In vitro efficacy of platelet glycoprotein IIb/IIIa antagonist in blocking platelet function in plasma of patients with heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is an important complication following administration of heparin. Platelet activation and aggregation induced by heparin/platelet factor 4/immunoglobulin complexes are thought to be the underlying mechanism for this condition, so it was hypothesized that abciximab (a humanized murine monoclonal antibody directed against the glycoprotein IIb/IIIa receptor) would prevent heparin-induced platelet aggregation and activation in plasma from patients with HIT. Platelet aggregation was tested in vitro with platelet-poor plasma (obtained from 23 patients with HIT), platelet-rich plasma (from normal donors with known reactivity), heparin (0.5 U/ml), and ascending doses of abciximab (0.07-0.56 microg/ml). The ability of abciximab to prevent platelet activation was also evaluated using flow cytometry (P selectin expression, mepacrine release, microparticle formation) and platelet factor 4 immunoassay. In vitro, abciximab inhibited heparin-induced platelet aggregation in a dose-dependent fashion (IC50 0.103 microg/ml) and inhibited microparticle formation, the expression of P-selectin, release of mepacrine and platelet factor 4. These findings suggest that abciximab may be useful in treatment of patients with HIT and warrants further clinical evaluation.

Heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a potentially serious complication of heparin therapy and is being encountered more frequently in patients with cardiovascular disease as use of anticoagulant therapy becomes more widespread. Our understanding of the pathophysiology of this immune-mediated condition has improved in recent years, with heparin-platelet factor 4 complex as the culprit antigen in most patients. New sensitive laboratory assays for the pathogenic antibody are now available and should permit an earlier, more reliable diagnosis, but their optimal application remains to be defined. For patients in whom HIT is diagnosed, immediate discontinuation of heparin infusions and elimination of heparin from all flushes and ports are mandatory. Further management of patients with HIT is problematic at present, as there are no readily available alternative anticoagulant agents in the United States with proven efficacy in acute coronary disease. The direct thrombin inhibitors appear to be the most promising alternatives to heparin, when continued use of heparin is contraindicated, and the results of several multicenter trials evaluating their application in patients with HIT are awaited.

Bilateral subacromial bursitis with macroscopic rice bodies: ultrasound, CT and MR appearance

The radiological findings of ultrasound, CT and MR of a case of bilateral subacromial bursitis with macroscopic rice bodies is described. The previous literature is also reviewed.

The clinical impact of platelet glycoprotein IIb/IIIa receptor blockade in cardiovascular medicine

Several of the adverse events that occur in acute coronary syndromes and after percutaneous coronary revascularization procedures are believed to be mediated by platelets. Recently, using molecular biology techniques, the platelet glycoprotein IIb/IIIa receptor was identified as the final common pathway for platelet aggregation. Thus, blocking the action of this receptor would seem to be an attractive proposition for reducing ischemic complications. A monoclonal antibody was the first agent in this new pharmacological family to be designed, but several peptide and peptide-like substances have subsequently been developed. This paper reviews the development of this class of agents and the various preclinical and clinical trials that have been undertaken. Early studies evaluated such agents during percutaneous coronary revascularization procedures. Because of the overwhelming benefits observed in such patients, together with the current limitations of treatments for acute coronary syndromes, the scope of investigations has been extended. Preliminary reports have been encouraging.

Benefit of early sustained reperfusion in patients with prior myocardial infarction (the GUSTO-I trial). Global Utilization of Streptokinase and TPA for occluded arteries

The primary objective of this study was to characterize a large cohort of patients receiving thrombolytic therapy for acute myocardial infarction with respect to the group with a prior event. Patients were randomly assigned to 1 of 4 thrombolytic strategies. Baseline characteristics, 30-day outcomes, and 1-year mortality were compared between patients with (n = 6,704) and without (n = 34,143) prior myocardial infarction. Patients with prior myocardial infarction presented to the hospital earlier than those having their first event, but institution of thrombolytic therapy was delayed. Mortality at 30 days (11.7% vs 5.9%, p = 0.001) and 1 year (17.3% vs 8.2%, p < 0.001) was greater among patients with prior infarction, and independent of other demographic variables. Accelerated alteplase was more effective than streptokinase or combination therapy (30-day mortality 10.4% vs 12.2%, p = 0.012; 1-year mortality 15.9% vs 17.8%, p = 0.041). Infarct vessel patency did not differ between those with and without prior myocardial infarction (67.3% vs 67% at 90 minutes, p = 0.92); however, recurrent ischemia was more common in patients with prior myocardial infarction. Patients with healed myocardial infarction should be educated to ensure early hospital admission if they develop symptoms suggestive of acute infarction, and upon hospital arrival should be promptly triaged to receive reperfusion therapy with accelerated alteplase.

