Electrocardiogram(ECG or EKG)

ECE/BIOM 537: Biomedical Signal ProcessingColorado State University

Student: Minh Anh NguyenEmail: minhanhnguyen@q.com

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, whichpumps deoxygenated blood to the lungs so they can release CO2

and pick up O2

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

Pump2Pump1

http://curr316-sp2013.wikispaces.com/Human+Anatomy+and+Physiology

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.

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.

Example of ECG recording of a healthy heartbeat

PR interval : 0.12 -0.2secQRS complex: 0.08 – 0.10 secQT interval : 0.4 – 0.43 secRR interval: 0.6 – 1.0 sec

P wave: 0.08 – 0.10 secHeart rate= 75 beats/min

http://prajent.hubpages.com/hub/How-to-read-a-normal-ECGElectrocardiogram

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

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.

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

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

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

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

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

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 at70 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

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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.

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