- measured from the begining of the P wave to the 1st part of the QRS complex (which may be a Q wave or R wave)

ECG Basics Flashcards by Poto Toleafoa

ECG paper speed is ordinarily…

25 mm/sec

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small box = ___ sec

0.04 sec

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5 small boxes = 1 large box = ____ sec

0.20 sec

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P wave represents

atrial depolarization

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P wave duration is generally

<0.12 sec (3 small boxes)

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P wave amplitude

<0.25 mv (2.5 small boxes)

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PR interval includes

P wave + PR segment

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PR segment is

measured from the begining of the P wave to the 1st part of the QRS complex (which may be a Q wave or R wave)

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PR interval includes…

time for atrial depolarization (P wave) & conduction through the AV nodes & the His-Purkinje system (which constitutes the PR segment).

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PR interval duration

0.12 - 0.20 sec (3 to 5 small boxes)

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Length of the PR interval changes with?

Heart rate

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PR interval is shorter at…

faster heart rates due to sympathetically mediated enhancement of atrioventricular (AV) nodal conduction

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PR interval is longer when…

the rate is slowed as a consequence of slower AV nodal conduction resulting from withdrawal of sympathetic tone or an increase in vagal input.

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QRS complex represents

ventricular depolarization

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Small Q waves are often seen in leads _______ as a result of initial septal depolarization.

I, aVL & V4 - V6

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Q wave in the QRS complex is…

the initial negative deflection.

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1st positive deflection of the QRS complex is

R wave

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R wave in the QRS complex represents

depolarization of the left ventricular myocardium.

NOTE: right ventricular depolarization is obscured because the left ventricular myocardial mass is much greater than that of the right ventricle.

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The small R wave in lead V1 represents

intial septal depolarization

S wave in the QRS complex is the

negative deflection following the R wave

S wave represents

terminal depolarization of the high lateral wall

Lower case letters (q, r, or s) are used for…

relatively small amplitude waves of <0.5mV (<5mm with standard calibration)

An entirely negative QRS complex is called a

QS wave

QRS complex duration

0.06 - 0.10 sec (1.5 - 2.5 small boxes)

Explain R wave progression & in what leads?

- R wave should progress in size across the precordial leads (V1 - V6). - Normally there is a small R wave in lead V1 with a deep S wave. - The R wave amplitude should increase in size until V4 - V6 while the S wave becomes less deep.

ST segment occurs

after ventricular depolarization has ended & before repolarization has begun.

J point

It is the intersection of the end of the QRS complex & the initial part of the ST segment.

T wave represents

ventricular repolarization

Why is the T wave asymmetrical & has a variable amplitude? (T wave is broad, has slow upstroke & a more rapid downslope to the isoelectric lune following its peak)

This is because: - the rate of repolarization is slower than depolarization.

Difference in characteristics of T wave vs P wave

- Since the rate of repolarization is slower than depolarization, the T wave is broad, has a slow upstroke, & a more rapid downslope to the isoelectric line following its peak. Thus, the T wave is asymmetric & the amplitude is variable. - - In addition, the T wave is usually smooth up and down. - If there is any irregularity on the T wave (bump, notch, rippled, etc) a superimposed P wave should be considered.

QT interval consists of

- QRS complex - ST segment - T wave

QT interval is primarily a measure of...

ventricular repolarization

If the _____ duration is increased, this will lead to an increase in QT interval but doesn't a change in ventricular repolarization.

- QRS complex

A widened QRS must be considered if a ____________ is being evaluated.

prolonged QT interval

The QT interval is dependent upon...

heart rate = shorter at faster heart rates & longer when the rate is slower.

Clinicians also need to be mindful of the fact that since the QRS widens in the setting of a bundle branch block, the ____________ will also increase.

QT interval

U wave may be seen in some leads especially the precordial leads...

V2 - V4

U wave is more evident in some circumstances such as...

hypokalemia & bradycardia

Normal QRS axis =

if the QRS is (+) (upright) in both leads I and II, then the axis falls between -30 & 90 degree which is normal.

Left axis deviation =

If the QRS complex is is (+) in lead I but (-) in lead II, the it is left axis deviation (-30 to -90 degree).

Right axis deviation =

If the QRS complexes are (-) in lead I and (+) in aVF, then it is right axis deviation (90 to 180 degree).

Extreme axis deviation =

If the QRS complexes are (-) in both I & aVF, then the axis is extreme (180 to -90 degrees).

8 steps in interpretating an ECG:

1. Rate 2. Rhythm 3. Axis 4. Intervals 5. P wave 6. QRS complex 7. ST segment T wave 8. Overall interpretation

Short PR intervals may suggest of...

Wolff-Parkinson White syndrome

Long QRS intervals represent...

- bundle branch block - ventricular pre-excitation - ventricular pacing - ventricular tachycardia