ECG Lead Theory 2022 PDF

Diploma in ECG Interpretation (c) D Richley 2022  ECG lead theory Dr Dave Richley The cardiac conduction system (c) D Richley 2022 Relationship between sequence of electrical events and ECG 1. Atrial 2. AV nodal 3. Ventricular 4. Vent...

Diploma in ECG Interpretation (c) D Richley 2022  ECG lead theory Dr Dave Richley The cardiac conduction system (c) D Richley 2022 Relationship between sequence of electrical events and ECG 1. Atrial 2. AV nodal 3. Ventricular 4. Ventricular depolarisation depolarisation depolarisation repolarisation P wave PR segment QRS complex T wave (c) D Richley 2022  Standard limb electrode positions Read Your Red Right arm (below elbow) Yellow Left arm (below elbow) Green Left leg (below knee) Book Good Black Right leg (below ankle) The limb electrodes are considered to form an equilateral triangle with the heart at its centre (c) D Richley 2022 The ‘standard’ limb leads: I, II and III (c) D Richley 2022 The ‘standard’ limb leads: I, II and III (c) D Richley 2022 The ‘standard’ limb leads: I, II and III (c) D Richley 2022 Einthoven’s triangle (c) D Richley 2022 ‘Augmented unipolar’ limb leads (c) D Richley 2022  The 6 limb leads + aVR aVL + I - + III II aVF + + + (c) D Richley 2022 Hexaxial reference system (c) D Richley 2022  Limb Leads All limb leads are mathematically related to each other From any 2 leads, remainder can be calculated Eg: Lead I = VLA – VRA Lead III = VLL - VLA Lead I + Lead III = VLA – VRA + VLL – VLA = VLL - VRA = Lead II (c) D Richley 2022 ECG appearances in limb leads differ according to the orientation of the lead in relation to the direction of current flow (c) D Richley 2022  Right leg electrode Used in a circuit to reduce interference Is not an earth electrode Can be placed anywhere (c) D Richley 2022 Limb leads register electrical activity in the frontal plane: right/left and up/down. Chest leads are needed to record electrical activity in the horizontal (transverse) plane. (c) D Richley 2022  The standard chest electrode positions V2 4th intercostal space, left sternal edge V1 V3 4th intercostal space, exactly midway between right sternal edge V2 and V4 V5 horizontal with V4, anterior axillary line V6 horizontal with V4, mid- axillary line V4 5th intercostal space, mid- clavicular line (c) D Richley 2022  Wilson’s central terminal - Negative pole of chest leads is formed by electrically joining together the three limb electrodes (c) D Richley 2022  The chest leads spine Wilson’s central terminal LA LA LV V6 V5 V4 V1 V2 V3 sternum All chest electrodes are positive poles(c) D Richley 2022 aVR aVL I V1 V2 III II aVF (c) D Richley 2022 Typical format of a 12-lead ECG (c) D Richley 2022