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12-Lead EKG MEPN Level IV 1 EISLO’s • Discuss the changes in T wave and ST segment morphology with an MI • List the criteria for identification of right or left bundle branch blocks. • List the anatomically congruent leads associated with an inferior, lateral and anterior wall MI • Describe morphology of Q wave presence 2 Myocardial A&P http://www.healthline.com/vpvideo/how-the-heart-works 3 Heart wall - Three layers Epicardium (outer) visceral layer of pericardium thin, transparent smooth, slippery Myocardium (middle) mass of cardiac muscle Endocardium (inner) endothelium over thin connective tissue smooth lining for the chambers and valves continuous with blood vessel endothelium 4 5 Cardiac Enzymes • Myoglobin – Released by all striated muscle – Rises fast (2 hours) after myocardial infarction – Peaks at 6 - 8 hours – Returns to normal in 20 - 36 hours • • Troponin – – – – More specific for myocardial injury Rises 2-6 hours after injury Peaks in 12 hours Remains elevated for 5-14 days CK – – – – – Released by all muscles in the body Rises in 4-6 hours after injury Peaks in 24 hours Returns to normal in 3-4 days CK-MB is myocardial “specific” • Peaks in 3-4 hours • Returns to normal in 2 days 6 Coronary Blood Flow Arteries first branches off the aorta blood moves more easily into the myocardium when it is relaxed between beats during diastole blood enters coronary capillary beds 7 Collateral Circulation 8 9 Coronary Circulation 10 Coronary Circulation Pathologies Compromised coronary circulation due to: emboli: blood clots, air, amniotic fluid, tumor fragments fatty atherosclerotic plaques smooth muscle spasms in coronary arteries Problems ischemia (low supply of nutrients) hypoxia (low supply of O2) infarct (cell death) 11 Internodal tracts Bundle of His Right Bundle Branch 12 SA Node 13 Intranodal Pathways 14 AV Node Conduction Normal conduction pathway from atria to ventricles Limits number of atrial impulses sent to the ventricles 15 Bundle Branches 16 Action Potential Phase 0 Begins at -70 mV with a slow influx of sodium ions; gradually raising the potential toward threshold When threshold is reached fast sodium channels open; causing the cell to fire Phase 1 Rapid sodium pumps are slowed by influx of potassium Phase 2 Plateau phase Sodium influx slows; calcium begins to enter the cell Calcium stimulates cellular contraction by stimulating the myocyte Phase 3 Reverse pumps open; rapid repolarization Phase 4 Back to the -70 mV resting potential 17 Myocardial Action Potential Depolarization Phase 1 of the action potential Stimulation of the cardiac cell by the pacemaker cell causing an influx of Na and Ca, outflow of K. Repolarization Phase 2 of the action potential No impulse entering the cells can cause it to depolarize Relative refractory period Phase 3 of the action potential Impulses entering the cardiac cell now can cause serious, uncontrolled reactions. Absolute refractory period Phase 4 of the action potential The return of the cardiac cells to resting state. 18 EKG Basics 25 mm per sec Each small box - horizontally = 0.4 sec Each small box - vertically = 1 mm 19 EKG Review - Analysis Rhythm Regular or irregular Rate Too fast, too slow, just right P waves Upright, inverted, not there, not related P-R Interval 0.12-0.20; >0.20; <0.12 QRS complex <0.12 QT Interval .34-.44 20 P wave: Represents positive and negative deflections of atrial contraction and relaxation PR Interval: Distance between the P wave and the Q/R wave .12 -20 QRS Complex: represents ventricular depolarization •Q wave: First negative deflection •R Wave: First positive deflection •S Wave: second negative deflection ST Segment: Essentially isoelectric, slopes gently upward •Normal > .08 sec J point: the point where the S wave meets the isoelectric line T Wave: Ventricular repolarization •always upright in leads I, II, V2-V6 •aVR is always negative. •Leads III, aVL, aVF, and V1 can be positive or negative U Wave: unclear etiology, commonly seen in V2-V3 due to proximity to ventricular mass; common in bradycardia, hypokalemia, digitalis 21 QT interval beginning of the QRS complex to the end of the T wave represents ventricular depolarization and repolarization ---- Changes with heart rate QTc QT corrected for heart rate QT / R-R = QTc Evaluates the recovery of the ventricle 22 ECG Leads • 6 limb leads (frontal plane) – 3 bipolar leads – 3 unipolar leads • 6 precordial leads (horizontal plane) – V1 – V6 23 Einthoven’s Triangle Limb Leads BIPOLAR Lead I RA (-) to LA (+) Lead II RA (-) to LL (+) Lead III LA (-) to LL (+) 24 AUGMENTED (UNIPOLAR) LEADS Augmented leads combine 2 leads together (the null point) from the center point of the triangle with one positive pole. aVR (Augmented Voltage Right Arm positive) is a combination of bipolar Leads I and II aVL (Augmented Voltage Left Arm Positive) is a combination of I and III aVF (Augmented Voltage Left Foot positive) is a combination of Bipolar Leads II and III 25 WHAT ARE THE LEADS LOOKING AT? I & AVL II, III & AVF LIMB and AUGMENTED LEADS 26 Precordial Lead Placement V1 – 4th intercostal