Age-related changes in the magnitude of ventricular depolarization vector: analyses by magnetocardiogram.

The magnetocardiogram has the beneficial feature that permits the strength and location of the current dipole to be estimated. This study examines the issue of whether the magnitude of the heart current during depolarization phase was influenced by the age of healthy subjects. The magnetocardiograms were recorded by means of a second-derivative SQUID (superconducting quantum interference device) magnetometer (BT Corp, Model BMP, San Diego, CA) in 150 healthy subjects. The subjects were subgrouped into 5 age-based categories according to the age. The current dipole of the maximum QRS complex was determined from isofield contour maps during the ventricular depolarization phase, and no significant differences were observed in the magnitude in the current source for any age category. However, the amplitudes of the RV5 and SV1 + RV5 in the standard electrocardiogram were larger in 65 to 74-year-old women than other age groups, and the SV1 + RV5 was smaller for the 45 to 74-year-old men than for the men aged 25 to 44 years. These findings suggest that the age-associated changes in the QRS complex observed by the electrocardiogram are caused by increased electric resistance and not by the heart current itself. The results additionally suggest that no effects of aging were observed in the actual heart current of the heart during the depolarization phase.