Predictive value of inducible endothelial cell adhesion molecule expression for acute rejection of human cardiac allografts

We conducted a prospective longitudinal study to determine the clinical significance of endothelial adhesion molecule expression in endomyocardial biopsies from human cardiac allografts. Ten to 18 (mean 13) consecutive allograft biopsies were obtained from 20 serial human transplant recipients over a one-year period. A total of 267 biopsies was examined. The expression of endothelial adhesion molecules intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin, as well as the presence of CD3+ T cell infiltrates was assessed by immunocytochemical staining of frozen sections. Separate specimens taken at the same time were analyzed histologically for ischemic injury or rejection. ICAM-1--and, to a lesser extent VCAM-1--was expressed at low levels in normal biopsies. E-selectin was only expressed in 15% of histologically normal biopsy specimens. Ischemic injury noted in the immediate posttransplant period was associated with increased expression of all three adhesion molecules. VCAM-1 expression increased both with the degree of CD3+ T cell infiltrates (P < 0.001) and with the degree of rejection (P < 0.05). ICAM-1 increased over constitutive levels in association with diffuse CD3+ infiltrates (P < 0.001) and with rejection (P < 0.05). E-selectin was increased on occasional vessels in association with CD3+ infiltrates (P < 0.001), but was not associated with active rejection. Increases in E-selectin were most likely to occur in biopsies just prior to rejection episodes (odds ratio 3.3), and were least likely to occur in biopsies following rejection (odds ratio 0.3). ICAM-1, but not VCAM-1, was also elevated in prerejection specimens. VCAM-1 and ICAM-1 declined in postrejection specimens. These data suggest a dynamic pattern in the expression of endothelial cell adhesion molecules during the course of cardiac allograft rejection. This study also suggests that endothelial E-selectin expression may be a useful clinical marker of impending rejection. Finally, inducible VCAM-1 expression may be a helpful adjunct in the diagnosis of ongoing acute rejection, and decreases in its expression may be indicative of successful antirejection therapy.

Recovery and viability of an acute myocardial infarct after transmyocardial laser revascularization

OBJECTIVES

The short- and long-term effectiveness of transmyocardial laser revascularization was evaluated in the setting of an acute myocardial infarction.

BACKGROUND

Theoretically, transmyocardial laser revascularization allows direct perfusion of the ischemic area as ventricular blood flows through the channels to the myocardium.

METHODS

Infarcts were created by coronary occlusion in 30 sheep. Eighteen of these sheep were studied to assess short-term efficacy. The infarct was reperfused after 1 h by either removing the occlusion or by laser drilling using a high power carbon dioxide laser. The occlusions were left in place for the control group. To monitor regional recovery, percent systolic shortening was measured. To evaluate long-term effectiveness, 12 additional sheep underwent creation of an infarct. Six were treated with the laser, and six were untreated. The animals were restudied 30 days later.

RESULTS

In the short-term experiment, the control and reperfusion groups exhibited no recovery of regional contractility. The laser group demonstrated improvement throughout the recovery period. There was a significant difference in the area of necrosis within the same area at risk (reperfusion group 44 +/- 6% and control group 39 +/- 5% vs. laser group 6 +/- 2%). After 30 days, none of the control animals showed evidence of contraction in the infarct, whereas the laser-treated animals did. Histologic analysis of the laser-treated infarcts revealed patent channels surrounded by viable myocardium. The control-group infarcts were necrotic and scarred.

CONCLUSIONS

On the basis of both short- and long-term improved contractility, as well as diminished necrosis in the area at risk, these results indicate that transmyocardial laser revascularization may be an alternative method of treating ischemic heart disease.

Effect of 2-amino oleic acid exposure conditions on the inhibition of calcification of glutaraldehyde cross-linked porcine aortic valves

Postimplant calcific degeneration is a frequent cause of clinical failures of glutaraldehyde cross-linked porcine bioprosthetic heart valves (BPHV). It was demonstrated previously that 2-amino oleic acid (AOA) used as a bioprosthesis treatment was highly effective in mitigating aortic valve cusp but not aortic wall calcification. Our main objective was to study the efficacy of various AOA exposure conditions for inhibiting calcification of both cusps and aortic wall tissues using rat subdermal implants. BPHV tissues were treated with a saturated AOA solution for different time intervals before experimental. Aortic wall AOA levels were consistently lower than that of the cusps after the same exposure times. The diffusion of calcium ion across both cusp and aortic wall tissues was evaluated, and the results demonstrated that there was an AOA exposure time-dependent retardation of calcium ion penetration for cusp but not aortic wall. An 8-month extraction study was performed to determine the stability of AOA binding. When Tween 80 was used as an extraction medium, cusp and aortic wall retained 12.9 and 48.7%, respectively, of their initial AOA levels. AOA inhibition of calcification in rat subdermal implants (60 days) was found to be exposure time-dependent with maximum treatment time (120 h), resulting in the lowest calcium levels (20.1 +/- 10.3 and 71.4 +/- 5.4 micrograms/mg of cusp and aortic wall, respectively) as compared with controls (219.1 +/- 6.8 and 104.9 +/- 8.5 micrograms/mg of cusp and aortic wall, respectively). The significance of AOA binding on BPHV tissue was determined by either blocking or reducing BPHV's (cusp and aortic wall) free aldehyde residues with lysine or NaBH4, respectively, before AOA treatment. For aortic cusps, the AOA contents after 72 h were 98.3 +/- 2.7, 34.2 +/- 3.6, and 54.1 +/- 3.0 nM/mg of tissue for AOA (control), lysine-pretreated (plus AOA) and NaBH4-pretreated (plus AOA) tissues, respectively. However, their calcium levels after 60 days of rat subdermal implant were all comparable (i.e., 48.1 +/- 6.2, 38.2 +/- 9.1, and 47.0 +/- 15.0 micrograms calcium per mg of tissue). Similar results were observed on BPHV aortic wall. It can thus be concluded that AOA inhibition of BPHV calcification is exposure time-dependent, but the efficacy of AOA for aortic wall is less than that noted for aortic cusps, perhaps because of lower AOA binding and differences in calcium diffusion kinetics.