The first case of the p phenotype in a Gurkha Nepalese

A serum sample from a Gurkha Nepalese soldier, residing in Hong Kong, was found to cause hemolysis of reagent ABO red cells (RBCs) in the reverse blood grouping test. Subsequent follow-up studies revealed that he was of the p phenotype, with potent anti-PP1Pk that was strongly hemolytic both at room temperature and 37 degrees C. The anti-PP1Pk was composed of IgG and IgM, and its various components were separable.

An unusual case of acute onset of cardiac failure

Rupture of the aortic sinus of Valsalva is one of the rare causes of acute dyspnoea. Modern advances have enabled diagnosis to be made easily with echocardiography as illustrated in this case. The treatment of choice is surgery with excellent prognosis if detected early. Therefore a high index of suspicion is required to diagnose this potentially threatening but yet treatable condition.

Effect of platelet glycoprotein IIb/IIIa receptor inhibition on distal embolization during percutaneous revascularization of aortocoronary saphenous vein grafts. EPIC Investigators. Evaluation of IIb/IIIa platelet receptor antagonist 7E3 in Preventing Ischemic Complications

Percutaneous treatment of narrowed aortocoronary saphenous vein graft disease represents a viable option for patients with recurrent angina following coronary artery bypass grafting. Present strategies are limited by high rates of distal embolization, non-Q-wave acute myocardial infarction (AMI), and restenosis. Because these complications may be mediated by platelets, inhibition of platelet glycoprotein IIb/IIIa receptor, the final common pathway for aggregation, may improve clinical outcomes. In the Evaluation of IIb/IIIa platelet receptor antagonist 7E3 in Preventing Ischemic Complications (EPIC) trial, 2,099 patients undergoing high-risk percutaneous coronary revascularization were randomized to receive abciximab bolus and infusion, abciximab bolus followed by placebo infusion or placebo. A total of 101 patients were treated for narrowing of saphenous vein grafts, 38 in the bolus and infusion group, 34 in the bolus group and 29 in the placebo group. Clinical end points included all-cause mortality, nonfatal AMI and need for repeat revascularization at 30 days. Compared with placebo, bolus and infusion therapy resulted in a significant reduction in distal embolization (2% vs 18%, p = 0.017) and a trend towards reduction in early large non-Q-wave AMI (2% vs 12%, p = 0.165). The occurrence of a 30-day composite end point was similar among the 3 treatment groups. At 6 months, there was also no difference in the composite end point. These results suggest that adjunctive therapy with abciximab during percutaneous treatment of narrowed saphenous vein grafts reduces the occurrence of distal embolization, and possibly non-Q-wave AMI.

Influence of diabetes mellitus on clinical outcome in the thrombolytic era of acute myocardial infarction. GUSTO-I Investigators. Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries

OBJECTIVES

This study was undertaken to define and better understand the characteristics and outcomes of patients with diabetes treated for acute myocardial infarction with contemporary thrombolysis.

BACKGROUND

Although thrombolysis has substantially improved survival of patients with myocardial infarction, diabetes mellitus remains an independent predictor for a poor prognosis.

METHODS

We characterized the contemporary relation between diabetes and outcome after myocardial infarction treated with thrombolytic agents from a large international cohort. Of 41,021 patients randomized to receive accelerated tissue-type plasminogen activator (t-PA), streptokinase or a combination of both agents in the Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries study, there were 5,944 patients with diabetes and 34,888 patients without diabetes.

