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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]
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]
In lead V 1, the QRS complex is often entirely negative (QS morphology), although a small initial R wave may be seen (rS morphology). In the lateral leads (I, aVL, V 5-V 6) the QRS complexes are usually predominantly positive with a slow upstroke last >60ms to the R-wave peak. [4] Notching may be seen in these leads but this is not universal.
Diagram showing how the polarity of the QRS complex in leads I, II, and III can be used to estimate the heart's electrical axis in the frontal plane. The QRS complex is the combination of three of the graphical deflections seen on a typical electrocardiogram (ECG or EKG). It is usually the central and most visually obvious part of the tracing.
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]
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.
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]
ST-T vector opposite to QRS without digitalis; ST-T vector opposite to QRS with digitalis; 3 1 Negative terminal P mode in V 1 1 mm in depth and 0.04 sec in duration (indicates left atrial enlargement) 3 Left axis deviation (QRS of −30° or more) 2 QRS duration ≥0.09 sec 1 Delayed intrinsicoid deflection in V 5 or V 6 (>0.05 sec) 1