Intraoperative echocardiographic detection of regurgitant jets after valve replacement

BACKGROUND

Paravalvular jets, documented by intraoperative transesophageal echocardiography, have prompted immediate valve explantation by others, yet the significance of these jets is unknown.

METHODS

Twenty-seven patients had intraoperative transesophageal two-dimensional color Doppler echocardiography, performed to assess the number and area of regurgitant jets after valve replacement, before and after protamine. Patients were grouped by first time versus redo operation, valve position and type.

RESULTS

Before protamine, 55 jets were identified (2.04+/-1.4 per patient) versus 29 jets after (1.07+/-1.2 per patient, p = 0.0002). Total jet area improved from 2.0+/-2.2 cm2 to 0.86+/-1.7 cm2 with protamine (p<0.0001). In all patients jet area decreased (average decrease, 70.7%+/-27.0%). First time and redo operations had similar improvements in jet number and area (both p>0.6). Furthermore, mitral and mechanical valves each had more jets and overall greater jet area when compared to aortic and tissue valves, respectively.

CONCLUSIONS

Following valve replacement, multiple jets are detected by intraoperative transesophageal echocardiography. They are more common and larger in the mitral position and with mechanical valves. Improvement occurs with reversal of anticoagulation.

Emergency coronary artery bypass graft surgery in abciximab-treated patients

BACKGROUND

Although the platelet antiaggregant abciximab is frequently used with percutaneous coronary interventions, results of emergency coronary artery bypass graft operations in patients recently treated with abciximab are poorly characterized.

METHODS

During a 29-month period, 12 patients required emergency coronary artery bypass grafting within 12 hours (mean, 1.9 hours) of abciximab therapy. Our full standard heparin dose regimen was used (mean heparin dose, 53,000 U per patient). Each patient received a single platelet transfusion dose after protamine administration, and further blood products were transfused as necessary. Clinical outcome and transfusion requirements were compared with predicted results based on risk-adjusted historical patients.

RESULTS

No patients died and none were returned to the operating room for coagulopathy-related bleeding. Per patient transfusion requirements were as follows: red blood cells, 3.6 units; apheresis platelets, 1.4 units; and fresh frozen plasma, 1.5 units. As compared with predicted values, there was no excessive incidence of mortality, stroke, or red blood cell transfusion requirements.

CONCLUSIONS

Emergency coronary artery bypass graft operations using full-dose heparin can be performed successfully in acutely ischemic abciximab-treated patients. Prophylactic transfusion of platelets after protamine administration appears to be useful.

Development of heparin antagonists with focused biological activity

Heparin, a complex glycosaminoglycan, has long been used to temporarily render the blood incoagulable during extracorporeal circulation, cardiovascular surgery, and other arterial interventions. But bleeding complications are especially common when the arterial tree is violated, occurring in as many as 10-15% of cases. For cardiovascular surgery and many related interventions, protamine has long been the standard antagonist when acute and complete neutralization of heparin s anticoagulant effect is necessary. Protamine s efficacy is related in part to its total net cationic charge, but unfortunately so is its toxicity. For these reasons, there is renewed interest in developing heparin antagonists which will replace the use of protamine. At Commonwealth Biotechnologies, Inc., we have used a rationale design approach for the preparation of a family of low molecular weight helix peptides which bind heparin with high affinity. For each of the new compounds, we have assessed their ability to bind heparin using isothermal titration calorimetry and circular dichroism spectrometry and have examined potential complexes formed with the anticoagulant pentasaccharide unit of heparin using molecular modeling techniques. The biological potencies of these compounds were assessed in ex vivo experiments where their ability to compete with antithrombin for binding heparin was determined. The best of the compounds, designated HepArrestTM, is highly effective in reversing heparin-mediated and HepArrest is a safer drug than protamine because of reduced adverse hemodynamic side effects compared with those associated with protamine. HepArrest binds low molecular weight heparins and causes reversal of anticoagulation by low molecular weight heparins, as determined by activated partial thromboplastin time, thrombin time, or factor Xa neutralization assays. These highly promising preclinical results indicate that HepArrest is a novel heparin neutralizing agent that may well fill a substantial unmet need for vascular surgeons and cardiac anesthesiologists who perform coronary artery bypass grafts and several other major vascular surgeries, as well as for cardiologists and interventional radiologists.

