Measurement of Aortic Regurgitation by Upstream Sampling with Continuous Infusion of Indicator

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Abstract
A direct and theoretically valid method for the measurement of aortic regurgitation involves the recording of indicator concentrations from the left ventricle and a downstream site during aortic root injection. However, this method has yielded erratic results when applied to man in our laboratory when using the sudden injection technique. Moreover, others have found a systematic overestimate of backflow when the sudden injection technique was compared with flowmeter measurements in dogs with experimental aortic regurgitation. If defects in the method are due primarily to a critical dependence of indicator distribution on the timing of injection or to beat-to-beat variations in the forward or regurgitant stroke volumes, these difficulties could conceivably be overcome by substituting continuous infusion of indicator for sudden single injections. Therefore, the upstream sampling method, using continuous infusion of indicator, was evaluated in 18 patients with aortic regurgitation during retrograde aortic and transseptal left ventricular catheterization. The continuous infusion technique was compared with the technique of sudden injection in 10 patients and with aortic valvulography in 14 patients. Measurements of forward flow obtained with continuous infusions into the aortic root were not significantly different from measurements obtained with sudden injections into the pulmonary artery. Recordings of indicator concentrations from the left ventricle, during continuous infusions into the aortic root, demonstrated readily evident equilibrium plateaus. The resultant measurements of regurgitant flow were highly reproducible and not impaired by nonsimultaneity of upstream and downstream sampling. The percentage error of estimate at 95% confidence limits was 22% of the measurement for regurgitant flow, 13% for total flow, and 9% for the regurgitant fraction of total flow. The corresponding errors of estimate for the sudden injection technique were four times larger. Regurgitant flow by the continuous infusion method ranged from 0.8 to 30.0 L/min, total flow from 3.0 to 36.0 L/min, and the regurgitant fraction of total flow from 12 to 86%. Ranking of patients by the magnitudes of regurgitant and total flow did not correspond to ranking by angiographic criteria of severity. However, an excellent correlation prevailed between angiographic grade and the regurgitant fraction of total flow, demonstrating that this variable is the most meaningful expression of severity. The correlation (0.997) between the angiographic grade and the regurgitant fraction measured by the continuous infusion technique was clearly superior to that obtained with the sudden injection technique (0.894). Mild regurgitation was equivalent to a regurgitant fraction of 75%. It is concluded that the upstream sampling method during continuous infusion of indicator, because of its sensitivity, reliability, applicability to multiple measurements, and validity in the presence of mitral regurgitation, is the most useful method for quantifying aortic regurgitation in man.