Mean modal vectors of P₁, P₂ and QRS were determined in the 3 planes of a semi-orthogonal EKG lead system in 17 horses and ponies with chronic obstructive pulmonary disease (COPD) and in 17 clinically normal horses and ponies. Subjects were paired so that the heart rates of each pair were not dissimilar by more than 2 cycles per minute.
Probably significant differences were observed between the mean angles of P₁ vectors in the transverse and sagittal planes (T plane, normal = 324° ± 24,6°, COPD = 342° ± 21,0°, t = 2,0, P < 0,05; S plane, normal = 331° ± 22,6°, COPD = 348° ± 16,2°, t = 2,52, P < 0,02). There were no significant differences between the mean angles of planar modal QRS vectors of normal subjects and those of COPD subjects.
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