ecg

BIO-ELECTRIC SIGNAL&

ELECTRO-CARDIOGRAPHY

H.K.PIRCSIO, CSIR COMPLEX, PUSA CAMPUS

NEW DELHI-110012

BIO-ELECTRIC SIGNAL

BIO-ELECTRIC SIGNAL

►CELL : Ionic conductor separated from outside environment by semi-permeable membrane

►Human Cells: Dia : I micron to 100 microns

►Membrane Thickness : 0.01 micron

BIO - ELECTRIC POTENTIAL

ELECTROCARDIOGRAM►Internal Resting Potential: -90mv►During Depolarisation Cell Potential

Changes to +20mv

Normal Impulse Conduction

Sinoatrial node

AV node

Bundle of His

Bundle Branches

Purkinje fibers

Impulse Conduction & the ECG

Sinoatrial node

AV node

Bundle of His

Bundle Branches

Purkinje fibers

The “PQRST”

►P wave - Atrial

depolarization

• T wave - Ventricular repolarization

• QRS - Ventricular depolarization

The PR Interval

Atrial depolarization +

delay in AV junction (AV node/Bundle of His)

(delay allows time for the atria to contract before the ventricles contract)

For more presentations www.medicalppt.blogspot.com

Pacemakers of the Heart

►SA Node - Dominant pacemaker with an intrinsic rate of 60 - 100 beats/minute.

►AV Node - Back-up pacemaker with an intrinsic rate of 40 - 60 beats/minute.

►Ventricular cells - Back-up pacemaker with an intrinsic rate of 20 - 45 bpm.

Sequence of Impulse Travel

Conduction Analysis

► Normal" conduction implies normal sino-atrial (SA) normal atrio-ventricular (AV)normal intraventricular (IV) conduction.

► The diagram illustrates the normal cardiac conduction system.

ELECTROCARDIOGRAM

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 "after depolarizations" in the ventricles

ECG Waves and Intervals:

► 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 of atrial rate)

The ECG Paper

►Horizontally One small box - 0.04 s One large box - 0.20 s

►Vertically One large box - 0.5 mV

Step 1: Calculate Rate

►Option 1 Count the # of R waves in a 6 second

rhythm strip, then multiply by 10. Reminder: all rhythm strips in the Modules

are 6 seconds in length.

Interpretation? 9 x 10 = 90 bpm

3 sec

3 sec

Step 2: Determine regularity

► Look at the R-R distances (using a caliper or markings on a pen or paper).

► Regular (are they equidistant apart)? Occasionally irregular? Regularly irregular? Irregularly irregular?

Interpretation? Regular

R R

Step 3: Assess the P waves

►Are there P waves?►Do the P waves all look alike?►Do the P waves occur at a regular rate?►Is there one P wave before each QRS?Interpretation?

Normal P waves with 1 P wave for every QRS

Step 4: Determine PR interval

►Normal: 0.12 - 0.20 seconds. (3 - 5 boxes)

Interpretation? 0.12 seconds

Step 5: QRS duration

►Normal: 0.04 - 0.12 seconds. (1 - 3 boxes)

Interpretation?0.08 seconds

Rhythm Summary

► Rate 90-95 bpm► Regularity regular► P waves normal► PR interval 0.12 s► QRS duration 0.08 sInterpretation?

Normal Sinus Rhythm

NSR Parameters

►Rate 60 - 100 bpm►Regularity regular►P waves normal►PR interval 0.12 - 0.20 s►QRS duration 0.04 - 0.12 s

Any deviation from above is sinus tachycardia, sinus bradycardia or

an arrhythmia

Arrhythmia Formation

Arrhythmias can arise from problems in the:

• Sinus node• Atrial cells• AV junction• Ventricular cells

SA Node Problems

The SA Node can:►fire too slow►fire too fast

Sinus BradycardiaSinus Tachycardia

Sinus Tachycardia may be an appropriate response to stress.

