Relation of systemic sympathetic nervous system activation to echocardiographic left ventricular size and performance and its implications in patients with mitral regurgitation

We have previously demonstrated that the systemic sympathetic nervous system (SNS) is activated in proportion to an increase in cineventriculographic left ventricular (LV) end-systolic volume and decrease in ejection fraction (EF) in patients with chronic mitral regurgitation (MR). However, the relation between noninvasive echocardiographic measures of LV size and performance and systemic SNS activation and their clinical implications in patients with MR is not known. We studied 17 MR patients with echocardiography, arterial norepinephrine (NE) sampling, and [3H]-NE infusions and arterial blood sampling to determine NE kinetic parameters using a 2-compartment analysis, including extravascular NE release rates (NE2, index of SNS activity) and the metabolic clearance rate from the vascular compartment. The arterial NE values correlated with LV end-systolic dimensions (r = 0.50, p = 0.04), but not with LV end-diastolic dimensions, and EF or fractional shortening measures. The NE2 values correlated with LV end-systolic dimensions (r = 0.53, p = 0.03) and inversely with LVEF (r = −0.45, p = 0.07) and fractional shortening (r = 0.43, p = 0.08) measures, but not with LV end-diastolic dimensions. The metabolic clearance rate values showed an inverse correlation with LV end-diastolic (r = −0.52, p = 0.03) and end-systolic (r = −0.49, p = 0.04) dimensions, but not with LV performance measures. The increase in NE2 values was progressive as the LV end-systolic dimensions increased and more marked at LV end-systolic dimensions ≥40 mm. Thus, activation of the SNS is related to an increase in echocardiographic LV end-systolic dimensions and a decrease in LV performance measures in chronic MR.