© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 1 Fast & Easy ECGs, 2E ST Segments, T Waves, QT Intervals, and U Waves Fast & Easy ECGs, 2nd E – A Self- Paced Learning Program 99

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 2 Fast & Easy ECGs, 2E Other Key Steps Q Q To thoroughly assess the ECG, examine the ST segments, T waves, QT intervals and U waves

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 3 Fast & Easy ECGs, 2E ST Segment Isoelectric line that follows the QRS complex and connects it to the T wave Represents the end of ventricular depolarization and beginning of ventricular repolarization I I

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 4 Fast & Easy ECGs, 2E Measuring ST Segments PR segment is the baseline from which to evaluate the degree of displacement of the ST segment from the isoelectric line Draw a straight line (or use a paper) extending from the PR segment out past the J point Intervals should be at same level horizontally

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 5 Fast & Easy ECGs, 2E Measuring ST Segments Alternatively, the TP interval can be used – space between the T wave and the P wave of the beat that follows it Intervals should be at same level horizontally

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 6 Fast & Easy ECGs, 2E Measuring ST Segments For proper measurement, we use a point 0.04 seconds (one small box) after the J point to identify the presence of elevation or depression An elevated ST segment is one that is 1 mm or more above the baseline An depressed ST segment is one that is 1 mm or more below the baseline

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 7 Fast & Easy ECGs, 2E Abnormal ST Segments Abnormal ST segments are indicative of abnormal ventricular repolarization – Two types are ST segment elevation and ST segment depression – ST segments may also be absent or indistinguishable

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 8 Fast & Easy ECGs, 2E Abnormal ST Segments An elevated ST segment is one that is 1 mm or more above the baseline A depressed ST segment is one that is 1 mm or more below the baseline

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 9 Fast & Easy ECGs, 2E ST Elevation and Depression Elevation or depression of the ST segment is a hallmark feature of myocardial ischemia and injury I I

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10 Fast & Easy ECGs, 2E T Waves Represent completion of ventricular repolarization (recovery) Is a wide, broad waveform I I

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 11 Fast & Easy ECGs, 2E Measuring T Waves To measure the T wave, identify its starting and ending point, then move to the center of the waveform Next, count the number of small boxes between the isoelectric line and the top of the waveform I I

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 12 Fast & Easy ECGs, 2E Abnormal T Waves Include those that are tall, peaked or tented, inverted (in leads where they should be upright), biphasic, flat, wide, and heavily notched and those having bumps

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 13 Fast & Easy ECGs, 2E Abnormal T Waves Indicate presence of abnormal ventricular repolarization

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 14 Fast & Easy ECGs, 2E QT Intervals Extends from beginning of the QRS complex to the end of the T wave Duration varies according to age and sex, but it is usually between 0.36 and 0.44 seconds

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 15 Fast & Easy ECGs, 2E Measuring QT Intervals First locate the isoelectric line immediately preceding the Q wave (or R wave if there is no Q wave) Next, locate the end of the T wave Count the number of boxes in between these two points

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 16 Fast & Easy ECGs, 2E Abnormal QT Intervals An abnormal QT interval duration can indicate myocardial irregularity Two types of abnormal QT intervals are prolonged QT intervals and shortened QT intervals

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 17 Fast & Easy ECGs, 2E U Waves Small wave that follows the T wave. Not always seen Origin is thought to represent repolarization of the papillary muscles or Purkinje fibers

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 18 Fast & Easy ECGs, 2E U Waves Most often seen in hypokalemia May also be present in hypercalcemia, thyrotoxicosis, digitalis toxicity, epinephrine and Class 1A and 3 antidysrhythmics use, mitral valve prolapse, left ventricular hypertrophy, congenital long QT syndrome and intracranial hemorrhage

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 19 Fast & Easy ECGs, 2E Practice Makes Perfect In this tracing, determine the type of ST segments, T waves, QT intervals and if U waves are present I I

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 20 Fast & Easy ECGs, 2E Practice Makes Perfect In this tracing, determine the type of ST segments, T waves, QT intervals and if U waves are present I I

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 21 Fast & Easy ECGs, 2E Practice Makes Perfect In this tracing, determine the type of ST segments, T waves, QT intervals and if U waves are present I I

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 22 Fast & Easy ECGs, 2E Practice Makes Perfect In this tracing, determine the type of ST segments, T waves, QT intervals and if U waves are present I I

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 23 Fast & Easy ECGs, 2E Practice Makes Perfect In this tracing, determine the type of ST segments, T waves, QT intervals and if U waves are present I I

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 24 Fast & Easy ECGs, 2E Summary Assessing the ST segments, T waves, QT intervals, and U waves is a part of analyzing an ECG tracing The ST segment is the isoelectric line that follows the QRS complex and connects it to the T wave. It represents the end of ventricular depolarization and the beginning of ventricular repolarization

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 25 Fast & Easy ECGs, 2E Summary ST segment depression or elevation can be evaluated by comparing the ST segment with the PR segment. It is considered elevated if it is above the baseline and depressed if it is below it Elevation or depression of the ST segment is a hallmark feature of myocardial ischemia and injury

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 26 Fast & Easy ECGs, 2E Summary The T wave represents the completion of ventricular repolarization The T wave is larger than the P wave and slightly asymmetrical. It is oriented in the same direction as the preceding QRS complex Abnormal T waves indicate the presence of abnormal ventricular repolarization Tall or peaked and inverted T waves (in certain leads) may be seen in myocardial ischemia

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 27 Fast & Easy ECGs, 2E Summary The QT interval represents the time needed for ventricular depolarization and repolarization It extends from the beginning of the QRS complex to the end of the T wave Its duration varies according to age, sex, and heart rate, but it is usually between 0.36 and 0.44 seconds In certain conditions, such as myocardial ischemia or infarction, a prolonged QT interval can predispose the patient to life-threatening ventricular dysrhythmias

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. 28 Fast & Easy ECGs, 2E Summary When present, the U wave is a small, rounded wave that follows the T wave. It has the same polarity as the T wave. Prominent U waves are most often seen in hypokalemia