The gastrointestinal tract: an underestimated organ as demonstrated in an experimental LVAD pig model

Alarms and Their Outcomes in Left Ventricular Assist Device Patients

Low flow and suction alarms are provided to alert caregivers of changes in left ventricular assist device pump function but may be reset in clinical practice. We investigated the incidence and underlying causes of these alarms as well as their prognostic significance. HeartWare ventricular assist device patients (n = 113) were divided into quartiles based on their frequency of low flow and suction alarms. Survival and adverse events (thrombus, stroke, bleeding, and right heart failure) were compared between quartiles. Low flow alarms peaked in the first few months of pump support before dropping down to near negligible levels. Suction alarm frequency remained relatively constant throughout pump support. Although pump speeds (p < 0.001) and flow (p = 0.01) decreased over time, there was an increase in suction alarm frequency (p = 0.018), with no changes in low flow alarms. Patients with smaller body size (p = 0.016) and lower pump flows (p = 0.008) had higher frequencies of low flow alarms on multiple regression (p < 0.001). Patients with the highest low flow alarm frequency demonstrated poorer survival (p = 0.026). There was no relationship between suction alarm frequency and survival. There was also no relationship between either low flow or suction alarm frequency with strokes, gastrointestinal bleeds, pump thrombus, or right ventricular failure. Duration of alarm and intervention in response to the alarm was not assessed in this study. Further studies examining alarm duration and responses may inform future pump alarm algorithms.

Tumor necrosis factor-α levels and non-surgical bleeding in continuous-flow left ventricular assist devices

BACKGROUND

Non-surgical bleeding (NSB) due to angiodysplasia is common in left ventricular assist device (LVAD) patients. Thrombin-induced angiopoietin-2 (Ang-2) expression in LVAD patients leads to altered angiogenesis and is associated with lower angiopoietin-1 (Ang-1) and increased NSB. However, the mechanism for decreased Ang-1, made by pericytes, is unknown and the origin of thrombin in LVAD patients is unclear. We hypothesized that high tumor necrosis factor-α (TNF-α) levels in LVAD patients induce pericyte apoptosis, tissue factor (TF) expression and vascular instability.

METHODS

We incubated cultured pericytes with serum from patients with heart failure (HF), LVAD or orthotopic heart transplantation (OHT), with or without TNF-α blockade. We performed several measurements: Ang-1 expression was assessed by reverse transcript-polymerase chain reaction (RT-PCR) and pericyte death fluorescently; TF expression was assessed by RT-PCR in cultured endothelial cells incubated with patient plasma with or without TNF-α blockade; and TF expression was assessed in endothelial biopsy samples from these patients by immunofluorescence. We incubated cultured endothelial cells on Matrigel with patient serum with or without TNF-α blockade and determined tube formation by microscopy.

RESULTS

Serum from LVAD patients had higher levels of TNF-α, suppressed Ang-1 expression in pericytes, and induced pericyte death, and there was accelerated endothelial tube formation compared with serum from patients without LVADs. TF was higher in both plasma and endothelial cells from LVAD patients, and plasma from LVAD patients induced more endothelial TF expression. All of these effects were reversed or reduced with TNF-α blockade. High levels of TNF-α were associated with increased risk of NSB.

CONCLUSIONS

Elevated TNF-α in LVAD patients is a central regulator of altered angiogenesis, pericyte apoptosis and expression of TF and Ang-1.

Left ventricular assist devices and gastrointestinal bleeding: a narrative review of case reports and case series

BACKGROUND

The use of left ventricular assist devices (LVADs) has become a state-of-the-art therapy for advanced cardiac heart failure; however, multiple reports in the literature describe an increased risk for gastrointestinal (GI) bleeding in these patients. We characterized this association by reviewing recent studies on this topic.

HYPOTHESIS

GI bleeding occurs frequently in patients with LVADs, especially with devices with nonpulsatile flow patterns.

METHODS

We performed a comprehensive literature review to identify articles that reported GI bleeding in patients with LVADs. Databases used included PubMed, EMBASE, Scopus, Web of Knowledge, and Ovid. Baseline and outcome data were then ed from these reports.

