Corticomedullary shunting after ischaemia and reperfusion in the porcine kidney?

BACKGROUND: Renal perfusion may redistribute from cortex to medulla during systemic hypovolaemia and after renal ischaemia for other reasons, but there is no consensus on this matter. We studied renal perfusion after renal ischaemia and reperfusion. METHODS: Renal perfusion distribution was examined by use of 153Gadolinium-labeled microspheres (MS) after 2 h (hrs) and 4 h ischaemia of the pig kidney followed by 4 h of reperfusion. Intra-arterial injected MS are trapped in the glomeruli in renal cortex, which means that MS are not present in the medulla under normal physiological conditions. RESULTS: Visual evaluation after reperfusion demonstrated that MS redistributed from the renal cortex to the medulla in 6 out of 16 pigs (38%) subjected to 4 h ischaemia and in one out of 18 pigs subjected to 2 h ischaemia. Central renal uptake of MS covering the medullary/total renal uptake was significantly higher in kidneys subjected to 4 h ischaemia compared with pigs subjected to 2 h ischaemia (69 ± 5% vs. 63 ± 1%, p < 0.001), and also significantly higher than in the contralateral kidney (69 ± 5% vs. 63 ± 2%, p < 0.001). Analysis of blood and urine demonstrated no presence of radioactivity. CONCLUSION: The study demonstrated the presence of MS in the renal medulla in response to renal ischaemia and reperfusion suggesting that severe ischaemia and reperfusion of the pig kidney leads to opening of functional shunts bypassing glomeruli.

Establishment and characterization of porcine focal cerebral ischemic model induced by endothelin-1.

BACKGROUND AND PURPOSE: Due to well-developed Circle of Willis in pigs, it is technically challenging to make persistent focal ischemic stroke based on occlusion of cerebral arteries. Endothelin-1 could cause a focal lesion by forcing transient but strong vasoconstriction in the circumscribed injected area. Its use in porcine stroke model has drawn attention lately. However, all the porcine endothelin-1 induced models were euthanized soon after surgery. Whether the brain lesion is persistent, and whether they could cause neurological deficit are not known. This research aims to provide a more detailed characterization of endothelin-1 induced porcine cerebral ischemic model by evaluating the change of neurological function and the brain lesion monitored by MRI of the pigs. METHODS: Danish Domestic pigs were randomly divided into two groups: a group receiving endothelin-1 (ET-1 group, n=6) and a sham group (n=6). After the fronto-temporal craniotomy, pigs in the ET-1 group received 200µl endothelin-1 injected within a cortical area of one cm2; pigs in the sham group received only saline injections. Neurological deficit evaluation and MRI scanning were done 24h and 72h after operation. Afterwards, hematoxylin and eosin staining was conducted to detect the morphological characteristics of the damaged brain tissue. RESULTS: The average performance score in the pigs of the ET-1 group was 9.67±1.03 and 9.00±1.26 respectively, at 24h and 72h after surgery, which was significantly higher than that of the pigs in sham group. The brain lesion percentage detected by MRI was 12.26±0.60%, and 10.33±0.51% respectively, at 24h and 72h after surgery in the ET-1 group. Microscopy showed extended pyknotic neuronal perikarya in neurons located in the ischemic area. CONCLUSIONS: The endothelin-1 induced porcine cerebral ischemic model is technically easier, and able to create cerebral ischemia severe enough to cause a functional neurological deficit as well as observable lesions on MRI. It is a suitable model for long-term cerebral ischemia research.

Pharmacokinetics of the phosphatidylserine tracers 99mTc-lactadherin and 99mTc-annexin V in pigs.

