Atrial depolarisation Electrically both atria act almost as one. They have relatively little muscle and generate a single, small P wave. P wave amplitude rarely exceeds two and a half small squares (0.25 mV). The duration of the P wave should not exceed three small squares (0.12 s). The wave of depolarisation is directed inferiorly and towards the left, and thus the P wave tends to be upright in leads I and II and inverted in lead aVR. Sinus P waves are usually most prominently seen in leads II and V1. A negative P wave in lead I may be due to incorrect recording of the electrocardiogram (that is, with transposition of the left and right arm electrodes), dextrocardia, or abnormal atrial rhythms. Normal P waves may have a slight notch, particularly in the precordial (chest) leads. Bifid P waves result from slight asynchrony between right and left atrial depolarisation. A pronounced notch with a peaktopeak interval of > 1 mm (0.04 s) is usually pathological, and is seen in association with a left atrial abnormality—for example, in mitral stenosis.
The R wave in lead V6 is smaller than the R wave in V5, since the V6 electrode is further from the left ventricle. The depth of the S wave, generally, should not exceed 30 mm in a normal individual (although > 30 mm are occasionally recorded in normal young male adults) In another website it is also shown that small q wave seen in leads III and aVF Normal q-waves reflect normal septal activation (beginning on the LV septum); they are narrow (<0.04s duration) and small (<25% the amplitude of the R wave). They are often seen in leads I and aVL when the QRS axis is to the left of +60o, and in leads II, III, aVF when the QRS axis is to the right of +60o. Septal q waves should not be confused with the pathologic Q waves of myocardial infarction (http://medstat.med.utah.edu/kw/ecg/ecg_outline/Lesson3/index.html)
Sokolow + Lyon (Am Heart J, 1949;37:161) S V1+ R V5 or V6 > 35 mm Cornell criteria (Circulation, 1987;3: 565-72) SV3 + R avl > 28 mm in men SV3 + R avl > 20 mm in women Framingham criteria (Circulation,1990; 81:815-820) R avl > 11mm, R V4-6 > 25mm S V1-3 > 25 mm S V1 or V2 + R V5 or V6 > 35 mm R I + S III > 25 mm Romhilt + Estes (Am Heart J, 1986:75:752-58) Point score system
ST segment depression is always an abnormal finding, although often nonspecific (http://medstat.med.utah.edu/kw/ecg/ecg_outline/Lesson3/index.html)
As a general rule, T wave amplitude corresponds with the amplitude of the preceding R wave, though the tallest T waves are seen in leads V3 and V4. Tall T waves may be seen in acute myocardial ischaemia and are a feature of hyperkalaemia.
Poor Man's Guide to upper limits of QT: For HR = 70 bpm, QT<0.40 sec; for every 10 bpm increase above 70 subtract 0.02 sec, and for every 10 bpm decrease below 70 add 0.02 sec. For example: QT < 0.38 @ 80 bpm QT < 0.42 @ 60 bpm
Tutorial in ecg
Tutorial in ECG Dr. Chew Keng Sheng Emergency MedicineUniversiti Sains Malaysia http://emergencymedic.blogspot.com
The Basics• Standard calibration – 25 mm/s – 0.1 mV/mm• Electrical impulse that travels towards the electrode produces an upright (“positive”) deflection relative to the isoelectric baseline
Vertical and horizontalperspective of the ECG Leads Leads Anatomical II, III, aVF Inferior surface of heart V1 to V4 Anterior surface of heart I, aVL, V5, and Lateral surface V6 of heart V1 and aVR Right atrium
Location of MI and Affected Coronary ArteriesLocation of MI Affected ArteryLateral Left circumflexAnterior LADSeptum LADInferior RCAPosterior RCARight Ventricle RCA
P wave • Always positive in lead I and II in NSR • Always negative in lead aVR in NSR • < 3 small squares in duration • < 2.5 small squares in amplitude • Commonly biphasic in lead V1 • Best seen in leads II
Right Atrial Enlargement• Tall (> 2.5 mm), pointed P waves (P pulmonale
