Chronic Heart Failure Model Induced by Coronary Embolization in Sheep

Objective

To create a model of chronic heart failure in a large animal.

Methods

Heart failure was induced in sheep by single intracoronary injection of polymer macrobeads, which were administered into left main coronary artery (n=3) or selectively into left anterior descending (n=4) or left circumflex (n=5) coronary artery. The animals were followed by echocardigraphy for 20 weeks. Measurements comprised fractional area change (FAC), and diastolic ventricular area (EDVA) and regional wall-thickening fraction (WT%).

Results

EDVA increased from 14.2±2.1 cm2 prior to embolization to 16.9±3.1 cm2 on day 1 (p<0.05), and remained significantly increased until completion of the follow-up period. FAC dropped from 47.9±4.6% at baseline to 29.3±4.4% on day 1 (p<0.001) and remained significantly depressed until 20 weeks later. In 9 selectively embolized animals WT% of the embolized area decreased from 33.8±8.0% at baseline to 5.3±2.6% on day 1 and remained significantly decreased.

Conclusions

A simple model of chronic heart failure was developed. It shows relatively high stability over time and may prove beneficial in experimental work on ventricular assist devices.

[Levels of troponin I, tropoinin T, isoenzyme MB creatine kinase and myoglobins in blood serum for perioperative diagnosis of myocardial infarction in patients after coronary artery bypass graft surgery with extracorporeal circulation]

We studied plasma levels of troponin I (cTnI), troponin T (cTnT), creatine kinase MB (CKMBmass) and myoglobin (MB) in patients undergoing coronary artery bypass surgery with extracorporeal circulation and cardioplegia. In group 1 (25 patients without perioperative myocardial infarction) plasma levels of all markers studied were elevated after operation. In group 2 (24 patients with perioperative myocardial infarction) plasma concentrations of all markers exceeded several times levels observed in patients without myocardial infarction with maximal value for MB at 12 hours after operation; for cTnI and CKMBmass at 16 hours after surgery and for cTnT at 32 hours after the end of operation. ROC curves show cut-off value for CKMBmass 20.3 ng/ml (sensitivity 79% and specificity 89%); for cTnI cut-off value was 0.8 ng/ml (sensitivity 80% and specificity 94%) for cTnT the cut-off value was 0.41 ng/ml (sensitivity 86% and specificity 88%) and for MB the cut-off value was 419 ng/ml (sensitivity 85% and specificity 70%).

CONCLUSION

All markers studied are reliable biochemical tests for perioperative myocardial infarction, however, the analysis of ROC curves suggested that cTnI and cTnT might be more useful for diagnosis of perioperative myocardial infarction after conventional coronary artery bypass surgery.

PET reversed mismatch in an experimental model of subacute myocardial infarction

The aim of this study was to evaluate the relationship between flow/metabolism, histology and functional follow-up in a sheep model of subacute myocardial infarction. In eight juvenile sheep, a myocardial infarction was induced by intracoronary injection of macrobeads. Left ventricular function was evaluated using echocardiography. 2-[18F]fluoro-2-deoxy-D-glucose (18F-FDG)/nitrogen-13-labelled ammonia (13NH3) positron emission tomography (PET) was performed at 6 weeks and 16 weeks after embolization. In five sheep, a dynamic carbon-11 acetate study was performed. In each animal, two regions of interest were defined on the polar map, corresponding to the embolized and the non-embolized region. After the final measurements, the hearts were processed for histological evaluation. PET revealed a moderately decreased flow and oxidative metabolism in the embolized region at 6 weeks, without significant changes at follow-up. At 6 weeks, 18F-FDG uptake in the embolized area was more severely decreased as compared to the flow index in the embolized area (P < 0.05). At 16 weeks, 18F-FDG metabolism had significantly recovered (P < 0.05). Serial echocardiography showed a persistent decrease in global and regional left ventricular function. Histology revealed a mix of micro-infarcted and viable tissue in the embolized region. In this model of subacute myocardial infarction, a PET "reversed mismatch" pattern was observed, with partial recovery of 18F-FDG uptake at follow-up. The histological counterpart of this PET pattern appears to be patchy necrosis.

