Essentials of 12 Lead ECG Interpretation Terry White, RN, EMT-P Topics Anatomy Revisited The 12 Lead ECG Device The 12 Lead ECG Format Waveform Components Lead Views Anatomy Revisited RCA
right ventricle inferior wall of LV posterior wall of LV (75%) SA Node (60%) AV Node (>80%) LCA
septal wall of LV anterior wall of LV lateral wall of LV posterior wall of LV (10%) Anatomy Revisited
SA node Intra-atrial pathways AV node Bundle of His Left and Right bundle branches left anterior fascicle left posterior fascicle Purkinje fibers The 12 Lead ECG Device
Device serves as a voltmeter measures the flow of electricity Unipolar vs Bipolar Leads Bipolar Leads 1 positive and 1 negative electrode RA always negative LL always positive
Traditional limb leads are examples of these Lead I Lead II Lead III View from a vertical plane Unipolar Leads 1 positive electrode & 1 negative reference point
calculated by using summation of 2 negative leads Augmented Limb Leads aVR, aVF, aVL view from a vertical plane Precordial or Chest Leads V1-V6 view from a horizontal plane The 12-Lead ECG Format
Leads typically produced by devices used prehospital The 12-Lead ECG Format Fields not typically produced by devices used prehospital The 12-Lead ECG Format Device prints out 2.5 sec each of Leads I, II, III
then switches to aVR, aVL, aVF then switches to V1, V2, V3 and then to V4, V5, V6 (varies by device) Device computer analyzes all 10 sec of all 12 leads but only prints 2.5 sec of each group The 12-Lead ECG Format The computer diagnosis is not always accurate!!! The 12-lead ECG Format
The computer IS very accurate at measuring intervals & durations Waveform Components: R Wave First positive deflection; R wave includes the downstroke returning to the baseline Waveform Components: Q Wave
First negative deflection before R wave; Q wave includes the negative downstroke & return to baseline Waveform Components: S Wave Negative deflection following the R wave; S wave includes departure from & return to baseline Waveform Components: QRS
Q waves Can occur normally in several leads Normal Q waves called physiologic Physiologic Q waves < .04 sec (40ms) Pathologic Q >.04 sec (40 ms) Waveform Components: QRS Q wave
Measure width Pathologic if greater than or equal to 0.04 seconds (1 small box) Waveform Components: QS Complex Entire complex is negatively deflected; No R wave present Waveform Components: J-Point Junction between end of QRS and beginning of ST segment; Where QRS stops & makes a sudden sharp change of direction
Waveform Components: ST Segment Segment between J-point and beginning of T wave Waveform Components: ST Segment Need reference point Compare to TP segment DO NOT use PR segment as reference! ST
TP Waveform Components: Practice Find J-points and ST segments Waveform Components: Practice Find J-points and ST segments Lead Views
Lead Groups I aVR V1 V4 II aVL V2 V5
III aVF V3 V6 Limb Leads Chest Leads Inferior Wall
II, III, aVF View from Left Leg inferior wall of left ventricle I aVR V1 V4 II aVL
V2 V5 III aVF V3 V6 Inferior Wall Posterior View
portion resting on diaphragm ST elevation suspect inferior injury I aVR V1 V4 II aVL V2
V5 III aVF V3 V6 Inferior Wall Lateral Wall
I and aVL View from Left Arm lateral wall of left ventricle I aVR V1 V4 II aVL
V2 V5 III aVF V3 V6 Lateral Wall V5 and V6
Left lateral chest lateral wall of left ventricle I aVR V1 V4 II aVL V2
V5 III aVF V3 V6 Lateral Wall I, aVL, V5, V6 ST elevation suspect
lateral wall injury Lateral Wall I aVR V1 V4 II aVL
V2 V5 III aVF V3 V6 Anterior Wall V3, V4
Left anterior chest electrode on anterior chest I aVR V1 V4 II aVL V2
V5 III aVF V3 V6 Anterior Wall V3, V4 ST segment elevation
suspect anterior wall injury I aVR V1 V4 II aVL V2
V5 III aVF V3 V6 Septal Wall V1, V2 Along sternal borders
Look through right ventricle & see septal wall I aVR V1 V4 II aVL V2
V5 III aVF V3 V6 Septal V1, V2 septum is left ventricular tissue
I aVR V1 V4 II aVL V2 V5
III aVF V3 V6 ST Segment Analysis For each complex, determine whether the ST segment is elevated one millimeter or more above the TP segment 12-Lead ECG
AMI recognition Two things to know What to look for Where you are looking AMI Recognition What to look for ST segment elevation One millimeter or more (one small box) Present in two anatomically contiguous leads
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