Left Atrial Enlargement• Prominent terminal P negativity (biphasic) in lead V1 (i.e., "Pterminal force") duration >0.04s, depth >1 mm
Left Atrial Enlargement• Notched/bifid (‘M’ shaped) P wave (P ‘mitrale’) in limb leads with the interpeak duration > 0.04s (1 mm)
RAH and LAHRight Atrial Hypertrophy Left Atrial Hypertrophy
Short PR Interval • WPW (Wolff ParkinsonWhite) Syndrome • Accessory pathway (Bundle of Kent) allows early activation of the ventricle (delta wave and short PR interval)
QRS Complexes• Nonpathological Q waves are often present in leads I, III, aVL, V5, and V6• The R wave in lead V6 is smaller than the R wave in V5• The depth of the S wave, generally, should not exceed 30 mm• Pathological Q wave > 2mm deep and > 1mm wide or > 25% amplitude of the subsequent R wave
RVH Changes• A tall positive (R) wave – instead of the rS complex normally seen in lead V1 – an R wave exceeding the S wave in lead V1 – in adults the normal R wave in lead V1 is generally smaller than the S wave in that lead• Right axis deviation (RAD)• Right ventricular "strain" T wave inversions
Left Ventricular Hypertrophy• Sokolow & Lyon Criteria (Am Heart J, 1949;37:161) – S in V1+ R in V5 or V6 > 35 mm• An R wave of 11 to 13 mm (1.1 to 1.3 mV) or more in lead aVL is another sign of LVH• Others: Cornell criteria (Circulation, 1987;3: 56572) – SV3 + R avl > 28 mm in men – SV3 + R avl > 20 mm in women
ST Segment• Normal ST Segment is flat (isoelectric) – Same level with subsequent PR segment• Elevation or depression of ST segment by 1 mm or more, measured at J point IS ABNORMAL• “J” (Junction) point is the point between QRS and ST segment
Variable Shapes Of ST Segment Elevations in AMIGoldberger AL. Goldberger: Clinical Electrocardiography: A Simplified Approach. 7thed: Mosby Elsevier; 2006.
T wave• The normal T wave is asymmetrical, the first half having a more gradual slope than the second half• The T wave should generally be at least 1/8 but less than 2/3 of the amplitude of the corresponding R wave• T wave amplitude rarely exceeds 10 mm• Abnormal T waves are symmetrical, tall, peaked, biphasic or inverted.
T wave• As a rule, the T wave follows the direction of the main QRS deflection. Thus when the main QRS deflection is positive (upright), the T wave is normally positive.• Other rules – The normal T wave is always negative in lead aVr but positive in lead II. – Leftsided chest leads such as V4 to V6 normally always show a positive T wave.
QT interval• QT interval decreases when heart rate increases• A general guide to the upper limit of QT interval. For HR = 70 bpm, QT<0.40 sec. – For every 10 bpm increase above 70 subtract 0.02 sec. – For every 10 bpm decrease below 70 add 0.02 sec• As a general guide the QT interval should be 0.35 0.45 s, and should not be more than half of the interval between adjacent R waves (RR interval).
QT Interval• The QT interval increases slightly with age and tends to be longer in women than in men.• Bazetts correction is used to calculate the QT interval corrected for heart rate (QTc): QTc = QT/ Sq root [RR in seconds]
U wave• Normal U waves are small, round, symmetrical and positive in lead II, with amplitude < 2 mm (amplitude is usually < 1/3 T wave amplitude in same lead)• U wave direction is the same as T wave direction in that lead• More prominent at slow heart rates and usually best seen in the right precordial leads.• Origin of the U wave is thought to be related to afterdepolarizations which interrupt or follow repolarization
Calculation of Heart Rate• Method 1: Count the number of large (0.2- second) time boxes between two successive R waves, and divide the constant 300 by this number OR divide the constant 1500 by the number of small (0.04-second) time boxes between two successive R waves.• Method 2: Count the number of cardiac cycles that occur every 6 seconds, and multiply this number by 10.
Cardiac Arrest & Peri-arrest Rhythms• Cardiac Arrest • Peri arrest rhythms – Shockable – Tachyrrhythmias • VF, Pulseless VT – Bradyarrhythmias – Non Shockable Drugs to control • Asystole, PEA rate Drugs to revert the rhythms
When The Arrhythmias Is UnstableFour main signs1. Signs of low cardiac output – systolic hypotension < 90 mmHg, altered mental status2. Excessive rates: <40/min or >150/min3. Chest pain4. Heart failure• If unstable, electrical therapy: cardioversion for tachyarrhythmias, pacing for bradyarrhythmias
Four Rhythms At Risk Of Developing Asystole1. Recent asystole2. Mobitz II 2nd degree AV Block3. Complete Heart Block (especially with broad QRS or initial heart rate <40/min)4. Ventricular standstill more than 3 secFor these, consider also electrical therapy – Only mentioned in European Resuscitation Council Guidelines 2005
Bradyarrhythmias• 2nd degree Mobitz type 1• the block is at AV Node• Often transient• Maybe asymptomatic• 2nd degree Mobitz type 2• Block most often below AV node, at bundle of His or BB• May progress to 3rd degree AV block
Tachyarrhythmias• For stable tachyarrhythmias, we need to further decide whether it is NARROW QRS or WIDE QRS• For each type, further divide into – Regular – Irregular
Tachyarrhythmias• Narrow QRS tachyarrhythmias – Regular • Sinus Tachycardia, PSVT, atrial flutter with regular AV conduction – Irregular • Atrial Fibrillation, Atrial flutter with variable AV Block• Wide (Broad) QRS tachyarrhythmias – Regular • Ventricular Tachycardia, SVT with BBB – Irregular • Polymorphic VT, AF with BBB
Four Features Suggestive Ventricular Origin• Concordance Polarity• Fusion beats and Capture beats• Bizzare QRS complexes• AV Dissociation
Atrio-Ventricular Tachyarrhythmias• AVNRT versus AVRT• AVNRT = atrioventricular nodal reentrant tachycardia – Due to reentrant circuit loop formed by 2 pathways, slow and fast, in the AV node (micro-reentry)• AVRT = atrioventricular reentrant tachycardia – Due to a large re-entry circuit caused by an aberrant myocardial accessory pathways or bypass tracts
Atrio-Ventricular TachyarrhythmiasAVNRT AVRTMicro-reentry due to two pathways Macro-reentry due to an accessorywithin the AV Node pathways or bypass tractsAffects all ages, but associated with Tends to present at earlier age thanIHD, Rheumatic HD, etc AVNRT; male: female = 2:1; seen in WPW; also associated with Ebstein anomalyMost common form of Paroxysmal 2nd most common form of PSVTsSVTsCauses rapid, almost simultaneous Called orthodromic AVRT ifdepolarization of both ventricles and anterograde conduction throughatria normal His-Purkinje pathway and retrograde conduction through accessory pathway Called antidromic if anterograde conduction through accessory pathway; retrograde conduction
Atrio-Ventricular TachyarrhythmiasAVNRT AVRTQRS complex typically narrow and Orthodromicregular; rate 120 – 250bpm Because ventricle depolarization occurs along normal pathway, QRSBecause atrial depolarization and narrow.ventricle depolarization occur Because atria depolarized late alongsimultaneously, P wave maybe accessory pathway, P wave follows“buried” ; or visible just after or QRS complex;immediately before QRS complex Difficult to differentiate from AVNRT Antidromic Because ventriicles are aberrantly depolarized, a bizarre wide QRS complex tachycardia results; difficult to differentiate from VT or SVT with aberrancy
Paroxysmal supraventricular tachycardia. Atrioventricular nodal reentrant tachycardia. Thepatients heart rate is approximately 146 beats per minute with a normal axis. Note the pseudoS waves in leads II, III, and aVF. Also note the pseudo R waves in V1 and aVR. These deflectionsrepresent retrograde atrial activation.
AV nodal reentrant tachycardia. In yellow, is evidenced the P wave that falls after the QRScomplex.
Paroxysmal supraventricular tachycardia. The left panel depicts antidromic atrioventricularreentrant tachycardia. The right panel depicts sinus rhythm in a patient with antidromicatrioventricular reentrant tachycardia. Note that the QRS complex is an exaggeration of thedelta wave during sinus rhythm.
AVNRT. The rhythm has a typical regular, narrow complex pattern.
Recommended Resources• ABC of Clinical Electrocardiography – www.bmj.com• Goldberger: Clinical Electrocardiography: A Simplified Approach, 6th edition. – Access via www.mdconsult.com• ECG Learning Center – http://medstat.med.utah.edu/kw/ecg/index.htm l• ECG Library – http://www.ecglibrary.com/ecghome.html
Thank You Contact me: Dr. K.S. Chew email@example.com://emergencymedic.blogspot.com