ELECTROCARDIOGRAM► InternalResting Potential: -90mv► During Depolarisation Cell Potential Changes to +20mv
Normal Impulse ConductionSinoatrial node AV node Bundle of HisBundle Branches Purkinje fibers
Impulse Conduction & the ECG Sinoatrial node AV node Bundle of His Bundle Branches Purkinje fibers
The “PQRST” ►P wave - Atrial depolarization • QRS - Ventricular depolarization • T wave - Ventricular repolarization
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)
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. For more presentations www.medicalppt.blogspot.com
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.
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 3 3 sec sec ► 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
Step 2: Determine regularity R R► 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
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
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 FormationArrhythmias can arise from problems in the: • Sinus node • Atrial cells • AV junction • Ventricular cells
SA Node ProblemsThe SA Node can:► fire too slow Sinus Bradycardia► fire too fast Sinus Tachycardia Sinus Tachycardia may be an appropriate response to stress.
Atrial Cell ProblemsAtrial cells can:► fire occasionally from Premature Atrial a focus Contractions (PACs)► firecontinuously due Atrial Flutter to a looping re-entrant circuit
►A re-entrant pathway occurs when an impulse loops and results in self- perpetuating impulse formation.
Atrial Cell ProblemsAtrial cells can also:• fire continuously Atrial Fibrillation from multiple foci or fire continuously Atrial Fibrillation due to multiple micro re-entrant “wavelets”
Teaching Moment Atrial tissueMultiple micro re-entrant “wavelets”refers to wanderingsmall areas ofactivation whichgenerate fine chaoticimpulses. Collidingwavelets can, in turn,generate new foci ofactivation.
AV Junctional ProblemsThe AV junction can:► fire continuously due Paroxysmal to a looping re-entrant Supraventricular circuit Tachycardia► block impulses coming AV Junctional from the SA Node Blocks
Ventricular Cell ProblemsVentricular cells can:► fire occasionally from Premature Ventricular 1 or more foci Contractions (PVCs)► fire continuously from Ventricular Fibrillation multiple foci► fire continuously due Ventricular Tachycardia to a looping re- entrant circuit
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.
Rhythm #3• Rate? 70 bpm• Regularity? occasionally irreg.• P waves? 2/7 different contour• PR interval? 0.14 s (except 2/7)• QRS duration? 0.08 sInterpretation? 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 Normal AbnormalSignal moves rapidly Signal moves slowlythrough the ventricles 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
Orientation of the 12 Lead ECG► 12-lead ECG provides spatial information about the hearts 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)
Einthovens TriangleEach of the 6 frontal planeleads has a negative andpositive orientation (asindicated by the + and -signs). It is important torecognize that Lead I (and toa lesser extent Leads aVR andaVL) are right Ûleft inorientation. Also, Lead aVF(and to a lesser extent LeadsII and III) are superiorÛinferior in orientation. Thediagram further illustrates thefrontal plane hookup.
LOCATION OF CHEST ELECTRODES IN 4TH AND 5TH INTERCOSTAL SPACES:V1: right 4th intercostal spaceV2: 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 ac0 – 500 mv dc
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
ELECTROCARDIOGRAPHCorrective Maintenance & Repair:► Ckt Board Component Replacement:1. Do not apply excessive heat2. Apply heat to the component leads and remove the component with a perpendicular pull from the board3. Do not force replacement component leads into a hole clogged with excessive solder► Stylus Replacement► Pressure Roller Assembly
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.
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
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.