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62 Cards in this Set
- Front
- Back
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What does an EKG detect?
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The polarization and repolarization of myocardial cells aka when intracellular potential flips from negative to pos then back
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What are cardiac vectors?
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The magnitude and direction that the wave of depolarization is travelling across heart. It is perpendicular to margin btwn pos and neg areas
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Can the magnitude and direction of cardiac vectors change during cardiac cycle?
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Yes
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Define a dipole.
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A positive and negative charge seperated by a small distance
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Define a vector
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A physical quantity that has magnitude and direction
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What increases the magnitude of a cardiac vector?
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The length of the border of dipoles.
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What plane do EKG's project the 3D cardiac vectors within?
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Frontal for limb leads and transverse for chest leads
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What leads read cardiac cycle in frontal plane? Transverse plane?
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Bipolar limb leads=Enthoven leads=I,II,III
Augumented unipolar limb leads=augumented leads=avR, avL, avF -R, L, F denote which extremity is hooked to a terminal of its own Chest leads are transverse visualizing |
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What do leads read?
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Potential difference between 2 points
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Where are the apicies of Einthovens triangle? And where does cardiac vector lie?
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Shoulders and pubic region,
in middle of E's triangle |
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What increases the magnitude of a cardiac vector?
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The length of the dipole border between positive and negative areas
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What leads read cardiac cycle in frontal plane? Transverse plane?
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Frontal) Bipolar limb leads=Enthoven leads=I,II,III
Augumented unipolar limb leads=augumented leads=avR, avL, avF -R, L, F denote which extremity is hooked to a +-ve terminal Transverse=Chest leads V1-V6 |
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What do leads read?
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Potential difference between 2 points
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Where are the apicies of Einthovens triangle? And where does cardiac vector lie?
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Shoulders and pubic region,
in middle of E's triangle |
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What are the arrangments of charges at the apices and limb leads at the sides of E's triangle?
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Upper rt shoulder(rt arm lead reads)=Neg,Neg poles
Upper left shoulder(L arm lead reads=Pos,Neg poles Pubic region(LL lead reads)=Pos,Pos poles I=top II=right III=left |
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How does a depolarization traveling toward a positive electrode trace on an EKG?
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Upward deflection
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What does a depolarization traveling toward negative leads read as? Why?
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Downward deflection, B/c its traveling away from the positive
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Why are QRS waves usually upward EKG deflections in bipolar limb leads?
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Because during QRS wave heart depolarization moves from neg to pos in all 3 bipolar leads
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What is Einthovens Law?
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QRS magnitude of Leads I+II= magnitude of III
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What direction does the aVR lead deflection go? Why?
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p-wave, QRS, t-wave all negative(downward)
Atrial\ventricular depolarization and ventricular repolarization all away from lead |
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What directions do the P and T waves and the QRS complex deflect in aVL and aVF limb leads? Why?
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Positive(Upward), ventricular depolarization toward leads
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What do aVF, aVR, aVL denote with respect to pos electrode placment?
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Positive electrode on foot, right arm, left arm and by convention the other 2 leads are negative
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What leads make up the 6 intersecting limb leads of and EKG?
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bipolar limb leads and augumented unipolar limb leads
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What is the only unipolar limb lead with a negative\downward set of deflections?
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aVR
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What are the lateral limb leads? And why are they called lateral?
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aVL and I because the positive charges point laterally
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Which EKG leads are the inferior limb leads? And why are they called "inferior"?
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II, III, aVF becuase their polar charge is directed inferiorly
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Are chest leads unipolar or bipolar? Charge?
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Unipolar, positive
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Where is the transverse plane that chest leads visualize?
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4th to 5th intercostal space
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Which chest leads are located over:
RS of heart interventricular septum(R\L bundle branches) LS of heart |
RS V1 and V2
IVS V3 and V4 LS V5 and V6 |
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Which lead is closer to the LV, V3 or V4?
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V4
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Which chest lead tracing is mostly negative? Mostly positive?
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V1-neg
V6-pos |
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Why do we want to determine the vectors from EKG traces?
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To see mean axis of deviation aka mean axis of depolarization
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WHat can the axis of deviation tell you?
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Hypertrophied side of the heart
hypertrophy=inc depolarization QRS vector mean toward hypertrophied side |
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When would you see RV hypertrophy?
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Chronic lung disease, tall thin people
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When would you see LV hypertrophy?
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Pregnancy, obesity
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How do you determine the mean vector for a given wave?
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magnitude of positive deflections + sum of magnitudes of negative deflections in a given wave= mean vector of wave
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How can an EKG be affected by a fever?
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Fever= increased temperature which increases heart rate
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What are the 3 branches of the SA node?
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Posterior, Middle, Anterior Internodal tracts and Bauchmans bundle to Left Atrium
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How does breathing affect the rate of SA node firing?
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Inspiration increases FR
Expiration decreases FR |
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Depolarization of which SA branch is not seen on and EKG?
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Bauchmanns Bundle to left atrium
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What does the P wave represent?
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Atrial depolarization
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What are the 3 types of foci that can take over pacemaker potential if SA node fails?
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Atrial Automaticity foci
Junctional Automaticity foci Ventricular Automaticity foci |
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Where are Atrial automaticity foci located?
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In atrial conduction system
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Where are junctional automaticity foci located?
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In the middle and distal AV node
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Where are Ventricular automaticity foci located?
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In the bundle of his and bundle fibers
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What is another name for automaticity foci?
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ectopic foci
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What are the automaticity ranges for the 4 automaticity foci?
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Ventricular AF=20-40
Junctional AF=40-60 Atrial AF=60-80 SA node=72 bpm |
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What is overdrive supression?
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Concept that faster pacemakers suppress slower ones
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Where is the PQ interval on an EKG trace?
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Beginning of P wave to beginning of Q wave
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Where is the QT interval on EKG trace?
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Beginning of Q wave to end of T wave
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Where is the ST segment on a EKG trace?
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End of QRS complex to beginning of T wave
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During which phase of the EKG are the ventricles completely depolarized?
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QRS complex
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What part of heart contraction cycle does the P wave represent?
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Atrial contraction\depolarization
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What part of heart contraction cycle does the QRS represent?
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Ventricular depolarization
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What part of heart contraction cycle does the T wave represent?
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Ventricular repolarization
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Why is an adequate PQ interval important to cardiac function?
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Represents ventricular filling time
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What part of heart contraction cycle does the ST segment represent?
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Plateau phase of contractile cells fast action potential cycle
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What changes the P wave?
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Speed of conduction through atria
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Why isn't atrial repolarization usually seen on EKG?
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Masked by the QRS complex
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What is the normal range of time for PQ interval?
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.12-.20 seconds
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How does speeding the atrial conduction rate change the PQ interval?
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Decreases it
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