Onset and progression of calcification in porcine aortic bioprosthetic valves implanted as orthotopic mitral valve replacements in juvenile sheep

The purpose of this study was to characterize the onset and progression of mineralization in porcine bioprosthetic valves implanted in sheep and to test the hypothesis that such valves simulate calcification that is observed clinically and in other experimental models. Hancock I porcine aortic bioprosthetic valves (Medtronic Heart Valve Division, Irvine, Calif.) were implanted as orthotopic mitral valve replacements in juvenile sheep, retrieved after 1 to 124 days, and analyzed as follows: gross inspection, radiography, light, transmission, and surface scanning electron microscopy, and calcium analysis by absorption spectroscopy. Mineralization increased with increasing time after implantation in both valve cusps and adjacent aortic wall. Mean cuspal calcification was 80 micrograms/mg in valves removed after 3 to 4 months. Nevertheless, considerable variability among valves was apparent in the level of calcification noted at specific time intervals. Virtually all aspects of the morphologic characteristics were identical to those previously noted for clinical explants and experimental specimens, both subcutaneous and circulatory. In particular, ultrastructural examination revealed that the earliest calcific deposits were associated with devitalized cuspal connective tissue cells and their fragments. Collagen calcification was sparse. Both surface scanning and transmission electron microscopy indicated a lack of endothelial or blood-derived cells on the valves at all sampling times. We conclude that porcine bioprosthetic valves implanted as mitral valves in sheep provide a useful calcification model, simulating morphologic and pathobiologic events that occur clinically and in noncirculatory models. However, sufficient specimen replicates must be done to overcome variability in calcification among valves and sampling sites.

Angiotensin-converting enzyme inhibition prolongs survival and modifies the transition to heart failure in rats with pressure overload hypertrophy due to ascending aortic stenosis

BACKGROUND

We tested the hypotheses that long-term administration of the angiotensin-converting enzyme (ACE) inhibitor fosinopril will regress hypertrophy, modify the transition to heart failure, and prolong survival in rats with chronic left ventricular (LV) pressure overload due to ascending aortic stenosis.

METHODS AND RESULTS

Aortic stenosis was created in weanling male Wistar rats by a stainless steel clip placed on the ascending aorta. Age-matched control animals underwent a sham operation (Sham group, n = 57). Six weeks after surgery, rats with aortic stenosis were randomized to receive either oral fosinopril 50 mg.kg-1.d-1 (Fos/LVH group, n = 38) or no drug (LVH group, n = 36) for 15 weeks. Pilot studies confirmed that this dosage produced significant inhibition of LV tissue ACE in vivo. Animals were monitored daily, and survival during the 15-week treatment period was assessed by actuarial analysis. At 15 weeks, in vivo LV systolic and diastolic pressures and heart rate were measured. To assess contractile function, the force-calcium relation was evaluated by use of the isovolumic buffer-perfused, balloon-in-LV heart preparation at comparable coronary flow rates per gram LV weight. Quantitative morphometry was performed. Mortality during the 15-week trial was significantly less in the Fos/LVH group than in the LVH group (3% versus 31%, P < .005). No deaths occurred in the Sham group. In vivo LV systolic pressure was similar between Fos/LVH and LVH hearts (223 +/- 10 versus 232 +/- 9 mm Hg) and significantly higher than the Sham group (99 +/- 3 mm Hg, P < .05). In vivo LV diastolic pressure was significantly lower in Fos/LVH hearts than in LVH hearts (10 +/- 2 versus 15 +/- 2 mm Hg), and both were significantly higher than in the Sham group (5 +/- 1 mm Hg, P < .05). Heart rate was similar among all groups. Despite equivalent elevation of LV systolic pressure, fosinopril resulted in regression of myocyte hypertrophy in Fos/LVH versus LVH (myocyte cell width, 14.8 +/- 0.5 versus 20.8 +/- 2.2 microns, P < .05) to normal levels (Sham, 16.3 +/- 0.9 microns). Quantitative morphometry demonstrated that the regression of LV myocyte hypertrophy in the Fos/LVH group was associated with a relative increase in the fractional volume of fibrillar collagen and noncollagen interstitium. In the isolated heart experiments, LV systolic developed pressure relative to perfusate [Ca2+] was significantly higher in Fos/LVH hearts than in LVH hearts. The improvement in systolic function was not related to any difference in myocardial high-energy phosphate levels, since LV ATP and creatine phosphate levels were similar in Fos/LVH and LVH hearts.

CONCLUSIONS

In rats with ascending aortic stenosis, chronic ACE inhibition with fosinopril improved survival, decreased the extent of LV hypertrophy, and improved cardiac function despite persistent elevation of LV systolic pressure. The favorable effects of fosinopril may be related in part to inhibition of the effects of cardiac ACE on myocyte hypertrophy rather than to systemic hemodynamic mechanisms.

Mechanism of efficacy of 2-amino oleic acid for inhibition of calcification of glutaraldehyde-pretreated porcine bioprosthetic heart valves

BACKGROUND

Calcification is a frequent cause of the clinical failures of glutaraldehyde-pretreated bioprosthetic heart valves (BPHV) fabricated from glutaraldehyde-cross-linked porcine aortic valves. 2-Amino oleic acid (AOA) has been shown in previous in vivo studies to be a promising anticalcification agent. Our objective was to investigate the mechanism of calcification inhibition mediated by AOA pretreatment of porcine aortic valve bioprostheses.

