Effects of intermittent lower limb ischaemia on coronary blood flow and coronary resistance in pigs.

AIM: Intermittent limb ischaemia prior to cardiac ischaemia is a cardioprotective stimulus. This study was to investigate whether this peripheral stimulus had any effects on basal coronary blood flow and resistance, and to explore its potential mechanisms by studying the effect of femoral nerve transection and Katp blockade by glibenclamide. METHODS: Remote ischaemic preconditioning (rIPC) was induced by four 5-min cycles of lower limb ischaemia. Coronary resistance was measured using standard formulae and coronary blood flow in the left anterior descending artery (LAD) by a flow probe. In experiment 1, coronary ischaemia was induced by inflation of a cuff placed around the mid-LAD, and inflated until cessation of flow. Left ventricular (LV) function was assessed using dp/dt and Tau at 1 and 30 min of ischaemia. Experiment 1: 20 pigs were randomized to control (n = 6), rIPC (n = 7) or femoral nerve transection + rIPC (n = 7) groups. The femoral nerve was transected before the rIPC protocol. All data were collected at fixed heart rates of 120 bpm. Coronary resistance was decreased and flow was increased significantly by the rIPC stimulus (P = 0.003, P = 0.016, paired t-test), and these changes were preserved after femoral nerve transection. Experiment 2: 19 pigs were randomized to control (n = 5), rIPC (n = 8) or glibenclamide-treated rIPC (n = 6) groups. Data were collected at baseline, and during incremental pacing between 120 and 180 bpm. RESULTS: Experiment 1: Coronary resistance was decreased and flow was increased significantly by rIPC stimulus (P = 0.003, P = 0.016, paired t-test), and these changes were preserved after femoral nerve transaction. rIPC was associated with superior LV function (dp/dt(max)) at 30 min, compared with controls and the rIPC + femoral nerve transaction group. Experiment 2: Coronary resistance was significantly lower, and LAD flow was significantly higher in rIPC group (P < 0.0001, P = 0.0008, two-way anova). These effects were reversed in the glibenclamide group. CONCLUSION: The rIPC stimulus leads to reduced coronary resistance and increased flow. This effect, while modified by glibenclamide appears to be a generic effect of remote ischaemia rather than a direct preconditioning effect.

Intermittent peripheral tissue ischemia during coronary ischemia reduces myocardial infarction through a KATP-dependent mechanism: first demonstration of remote ischemic perconditioning.

Remote ischemic preconditioning reduces myocardial infarction (MI) in animal models. We tested the hypothesis that the systemic protection thus induced is effective when ischemic preconditioning is administered during ischemia (PerC) and before reperfusion and examined the role of the K(+)-dependent ATP (K(ATP)) channel. Twenty 20-kg pigs were randomized (10 in each group) to 40 min of left anterior descending coronary artery occlusion with 120 min of reperfusion. PerC consisted of four 5-min cycles of lower limb ischemia by tourniquet during left anterior descending coronary artery occlusion. Left ventricular (LV) function was assessed by a conductance catheter and extent of infarction by tetrazolium staining. The extent of MI was significantly reduced by PerC (60.4 +/- 14.3 vs. 38.3 +/- 15.4%, P = 0.004) and associated with improved functional indexes. The increase in the time constant of diastolic relaxation was significantly attenuated by PerC compared with control in ischemia and reperfusion (P = 0.01 and 0.04, respectively). At 120 min of reperfusion, preload-recruitable stroke work declined 38 +/- 6% and 3 +/- 5% in control and PerC, respectively (P = 0.001). The force-frequency relation was significantly depressed at 120 min of reperfusion in both groups, but optimal heart rate was significantly lower in the control group (P = 0.04). There were fewer malignant arrhythmias with PerC during reperfusion (P = 0.02). These protective effects of PerC were abolished by glibenclamide. Intermittent limb ischemia during myocardial ischemia reduces MI, preserves global systolic and diastolic function, and protects against arrhythmia during the reperfusion phase through a K(ATP) channel-dependent mechanism. Understanding this process may have important therapeutic implications for a range of ischemia-reperfusion syndromes.

Remote ischaemic preconditioning protects against cardiopulmonary bypass-induced tissue injury: a preclinical study.

