ECG Basics

KIN 4306

what are the polarities of Lead I of Einthoven’s triangle?

RA: (-)

LA: (+)

what are the polarities of lead II of Einthoven’s triangle?

RA: (-)

LL: (+)

what are the polarities of lead III of Einthoven’s triangle?

LA: (-)
LL: (+)

what are the dimensions of a small box on ECG paper?

1mm x 1mm

what does 1 small box represent in msec and mV?

40 msec (0.04 sec)

0.1 mV

what are the dimensions of a large box on ECG paper?

5mm x 5mm

what does one large box represent on ECG paper in msec and mV

200 msec (0.20 sec)

0.5 mV

what does the P wave represent?

atrial depolariation

what does the QRS complex represent

ventricular depolarization

what does the T wave represent?

ventricular repolarization

what does the individual Q wave represent?

depolarization of the interventricular septum

what does the individual R wave represent?

depolarization of the inner ventricular walls

what does the individual S wave represent

depolarization of the outer ventricular wall

what does the ST segment represent

end of ventricular depolarization to start of ventricular repolarization

normal p wave duration and amplitude

duration: <120 msec

amplitude: <0.25 mV

normal PR interval duration

120-200 msec

normal QRS complex duration

60-100 msec

pathological duration for QRS complex

>120 msec

what is the duration for a pathological Q wave

>40 msec

what is the amplitude for a pathological Q wave

depth > 2mm

what is the normal amplitude for T wave

<0.5 mV

how do you calculate HR using the 1500 method

1500 / the average of 3 non-consecutive R-R intervals

what are the normal QTc values for men and women?

men: <0.44 sec

women: <0.46 sec

what is an abnormally short QTc value?

<0.35 sec

ECG changes for myocardial ischemia

ST segment depression

T wave inversion

ECG changes for myocardial infarction

ST segment elevation

T wave tombstoning

pathological Q waves

brief temporary loss of O2 and nutrient delivery due to partial coronary artery occlusion

myocardial ischemia

prolonged loss of O2 and nutrient delivery due to complete coronary artery obstruction

myocardial infarction