METHODS AND RESULTS

BPHV tissues were treated with an AOA solution for 72 hours before experimentation. The diffusion of AOA across both cusp and aortic wall was evaluated. The lag time for AOA to diffuse across the aortic wall was prolonged compared with that of the cusp. An extraction study was performed to determine the stability of AOA binding; the results indicated that the binding was relatively stable regardless of solvent extraction conditions. The interaction between ionic calcium and AOA on treated tissue also was investigated by evaluating the patterns of calcium diffusion across both treated and untreated tissues. The results showed that AOA significantly reduced the diffusion of calcium. AOA inhibition of aortic valve calcification (calcium level, 5.5 +/- 3.0 mg/g of tissue compared with control; calcium level, 91.2 +/- 19.5 mg/g of tissue) but not aortic wall (calcium level, 158.7 +/- 10.3 mg/g of tissue compared with control; calcium level, 157.5 +/- 7.9 mg/g of tissue) was demonstrated on representative specimens from valves implanted in left ventricular apicoaortic shunts explanted after 150 days.

CONCLUSIONS

AOA covalently binds to glutaraldehyde-pretreated bioprosthetic heart valve tissue, presumably as the result of an aldehyde-amino reaction. Covalently bound AOA diminishes Ca2+ diffusion compared with non-AOA-pretreated bioprosthetic tissues. This may explain in part the anticalcification mechanism of AOA. Furthermore, AOA inhibits calcification of porcine BPHV cusps in the circulation.

Endothelial and smooth muscle cells express leukocyte adhesion molecules heterogeneously during acute rejection of rabbit cardiac allografts

Interactions of leukocytes with vascular wall cells figure prominently in acute rejection and development of vascular occlusive disease after cardiac transplantation. To investigate the time course and distribution among different types of vessels of expression of endothelial leukocyte adhesion molecules, issues difficult to address in humans, we studied heterotopic transplants of Dutch-Belted rabbit hearts into New Zealand white recipients without immunosuppression (average time to graft failure 8.2 +/- 0.4 days). We found constitutive expression of vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) by coronary arterial endothelium in normal rabbits, whereas myocardial capillaries and the endocardial lining cells showed little or no expression of VCAM-1. VCAM-1 expression increased within 1 day after transplantation on the endothelium of the transplanted aorta and endocardium and on myocardial microvascular endothelial cells. ICAM-1 expression increased remarkably on all endothelia studied from 2 to 8 days after transplantation. Adhesion molecule expression on coronary artery endothelial cells also increased during severe allograft rejection (from a histological score of 1.7 +/- 0.6 pretransplant to 4.8 +/- 0.2 8 days after transplant for VCAM-1 and from 0.9 +/- 0.6 to 4.4 +/- 0.3 for ICAM-1, n = 43 arteries in 5 animals, mean +/- SD). In addition, coronary artery and aortic smooth muscle cells also showed induction of VCAM-1 and ICAM-1 8 days after transplant. We conclude that endothelial activation in a transplanted organ can occur rapidly and varies among microvascular, endocardial, and coronary artery endothelial cells, a point germane to the interpretation of endomyocardial biopsies. Augmented expression of adhesion molecules precedes temporally leukocyte accumulation in vessels. In addition, our finding of activation of coronary artery smooth muscle cells during acute rejection suggests that such episodes may contribute to the development of accelerated coronary arteriosclerosis.

Immediate evaluation of endomyocardial biopsies for clinically suspected rejection after heart transplantation

BACKGROUND

Acute rejection may be suspected in heart transplant recipients in the setting of new onset of clinical symptoms or alterations in cardiac function. Immediate diagnosis may be obtained by performing a frozen section on endomyocardial biopsy (EMB) specimens. However, little is known about the indications for, and the diagnostic reliability of, this procedure.

METHODS AND RESULTS

EMBs with frozen section (n = 98) from 65 of 214 consecutive orthotopic heart transplant recipients were reviewed and divided into early (< or = 45 days; n = 47) and late (> 45 days; n = 51) posttransplant periods. Frozen section diagnoses (means = 1.5 EMB samples) were compared with corresponding permanent section diagnoses (means = 4.4 EMB samples), and clinical indications were analyzed. Comparison of frozen and permanent section interpretation revealed concordant pathological processes-rejection (n = 31) versus no rejection (n = 37) versus ischemic injury (n = 20)-in 88 of 98 (90%) cases. Discordant pathological processes on frozen versus permanent section in 10 of 98 (10%) cases could be attributed to ischemic injury (n = 5), sampling (n = 4), and infection (n = 1). In the 92 cases with defined clinical indications, the indication and number of EMBs positive for rejection early and late after transplantation were arrhythmia: 2 of 12 early, 4 of 10 late; congestive heart failure: 1 of 2 early, 5 of 12 late; fever: 0 of 2 early, 1 of 4 late; echo abnormality: 0 of 5 early, 0 of 1 late; syncope: 1 of 5 early, 0 of 1 late; hypotension: 1 of 3 early, 1 of 2 late; noncompliance: 0 of 0 early, 4 of 5 late; more than one of the above: 3 of 7 early, 2 of 5 late; other: 1 of 7 early, 1 of 9 late; total: 9 of 43 early, 18 of 49 late.

CONCLUSIONS

Frozen section on EMB specimens accurately reflected the permanent section diagnosis in 90% of cases. No specific clinical indication predicted EMB rejection positivity with high sensitivity in either the early or late posttransplant periods.