BACKGROUND: Phosphatidylserine (PS) is a phospholipid normally located in the inner leaflet of the cell membrane. PS is translocated from the inner to the outer leaflet of the plasma membrane during the early stages of apoptosis and in necrosis. In cell and animal studies, reversible PS externalisation to the outer membrane leaflet has been observed in viable cells. Hence, PS markers have been proposed as markers of both reversibly and irreversibly damaged cells. The purpose of this experimental study in pigs was to investigate the kinetics of the newly introduced PS marker technetium-99m-labelled lactadherin (99mTc-lactadherin) in comparison with the well-known PS tracer 99mTc-annexin V with special reference to the renal handling of the tracers. The effective dose for humans was estimated from the biodistribution in 24 mice. METHODS: Nine anaesthetised pigs randomly allocated into two treatment groups were administered a single injection of either 99mTc-lactadherin or 99mTc-annexin V. Renal perfusion was assessed by simultaneous injection of 51Cr-EDTA. Throughout the examinations, planar, dynamic scintigraphy of the trunk was performed, urine was collected and arterial and renal vein blood was sampled. The effective dose was estimated using the adult male phantom from the RADAR website. RESULTS: 99mTc-lactadherin was cleared four times faster from plasma than 99mTc-annexin V, 57 ± 13 ml/min (mean ± SD) versus 14 ± 2 ml/min. 99mTc-lactadherin had a predominant uptake in the liver, whereas 99mTc-annexin V was primarily taken up by the kidneys. The estimated effective human dose after single injection of 99mTc-lactadherin and 99mTc-annexin V was 5.8 and 11 µSv/MBq, respectively. CONCLUSIONS: The high hepatic uptake of 99mTc-lactadherin compromises the use of 99mTc-lactadherin for imaging PS externalisation in the liver. Due to scatter from the liver, the use of in vivo visualisation of PS externalisation in the lower thorax and upper abdomen by 99mTc-lactadherin is challenged, but not precluded. In contrast to 99mTc-annexin, 99mTc-lactadherin has a low renal uptake and may be the preferred tracer for imaging PS externalisation in the kidneys. The effective dose after injection of 99mTc-lactadherin and 99mTc-annexin was low. Recommendations regarding the clinical use of 99mTc-lactadherin must await tracer kinetic studies in patients.

Estimating risk of pulmonary neoplastic embolism during vertebroplasty.

STUDY DESIGN: Vertebroplasty was simulated on a pig model. OBJECTIVE: To evaluate the risk of neoplastic tissue migration into lungs during vertebroplasty. SUMMARY OF BACKGROUND DATA: The application of vertebroplasty in spinal metastasis is not well documented. The risk of neoplastic tissue migration into the lungs during vertebroplasty remains unknown. METHODS: A cancer model was built in 11 Landrace pigs (50 kg) by injecting 99mTc-labeled albumin macroaggregates into the center of L5 and L6 prior to vertebroplasty. Continuous scintigraphic imaging was performed with 1-minute frames over the lungs and vertebrae before and after injection to ensure steady state and baseline. We surveyed free TcO4- in thyroid. Twenty minutes after the 99mTc injection, 2-level vertebroplasty was performed at L5 and L6 with 3 Jamshidi needles in each vertebra. Into each vertebra, on average, 2.8 ± 1.1 mL of poly(methyl methacrylate) cement (Depuy CMW, Blackpool, UK) was injected. Quantitative scintigrams were obtained within 90 minutes after vertebroplasty. X-rays and quantitative computed tomography scans quantified cement distribution. Means of 99mTc activity before and after vertebroplasty were compared in a paired t test. RESULTS: In this cancer model, we found an 80% risk of tissue migration to the lungs when performing vertebroplasty. In average, the study showed a significant amount of macroaggregate migration of 1.87% total range from 0% to 8% (CI: 0.05%-0.37%) with P = 0.045. There was no free TcO4- in the thyroid. Despite the standardized procedure, we found a large interindividual variation of pulmonary embolism. CONCLUSION: It is demonstrated that there exists a significant risk of exporting neoplastic disease or fatty tissue to the lungs when performing vertebroplasty. A similar adverse effect can be expected with balloon kyphoplasty. In patients with metastatic disease, vertebroplasty should be limited to those with short life expectancy.

Adaptation of nonrevascularized human hibernating and chronically stunned myocardium to long-term chronic myocardial ischemia.