RESULTS

We identified 10 case reports and 22 case series with 1543 patients. The mean age was 54.2 years. Most patients had nonpulsatile LVADs (1316, 85.3%). Three hundred and seventeen patients (20.5%) developed GI bleeding; this occurred more frequently in patients with nonpulsatile LVADs. Multiple procedures were performed without complications but often did not identify a definite bleeding site. Suspect lesions occurred throughout the GI tract but were more frequent in the upper GI tract. Many patients had arteriovenous malformations. All patients received medical therapy. None of the patients had their LVAD replaced. The use of anticoagulation did not appear to predispose these patients to more GI bleeding episodes.

CONCLUSIONS

Patients with LVADs have frequent GI bleeds, especially from arteriovenous malformations, which can occur throughout the GI tract. Most diagnostic and therapeutic interventions can be used safely in these patients. The pathogenesis of the GI bleeding in these patients may involve the use of anticoagulant medications, the formation of arteriovenous malformations, loss of von Willebrand factor activity, and mucosal ischemia.

Left ventricular assist devices and gastrointestinal bleeding: a narrative review of case reports and case series

BACKGROUND

The use of left ventricular assist devices (LVADs) has become a state-of-the-art therapy for advanced cardiac heart failure; however, multiple reports in the literature describe an increased risk for gastrointestinal (GI) bleeding in these patients. We characterized this association by reviewing recent studies on this topic.

HYPOTHESIS

GI bleeding occurs frequently in patients with LVADs, especially with devices with nonpulsatile flow patterns.

METHODS

We performed a comprehensive literature review to identify articles that reported GI bleeding in patients with LVADs. Databases used included PubMed, EMBASE, Scopus, Web of Knowledge, and Ovid. Baseline and outcome data were then ed from these reports.

RESULTS

We identified 10 case reports and 22 case series with 1543 patients. The mean age was 54.2 years. Most patients had nonpulsatile LVADs (1316, 85.3%). Three hundred and seventeen patients (20.5%) developed GI bleeding; this occurred more frequently in patients with nonpulsatile LVADs. Multiple procedures were performed without complications but often did not identify a definite bleeding site. Suspect lesions occurred throughout the GI tract but were more frequent in the upper GI tract. Many patients had arteriovenous malformations. All patients received medical therapy. None of the patients had their LVAD replaced. The use of anticoagulation did not appear to predispose these patients to more GI bleeding episodes.

CONCLUSIONS

Patients with LVADs have frequent GI bleeds, especially from arteriovenous malformations, which can occur throughout the GI tract. Most diagnostic and therapeutic interventions can be used safely in these patients. The pathogenesis of the GI bleeding in these patients may involve the use of anticoagulant medications, the formation of arteriovenous malformations, loss of von Willebrand factor activity, and mucosal ischemia.

Hemodynamic Support With the Pulsatile Catheter Pump in a Sheep Model of Acute Heart Failure

This study was aimed to mimic clinical heart failure (HF) conditions and to assess the effect of pulsatile catheter (PUCA) pump support on hemodynamics and tissue perfusion in a sheep model of acute HF. In 14 sheep, HF was induced by partial occluding the middle left circumflex coronary artery combined with pacemaker-induced tachycardia. PUCA pump was then activated to support the HF for 3 h. Hemodynamic parameters were recorded at baseline, HF, and then every 30 min during experiments. Blood samples were taken in carotid artery (CA), pulmonary artery (PA), and coronary sinus (CS) for the determination of oxygen saturation (SO2) and lactate concentration as markers of tissue perfusion. Results showed that HF model was induced successfully in 10 sheep and failed in four sheep due to refractory ventricular fibrillation. PUCA pump support was successful in seven out of 10 sheep for 3 h. Three cases failed due to technical problems. After HF (n = 10), cardiac output (CO) was decreased from 3.7 +/- 0.5 to 2.0 +/- 0.5 L/min (P < 0.001). Mean arterial pressure (MAP) was lowered from 116.1 +/- 14.2 to 68.1 +/- 14.7 mm Hg (P < 0.001). In seven sheep supported with PUCA pump, MAP rose from 68.9 +/- 15.2 to 94.7 +/- 14.7 mm Hg (P = 0.005), systolic blood pressure increased from 86.6 +/- 17.0 to 112.6 +/- 17.1 mm Hg (P = 0.009), and diastolic blood pressure increased from 57.7 +/- 12.6 to 79.9 +/- 13.9 mm Hg (P = 0.011). CO remained at about 2.0 L/min. SO2 in CA, PA, and CS decreased significantly after HF (P < 0.001), with an increase after support (compared with HF, P < 0.001, 0.066 and 0.114, respectively). Lactate concentrations increased gradually in CA, PA, and CS toward the end of experiments without difference among different sampling sites. This HF model in sheep is simple, easy to manipulate, reproducible and reflecting clinical HF conditions. PUCA pump can maintain the hemodynamic status for 3 h in this acute HF model.

