Use of relaxation half-time as an index of ventricular relaxation in clinically normal cats and cats with hypertrophic cardiomyopathy

A. Lynelle Golden From the Departments of Urban Practice and Animal Science, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37901.

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Janice M. Bright From the Departments of Urban Practice and Animal Science, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37901.

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 MS, DVM

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SUMMARY

Relaxation half-time (t½) was evaluated as a measure of isovolumic ventricular relaxation in clinically normal cats and cats with hypertrophic cardiomyopathy. Relaxation half-time was determined directly from the left ventricular pressure tracing as the time required for the left ventricular pressure at the beginning of isovolumic relaxation to decrease by half.

The value of t½ was unaffected by moderate changes in heart rate, inotropic state, and afterload in clinically normal cats. However, t½ increased significantly (P = 0.003) with increased preload. The value of t½ was significantly higher (P = 0.0003) in a group of cats with hypertrophic cardiomyopathy, compared with that of a group of clinically normal cats. Although t½ must be interpreted in the context of changes in loading conditions, the index is useful as a measure of relaxation in clinically normal cats and cats with hypertrophic cardiomyopathy.

SUMMARY

Relaxation half-time (t½) was evaluated as a measure of isovolumic ventricular relaxation in clinically normal cats and cats with hypertrophic cardiomyopathy. Relaxation half-time was determined directly from the left ventricular pressure tracing as the time required for the left ventricular pressure at the beginning of isovolumic relaxation to decrease by half.

The value of t½ was unaffected by moderate changes in heart rate, inotropic state, and afterload in clinically normal cats. However, t½ increased significantly (P = 0.003) with increased preload. The value of t½ was significantly higher (P = 0.0003) in a group of cats with hypertrophic cardiomyopathy, compared with that of a group of clinically normal cats. Although t½ must be interpreted in the context of changes in loading conditions, the index is useful as a measure of relaxation in clinically normal cats and cats with hypertrophic cardiomyopathy.

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