The effect of sudden failure of a rotary blood pump on left ventricular performance in normal and failing hearts

We investigated the hemodynamic effect of regurgitation (or back-flow) due to sudden failure of a rotary blood pump (diagonal pump). Seven healthy sheep (Group C) and 7 with chronic heart failure (Group F) were studied. Chronic heart failure was obtained by intracoronary injection of microspheres several weeks earlier. Left ventricular function and ventricular efficacy were assessed by the pressure-volume relationship. The back-flow through the stopped pump was significantly lower in Group F (2.3 +/- 0.34 L/min) than in Group C (2.8 +/- 0.33 L/min). Mean aortic blood pressure dropped significantly from 68.3 +/- 9.65 to 61.9 +/- 9.75 mm Hg in Group C and from 62.5 +/- 9.12 to 51.5 +/- 9.08 in Group F but remained stable during the 15 min period of pump stop. Parameters of left ventricular contractility (preload recruitable stroke work) dropped significantly in both groups, remained stable during the pump stop, and returned to baseline values 30 min after the end of back-flow. The ventricular efficacy (in terms of energy transfer) was tolerant against this acute volume overload even in the failing hearts. Sudden pump failure of a rotary blood pump leads to an acute depression of the hemodynamic state and myocardial contractility. However, this depression remained stable over 15 min, did not lead to further deterioration of the animals, and was completely reversible.

The influence of stenting on the behavior of amino-oleic acid-treated, glutaraldehyde-fixed porcine aortic valves in a sheep model

BACKGROUND AND AIM OF THE STUDY

The durability of freehand-sewn aortic valve homografts used for valve replacement in humans is greater than for stented aortic homografts. In analogy with this, it is expected that the durability of a stentless heterograft will be superior to that of its stented counterpart. Our objective was to investigate the influence of stenting on amino-oleic acid (AOA)-treated, glutaraldehyde-fixed porcine aortic valve bioprostheses.

METHODS

Twelve young sheep underwent implantation of porcine aortic valves in the pulmonary artery: six porcine aortic stentless valves (Freestyle) and six porcine aortic stented valves (Mosaic). In each series, three valves were explanted after three months, and three after six months. Valves were analyzed by gross inspection, radiography, histology, and transmission electron microscopy. Quantitative determination of calcium content was made with atomic absorption spectrometry.

RESULTS

The porcine aortic stentless valve showed extensive calcification of its aortic wall portion, but had perfectly functioning, pliable cusps without calcification up to six months. The cusps of porcine aortic stented valves were also pliable and functioning without calcification up to six months. Only minimal calcification was seen in the aortic wall of the stented valves. At six months after implantation the cusps of stentless valves contained significantly less calcium than those of stented valves (2.7+/-1.2 microg/mg and 7.9+/-2.3 microg/mg, respectively; p = 0.011). However, the aortic wall from stentless valves contained significantly more calcium than that of stented valves (three-month explants: 39.2+/-14.4 versus 7.2+/-2.8 microg/mg; p <0.05; six-month explants: 49.3+/-14.0 versus 14.1+/-5.9 microg/mg; p <0.05).

CONCLUSION

These data suggest that stenting does influence cuspal calcification of AOA-treated, glutaraldehyde-fixed porcine aortic valves.

Micropumps to support the heart during CABG

OBJECTIVE

To show the effect of myocardial support by micropumps during beating heart CABG for triple vessel disease.

METHODS

In 12 sheep, three coronary arteries (LAD, intermediate branch and circumflex) were consecutively occluded for 10 min. The animals were divided in two groups: group 1 without support (n=6) and group 2 with biventricular support of intravascular micropumps. The pumps (diameter 6.4 mm) were placed through peripheral access (femoral artery and jugular vein) and advanced under fluoroscopic guidance. The hemodynamic evolution was analyzed during the procedure and 2 h of reperfusion. Myocardial flow was assessed by colored microspheres. Differences between groups were analyzed by ANOVA for repeated measurements and post-hoc testing in case of significance.

RESULTS

All of the pump-supported animals survived the procedure, 1 of the control animals died of resistant ventricular fibrillation. At the end of the reperfusion period, the hemodynamic performance and myocardial contractility was significantly better in the pump-supported group (cardiac output: 2.4+/-0.9 vs. 3.3+/-0.9 l/min, P=0.0192; mean arterial blood pressure: 51+/-23 vs. 73+/-9 mmHg, P=0. 036; first derivative of the left ventricular pressure: 561+/-271 vs. 947+/-316 mmHg/s, P=0.0074). After the procedure, subendocardial blood flow was significantly better in all areas of the left ventricle in group 2 (0.935+/-0.427 ml/min per g vs. 0.409+/-0.183 ml/min per g in group 1; P=0.0366).

