This document provides an overview of electrocardiograms (ECGs) including what they are used for, how they work, and how to interpret the different parts of an ECG tracing. An ECG records the electrical signals of the heart and can be used to diagnose heart conditions. It describes the normal anatomy and function of the heart as well as defining the typical waves, intervals and rates that make up a normal ECG tracing such as the P, QRS, T waves and PR interval. Abnormalities that can be detected from an irregular heartbeat like atrial fibrillation are also discussed.

1. Electrocardiogram
(ECG or EKG)
ECE/BIOM 537: Biomedical Signal Processing
Colorado State University
Student: Minh Anh Nguyen
Email: minhanhnguyen@q.com

2. Heart
• The heart is made up of cardiac muscles
• The heart is a dual pump that drives the blood in
2 serial circuits: the systemic and pulmonary
circulation
– Systemic circulation is pumped
on the left side of the heart, which
pumps blood from the lung to
the body
– pulmonary circulation is pumped
on the right side of the heart, which
pumps deoxygenated blood to the
lungs so they can release CO2
and pick up O2

3. The Heart (Cont.)
• The heart has 4 chambers: right and left atria,
right and left ventricle that are connect by valves
• The atria are the two upper chambers separated by the
interatrial septum into the left and right
• Atria receive blood returning to the heart from the body
• The muscles of the atria contract
• Ventricles are the lower chambers
which pump blood out of the heart
• The muscles of ventricles
independently relax
Pump2
Pump1
http://curr316-sp2013.wikispaces.com/Human+Anatomy+and+Physiology

4. Why is an ECG is used?
• To diagnose poor blood flow to the heart muscle
• To diagnose abnormal of the heart such as the
heart chamber enlarge
• To check the health of the heart when other
conditions are present such as high blood
pressure, high cholesterol, diabetes, etc.
• To check thickness of the wall of the heart
• To find the cause of a heart attack, and the cause
of symptoms of heart disease such as shortness
of breath, dizziness, irregular heartbeats.

5. What is an Electrocardiogram?
• A medical device which is used to measure and
monitor the rate and regularity of heartbeats.
• Each heartbeat is triggered by an electrical
impulse, which is normally generated from cells in
the upper right chamber of the heart.
• The ECG records these signals as they travel
though the heart.
• Doctors can use these results to determine the
size and position of the chambers in the heart,
and diagnose various heart diseases.

6. Example of ECG recording of a healthy
heartbeat
PR interval : 0.12 -0.2sec
QRS complex: 0.08 – 0.10 sec
QT interval : 0.4 – 0.43 sec
RR interval: 0.6 – 1.0 sec
P wave: 0.08 – 0.10 sec
Heart rate= 75 beats/min
http://prajent.hubpages.com/hub/How-to-read-a-normal-ECGElectrocardiogram

7. The P Wave of an ECG
• Indicates depolarization of atrium
• It looks like a small bump upwards from the base
line
• The shape of a P-wave is smooth and rounded
• The depolarization of the atrium during the P
wave causes the atrium to contact and fill the
ventricle
• Correlates with conduction time through atrial
• The initial recording of the P wave lasts for
approximately 90ms and the amplitude is not
greater than 2.5 x10-4
V

8. The QRS interval of an ECG
• Q marks the initial depolarization of a ventricle
spectrum
• The electricity spreads from right to left through the
spectrum
• Atrial repolarization is not seen on a normal ECG
because it is buried by the QRS complex
• The QRS complex lasts for approximately 80 ms and
has an amplitude of 1mV, which is measured from
the top of the R wave to the bottom of the S wave.
• Lengthening of the QRS indicates some blockage of
electrical action in the conducting system
• The QRS complex is caused by potentials generated
when the ventricles depolarize followed by their
contraction to force blood to the systemic circulation
to feed the other body tissues.

9. The PR and QT interval of an ECG
• PR Interval:
– The period from beginning of P wave to beginning of Q
wave.
– Represents the heart rate
– This interval shortens with increased heart rate.
– Correlates with conduction time through AV node
– The PR interval lasts 0.16 seconds
• QT interval:
– The period from beginning of Q wave to end of T wave
– Represents the entire periods of depolarization and
repolarization of ventricle
– The QT interval lasts 0.35 seconds

10. The T and U waves of an ECG
• T wave:
– Represents repolarization of the ventricles
– Occurs during repolarization when the atria are
relaxed and filled with blood again to restart the cycle
– The voltage of a T wave is 0.2 to 0.3 mV
• U wave:
– A second wave following the T wave
– Represents depolarization of the papillary muscle
(rarely seen)
– A large U wave means electrolyte abnormality
(hypokalemia) or drug effects

11. The ST and PR segments of an ECG
• ST Segment
– It is the portion of the tracing falling between the QRS
complex and the T wave.
– The period from the beginning of the S wave to beginning
of the T wave
– The length of the ST segment shortens with increasing
heart rate
– Represent repolarization of the ventricle
– The ventricle is contracting, but no electricity is flowing
• PR segment:
– The isoelectric tracing that follows the P wave and ends
with the deflection of the Q wave.
– It represents the delay of the electrical impulse at the
atrioventricular node.
– PR segment depression may indicate atrial injury

12. Example of an ECG recording of an
irregular heartbeat
• These waves, rates, voltages, intervals, and their
position must be present when reviewing the
ECG results
• If there are missing waves, then the ECG is not
normal and heart disease may be present
http://www.clinicaljunior.com/cardiologyecg.html

13. Atrial Fibrillation
• The most common cause for an irregular heart
rhythm is atrial fibrillation or AF.
• Atrial fibrillation occurs when the atria lose their
ability to beat and contract in an organized way,
which leads to random heart beats.
• In AF, blood pools in the atria, but it isn't pumped
completely into the heart's two lower chambers;
the heart's upper and lower ventricles don't work
together as they should, which causes heart
failure

14. Heart Rates
• The information on the ECG can be used to determine
heart rate:
– Count the number of QRS complexes over a 6 second
interval multiply by 10. The heart is beating at
70 beats/min in
the adjacent image
– Count the number of small boxes a for typical R-R
interval, and divide 1500 by
this number. The heart is
Beating 75 (BPM) in the wave
forms depicted here 
http://www.practicalclinicalskills.com/ekg-lesson.aspx?coursecaseorder=5&courseid=301

15. Heart Rates (Cont.)
• The average adult has a heart rate of 60-100
beats/min (BPM)
• If the heart rate is < 60 BPM, then bradycardia
will happen
– AV heart block and atrial fibrillation with slow
ventricular response
• If the heart rate is > 100 BPM, then
tachycardia will occur
– atrial tachycardia, ventricular tachycardia and
atrial fibrillation with rapid ventricular response.

16. References
• Najarian, K. (2012). Electrocardiogram. In Biomedical
signal and image processing (2nd ed.). Boca Raton:
Taylor & Francis/CRC Press.
• http://www.clinicaljunior.com/cardiologyecg.html
• http://www.learntheheart.com/cardiology-
review/atrial-fibrillation/
• http://prajent.hubpages.com/hub/How-to-read-a-
normal-ECGElectrocardiogram
• http://www.madsci.com/manu/ekg_part.htm
• http://www.practicalclinicalskills.com/ekg-
lesson.aspx?coursecaseorder=5&courseid=301