Objective—To evaluate cardiac function parameters
in a group of active and hibernating grizzly bears.
Animals—6 subadult grizzly bears.
Procedure—Indirect blood pressure, a 12-lead ECG,
and a routine echocardiogram were obtained in each
bear during the summer active phase and during
Results—All measurements of myocardial contractility
were significantly lower in all bears during hibernation,
compared with the active period. Mean rate of
circumferential left ventricular shortening, percentage
fractional shortening, and percentage left ventricular
ejection fraction were significantly lower in bears during
hibernation, compared with the active period.
Certain indices of diastolic function appeared to indicate
enhanced ventricular compliance during the
hibernation period. Mean mitral inflow ratio and isovolumic
relaxation time were greater during hibernation.
Heart rate was significantly lower for hibernating
bears, and mean cardiac index was lower but not significantly
different from cardiac index during the
active phase. Contrary to results obtained in hibernating
rodent species, cardiac index was not significantly
correlated with heart rate.
Conclusions and Clinical Relevance—Cardiac function
parameters in hibernating bears are opposite to
the chronic bradycardic effects detected in nonhibernating
species, likely because of intrinsic cardiac muscle
adaptations during hibernation. Understanding
mechanisms and responses of the myocardium during
hibernation could yield insight into mechanisms of
cardiac function regulation in various disease states in
nonhibernating species. (J Am Vet Med Assoc 2003;223:1170–1175)