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    Add as FriendNormal Electrocardiography

    by: G Pruthvi

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    1 : NORMAL ELECTROCARDIOGRAM G PRUTHVI PG IN GENERAL MEDICINE
    2 : OUTLINE HISTORY INTRODUCTION ECG LEADS AND RECORDING ECG WAVE FORMS AND INTERVALS ECG INTERPRETATION ARTIFACTS IN ECG NORMAL VARIANTS IN ECG
    3 : History 1895 - William Einthoven , credited for the invention of ECG. 1924 - the noble prize for physiology or medicine is given to William Einthoven for his work on ECG. 1942- Goldberger increased Unipolar lead voltage by 50% and made Augmented leads
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    5 : MODERN ECG INSTRUMENT
    6 : Introduction Ecg is defined as graphic recording of electric potentials generated by the heart. Electric currents that spread through the heart are produced by three components:cardiac pacemaker cells,specialized conduction tissue & heart muscle itself. Ecg however records only the depolarisation & repolarisation potentials generated by the atrial & ventricular myocardium.
    7 : Recording of ECG ECG graphs: 1 mm squares 5 mm squares Paper Speed: 25 mm/sec standard Voltage Calibration: 10 mm/mV standard
    8 : ECG Paper: Dimensions 5 mm 1 mm 0.1 mV 0.04 sec 0.2 sec Time Voltage
    9 : Electrocardiograph It is a sophisticated galvanometer,a sensitive electromagnet,which can detect and record changes in electro magnetic potential. It has a positive & negative pole. The wire extensions from these poles are connected to electrodes The paired electrodes together constitute a lead When the paired electrodes are orientated in any particular direction, the theoretical straight line joining the electrodes is known as axis of that lead.
    10 : ECG Leads Leads are electrodes which measure the difference in electrical potential between either: 1. Two different points on the body (bipolar leads) 2. One point on the body and a virtual reference point with zero electrical potential, located in the center of the heart (unipolar leads)
    11 : ECG Leads The standard ECG has 12 leads: 3 Standard Limb Leads 3 Augmented Limb Leads 6 Precordial Leads The limb leads record potentials transmitted on to the frontal plane & chest leads record potentials transmitted on to the horizontal plane. The axis of a particular lead represents the viewpoint from which it looks at the heart.
    12 : Standard Limb Leads
    13 : Precordial Leads
    14 :
    15 : Summary of Leads
    16 : Localising the arterial territory Inferior II, III, AVF Lateral I, AVL, V5-V6 Anterior / Septal V1-V4
    17 : Standard sites unavailable Patient pathology Amputation or burns or bandages? should be placed as closely as possible to the standard sites
    18 : Arrangement of Leads on the EKG
    19 : SPECIAL LEADS V3R,V4R V7,V8,V9 Lewis leads or S5 has the left arm electrode in 2nd intercostal space at right sternal border and right arm electrode in 4th intercostal space at right sternal border. It is read is Lead 1 .The Lewis lead configuration can help to detect atrial activity and its relationship to ventricular activity and it is supposed to demonstrate atrial activity much better to aid in identification of atrial flutter and broad complex tachycardia. Brugada leads-here V3 kept in Rt 3rd IC space and V5 kept in left 3rd IC space
    20 : Right Sided & Posterior Chest Leads
    21 :
    22 : ECG Wave forms & Intervals
    23 : Normal P wave Atrial depolarisation It is best seen & studied in lead II because the frontal P wave axis is usually directed to the positive pole of this lead. Duration 80 to 100 msec Maximum amplitude 2.5 mm Axis +45 to +65 Biphasic in lead V1
    24 : Normal P wave
    25 : Normal QRS complex Produced due to ventricular depolarization It corresponds to phase ‘0’ of ventricular action potential Completely negative in lead aVR , maximum positivity in lead II rS in right oriented leads and qR in left oriented leads Transition zone commonly in V3-V4 RV5 > RV6 normally Normal duration 50-110 msec, not more than 120 msec Physiological q wave in frontal leads is not > 0.03 sec in duration
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    27 : Amplitude of QRS Depends on the following factors 1.electrical force generated by the ventricular myocardium 2.distance of the sensing electrode from the ventricles 3.Body build :a thin individual has larger complexes when compared to obese individuals 4.direction of the frontal QRS axis
    28 : J Point It refers to the point on ECG which coincides with the end of depolarization and start of repolarization of ventricles, i.e.it occurs at the end of QRS complex. At this point since all parts of ventricles are depolarized, so no current is flowing around the heart. Therefore, at J point the potential of ECG exactly zero voltage.
