NORMAL VECTOR MAGNETOCARDIOGRAM .2. EFFECT OF CONSTITUTIONAL VARIABLES

The effects of age, sex, height, weight, and dimensions of the thorax on the vector magnetocardiogram (VMCG) were studied in 290 normal subj ects. The effect of sex on 141 VMCG parameters was tested with the Man n-Whitney U test, and the effects of age and body dimensions on the ma le and female subjects were tested with the Kruskal-Wallis H test. Sim ilar analyses were applied for a comparison of the vector electrocardi ogram (VECG) in a subgroup of 200 normal subjects. Sex had the most pr onounced effect on the VMCG, a total of 58% of the instantaneous time- normalized QRS and T amplitude parameters were significantly (P < .01) different in men and women (47% for the VECG). In women, the absolute VMCG amplitudes were, on average, about 60% of those in men. In the V ECG, the corresponding portion was about 85%. In men and women, 50 and 26% of the time-normalized amplitude parameters, respectively, were s ignificantly (P < .01) affected by age; the main effect was a decrease in most VMCG amplitudes with increasing age. In the VECG, the corresp onding effect was not as statistically significant. The effect of cons titutional variables of the body on the VMCG and VECG was, in most cas es, not statistically significant. Multiple correlation analysis showe d that the five noncardiac factors together explained, at most, 16 and 28% of the variability in the instantaneous, time-normalized QRS ampl itudes for men and women, respectively. In the VECG, these figures wer e 13 and 18%, respectively. This study shows clearly that in the VMCG, a larger portion of normal variability is due to the effect of noncar diac factors than in the VECG. It is important to take sex and age int o consideration when conducting studies of the clinical value of magne tocardiography. Key words: magnetocardiogram, vectorcardiogram, noncar diac factors, computer analysis.