Search Results
You are looking at 1 - 2 of 2 items for
- Author or Editor: William F. Christensen x
- Refine by Access: All Content x
Abstract
Objective
To develop a clinically useful model for predicting QT interval duration as a function of heart rate in healthy cats.
Animals
20 healthy cats.
Procedure
For all cats, results of a physical examination, electrocardiography, and echocardiography were normal. Twenty-four hour heart rate and rhythm data were collected by means of ambulatory electrocardiography. Hourly ECG segments were obtained from the 24-hour recordings. Mean heart rate and the mean of 5 qt interval measurements were calculated for each of 479 usable ECG segments. Analysis of covariance was used to develop models to describe variability in qt interval duration.
Results
Prediction equations (R 2 = 0.81) including terms for heart rate, (heart rate)2, age group (1 to 4 vs 8 to 14 years old), and their interactions were developed. Sex, individual cat, and time of day were of little value in predicting qt interval duration. A simplified prediction equation without age group (R 2 = 0.71) also was developed and had better predictive ability than reported correction formulas for qt interval duration.
Conclusions and Clinical Relevance
Prediction equations with 95% prediction intervals for expected qt interval duration in healthy cats were generated. Abnormal qt interval duration can be associated with cardiac electrical instability, yet qt interval duration is greatly influenced by heart rate. Results of the present study provide reference ranges for expected qt interval duration as a function of heart rate in healthy cats. (Am J Vet Res 1999;60:1426–1429)
Abstract
Objective—To evaluate cardiac function parameters in a group of active and hibernating grizzly bears.
Design—Prospective study.
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 hibernation.
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)
