A special case of a circular coaxial cable with heavy conduction loss was studied by full-wave analysis, and compared with the quasi-transverse electromagnetic (TEM) solutions. It was found that at high frequencies the tangential electrical fields will be much greater than the values reported in the literature. Despite relatively strong longitudinal E-fields and radial currents, the comparison revealed that, provided the circuit parameters are properly evaluated, the errors introduced by a simple distributed circuit model under the quasi-TEM assumption are not excessively large. Therefore, the telegraphist's equations may give good results up to frequencies of 10 GHz or higher for transmission lines of small geometries commonly found in microelectronics packaging. A second case of three coupled microstrips of rectangular cross-section was also analyzed and compared with network measurements. It was found that the dispersion occurring in microelectronics packaging interconnects at frequencies up to the microwave band is anomalous.