RESULTS

Patients with diabetes were older and more likely to be female, to present with anterior wall infarction, to receive thrombolysis later and to have triple-vessel coronary artery disease. Mortality at 30 days was highest among diabetic patients treated with insulin (12.5%) compared with non-insulin-treated diabetic (9.7%) and nondiabetic (6.2%) patients (p < 0.001). Mortality was lowest among those with diabetes receiving accelerated t-PA, which is consistent with the results of the overall patient cohort. Although stroke occurred more frequently among diabetic (1.9%) than nondiabetic patients (1.4%, p < 0.001), there was no significant difference in the rates of intracranial hemorrhage. Cardiac failure, shock, atrioventricular block and atrial flutter/ fibrillation were more common among diabetic patients. The proportion of patients undergoing revascularization was similar between patients with and without diabetes, although diabetic patients were more likely to undergo coronary artery bypass graft surgery (10.4% vs. 8.3%). Diabetes remained an independent predictor for mortality at 1-year follow-up (14.5% vs. 8.9%, p < 0.001).

CONCLUSIONS

Diabetes, alone and in association with its comorbidities, portends a substantially worse 30-day and 1-year prognosis for patients with myocardial infarction.

Report on anti-Dib encountered in two Hong Kong Chinese

Two cases of anti-Dib, a rarely encountered antibody, were identified in serum samples referred by hospital blood banks during the past 13 months. Case 1 is a 41-year-old female who required blood for elective surgery. Case 2 is a premature infant suffering from mild neonatal jaundice on day 2 after birth. The anti-Dib in both cases exhibited marked dosage effect. The titer/score against Di(a+b+) and Di(a-b+) red blood cells (RBCs) in case 1 was 8/10 and 32/32, respectively, and in case 2, 4/18 and 32/46. The monocyte monolayer assay (MMA) also gave a similar pattern of results, being l5 percent and 100 percent reactive when tested with Di(a+b+) and Di(a-b+) RBCs in case 1, and 0.4 percent (within normal range) and l4.4 percent in case 2. The patient in case 1 underwent her operation without blood transfusion. The infant in case 2 was treated by phototherapy and subsequently recovered without the need for exchange transfusion.

Serologic characteristics of H-deficient phenotypes among Chinese in Hong Kong

BACKGROUND

The occasional presence of H-deficient red cells among both referred and donor blood samples prompted the mass screening of donated blood in Hong Kong for H-deficient phenotypes; 96 percent of the donors tested are Chinese from the southern province of Kwongtung.

STUDY DESIGN AND METHODS

Donor blood was screened for H-deficient red cells with the use of Ulex europaeus. Lewis phenotyping was carried out on all H-deficient individuals, and saliva testing was performed on most such individuals. The thermal amplitude and potency of their anti-H and anti-HI in the serum were also estimated.

RESULTS

Between 1984 and 1993, 28 H-deficient blood donors were identified; 16 H-deficient patient samples were also identified, and family studies revealed an additional 7 H-deficient subjects. The H-deficient red cells did not react with anti-H lectin, the levels of ABH substances in saliva were normal or near-normal, normal levels of A or B transferase were found in plasma, minute quantities of A or B (in persons who were genetically group A or B) were detected on the red cells, and anti-H or anti-HI was detected in the serum (about 66.7% of which reacted at 37 degrees C). Atypical anti-A or anti-B was demonstrated in 81.8 percent of the cases.

CONCLUSION

The H-deficient phenotype among the Hong Kong Chinese seems to represent a homogeneous group. Despite the presence of normal quantities of ABH substance in the saliva, anti-H or anti-HI that was active at 37 degrees C was detected in most cases. The incidence of the H-deficient phenotype was 1 in 15,620.

Absence of increased in-hospital complications with reused balloon catheters

A reanalysis of data from a prospective Canadian study suggests that catheter reuse is not associated with an increased rate of in-hospital complications. However, these results should be replicated in clinical trials before catheter reuse becomes routinely established.

Haemophilus parainfluenzae infective endocarditis

Gram-negative endocarditis was uncommon in the past, accounting for 1% to 3% of cases. With the advent of antibiotics, immunosuppressive agents and narcotic abuse, the number has increased to 5% to 10% in the native valves and as high as 17% in the prosthetic valves, with Haemophilus species as the commonest aetiological agent, accounting for about 1% of the cases. We report a case of Haemophilus parainfluenzae endocarditis in a 39-year-old man who presented with heart failure and persistent fever. Echocardiography showed bi-leaflet mitral valve prolapse and severe mitral regurgitation. A small vegetation was seen at the flail anterior valve leaflet. He responded well to 4 weeks of intravenous ampicillin at 9 g/day and 2 weeks of gentamicin at 4 mg/kg/day, and subsequently underwent valve replacement.

