HEART-RATE-VARIABILITY IN THE DOG - IS IT TOO VARIABLE

The purpose of the study was to evaluate resting heart rate variabilit y (HRV) as a simple noninvasive screening test for early autonomic der angement, heralding the development of occult dilated cardiomyopathy h y (DCM). Time and frequency domain HRV parameters were evaluated in 32 healthy Doberman pinschers, as potential predictors of the developmen t of occult DCM within the following year and correlated with plasma c atecholamimes, markers of sympathoexcitation. Tell Dobermans with occu lt DCM and 8 Dobermans with congestive heart failure (CHF) were positi ve controls. Seven of the 32 ''healthy'' dogs developed occult DCM ove r the course of the study. None of the HRV parameters were associated with the development of occult DCM based on univariate logistic regres sion. In dogs who developed occult DCM, plasma norepinephrine (NE) was inversely correlated with % fractal power (r = -0.81, P = 0.05). In d ogs with occult DCM (positive controls), plasma NE was inversely corre lated with fractal power (r = -0.81, r = 0.03), total power (r = -0.08 , P = 0.03), high frequency power (r = -0.75, P 0.05) and the standard deviation of the RR (r = -0.83, P = 0.02). The great inherent variabi lity of the Lest may have limited our ability to discriminate between physiologic and pathophysiologic data, rendering this methodology inad equate as a screening test for early occult DCM. However, the negative correlations of NE with various forms of spectral power in dogs with occult DCM suggests that early in the natural history of DCM, there is parasympathetic withdrawal. A reduction in the nonharmonic, fractal c omponent may be the first recognizable abnormality in the power spectr um of dogs who will develop DCM.