A mixed effects model for the analysis of repeated measures cross-over studies

A mixed effects model is developed for cross-over trials in which the response is measured repeatedly within each time period. Relative to previous work on repeated measures cross-overs, the methodology synthesizes two important features. First, our procedure eliminates preliminary testing for carry-over, defined loosely as the component of a response that is due to treatment in the preceding period. This is achieved by generalizing the methodology to cross-over designs in which preliminary testing for carry-over is unnecessary. We focus largely on 'simple' carry-over, that is, carry-over that lasts for exactly one period and is independent of the treatment administered in the period in which the carry-over occurs. However, we also illustrate a modification of the procedure for a repeated measures cross-over design which uses a more complicated model of carry-over. Second, the model allows both the between- and within-subject variance to differ among treatments. Conditions are described wherein closed-form (CF) solutions to the variance components as well as closed-form hypothesis tests of the treatment differences exist. Flexibility in the model is illustrated with an example in which inference based on the CF likelihood-based estimates of the variance, and estimates formed using an iterative routine (PROC MIXED) are compared.

Use of protamine to augment adenovirus-mediated cancer gene therapy

Improving the therapeutic potential of adenoviral (Ad) suicide gene therapy has become an area of intense investigation since the inception of gene therapy strategies for cancer treatment. Poor efficiency of gene transfer to target tissues has become one of the most important limitations to Ad-based gene therapy. Since polycations have been shown to enhance adenovirus-mediated gene transfer in epithelial cells both in vitro and in vivo, we hypothesized that polycations could augment treatment efficacy in animals with established tumor. To address this hypothesis, protamine sulfate, a polycation already safely administered in humans, was complexed with a recombinant Ad (E1E3-deleted) vector containing the herpes simplex 1 thymidine kinase (HSVtk) suicide gene to treat cancer cell lines in vitro and in animals bearing intraperitoneal tumor. In the presence of 5 microg/ml protamine, the efficiency of gene transfer to a number of cancer cell lines normally resistant to adenovirus was significantly enhanced. Protamine's effect in vitro was found to be inversely proportional to the level of expression of the high affinity Ad binding site, coxsackievirus and adenovirus receptor (CAR), on the sur- face of the various cell lines tested. Ad.tk infected tumor cells were rendered 2.5- to three-fold more sensitive to 20 microM ganciclovir (GCV) in the presence of protamine. Protamine also augmented the in vivo transfer efficiency of the marker gene, LacZ (contained in an Ad vector), on the surface of tumors derived from an intraperitoneal mouse model. Quantitative imaging revealed 50% tumor surface transduced with LacZ when treatment was performed in the presence of 50 microg/ml protamine compared with 12% tumor surface in controls. However, experiments performed utilizing intraperitoneal administration of Ad.tk/GCV in the presence or absence of 50 microg/ml protamine demonstrated no significantly improved median survival in mice bearing established intraperitoneal tumors. Similarly, in Fischer rats bearing intrapleural tumor, no improvement in anti-tumor response was observed when Ad treatment was performed intrapleurally in the presence of protamine. Thus, although protamine induced an enhancement of Ad-mediated gene transfer in vitro and in vivo, its use as an adjunct to intracavitary Ad-based cancer gene therapy in vivo appears to be limited.

Hemostatic agents and their safety

The pharmacologic management of hemostasis in patients undergoing cardiopulmonary bypass may be accompanied by adverse responses. Evaluating the safety profile of hemostatic agents (eg, lysine analogs, aprotinin, protamine, or even donor blood) should be done objectively. Subsequent to early anecdotal reports, the safety profile of aprotinin, a broad-spectrum serine protease inhibitor, has been thoroughly evaluated in multiple double-blind, placebo-controlled, multicenter studies. Although associated with decreased fibrinolysis, aprotinin has not been associated with an increased risk of post-cardiopulmonary bypass myocardial infarction, graft closure, stroke, or increased risk of renal dysfunction from US studies. As with any polypeptide, there is a risk of anaphylaxis, which is influenced not only by prior exposure but also by time since prior exposure. In a similar fashion, after early anecdotal reports, evaluations involving large numbers of patients have helped define adverse reactions to protamine. Adverse reactions to blood products also must be considered in any safety comparisons involving hemostatic agents.