OBJECTIVES: To test the hypothesis that remote ischaemic preconditioning (rIPC) reduces injury after cardiopulmonary bypass (CPB). DESIGN: Randomised study with an experimental model of CPB (3 h CPB with 2 h of cardioplegic arrest). Twelve 15 kg pigs were randomly assigned to control or rIPC before CPB and followed up for 6 h. INTERVENTION: rIPC was induced by four 5 min cycles of lower limb ischaemia before CPB. MAIN OUTCOME MEASURES: Troponin I, glial protein S-100B, lactate concentrations, load-independent indices (conductance catheter) of systolic and diastolic function, and pulmonary resistance and compliance were measured before and for 6 h after CPB. RESULTS: Troponin I increased after CPB in both groups but during reperfusion the rIPC group had lower concentrations than controls (mean area under the curve -57.3 (SEM 7.3) v 89.0 (11.6) ng.h/ml, p = 0.02). Lactate increased after CPB in both groups but during reperfusion the control group had significantly more prolonged hyperlactataemia (p = 0.04). S-100B did not differ between groups. Indices of ventricular function did not differ. There was a tendency to improved lung compliance (p = 0.07), and pulmonary resistance changed less in the rIPC than in the control group during reperfusion (p = 0.02). Subsequently, peak inspiratory pressure was lower (p = 0.001). CONCLUSION: rIPC significantly attenuated clinically relevant markers of myocardial and pulmonary injury after CPB. Transient limb ischaemia as an rIPC stimulus has potentially important clinical applications.

KATP channel activation induces ischemic preconditioning of the endothelium in humans in vivo.

BACKGROUND: Endothelial dysfunction contributes to ischemia-reperfusion injury (IRI) and is reduced by ischemic preconditioning (IPC). IPC may involve activation of ATP-sensitive potassium channels (K(ATP)). We determined whether modulation of K(ATP) channels occurs in endothelial IPC in humans. METHODS AND RESULTS: IRI of the forearm was induced by inflating a blood pressure cuff to 200 mm Hg for 20 minutes in healthy volunteers. K(ATP) activation was modulated by intra-arterial glibenclamide (blocker) and diazoxide (opener). Endothelial function (response to intra-arterial acetylcholine) was assessed with forearm plethysmography before and after (1) 15-minute reperfusion, (2) IRI preceded by IPC (3 five-minute periods of ischemia), (3) IRI preceded by IPC with glibenclamide, (4) IPC followed by glibenclamide before IRI, (5) IRI preceded by diazoxide, and (6) IRI preceded by coinfusion of glibenclamide with diazoxide. IRI caused endothelial dysfunction (P=0.002), which IPC prevented (P=0.40). Glibenclamide abolished IPC when given contemporaneously with (P=0.003) or during IRI (P=0.0005). Diazoxide prevented endothelial dysfunction after IRI (P=0.68) but not when coinfused with glibenclamide. CONCLUSIONS: Glibenclamide abolishes and diazoxide mimics endothelial IPC in humans. The time course of the effect of glibenclamide suggests involvement of K(ATP) channels as effectors of endothelial IPC in vivo. These data may have implications for understanding the therapeutic role of agents that modulate K(ATP) channel function.

Infliximab improves endothelial dysfunction in systemic vasculitis: a model of vascular inflammation.

BACKGROUND: Endothelial vasomotor dysfunction and markers of systemic inflammation are independent determinants of cardiovascular risk. However, the link between clinical inflammation and endothelial dysfunction is unclear. The aim of this study was to use anti-neutrophil cytoplasmic antibody-associated systemic vasculitis (AASV) as a model of systemic inflammation in which to test the hypothesis that inflammation is associated with endothelial dysfunction and can be reversed with anti-tumor necrosis factor-alpha (TNF-alpha) therapy. METHODS AND RESULTS: Fourteen patients with active AASV and 21 age-matched control subjects were studied. Endothelial function was assessed through the use of forearm plethysmography and related to clinical disease activity: Birmingham Vasculitis Activity Score (BVAS) and serum levels of C-reactive protein (CRP), interleukin-6 (IL-6), and TNF-alpha. The effects of anti-TNF-alpha therapy (infliximab), either alone (n=6) or in combination with standard treatment (n=4), on endothelial function were subsequently determined. Patients had a mean BVAS of 11+/-1, and CRP and IL-6 were higher in the AASV group than in control subjects (34.8+/-10.5 versus 1.6+/-0.2 pg/mL, P<0.001; 9.0+/-0.7 versus 6.7+/-0.6 pg/mL, P=0.02). Forearm blood flow response to acetylcholine (ACh) was reduced in the patients compared with control subjects (P=0.002), but sodium nitroprusside (SNP) responses were not (P=0.3). The response to ACh improved with infliximab treatment (P=0.004) in particular, with infliximab alone (P=0.03). CONCLUSIONS: AASV is associated with endothelial dysfunction. Anti-TNF-alpha therapy, alone or in combination with standard treatment, results in clinical remission, reduced inflammation, and improved endothelium-dependent vasomotor responses.