It is unknown whether human chronically ischemic dysfunctional myocardium degenerates over time or adapts to chronic ischemia. We studied whether perfusion, metabolism, and contractile function and reserve can be preserved in nonrevascularized human chronically stunned and hibernating myocardium. We studied 16 event-free, medically treated patients with ejection fractions of 31 +/- 2% and chronically stunned or hibernating myocardium in 56 +/- 5% of the left ventricle on technetium-99m sestamibi single-photon emission computed tomography/fluorine-18 fluorodeoxyglucose (FDG) positron emission tomography. Patients underwent repeat single-photon emission computed tomography, positron emission tomography, and tissue Doppler echocardiography at rest and during stress at follow-up after 25 +/- 4 months, and we investigated whether measurements of myocardial viability remained stable over time. Patients were stable with respect to New York Heart Association class and global left ventricular function (30 +/- 2%, p = 0.81). Wall motion score was unaltered in hibernating myocardium and chronically stunned regions, and a contractile reserve by tissue Doppler stress echocardiography was preserved. Overall, 74% of hibernating myocardium and chronically stunned regions retained their initial perfusion/metabolism pattern at follow-up. In hibernating myocardium, initial and follow-up sestamibi uptakes (53 +/- 1% and 53 +/- 2%, p = 0.85) and FDG uptakes (76 +/- 1% and 74 +/- 1%, p = 0.21) did not differ. In chronically stunned regions, sestamibi uptake displayed a minor decrease at follow-up (70 +/- 1% vs 67 +/- 1%, p <0.01) and FDG uptake remained constant (68 +/- 2% and 67 +/- 1%, p = 0.21). In conclusion, myocardial perfusion, FDG uptake, and contractile function in nonrevascularized chronically stunned and hibernating myocardium adapt to chronic ischemia in patients who are free of events. In chronically stunned regions, adaptation may be less complete than in hibernating myocardium.

Hemodynamic function of the standard St. Jude bileaflet disc valve has no clinical impact 10 years after aortic valve replacement.

OBJECTIVES: Size mismatch and impaired left ventricular function have been shown to determine the hemodynamic function of the standard St. Jude bileaflet disc valve early after aortic valve replacement (AVR). We aimed to analyse St. Jude valve hemodynamic function and its clinical impact in the survivors of a prospective series 10 years after AVR for aortic stenosis. DESIGN: Forty-three survivors aged 32-90 years from a prospective series attended a follow-up study with Doppler echo and radionuclide cardiography 10 years after AVR for aortic stenosis. Six patients with significant left sided valve regurgitation were excluded from further analysis: they had significantly lower St. Jude valve gradient and left ventricular ejection fraction (LVEF) and larger mass index (LVMi) than 37 without. RESULTS: In the 37 patients without left sided valve regurgitation peak and mean gradients were inversely related to St. Jude valve geometric orifice area (GOA) indexed for either body surface area or left ventricular end-diastolic dimension (LVEDD). The gradients correlated directly with LVEDD but not with LVEF or LVMi. Eleven patients with hypertension had higher peak gradients (31+/-13 versus 22+/-8 mmHg, p<0.05), lower LVEF, and higher LVEDD and LVMi than 26 without. Peak gradient was greater than 35 mmHg in five hypertensive patients with normal LVEF but lesser than 30 mmHg in six with impaired LVEF. Supranormal LVEF and severe size mismatch identified the remaining patients (N=3) with peak gradient above 35 mmHg. In a multilinear regression analysis GOA indexed for LVEDD, hypertension, and LVEF were independently related to peak gradient. CONCLUSION: High gradients of the standard St. Jude bileaflet disc valve 10 years after AVR was primarily related to systemic hypertension and mismatch between valve and left ventricular cavity size. Hypertension and left sided valve regurgitation, but not St. Jude valve gradient or size mismatch, were the dominant determinants of left ventricular hypertrophy and impaired function.

Arterial concentration of 99mTc-sestamibi at rest, during peak exercise and after dipyridamole infusion.