Administration of protamine after coronary stent deployment

BACKGROUND

Prompt reversal of anticoagulation by protamine administration could be an important therapeutic option to treat serious procedural complications such as vessel rupture or major bleeding from the puncture site during coronary stent implantation. However, this therapeutic option is rarely used because of the possible risk of stent thrombosis.

METHODS

We retrospectively analyzed the incidence of acute and subacute stent thrombosis and vascular complications in 90 patients who received protamine (protamine group) and 1763 patients who did not receive protamine (control group) after successful coronary stent implantation. The 2 groups were matched for clinical, angiographic, and procedure characteristics.

RESULTS

No patients in the protamine group had adverse effects such as hypotension or vascular collapse during protamine administration. Acute stent thrombosis did not occur in any protamine group patient but did occur in 12 patients in the control group (0.7%) (P =.47). Subacute stent thrombosis occurred in 2 patients in the protamine group (2.1%) and in 15 in the control group (0.8%) (P =.20). By logistic regression analysis, protamine was not a determinant of stent thrombosis.

CONCLUSIONS

Reversal of anticoagulation by protamine after stent implantation does not predispose to stent thrombosis. This result has important clinical consequences because it allows the use of protamine in the treatment of coronary perforation and serious bleeding complications that may occur during coronary stent deployment.

The treatment of heparin resistance with Antithrombin III in cardiac surgery

PURPOSE

To report three patients who developed heparin resistance during cardiac surgery which was successfully managed with 1000 U Antithrombin III (AT III).

CLINICAL FEATURES

We observed heparin resistance prior to cardiopulmonary bypass (CPB) in one patient and during the CPB in two patients. In the first patient who was scheduled for mitral valve replacement, although heparin was administered sequentially up to 500 U x kg(-1) prior the CPB, the ACT value was 354 sec. After 1,000 U ATIII were administered the ACT was 395 sec and CPB was initiated. The ACT remained between 496 and 599 sec throughout CPB and a total of 260 mg protamine sulfate was given. In the other two patients following 300 U x kg(-1) heparin, the ACT was up to 400 sec and CPB was initiated. During CPB, ACT were decreased 360 sec and 295 sec in patients II and III respectively. Although heparin was added 1,500 U, ACT increased to > or = 400 sec could not be achieved. In the second patient ATIII activity was found 10%. After the administration of 1,000 U ATIII, ATIII activity was found to be 67% 40 min later and ACT were increased up to 400 sec. There was no thrombosis within the extracorporeal circuit, additional heparin was not required, less protamine was administered (< or = 3 mg x kg(-1)) and no excessive postoperative bleeding was observed in all patients.

CONCLUSION

We recommend that AT III supplementation should be considered to manage heparin resistance prior or during CPB in patients undergoing open heart surgery.

Relationship of protamine dosing with postoperative complications of carotid endarterectomy

Protamine sulfate (PS) neutralization of heparin (HEP) given during carotid endarterectomy (CEA) has been previously associated with an increased postoperative stroke rate. Dosing regimens of PS have varied in previous studies. The accuracy of PS dosing and its effect on postoperative complications was analyzed. The medical records of all patients undergoing elective CEAs from January 1993 to June 1996 in our institution were reviewed. A hematoma was defined as either an event requiring return to the operating room or when repeatedly identified in the medical record. The accuracy of dosing PS was determined utilizing a formula calculating the logarithmic exponential decay of HEP, which determined the residual HEP at the time of PS dosing. An ideal PS dose was then calculated and compared to the dose given. Statistical analyses was performed using a Fisher's exact test as well as the Student's t-test. Four hundred-seven CEAs were performed in 365 patients. There were 10/407 (2.5%) postoperative strokes (STROKE) and 11/407 (2.7%) hematomas, 3 of which required reoperation. Results indicate that (1) the administration of PS significantly reduced the incidence of postoperative hematoma; (2) there appears to be an association between the administration of PS and STROKE; (3) the inaccuracy in dosing PS appears to be based on a decision to dose PS to the total HEP given rather than the residual HEP on board at the time of neutralization. The effect of PS overdosing is unclear, but it may play a role in STROKE.

