Length-dependent regulation of left ventricular function in coronary surgery patients

Background: Load-dependent impairment of left ventricular (LV) function was observed after leg elevation in a subgroup of coronary surgery patients. T he present study investigated underlying mechanisms by comparing hemodynami c effects of an increase in LV systolic pressures with leg elevation to eff ects of a similar increase In systolic pressures with phenylephrine. Methods: The study was performed in patients undergoing elective coronary s urgery prior to cardiopulmonary bypass. High-fidelity LV pressure tracings (n = 25) and conductance LV volume data (n = 10) were obtained consecutivel y during leg elevation and after phenylephrine administration (5 mu g/kg). Results: Leg elevation resulted in a homogeneous increase in end-diastolic volume. The change in stroke volume (SV), stroke work (SW) and dP/dt(max) w as variable, with an increase In some patients but no change or a decrease in other patients. For a matched increase in systolic pressures, phenylephr ine increased SW and dP/dt(max) in all patients with no change in SV. Load dependence of relaxation (slope R of the tau-end-systolic pressure relation ) was inversely related for changes in SV, SW, and dP/dt(max) with leg elev ation but not with phenylephrine. Conclusions: The different effects of leg elevation and phenylephrine sugge st that the observed decrease in SV, SW, and dP/dt(max) with leg elevation in some patients could not be attributed to an impaired contractile respons e to increased systolic LV pressures. Instead, load-dependent impairment of LV function after leg elevation appeared related to a deficient length-dep endent regulation of myocardial function.