Thromboxane receptor blockade prevents pulmonary hypertension induced by heparin-protamine reactions in awake sheep

Pulmonary hypertension associated with cardiopulmonary bypass and cardiac surgery

BACKGROUND AND AIM

Pulmonary hypertension (PH) is frequently associated with cardiovascular surgery and is a common complication that has been observed after surgery utilizing cardiopulmonary bypass (CPB). The purpose of this review is to explain the characteristics of PH, the mechanisms of PH induced by cardiac surgery and CPB, treatments for postoperative PH, and future directions in treating PH induced by cardiac surgery and CPB using up-to-date findings.

METHODS

The PubMed database was utilized to find published articles.

RESULTS

There are many mechanisms that contribute to PH after cardiac surgery and CPB which involve pulmonary vasomotor dysfunction, cyclooxygenase, the thromboxane A2 and prostacyclin pathway, the nitric oxide pathway, inflammation, and oxidative stress. Furthermore, there are several effective treatments for postoperative PH within different types of cardiac surgery.

CONCLUSIONS

By possessing a deep understanding of the mechanisms that contribute to PH after cardiac surgery and CPB, researchers can develop treatments for clinicians to use which target the mechanisms of PH and ultimately reduce and/or eliminate postoperative PH. Additionally, learning about the most up-to-date studies regarding treatments can allow clinicians to choose the best treatments for patients who are undergoing cardiac surgery and CPB.

Surgical strategies for patients with congenital heart disease and severe pulmonary hypertension in low/middle-income countries

In this review, we discuss specific surgical strategies that are used in patients with congenital heart disease and severe pulmonary arterial hypertension. Our own experience, with the use of unidirectional valved patches in managing these patients, is also discussed in detail.

Unidirectional valved patch closure of ventricular septal defects with severe pulmonary arterial hypertension

Delayed presentation of ventricular septal defect (VSD) is common in developing countries. Such patients often have severe pulmonary arterial hypertension (PAH), which increases post-operative morbidity and mortality. To address these problems, we used our technique of unidirectional valved patch (UVP) for closure of VSD. Between January 2006 and December 2010, 17 patients (age 2-23 years, median 9 years) with a large VSD and severe PAH underwent VSD closure with UVP. Pre-operative mean indexed pulmonary vascular resistance (PVRI) was 10.9 ± 2.2 Wood units and mean pre-operative systemic saturation was 93.4 ± 2.6%. Shunt was bidirectional in 15 patients and predominantly right to left in two. After VSD closure, intra-operative transoesophageal echocardiography revealed a right to left shunt across the patch in three patients 2, 7 and 9 years of age who had pre-operative PVRI of 9.5, 9.8 and 11.1 Wood units, respectively. There were no in-hospital deaths and all patients had uneventful recovery. Mean follow-up was 30 ± 14.7 months and all patients are well without cyanosis. Echocardiography showed no shunt across the patch and all have systemic saturation >95%. We conclude that UVP is a promising technique in patients with large VSD and severe PAH.

Unidirectional valved patches for closure of septal defects in patients with severe pulmonary hypertension

Pulmonary hypertension due to delay in presentation, diagnosis, referral, and surgery for septal defects is not uncommon in the developing world and translates into high morbidity and mortality following open heart surgery to close these defects. Leaving a small atrial communication may not always be effective. Extracorporeal membrane oxygenation and inhaled nitric oxide therapy in the immediate postoperative phase may not be available or may not be financially feasible in many institutions which are economically challenged. Unidirectional valved patch is emerging as a new and effective solution to this problem and promises to make at least the immediate postoperative results more predictable in this subset of patients.

