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Precordial concordance, also known as QRS concordance is when all precordial leads on an electrocardiogram are either positive (positive concordance) or negative (negative concordance). [1]
ST elevation ≥1 mm in a lead with a positive QRS complex (i.e.: concordance) - 5 points; concordant ST depression ≥1 mm in lead V1, V2, or V3 - 3 points; ST elevation ≥5 mm in a lead with a negative (discordant) QRS complex - 2 points; ≥3 points = 90% specificity of STEMI (sensitivity of 36%) [2]
It is normal to have a narrow QS and rSr' patterns in V 1, and this is also the case for qRs and R patterns in V 5 and V 6. The transition zone is where the QRS complex changes from predominantly negative to predominantly positive (R/S ratio becoming >1), and this usually occurs at V 3 or V 4.
The sinus node should pace the heart – therefore, P waves must be round, all the same shape, and present before every QRS complex in a ratio of 1:1. Normal P wave axis (0 to +75 degrees) Normal PR interval, QRS complex and QT interval. QRS complex positive in leads I, II, aVF and V3–V6, and negative in lead aVR. [3]
This refers to the appearance of leads I and II. If the QRS complex is negative in lead I and positive in lead II, the QRS complexes appear to be "reaching" to touch each other. This signifies right axis deviation. Conversely, if the QRS complex is positive in lead I and negative in lead II the leads have the appearance of "leaving" each other.
To determine a true LAD, examine QRS in lead II. If the QRS complex is positive in lead II, then this is a normal axis. On the other hand, if QRS complex is negative in lead II, then this is a LAD. Another method of determining LAD is called the Isoelectric lead, which allows for a more precise estimation of the QRS axis. [3]
The hexaxial reference system is a diagram that is used to determine the heart's electrical axis in the frontal plane. The hexaxial reference system, better known as the Cabrera system, is a convention to present the extremity leads of the 12 lead electrocardiogram, [1] that provides an illustrative logical sequence that helps interpretation of the ECG, especially to determine the heart's ...
This measure has a false positive rate of 15-20% (which is slightly higher in women than men) and a false negative rate of 20–30%. [1] ST depression may be associated with subendocardial myocardial infarction, hypokalemia, or digitalis toxicity. [2]