Cardiac electrical resultant dipole moment of spontaneously hypertensive rats.

The cardiac electrical resultant dipole moment (RDM) of 17 spontaneously hypertensive rats (SHR) was compared with that of 17 Wistar-Kyoto rats (WKY), 65-100 days of age. Relative to body weight, left ventricular weight was 23% greater and right ventricular weight was 18% greater for SHR than for WKY. Left ventricular wall thickness was 11% larger and myocyte diameter was 13% larger for SHR than for WKY. RDM orientation for SHR was more dorsal, leftward, and cranial from middle to end of qRS. The second spatial magnitude peak of QRS, M2, was significantly smaller for SHR than for WKY (P less than 0.001) whereas M3 for SHR was significantly greater than for WKY (P less than 0.001). The alterations in RDM of SHR are greater than can be accounted for simply on the basis of increased cell size. The excitation sequence for SHR might be different from that of WKY. Results show the necessity of considering the details of the spatial magnitude curve during QRS.