Role of Reactive Oxygen Species in Kv Channel Inhibition and Vasoconstriction Induced by TP Receptor Activation in Rat Pulmonary Arteries

Voltage-gated potassium channels (Kv) and thromboxane A(2) (TXA(2)) have been involved in several forms of human and experimental pulmonary hypertension. We have reported that the TXA(2) analog U46619, via activation of TP receptors and PKCzeta, inhibited Kv currents in rat pulmonary artery smooth muscle cells (PASMC), increased cytosolic calcium, and induced a contractile response in isolated rat and piglet pulmonary arteries (PA). Herein, we have analyzed the role of reactive oxygen species (ROS) in this signaling pathway. In rat PA, U46619 increased dichlorofluorescein fluorescence, an indicator of intracellular hydrogen peroxide, and this effect was prevented by the NADPH oxidase inhibitor apocynin and by polyethyleneglycol-catalase (PEG-catalase, a membrane-permeable form of catalase). U46619 inhibited Kv currents in native PASMC and these effects were strongly inhibited by apocynin. The contractile responses to U46619 in isolated PA were inhibited by PEG-catalase and the NADPH oxidase inhibitors diphenylene iodonium (DPI) and apocynin. A membrane permeable of hydrogen peroxide, t-butyl hydroperoxide, also inhibited Kv currents and induced a contractile response. Activation of NADPH oxidase and the subsequent production of hydrogen peroxide are involved in the Kv channel inhibition and the contractile response induced by TP receptor activation in rat PA.

Cellular mechanisms of thromboxane A2-mediated contraction in pulmonary veins

Our objectives were to identify the relative contributions of [Ca2+]i and myofilament Ca2+ sensitivity in the pulmonary venous smooth muscle (PVSM) contractile response to the thromboxane A2 mimetic U-46619 and to assess the roles of PKC, tyrosine kinases (TK), and Rho-kinase (ROK) in that response. We tested the hypothesis that U-46619-induced contraction in PVSM is mediated by both increases in [Ca2+]i and myofilament Ca2+ sensitivity and that the PKC, TK, and ROK signaling pathways are involved. Isometric tension was measured in isolated endothelium-denuded (E-) canine pulmonary venous (PV) rings. In addition, [Ca2+]i and tension were simultaneously measured in fura-2-loaded E- PVSM strips. U-46619 (0.1 nM-1 microM) caused dose-dependent (P < 0.001) contraction in PV rings. U-46619 contraction was attenuated by inhibitors of L-type voltage-operated Ca2+ channels (nifedipine, P < 0.001), inositol 1,4,5-trisphosphate-mediated Ca2+ release (2-aminoethoxydiphenylborate, P < 0.001), PKC (bisindolylmaleimide I, P < 0.001), TK (tyrphostin A-47, P = 0.014), and ROK (Y-27632, P = 0.008). In PV strips, U-46619 contraction was associated with increases in [Ca2+]i and myofilament Ca2+ sensitivity. Both Ca2+ influx and release mediated the early transient increase in [Ca2+]i, whereas the late sustained increase in [Ca2+]i only involved Ca2+ influx. Inhibition of both PKC and ROK (P = 0.006 and P = 0.002, respectively), but not TK, attenuated the U-46619-induced increase in myofilament Ca2+ sensitivity. These results suggest that U-46619 contraction is mediated by Ca2+ influx, Ca2+ release, and increased myofilament Ca2+ sensitivity. The PKC, TK, and ROK signaling pathways are involved in U-46619 contraction.

Role of Endothelin-1 and Thromboxane A2 in the Pulmonary Hypertension Induced by Heparin–Protamine Interaction in Anesthetized Dogs