CONCLUSION

The supported heart is more resistant to repetitive local ischemia. Support by microaxial pumps can make beating heart surgery safer and applicable for more complex cases.

Are stentless aortic heterografts suitable for right ventricular outflow tract reconstruction? An experimental study in juvenile sheep

Allograft valved conduits are used routinely for reconstruction of the right ventricular outflow tract in children with congenital heart disease; however, allografts are scarce. The purpose of this study was to evaluate two stentless aortic valves that might be suitable alternatives for right ventricular outflow tract reconstruction. Twelve juvenile sheep underwent implantation of stentless aortic heterografts as an interposition in the pulmonary artery: six porcine aortic valves (Freestyle) and six fully pericardial valves (Pericarbon stentless). In each series, three valves were explanted after 3 months, the other three after 6 months. Valves were analyzed by gross inspection, radiography, and light microscopy. The porcine aortic stentless valve (Freestyle) showed extensive calcification of its aortic wall portion, with perfectly functioning, pliable cusps without calcification or fibrous overgrowth up to 6 months. The pericardial valves (Pericarbon stentless) showed extensive fibrous sheathing, causing progressive retraction of the leaflets and severe regurgitation. After 3 months, minimal calcification was seen in the pericardial wall. Calcification was more pronounced after 6 months, sometimes causing complete calcification of pericardial wall and leaflets, leading to a significant stenosis. We conclude that the pericardial stentless valve becomes rapidly dysfunctional after right-sided implantation as a result of fibrous sheathing and severe calcification. The porcine aortic stentless valve remains functional, but severe calcification of the aortic wall portion is problematic.

Chronic heart failure model induced by coronary embolization in sheep

OBJECTIVE

To create a model of chronic heart failure in a large animal.

METHODS

Heart failure was induced in sheep by single intracoronary injection of polymer macrobeads, which were administered into left main coronary artery (n=3) or selectively into left anterior descending (n=4) or left circumflex (n=5) coronary artery. The animals were followed by echocardigraphy for 20 weeks. Measurements comprised fractional area change (FAC), and diastolic ventricular area (EDVA) and regional wall-thickening fraction (WT%).

RESULTS

EDVA increased from 14.2+/-2.1 cm2 prior to embolization to 16.9+/-3.1 cm2 on day 1 (p<0.05), and remained significantly increased until completion of the follow-up period. FAC dropped from 47.9+/-4.6% at baseline to 29.3+/-4.4% on day 1 (p<0.001) and remained significantly depressed until 20 weeks later. In 9 selectively embolized animals WT% of the embolized area decreased from 33.8+/-8.0% at baseline to 5.3+/-2.6% on day 1 and remained significantly decreased.

CONCLUSIONS

A simple model of chronic heart failure was developed. It shows relatively high stability over time and may prove beneficial in experimental work on ventricular assist devices.

Calcification characteristics of porcine stentless valves in juvenile sheep

OBJECTIVE

To compare calcification characteristics of two porcine stentless valves (Toronto SPV and Freestyle) with different designs, fixation and antimineralization techniques using a juvenile sheep model of valve implantation inside the circulation.

METHODS

The stentless valves (n = 2 x 6) were implanted in juvenile sheep in the pulmonary artery as an interposition, while the circulation was maintained with a right ventricular assist device. The model was validated by the implantation of, clinically well-known, porcine (Hancock II) and pericardial (Pericarbon) valves. Half of the valves were explanted after 3 months, the rest after 6 months. Valves were examined macroscopically, by X-ray, light microscopy (HE, Masson, Von Giesson, Von Kossa, PTAH stains), and transmission electron microscopy. Quantitative determination of the calcium content of the cusps was performed with atomic absorption spectrometry.

RESULTS

After 3 months, the Freestyle had an extensively calcified aortic wall, most prominent at the outflow side of the porcine valve. After 6 months, calcification increased transmurally, but the valve cusps were free of calcification, and the inflow side was only slightly calcified. The Toronto SPV valve also started to calcify at the inflow side of the valve after 3 months with increased calcification after 6 months. The base of the Toronto SPV valve cusps showed slight calcification after 6 months of implantation.

CONCLUSIONS

The pattern of calcification of the porcine aortic wall differs between the two studied stentless valves, with calcification located predominantly at the outflow side in the Freestyle valve, but also at the inflow side in the Toronto SPV valve. The cusps of the Freestyle valve were less prone to calcification than those from the Toronto SPV valve.