KINS 4640 Axis, Rotation, Hypertrophy, and Enlargment

why aVR looks opposite

its + electrode is on the right arm, so the normal wave travels away from it, mostly negative

axis

overall direction of ventricular depolarization in the frontal plane

vector

arrow showing direction and magnitude

mean QRS vector

sum of all the small ventricular vectors, drawn from the AV node

lead angles on hexaxial wheel

I = 0; II = +60; aVF = +90; III = +120; aVL = -30; aVR = -150

normal axis

0 to +90 degrees

left axis deviation

0 to - 90 degrees

right axis deviation

+90 to +180 degrees

extreme axis deviation

-90 to -180 degrees

Q1 +, aVF +

normal (2 thumbs up)

Q1 -, aVF +

right axis deviation

Q1 +, aVF -

left axis deviation

Q1 -, aVF -

extreme right axis deviation

causes of LAD

heart displaced left, horizontal heart, obesity, LVH, loss of electrical activity in right heart

causes of RAD

heart displaced right, vertical heart, tall/thin, RVH, loss of electrical activity in left heart

hypertrophy vs infarction effect on axis

hypertrophy draws axis toward it; infarction pushes it away

finding axis; step 1

use lead I and aVF to pick the quadrant

finding axis; isoelectric method

find the limb lead with the flattest or most evenly +/- QRS; axis is perpendicular to it

finding axis; largest deflection method

fins the limb lead with the biggest QRS; axis points near that lead (check neighbors to pick the side)

perpendicular lead pairs

I and aVF; II and aVL; III and aVR

normal quadrant: isoelectric lead to axis

aVF = 0; III = +30; aVL = +60; I =+90

LAD quadrant

aVF = 0, II = -30; aVR =-60; I = -90

RAD quadrant

I = +90; aVR = +120; II = +150; aVF = +180

extreme quadrant

I = -90; aVL = -120; III = -150; aVF = -180

example

I+, aVF+ (normal); aVL most isoelectric; axis +60

rotation

same idea as axis but in the chest leads (horizontal plane)

normal transition zone

v3 or v4 (QRS about equal up and down)

transition in v1/v2

rightward rotation

transition in v5/v6

leftward rotation

rotation and hypertrophy/infarct

rotates toward ventricular hypertrophy, away from infarction

LVH

exaggerated QRS: very deep S in v1/v2; very tall R in v5/v6

LVH criterion

S in v1 or v2 + R in v5 or v6 >35 mm (14 + 22 = 36 mm = LVH)

RVH

large R in v1 that shrinks v2 to v4; no normal R wave progression (often RAD)

atrial enlargement

atrial dilation, not hypertrophy; shows up in the P wave

right atrial enlargement (P pulmonale)

tall P >2.5 mm in II, III, aVF; normal width; often from lung disease

left atrial enlargement (P mitrale)

wide P (>0.12 s, often notched) and negative part of P in v1 > 1 mm; often from mitral valve disease

RAE vs LAE

right = tall (amplitude); left = long (duration)