Effect of sampling site on Doppler-derived right ventricular systolic time intervals

FmmEi.CakdathofQRSurbudng~IandaVFin pathtswllhnonndaxls(A),leflaxkdevlatl6n(B)and lightward axh (c) (see text). QRS deflection in aVF is negative. Similarly, in Figure 1 C, the angle of 1 I .2” is added to 90” (lead aVF, largest net QRS defection) since the net QRS deflection in lead I is negative. Rapid calculation of the electrocardiographic frontal axis is desirable. The method described is simple and provides an acceptable approximation of the axis determined using the trigonometric tangent. The calculated angle may underestimate the true angle by less than 4.1 O without overestimation. Alternative methods to determine the axis are reliable but may require the use of tables or reference diagrams.3-6 Thus, advantages of this formula include its simplicity, which allows for rapid calculation of frontal plane axis without use of the more cumbersome hexaxial reference diagram or tables. It may be particularly useful where there is no equiphasic lead, such that Grant’s method’ is not easily applicable. The mean frontal plane axis may vary by 35O in an individual patient when different lead combinations are used.’ When more accurate determination is desired, an average of several lead combinations may be useful.’