    29 : ST Segment It is an isoelectric period between the end of QRS complex and beginning of T wave. It corresponds to phase ‘2’ of ventricular action potential.
    30 : Normal T wave Produced due to active ventricular repolarization. It corresponds to phase ‘3’ of ventricular action potential Same direction as the preceding QRS complex Smooth contours ,blunt apex with asymmetric limbs The T wave in V6 is greater than T wave in V1 normally Relatively tall T waves are seen in V2 toV4 leads Height < 5mm in limb leads and <10 mm in precordial leads May be tall in athletes
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    32 : Normal u wave Genesis of U wave is uncertain Best seen in midprecordial leads Isoelectric in lead aVL Height < 10% of preceding T wave Rarely exceeds 1 mm in amplitude May be tall in athletes (2mm)
    33 : PR Interval It starts from the beginning of the P wave to starting of QRS cmplex. Normal duration is 0.12-0.2osec. It includes atrial depolarisation & AV nodal delay.
    34 : QT Interval It starts from beginning of QRS complex to end of the T wave. The beginning of the QRS complex is best determined in a lead with a intial q wave commonly leads I,II,aVL,V5,V6. Lead AVL is normally used to measure QT interval because U wave is iso electric in this lead as its frontal plane axis is +60 degrees When the QT interval is measured from a lead where U wave is prominent the dip or notch between the T & U is taken as end of the Twave. The QT interval is corrected for what it would theoretically be at the rate of 60 beats/min
    35 : The corrected QT interval is known as QTc interval. Bazett’s formula states QTc =QT/vR-R Normal range of QTc is .35 to.43 sec A useful rule of thumb is that, with a normal heart rate of 60 to 100 beats for min, the QT interval should not exceed half the RR interval.
    36 : TP Interval It is measured from end of the T wave to the beginning of P wave It measures the diastolic period of heart Variable TP interval indicates AV dissociation It is considered as reference potential level
    37 : Normal ECG
    38 : ECG INTERPRETATION Standardization & technical features(including lead placement &artifacts) Heart rate Rhythm Axis P wave PR interval QRS interval T wave QT interval U wave Precordial R wave progression Abnormal Q waves ST segment
    39 : Determining the Heart Rate Rule of 300/1500 6 Second Rule
    40 : Rule of 300 Count the number of “big boxes” between two QRS complexes, and divide this into 300. (smaller boxes with 1500) for regular rhythms.
    41 : The Rule of 300 It may be easiest to memorize the following table:
    42 : 6 Second Rule ECGs record 6 seconds of rhythm per page, Count the number of beats present on the ECG Multiply by 10 For irregular rhythms.
    43 : RHYTHM The word rhythm of heart is used to refer part of the heart which is controlling activation sequence. Normal heart rhythm,with electrical activation beginning in SA node ,is called sinus rhythm.
    44 : P wave axis Normal frontal plane p wave axis is directed to the region of +45 to +65 Since most normal p waves are directed towards the region of +50 they will be mostly aligned with and directed towards the positive pole of standard lead II.