space right of sternum V2 - 4th intercostal space left of sternum V4 – 5th intercostal space midclavicular line V3 – midway between V2 and V4 V6 – 5th intercostal space midaxillary line V5 – same level as V4 at anterior axillary line between V4 and V6 27 RIGHT SIDED EKG Same lead position as left side – looks directly at the Right ventricle 28 Posterior leads: Posterior View V7 – lateral to V6 at posterior axillary line V8 – level of V7 at the mid-scapular line V9 – level of V8 at the paravertebral line (left posterior thorax midway from spine to V8) 29 30 PRECORDIAL LEADS V1 & V2 V3 & V4 V5 & V6 31 calibration marker LIMB LEADS AUGUMENTED LEADS PRECORDIAL LEADS Bottom line is continuous strip 32 R – Wave Progression 33 R – Wave Progression 34 Myocardial ischemia Various definitions are used. The term commonly refers to diffuse ST segment depression, usually with associated T wave inversion Myocardial injury Injury always points outward from the surface that is injured with ST segment elevation Myocardial infarction death of heart muscle 35 Ischemia, Injury, Infarction Waveforms 36 ST Segments ST segment should be electrically neutral 37 • Visual aid in determining: – Ischemia or injury to myocardium – Normal should be at baseline – Depressed ST segment - >2 mm below baseline 38 39 EKG 1 40 ST Segment Elevation • ST segment elevation is attributed to impending infarction – but can also be due to pericarditis or vasospastic (variant) angina. • The height of the ST segment is measured at a point 2 boxes after the end of the QRS complex – significant if it exceeds 1 mm in a limb lead or 2 mm in a precordial lead. 41 EKG 2 42 T Waves • T waves are normally positive in leads with a positive QRS • T waves are normally asymmetrical • T waves are normally not more than 5 mm high in limb leads or 10 mm high in precordial leads or 2/3 the height of the R wave 43 T wave Ischemia Hyperkalemia Ischemia Ischemia 44 Hyperkalemia EKG 3 45 ST-T Wave • Combination of infarction and often hyperkalemia • Called Tombstone ‘T’ because of the shape. • Usually a sign of impending cardiac death. 46 Inferior-Anterior-Lateral EKG 4 47 Pathology of an MI 48 Localization of ECG Pathology • Inferior: Abnormalities that appear in leads II, III, and aVF (called the inferior leads) indicate pathology on the inferior or diaphragmatic surface of the heart. • Lateral: Leads I, aVF, and V5-V6 are called lateral leads. Abnormality in these leads indicates pathology on the lateral, upper surface of the heart. • Anterior: Anterior pathology is seen in leads V1-V4, and often in lead I. 49 Overview of Infarcts Location of Infarct Arterial Supply Indicative Changes Reciprocal Changes Anterior LAD V1-V4 II, III, aVF Inferior RCA II, III, aVF I, aVL Lateral Circumflex I, aVL V5, V6 V1 Posterior Posterior Descending (RCA) V7, V8, V9 elevation V1, V2 ischemia Septal Septal Perforating (LAD) Posterior Descending (RCA Possible loss of R wave in V1, V2, V3 None 50 T Wave Elevation T ST Segment Elevation ST ST Q T Pathological Q Wave Q Q T T Wave Inversion 51 EKG Changes from Infarction First Detectable Change in EKG •Tall T-waves •increase in height •more symmetric •may occur in the first few minutes Hyper-acute Phase 52 Acute Phase •ST Segment Elevation •Primary indication of injury •Occurs in first hour to hours ST Segment Elevation in Leads •1mm or greater in limb leads •2 mm or greater in chest leads •Hallmark indication of AMI 53 54 CASE STUDY – EVOLUTION of MI 55 56 57 58 59 60 61 62 63 64 View of Inferior Heart Wall Leads II, III, aVF - Looks at inferior heart wall 65 Inferior 66 EKG 5 Inferior 67 EKG 6 View of Lateral Heart Wall Leads I and aVL – Looks at lateral heart wall – Looks from the left arm toward heart *Sometimes referred to as High Lateral or High Apical view* 68 View of Lateral Heart Wall Leads V5 & V6 – Looks at lateral heart wall – Looks from the left lateral chest toward heart *Sometimes referred to as Low Lateral or Low Apical view* 69 View of Entire Lateral Heart Wall Leads I, aVL, V5, V6 - Looks at the lateral wall of the heart from two different perspectives Lateral Wall 70 Lateral 71 EKG 7 Lateral EKG 8 72 View of Anterior Heart Wall • Leads V3, V4 – Looks at anterior heart wall – Looks from the left anterior chest 73 Anterior 74 EKG 9 7510 EKG View of Septal Heart Wall Leads V1, V2 - Looks at septal heart wall - Looks along sternal borders 76 Putting it ALL together ANTERIOR LATERAL S E P T A L LATERAL LATERAL INFERIOR 77 Q Waves • Definition – Septal depolarization – Normally present in I, aVL, V6 78 Two types of Q waves – Non-pathologic • Narrow, shallow Q waves • Not visible in all leads – Pathologic • > 0.04 in duration; at least 1/4 to 1/3 height of R wave • Represent an infarcted area of myocardium 79 PATHOLOGICAL Q WAVES 80 Bundle Branch Blocks If the QRS duration is > .12 there is usually an abnormality of conduction of the ventricular impulse 81 RBB Block Most common ventricular conduction defect Can be acute or chronic Acute RBBB is associated with an acute anterior MI 82 EKG 11 83 RBBB LBB Block Always indicates a diseased heart More common in older adults 84 EKG 12 LBBB 85 86