Transient limb ischemia induces remote ischemic preconditioning in vivo.

BACKGROUND: Ischemic preconditioning reduces local tissue injury caused by subsequent ischemia-reperfusion (IR), but may also have a salutary effect on IR injury of tissues remote from those undergoing preconditioning. We tested the hypothesis that limb ischemia induces remote preconditioning, reduces endothelial IR injury in humans, and reduces experimental myocardial infarct size. METHODS AND RESULTS: Endothelial IR injury of the human forearm was induced by 20 minutes of upper limb ischemia (inflation of a blood pressure cuff to 200 mm Hg) followed by reperfusion. Remote preconditioning was induced by three 5-minute cycles of ischemia of the contralateral limb. Venous occlusion plethysmography was used to assess forearm blood flow in response to acetylcholine at baseline and 15 minutes after reperfusion. Experimental myocardial infarction was achieved by 40 minutes of balloon occlusion of the left anterior descending artery in 15-kg pigs. Remote preconditioning was induced by four 5-minute cycles of lower limb ischemia. Triphenyltetrazolium staining was used to assess the extent of myocardial infarction. In the human study, the response to acetylcholine was significantly attenuated in the control group after 15 minutes' reperfusion, but remote preconditioning prevented this reduction. Limb ischemia caused a significant reduction in the extent of myocardial infarction relative to the area at risk compared with control (26+/-9% versus 53+/-8%, P<0.05). CONCLUSION: Remote ischemic preconditioning prevents IR-induced endothelial dysfunction in humans and reduces the extent of myocardial infarction in experimental animals. Transient limb ischemia is a simple preconditioning stimulus with important potential clinical applications.

Mortality from infective endocarditis: clinical predictors of outcome.

OBJECTIVE: To identify clinical markers available within the first 48 hours of admission that are associated with poor outcome in infective endocarditis. DESIGNS: Retrospective cohort study. SETTING: Teaching hospital. PATIENTS: 208 of 220 patients with infective endocarditis. METHODS: Consecutive patients with infective endocarditis presenting between 1981 and 1999 to a tertiary centre were studied. Clinical, echocardiographic, and haematological data recorded within 48 hours of admission were obtained. Data were analysed using logistic regression models. MAIN OUTCOMES MEASURES: Mortality at discharge and at six months. RESULTS: Data were obtained for 93% of patients who were eligible for inclusion. 194 (93%) were positive for Duke criteria. Mean age was 52 (1.2) years, and 138 (66%) were men. 82 (39%) were transferred from other hospitals. 181 (87%) were blood culture positive, and 47 (23%) infections were Staphylococcus aureus. The infection was located on aortic (n = 85, 41%), mitral (n = 77, 37%), tricuspid (n = 18, 9%), and multiple valves (n = 20, 10%). 67 (32%) had prosthetic valve endocarditis. 48% of the cohort were managed with antibiotics alone. Mortality at discharge was 18% and at six months 27%. Duration of illness before admission, age, sex, valve infected, infecting organism, and left ventricular function were not predictors of adverse mortality. However, abnormal white cell count, serum albumin concentration, serum creatinine concentration, or cardiac rhythm, the presence of two major Duke criteria, or visible vegetation conferred a poor prognosis. CONCLUSIONS: Conventional prognostic factors in this study did not appear to predict outcome early during hospital admission. However, simple clinical indices, which are readily available, are reliable, cheap, and potentially powerful predictors of poor outcome.

Ischemic preconditioning prevents endothelial injury and systemic neutrophil activation during ischemia-reperfusion in humans in vivo.

