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Load-sensitivity of regional tissue deformation in the right ventricle: isovolumic versus ejection-phase indices of contractility

¹ Center for Experimental Anaesthesiology, Emergency and Intensive Care Medicine, Department of Acute Medical Sciences, Katholieke Universiteit Leuven, Belgium
² Department of Anaesthesiology, University Hospital of the RWTH Aachen, Germany
³ Department of Cardiovascular Diseases, Katholieke Universiteit Leuven, Belgium

Correspondence to:
Dr P F Wouters, Director of the Center for Experimental Anaesthesiology, Emergency and Intensive Care Medicine, Department of Acute Medical Sciences, University Hospitals KULeuven, Herestraat 49, B-3000 Leuven, Belgium; Patrick.Wouters{at}uz.kuleuven.ac.be

ABSTRACT
Objective: Doppler myocardial imaging is increasingly being used to evaluate regional and global cardiac function. Quantitative measurements of tissue deformation obtained during ejection as well as isovolumic contraction have been proposed as new indices of contractility; however, their load-sensitivity remains a matter of controversy. Maximum strain rate (SR_max) and isovolumic strain acceleration (ISA_max) were compared with regard to sensitivity for inotropic state, heart rate and loading conditions in the right ventricle (RV), using pressure-volume analysis as the reference method.

Design: Prospective animal study.

Setting: University hospital laboratory.

Interventions: RV contractility was measured at baseline, after inotropic modulation with esmolol and dobutamine, at different atrial pacing rates and during controlled alterations of RV preload and afterload.

Main outcome measures: RV contractility was assessed with the slope (Mw) of preload recruitable stroke work and longitudinal SR_max and ISA_max.

Results: SR_max and ISA_max reflected the drug-induced changes in contractility, while only ISA_max increased with higher pacing rates. Acute lowering of RV preload did not affect either of the indices studied. In contrast, an increase in RV afterload consistently decreased SR_max (from 1.05 (SD 0.41) to 0.73 (SD 0.26) s^-1,p = 0.03) but had variable effects on ISA_max and Mw. However, a significant correlation was found between proportional changes in ISA_max and Mw during high-afterload conditions (r² = 0.89, p = 0.005).

Conclusions: Both SR_max and ISA_max reflected changes in RV contractility. ISA_max was less sensitive to changes in RV afterload than SR_max and may therefore be a more robust index of global RV contractility.