Pathology of substitute heart valves: new concepts and developments

All types of contemporary cardiac valve substitutes suffer deficiencies and complications that limit their success. Mechanical and bioprosthetic valves are intrinsically obstructive, especially in small sizes. Mechanical valves are associated with thromboembolic problems; the chronic anticoagulation used in virtually all mechanical valve recipients causes hemorrhage in some. Calcification limits the success of porcine and pericardial bioprostheses, allograft valves, and the yet experimental trileaflet polymeric prostheses. The predominant mechanism of calcification in porcine, pericardial, and allograft valves is cell mediated, being nucleated at the membranes and in organelles of the transplanted cells. In polymeric leaflet valves, calcification is both extrinsic (in adherent thrombus) and intrinsic (subsurface and acellular in the solid elastomer). Nevertheless, except for a few notable exceptions, contemporary mechanical valves are durable. Other important potential complications of prosthetic and bioprosthetic valves include paravalvular leak, endocarditis, or extrinsic interference with function. Moreover, aortic valvular allografts undergo progressive noncalcific degeneration, tearing, sagging, and/or retraction. Studies of retrieved long-term cryopreserved allograft explants demonstrate severe degeneration, with distortion of normal architectural detail, loss of endothelial and deep connective tissue cells, and variable inflammatory cellularity. Thus, they are morphologically nonviable valves, whose structural basis for function seems primarily related to the largely preserved collagen, and they are unlikely to have the capacity to grow, remodel, or exhibit active metabolic functions. Since calcification intrinsic to the cusps is the major pathologic process necessitating bioprosthetic valve reoperations, efforts to prevent formation of mineral deposits are active.(ABSTRACT TRUNCATED AT 250 WORDS)

Physicochemical properties of calcific deposits isolated from porcine bioprosthetic heart valves removed from patients following 2-13 years function

The purpose of this study was to characterize the physicochemical properties of calcific deposits that cause the failure of tissue-derived heart valve bioprostheses. This was done in an effort to understand the mechanism of pathologic biomineralization in the cardiovascular system and potentially prevent deterioration of bioprostheses. Calcific deposits taken from 10 failed bioprosthetic valves that had been implanted in patients for 2-13 years were characterized by chemical analysis, x-ray diffraction, FTIR spectroscopy, scanning electron microscopy, polarized light microscopy, and solubility measurements. The combined results identified the biomineral as an apatitic calcium phosphate salt with substantial incorporation of sodium, magnesium and carbonate. The average Ca/PO4 ratio for this "young" pathologic biomineral was approximately 1.3, considerably lower than approximately 1.7 found in mature atherosclerotic plaque biomineral and mature skeletal biomineral, both of which approximate hydroxyapatite in composition. Deproteinated calcific deposits from bioprostheses had thermodynamic solubilities comparable to those of both atherosclerotic plaque, typical pathologic biomineral and hydrolyzed octacalcium phosphate (OCP, Ca4H(PO4)3 x 2.5 H2O), a proposed precursor phase to biomineral apatite. This later finding, together with chemical composition and structural details of the bioprosthetic deposits themselves, supports a mechanism of cardiovascular calcification in which OCP plays a crucial role in the formation of the final apatitic phase. This suggests an approach toward prevention of bioprosthetic tissue calcification through control of the formation of the kinetically favored OCP precursor and/or its transformation into bioapatite.

Inhibition of calcification of glutaraldehyde pretreated porcine aortic valve cusps with sodium dodecyl sulfate: preincubation and controlled release studies

Calcification of bioprosthetic heart valves fabricated from glutaraldehyde pretreated bovine pericardium or porcine aortic valves (PAV) is a frequent cause of the failure of these devices. Of all strategies considered thus far, only detergent preincubations using compounds such as sodium dodecyl sulfate (SDS) inhibited PAV bioprosthetic mineralization in circulatory sheep bioprosthetic valve replacements. The present study sought to characterize the mechanism of action of SDS preinicubation. Results of transport and material characterization studies showed that SDS had a relatively high affinity for PAV, with a maximum uptake of 167.1 +/- 6.8 micrograms SDS/mg tissue over 24 h at 37 degrees C with a partition coefficient of 19.3. The PAV diffusion of SDS was 1.95 +/- 0.35 10(-6) cm2/sec. The principal effect of SDS on PAV was phospholipid extraction. The residual organic phosphate in the SDS pretreated tissue was 2.22 +/- 0.72 nmol/mg tissue compared to the control untreated group with 18.52 +/- 2.1 nmol/mg tissue. Incubations of PAV specimens in a 1% SDS solution for 24 h significantly inhibited calcification after 21 days in subdermal implants in 3-week-old male rats (PAV Ca2+ = 18.0 +/- 11.8 micrograms/mg) compared to control (177.8 +/- 6.0 micrograms/mg). In contrast, coimplants of 30% SDS silicone rubber polymers, for regional sustained SDS administration, did not impede PAV calcification in 21 day implants Ca2+ = 166.0 +/- 14.0 micrograms/mg compared to the nondrug silicone matrix controls, Ca2+ = 173.0 +/- 6.6 micrograms/mg). Thus, we conclude that the mechanisms of SDS inhibition of PAV calcification is due to material effects which occur during preincubation, and is not facilitated by sustained SDS administration.

Mechanisms causing coronary microvascular dysfunction following crystalloid cardioplegia and reperfusion

OBJECTIVE

The aim was to examine the mechanisms of coronary microvascular dysfunction during cardiopulmonary bypass and ischaemic arrest using a crystalloid cardioplegic solution.

METHODS

Porcine hearts were arrested with cold hyperkalaemic (K+ = 25 mmol.litre-1) cardioplegic solution for 1 h during cardiopulmonary bypass and then reperfused for 1 h. Selected hearts were arrested but not reperfused. Coronary vessels of non-instrumented pigs were used as controls. In vitro vascular responses of subepicardial and subendocardial arterioles were examined in a pressurised (40 mm Hg) no flow state with video microscopy.