Atrial Cell Problems

Atrial cells can:►fire occasionally

from a focus

►fire continuously due to a looping re-entrant circuit

Premature Atrial Contractions (PACs)

Atrial Flutter

►A re-entrant pathway occurs when an impulse loops and results in self-perpetuating impulse formation.

Atrial Cell Problems

Atrial cells can also:• fire continuously

from multiple foci or

fire continuously due to multiple micro re-entrant “wavelets”

Atrial Fibrillation

Atrial Fibrillation

Teaching Moment

Multiple micro re-entrant “wavelets” refers to wandering small areas of activation which generate fine chaotic impulses. Colliding wavelets can, in turn, generate new foci of activation.

Atrial tissue

AV Junctional Problems

The AV junction can:►fire continuously

due to a looping re-entrant circuit

►block impulses coming from the SA Node

Paroxysmal Supraventricular TachycardiaAV Junctional Blocks

Ventricular Cell Problems

Ventricular cells can:►fire occasionally

from 1 or more foci►fire continuously

from multiple foci►fire continuously

due to a looping re-entrant circuit

Premature Ventricular Contractions (PVCs)

Ventricular Fibrillation

Ventricular Tachycardia

Arrhythmias

►Sinus Rhythms►Premature Beats►Supraventricular Arrhythmias►Ventricular Arrhythmias►AV Junctional Blocks

Sinus Rhythms

►Sinus Bradycardia

►Sinus Tachycardia

Rhythm #1

30 bpm• Rate?• Regularity? regular

normal

0.10 s

• P waves?• PR interval? 0.12 s• QRS duration?

Interpretation? Sinus Bradycardia

Sinus Bradycardia

►Etiology: SA node is depolarizing slower than normal, impulse is conducted normally (i.e. normal PR and QRS interval).

Rhythm #2

130 bpm• Rate?• Regularity? regular

normal

0.08 s

• P waves?• PR interval? 0.16 s• QRS duration?

Interpretation? Sinus Tachycardia

Sinus Tachycardia

►Etiology: SA node is depolarizing faster than normal, impulse is conducted normally.

►Remember: sinus tachycardia is a response to physical or psychological stress, not a primary arrhythmia.

Premature Beats

►Premature Atrial Contractions (PACs)

►Premature Ventricular Contractions (PVCs)

Rhythm #3

70 bpm• Rate?• Regularity? occasionally irreg.

2/7 different contour

0.08 s

• P waves?• PR interval? 0.14 s (except 2/7)• QRS duration?

Interpretation? NSR with Premature Atrial Contractions

Premature Atrial Contractions

►Deviation from NSR These ectopic beats originate in the

atria (but not in the SA node), therefore the contour of the P wave, the PR interval, and the timing are different than a normally generated pulse from the SA node.

Premature Atrial Contractions

►Etiology: Excitation of an atrial cell forms an impulse that is then conducted normally through the AV node and ventricles.

Teaching Moment

►When an impulse originates anywhere in the atria (SA node, atrial cells, AV node, Bundle of His) and then is conducted normally through the ventricles, the QRS will be narrow (0.04 - 0.12 s).

PVCs

►Etiology: One or more ventricular cells are depolarizing and the impulses are abnormally conducting through the ventricles.

Teaching Moment

►When an impulse originates in a ventricle, conduction through the ventricles will be inefficient and the QRS will be wide and bizarre.

Ventricular Conduction

NormalSignal moves rapidly through the ventricles

AbnormalSignal moves slowly through the ventricles

Atrial Fibrillation

►Deviation from NSR No organized atrial depolarization,

so no normal P waves (impulses are not originating from the sinus node).

Atrial activity is chaotic (resulting in an irregularly irregular rate).