The use of low-dose heparin is safe in carotid endarterectomy and avoids the use of protamine sulfate

Controversy exists concerning the appropriate dose of heparin needed during carotid endarterectomy. Use of high-dose heparin (100 U/kg) during carotid endarterectomy may require the use of protamine to minimize perioperative bleeding complications. At the authors' institution the use of 30 U/kg heparin for arterial reconstruction has obviated the need for protamine. A retrospective study of carotid endarterectomies performed was undertaken. Patients undergoing combined procedures with carotid endarterectomy were excluded. A total of 420 carotid endarterectomies were performed in 330 patients. All received 3000 U of heparin or less during carotid endarterectomy. Non-fatal stroke and transient neurological deficits occurred in 0.48% and 1.9%, respectively. Mortality was 0.9%. Wounds were dry in 97%, swollen in 2.5% and bloody in 0.5%. No patient received protamine. Two patients were returned to the operating room for re-exploration because of hematoma. In conclusion, the use of protamine may be safely avoided with 30 U/kg heparin, and give acceptable stroke- and minimal complication rates.

Protamine inhibits angiogenesis and growth of C6 rat glioma; a synergistic effect when combined with carmustine

Protamine inhibits angiogenesis and blocks endothelial, fibroblast and platelet growth factors. Human and experimental gliomas spread and grow in response to both paracrine and autocrine release of these factors. Our objective was to study the effect of protamine administration on cell proliferation, angiogenesis and tumoral growth of C6 glioma. Additionally, we compared the antitumoral effect of protamine with that of another inhibitor of angiogenesis, suramin, and investigated a potential synergistic antitumoral action of low doses of protamine combined with the antineoplastic carmustine. C6 glioma cells were implanted subcutaneously in Wistar rats. A highly malignant glioma developed in 80% of animals; when the tumour reached a diameter of 1.5 cm, either protamine, suramin, carmustine or protamine plus carmustine were administered in various doses. Tumour parameters were measured and compared between groups. In a dose-dependent manner, protamine reduced tumour volume (P < 0.001), mitotic index (P < 0.05), vascular density (P < 0.05) and cell viability (P < 0.005) of C6 glioma. An ultrastructural study demonstrated membranous inclusions in the cytoplasm of 28% of tumoral and endothelial cells of tumours from animals treated with protamine. The inhibition of tumoral growth produced by moderate doses of protamine was similar to that produced by toxic doses of suramin. The combination of protamine and carmustine had a synergistic curtailing effect on tumoral growth (P < 0.001). Our results indicate that protamine is an effective agent against glioblastoma; in non-toxic doses it could potentiate the antineoplastic effect of nitrosoureas for the treatment of glial tumours.

[Anticoagulation of the extracorporeal circuit in chronic hemodialysis]

Continuous or intermittent use of unfractioned heparin is the anticoagulant of choice to prevent the extracorporeal circulation clotting during the hemodialysis session. However, low molecular weight heparin (LMVH) could be an alternative treatment especially in case of high risk bleeding or during some clinical conditions such as diabetes mellitus, cerebrovascular bleeding, malignant hypertension. LMVH may be given as a single initial bolus injection generally adequate. Heparinization must be lowered or stopped when an effective anticoagulation is previously used.

Complement activation and cytokine generation after modified Fontan procedure

BACKGROUND

The modified Fontan procedure separates the systemic and pulmonary circulations in patients born with a functional single ventricle. Delayed recovery is frequently observed after this procedure. It was our hypothesis that complement activation or cytokine generation may contribute to the pathophysiology of this problem.

METHODS

We measured activated complement C3, thromboxane B2, interleukin-6, and tumor necrosis factor-alpha levels by immunoassay in 16 patients undergoing Fontan procedure. Patient plasma samples were obtained preoperatively, on initiation of cardiopulmonary bypass, after administration of protamine, and 1, 4, 8, and 24 hours postoperatively.

RESULTS

There was no early or late mortality in this cohort of patients. Low cardiac output developed in 3 of 16 patients, and pleural effusions developed in 5. The median length of hospital stay was 9 days. Activated complement C3 levels increased from a baseline of 1,486 +/- 564 to 4,600 +/- 454 ng/mL after cardiopulmonary bypass and administration of protamine, and returned to baseline by 24 hours. The level of interleukin-6 increased from 42 +/- 32 to 176 +/- 22 pg/mL and at 24 hours remained elevated at 71 +/- 15 pg/mL. Neither thromboxane B2 nor tumor necrosis factor-alpha levels increased significantly.