BACKGROUND: Endothelial dysfunction leading to neutrophil infiltration of tissues has been implicated in tissue injury caused by ischemia-reperfusion (IR). Tissue injury during IR can be reduced by prior ischemic preconditioning (IPC). In humans, it is unclear whether endothelial dysfunction occurs during IR or whether IPC offers protection against endothelial dysfunction and inflammatory cell activation. We studied the effects of experimental IR on endothelial and neutrophil function in the human forearm in vivo and examined the protection afforded by IPC. METHOD AND RESULTS: The forearm was made ischemic for 20 minutes by inflating a blood pressure cuff to 200 mm Hg. We assessed endothelial function of conduit (radial artery flow-mediated dilation) and resistance vessels (blood flow responses to intra-arterial infusion of the endothelium-dependent dilator acetylcholine) in healthy volunteers before and after IR. IR reduced flow-mediated dilation of the radial artery at 15 minutes of reperfusion (7.7+/-1.5% to 3.5+/-0.9%) and the dilator response of resistance vessels to acetylcholine at 15, 30, and 60 minutes of reperfusion. IR did not reduce the dilator response of the radial artery to glyceryltrinitrate and only caused a small reduction of glyceryltrinitrate-induced dilation of resistance vessels at 60 minutes of reperfusion. IR caused an increase in neutrophil CD11b expression and platelet-neutrophil complexes in the circulating blood. IPC (three 5-minute episodes of ischemia) before IR prevented endothelial dysfunction and neutrophil activation. CONCLUSIONS: A clinically relevant period of ischemia-reperfusion causes profound and sustained endothelial dysfunction and systemic neutrophil activation. IPC attenuates both of these effects in humans.

Heterogenous nature of flow-mediated dilatation in human conduit arteries in vivo: relevance to endothelial dysfunction in hypercholesterolemia.

Flow-mediated dilatation (FMD) of conduit arteries is dependent on an intact endothelium, although the mechanisms are not fully understood. Using high-resolution ultrasound, we examined the role of endothelial mediators in radial artery dilatation in response to transient (short period of reactive hyperemia) and sustained (prolonged period of reactive hyperemia, hand warming, or an incremental infusion of acetylcholine into the distal radial artery) hyperemia. After short episodes of reactive hyperemia, FMD was abolished by local infusion of the nitric oxide synthesis inhibitor N:(G)monomethyl-L-arginine (5.3+/-1.2% versus 0.7+/-0.7%, P:<0.001). In contrast, basal vessel diameter and dilatation after prolonged episodes of reactive hyperemia, hand warming, and distal infusion of acetylcholine were not attenuated by nitric oxide synthesis inhibition. Inhibition of cyclooxygenase or local autonomic nervous system blockade also had no effect on FMD. Patients with hypercholesterolemia exhibited reduced FMD in response to transient hyperemia, but the response to sustained hyperemia was normal. These data suggest heterogeneity of endothelial responses to blood flow that are dependent on the characteristics of the flow stimulus. Dilatation after brief episodes of hyperemia is mediated by release of nitric oxide, whereas dilatation during sustained hyperemia is unaffected by NO synthesis inhibition. Hypercholesterolemia seems to differentially affect these pathways with impairment of the nitric oxide-dependent pathway and preservation of non nitric oxide-mediated dilatation to sustained flow stimuli.

Acute systemic inflammation impairs endothelium-dependent dilatation in humans.

BACKGROUND: We tested the hypothesis that endothelial dysfunction underlies the association between an acute inflammatory episode and the transiently increased risk of a cardiovascular event by examining the effects of an experimental inflammatory stimulus on endothelium-dependent vasodilation. METHODS AND RESULTS: Salmonella typhi vaccine was used to generate a systemic inflammatory response in healthy volunteers. In 12 subjects, dilatation of the brachial artery to flow and to sublingual nitroglycerin (NTG) was recorded (conduit vessel response), and in 6 subjects, venous occlusion plethysmography was used to measure forearm blood flow during intrabrachial infusion of the endothelium-dependent dilators acetylcholine (ACh) and bradykinin (BK) and the endothelium-independent dilators NTG and verapamil (resistance vessel response). Responses were assessed 16 hours before and 8 and 32 hours after vaccination. Vaccination resulted in elevations in white cell count and serum levels of interleukin-6 and interleukin-1 receptor antagonist. Eight hours after vaccination, resistance vessel responses to BK (P:=0.0099) and ACh (P:=0.0414) were markedly attenuated, and brachial artery flow-mediated dilatation was depressed. Resistance vessel responses to verapamil and NTG were unchanged, as was the conduit vessel response to NTG. Thirty-two hours after vaccination, resistance vessel responses to BK and ACh had returned to normal. CONCLUSIONS: S typhi vaccine generates a mild inflammatory reaction associated with temporary but profound dysfunction of the arterial endothelium in both resistance and conduit vessels to both physical and pharmacological dilator stimuli. This finding might explain the association between infection and inflammation and the enhanced risk of an acute cardiovascular event.