True statement about instantaneous means vector:
Correct Answer: All
Description: All A,B,C Equal & same as mean QRS vector; It is drawn through the centre of vector in a direction from base toward apex; Summated vector of generated potential at paicular instant cause by inflowing septal depolarization; When a vector is exactly horizontal and directed toward the person's left side, the vector is said to extend in the direction of 0deg.At a given time (instant) during the cardiac cycle, hea current flows in a paicular direction. A vector (arrow) points in direction of the electrical potential generated by the current flow, with the arrowhead in the positive direction. The length of arrow is drawn propoional to the voltage of the potential. This is called resultant vector in the hea at a given instant.At the instant of paial depolarization of ventricles (septum & apical endocardial walls shown by negative signs and shaded area), the electrical current flows between the depolarized areas inside the hea and non-depolarized areas on the outside of hea (shown by long elliptical arrows). Overall, far more current flows downward from the base of ventricle toward the apex than in upward direction. So instantaneous mean vector (i.e.) the summated vector of generated potential at this paicular instant) during septal depolarization is represented by the long black arrow drawn through the centre of the ventricles in a direction from base toward apexQ.Directions of vector: When a vector is exactly horizontal and directed towards the person's left side, the vector is said to extend in the direction of 0 degree . From this 0deg reference point, the scale of vector direction rotates clockwise. So when the vector extends from above to veically straight downward, it is in the direction of 90deg. When it extends from person's left to right the direction is 180deg; and when it extends straight upwards, it has a direction of -90deg (or + 270deg).Direction of VectorMean QRS vector: is the average direction of the vector during spread of the depolarization wave through ventricles. In a normal hea it is about +59deg which means that during most of depolarization the apex of heat remains positive with respect to the base of hea.If it is assumed that three ECG electrode locations form the points of an equilateral triangle (Einthoven's triangle) and the hea lies in the centre of this triangle; the vector at any given movement in two dimensions of frontal plane can be calculated from any two standard limb leads.Mean QRS vector (electrical axis of heat) is plotted by using the average QRS deflection in each lead (or by measuring the net differences between the positive of negative peaks of QRS). The normal direction of mean QRS vector is -30deg to +110deg. Left axis detion is present if calculated axis falls to left of -30deg and may be d/t left ventricular hyperophy. Right axis detion is present if axis falls to the right of +110deg and suggests right ventricular hyperophy.
Category:
Physiology
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