Aortic valve disorders and left ventricular assist devices

Aortic valve disorders are important considerations in advanced heart failure patients being evaluated for left ventricular assist devices (LVAD) and those on LVAD support. Aortic insufficiency (AI) can be present prior to LVAD implantation or develop de novo during LVAD support. It is usually a progressive disorder and can lead to impaired LVAD effectiveness and heart failure symptoms. Severe AI is associated with worsening hemodynamics, increased hospitalizations, and decreased survival in LVAD patients. Diagnosis is made with echocardiographic, device assessment, and/or catheterization studies. Standard echocardiographic criteria for AI are insufficient for accurate diagnosis of AI severity. Management of pre-existing AI includes aortic repair or replacement at the time of LVAD implant. Management of de novo AI on LVAD support is challenging with increased risks of repeat surgical intervention, and percutaneous techniques including transcatheter aortic valve replacement are assuming greater importance. In this manuscript, we provide a comprehensive approach to contemporary diagnosis and management of aortic valve disorders in the setting of LVAD therapy.

A Physical Heart Failure Simulation System Utilizing the Total Artificial Heart and Modified Donovan Mock Circulation

With the growth and diversity of mechanical circulatory support (MCS) systems entering clinical use, a need exists for a robust mock circulation system capable of reliably emulating and reproducing physiologic as well as pathophysiologic states for use in MCS training and inter-device comparison. We report on the development of such a platform utilizing the SynCardia Total Artificial Heart and a modified Donovan Mock Circulation System, capable of being driven at normal and reduced output. With this platform, clinically relevant heart failure hemodynamics could be reliably reproduced as evidenced by elevated left atrial pressure (+112%), reduced aortic flow (-12.6%), blunted Starling-like behavior, and increased afterload sensitivity when compared with normal function. Similarly, pressure-volume relationships demonstrated enhanced sensitivity to afterload and decreased Starling-like behavior in the heart failure model. Lastly, the platform was configured to allow the easy addition of a left ventricular assist device (HeartMate II at 9600 RPM), which upon insertion resulted in improvement of hemodynamics. The present configuration has the potential to serve as a viable system for training and research, aimed at fostering safe and effective MCS device use.

Competitive complexation of trace metals with dissolved humic acid

In this study we investigated the effects of competing trace metals and Ca2+ on Cd(II), Pb(II), and Cu(II) complexation by humic acid extracted from groundwater in Orange County, California. Two types of titration experiments were conducted, those using a single metal and those in which the humic acid had been preequilibrated with a competing metal (either a trace metal or Ca2+). The labile metal concentration in the titration was determined by differential pulse polarography (DPP). Results show the different effects of competing trace metal ions and the effect of Ca2+. Both trace metals and Ca2+ do not compete effectively with Cd(II) complexation. While no effects of Cu(II) on Pb(II) complexation were observed, the presence of Cd(II) appeared to slightly enhance the binding between Pb(II) and humic acid. The addition of Pb(II) decreased the amount of Cu(II) complexation, but Cd(II) caused a slight increase at the lower concentrations. Calcium, however, decreased the amount of complexation for all three metals. Results indicate that the metals are not necessarily competing for the same sites. Conformational changes that occur when trace metals bind to the different sites may cause this competing or enhanced effect. Since Ca(II) is introduced at two orders of magnitude higher in concentration than the trace metals, it can outcompete the trace metal for sites where electrostatic interactions dominate. The results indicate that in groundwater situations, where more than one metal is present, the effect of other metals must be considered in predicting metal speciation.