Introduction to ECG EEE 491 Biomedical Engineering Compiled by Dr. Khawza I Ahmed.

Introduction Introduction to ECGto ECG

EEE 491 Biomedical EngineeringEEE 491 Biomedical Engineering

Compiled by Dr. Khawza I AhmedCompiled by Dr. Khawza I Ahmed

What is ECG?What is ECG? The electrocardiogram (ECG) is a time-varying The electrocardiogram (ECG) is a time-varying

signal reflecting the ionic current flow which signal reflecting the ionic current flow which causes the cardiac fibers to contract and causes the cardiac fibers to contract and subsequently relax. The surface ECG is obtained subsequently relax. The surface ECG is obtained by recording the potential difference between two by recording the potential difference between two electrodes placed on the surface of the skin. A electrodes placed on the surface of the skin. A single normal cycle of the ECG represents the single normal cycle of the ECG represents the successive atrial depolarisation/repolarisation and successive atrial depolarisation/repolarisation and ventricular depolarisation/repolarisation which ventricular depolarisation/repolarisation which occurs with every heart beat. occurs with every heart beat.

Simply put, the ECG (EKG) is a device that Simply put, the ECG (EKG) is a device that measures and records the electrical activity of the measures and records the electrical activity of the heart from electrodes placed on the skin in heart from electrodes placed on the skin in specific locationsspecific locations

What the ECG is used What the ECG is used for?for?

Screening test for coronary artery disease, Screening test for coronary artery disease, cardiomyopathies, left ventricular hypertrophycardiomyopathies, left ventricular hypertrophy

Preoperatively to rule out coronary artery diseasePreoperatively to rule out coronary artery disease Can provide information in the precence of metabolic Can provide information in the precence of metabolic

alterations such has hyper/hypo calcemia/kalemia etc.alterations such has hyper/hypo calcemia/kalemia etc. With known heart disease, monitor progression of the With known heart disease, monitor progression of the

diseasedisease Discovery of heart disease; infarction, coronal Discovery of heart disease; infarction, coronal

insufficiency as well as myocardial, valvular and insufficiency as well as myocardial, valvular and cognitial heart diseasecognitial heart disease

Evaluation of ryhthm disordersEvaluation of ryhthm disorders All in all, it is the basic cardiologic test and is widely All in all, it is the basic cardiologic test and is widely

applied in patients with suspected or known heart applied in patients with suspected or known heart diseasedisease

Measuring ECGMeasuring ECG

ECG commonly measured via 12 ECG commonly measured via 12 specifically placed leadsspecifically placed leads

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The 12-LeadsThe 12-Leads

The 12-leads include:The 12-leads include:

–3 Limb leads (I, II, III)

–3 Augmented leads (aVR, aVL,

aVF)–6 Precordial leads

(V1- V6)

Typical ECGTypical ECG

A typical ECG period consists of A typical ECG period consists of P,Q,R,S,T and U wavesP,Q,R,S,T and U waves

ECG Intervals / SegmentsECG Intervals / Segments

PR: 0.12-0.20 sec

QRS: <0.10 sec

QT: 0.30-0.40 sec (60 bpm)

ECG WavesECG Waves P wave: the P wave: the

sequential activation sequential activation (depolarization) of the (depolarization) of the right and left atriaright and left atria

QRS comples: right QRS comples: right and left ventricular and left ventricular depolarizationdepolarization

T wave: ventricular T wave: ventricular repolarizationrepolarization

U wave: origin not U wave: origin not clear, probably clear, probably ”afterdepolarizations” ”afterdepolarizations” in the ventrices in the ventrices

ECG ExampleECG Example

ECG Signal GenerationECG Signal Generation

Action PotentialAction Potential

Electrocardiogram (ECG/EKG)Electrocardiogram (ECG/EKG) Is a recording of electrical activity of heart conducted thru ions in Is a recording of electrical activity of heart conducted thru ions in

body to surfacebody to surface

13-60

Cardiac Cellular Cardiac Cellular Electrical ActivityElectrical Activity

Typical Equilibrium Potentials:

Na(+) ~+40mV

K(+) ~-90mV

C(++) ~+150mV

ECG recordingECG recording

ECG recordingECG recording

ECG recordingECG recording

ECG recordingECG recording

ECG recordingECG recording

3 distinct waves are 3 distinct waves are produced during produced during cardiac cyclecardiac cycle

P waveP wave caused by caused by atrial depolarizationatrial depolarization

QRS complexQRS complex caused caused by ventricular by ventricular depolarizationdepolarization

T waveT wave results from results from ventricular ventricular repolarizationrepolarization

ECG

Fig 13.2413-63

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 block

• 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

ST segment:• Connects the QRS complex and T wave• Duration of 0.08-0.12 sec (80-120 msec

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

Fig. 13.24bFig. 13.24b

Fig. 13.24cFig. 13.24c

Fig. 13.24dFig. 13.24d

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

•QRS complex:

• Represents 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

• 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 block

Fig. 13.24gFig. 13.24g

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

ST segment:• Connects the QRS complex and T wave• Duration of 0.08-0.12 sec (80-120 msec

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

ECG recordingECG recording

ECG recordingECG recording

ECG recordingECG recording

ECG recordingECG recording

ECG recordingECG recording

ECG recordingECG recording

ECG recordingECG recording