Term
| describe the charge of heart muscle during resting and active states and what affect this has on the electrical current in the heart. |
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Definition
during the resting state cells are negatively charged, and positively charged during active state (due to depolarization)
this causes the wave of depolarization (contraction) to flow through the heart as a positively charged current |
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Term
| what direction is a positive / negative current deflected on an EKG? |
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Definition
positive current is deflected upward
negative current is deflected downward |
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Term
| what two functions do the AV valves perform? |
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Definition
to prevent backflow of blood into the atria
and to electrically isolate the ventricles from the atria |
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Term
| where is the only place electrical activity is allowed to pass between the atria and ventricles and where is it located? |
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Definition
| the AV node, in the interventricular septum at the level of the AV valves |
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Term
| what purpose does the AV node serve? |
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Definition
| to delay the electrical impulse to the ventricles in order to allow for adequate filling of the ventricles |
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Term
| describe the components of the QRS complex and what does it represent. |
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Definition
the Q wave is the initial negative deflection
the R wave is the positive deflection
and the S wave is any negative deflection following the positive deflection
it represents a depolarization of all of the ventricular myocardium |
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Term
| what is the duration of a typical QRS segment? |
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Definition
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Term
| what does the T wave represent and which way is it deflected? |
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Definition
| it represents ventricular repolarization and in most cases is in the same direction as the QRS complex |
|
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Term
| describe the depolarization / repolarization direction of the myocardium and what affect this has on EKG wave deflection. |
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Definition
depolarization occurs from endocardium to epicardium and repolarization occurs from epicardium to endocardium
the two functions are oppositely charged moving in opposite directions and therefore cause identical deflection on the EKG |
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Term
| what does the P wave represent and which way is it deflected? |
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Definition
| it represents atrial depolarization and causes a deflection in the same direction as the QRS |
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Term
| what does the PR interval represent and why is there no atrial repolarization wave? |
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Definition
it represents the AV nodal delay
because it is buried in the QRS segment |
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Term
| how are the different phases of the ventricular AP curve represented on an EKG? |
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Definition
phase 0-1 corresponds with the QRS segment
phase 2 corresponds with the ST segment
phase 3 corresponds with the T wave
phase 4 corresponds with the T-P and P-R intervals |
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Term
| at what speed does an EKG strip normally move and therefore how fast between small and large blocks? |
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Definition
25mm/sec
0.04 sec per small block
0.2 sec per large block |
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Term
| where are the three limb leads located and which direction are they oriented? |
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Definition
lead I is neg on the right arm and pos on the left arm
lead II is neg on the right arm and pos on the left foot
lead III is neg on the left arm and pos on the left foot |
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Term
| describe the different configurations for augmented limb leads and what do they measure. |
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Definition
augmented limb leads attach a positive electrode to one of the limbs (right or left arm, or left foot), and negative electrodes to the other two limbs. the opposite end of each electrode is attached to the corresponding pole on the EKG device.
these leads are designated aVF, aVR, and aVL for left foot, and right and left arms respectively
they allow for the electric potential to be measured in the direction of the positive lead |
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Term
| which leads are termed the "lateral" leads and which the "inferior" leads and why? |
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Definition
lateral - leads I and aVL
inferior - leads II, III, and aVF
because they look at the lateral and inferior sides of the heart, respectively |
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Term
| what are the chest leads and why are they important? |
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Definition
they are designated V1-V6
they establish another dimension for viewing the electrical activity in the heart, the horizontal (or transverse) plane, in addition to the frontal plane established by the limb and augmented leads |
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Term
| true or false, all of the chest leads are positive leads? |
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Definition
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Term
| describe the progression of the QRS complex from V1 to V6. |
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Definition
| the QRS complex evolves from V1 with a small R wave and large S wave to V6 with a large R wave and small S wave |
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Term
| what parts of the heart do the different chest leads look at? |
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Definition
V1 and 2 look at the right ventricle
V5 and 6 look at the left ventricle
and V3 and 4 look at the interventricular septum |
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Term
| what is the first measurement taken when reading and EKG and how is it measured? |
|
Definition
rate
from R wave to R wave, each large block represents 200ms and each small wave 40ms
progression is (300, 150, 100, 75, 60, 50...) |
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Term
| which lead is usually displayed at the bottom for measuring heart rhythm? |
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Definition
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Term
| how is the EKG axis determined and what does it show? |
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Definition
the axis is determined by the deflection of the QRS segment in leads I and aVF (should be positive in both)
the axis is the overall direction of the electrical stimulus within the heart, due to the larger size of the left ventricle the overall direction should be down and to the (pt's) left |
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Term
| how are abnormal axis deviations read on an EKG? |
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Definition
in extreme RAD leads I and aVF will be neg
in RAD lead I will be neg and aVF will be pos
in LAD lead I will be pos and aVF will be neg
(normal axis both I and aVF are pos) |
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Term
| how is EKG right/left axis rotation determined? |
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Definition
| based on the "transitional zone" in which the R and S waves deflect approximately equal on chest leads V3 and 4. if the transitional zone occurs before V3 it is rightward (or counterclockwise) rotation, and if it occurs after V4 it is lefward (or clockwise) rotation |
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Term
| what feature functions as the tail for the QRS vector and also the center of a circle surrounding the heart when determining EKG axis? |
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Definition
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Term
| what information can be gathered from EKG axis? |
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Definition
| position of the heart, hypertrophy, and infarction |
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Term
| what does an isoelectric QRS segment mean? |
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Definition
| that the direction of depolarization occurs perpendicular to the lead |
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Term
| how is atrial enlargement determined on an EKG? |
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Definition
| looking at lead V1 (directly over atria) a diphasic P wave indicates enlargement |
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Term
| how do you determine which atria is enlarged on an EKG? |
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Definition
| which atria is enlarged is determined by the size of each component of the P wave, if the initial component is larger it is right atrial enlargement, and if it is the terminal component it is left atrial enlargement |
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Term
| which components on a diphasic P wave are usually positive and which negative? |
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Definition
| the initial component is usually positive, and the terminal component is usually negative |
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Term
| how is right ventricular hypertrophy determined on an EKG? |
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Definition
| looking at lead V1 the R component of the QRS complex is much larger than the S component and the R wave gets progressively smaller in V2-4 |
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Term
| how is left ventricular hypertrophy determined on an EKG? |
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Definition
there is a large S wave in V1 and a large R wave in V5
adding the depth of the S wave and height of the R wave, a sum greater than 35mm indicates LVH |
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Term
| what is the myocardial infarction triad and is it necessary for all three to be present to diagnose an MI? |
|
Definition
ischemia, injury, necrosis
no |
|
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Term
| what is the characteristic sign of ischemia on an EKG and where is it read? |
|
Definition
an inverted symmetrical T wave
it is found easiest in the chest leads |
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Term
| what does ST elevation on an EKG signify? |
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Definition
acute injury such as myocardial infarction
it is usually the earliest sign of infarction on an EKG |
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