Common, affects 2-4%, up to 5-10% if > 80 years old

ELECTROCARDIOGRAM

ELECTROCARDIOGRAM

Orientation of the 12 Lead ECG► 12-lead ECG provides spatial information about

the heart's electrical activity in 3 approximately orthogonal directions:

►  Right► Left►  Superior► Inferior►  Anterior► Posterior► Each of the 12 leads represents a particular

orientation in space, as indicated below (RA = right arm; LA = left arm, LF = left foot):

Orientation of the 12 Lead ECG► Bipolar limb leads (frontal plane): ►  Lead I: RA (-) to LA (+) (Right Left, or lateral)►  Lead II: RA (-) to LF (+) (Superior Inferior)►  Lead III: LA (-) to LF (+) (Superior Inferior)

►   Augmented unipolar limb leads (frontal plane): ►  Lead aVR: RA (+) to [LA & LF] (-) (Rightward)►  Lead aVL: LA (+) to [RA & LF] (-) (Leftward)►  Lead aVF: LF (+) to [RA & LA] (-) (Inferior)

►   Unipolar (+) chest leads (horizontal plane):►  Leads V1, V2, V3: (Posterior Anterior)►  Leads V4, V5, V6:(Right Left, or lateral)

Einthoven's Triangle

Each of the 6 frontal plane leads has a negative and positive orientation (as indicated by the '+' and '-' signs). It is important to recognize that Lead I (and to a lesser extent Leads aVR and aVL) are right Ûleft in orientation. Also, Lead aVF (and to a lesser extent Leads II and III) are superior Ûinferior in orientation. The diagram further illustrates the frontal plane hookup.

STANDARD LIMB LEADS

ELECTROCARDIOGRAPH

ELECTROCARDIOGRAPH

ELECTROCARDIOGRAPH

ELECTROCARDIOGRAPH

LOCATION OF CHEST ELECTRODES IN 4TH AND 5TH INTERCOSTAL SPACES:

V1: right 4th intercostal space

V2: left 4th intercostal spaceV3: halfway between V2

and V4V4: left 5th intercostal space, mid-clavicular lineV5: horizontal to V4, anterior axillary lineV6: horizontal to V5, mid-

axillary line

ELECTROCARDIOGRAPHVoltages Present at the Input of ECG:

1mv Heart signal (Wanted)

0 – 10 v ac common mode 50Hz (Unwanted)

0 – many microvolts differential 50 Hz ac

0 – 500 mv dc

ELECTROCARDIOGRAPH

ELECTROCARDIOGRAPHGood Design Advantages:

Patient Protection Distortion Elimination Defibrillator Protection High Common Mode Rejection Constant Trace Intensity

ELECTROCARDIOGRAPHElectrical Specification: Common Mode Rejection Ratio: 114 db or

greater

Isolation Impedance: 30 MΩ from patient to chassis

Input Impedance: Buffer Amplifier Greater than 50 MΩ shunted by 1500 pf

Frequency Response: 3db down at 100Hz

ELECTROCARDIOGRAPH

ELECTROCARDIOGRAPH

ELECTROCARDIOGRAPH

Maintenance: Test Equipment Required:

Stylus Pressure Gauge (0 – 5 gms) Signal Generator Multimeter Oscilloscope

ELECTROCARDIOGRAPH Performance checks:

1. Stylus Pressure: 2 – 3 gms2. Trace Intensity3. Centering4. Gain5. Internal Calibration STD 1mv6. Gain Balance

ELECTROCARDIOGRAPH

Preventive Maintenance:

►Electrical checks►Mechanical Inspection►Cleaning►Lubrication: Every 2000 years

ELECTROCARDIOGRAPH

►ECG OPERATION:

►Electrode Colour Coding:For hewlett-packard/Burdick ECG’S

• RA White• La Black• LL Red• RL Green• V Brown

ELECTROCARDIOGRAPH

►Electrode Colour Coding:For European ECG Mc/s

• RA Red• LA Yellow• LL Green• RL Black• V Brown/White

ELECTROCARDIOGRAPH

ELECTROCARDIOGRAPHCorrective Maintenance & Repair:► Ckt Board Component Replacement:1. Do not apply excessive heat 2. Apply heat to the component leads and

remove the component with a perpendicular pull from the board

3. Do not force replacement component leads into a hole clogged with excessive solder

► Stylus Replacement► Pressure Roller Assembly

BIO-ELECTRIC SIGNAL

Lead Selection Ckt►Lead Selection ckt: IC104,105,106,107►Clock pulse & Control pulse are provided

to 4-bit binary up down counter IC 106 (4029)

►Counter counts up when ADV is pressed & counts down when Rev is pressed

►IC107 (4051) enables one of the eight LED’S to indicate lead selection.