This study aimed to study the role of thromboxane A2 (TXA2) and endothelin-1 (ET-1) in the pulmonary hypertension induced by interaction of heparin-protamine in anesthetized dogs. The effect of inhaled nitric oxide (NO) was also investigated in this model. Dogs were anesthetized and instrumented for acquisition of mean arterial blood pressure, mean arterial pulmonary pressure (MPAP), and pulmonary pressure gradient (PPG). Cardiac index (CI), heart rate, and index of systemic vascular resistance were also obtained. Intravenous administration of heparin (500 IU/kg) 3 minutes before protamine (10 mg/kg) caused marked pulmonary hypertension, as evaluated by the increase in MPAP and PPG. This was accompanied by systemic hypotension, CI decrease, and tachycardia. Indomethacin (10 mg/kg), dazoxiben (10 mg/kg), or tezosentan (10-mg/kg bolus plus 10-mg/kg/h infusion) significantly reduced the increase in MPAP and PPG, but had no effect on the systemic hypotension. Similar results were obtained with inhaled NO (3 ppm). Plasma TXB2 levels were markedly elevated during the pulmonary hypertension, and this was abolished in indomethacin-treated dogs. Our study shows that interaction of heparin-protamine in anesthetized dogs lead to TXA2- and ET-1-mediated pulmonary hypertension. Drugs that interfere with the synthesis of these mediators as well as inhaled NO may be of beneficial value to control this disorder.

Effect of site of venous protamine administration, previously alleged risk factors, and preoperative use of aspirin on acute protamine-induced pulmonary vasoconstriction

OBJECTIVE

To determine whether the incidence of protamine-induced pulmonary vasoconstriction (PIPV) is influenced by central venous versus peripheral venous infusion of protamine and whether aspirin ingestion within a week of surgery would decrease the incidence of PIPV.

DESIGN

Single-institution, prospective, observational, randomized trial.

SETTING

University teaching hospital.

PARTICIPANTS

One thousand four hundred ninety-seven consecutive patients undergoing cardiopulmonary bypass procedures.

INTERVENTION

Protamine neutralization of heparin by infusion pump via either central venous or peripheral venous route.

MEASUREMENTS AND MAIN RESULTS

Five previously suspected risk factors (valve surgery, prior protamine exposure, history of pulmonary hypertension, fish allergy, and vasectomy), aspirin ingestion within 7 days of surgery, and demographic information were recorded. PIPV was defined as an abrupt increase in mean PA pressure of 7 mmHg or more with associated right ventricular dysfunction as assessed by observation of the right ventricle in the field and regional wall motion abnormality by transesophageal echocardiogram and hypotension (systolic blood pressure < or = 90 mmHg). Data were collected via continuous strip chart recording. A total of 10 patients (0.6%) developed PIPV during protamine infusion. The incidents were similar with respect to the site of venous administration. Prior exposure to protamine was associated with a greater incidence of PIPV (odds ratio 6.9; p < 0.01). Other previously suspected risk factors did not achieve statistical significance. None of the 766 patients who ingested aspirin experienced PIPV as opposed to 10 of the 731 patients who did not ingest aspirin (odds ratio 0.08; p < 0.001).

CONCLUSIONS

Although the site of venous protamine administration does not influence incidence of PIPV, aspirin ingestion within 1 week of surgery may decrease it. These data also confirmed other studies suggesting that previous protamine administration predisposes to this protamine reaction.

Pulmonary artery vasoconstriction but not [Ca2+]i signal stimulated by thromboxane A2 is partially resistant to NO

To characterize the thromboxane A2 (TXA2) -induced resistance to the vasodilator effects of the nitric oxide (NO)/cGMP pathway in pulmonary arteries, we have studied the effects of the NO donor sodium nitroprusside on intracellular calcium concentration ([Ca2+]i) and contractile force recorded simultaneously in isolated piglet pulmonary arteries loaded with fura-2 and contracted with norepinephrine or the TXA2 mimetic U46619 and by activation of protein kinase C (PKC) with phorbol 12-myristate 13-acetate. In the TXA2 mimetic- and phorbol 12-myristate 13-acetate plus norepinephrine-stimulated arteries, nitroprusside exhibited lower vasodilator efficacy (and lower potency in the TXA2 mimetic-stimulated arteries) but similar reductions in [Ca2+]i compared with arteries activated by norepinephrine. The nonselective serine/threonine kinase inhibitor staurosporine, but not the selective inhibitor of PKC bisindolylmaleimide, potentiated the relaxation of nitroprusside in the TXA2 mimetic-stimulated arteries. In conclusion, the resistance to NO/cGMP-induced vasodilation in arteries stimulated by TXA2 and PKC involves a reduced ability of the Ca2+-independent mechanisms for smooth muscle vasodilation. The resistance to NO in arteries stimulated by TXA2 is sensitive to staurosporine but not to bisindolylmaleimide, suggesting the involvement of an activation of a serine/threonine kinase distinct from PKC.

