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Flashcards in ECG Deck (16)

P wave

First short upward movement of the EKG tracing.

- atrial depolarization: It indicates that the atria are contracting, pumping blood into the ventricles.


The QRS complex

Normally beginning with a downward deflection, Q; a larger upwards deflection, a peak (R); and then a downwards S wave.

- The QRS complex represents ventricular depolarization and contraction, emptying the ventricles


PR interval

indicates the transit time for the electrical signal to travel from the sinus node to the ventricles.


T wave

normally a modest upwards waveform, representing ventricular repolarization and relaxation


How do you calculate accurate HR using an EKG?

Count the number of large squares from R peak to R peak, and divide that by 300.
- ie: 300/5 = 60


How many squares = 1 second?
How many large squares = 6 seconds?
How many seconds does 1 large square =?
How many seconds does 1 small square =?

5 large squares
30 large squares = 6 seconds
1 large square = 0.2 sec
1 small square = 0.04 sec


In individuals with irregular heart rates, how do you measure an accurate heart rate?
- what if there are 7 R waves found in that interval, how many beat in 1 min?

Count 30 large squares (6 seconds) and then count how many R waves are found in the 30 large squares.

7 beats in 6 seconds
- There are 60 seconds in 1 min
- There are 70 beats in 1 min


In a normal heart, the time between the onset of atrial depolarization (beginning of P wave) and the onset of ventricular depolarization (beginning of QRS complex) normally varies between what time frame?

PR interval = 0.12s - 0.2s
or 3 - 5 small squares

- many imp disorders are associated with alterations in the PR interval


The PR interval is largely determined by what?

physiological delay of the depolarization wave in the AV node and transit in the bundle of his.

- many imp disorders are associated with alterations in the PR interval


The QRS interval duration is largely determined by what? What is the width of the QRS interval typically?

time taken for ventricular depolarization to be completed.

Normally less than or equal to 3 small squares
(no more than 3 ss!)


QT interval
- how many squares is it usually?

Time between the onset of ventricular depolarization and the end of the ventricular repolarization (beginning of QRS complex and end of T wave)

Normally less than 11 ss at a heart rate of 60 beats per min.


Does the QT interval expand or decrease as the heart rate speeds up?

QT interval gets shorter as heart speeds up

- at higher heart rates, possible to miss underlying prolonged QT interval


If you find that QT interval is 8 ss, how many seconds is that?

0.32 seconds

1 small square = 0.04 sec
8 small squares = 0.32 sec


Corrected QT interval = ?

QT / squareroot(RR)


Ventricular depolarization

"ventricular systole"
Coordinated transmission of stimulus (cation flows) leading to contraction of the ventricles.


Ventricular repolarization

Last event of the cycle.
Restoring of the resting state.
Begins with the closure of the slow calcium channels and opening of the potassium channels.

- Repolarization proceeds from the apex of the heart to the base of the heart.