RESULTS

Following 1 h of ischaemic cardioplegia, endothelium dependent relaxations of epicardial arterioles to the receptor mediated agent ADP and the non-receptor-mediated agent calcium ionophore A23187 were moderately reduced, and the contractile responses to KCl or the thromboxane A2 analogue U46619 were reduced compared to responses of vessels from control animals. After 1 h of reperfusion, U46619 caused contraction greater than control values, while contraction to KCl and endothelium dependent relaxations to ADP or A23187 were further reduced. Responses of endocardial microvessels to serotonin were slightly more affected by cardioplegia and reperfusion than were epicardial vessels, while the effect on responses of epicardial and endocardial vessels to bradykinin or A23187 were similar. Endothelium independent relaxation to sodium nitroprusside was not altered in any of the experimental groups. The addition of manganese superoxide dismutase to the cardioplegic solution markedly preserved endothelium dependent responses to ADP and A23187 and contractile response to U46619, compared to the responses of vessels from the plain crystalloid cardioplegia group, but had no effect on relaxation to sodium nitroprusside or on contraction to KCl. Five hours of normokalaemic hypothermia (5-10 degrees C) in Krebs buffer had minimal effect on vasodilator responses. Electron microscopy revealed preserved endothelial and smooth muscle cell structure, and focal mononuclear leucocyte-endothelium adherence following cardioplegic arrest and reperfusion.

CONCLUSIONS

Ischaemic cardioplegia-reperfusion induced endothelium dependent and direct smooth muscle microvascular dysfunction is at least partially mediated by prolonged exposure of vessels to hyperkalaemia and to the generation of oxygen derived free radicals. Leucocytes probably mediate injury during reperfusion, while hypothermia has minimal effect on recovery of vasomotor function.

Synergistic inhibition of the calcification of glutaraldehyde pretreated bovine pericardium in a rat subdermal model by FeCl3 and ethanehydroxydiphosphonate: preincubation and polymeric controlled release studies

Calcification is a frequent cause of the clinical failure of bioprosthetic heart valves fabricated from glutaraldehyde-pretreated porcine aortic valves or glutaraldehyde-pretreated bovine pericardium (GPBP). We investigated the hypothesis that ferric chloride (FeCl3) and sodium-ethanehydroxydiphosphonate (EHDP) may act synergistically to prevent bioprosthetic tissue calcification. Pre-incubations and controlled release systems were studied individually. FeCl3-EHDP polymeric controlled release matrices were formulated using silicone rubber and evaluated for in vitro release kinetics at pH 7.4 and 37 degrees C. The effects of Fe-EHDP synergism on GPBP calcification were investigated with 21 d subdermal implants in 3 wk-old male rats. Results demonstrated that levels of Fe3+ and EHDP uptake, measured in GPBP tissues pre-incubated first in an FeCl3 solution (10(-5) M) followed by an EHDP solution (0.1 M), were higher than in the reverse order of incubation. In the first series of rat implants, GPBP was pre-incubated in either FeCl3 or Na2EHDP solutions, or sequential pre-incubations of first FeCl3 and then Na2EHDP solutions, or the reverse. The inhibition of calcification was greatest when FeCl3 (first pre-incubation, 10(-5) M) was combined with Na2EHDP (second pre-incubation, 0.1 M) (1.78 +/- 0.2 micrograms of Ca2+/mg of dried tissue) compared with the other pre-incubation groups: EHDP (first pre-incubation) combined with FeCl3 (second pre-incubation) (21.7 +/- 6.4), FeCl3 solution alone at 10(-5) M (27.9 +/- 10.7), Na2EHDP solution alone at 0.1 M (52.3 +/- 11.9) and the control group (72.3 +/- 10.2). In a second series of implants, GPBP specimens were co-implanted with individual controlled release systems containing one of the following formulations (weight percentage in silicone rubber): 1% FeCl3, 20% CaEHDP, 20% protamine sulphate, 1% FeCl3-20% CaEHDP, and 1% FeCl3-20% protamine sulphate. The 1% FeCl3-20% CaEHDP silicone-rubber matrices were the most effective for inhibiting GPBP mineralization (13.7 +/- 3.0 micrograms Ca2+/mg of dried tissue) compared with non-drug silicone co-implant controls (74.7 +/- 5.58 micrograms Ca2+/mg of dried tissue) and other polymeric treatment groups (32.3 +/- 2.3-80.0 +/- 19.7). No adverse effects on bone or overall growth of any treatment protocols were noted. Thus, combinations of FeCl3 and EHDP, using either pre-incubations or polymeric controlled release, were synergistic for inhibiting GPBP calcification.

Prototype miniature endoluminal MR imaging catheter

PURPOSE

The feasibility of a miniature endoluminal magnetic resonance (MR) detection coil was investigated for imaging mural and perimural anatomy of small, tubular structures.

MATERIALS AND METHODS

To this end, remotely tunable, single-loop, multiturn, receive-only radio-frequency coils, housed in 6-9-F arterial sheaths, were built. A 1.9-T imager was used. Phantom excitation was accomplished with a 62-mm-diameter bird-cage quadrature coil, and ex vivo specimen excitation was accomplished with a single-turn, untuned wire loop. Phantom images obtained with use of a 9-F catheter coil showed a signal-to-noise improvement on the border of 20 dB compared with images obtained with the quadrature coil. An 8-F catheter coil was used to obtain high-resolution (100 microns in-plane pixel size, 500 microns section thickness) spin-echo images (repetition time = 2,400 msec, echo time = 53 msec) of the wall of a fresh ex vivo human popliteal artery.

RESULTS

Prospectively, these images were suggestive of the presence of diffuse intimal hyperplasia, medial calcification, and focal atherosclerotic plaque. These findings were confirmed histologically. Three-dimensional restacking of the axial images simplified examination of the normal layers and pathologic changes within the wall. The improved signal-to-noise characteristics of these miniature coils permit fast high-resolution imaging, allowing visualization of microscopic anatomic details.

