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How to Use This Section
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This chapter includes criteria for the diagnosis of basic electrocardiographic waveforms and cardiac arrhythmias. It is intended for use as a reference and assumes a basic understanding of the electrocardiogram (ECG).
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Electrocardiographic interpretation is a "stepwise" procedure, and the first steps are to study and characterize the cardiac rhythm.
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Categorize what you see in the 12-lead ECG or rhythm strip, using the three major parameters that allow for systematic analysis and subsequent diagnosis of the rhythm:
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Mean rate of the QRS complexes (slow, normal, or fast).
Width of the QRS complexes (wide or narrow).
Rhythmicity of the QRS complexes (characterization of spaces between QRS complexes) (regular or irregular).
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Step Two (Morphology)
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Step 2 consists of examining and characterizing the morphology of the cardiac waveforms.
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Examine for atrial abnormalities and bundle branch blocks (BBBs) (See Bundle Branch Block).
Assess the QRS axis and the causes of axis deviations (See The Mean QRS Axis in the Frontal Plane (Limb Leads)).
Examine for signs of left ventricular hypertrophy (See Left Ventricular Hypertrophy).
Examine for signs of right ventricular hypertrophy (See Right Ventricular Hypertrophy (RVH)).
Examine for signs of myocardial infarction, if present (See Myocardial Injury, Ischemia, and Infarction).
Bear in mind conditions that may alter the ability of the ECG to diagnose a myocardial infarction (See Test Performance Characteristics for Electrocardiographic Criteria in the Diagnosis of Myocardial Infarction).
Examine for abnormalities of the ST segment or T wave (See Tables 7–6, Table 7–7, Table 7–8, and Table 7–9).
Assess the QT interval (See Prolonged QT Interval).
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