Begin with lead V 1 and repeat the numbers in the box below in the following order. Haisty and coworkers studied patients with normal hearts documented by coronary arteriography and patients with documented myocardial infarction inferior, anterior, 63 posterior, and inferior and anterior Table 7—4.
Shown below are the sensitivity, specificity, and likelihood ratios for the best-performing infarct criteria. Conditions that can produce pathologic Q waves, ST-segment elevation, or loss of R-wave height in the absence of infarction are set out in Table 7—5. An acute infarction manifests ST-segment elevation in a lead with a pathologic Q wave. The T waves may be either upright or inverted. An old or age-indeterminate infarction manifests a pathologic Q wave, with or without slight ST-segment elevation or T-wave abnormalities.
Half of these patients have ventricular aneurysms. There are two possibilities for the major electrocardiographic diagnosis: myocardial infarction or acute injury. If there are pathologic changes in the QRS complex, one should make a diagnosis of myocardial infarction—beginning with the primary area, followed by any contiguous areas—and state the age of the infarction. If there are no pathologic changes in the QRS complex, one should make a diagnosis of acute injury of the affected segments—beginning with the primary area and followed by any contiguous areas.
Table 7—6 summarizes major causes of ST-segment elevations. Table 7—7 summarizes major causes of ST-segment depressions or T-wave inversions. Leads V 2 and V 3 are close to the ventricular mass and small-amplitude signals may be best seen in these leads. Abnormal U waves have increased amplitude or merge with abnormal T waves and produce T—U fusion.
A prolonged QT interval conveys adverse outcomes. The QT interval is inversely related to the heart rate. Measure the QT interval in either lead V 2 or V 3 , where the end of the T wave can usually be clearly distinguished from the beginning of the U wave. If the rate is regular, use the mean rate of the QRS complexes. If the rate is irregular, calculate the rate from the immediately prior R—R cycle, because this cycle determines the subsequent QT interval. Use the numbers you have obtained to classify the QT interval using the nomogram below.
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The five causes of a short QT interval are hypercalcemia, digitalis, thyrotoxicosis, increased sympathetic tone, and genetic abnormality. This error should not occur but it does occur nevertheless. The lead appears to have no signal except for a tiny deflection representing the QRS complex. There are usually no discernible P waves or T waves. RL—RA cable reversal is shown here. Hypothermia is usually characterized on the ECG by a slow rate, a long QT, and muscle tremor artifact.
An Osborn wave is typically present. There is usually widespread ST-segment elevation with concomitant PR-segment depression in the same leads. The PR segment in aVR protrudes above the baseline like a knuckle, reflecting atrial injury. Only lead V 6 is used.
The lead with the best sensitivity is V 4. To view other topics, please sign in or purchase a subscription. Anesthesia Central is an all-in-one web and mobile solution for treating patients before, during, and after surgery. Complete Product Information. Guide to Diagnostic Tests. Tags Type your tag names separated by a space and hit enter. How to Use This Section. Evans, MD, who was the author of this chapter in the first edition of the book. Figure 7—1. Anatomic classification of tachycardias.
Adapted with permission from Kusumoto FM: Arrhythmias.
How to read an Electrocardiogram (ECG). Part One: Basic principles of the ECG. The normal ECG
Figure 7—2. Arrows show the first four atrial deflections in each SVT. In sinus tachycardia, the P wave has a normal morphology, and the PR interval is normal. In atrial tachycardia, the P wave is abnormal positive in V 1 , and the PR interval is prolonged because of decremental conduction in the AV node. The P wave is usually located relatively close to the preceding QRS complex because the accessory pathway conducts rapidly.
Figure 7—3. Initiation of SVT in a patient with an accessory pathway. During sinus rhythm, the ventricles are activated via the accessory pathway and the AV node-His bundle.
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Because the accessory pathway conducts rapidly and inserts into regular ventricular myocardium, the PR interval is short and a delta wave is observed large arrows. The atria are activated retrogradely by the accessory pathway small arrows , and orthodromic AVRT is initiated. Figure 7—4. In atrial fibrillation, continuous chaotic activation of the atria results in continuous low-amplitude fibrillatory waves. Figure 7—5. Lead II from a wide complex tachycardia.
Reproduced, with permission, from Haisty WK Jr et al. Performance of the automated complete Selvester QRS scoring system in normal subjects and patients with single and multiple myocardial infarctions. J Am Coll Cardiol ; Citation McPhee, Stephen J. Anesthesia Central , anesth. McGraw-Hill Education; Accessed September 22, McPhee, S. In Guide to Diagnostic Tests.
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In: Guide to Diagnostic Tests. Approach to Diagnosis of the Cardiac Rhythm B. First things first. Knowing the basic parts of an ECG tracing will lay a good foundation for everything else that is to come. The different waves, complexes and intervals need to be ingrained in your brain. How many seconds is a full ECG tracing? How much time does each big box and each little box represent? This is not the time to learn the crazy things such as the different P-wave morphologies that occur with atrial enlargements and ectopic atrial rhythms — but rather, just to know what the normal P wave looks like and what it represents.
Read ECG Basics. To determine whether bradycardia, a normal heart rate or tachycardia is present requires the knowledge to calculate the heart rate on the ECG.
Remember to apply these techniques to both the atrial rate, measured by the rate of the P wave, and the ventricular rate, measured by the rate of the QRS complex. Read Determining Rate. The axis on the ECG can give a clue to many different pathologic states. Unless you are going into electrophysiology as a career, the only axis that you need to measure is that of the QRS complex. Be sure to know the causes of left axis deviation, right axis deviation and when the axis is indeterminate northwestern.
Also, know the quick shortcuts to determine the axis.
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Read Determining Axis. Learning a normal sinus rhythm was taken care of in Step 1. Now, learn the below rhythms like the back of your hand. Be sure to review multiple examples of each in the individual ECG Reviews and Criteria sections below. Sometimes this can be the most difficult part. Atrial enlargements are not too bad, but the criteria for left ventricular hypertrophy can drive you crazy. No need to memorize then all, just the main two or three.
A T wave follows the QRS complex and indicates ventricular repolarization. Unlike a P wave, a normal T wave is slightly asymmetric; the peak of the wave is a little closer to its end than to its beginning. When a T wave occurs in the opposite direction of the QRS complex, it generally reflects some sort of cardiac pathology. If a small wave occurs between the T wave and the P wave, it could be a U wave.
The biological basis for a U wave is unknown. One of the quickest ways is called the sequence method. To use the sequence method, find an R wave that lines up with one of the dark vertical lines on the ECG paper. If the next R wave appears on the next dark vertical line, it corresponds to heart rate of beats a minute. The dark vertical lines correspond to , , , 75, 60, and 50 bpm.
There are more accurate ways to determine heart rate from ECG, but in life-saving scenarios, this method provides a quick estimate. If your employer verifies that they will absolutely not accept the provider card, you will be issued a prompt and courteous refund of your entire course fee.
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