CONCLUSIONS

The data demonstrate threefold to four-fold increases in activated complement C3 and interleukin-6, indicating that both humoral and cellular systems are affected. It is our conclusion that complement and cytokine activation may contribute to the delayed recovery observed after Fontan procedure.

Safety issues in heparin and protamine administration for extracorporeal circulation

This article reviews past approaches to heparin and protamine dosing and summarizes current practice. The author elucidates his experience with the Celite activated coagulation time (ACT), with attention to his adoption of a value of 400 seconds for this time; the adoption of an ACT of 480 seconds by Bull et al (J Thorac Cardiovasc Surg 69:674-684, 1975) and Young et al (Ann Thorac Surg 26:231-240, 1978); the proposed use of heparin response curves by Bull et al; the author's experience with a unitized dosing system to individualize dosing of heparin; and the use for this purpose by Despotis et al (J Thorac Cardiovasc Surg 110:46-54, 1995) of a system based on protamine titration. In more than 270 adult cardiac surgery patients, the unitized dosing system identified patients with high sensitivity or resistance to heparin and facilitated exact individualized doses to be given to produce the desired effect. Thus, less heparin was used in short bypass runs. Patients received less protamine than they would have with any other formula, and there was less blood loss and fewer transfusions required. Currently, no claims for efficacy or safety can be made for maintaining heparin concentrations greater than 3 U/mL. Pending further clarification, heparin dosage cannot be safely reduced when using heparin-bonded circuits. Aprotinin is not a procoagulant during cardiopulmonary bypass. Emerging studies suggest that graft patency is not affected by aprotinin use. The Celite ACT should not be used to monitor heparin effect and safety when using aprotinin; the kaolin ACT should be used instead.

Effect of prostaglandin E1 on pulmonary hypertension after protamine injection during cardiac surgery

BACKGROUND

The effects of prostaglandin E1 on pulmonary hypertension were assessed after protamine injection at the end of cardiopulmonary bypass during cardiac surgery.

METHODS

Ten patients scheduled for cardiac surgery presented with pulmonary hypertension (mean pulmonary artery pressure greater than 30 mmHg) after protamine injection and were treated by infusion of 0.02 microg x kg(-1) x min(-1) prostaglandin E1. Hemodynamic measurements were made on occasions after cardiopulmonary bypass. Prostaglandin E1 decreased pulmonary artery pressure, pulmonary vascular resistance, right ventricular stroke work index and pulmonary vascular resistance/systemic vascular resistance ratio, but did not change blood pressure, systemic vascular resistance, left ventricular stroke work index or cardiac output.

CONCLUSION

Prostaglandin E1 normalized pulmonary hypertension after protamine injection, but did not change arterial blood pressure and cardiac output.

Reduction of allogeneic blood transfusions after open heart operations by lowering cardiopulmonary bypass prime volume

BACKGROUND

Despite recent advances in blood conservation techniques, up to 30% to 80% of patients undergoing open heart operations require allogeneic blood transfusions. A prospective, randomized study was performed to test the effect of lowering cardiopulmonary bypass prime volume (as an additional component of an integrated blood conservation strategy) on clinical outcome and allogeneic blood transfusion.

METHODS

One hundred fourteen patients undergoing open heart operations were randomized to either full prime (FP) volume (1,400 mL of Plasmalyte solution) or reduced prime (RP) volume (600 to 800 mL). The reduction of prime volume was achieved by slowly draining the cardiopulmonary bypass circuit into a cell-saving device before the initiation of bypass. Firm transfusion thresholds were observed.

RESULTS

There were no significant differences between the groups with respect to baseline characteristics, body surface area, type and urgency of the procedures, perfusion technique, and hematologic profile. Mortality (FP, 1.7%; RP, 0%; p approximately 1.0) and overall morbidity (FP, 28.1%; RP, 22.8%; p = 0.53) were similar. However, transfusion requirements were significantly lower in the RP group: total donor exposure, 3.8 +/- 10.1 versus 1.0 +/- 2.4 units (p = 0.044); percentage of patients transfused, 54% (n = 31) versus 35% (n = 20) (p = 0.036). Twenty-four-hour chest tube drainage was similar: 455 +/- 223 mL for FP versus 472 +/- 173 mL for RP (p = 0.66). The lowest hematocrit on bypass was significantly higher in the RP group: 29.3% +/- 4% versus 26.3% +/- 5.3% (p = 0.009).

