally polarized areas, even between heartbeats
what are some abnormalities that cause current of injury
Mechanical trauma, infectious processes, Ischemia (most common cause)
What is the most common cause for current of injury
Ischemia
What are the effects of current of injury on QRS complex
Abnormal negative current flows from infarcted area and spreads toward the rest of the ventricles
What is a J point
reference point for analyzing current of injury
occurs at the very end of the QRS complex and is the point at which all parts of the ventricle, including the injured areas, have become depolarized
