Altered inotropic and lusitropic responses to heart rate in conscious dogs with tachycardia-induced heart failure

Second Department of Internal Medicine, Toyama Medical and Pharmaceutical University, Toyama, Japan.

OBJECTIVES: The effects of increasing heart rate on left ventricular contraction and relaxation were examined in conscious dogs with tachycardia-induced heart failure under autonomically blocked conditions. BACKGROUND: Previous studies using isolated myocardium have shown attenuated positive inotropic responses to stimulation frequency in heart failure. However, these responses have not been well examined in intact preparations in the presence of heart failure with autonomic system blockade, where the intrinsic ventricular responses to increasing heart rate could be revealed. METHODS: Seven dogs were instrumented with a micromanometer and a conductance volume catheter. After autonomic blockade to eliminate neural reflexes, left ventricular contractile properties were quantified by the slope of the end-systolic pressure-volume relation (ventricular elastance), and left ventricular relaxation was assessed by the time constant of isovolumetric ventricular pressure decay. RESULTS: Increasing the heart rate by 60 beats/min enhanced ventricular elastance by 71 +/- 18% (mean +/- SD) and decreased end-systolic volume by 6 +/- 5% in normal hearts. In failing hearts, ventricular elastance increased by only 21 +/- 20%, and end-systolic volume did not change appreciably. Although the reduction in left ventricular end-diastolic and minimal pressures by tachycardia was smaller in the failing heart, ventricular relaxation rate remained unaltered both in the normal heart and in the failing heart. CONCLUSIONS: Under conscious but autonomically blocked conditions, effects of increasing heart rate on the failing left ventricle are characterized by a predominant attenuation of the inotropic response rather than of the lusitropic response.

This article has been cited by other articles:

				W. Shen, R. M. Gill, B. D. Jones, J.-P. Zhang, A. K. Corbly, and M. I. Steinberg Combined Inotropic and Bradycardic Effects of a Sodium Channel Enhancer in Conscious Dogs with Heart Failure: A Mechanism for Improved Myocardial Efficiency Compared with Dobutamine J. Pharmacol. Exp. Ther., November 1, 2002; 303(2): 673 - 680. [Abstract] [Full Text] [PDF]

				P. Colin, B. Ghaleh, L. Hittinger, X. Monnet, M. Slama, J.-F. Giudicelli, and A. Berdeaux Differential effects of heart rate reduction and beta -blockade on left ventricular relaxation during exercise Am J Physiol Heart Circ Physiol, February 1, 2002; 282(2): H672 - H679. [Abstract] [Full Text] [PDF]

				S. E. Litwin, D. Zhang, P. Roberge, and G. D. Pennock DITPA prevents the blunted contraction-frequency relationship in myocytes from infarcted hearts Am J Physiol Heart Circ Physiol, March 1, 2000; 278(3): H862 - H870. [Abstract] [Full Text] [PDF]

				P. E. Marik Pulmonary Artery Catheterization and Esophageal Doppler Monitoring in the ICU Chest, October 1, 1999; 116(4): 1085 - 1091. [Abstract] [Full Text] [PDF]

				H. A. Remah, H. Asanoi, S. Joho, A. Igawa, T. Kameyama, T. Nozawa, and H. Inoue Modulation of left ventricular diastolic distensibility by collateral flow recruitment during balloon coronary occlusion J. Am. Coll. Cardiol., August 1, 1999; 34(2): 500 - 506. [Abstract] [Full Text] [PDF]