    45 : The QRS Axis The average direction of spread of depolarisation wave through the ventricles as seen from the front is called the cardiac axis. By near-consensus, the normal QRS axis is defined as ranging from -30° to +100°. -30° to -90° is referred to as a left axis deviation (LAD) +100° to +180° is referred to as a right axis deviation (RAD)
    46 :
    47 : Determining the Axis The Quadrant Approach The Equiphasic Approach
    48 : The Quadrant Approach 1. Examine the QRS complex in leads I and aVF to determine if they are predominantly positive or predominantly negative. The combination should place the axis into one of the 4 quadrants below.
    49 : Equiphasic approach The cardiac axis is at right angles to the lead in frontal plane in which R and S waves are of equal size. If R and S waves are not equal then axis points towards the lead where R wave is larger than the S wave and viceversa.
    50 : Using leads I, II, III
    51 : Artifacts in ECG Electrical artifacts : external or internal external can be minimized by straightening the lead wires internal can be due to muscle tremors , shivering, hiccoughs .
    52 : overdamping When the pressure of the stylus is too firm on the paper so that it’s movements are retarded The ecg deflexions are inscribed more slowly so that they become fractionally wider Results in diminished amplitude of deflexions? a small S wave may disappear
    53 : Underdamping or overshoot When the writing stylus is not pressed firmly enough against the paper Results in overshoot of the upswing and downswing of the writing stylus,resulting in sharp spikes at the corners Effects:deflexions are inscribed more rapidly ? resulting in fractionally narrower complexes
    54 : Artifacts in ECG
    55 : REVERSAL OF LEADS Reversal of arm leads is the most common lead placement error and is the easiest to recognize because of negative P wave in L1. In patients with AF or unrecognizable P waves, if the polarity of QRS in L1 is different from that of left precordial leads V5 and V6, arm lead reversal is suspected.
    56 : ECG
    57 : In case of reversal of arm leads the morphology of complexes in the limb leads resembles dextrocardia. However dextrocardia and reversal of arm leads can be differentiated on the basis of QRS complexes in the precordial leads. In dextrocardia as we progress from V1 to V6 QRS complex becomes progressively smaller and displays mostly QS or rS in V5 or V6. In reversal of arm leads the progression of QRS from V1 to V6 is normal.
    58 : Normal variants of ECG Sinus arrhythmia Early repolarisation syndrome Persistent juvenile pattern Non specific T wave changes
    59 : Sinus arrhythmia Characterized by alternating periods of slow and rapid rates. It is due to irregular fluctuating discharge of SA node. Mostly associated with phases of respiration(respiratory sinus arrhythmia) The period of faster rate occur during end of inspiration, slower rate towards end of expiration. The mechanism is mediated by reflex stimulation of vagus nerve from receptors in lungs. It is accentuated by vagotonic procedures like carotid sinus compression and abolished by vagolytic procedures like exercise,atropine.
    60 : One P wave for one QRS complex Constant PR interval Normal P,QRS,T complexes with alternating periods of gradually lengthening and shortening of P-P intervals. Respiratory sinus arrhythmia is normal physiological phenomenon and most marked in young persons.
    61 : Early repolarisation syndrome Also called athletes heart Characterized by Prominent j(junctional) waves concave upward minimally elevated,ST segments Relatively tall and frequently symmetrical T waves Occasionally inverted T waves Prominent but narrow initial Q waves in left oriented leads Tall R waves in left precordial waves Prominent mid precordial U waves Rapid precordial transition A tendency to counterclockwise electrical rotation Sinus bradycardia or normal but slow sinus rates
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    63 : Persistent Juvenile pattern Characterized by inversion of T waves in right precordial leads V1 to V4. T wave inversions in V1toV4 are common in infancy and childhood If it persists in adults also then called persistent juvenile pattern. More common in negroes.
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    65 : Non specific T wave variants Inversion of T waves may occur as non specific manifestation in leads where T waves are normally upright. They may be found in following circumstances Anxiety and fear As an orthostatic response As a postprandial response As result of hyperventilation Idiopathic
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