The effect of differing rates and injection sites on the amount of protamine delivered before detection of hemodynamic alterations in dogs

OBJECTIVES

To determine the effect of the route and rate of protamine administration on the amount of protamine that could be delivered before a hemodynamic reaction occurred in dogs.

STUDY DESIGN

Prospective randomized experimental study.

ANIMALS

Twenty adult mixed-breed dogs weighing 25.1+/-2.5 kg.

METHODS

Before vascular surgery, the dogs were heparinized to reach an activated clotting time (ACT) of 300 seconds. After completion of the vascular surgery, protamine was administered intravenously until a hemodynamic reaction was recorded. The 4 groups of dogs were given protamine at 5 mg/min (slow) or 10 mg/min (fast) via the cephalic or the jugular veins. Systemic and pulmonary arterial pressures, central venous pressure (CVP), and pulmonary arterial occlusion pressure (PAOP) were recorded before and after protamine administration. The dose of protamine was recorded when a reaction occurred, which was defined as mean arterial pressure (MAP) <60 mm Hg or mean pulmonary arterial pressure (MPAP) >20 mm Hg or more than double the baseline value.

RESULTS

Significant decreases in systolic arterial pressure (SAP), MAP, and diastolic arterial pressure (DAP) and significant increases in systolic (SPAP), mean (MPAP), and diastolic (DPAP) pulmonary arterial pressures were recorded after protamine administration. The cephalic slow group had significantly fewer protamine reactions than other groups (chi-square = 8.57, P = .03, df = 3). Significantly more protamine could be delivered from the cephalic vein (52.5+/-14.5 mg) compared with the jugular vein (37.6+/-16 mg) before a reaction occurred (P = .048).

CONCLUSION

The rate of administration did not have an effect on the amount of protamine delivered. Adverse reactions were minimized when protamine was administered via the cephalic vein at a slow rate.

CLINICAL RELEVANCE

We would recommend delivering protamine after cardiopulmonary bypass or vascular surgery through a peripheral venous route.

Noncardiogenic pulmonary edema associated with protamine administration during coronary artery bypass graft surgery

Protamine sulfate is the only agent approved to reverse heparin-induced anticoagulation. As with any other drug, protamine has the potential to cause adverse effects that range from mild hypotension to potentially fatal events, such as noncardiogenic pulmonary edema (NCPE) and catastrophic pulmonary vasoconstriction. We report a case of NCPE after the administration of protamine to a patient undergoing coronary artery bypass graft surgery and discuss the diagnosis and management of this severe adverse event.

Extracorporeal heparin adsorption following cardiopulmonary bypass with a heparin removal device--an alternative to protamine

OBJECTIVES

To evaluate the therapeutic efficacy and applicability of a heparin removal device (HRD) based on plasma separation and poly-L-lysine (PLL) affinity adsorption as an alternative to protamine in reversing systemic heparinization following cardiopulmonary bypass (CPB).

DESIGN

A prospective study.

SETTING

University research laboratory.

SUBJECTS

Adult female swine (n=7).

INTERVENTIONS

Female Yorkshire swine (n=7, 67.3+/-3.5 [SEM] kg) were subjected to 60 mins of right atrium-to-aortic, hypothermic (28 degrees C) CPB. After weaning from CPB, the right atrium was recannulated with a two-stage, dual-lumen cannula which was connected to an HRD via extracorporeal circulation. Blood flow was drained at 1431.2+/-25.4 mL/min from the inferior vena cava, through the plasma separation chamber of the HRD (where heparin was bound to PLL), and reinfused into the right atrium. The HRD run time was determined by a previously established mathematical model of first-order exponential depletion.

