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Ecg 5th year 2016
- An ECG records the electrical activity of the heart over time using electrodes placed on the skin. It detects tiny electrical changes arising from the heart muscle contracting during each heartbeat. - The cardiac impulse originates in the sinoatrial node and travels through the atria and ventricles via specialized conduction pathways before the ventricles contract. - A standard 12-lead ECG provides multiple views of the heart to analyze the rate and rhythm of the heart as well as measure key intervals like the PR interval, QRS duration, and QT interval to identify any abnormalities.
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Ecg 5th year 2016
- 1. NORMAL ECG Prepared by:Dr Yousef Biuk
- 2. DEFINITION • Electrocardiography (ECG)is the process of recording the electrical activity of the heart over a period of time using electrodes placed on a patient’s body. These electrodes detect the tiny electrical changes on the skin that arise from the heart muscle depolarizing during each heartbeat.
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- 5. ELECTROPHYSIOLOGY • Cardiac impulseoriginates in the Sinoatrial (SA) node • Traverses the atria simultaneously – no special conduction wires in atria • Reaches AV node – delay • Enters bundle of His and branches through specialized conducting wires called Purkinje network activates both ventricles - QRS • First the septum from L to R, then right ventricle and then the left ventricle and finally the apex • Then the ventricles recover for next impulse
- 6. PACEMAKER 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.
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- 8. 12 LEAD ECG •Standard ECG is recorded in 12 leads • Six Limb leads – L1, L2, L3, aVR, aVL, aVF • Six Chest Leads – V1 V2 V3 V4 V5 and V6 • L1, L2 and L3 are called bipolar leads • L1 between LA and RA • L2 between LF and RA • L3 between LF and LA
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- 12. ECG PAPER • X-Axisrepresents time - 1 mm = 0.04 sec • Y-Axis represents voltage – 1 mm = 0.1 mV • One big square on X-Axis = 0.2 sec (big box) • Two big squares on Y-Axis = 1 milli volt (mV) • Each small square is 0.04 sec (1 mm in size) • Each big square on the ECG represents 5 small squares = 0.04 x 5 = 0.2 seconds • 5 such big squares = 0.2 x 5 = 1sec = 25 mm • One second is 25 mm or 5 big squares • One minute is 5 x 60 = 300 big squares
- 14. ECG INTERPRETATION • Rate:At usual speed (25mm/s) each ‘big square’ is 0.2s; each ‘small square’ is 0.04s. • To calculate the rate, divide 300 by the number of big squares per R–R interval; or divide 1500 by the number of small suares per R-R interval.
- 15. ECG INTERPRETATION • Rhythm:If cycles are not clearly regular, use the ‘card method’: lay a card along ECG, marking positions of 3 successive R waves. Slide the card to and fro to check that all intervals are equal.
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- 19. ECG WAVES • PWave is Atrial contraction – Normal 0.12 sec • PR interval is from the beginning of P wave to the beginning of QRS – Normal up to 0.2 sec • QRS is Ventricular contraction – Normal 0.08 sec • ST segment – Normal Isoelectic (electric silence) • QT Interval – From the beginning of QRS to the end of T wave – Normal – 0.40 sec • RR Interval – One Cardiac cycle 0.80 sec
- 20. THE P-WAVE • Thenormal P-wave: • Has a smooth contour • Is monophasic in lead II • Is biphasic in lead V1 • upright in II, III, & aVF but inverted in aVR • Has a duration 0f less than 0.12 sec or 3 small squares • Height ˂ 2.5 small square
- 21. P-WAVE ABNORMALITIES SEEN INLEAD II • In lead II two types of P-wave abnormalities can be seen. • Right atrial enlargement is seen as a taller than normal P- wave( increased amplitude) – P pulmonale • Left atrial enlargement seen as a P-wave with a notch in it. (Bifid P-wave) – P mitrale
- 22. OTHER P-WAVE ABNORMALITIES • AbsentP wave: AF, sinoatrial block, junctional (AV nodal) rhythm. • Dissociation between P waves and QRS complexes indicates complete heart block.
- 23. PR INTERVAL • Measurefrom start of P wave to start of QRS • Normal range: 0.12–0.2s (3–5 small squares) • A prolonged PR interval implies delayed AV conduction (1st degree heart block ) • A short PR interval implies unusually fast AV conduction down an accessory pathway, eg WPW
- 24. HEART BLOCK • 1stand 2nd degree (Mobitz I/II) heart block: • 3rd degree AV (complete heart) block:
- 25. QRS COMPLEX • normalduration: <0.12s. If ≥0.12s this suggests ventricular conduction defects, eg: a bundle branch block • Large QRS complexes suggest ventricular hypertrophy • Normal Q wave <0.04s wide and <2mm deep (<25% R) • Pathological Q waves may occur within a few hours of an acute MI
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- 29. ELECTRICAL AXIS • TheQRS electrical (vector) axis can have 4 directions • Normal Axis - when it is downward and to the left – southeast quadrant – from -30 to +90 degrees • Right Axis – when it is downward and to the right – southwest quadrant – from +90 to 180 degrees • Left Axis – when it is upward and to the left – Northeast quadrant –from -30 to -90 degrees • Indeterminate Axis – when it is upward & to the right – Northwest quadrant – from -90 to +180
- 32. CAUSES OF AXIS DEVIATION Causesof Left Axis Deviation: • Left anterior hemiblock • Inferior MI • WPW syndrome • LVH Causes of Right Axis Deviation: • RVH • Pulmonary embolism • Anterolateral MI • Left posterior hemiblock
- 33. QT INTERVAL • Measurefrom start of QRS to end of T wave • It varies with rate • Calculate corrected QT: QTc=QT/⏌RR =0.38–0.42s • Prolonged QT interval: acute myocardial ischaemia, myocarditis, bradycardia, U&E imbalance (Hypokalemia, Hypocalcemia, Hypomagnesemia)
- 34. ST SEGMENT • Usuallyisoelectric • ST elevation (>1mm) usually implies infarction • ST depression (>0.5mm) usually implies ischemia, NSTEMI
- 36. T-WAVE • Normally invertedin aVR, V1 and occasionally V2 • Abnormal if inverted in I, II, and V4–V6 • Peaked in hyperkalaemia and flattened in hypokalaemia
- 37. NORMAL ECG • Standardization– 10 mm (2 boxes) = 1 mV • Sinus Rhythm – Each P followed by QRS, R-R constant • P waves – always examine for in L2, V1, L1 • QRS positive in L1, L2, L3, aVF and aVL. – Neg in aVR • QRS is < 0.12 narrow, Q in V5, V6 < 0.04, < 2 mm deep • R wave progression from V1 to V6, QT interval < 0.4 • Axis normal – L1, L3, and aVF all will be positive • ST Isoelectric, T waves ↑, Normal T↓ in aVR,V1, V2
- 38. NORMAL VARIATIONS • Mayhave slight left axis due to rotation of heart • May have high voltage QRS – simulating LVH • T inversions in V2, V3 and V4 – Juvenile T ↓ • Similarly in women also T↓ • Low voltages in obese women and men • Non cardiac causes of ECG changes may occur
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