Normal limits of the orthogonal electrocardiogram and vectorcardiogram in adult women, ranging in age from 18 to 90 years, are presented. A comparison of results is made with those of normal age-matched men, and sex differences are analyzed from a total of 960 normal records (510 men and 450 women). For the majority of scalar and vectorial items, significant sex differences were found which in women included shorter QRS duration, smaller vector loops, and decreased P, Q, R, S, and T deflections. The upper normal limits of R x, R y, and R z amplitudes were 11 per cent, 20 per cent, and 30 per cent less, respectively, in women than in men. The sensitivity and specificity of electrocardiographic criteria, for high and low voltage, were significantly affected by these sex differences in amplitudes. For example, as a discriminator between normals and subjects with left ventricular hypertrophy, the upper normal limit of R x + R z amplitude sum was 3.10 millivolts in men but 2.50 millivolts in women. Hence, the use of the limit derived from males in a female population would decrease its sensitivity drasticially. Similar discrepancies existed in the sensitivity and specificity of electrocardiographic criteria for low voltage. Since the lower normal limit of R x amplitude was 0.51 millivolt in men but only 0.35 millivolt in women, a substantial number of normal women would be misclassified as having right ventricular hypertrophy or chronic obstructive pulmonary disease if the limit derived from males was used as a criterion. The absence of Q waves in Leads x and y was a common finding in each age and sex group and carries no diagnostic significance. While initial anterior QRS forces in Lead z were present in all normal men, they were smaller and even absent in 1 per cent of normal women. Hence, greater difficulties in electrocardiographic diagnosis of anteroseptal myocardial infarction in women may be encountered. Mean vectors at the end of QRS (point J) and early part of the ST segment were more inferiorly and anteriorly directed in men than in women. T waves in Lead z were always negative in men, but flat or positive T waves were observed in some of the normal women. Sex differences in the level of point J and the ST segment may have important bearings on the interpretation of exercise electrocardiograms. The shorter QRS duration in women signified the importance of sex-specific limits for ventricular conduction delays.
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Mar 11, 1989
P Croft + 1
Open Access
