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We’ve come a long way on our journey and are now ready to perform comprehensive 12-lead ECG interpretations. There’s more than one way to approach an ECG and some of you will find that one method works better for you than others. This chapter presents a method I believe you will find easy to understand and organize. When analyzing each item, return to the relevant chapters to review the diagnostic considerations in detail. You do have flexibility in what order you choose to address each element. But whatever method you use in practice, it’s vital that you follow a routine of structured reporting. This guarantees that all the key elements are reported consistently in every tracing. One of my teaching “mantras” is: You can have different styles, but not different standards.
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The following lists the essential elements that should be part of every ECG interpretation, something I like to call “The Diagnostic Dozen.”
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Technical aspects
Analyze the rhythm and rate
Make your measurements (PR, QRS, QT)
Determine the mean frontal plane QRS axis
P wave analysis
QRS complex analysis
Q wave inspection
Examine precordial R wave progression
ST segment analysis
T wave analysis (and U wave if present)
Synthesis
Comparison and clinical correlation
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STEP 1: TECHNICAL ASPECTS
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The first step in ECG interpretation is to assess the technical aspects of the tracing. Identify the name, gender, and age of the patient, items that will impact your interpretation. For example, interpreting the ECG of a pediatric patient is very different from that of an adult, a topic best left to textbooks devoted to that subject. And as we reviewed in Chapter 7, the criteria for left ventricular enlargement are different depending on age and gender. Inspect the tracing for overall quality, making sure it is satisfactory and devoid of excessive baseline artifact. If necessary, don’t hesitate to request a repeat tracing stating in your report that, “technical artifacts preclude accurate interpretation.” Check that the tracing is performed at normal paper speed (25 mm/sec), information that is routinely printed on each ECG. Also check the standardization, which can be confirmed as normal (10 mm/mV) by inspecting the calibration mark that appears either at the beginning or end of each tracing. At times the calibration is performed at half-standard, the machine making the adjustment to fit large complexes on one page. Note that half-standardization can be utilized for only the precordial leads with the limb leads recorded at normal calibration, which will be indicated by a two-tiered calibration mark. Finally, examine the tracing for an obvious lead reversal. As we reviewed in Chapter 4, clues to this include a highly unusual P wave and QRS complex in leads I and aVR, as well as an isolated “flat line” in any of leads I, II, or III.