Tracers for myocardial perfusion imaging during stress should not only have high cardiac uptake but they should also have a fast blood clearance to prevent myocardial tracer uptake after the ischaemic stimulus. The present study characterize the early phase of the arterial (99m)Tc-sestamibi (MIBI) time-activity curve after venous bolus injection at rest, during peak exercise and after dipyridamole infusion. We included 11 patients undergoing angioplasty for one-vessel disease (rest study) and 20 patients evaluated for the detection of haemodynamic significant coronary stenoses by (99m)Tc-sestamibi single photon emission computed tomography (SPECT) using either bicycle exercise testing (10 patients) or standard dipyridamole testing (10 patients). Arterial blood samples of 1 ml were taken from the left femoral artery (rest study) or the right radial artery (exercise and dipyridamole studies) every 5 s during the first 5 min postinjection. In the exercise and the dipyridamole studies blood sampling were extended to include blood samples every 5 min 5-30 min postinjection. Peak MIBI concentration was lower and decrease in concentration slower after tracer injection during exercise than during dipyridamole stress testing. This may cause an underestimation of perfusion defects during exercise because of MIBI uptake after the ischaemic stimulus. The implications of the study not only refer to the choice of stress modality when using MIBI. This study also underlines the importance of considering early blood clearance in addition to regional myocardial tracerkinetic aspects such as myocardial extraction fraction when new tracers are introduced.

Predictable changes in left ventricular mass and function during ten years after valve replacement for aortic stenosis.

BACKGROUND AND AIM OF THE STUDY: Left ventricular (LV) hypertrophy is the underlying basis for longevity after aortic valve replacement (AVR) for aortic stenosis (AS). However, a detailed account of changes in LV mass and function in the long term after AVR and identification of the determinants of such changes have not yet been presented. METHODS: Ninety-one unselected consecutive adult patients with AS underwent AVR and were followed up to 10 years, at which time 41 survivors without new mitral disease underwent repeat measurement of LV mass index (LVMi), ejection fraction (LVEF), fast filling fraction (LVFFF), and end-diastolic volume index (LVEDVi). A subgroup comprising 49 patients was also assessed at eight days, three months, and 1.5 years postoperatively. All measurements were analyzed in a longitudinal regression model for repeated measures. RESULTS: LVMi fell from 202 +/- 58 g/m2 (n = 91) via 150 +/- 45 g/m2 (n = 39) at 1.5 years to 139 +/- 40 g/m2 (n = 41) at 10 years in all patients, and to 124 +/- 31 g/m2 (n = 29) in non-hypertensive patients. The LVMi falls were paralleled by improvements in LVEF and LVEDVi. LVFFF was not correlated to LVMi before the 10-year study. The longitudinal model indicated progressive reduction of LVMi to 1.5 years, but no change thereafter. The predictor variables were preoperative LVMi and end-systolic dimension index (high values of both related to high postoperative LVMi), hypertension, and male gender. The model for LVEF indicated a rapid increase to three months, followed by a slight decrease to 1.5 years and further to 10 years, predicted by preoperative LVEF and LVFFF. LVFFF fell sharply by three months, had recovered somewhat at 1.5 years and fully at 10 years, positively related to preoperative LVFFF and inversely to end-systolic chamber radius:wall thickness ration and small-sized prosthetic valves. LVEDVi converged from extreme values over time predicted by preoperative LVEF, but rose with hypertension and coronary artery disease. Hemodynamic function of the prosthetic aortic valve at any of the measurement times had no impact. CONCLUSION: Changes in LV mass and function up to 10 years after AVR for AS were highly predictable. Poorer outcomes were related to preoperative excessive hypertrophy and indices of underlying irreversible myocardial disease and further compromised by hypertension and, to a lesser extent, coronary artery disease. The hemodynamic function of the aortic prosthetic valve did not seem to play a role.

Regression of left ventricular hypertrophy during 10 years after valve replacement for aortic stenosis is related to the preoperative risk profile.

