Whole blood from 15 volunteers was anticoagulated with hirudin (200U/l) and the response to a known submaximal concentration of collagen (0.6 microg/ml) was tested by impedance aggregometry. In 8 volunteers platelet counts were also taken before and after the maximum aggregatory response. These tests were repeated when the samples had rested for 24 h at room temperature. The median [interquartile range] aggregatory response immediately after sampling was 17.3 [16.7-18.4] ohms. At 24 h it was 17.7 [15.8-19.3] ohms (p = 0.88) although variance was increased (p = 0.006). The immediate platelet count before collagen exposure was 438 [381-510] x 10(9)/l and 258 [227-297] x 10(9)/l post-collagen. At 24 h the platelet count was 448 [443-473] x 10(9)/l (p = 0.224 versus immediate count) but variance was not increased (p = 0.215). After full aggregation the count fell to 284 [234-304] x 10(9)/l (p = 0.592 versus early post-collagen). Variances were similar (p = 0.558). Aggregate response ratios increased non-significantly after 24 h from 0.59 [0.53-0.62] to 0.64 [0.51-0.68] although variance was increased (p = 0.021). Full macroaggregatory responses by impedance aggregometry were seen after 24h storage of whole blood with hirudin at room temperature. This suggests both that distant assessment of platelet function using a standardized method is possible and a potential role of thrombin inhibition for platelet storage.

Anticoagulants↗

PubMed2000

Heparin, platelet aggregation, neutrophils, and cardiopulmonary bypass.

UNLABELLED: Cardiopulmonary bypass (CPB) is associated with both neutrophil activation and failure of platelets to form large stable aggregates. We aimed to determine the effects of heparin and of neutrophil activation on platelet aggregation in whole blood. Fourteen patients undergoing routine aortocoronary bypass grafting and NSAID-free for over 7 days were studied before and after heparinisation, and at end-CPB. Whole blood, anticoagulated with rHirudin, was stirred for 3 minutes, and macroaggregation in response to collagen (0.6 microg. mL(-1)) or the neutrophil stimulant fMLP (10(-7)M) was determined by whole blood impedance aggregometry. Microaggregation was measured by counting unaggregated single platelets (corrected for haemodilution). The blood of volunteers was studied in vitro. PATIENTS: Before CPB, heparin effectively abolished platelet macroaggregation induced by collagen (20.5 to 1.4 Ohms) or fMLP (3.9 to 0 Ohms (p<0.0001). CPB had no additional effect. Heparinisation also reduced the platelet count from 127 (110-170) to 95 (64-117). The inhibition of macroaggregation could not be reversed by ex vivo heparinase. VOLUNTEERS: In vitro, the same heparin concentration, as measured in vivo (4 micromL(-1)), inhibited collagen-induced macroaggregation (20.3 to 14.7 Omega), but this effect was less than that observed ex vivo and was reversed by heparinase. In vitro heparin promoted fMLP macroaggregation (2.9 to 8.6 Omega). The inhibition of macroaggregation resulted from heparinisation, per se, rather than CPB and was insensitive to heparinase. There was less inhibition by in vitro heparin, which was reversible by heparinase, indicating a direct effect of heparin in vitro. The disparate findings are suggestive of an indirect action by heparin in vivo on macroaggregation, although heparin had a small direct stimulatory action on microaggregation.

Anticoagulants↗

PubMed2000

Heparin-induced platelet dysfunction and cardiopulmonary bypass.

BACKGROUND: Cardiopulmonary bypass is associated with impaired platelet macroaggregation. Heparin contributes to platelet dysfunction before extracorporeal circulation. In vitro heparinization of whole blood does not impair macroaggregation. Heparin releases several endothelial proteins; thus heparin may inhibit macroaggregation indirectly. METHODS: Patients undergoing operations using cardiopulmonary bypass and ABO blood group compatible volunteers were studied. Whole blood impedance aggregometry assessed macroaggregation in response to collagen (0.6 microg ml(-1)) in blood diluted either with normal saline or with platelet poor plasma, obtained from patients at different stages of cardiopulmonary bypass. RESULTS: Before heparinization, blood diluted with its own platelet poor plasma recorded an impedance change of 13.0 (4.7 to 15.6) Ohms. Platelet poor plasma obtained after heparinization or during extracorporeal circulation reduced this response to 3.7 (1.1 to 8.4) and 2.0 (1.1 to 3.3) Ohms, respectively (both p < 0.0001 versus pre-heparin; n = 13). Macroaggregation in blood from volunteers was similarly inhibited by patients' platelet poor plasma (n = 30). The macroaggregatory response in blood sampled after heparinization for cardiopulmonary bypass, decreased gradually from 11.4 (8.2 to 15.9) Ohms immediately after sampling to 1.7 (1.4 to 4.1) Ohms 2 hours later (p < 0.0001; n = 11). CONCLUSIONS: In vivo heparinization induces plasma changes that inhibit platelet macroaggregation. This is an indirect, delayed inhibition that is transferable in vitro to normal platelets.

Blood Platelet Disorders↗

PubMed2000

The effects of heparin and extracorporeal circulation on platelet counts and platelet microaggregation during cardiopulmonary bypass.