Endotoxin challenge increases xanthine oxidase activity in cattle: effect of growth hormone and vitamin E treatment

In addition to its basic role in the metabolism of purine nucleotides, xanthine oxidoreductase (XOR) is involved in the generation of oxygen-derived free radicals and production and metabolic fate of nitric oxide (NO). Growth hormone (GH) and Vitamin E (E) have been shown previously to modify immune response to infection. Our objective was to determine in heifers the effect of endotoxin challenge (LPS; 3.0 microg/kg BW, i.v. bolus, Escherichia coli 055:B5) on xanthine oxidase (XO) activity in plasma and liver and the modification of this response by daily treatment with recombinant GH (0.1 mg/kg BW, i.m., for 12 days) or GH+E (E: mixed tocopherol, 1000 IU/heifer, i.m., for 5 days). In experiment 1, 16 heifers ( 348.7 +/- 6.1 kg) were assigned to control (C, daily placebo injections), GH, or GH+E treatments and were challenged with two consecutive LPS injections (LPS1 and LPS2, 48 h apart). After LPS1, plasma XO activity increased 290% (P < 0.001) at 3 h, reached peak (430%) at 24 h and returned to basal level by 48 h after LPS2. XO responses (area under the time x activity curve, AUC) were greater after LPS1 than LPS2 (P< 0.001). Total plasma XO responses to LPS (AUC, LPS1+LPS2) were augmented 55% (P < 0.05) over C with GH treatment but diminished to C responses in GH+E. There was a linear relationship (r2 = 0.605, P < 0.001) between total response in plasma XO activity and plasma nitrate + nitrate concentration. In experiment 2, 24 heifers ( 346 +/- 6 kg) were assigned to C or GH treatments and liver biopsy samples were obtained at 0, 3, 6, and 24h after a single LPS challenge. Hepatic XO activities increased 63.3% (P < 0.05) 6 h after single LPS challenge and remained elevated at 24 h (100.1%, P < 0.01) but were not affected by GH treatment. Results indicate that LPS-induced increases in plasma XO activity could be amplified by previous GH treatment but attenuated by E administration. The data also suggest that E may be effective in controlling some mediators of immune response associated with increased production of NO via the effect on XO activity and its production of superoxide anion as well as uric acid.

Abnormal gastric tonometric variables and vasoconstrictor use after left ventricular assist device insertion

BACKGROUND

Abnormal gastric tonometric variables, a surrogate for splanchnic ischemia, occur in approximately 50% of patients at the end of routine cardiac operations and are associated with postoperative morbidity. We sought to determine whether gastric tonometric variables deteriorate after left ventricular assist device insertion and to explore the association between abnormal gastric tonometric variables and vasoconstrictor use.

METHODS

Nineteen patients who had insertion of a left ventricular assist device were enrolled in a prospective, observational study. Automated air tonometry was used to determine the difference between gastric and arterial partial pressure of carbon dioxide (CO2 gap) at five time points perioperatively.

