1. نشرة المشترك من:
Ar-bme.com
ECG

2. Main points What is an ECG? How does it measure? What does it measure?
What do the parts of the resulting curve mean?
Why use an ECG?
What is the circuit to build one?

3. ECG History and Basics
Represents electrical activity (not contraction)
Marey, 1867, first electrical measurement from the heart.
Waller, 1887, first human ECG published.
Einthoven, 1895, names waves, 1912 invents triangle, 1924, wins Nobel Prize.
Goldberger, 1924, adds precordial leads (specific chest placement)

4. Heart Dipole and the ECG
Represent the heart as a single moving dipole
ECG measures projection of the dipole vector
Coarse simplification

5. ECG Variations in electrical potential at skin surface
Depolarizatin of cells near heart
Excitation and relaxation of heart muscle
Mechanical, electrical, acoustic

7. Measurements Heart rate (state atrial and ventricular, if different)
PR interval (from beginning of P to beginning of QRS)
QRS duration (width of most representative QRS)
QT interval (from beginning of QRS to end of T)

9. Parts of the Heart
The sinoatrial (SA) node is a section of nodal tissue that is located in the upper wall of the right atrium. The SA node is also referred to as the pacemaker of the heart.
The atrioventricular (AV) node is a section of nodal tissue that lies on the right side of the partition that divides the atria, near the bottom of the right atrium.
Purkinje fibers are fiber branches that extend from the atrioventricular bundle. They relay cardiac impulses to the ventricular cells causing the ventricles to contract.
HIS bundle is part of the specialized conduction system. The HIS bundle rapidly conducts electrical impulses from the AV node to the ventricles. Disease in the HIS bundle can produce a form of bradycardia (too slow heart rate) called heart block.

10. ECG Waves and Intervals: What Do They mean?
P wave: the sequential activation (depolarization) of the right and left atria
QRS complex: right and left ventricular depolarization (normally the ventricles are activated simultaneously)
ST-T wave: ventricular repolarization
U wave: origin for this wave is not clear - but probably represents "afterdepolarizations" in the ventricles
PR interval: time interval from onset of atrial depolarization (P wave) to onset of ventricular depolarization (QRS complex)
QRS duration: duration of ventricular muscle depolarization
QT interval: duration of ventricular depolarization and repolarization
RR interval: duration of ventricular cardiac cycle (an indicator of ventricular rate)
PP interval: duration of atrial cycle (an indicator or atrial rate)

11. Rhythm Analysis Really reading an ECG takes LOTS of practice
State basic rhythm (e.g., "normal sinus rhythm", "atrial fibrillation", etc.)
Identify additional rhythm events if present (e.g., "PVC's", "PAC's", etc)
Consider all rhythm events from atria, AV junction, and ventricles
Really reading an ECG takes LOTS of practice

12. Why use an ECG?
Patients with unexplained unconsciousness (syncope), near syncope or episodic dizziness in whom the cause is not obvious
Patients with unexplained recurrent palpitations
With pacemakers
Evaluation of frequent symptoms of palpitation, syncope, or near syncope to assess device function, so as to exclude myopotential inhibition and pacemaker mediated tachycardia and to assist in the programming of enhanced features.
Evaluation of suspected component failure or malfunction when device interrogation is not definitive in establishing a diagnosis
To assess the response to adjunctive pharmacological therapy in patients receiving Implantable Cardioverter defibrillator (ICD) therapy-slows down fast heart rate (pacemakers do opposite)

14. Heart Rate
In normal sinus rhythm, a resting heart rate of below 60 bpm is called bradycardia and a rate of above 90 bpm is called tachycardia.
Bradycardia
Diseases of sinoatrial node (heart’s pacemaker)
Weak, sluggish, dizzy, short of breath
Tachycardia
Normal response to increased activity/oxygen demands
Premature contractions
Atrial (PAC, PAB), Ventricular (PVC, PVB)
Caffeine, alcohol, decongestants
Hyperthyroidism, anemia, hypertension, stress

15. Now…The Circuit
PreAmp
Low Pass Filter
High Pass Filter

16. (frequency passes
if higher than
given frequency)
(frequency passes
if lower than
given frequency)

17. Noise Several sources 60Hz power lines – shielding, filtering
Other biopotentials – filtering
Motion artifacts – relaxed subject
Electrode noise – high quality electrodes, good contacts
Circuit noise – good design, good components

18. When measuring biopotentials (say ECG), EVERYTHING else creates noise
– power line interference
– even other biopotentials (like EEG, EMG, EOG)
are noise sources. These have characteristic frequencies. So use Band Pass Filters.
Pass only fL to fH attenuate the others.
fL fH

19. Frequencies of Biopotentials
Signal
Frequency range (Hz)
Amplitude range(mV)
ECG
0.01 – 300
0.05 – 3
EEG
0.1 – 100
0.001 – 1
EOG
0.1 – 10
0.001 – 0.3
EMG
50 – 3000
0.001 – 100

20. Our frequency range will be 0.05 to 200 Hz

22. Overall Gain

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