BACKGROUND: Cardiopulmonary bypass is associated with platelet activation and reduced platelet counts. Platelet activation may artifactually lower platelet counts by causing aggregation. In vivo platelet activation may increase existent platelet microaggregation ex vivo. We studied platelet counts and existent platelet microaggregation at different stages of cardiopulmonary bypass. METHODS: Twenty-one patients were studied before and after heparinization (300 U. kg(-1)) and at the end of cardiopulmonary bypass. Unaggregated (or single) platelets were counted in hirudin-anticoagulated blood, and total platelets were counted in ethylenediaminetetraacetic acid-anticoagulated blood. RESULTS: The total platelet count, 198 +/- 61 x 10(9). L(-1), was unaffected by heparin and stayed at 197 +/- 60 x 10(9). L(-1) (P =.7) but fell during extracorporeal circulation; the hemodilution-corrected count was 163 +/- 52 x 10(9). L(-1) (P =.0004). Heparinization reduced the unaggregated platelet count from (mean +/- 1 SD) 178 +/- 62 x 10(9). L(-1) to 155 +/- 60 x 10(9). L(-1) (P =.0001). Extracorporeal circulation had little additional effect. The hemodilution-corrected count was 142 +/- 48 x 10(9). L(-1) (P =.6). CONCLUSIONS: Heparinization caused platelet activation and increased existent platelet microaggregation ex vivo. During extracorporeal circulation, there was a reduction in total platelets that was greater than could be explained by hemodilution alone, but the unaggregated platelet count did not change significantly when corrected for hemodilution. Furthermore, the increased platelet microaggregation observed after heparinization was no longer evident after this loss. These findings suggest that during extracorporeal circulation, the platelets that formed into microaggregates after heparinization were lost from the circulation in preference to single platelets.

Adult↗

PubMed2000

Quantitative detection of platelet aggregates in whole blood without fixation.

Platelet counting detects lesser degrees of platelet aggregation than conventional aggregometry. In order to prevent progressive platelet aggregation or disaggregation after sampling it is customary to fix blood samples. However fixation may introduce other artefacts. We first compared stability of platelet counts in EDTA-, citrate- and r-hirudin-anticoagulated blood from healthy volunteers. Second, the stability of platelet counts in unfixed EDTA- and hirudin-anticoagulated blood was compared with glutaraldehyde-fixed blood in the same anticoagulants. Third, the effect of in vivo heparin administration on platelet counts in EDTA- and hirudin-anticoagulated blood was studied. Platelet counts within 2 h of collection were significantly higher in EDTA- than in hirudin- or citrate-anticoagulated blood (P = 0.002 vs. hirudin and P = 0.001 vs. citrate). Twenty-four hour counts in hirudin and EDTA were unchanged (P = 0.3 and P = 0.2, respectively, vs. earlier counts). Counts in citrate increased significantly (P = 0.007; n = 10). Platelet counts in fixed blood did not differ significantly from those in unfixed blood. Heparin administered for cardiopulmonary bypass reduced platelet counts in hirudin-anticoagulated blood from (mean +/- 1 standard deviation) 180 +/- 45 to 162 +/- 30 x 10(9) l-1 (P = 0.01; n = 14), without significantly lowering counts with EDTA-anticoagulation, consistent with increased platelet aggregation. Hirudin and EDTA provided stable platelet counts, suggesting that fixation is unnecessary.

Adult↗

PubMed2000

Porcine versus pericardial bioprostheses: eleven-year follow up of a prospective randomized trial.

BACKGROUND AND AIM OF THE STUDY: There is renewed interest in the pericardial heart valve as an alternative to the porcine bioprosthesis. The long-term results of a randomized trial comparing a second-generation pericardial valve against a well-tested porcine bioprosthesis are presented. Seven-year follow up has been reported previously. Production of the Bioflo pericardial prosthesis used in this trial was discontinued due to fears related to bovine spongiform encephalopathy. METHODS: Between February 1987 and March 1990, 170 patients undergoing aortic (AVR) or mitral (MVR) valve replacement were assigned randomly to receive either the Bioflo pericardial bioprosthesis or the Carpentier-Edwards (CE) supra-annular porcine bioprosthesis. Eighty-five patients received 93 Bioflo valves (46 AVR, 31 MVR, eight AVR+MVR), and the remaining 85 received 99 CE valves (48 AVR, 23 MVR, 14 AVR+MVR). Mean patient age was 61.0 years (range: 38-77 years) for the Bioflo group and 62.1 years (range: 41-77 years) for the CE group. Current follow up is 100% complete and totals 1,391 patient-years; mean +/- SD follow up was 8.2 +/- 3.4 years (maximum 12.2 years). RESULTS: The operative mortality rate was 4.12%. There were 70 patients still at risk at 11 years (31 Bioflo, 39 CE); of these, 91.4% were in NYHA classes I/II. No significant difference in survival or valve-related complications was seen between the groups. Mean (+/- SEM) survival at 11 years was 41.4 +/- 6.8% in the Bioflo group and 55.3 +/- 6.8% in the CE group (p = 0.15). There were 16 valve-related deaths (nine in the Bioflo group, seven in the CE group). At 11 years, freedom from valve-related mortality was 89.5 +/- 3.9% for the Bioflo group and 91.0 +/- 3.5% for the CE group (p = 0.4). Valve position had no impact on survival. At 11 years, freedom from structural valve deterioration was 83.9 +/- 5.4% and 87.5 +/- 4.2% in the Bioflo and CE groups, respectively (p = 0.9). CONCLUSION: Over the 11-year period of follow up, clinical performance of the Bioflo pericardial valve was comparable with that of the Carpentier-Edwards supra-annular porcine bioprosthesis. No difference was apparent between the two valve types when implanted in either the aortic or the mitral position.

Animals↗

PubMed1998

Acute traumatic cardiac tamponade treated solely by percutaneous pericardial drainage.

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Adult↗