BACKGROUND: Previous studies have suggested that regression of hypertrophy may be the underlying determinant of longevity and left ventricular function after valve replacement (AVR) for aortic stenosis (AS). The potential for hypertrophy regression could therefore be related to the preoperative risk profile. METHODS: Ninety-one consecutive patients with AS had a "project" Doppler-echo and radionuclide ventriculography in addition to the standard investigation programme prior to AVR with a disc valve (19-29mm, n=82), a caged ball valve (26-29mm, n=8), or a stented porcine valve (26mm, n=1); 49 (group A) were selected for a serial follow-up study while 42 served as controls (group B). Forty-two group A patients took part in a 1.5-year examination while 47 (26 group A, 21 group B) patients were studied at 10 years. RESULTS: Groups A and B were comparable as regards all pre- and intra-operative data including left ventricular mass index (LVMi). A previously developed preoperative prognostic index (PI) separated the patients into groups with low (n=23), intermediary (n=19) and high risk (n=49) with 10-year survivals of 87%, 58% and 43% (P<0.01). LVMi dropped from 202+/-58g/m(2)preoperatively to 152+/-45g/m(2)(P<0.0001) at 1.5 years, and 139+/-40g/m(2)(P<0.0001) at 10 years (three and six patients, respectively, with paravalvular leak or mitral regurgitation excluded). PI correlated with preoperative (r=0.51, P<0.001), 1.5-year (r=0.46, P<0.01), and 10-year LVMi (r=0.41, P<0.01). Also preoperative left ventricular ejection fraction correlated with the three LVMi measurements. Patients with systemic hypertension had higher LVMi at 1.5 years (193+/-42, n=6 vs 144+/-42, n=33, P<0.05) and 10 years (175+/-39, n=12 vs 124+/-31g/m(2), n=29, P<0.001). Patients with low, intermediary or high PI, excluding those with hypertension, had 1.5-year LVMi of 110+/-35 (n=8), 134+/-43 (n=9) and 164+/-33g/m(2)(n=16; P<0.01), respectively, and 10-year LVMi of 116+/-25 (n=17), 126+/-27 (n=6), and 146+/-41g/m(2)(n=6; P<0.05), respectively. There was no relation between LVMi at 1.5 or 10 years and peak or mean Doppler gradient, prosthetic valve size, or valve size index. CONCLUSIONS: Left ventricular hypertrophy regression for patients who survived up to 10 years after AVR for AS is dependent on the preoperative risk profile indicating that irreversible myocardial disease is the underlying factor. Systemic hypertension is an important factor in its own right.

Neutrophils and platelets accumulate in the heart, lungs, and kidneys after cardiopulmonary bypass in neonatal pigs.

OBJECTIVE: Cardiac surgery with cardiopulmonary bypass elicits a systemic inflammatory response. An exaggerated response is associated with organ dysfunction and increased morbidity and mortality. DESIGN: The aim of the present study was to investigate whether the cardiopulmonary bypass procedure in itself results in accumulation of isotope-labeled platelets, polymorphonuclear neutrophils, and fibrinogen at organ levels in neonatal pigs and to monitor changes in organ function. SETTING: Pediatric cardiopulmonary bypass setup with 60 mins of aortic cross-clamp time and 120 mins of hypothermic cardiopulmonary bypass time. SUBJECTS: Thirty piglets were allocated to sternotomy alone (sham group, n = 15) or to sternotomy and cardiopulmonary bypass (n = 15). MEASUREMENTS AND MAIN RESULTS: Isotope-labeled autologous polymorphonuclear neutrophils, platelets, and commercially available fibrinogen were infused, and the specific accumulation at organ level was measured in a gamma counter 4 hrs after termination of cardiopulmonary bypass. Concomitant changes in oxygenation index and cardiac output were registered. Animals exposed to cardiopulmonary bypass showed a significantly higher technetium-99m-polymorphonuclear neutrophil accumulation in the lungs and kidneys, whereas indium-111-platelets accumulated in the heart and kidneys compared with the sham group. There was a significantly larger increase in oxygenation index and significantly larger decrease in cardiac output between the pre- and postcardiopulmonary bypass period in the cardiopulmonary bypass group compared with the sham group. CONCLUSIONS: The cardiopulmonary bypass procedure without cardiac surgery elicits organ dysfunction in terms of impaired respiratory and hemodynamic function. Platelets and polymorphonuclear neutrophils were entrapped in the heart, lungs, and kidneys of cardiopulmonary bypass animals, indicating that cell accumulation may contribute to the developing organ dysfunction.