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Flashcards in EKG Deck (35):

Direction of electrical current flow by convention is from ______ to ______ charged areas

negatively; positively


At rest the cell surface is ______ charged



How many reference axes are in the frontal plane (limb leads)?

How many in the transverse plane?

6 and 6


What are unipolar leads? Which ECG electrodes are unipolar?

Unipolar leads  have no single negative pole - their negative pole is a composite reference of other leads averaged

Include aVR, aVF, aVL, V1-V6


What are bipolar leads? Which electrodes are bipolar leads?

Bipolar leads have a single electrode as the positive pole and a single electrode as the negative reference

Include leads I, II, and III


What lead is associated with each degree below from the "Circle of axes"?







-150º: aVR

-30º: aVL

0º: Lead I

60º : Lead II

90º: aVF

120º: Lead III

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Electrical force directed toward + pole of a lead generates a ______ deflection in that lead

Force directed away from + pole of a lead results in ______ deflection in that lead

positive; negative


Magnitude of deflection is determined by...

How parallel the electrical force is to the lead axis - the more parallel the greater the magnitude of deflection in that lead


What is the sequence of Normal Cardiac Activation?

SA node → AV node → Bundle of His → Mainstem Left bundle branch → right bundle branch and Posterioinferior left bundle branch → Purkinje fibers

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Sequence of Cardiac Depolarization (6)

  1. Depolarize atria
  2. Depolarize septum from left to right
  3. Depolarize anteroseptal region of myocardium toward the apex
  4. Depolarize bulk of ventricular myocardium from endocardium to epicardium
  5. Depolarize posterior portion of base of the left ventricle
  6. Ventricles are now depolarized

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Why is depolarization in the ventricles eventually directed leftward and posterior, toward V6?


As lateral wall left ventricular (LV) is depolarized, electrical forces of thick LV outweigh RV and depolarization is directed toward that side

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What to look for when interpreting EKG

Heart rate

Intervals (PR, QRS, QT)

Calculate mean QRS axis

Evaluate P wave for abnormalities

Evaluate QRS for abnormalities

Evaluate for abnormalities of ST/T wave


EKG is recorded on a grid divided by lines space __ apart both in horizontal and vertical directions

Vertical axis measures  ______

Horizontal axis measures ______

1mm apart




Normal heart rhythm on EKG findings include (4)

  1. Every P followed by QRS
  2. Upright P in leads I, II and III
  3. PR interval between 120 and 200ms
  4. HR between 60-100 bpm


If HR is less than ___ it is termed sinus bradycardia

If HR is more than ___ it is termed sinus tachycardia

less than 60; more than 100


Heart rate (bpm) calculation?

What if the rhythm is irregular?

HR = 1500/#small boxes between two consecutive beats

Irregular rhytm: count #QRS during 6 sec and multiply by 10


Calculating intervals

PR interval: (normal = 0.12-0.2 sec)

QRS interval: (normal < 0.1 sec)

QT interval: 

QT corrected: (normal < .44 sec)

  • PR interval: onset of P to onset of QRS
  • QRS interval: beginning to end of qRS
  • QT interval: onset QRS to end of T wave
  • QT corrected: measured QT/square of RR interval (seconds)


What is the mean QRS axis?

What is normal?

What constitutes a left axis deviation?

What constitutes a right axis deviation?

Definition: average of instantaneous electrical forces generated during ventricular depolarization in frontal plane

Normal: -30º to +90º

Left axis deviation: negative to -30º

Right axis deviation: positive to +90º


If net QRS in leads  _ and __ are positive, axis is in normal range

I and II


Geometric method of determining mean QRS axis?

  1. Measure magnitude of QRS
  2. Mark on circle of axes, + 2 units at lead with highest amp. and another unit with negative amplitude (at approximately -1 unit)
  3. Draw two perpendiculars
  4. Connect center of circle with intersection of two perpendiculars
  5. Estimate axis of this line

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Inspection method of determining mean QRS?

  1. Identify lead where QRS is isoelectric (flat line)
  2. Identify axis perpendicular to isoelectric lead
  3. QRS is in line with perpendicular axis

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Abnormalities of P wave are commonly measured with which leads?

Lead II (60°) and V1 (toward right heart)

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Left ventricular hypertrophy increases the amplitude of electrical forces directed to the ____ and _____

left; posteriorly


Right ventricular hypertrophy can shift the QRS vector to the _____


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LVH findings on EKG for V1 and aVL leads

S in V1 > 24mm

R in aVL > 13mm

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RVH findings on EKG (5)

Tall R wave in V1

Right axis deviation

T wave inversion in V1-V3

Delatyed precordial transition zone in V6

Right atrial abnormality

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Interruption of the left anterior fascicle or division (LAD) results in...

Right interruption of left posterior fascicle or division (LPD) results in...

  • Initial inferior followed by dominant superior direction of activation
  • Initial superior followed by a dominant inferior direction of activation

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What condition can lead to more than one R wave in the V1 lead?

How does this condition present in the V6 lead?

Right bundle branch block (RBBB)

Causes abnormal broad S wave in V6

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Recognize LBBB patterns in V1 and V6 leads

Loss of normal right to left depolarization

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On EKG what is the difference between STEMI and non-STEMI ischemia?

STEMI = transmural (epicardial) injury: ST elevation

Non-STEMI = subendocardial injury: ST depression

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Acute ischemia may alter ventricular action potentials by inducing...

  1. Lower resting membrane potential
  2. Decreased amplitude and velocity of phase 0
  3. Abbreviated action potential duration

* resulting currents of injury are reflected on ECG by deviation of the ST segment

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What is the most likely cause of ST elevation or depression in one isolated lead?

Probably an error - Important that ST changes are in multiple leads that mae sense in groupings


Where do pathologic Q waves develop?

In leads overlying infarcted tissue because necrotic tissue does not generate electrical forces - Lead overlying necrotic tissue detects currents from healthy tissue on opposite regions directed away from infarct

Leads to downward deflection of Q wave

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Conditions associated with ST and T wave changes

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Hypercalcemia can lead to shortening of the ___ interval