Electrocardiography Flashcards
Electrophysiology
Branch of physiology concerned with the recording and analysis of the electrical activity of the heart
Electrocardiogram
Recording of electrical potentials produced by cardiac tissues as recorded from the surface of the body
Electrogram
Graphic recording of electrical activity of heart from surface of heart
Instantaneous vector
Net voltage measured on the body surface
The algebraic sum of all the myocardial action potentials moving in many directions
Voltage of instantaneous vector
Number of cells being depolarized or repolarized at any instant
Direction of instantaneous vector
Depends on which anatomic regions of the heart is dominant at that instant
Series of instantaneous vectors representing the depolarization of the atria
P vector
Series of instantaneous vectors representing the depolarization of the ventricles
QRS Vector
Series of instantaneous vectors representing the repolarization of the ventricles
T vector
Instantaneous vectors are summarized as
Initial, Mean, and Terminal vectors
Average or mean vector
Mean magnitude, direction, and polarity for that time period
P vector initial
(AIR) anteriorly, inferiorly, rigtward
P vector mean
(AIL)Anteriorly, inferiorly, leftward
P vector terminal
Posteriorly, inferiorly, leftward
QRS vector initial
Anteriorly, inferiorly, rightward
QRS vector
Posteriorly, inferiorly, leftward
QRS vector terminal
Posteriorly or anteriorly, inferiorly or superiorly, leftward or rightward
T vector
Posteriorly, inferiorly, leftward
Cancellation effects
90% of the vectors during cardiac depolarization and repolarization are directed in opposite directions
Plane of view by limb leads
Frontal plane
Plane of view for chest leads
Horizontal or transverse plane
Bipolar limb leads
Diff of electrical potential between two sites, Leads I-III
Lead I
+ left arm, - right arm
Lead II
+left leg, - right arm
Lead III
+left leg, - right arm
Einthoven triangle
Apices: shoulders and pubic region
Central battery: heart
Triaxial reference figure of Bayley
Unipolar limb leads
Potentials are compared to 0 and not to another potential
Lead aVR
Right arm
Lead aVL
Left arm
Lead aVF
Left foot
Hexaxial reference figure
Incorporation of axes of all limb leads
V1 and V2
Anterior; facing epicardial surface of right ventricle
V3 and V4
Septal; transition zone
V5 and V6
Faces the epicardial surface of left ventricle; lateral
Electrographic paper horizontal lines
Time; 1mm = 0.04 sec
Electrographic paper vertical lines
Voltage; 10mm = 1mV
Recording speed of electrocardiograph
25mm per second
P wave
<0.10 sec; amp = 2-3mm
T wave
<5mm for limb leads
<10mm for chest leads
0.10-0.25 sec
U wave occurence
Sinus bradycardia, hypokalemia, quinidine therapy
PR interval
0.12-0.2 sec; prolonged in AV block
QRS interval
<0.10 sec for limb leads
<0.11 sec for chest leads
QT interval
Ventriclular electric systole; 0.28-0.45seconds
ECG provides insights on
Anatomic orientation of the heart
Relative sizes of cardiac chambere
Variety of disturbances of rhythm and conduction
Extent, location, and progress of ischemic changes to myocardium
Effects of altered electrolyte concentrations and influence of certain drugs
The ff should be examined in an ECG
Rhythm, Rate,P wave, QRS complex, T wave, PR interval, QRS interval, ST segment, Mean elctrical axis
Left axis deviation
If axis < -30 degrees
Occurs in short stocky people and in left ventricular hypertrophy
Right axis deviation
> +90 degrees
Occurs in tall and thin people and in Right ventricular hypertrophy