►IC104 (4011) & IC105 (4001) ensures only one clock pulse is produced whenever one of the switches is pressed.

Microcontroller based ECGBPL 6108T

Microcontroller based ECGBPL 6108T

salient features ► CARDIART 6108T is a portable 12-lead

electrocardiograph with a single channel printing system, capable of processing all ECG leads simultaneously.

► Automatic and manual recording modes.► Built in rechargeable battery for mains

independent use.► With a fully charged battery, it is possible to take

200 complete ECGs in auto mode.► Printing the ECG on 50-mm paper using quality

thermal printer.► The acquired and memorized signal in automatic

mode can be printed on paper for an unlimited number of times.

salient features

• Compact design and low weight for portability.

• The “active recording” time: the time necessary to acquire and memorize the ECG signal is only 10 seconds. Consequently, effects of interference and muscle tremors are reduced.

• Selectable parameter measurement program.

TECHNICAL SPECIFICATIONS ►Power supply : 230V ± 10%►Power consumption : Less than

12W►Battery : Internal rechargeable

NiMH 9.6V 1500mAH ►Recording system : Thermal

printer, 8 dots/mm

►ECG Leads : Standard 12 leads Acquired 8 leads

Reconstructed 4 leads

(III, aVR, aVL, aVF)

TECHNICAL SPECIFICATIONS►Recording sensitivity

Manual mode: 2.5 - 5 -10 - 20 mm/mV ±

5% Auto mode: dependent on the

signal strength,

Optimizes automatically to 2.5 -5 -10 - 20 mm/mV ± 5%

►Signal Memory : 10 Seconds for each lead in Auto mode

►Operating modes: Manual – acquisition and printing in real time

Auto - simultaneous acquisition

►Safety Standard : Compliant to Class II type IEC-601-1 &

601-2-25 Standards

► CARDIART 6108T complies with IEC standard for safety and electromagnetic compatibility.

► Place the electrocardiograph as far as possible from electrical lines or from source of static electricity. The ECG signal can be disturbed if the electrocardiograph is situated in proximity to source of high voltage or electrical lines.

► Avoid placing electrocardiograph close to other diagnostic or therapeutic equipment like X- ray machines, ultrasound machines, electrically operated beds etc that could be a source of excessive interference and ECG signal distortion.

► Avoid the use of mobile phones in the vicinity.► Keep electrocardiograph away from other electrical

equipment, switch OFF such equipment when recording an ECG.

Charging the internal batteries

► CARDIART 6108T uses NiMH rechargeable internal batteries and are protected against

► over current by means of polymer resettable fuse. To charge the batteries connect the

► “battery charger” to the connector on the back of the device. The “battery charger “ is

► protected against short circuits by an internal fuse.► Caution: All devices are delivered with the batteries

“fully charged

System Block Diagram

Battery Charger circuit

ECG section► The major activities of this section are as below:► High voltage protection of the circuits when the

patient is given shock from a defibrillator.► Deriving standard bi-polar and uni-polar ECGs

from the electrodes connected to the human body.

► Rejection of common mode ac interference signal.

► Fixed gain amplification of low level ECG signals.

► Lead off or poor contact identification.► Removing the low frequency or dc from the ECG

signal through ac coupling.► Second stage amplification and DC level

shifting to provide proper interface to ADC.

Defibrillator protection circuit

First Stage Amplifier

Second stage amplifier

ECG to ADC interface

Right leg drive

Print head Interface circuit

Motor control circuit

Print format: