Understanding basics of EKG By Alula A.(R III) www.le.ac.uk
Topic for discussion Understanding of cellular electrophysiology Basics Rate Rhythm Axis Intervals P wave QRS ST/T wave Abnormal EKGs
Understanding electrophysiology The EKG is nothing more than a recording of the heart's electrical activity
Cardiac cells Resting state(mme pump) Depolarization /Repolarization
The Cells of the Heart and action potential
EKG basics
Electrode placement Right precordial leads V1: right 4 th intercostal space V2: left 4 th intercostal space V3: halfway between V2 and V4 Left Precordial leads V4: left 5 th intercostal space, MCL V5: horizontal to V4, anterior axillary V6: horizontal to V5, mid-axillary line
Limb leads
EKG grid The wave on EKG primarily reflect the electrical activity of myocardial cell Three chief characteristics of the waves. Duration Amplitude Configuration
EKG strip
Einthoven's Triangle
The Six Precordial Leads Record forces moving anteriorly and posteriorly 12
Order of depolarization
Follow the way
Interpretation steps RRAI- P-QRS-T Rate Rhythm Axis Intervals P wave QRS T
Rate Atrial/ Ventricular rate 60-90 bpm Regular RR; 1500/small box or 300/large box Irregular RR # of QRS waves in 6 sec X 10 # of QRS on the whole EKG(10 Sec) X6
Rhythm Normal sinus Rhythm( originated from SA) The P waves in leads I and II upright Same morphology before each QRS Read on the rhythm strip at lead II if not V1
Axis Two technique; I. Identification of isoelectric lead or II. Look for lead I and avf If needed look for lead II QRS axis Frontal Plane QRS Axis: +90 o to -30 o (in the adult)
Normal Axis
Left axis lead I +ve and avf -ve Look lead II +ve = normal axis -ve = left axis deviation - LA fascicular block - Inferior MI - Pacemaker
Right axis lead I - ve and avf +ve - RVH - Left posterior fascicular block - PE
Intervals PR interval Normal 0.12-0.20 sec QT interval QT c < 0.40 sec Bazett's Formula: QT c = (QT)/SqRoot RR (in seconds)
P wave Bi atrial activation Right to left Lead II or V1 - duration < 0.12 sec - 3 blocks wide - amplitude < 2.5 mm 2.5 blocks high
P wave Normal Up in lead II Down in avr Biphasic, up or down in V1, III Same morphology and PR before each QRS Abnormal too wide, too tall, different, unclear, funny (i.e. LAE, RAE, wandering pacemaker/mat, a fib respectfully)
Wandering Pacemaker at least 3 different P wave morphologies in a Ventricular response is irregularly irregular, COPD
QRS Duration < 0.10 sec QRS amplitude - variable from lead to lead and from person to person Comment: pathologic Q waves, abnormal voltage
QRS Q wave Narrow (<0.04s duration) and Small (<25% the amplitude of the R wave) 0.1mv Often seen in leads I and avl when the QRS axis is to the left of +60 o, and leads II, III, avf when the QRS axis is to the right of +60 o. R-waves begin in V1 or V2 and progress in size to V5. R-V6 < R-V5. In reverse, the S-waves begin in V6 or V5 and progress in size to V2. S- V1 is usually smaller than S-V2 The usual transition from S>R in the right precordial leads to R>S in the left precordial leads is V3 or V4
ST wave Normal V1-V3 concave upwards
ST / ST- T wave Abnormal ST elevation and/or Depression ST elevation **compare J point to the TP level not PR**
Early repolarization- concave upwards
ST elevation Convex or straight upward ST
ST segment depression abnormal but non specific
T wave The normal T wave is usually in the same direction as the QRS except in the right precordial leads( V1-V3) T wave amplitude is 1/3-2/3 of R wave Always upright in leads I, II, V3-6, and Always inverted in lead avr
U wave Afterdepolarizations which interrupt or follow repolarization U wave 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
Conclusion ECG interpretations i. Measurements ii. Rhythm analysis iii. Conduction analysis iv. Waveform description v. ECG interpretation (normal, abnormal, bordeline) i. Comparison with previous ECG (if any) Remember RRAI P-QRS-T
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