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12 Lead Interpretation Objectives • • • • • Ischemia, injury and infarction ECG complex review J point ST segment STEMI recognition Ischemia to Infarct • • • • • Infarction is an evolving process As the infarct evolves ECG changes may occur quickly or more gradually These changes may be seen on the 12 lead as they evolve Acquiring more then one 12 lead may be necessary A normal 12 lead does not rule out acute myocardial infarction The ECG Complex • • • • The J point is the point where the S wave ends and the ST segment begins ST elevation is measured after the J point The ST segment is compared to the base line The base line or isoelectric line is found at the bottom of the calibration bar J point ST Segment • • • Starts with the J point Ends with the beginning of the T wave Elevation or depression of the ST segment is measured 0.08 seconds (2 small squares) to the right of the J point ST segment PR Interval • • • Begins at the end of the P wave Ends at the beginning of the QRS When determining the isoelectric or baseline find the PR interval of 2 consecutive complexes, draw a line using a straight edge and measure ST elevation from this line; this is the most accurate way to determine if the ST segment is elevated PR Interval Isoelectric line TP Segment • • • • Begins at the end of the T wave Ends at the beginning of the P wave Can be used as a back up to the PR interval to determine the baseline when assessing ST elevation Not as accurate as the PR interval TP segment Hyperacute T-wave • As an acute myocardial infarction develops various 12 lead ECG changes occur • Initially the 12 lead ECG may show tall or hyperacute T-waves signifying cardiac ischemia – may only be present for a short time after ischemia has begun (5 to 30 minutes) • Paramedics may not see this change as many patients wait for at least 30 minutes to call EMS T-wave ST segment elevation • • • • • • Usually seen with in the first few hours after the onset of symptoms Changes may be very subtle or pronounced Any elevation in 2 contiguous leads is significant ST segment elevation greater than 1mm or 2mm in precordial leads (V1 through V6) 1mm = 1 small square on the ECG paper For more information on ST segment abnormality click on this link: http://www.madsci.com/manu/ekg_st-t.htm Measure ST elevation from this point J point PR Interval 2mm or 2 small squares Tombstones • Pronounced ST segment elevation may appear as tombstones • Tombstones are a result of the fusing of the ST segment and T wave tombstone Pathological Q wave • • • • Indicate a loss of viable myocardium May develop 1 to 2 hours after the onset of symptoms but can take anywhere from 12 to 24 hours to develop Abnormal Q waves are at greater then one third of the R wave height deep and greater then 1mm (or 1 small square) wide Q waves may be visible in a patient without infarct but will not meet the parameters to be considered abnormal Greater than 1mm wide Reciprocal Changes • • • Are seen as ST depression in the opposite leads from where the ST elevation is seen Leads II, III and aVF are opposite to Leads I, aVL, and all of the V leads Therefore, if there is ST elevation in leads II, III and aVF any ST depression (if present) would be seen in leads I, aVL and any of the V leads Reciprocal Changes • • • ST segment depression seen in the opposite leads from ST segment elevation Highly sensitive as an indicator of acute MI Frequently seen in larger infarctions ST elevation Reciprocal ST depression The 12 Lead Printout Calibration bar (the isoelectric line is indicated by the bottom of the calibration bar) 25mm/sec Paper speed indicates how fast the paper moves (5 larger squares = 1 second) On the Zoll 12 lead printout there is a break in the ECG to indicate where the tracing changes to the next lead Practice Locate the J point in each of the above complexes Click the mouse to check your location The J point is at the end of the S. This is located where the upstroke of the S changes to become horizontal. Practice Isoelectric Line Isoelectric Line Isoelectric Isoelectric Line Elevated Depressed • Locate the J point in each of the above complexes • Identify ST segment abnormalities • Click the mouse to check your answers • The red dot shows the J point • The red line shows the ST segment 0.08 seconds (2 small squares) from the J point Normal 12 Lead • • • Notice where the J point is for one complex in each lead Also look at the ST segment for one complex in each lead This an example of a 12 lead that the Zoll E series will generate Practice ECG # 1 • • • • • Look for the J point and ST elevation in the above 12 lead Look for reciprocal changes Which lead groups are involved? What area of the heart is involved? Which coronary artery feeds this area of the heart? Answer ECG # 1 • • • • Leads II, III, aVF all have ST elevation, these are contiguous inferior leads Leads I, aVL, V2, V3 and V4 all have ST depression signifying reciprocal changes These changes are consistent with an acute inferior MI In 90% of the population the inferior aspect of the heart blood supply is via the right coronary artery Practice ECG # 2 • • • • • Look for the J point and ST elevation in the above 12 lead Look for reciprocal changes Which lead groups are involved? What area of the heart is involved? Which coronary artery feeds this area of the heart? Answer ECG # 2 • • • • • ST elevation in Leads I, aVL, V2, V3, V4, V5 Lead II and III show reciprocal changes as well as evidence of an old MI (in the form of a pathological Q wave) Lateral leads (I, aVL and V5) as well as Anterior and septal lead groups (V2, V3 and V4) Anterior and Lateral are the main areas of the heart involved Left anterior descending and the left circumflex arteries supply this area of the heart Practice ECG # 3 • • • • • Look for the J point and ST elevation in the above 12 lead Look for reciprocal changes Which lead groups are involved? What area of the heart is involved? Which coronary artery feeds this area of the heart? Answer ECG # 3 • • • • • ST elevation in leads II, III and aVF Reciprocal changes in leads I, aVL, V2 and V3 Leads II, III and aVF are contiguous inferior leads This is an acute inferior MI This area of the heart is supplied by the right coronary artery in 90% of the population Practice ECG # 4 • • • • • Look for the J point and ST elevation in the above 12 lead Look for reciprocal changes Which lead groups are involved? What area of the heart is involved? Which coronary artery feeds this area of the heart? Answer ECG # 4 • • • • • ST elevation in leads I, V2, V3, V4, V5, V6 and aVL Reciprocal changes shown in leads III and aVF V3 and V4 are anterior leads, I, aVL, V5 and V6 are lateral leads This is an acute anteriolateral MI Left anterior descending and left circumflex arteries supply these areas of the heart Practice ECG # 5 • • • • • Look for the J point and ST elevation in the above 12 lead Look for reciprocal changes Which lead groups are involved? What area of the heart is involved? Which coronary artery feeds this area of the heart? Answer ECG # 5 • • • • • ST elevation in leads II, III, aVF and V6 Reciprocal changes in leads V2, V3 and V4 II, III and aVF are inferior leads, V6 is a lateral lead and ST elevation must be present in at least 2 leads that view the same area of the heart This is an acute inferior MI The inferior area of the heart is supplied by the right coronary artery in 90% of the population Practice ECG # 6 • • • • • Look for the J point and ST elevation in the above 12 lead Look for reciprocal changes Which lead groups are involved? What area of the heart is involved? Which coronary artery feeds this area of the heart? Answer ECG # 6 • • • • • ST elevation in leads V1, V2, V3 and V4 There are no obvious reciprocal changes V1 and V2 are septal leads, V3 and V4 are anterior leads This is an acute anterioseptal MI The left anterior descending artery supplies this area of the heart Thank You for participating in Sunnybrook – Osler Centre for Prehospital Care online education! If you have any questions please bring them with you to class!