MEASUREMENTS AND MAIN RESULTS

Heart rate, mean arterial pressure, pulmonary arterial pressure, central venous pressure, kaolin and celite activated clotting time (ACT), activated partial thromboplastin time (APTT), heparin concentration, and plasma free hemoglobin were obtained before, during, and after the use of the HRD. Pre-CPB ACT was 167+/-89 secs (kaolin) and 99+/-7 secs (celite), and APTT was 34+/-5 secs. The HRD run time averaged 27.4 +/-1.5 mins targeted to remove 90% total body heparin. Use of the HRD was not associated with any adverse hemodynamic reactions or increases in plasma free hemoglobin. The heparin concentration immediately following CPB was 4.85+/-0.24 units/mL, with ACT >1000 secs and APTT >150 secs in all animals. During heparin removal, total body heparin content followed first-order exponential depletion kinetics. At the end of the HRD run, heparin concentration decreased to 0.51+/-0.09 units/mL, with kaolin ACT returning to 177+/-22 secs, celite ACT returning to 179+/-17 secs, and APTT returning to 27+/-3 secs (p > .05 vs. pre-CPB baseline for all variables).

CONCLUSIONS

The HRD is capable of reversal of anticoagulation following CPB without significant blood cell damage or changes in hemodynamics. The HRD, therefore, can serve as an alternative to achieve heparin clearance in clinical situations where use of protamine may be contraindicated.

Thromboxane inhibition and monocrotaline-induced pulmonary hypertension in rats

Monocrotaline (MCT)-induced pulmonary hypertension (PH) is a useful model for the investigation of this disorder in humans. The role of thrombocytes in the genesis of PH has already been addressed; however, the exact mechanism by which they induce PH remains to be elucidated. We investigated the effects of a thromboxane A2 (TXA2) synthase inhibitor (OKY-046) and a TXA2/prostaglandin H2 (PGH2) receptor antagonist (ONO-8809) on the development of MCT-induced PH. A single dose of MCT (60 mg/kg bodyweight; BW) was injected subcutaneously in Wistar rats 24 h after the administration of OKY-046 or ONO-8809. The TXA2 inhibitors were administered by gavage daily for 3 weeks. Urinary excretion of eicosanoids was determined by radioimmunoassay. At the end of the treatment period, the lungs, heart and kidneys were morphologically examined. The per cent medial thickness of the muscular pulmonary arteries (%MT) and the ratio of the right to the left ventricular mass including the septum (RV/LV + S) increased significantly in MCT-treated rats compared with the control rats. The %MT was attenuated by the administration of ONO-8809. Either OKY-046 or ONO-8809 attenuated the increase in RV/LV + S. In addition, both TXA2 inhibitors reduced urinary excretion of 11-dehydro-TXB2, particularly during the early phase of PH, suggesting that platelet aggregation was reduced. These findings suggest that the inhibition of TXA2 by synthase inhibition or receptor antagonism reduces or delays the development of MCT-induced PH in rats, probably by inhibiting platelet aggregation.

Involvement of fibrinogen in protamine-induced pulmonary hypertension

Protamine reversal of heparin anticoagulation occasionally results in pulmonary hypertension as well as systemic hypotension. To examine the contribution of blood components to this induction of pulmonary hypertension, we developed an isolated rat lung perfusion model and perfused heparinized plasma, heparinized serum, and Hepes (4% bovine serum albumin, 20 mM N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid, 5 mM glucose, in warm physiological saline) buffer solution with or without fibrinogen. Perfusion with heparinized plasma and Hepes buffer solution with fibrinogen caused pulmonary hypertension; perfusion with heparinized serum or Hepes buffer solution without fibrinogen did not, suggesting that fibrinogen is involved in the induction of pulmonary hypertension. We also labeled protamine with 125I and compared the amounts of protamine accumulating in the lung with different concentrations of fibrinogen. The amount of protamine trapped in the lung increased according to the concentration of fibrinogen. Fibrinogen may accelerate the reaction between pulmonary endothelial cells and protamine or protamine-heparin complexes. In the mechanism of protamine-induced pulmonary hypertension, fibrinogen, as well as heparin and protamine, may be an essential component.