CONCLUSIONS

With further development, this technology may be useful for studying atherosclerosis and for providing imaging guidance during endoluminal MR interventions.

Distribution and functional significance of cardiac angiotensin converting enzyme in hypertrophied rat hearts

BACKGROUND

The intracardiac conversion rate of angiotensin (Ang) I to Ang II and the expression of angiotensin converting enzyme (ACE) mRNA are amplified in rat hearts with left ventricular hypertrophy (LVH). To examine whether the accelerated intracardiac Ang II generation in LVH is related to an induction of cardiac ACE, we studied localization and function of cardiac ACE in hypertrophied rat hearts using specific ACE inhibitors.

METHODS AND RESULTS

Cardiac ACE was localized and quantified in hearts from male Wistar rats with LVH due to chronic experimental aortic stenosis and from control rats. With the ACE inhibitor 125I-351A, a derivative of lisinopril, as a radioligand on coronal sections of LVH and control hearts, in vitro autoradiography demonstrated ACE binding in aorta, coronary arteries, atria, and ventricles of both groups. Quantitative analyses revealed that ACE density (counts per minute per cross-sectional area of tissue) was twofold higher within the myocardium of hypertrophied left ventricles compared with controls (p < 0.005). Quantitative morphometry demonstrated a modest increase in the fractional volume of myocytes as well as capillary volume without an increase in the fractional volume of endothelial cells in left ventricular tissue from aortic stenosis rats. These data suggest that an increase in endothelial cell volume per se cannot alone account for the observed doubling of ACE density and support an upregulation of ACE production in hypertrophied tissue. The role of cardiac ACE in intracardiac conversion of Ang I to Ang II and its specific inhibition was studied in isolated, isovolumic beating, buffer-perfused LVH and control hearts. Biochemical conversion rates as well as functional changes in response to 3 x 10(-7) M Ang I were examined in the absence or presence of the ACE inhibitor enalaprilat (4 x 10(-6) M). After a brief stabilization period, groups of LVH and control hearts were subjected to the following infusion protocols: 15 minutes of vehicle followed by 30 minutes of Ang I plus vehicle, 15 minutes of enalaprilat followed by 30 minutes of Ang I plus enalaprilat (enal/Ang I), or 45 minutes of vehicle only to allow comparison with a time control. Intracardiac Ang I-to-Ang II conversion rate was fourfold higher in LVH than in control hearts (p < 0.05). Infusion of enalaprilat reduced the intracardiac Ang I-to-Ang II conversion rate in LVH hearts by 70% (p < 0.05 versus Ang I). At similar levels of constant coronary flow per gram, Ang I increased coronary perfusion pressure by 23 +/- 5 mm Hg (p < 0.01 versus vehicle) in LVH hearts and by 36 +/- 10 mm Hg (p < 0.005 versus vehicle) in control hearts. When enalaprilat was infused with Ang I, the increase in perfusion pressure was limited to 5 +/- 5 mm Hg (NS versus vehicle) in LVH hearts and 12 +/- 3 mm Hg (p < 0.05 versus vehicle) in control hearts and was significantly lower than in hearts infused with Ang I only (p < 0.05 in LVH and p < 0.05 in control hearts, respectively). Systolic function was not affected by either infusion protocol. In contrast, Ang I infusion was associated with diastolic dysfunction. In LVH hearts, left ventricular end-diastolic pressure (LVEDP) increased from 10 +/- 1 mm Hg at baseline to 25 +/- 2 mm Hg at the end of the Ang I infusion (p < 0.001 versus vehicle), which was inhibited by infusion of enalaprilat. In control hearts, there was a lesser increase in LVEDP from 10 +/- 1 mm Hg to 15 +/- 1 mm Hg in response to Ang I (p < 0.05 versus LVH). Control hearts treated with enalaprilat with Ang I displayed no increase in LVEDP:

CONCLUSIONS

These observations indicate that ACE protein is increased within the myocardium of LVH hearts, extending recent findings of increased cardiac ACE activity and mRNA levels in this model of pressure-overload LVH in the rat. Blockade of the enzyme by an ACE inhibitor decreases intracardiac Ang I-to-Ang II conversion rate and prevents the functional changes of Ang I-to-Ang II activation

Effects of metallic ions and diphosphonates on inhibition of pericardial bioprosthetic tissue calcification and associated alkaline phosphatase activity

This study focused on the association of extrinsic alkaline phosphatase (AP) activity with both early and advanced calcification of glutaraldehyde-pretreated bovine pericardial bioprosthetic (GPBP) tissue, and the inhibition of both calcification and AP activity by pre-incubation in diphosphonates (sodium-ethanehydroxydiphosphonate [NaEHDP], aminopropanehydroxydiphosphonate [APD]) and metallic salts (FeCl3, Ga(NO3)3, AICI3). GPBP specimens were implanted subcutaneously in 3 wk old male rats after pre-incubation. Following explantation of the tissue at 72 h and 21 d, calcification was assessed morphologically by light microscopy and chemically by atomic adsorption spectroscopy for calcium content and by molybdate complexation for phosphorus. AP activity was characterized by enzymatic hydrolysis of paranitrophenyl phosphate and by histochemical studies. In both control and pretreated groups, AP levels were greater in 72 h explants than 21 d retrievals, which demonstrated extensive calcification in control explants. All pre-incubations that resulted in inhibition of calcification after 21 d, except for APD, were associated with 72 h AP content which was lower than control specimens. The typical time of initiation of calcification was 72 h, as determined by previous studies with this model system. Covalently bound APD inhibited calcification. Increased AP activity in the APD group may be due to the toxicity of this agent with resultant acute inflammation, or other incompletely understood effects of diphosphonates on calcification and AP. Furthermore, EHDP and Ga3+ incubations were also associated with decreased GPBP AP at 72 h compared to control, but were not effective for inhibiting calcification after 21 d. We concluded that inhibition of peak GPBP AP activity is not necessarily associated with the prevention of GPBP mineralization.