CONCLUSIONS

Lowering cardiopulmonary bypass prime volume resulted in a significant decrease in allogeneic blood product use. Because postoperative 24-hour chest tube drainage was similar in both groups, and hematocrit during bypass was higher in the RP group, the reduction in allogeneic blood transfusions appears to be related to a decrease in prime-induced hemodilution. This technique is effective, simple, and safe. It therefore should be strongly considered for patients undergoing operations using normothermic or near-normothermic cardiopulmonary bypass who are at high risk for allogeneic blood transfusion.

Monitoring and management of anticoagulation in children requiring extracorporeal circulation

Pharmacologic manipulation of hemostasis is a prerequisite for cardiac surgery with cardiopulmonary bypass (CPB) to prevent clot formation in the extracorporeal circuit. Children who require surgical correction of congenital heart defects are at increased risk for prolonged and excessive bleeding after separation from CPB. Heparin remains the anticoagulant of choice for surgery requiring CPB. Traditional regimens of empiric heparin dosing and a fixed-dose ratio of protamine to heparin for reversal of anticoagulation do not account for individual differences in the half-life of heparin, clearance of heparin, and duration of CPB, particularly in children. In addition, the use of prolongation of the activated clotting time (ACT) as a measure of adequate anticoagulation does not account for alterations in ACT by factors unrelated to heparin activity, including hemodilution and hypothermia, that are frequently present during CPB. This manuscript reviews the pitfalls in the management of anticoagulation for children undergoing surgery that requires CPB. Pertinent literature related to the use of aprotinin, a serine protease inhibitor that has been shown to improve hemostasis during and after CPB, is discussed. It is hoped that this article will provide a practical guideline for the rational management of anticoagulation in children with congenital heart disease undergoing CPB surgery.

A novel protamine variant reversal of heparin anticoagulation in human blood in vitro

PURPOSE

Protamine reversal of heparin anticoagulation during cardiovascular surgery may cause severe hypotension and pulmonary hypertension. A novel protamine variant, [+18RGD], has been developed that effectively reverses heparin anticoagulation without toxicity in canine experiments. Heretofore, human studies have not been undertaken. This investigation hypothesized that [+18RGD] would effectively reverse heparin anticoagulation of human blood in vitro.

METHODS

Fifty patients who underwent anticoagulation therapy during vascular surgery had blood sampled at baseline and 30 minutes after receiving heparin (150 IU/kg). Activated clotting times were used to define specific quantities of [+18RGD] or protamine necessary to completely reverse heparin anticoagulation in the blood sample of each patient. These defined amounts of [+18RGD] or protamine were then administered to the heparinized blood samples, and percent reversals of activated partial thromboplastin time, thrombin clotting time, and antifactor Xa/IIa levels were determined. In addition, platelet aggregation assays, as well as platelet and white blood cell counts were performed.

RESULTS

[+18RGD] and protamine were equivalent in reversing heparin as assessed by thrombin clotting time, antifactor Xa, antifactor IIa levels, and white blood cell changes. [+18RGD], when compared with protamine, was superior in this regard, as assessed by activated partial thromboplastin time (94.5 +/- 1.0 vs 86.5 +/- 1.3% delta, respectively; p < 0.001) and platelet declines (-3.9 +/- 2.9 vs -12.8 +/- 3.4 per mm3, respectively; p = 0.048). Platelet aggregation was also decreased for [+18RGD] compared with protamine (23.6 +/- 1.5 vs 28.5 +/- 1.9%, respectively; p = 0.048).

CONCLUSIONS

[+18RGD] was as effective as protamine for in vitro reversal of heparin anticoagulation by most coagulation assays, was statistically more effective at reversal than protamine by aPTT assay, and was associated with lesser platelet reductions than protamine. [+18RGD], if less toxic than protamine in human beings, would allow for effective clinical reversal of heparin anticoagulation.