Involvement of protein kinase C in reduced relaxant responses to the NO/cyclic GMP pathway in piglet pulmonary arteries contracted by the thromboxane A2-mimetic U46619

1. Impairment of nitric oxide (NO)/cyclic GMP production and/or increased activities of thromboxane A2 (TXA2) and endothelin-1 (ET-1) have been associated with pulmonary hypertension. We have analysed the interactions of noradrenaline (NA), the TXA2-mimetic U46619 and ET-1 with the relaxation induced via cyclic GMP in isolated piglet intrapulmonary arteries. 2. The contractions induced by NA were augmented by endothelium removal or by methylene blue and pre-contracted rings were fully relaxed by acetylcholine, sodium nitroprusside (SNP), atrial natriuretic peptide and 8-bromo-cyclic GMP. In contrast, U46619- and ET-1 induced contractions were endothelium-independent and only partially relaxed by the latter vasodilators. Whereas the reduced responses to SNP in arteries contracted by U46619 were independent of the U46619-induced tone, a higher concentration of ET-1 (tone higher than that induced by NA) was required to reduce the vasodilator responses to SNP. NA, U46619 and ET-1 had no effect on the SNP-induced increases in cyclic GMP. 3. The reduced relaxant responses to SNP in arteries pre-contracted by U46619 were specific for piglet pulmonary arteries since they were not observed in piglet mesenteric or coronary arteries or in rat pulmonary arteries. Furthermore, there were no differences in the relaxant response to the adenylate cyclase activator forskolin in piglet pulmonary arteries pre-contracted by either NA, U46619 or ET-1. 4. SNP-induced relaxation was inhibited by thapsigargin (but not by inhibition of the membrane Na+/ K+ ATPase nor K+ channels) indicating a role for Ca2+ sequestration by the Ca2+ ATPase in the effects of SNP. 5. The phorbol ester 12-myristate, 13-acetate inhibited the relaxant response to SNP. The inhibitory effect of U46619 on SNP-induced relaxation was abolished by the protein kinase C inhibitor (PKC) staurosporine suggesting that PKC may be a part of the signal transduction mechanism. 6. In summary, piglet pulmonary arteries when activated by a TXA2-mimetic show abnormally reduced relaxant responses to the NO/cyclicGMP pathway. This effect appears to be mediated by activation of PKC.

[New antithrombotic agents in coronary disease]

Aspirin is effective in, treating patients with unstable angina or myocardial infarction. However, questions remain about the optimal dose of aspirin and aspirin-resistance in subgroups of patients. Heparin also has beneficial effects mostly during the acute phase of unstable angina, but thrombolytics are effective only in acute myocardial infarction and not in unstable angina. Recently, low molecular weight heparins have proved to be as effective (FRIC trial) or more effective (ESSENCE trial) than unfractionated heparin in unstable angina. Ongoing studies (TIMI 11B) are evaluating the efficacy of a prolonged administration of low molecular weight heparin to alter the chronic process of unstable angina. The new antiplatelet drugs directed against GP IIb/IIIa receptors are now available to improve the acute results of high risk percutaneous transluminal angioplasty (PTCA). This new drug (c7E3) binds rapidly to GP IIb/IIIa and prevents fibrinogen binding to the receptor. This very potent and irreversible effect prevents platelet aggregation and decreases the incidence of acute occlusions following PTCA. especially in patients with unstable angina. The counterpart is an increased risk of hemorrhage, knowing that patients receive simultaneously aspirin and heparin. The first results of the EPILOG study also demonstrate a better outcome in elective angioplasty without significant increase of serious bleeding, thanks to a low dose heparin regimen. In contrast to thrombolytics, the GP IIb/IIIa antagonist does not increase the risk of intracranial bleeding. The results of the CAPTURE trial also confirm the clinical benefit obtained with this drug in refractory unstable angina. The reduction of death and myocardial infarction is very consistent throughout the studies performed with c7E3. The Kaplan-Meier curves of freedom of death and myocardial infarction diverge immediately after start of study medication. The acute benefits are preserved at 3 years in the EPIC trial. Similar trends were present during the acute phase with other compounds (tirofiban, integrelin), meaning that a class effect may exist but the long term results are disappointing. The results with new direct antithrombins such as hirudin, or hirulog in acute myocardial infarction or in PTCA for unstable angina are negative. The development of new potent oral antiplatelet drugs might change the treatment of acute coronary syndromes in the future. The current progress made with antithrombotic drugs should improve the prognosis of acute coronary syndromes.

