(h,k)-Arbiters for h-out-of-k mutual exclusion problem

Abstracth-Out-of-k mutual exclusion is a generalization of the 1-mutual exclusion problem, where there are k units of shared resources and each process requests h(1⩽h⩽k) units at the same time. Though k-arbiter has been shown to be a quorum-based solution to this problem, quorums in k-arbiter are much larger than those in the 1-coterie for 1-mutual exclusion. Thus, the algorithm based on k-arbiter needs many messages. This paper introduces the new notion that each request uses different quorums depending on the number of units of its request. Based on the notion, this paper defines two (h,k)-arbiters for h-out-of-k mutual exclusion: a uniform (h,k)-arbiter and a (k+1)-cube (h,k)-arbiter. The quorums in each (h,k)-arbiter are not larger than the ones in the corresponding k-arbiter; consequently, it is more efficient to use (h,k)-arbiters than the k-arbiters. A uniform (h,k)-arbiter is a generalization of the majority coterie for 1-mutual exclusion. A (k+1)-cube (h,k)-arbiter is a generalization of square grid coterie for 1-mutual exclusion

Single-center experience with a minimally invasive apicoaxillary external ventricular assist device

Von H. Kalb

Left ventricular assist device implantation after acute anterior wall myocardial infarction and cardiogenic shock: A two-center study

ObjectiveLeft ventricular assist device (LVAD) insertion after anterior wall myocardial infarction complicated by cardiogenic shock is an accepted modality of support in select patients. Results of primary revascularization for these patients are poor. We seek to determine the outcomes of patients with myocardial infarction and shock who undergo LVAD insertion alone versus surgical revascularization before LVAD insertion.MethodsSeventy-four patients at 2 institutions underwent LVAD implantation for myocardial infarction and shock over a 12-year period. Twenty-eight underwent direct LVAD placement, and 46 underwent revascularization through coronary artery bypass grafting before LVAD placement. Variables examined included patient demographics, myocardial infarction–LVAD interval, bridge to transplantation, early mortality (≤30 days), survival after LVAD placement, and posttransplantation survivals.ResultsThere were no differences in demographics between the 2 groups. The group undergoing revascularization before LVAD placement had a lower bridge to transplantation, higher early mortality, and lower overall 6- and 12-month survivals after LVAD placement compared with the group undergoing direct LVAD placement (45.50% vs 70.40%, P = .041; 39.10% vs 14.30%, P = .020; 89.3% and 82.1% vs 54.4% and 52.2%, respectively, P = .006). Posttransplantation survival and LVAD explantation rates were equivalent in both groups.ConclusionsCoronary artery bypass grafting before LVAD insertion for cardiogenic shock complicating myocardial infarction adversely affects survival. Confirmation of these findings would require conducting a large, multicenter, randomized clinical trial comparing revascularization versus LVAD support as primary therapy in this setting

Hypertension: an unstudied potential risk factor for adverse outcomes during continuous flow ventricular assist device support

In end-stage heart failure, left ventricular assist devices (LVADs) represent an exciting new frontier in which post-device implantation survival approaches that of heart transplant. However, expansion of this technology is still limited by complications that impact morbidity and mortality. Thus, it is essential to identify and optimize modifiable predictors of poor outcomes. One such predictor may be hypertension (HTN). Not only may chronic HTN as a traditional cardiovascular risk factor be present during long-term LVAD support, but HTN may also contribute to device malfunction or device-associated complications. Although current guidelines identify blood pressure (BP) control as important to outpatient continuous flow (CF) LVAD management, there is no evidence base to support these guidelines. Indeed, our comprehensive literature search did not identify any studies that evaluated post-device implantation HTN as a potential predictor of adverse CF-LVAD outcomes. HTN among CF-LVAD patients is likely a relatively unstudied factor because of difficulties using standard noninvasive techniques to measure BP in the setting of reduced pulsatile flow. Fortunately, recent research has elucidated the meaning of Doppler BP measurements and validated a slow-cuff deflation system for BP measurements in the setting of CF-LVAD support. Therefore, CF-LVAD researchers and clinicians may (1) consider potential mechanisms relating HTN to poor outcomes, (2) realize that HTN management is a stated goal despite scarce evidence, and (3) utilize the new reliable and valid methods for outpatient BP measurement that make research and management possible. It is critical and now feasible that research on HTN in the CF-LVAD patient population move forward

Normalization of Pulmonary Hypertension by the Use of Left Ventricular Assist Device in Patients with End-stage Heart Failure: A Possible Contribution to Donor Pool Expansion in Lung Transplantation

SummaryHeart transplantation alone has been recognized to be contraindicated when pulmonary hypertension (PH) and elevated pulmonary vascular resistance (PVR) are irreversible, irrespective of any medical intervention by the use of inotropic agents or pulmonary vasodilators, because such patients are at an increased risk of post-transplantation right ventricular failure and mortality. Therefore, end-stage heart failure patients with concomitant fixed PH and irreversibly high PVR are considered to be heart–lung transplant candidates. Recently, left ventricular assist device (LVAD) therapy has been reported to normalize PVR through persistent unloading of the left ventricle, even in patients with medically refractory PH. Therefore, LVAD therapy could make such patients suitable for “heart-only” transplants, which contributes to appropriate donor lung allocation for lung-only candidates. We review the literature regarding LVAD use for secondary PH and present a case with end-stage heart failure that could avoid a heart–lung transplant owing to LVAD therapy