Normal EKG

Question 1

P-wave =

Answer 1

Atrial depolarization and AVN ‘charging up’

Reading from Lead 1 (neg on right arm)
—> net polarization is to the left side, because the right atrium has the SAN and fires first

If abnormal = pacemaker somewhere not the SAN

Question 2

PR interval

Answer 2

Time between the start of atrial and ventricular depolarization

A.k.a the atrium depolarizing, going to the AVN, and then first starting to go to the bundle of His

If abnormal = preexcitation syndrome or a first degree AV block

Question 3

QRS complex

Answer 3

Ventricular depolarization

Q = depolarization of the ventricles (downward because wave going away from + electrode)…the septal fascicle of the left bundle is activated first

R = where the whole ventricle is really being depolarize…net MEA toward +

S = few small areas of the ventricles are depolarized but travel in a left to right direction, small downward dip

If abnormal = abnormal conduction or delay of conduction…can be due to a bundle branch block, toxic drugs, an ectopic heartbeat or hyperkalemia

Question 4

ST interval and T-wave

Answer 4

ST interval = time from the last depolarization of the ventricles to the start of the repolarization of the ventricles

Abnormal = elevation or depression could be due to a myocardial infarction, ischemia, solute problems, or toxic drugs

T-wave = goes up because the repolarization goes from epicardium to endocardium (out to in)

Abnormal = repolarization is commonly affected by heart disease….ischemia, MI or angina….an inverted T-wave can result from ischemia, an infarct, or hypertrophy

Question 5

QT/ST interval

Answer 5

The difference from the beginning of ventricular depolarization and ventricular repolarization

Question 6

What is the repolarization of the atria ‘blocked by’…why can it not be read on an EKG

Answer 6

It is blocked by the QRS complex

Question 7

The leads of the Einhoven’s triangle

Answer 7

Lead 1 = right arm to left arm

Lead 2 = right arm to left leg

Lead 3 = left arm to left leg

***right leg is NOT used at all!

Question 8

Voltage changes and their deflection direction of EKG

Answer 8

Depolarization TOWARD (+) = UP

Depolarization TOWARD (-) = DOWN

Repolarization TOWARD (+) = DOWN

Repolarization TOWARD (-) = UP

Question 9

Halfway through the whole change of the atria or the ventricles…there is a

Answer 9

Maximum of heterogenous cells = farthest reading away from zero…past this point…

Start going back to zero

Question 10

3 ways amplitude on EKG be affected?

Answer 10

1. Amount of cells/mass involved
2. Synchrony with which the cells fire…QRS is higher due to function of purkinje fibers
3. Angle of depolarization or repolarization with respect to the direction of the leads

Question 11

Mean electrical axis (MEA)

Answer 11

If you add up all the vectors, you get one big vector

Each cardiac cell = one vector

Usually pointed down and to the left

Question 12

MEA of a tall, skinny person

Answer 12

Will have a heart that is more up and down…

So MEA = more vertical (therefore the amplitude will be lowered in lead 1)

Question 13

MEA in short, stout person

Answer 13

MEA = more horizontal

Higher amplitude

Question 14

Left ventricular hypertrophy effect on MEA

Answer 14

Pushes MEA more horizontally and results in more dramatic depolarization spikes

Question 15

Right ventricular hypertrophy effect on MEA

Answer 15

Pushes MEA toward the right side more and can result in a larger S wave in some leads