Unidirectional valve patch for repair of cardiac septal defects with pulmonary hypertension

BACKGROUND

Congenital septal defects with a large left-to-right shunt often cause pulmonary hypertension, which complicates surgical repair of the defects.

METHODS

Twenty-four patients with congenital cardiac septal defects and severe pulmonary hypertension had operation to close the septal defect using a unidirectional valve patch during a 3-year period. The ratio of systolic pulmonary artery pressure to systolic arterial blood pressure was near to or more than 1.0 in all patients.

RESULTS

Two patients died in the hospital after operation, and there have been no deaths during intermediate term follow-up. Mean pulmonary artery pressure decreased from 80 +/- 12 mm Hg to 56 +/- 18 mm Hg. The ratio of pulmonary artery pressure to systemic arterial pressure dropped from 1.1 +/- 0.1 mm Hg to 0.7 +/- 0.1 mm Hg. The unidirectional valve patch functioned allowing right to left shunting in 4 patients with a systolic pulmonary artery pressure more than systolic arterial blood pressure immediately after closure of a septal defect. The patch sealed or was effectively closed by the third postoperative day. There was impressive improvement in symptoms and exercise tolerance after operation during the 3-month to 3-year (mean, 1.1 year) follow-up period.

CONCLUSIONS

The unidirectional valve patch is useful for management of patients having operation to close cardiac septal defects in the presence of severe pulmonary hypertension.

Protamine-induced pulmonary venoconstriction in heparinized pigs

Reversal of heparin anticoagulation with protamine may be associated with acute pulmonary vasoconstriction. The specific site of pulmonary vasoconstriction has not been determined. This study was designed to determine the site of protamine-induced pulmonary vasoconstriction and the role of nitric oxide (NO) after protamine injection. Pigs were anesthetized and instrumented with catheters for monitoring pulmonary arterial, systemic arterial, and central venous pressures. Pulmonary capillary pressure was estimated using the arterial occlusion concept, while left atrial pressure was estimated from the equilibrium wedge pressure. Hemodynamic measurements were made during baseline, before and after heparin (200 U/kg), at peak pressure response after protamine injection (2 mg/kg), and 10 and 30 min thereafter. In the control group, pulmonary vascular resistance (PVR) values during baseline and after heparin were identical (2.7 +/- 0.4 mm Hg.L-1.min-1). At peak protamine response (1-2 min) PVR increased to 8.0 +/- 1.6, but returned to baseline value after 10 min (2.8 +/- 0.3) and remained stable for 30 min (2.2 +/- 0.3). The increase in PVR after protamine was primarily due to an increase in venous resistance from 1.0 +/- 0.2 to 4.9 +/- 1.4 mm Hg.L-1.min-1, and a much smaller increase in arterial resistance from 1.7 +/- 0.3 to 3.4 +/- 0.6 mm Hg.L-1.min-1. A second group was treated with nitrow-L-arginine (LNA, 20 mg/kg) to inhibit NO release, and then heparin and protamine were administered as in the first group. Heparin had no effect on pressures, but protamine increased PVR by the same magnitude as in Group 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Eicosanoid biosynthesis in patients with stable angina: beneficial effects of very low dose aspirin

OBJECTIVE

We assessed the production of eicosanoids and the effects of very low dose aspirin in patients with stable angina under basal conditions and during rapid atrial pacing.