Blood and albumin cardioplegia preserve endothelium-dependent microvascular responses

Alterations of vascular reactivity may be a cause of reduced myocardial perfusion after cardioplegic arrest. The effects of blood and albumin cardioplegia on endothelium-dependent coronary microvascular function and ultrastructure were examined after cardiopulmonary bypass, ischemic arrest, and reperfusion. During cardiopulmonary bypass, porcine hearts were arrested with either blood, albumin-crystalloid, or crystalloid cardioplegia for 1 hour, followed with reperfusion for 1 hour. Noninstrumented pigs were used as controls. Coronary microarterial vessels (90 to 190 microns in diameter) were studied in a pressurized, no-flow state with video microscopic imaging and electronic dimension analysis. Ischemic arrest with crystalloid cardioplegia markedly reduced endothelium-dependent relaxations to the adenine nucleotide adenosine diphosphate and the calcium ionophore A23187. Enhanced contractile responses were observed to the platelet-derived vasoactive substance serotonin and to the thromboxane A2 analogue U46619. Indomethacin corrected the enhanced contractile responses to serotonin, indicating the enhanced release of a constrictor prostanoid substance. Indomethacin had no effect on the impaired relaxations to adenosine diphosphate or A23187. Endothelium-dependent relaxations to adenosine diphosphate, serotonin, and A23187 were significantly preserved with either blood or albumin-crystalloid cardioplegia, whereas contractile responses to U46619 were normal. Endothelium-independent relaxation to nitroprusside was similar in all groups, indicating normal smooth muscle responsiveness. Electron microscopy revealed minimal alterations of vascular morphology of vessels in both crystalloid and blood cardioplegia groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Computational structural analysis based on intravascular ultrasound imaging before in vitro angioplasty: prediction of plaque fracture locations

OBJECTIVES

This in vitro study was designed to test the hypothesis that a structural analysis based on intravascular ultrasound images of atherosclerotic vessels obtained before angioplasty can be used to predict plaque fracture locations and balloon pressures required to cause fracture.

BACKGROUND

Intravascular ultrasound imaging performed before interventional procedures has potential for providing information useful for guiding therapeutic strategies.

METHODS

Intravascular imaging was performed on 16 atherosclerotic human iliac vessel segments obtained freshly at autopsy; balloon angioplasty was then performed with 1-min inflations at 2 atm, increasing in 2-atm increments until fracture of the lumen surface occurred. Fracture locations were confirmed by histopathologic examination. Structural analysis of these images was performed with a large strain finite element analysis of the image that calculated the distribution of stress in the vessel with 2 atm of lumen pressure.

RESULTS

Structural analysis demonstrated a total of 30 high circumferential stress regions in the vessels (mean 1.9 high stress regions/vessel). A total of 18 plaque fractures occurred in the 16 vessel segments. Of the 17 fractures that occurred in the 15 specimens with regions of high circumferential stress, 14 (82%) occurred at a high stress region (p < 0.0001). However, there was no significant relation between the peak stresses estimated by structural analysis and the ultimate balloon inflation pressure required to cause fracture.

CONCLUSIONS

Structural analysis based on intravascular ultrasound imaging performed before in vitro balloon angioplasty can predict the locations of plaque fracture that usually accompany angioplasty. However, these data suggest that intravascular ultrasound may not be useful for predicting the ultimate balloon inflation pressure necessary to cause fracture, possibly because of the variable fracture properties and microscopic structure of atherosclerotic tissues.

Relaxation responses of the coronary microcirculation after cardiopulmonary bypass and ischemic arrest with cardioplegia: implications for the treatment of postoperative coronary spasm

Coronary arteriolar spasm may occur following cardiopulmonary bypass and ischemic arrest, resulting in impaired cardiac function. Because myocardial perfusion is principally regulated by the microcirculation, the in vitro effects of various clinically used vasodilating drugs on porcine coronary microvessels less than 200 microns in diameter were examined following cardioplegic arrest and reperfusion. After 1 hour of ischemic arrest using either crystalloid or blood cardioplegia solutions followed by 1 hour of reperfusion, microvessels were studied in a pressurized (40 mmHg), no-flow state, and imaged with a video tracking device. Vessels were preconstricted by 30% to 60% of their resting diameter using acetylcholine, and various vasodilatory agents were applied extraluminally. Responses to the beta-adrenergic receptor agonist isoproterenol and the nitrovasodilator sodium nitroprusside were minimally altered by either cardioplegia solution as compared to control. In contrast, relaxation responses to both the calcium channel antagonist nifedipine and nitroglycerin were diminished after ischemic arrest and reperfusion. Relaxation responses were similar with crystalloid or blood cardioplegia for all drugs tested. Despite its somewhat attenuated response, nifedipine remained the most potent vasodilator of those studied. It is concluded that (1) following ischemic arrest with either crystalloid or blood cardioplegia solutions, responses to sodium nitroprusside and isoproterenol were minimally altered, while responses to nifedipine and nitroglycerin were attenuated; (2) relaxation responses of coronary arterioles were not significantly different with either blood or crystalloid cardioplegia; and (3) despite a slightly decreased response after cardioplegia, nifedipine was the most potent vasodilator of coronary arterioles, and may be the best choice for treating postoperative coronary arteriolar spasm.