RESULTS

Compared with baseline, systemic blood flow was significantly increased at the end of operation (1.9 +/- 0.6 versus 2.9 +/- 0.7 L x min(-1) x m(-2), p < 0.0001). Tonometric variables, which were normal at baseline, became abnormal in 90% of patients (baseline CO2 gap 4 +/- 2 mm Hg versus end of operation CO2 gap 24 +/- 15 mm Hg, p < 0.0001). Elevated CO2 gaps correlated with larger doses of norepinephrine (r = 0.69, p = 0.001) and vasopressin (r = 0.88, p < 0.0001). Abnormal gastric tonometric variables at the end of operation correlated with postoperative intensive care unit length of stay (r = 0.70, p = 0.0009) and multiple organ dysfunction score (r = 0.64, p = 0.0033).

CONCLUSIONS

Despite a significant increase in systemic blood flow after left ventricular assist device implantation, abnormal gastric tonometric variables developed and were associated with larger vasoconstrictor dose. These data provide evidence that gastric ischemia can develop independently of changes in systemic blood flow and support the potential role of vasoconstrictors as a cause of splanchnic ischemia.

Effect of variation in systemic blood flow on plasma TNF-alpha in a pig model with left ventricular assist device

Tumor necrosis factor-alpha (TNF-alpha) release has been implicated in a sepsis-like syndrome following cardiopulmonary bypass (CPB). This also may be important in patients who have had a left ventricular assist device (LVAD) implanted. This report investigates the effect of reducing systemic blood flow on hemodynamic response, mixed venous oxygen saturation (SvO(2)), and the release of TNF-alpha. LVADs were implanted in 9 pigs. The aorta was clamped, and thus the LVAD flow represented the entire systemic blood flow. Plasma TNF-alpha in the femoral artery (FA) and superior mesenteric vein (SMV) was measured at baseline and following systemic blood flow changes. Simultaneously, hemodynamic parameters and oxygen saturation in the pulmonary artery (SvO(2)) were measured. Following reductions in systemic blood flow, plasma TNF-alpha increased gradually to a maximum level at a systemic blood flow of 20%. There was no significant difference between TNF-alpha levels in the SMV and the FA. There was a significant (p < 0.05) correlation between cardiac index, stroke volume index, and TNF-alpha. The SvO(2) decreased significantly (p < 0.05) at a systemic blood flow of 30 and 20%. A rise in TNF-alpha occurred when the SvO(2) was less than 75%. The data demonstrate that a reduction in systemic blood flow causes an increase in plasma TNF-alpha. This can lead to the development of a sepsis-like syndrome in a group of patients who already are hemodynamically compromised. While weaning short-term LVAD support, rapid diminution of the cardiac output and the pump flow must be avoided.

Intestinal tissue oxygenation and tumor necrosis factor-alpha release during systemic blood flow changes in pigs with left ventricular assist devices

We previously demonstrated that tumor necrosis factor-alpha (TNF-alpha) increased following a reduction in systemic blood flow to 60% or less of the original cardiac output using a left ventricular assist device (LVAD). The aim of this study was to investigate the effect of reducing systemic blood flow on tissue oxygenation in the gastrointestinal tract (GIT) and the consequences of this on TNF-alpha release. LVADs were implanted in 9 pigs. The aorta was clamped, and thus the LVAD flow represented the entire systemic blood flow. Plasma TNF-alpha of the superior mesenteric vein was measured at baseline and during systemic blood flow changes. Simultaneously, pH, lactate, oxygen delivery index (DO(2)I), oxygen consumption index (VO(2)I), and oxygen extraction (O(2)ER) in the GIT were measured. The pH decreased and the lactate level increased significantly (p < 0.05) at a systemic blood flow of 50% or less. The VO(2)I was positively correlated with DO(2)I. The O(2)ER increased significantly (p < 0.05) with reductions in systemic blood flow to 30% or less. There was a significant (p < 0.01) correlation between TNF-alpha and O(2)ER at levels higher than 55%. These data demonstrate that the GIT oxygenation is inadequate with a reduction in systemic blood flow to 50% and that GIT oxygenation becomes critical at a reduction of 30%. During LVAD weaning, careful attention must be given to the GIT. The pH and lactate may be good markers of the adequacy of tissue oxygenation in the GIT.