BACKGROUND

Platelet activation occurs in acute ischemic syndromes but is still controversial in stable angina. Very low dose aspirin is known to be platelet selective and can be used to test the hypothesis of the platelet origin of increased thromboxane production in stable angina.

METHODS

Urinary excretion of eicosanoids was measured in 42 patients, including 24 patients with and 18 patients without coronary artery disease. The effects of 50 mg/day of aspirin were measured at rest and during pacing-induced ischemia in 10 patients with stable angina and were compared with a similar group of patients not treated by aspirin.

RESULTS

Excretion of 11-dehydro-thromboxane B2 was 2.6 times higher in patients with stable angina than in healthy subjects (mean [+/- SEM] 74.8 +/- 13.0 [24 patients] vs. 29.0 +/- 5.4 [18 patients] ng/mmol of creatinine, p < 0.01). Urinary prostacyclin metabolite levels did not differ between the two groups. Treatment for 8 days with 50 mg/day of aspirin inhibited platelet cyclooxygenase, as reflected by the 97% reduction of in vitro serum thromboxane production. This aspirin regimen normalized the level of urinary thromboxane metabolites in patients with angina (17.3 +/- 3.4 ng/mmol of creatinine [10 patients], p < 0.001 from baseline level before treatment) and did not change prostacyclin metabolite levels. Atrial pacing in patients with angina not treated with aspirin caused lactate and thromboxane release into the coronary sinus. In patients with very low dose aspirin therapy, pacing did not cause thromboxane release despite inducing myocardial ischemia. However, fractional lactate extraction decreased less sharply in patients with than without aspirin therapy.

CONCLUSIONS

Thromboxane production is greatly increased in patients with stable angina. Very low dose aspirin administered to these patients reduces thromboxane synthesis to normal levels, preserves prostacyclin biosynthesis and prevents acute thromboxane release into the coronary circulation during pacing-induced ischemia. Our data suggest that platelets (not monocytes/macrophages) are activated in stable angina to produce thromboxane.

Protamine and protamine-insulins exacerbate the vascular response to injury

Endothelial cells and smooth muscle cells produce heparinlike compounds that are growth inhibitory for vascular smooth muscle cells, and it has been suggested that these compounds play a regulatory role that is perturbed with vascular injury. Indeed, exogenous heparin preparations effectively suppress smooth muscle cell proliferation following injury imposed on vascular endothelium. We now report that protamine, an agent that binds heparin and negates its anticoagulant properties, has potent stimulatory effects on vascular smooth muscle cell proliferation. The administration of protamine, alone or as part of commonly used insulin preparations, stimulated the proliferation of cultured smooth muscle cells, exacerbated vascular smooth muscle cell proliferative lesions in laboratory rats, and interfered with the growth-inhibitory effects of heparin in culture and in vivo. These results confirm the importance of endogenous heparinlike compounds in arterial homeostasis and may require reconsideration of protamine use following vascular reparative procedures and in diabetics.

The modified Fontan procedure: physiology and anesthetic implications

The modified Fontan operation has gained wide acceptance as a functional corrective procedure for patients with CHD with single ventricle physiology. Long-term survival and palliation of symptoms are excellent with most patients able to lead normal lives. The absence of a pulmonary contractile ventricle means that the single ventricle is responsible for perfusion of both the pulmonary and systemic circulations. Elevated systemic venous pressure is required to overcome PVR and this state of systemic venous hypertension has a significant impact on the anesthetic and postoperative care of these patients.