10. What is an ECG?
The electrocardiogram (ECG) is a
representation of the electrical events of
the cardiac cycle.
Each event has a distinctive
waveform, the study of which can lead to
greater insight into a patient’s cardiac
pathophysiology.
11. ECG Leads
Leads are electrodes which measure the
difference in electrical potential between
either:
1. Two different points on the body (bipolar
leads)
2. One point on the body and a virtual reference
point with zero electrical potential, located in
the center of the heart (unipolar leads)
12. EKG Leads
The standard EKG has 12 leads: 3 Standard Limb Leads
3 Augmented Limb Leads
6 Precordial Leads
The axis of a particular lead represents the
viewpoint from which it looks at the heart.
39. Elements of the ECG:
P wave: Depolarization of both atria;
Relationship between P and QRS helps distinguish
various cardiac arrhythmias
Shape and duration of P may indicate atrial
enlargement
PR interval: from onset of P wave to onset of QRS
Normal duration = 0.12-2.0 sec (120-200 ms) (3-4
horizontal boxes)
Represents atria to ventricular conduction time
(through His bundle)
Prolonged PR interval may indicate a 1st degree heart
bloc
40. QRS complex: Ventricular depolarization
Larger than P wave because of greater muscle mass of
ventricles
Normal duration = 0.08-0.12 seconds
Its duration, amplitude, and morphology are useful in
diagnosing cardiac arrhythmias, ventricular
hypertrophy, MI, electrolyte derangement, etc.
Q wave greater than 1/3 the height of the R
wave, greater than 0.04 sec are abnormal and may
represent MI
41. ST segment:
Connects the QRS complex and T wave
Duration of 0.08-0.12 sec.
T wave:
Represents repolarization or recovery of ventricles
Interval from beginning of QRS to apex of T is referred to as the
absolute refractory period
QT Interval
Measured from beginning of QRS to the end of the T wave
Normal QT is usually about 0.40 sec
QT interval varies based on heart rate
44. Rule of 300
Take the number of “big boxes” between neighboring
QRS complexes, and divide this into 300. The result will
be approximately equal to the rate
Although fast, this method only works for regular
rhythms.
45. What is the heart rate?
www.uptodate.com
(300 / 6) = 50 bpm
46. What is the heart rate?
www.uptodate.com
(300 / ~ 4) = ~ 75 bpm
48. Themay be easiest300
It
Rule of to memorize the following table:
# of big Rate
boxes
1 300
2 150
3 100
4 75
5 60
6 50
49. 6 Second Rule
As most EKGs record 10 seconds of rhythm per
page, one can simply count the number of beats
present on the EKG and multiply by 10 to get the
number of beats per 60 seconds.
This method works well for irregular rhythms.
50. What is the heart rate?
The Alan E. Lindsay ECG Learning Center ; http://medstat.med.utah.edu/kw/ecg/