Impaired endothelium-dependent coronary microvascular relaxation after cold potassium cardioplegia and reperfusion

Myocardial dysfunction after cardiac operations might be influenced by altered myocardial perfusion in the postoperative period. To investigate possible alterations in vascular reactivity, in vitro coronary microvascular responses were examined after ischemic cardioplegia with use of a porcine model of cardiopulmonary bypass. Since myocardial perfusion is primarily regulated by arteries less than 200 microns in diameter, these vascular segments were examined. After 1 hour of ischemic arrest with cold crystalloid cardioplegia and 1 hour of reperfusion, microvessels (100 to 190 microns in diameter) were pressurized in a no-flow state, preconstricted by 30% to 60% of the baseline diameter with acetylcholine, and examined with video microscopic imaging and electronic dimension analysis. Endothelium-dependent relaxations to bradykinin (55% +/- 13% versus 99% +/- 1% = maximum relaxation of the preconstricted diameter in cardioplegia-reperfusion vessels versus control vessels, respectively; p < 0.05) and the calcium ionophore A 23187 (33% +/- 6% versus 90% +/- 4%; p < 0.05) were markedly impaired while endothelium-independent relaxation to sodium nitroprusside was similar to control value. After 1 hour of ischemic cardioplegia without reperfusion, endothelium-dependent relaxation was only slightly affected. Transmission electron microscopy showed minimal endothelial damage after ischemic cardioplegia and reperfusion. These findings have important implications regarding coronary spasm and cardiac dysfunction after cardiac operations.

Effects of fixation back pressure and antimineralization treatment on the morphology of porcine aortic bioprosthetic valves

Calcification frequently causes failure of porcine aortic valve bioprostheses; changes in collagen configuration induced by high-back-pressure fixation have deleterious effects on porcine aortic valve mechanics. Although modified porcine aortic valve bioprostheses that include the use of lower-pressure fixation and antimineralization treatments are used clinically, the morphologic characteristics of these valves are not known. We evaluated, by light and scanning and transmission electron microscopy, the comparative structural details of clinically processed Hancock Standard (no antimineralization treatment, 80 mm Hg fixation), Hancock II (T-6 antimineralization treatment, fixed initially at 1.5 mm Hg, then 80 mm Hg) and Intact (toluidine blue antimineralization treatment, zero-pressure-fixed [0 mm Hg]) porcine aortic valve bioprostheses as well as true low-pressure (1.5 mm Hg) fixed valves, zero-pressure-fixed porcine aortic valves (with no further treatment), and freshly fixed porcine aortic valve cusps as controls. Commercially processed valves had near-complete loss of endothelium and amorphous extracellular matrix and autolytic changes in the cuspal connective tissue cells. Both 80 and 1.5/80 mm Hg fixed valves, but not zero-pressure-fixed cusps (Intact valves, zero-pressure-fixed porcine aortic valves or immediately fixed porcine aortic valve cusps), had overall flattening and compression with near-complete loss of transverse cuspal ridges and collagen crimp; valves fixed at 1.5 mm Hg had intermediate features. T-6 and toluidine blue treatments induced no definite incremental microscopic changes attributable to the antimineralization treatment. No degenerative changes in collagen were noted in any valves that underwent antimineralization treatment. These studies indicate that valves fixed at zero but not at 80 or 1.5/80 mm Hg pressure retain collagen architecture virtually identical to that of relaxed native porcine aortic valve cusps and that the antimineralization treatments studied do not adversely affect collagen morphology.

Antimineralization treatments for bioprosthetic heart valves. Assessment of efficacy and safety

Since calcification limits the durability of contemporary bioprosthetic heart valves, antimineralization treatments are being widely investigated. Potential antimineralization treatments must have sustained prevention of mineralization without adverse effects. The preclinical investigation of efficacy and safety of antimineralization treatments comprises four essential steps: (1) subcutaneous implantation in small animals, (2) in vitro biomechanical studies of hemodynamics and durability, (3) morphology of unimplanted valves, and (4) circulatory implants in large animals.

Experimental evaluation of an autologous tissue heart valve

The goal of the autologous tissue heart valve (ATHV) prosthesis project has been the development of a non-antigenic, non-calcifying bioprosthesis of greater durability than heterograft or homograft bioprostheses. It is made in the operating room, at a sterile work bench, during surgery for heart valve replacement. Autologous pericardium is used for valve construction after a five minute immersion in 0.6 per cent glutaraldehyde buffered to pH 7.4 with phosphate. The stent-mounted trileaflet prosthesis can be made in five minutes with a semi-automated method that uses two concentric mating stents that substitute clamping for sewing of the tissue. In vitro testing, to include pulse duplicator, accelerated wear tester, static testing for leakage and tensile strength testing, has been performed with ATHVs made with glutaraldehyde-tanned bovine and ovine pericardium. Transvalvular pressure gradients were measured at 3.3-7.3 mmHg at flow rates of 4-5 l/min. Six valves have been tested beyond 800,000,000 cycles with full opening and closing at differential closing pressures of 125 mmHg. One of the valves developed a 2mm leaflet tear after 26,000,000 cycles but the remaining five survived intact. No fractures were seen in the Dacron covered Delrin stents. Six ATHVs were implanted in juvenile sheep for five months. One animal died after five months of infective endocarditis secondary to an unrecognized deep wound infection and the other five were electively sacrificed at the same time interval. Four valves were fully competent at terminal elective cardiac catheterization and one showed minimal insufficiency attributed to a paravalvular leak. The leaflet tissue was free of generalized calcification in all instances. There was no evidence of leaflet tissue thickening or shrinkage. The mean calcium content at necropsy of the 15 leaflets from the five valves was 8.357 mg/g of tissue. There is experimental evidence that an ATHV made of pericardium treated briefly with glutaraldehyde may achieve the goal of a non-calcifying, more durable bioprosthesis.