Afterload corrected fractional area change (FACac): a simple, relatively load-independent measurement of left ventricular contractility in humans.
Afterload corrected fractional area change (FACac) is a simple measurement of contractility which can be acquired during surgery without the need to acutely alter volume. We have validated it against the load-independent measurement, stroke force / end-diastolic area relationship (SF/EDA) in patients undergoing cardiac surgery. SF/EDA regressions were analysed before and after cardiopulmonary bypass in 39 patients and compared with simultaneously acquired FACac data. End-systolic and end-diastolic areas (ESA and EDA) were measured by transesophageal echocardiography and substituted for ventricular volumes. Pulmonary capillary wedge pressure was substituted for end-diastolic pressure and peak-systolic pressure for end-systolic pressure. Stroke force is the integral of the pressure-area loop and a square shape was assumed for calculation. FACac = FAC x log 10(SVRI) x 100%, where SVRI is calculated without multiplication by 80. Comparison of the methods was done by ordinary least products regression analysis where SF/EDA = a+b (FACac). a = 0.004 (95% CI -5.46 to 5.46). b = 0.857 (95% CI 0.777 to 0.936). Agreement between SF/EDA and FACac was identified by the absence of fixed bias. Both SF/EDA and FACac identified a reduction in contractility following cardiopulmonary bypass of similar magnitude suggesting load-independence of FACac. In contrast, the load-dependent indexes, cardiac index and FAC, increased in value but in the presence of reduced afterload. FACac may be used as a simplified index to reflect a relatively load-independent index of left ventricular contractility. Its simplicity offers promise of clinical utility.
Royse
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CF
Department of Anaesthesia, The Royal Melbourne Hospital, P.O.Box 1022, Research, Victoria, 3095 Australia.
Royse
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AG
D006348:Cardiac Surgical Procedures; D002315:Cardiopulmonary Bypass; D017548:Echocardiography, Transesophageal; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D007430:Intraoperative Care; D008875:Middle Aged; D009200:Myocardial Contraction / Q000502:physiology*; D012044:Regression Analysis; D016277:Ventricular Function, Left / Q000502:physiology*