Lungs in thalassaemia major patients receiving regular transfusion

Progressive tissue iron deposition from multiple blood transfusions is common in beta-thalassaemia and pulmonary iron deposition may result in parenchymal damage. The objectives of this study were to: 1) determine the predominant pulmonary dysfunction in patients with thalassaemia major; and 2) demonstrate that parenchymal disease, if present, is at the level of the alveolocapillary membrane. Fourteen thalassaemia major patients (13 nonsmokers) receiving regular blood transfusion and without any history of chronic respiratory disease were recruited. Pulmonary function tests and echocardiography were performed before the scheduled transfusions. Three patients with the most restricted lung function were selected for high resolution computerized tomography (CT) of the lungs. One patient had an obstructive pattern with a forced expiratory volume in one second as percentage of forced vital capacity (FEV1/FVC) of 71%. Four patients demonstrated a restrictive pattern, as defined by total lung capacity (TLC) less than 80% predicted with normal FEV1/FVC%. Twelve patients had pulmonary transfer factors for carbon monoxide (TL,CO) below 80% pred, even after correction for the anaemia, indicating parenchymal disease. Eight of these 12 patients had alveolocapillary membrane defect, as demonstrated by a gas transfer factor of the pulmonary membrane (Tm) less than 80% pred. Mean resting arterial oxygen saturation was 95 +/- 2 (range 92-98) %. Eleven patients had oxygen desaturation of 5% or more during exercise on a bicycle ergometer, consistent with interstitial lung disease. There was no clinical or echocardiographic evidence of heart failure. Percentage predicted TLC was inversely correlated with age (r = -0.547; p = 0.043). Both percentage predicted TLC and TL,CO were not correlated with iron burden or desferoxamine ratio. High resolution CT in the three selected patients showed no evidence of pulmonary fibrosis. We conclude that thalassaemia major patients have a predominant restrictive lung dysfunction with pulmonary parenchymal disease and alveolocapillary membrane block. The restrictive and interstitial lung disease could not be accounted for by iron loading or pulmonary fibrosis in our patients.

Cost-efficacy modeling of catheter reuse for percutaneous transluminal coronary angioplasty

OBJECTIVES

Our goal was to provide the range of cost savings associated with various catheter reuse strategies.

BACKGROUND

Percutaneous transluminal coronary angioplasty catheters are commonly reused in several countries outside the United States. However, the cost-effectiveness of such reuse strategies has not been evaluated.

METHODS

Three theoretical models of catheter reuse were constructed using the actual costs for treating patients with coronary angioplasty at the Cleveland Clinic. Costs were calculated based on the number of balloon catheters, the amount of contrast agent used and the rates for urgent revascularization that were observed in a prospective Canadian study on catheter reuse.

RESULTS

The median cost to treat a lesion by means of coronary angioplasty using new catheters was $8,800 per patient. In reuse models, the potential to reduce cost depended on the number of balloon catheters used and the rates of urgent revascularization. The "best care" scenario offered a potential savings of $480 (5.5% of total in-hospital cost), whereas the "worst case" scenario resulted in an increased cost of $1,075 (12.2% of total in-hospital cost) compared with the single-use strategy. Cost of the "likely case" scenario was similar to that of the single-use strategy. Sensitivity analyses identified the different rates of revascularization and cost of balloon catheters required to offset potential savings in each strategy.

CONCLUSIONS

Although reusing coronary angioplasty catheters may reduce total in-hospital costs, even a modest increase in complications requiring urgent revascularization may offset any potential savings. However, if an increase in complications and procedure time can be avoided, the reuse strategy has significant economic potential and, ultimately, may be extended to other percutaneous coronary interventional equipment.

Importance of case mix during training in interventional cardiology

Adequate case mix is an important component of a physician's training in interventional cardiology. Physicians who seek competence in this area should have experience with patients who undergo interventional procedures for a variety of indications using a variety of techniques in a variety of situations. Future guidelines for physician training in interventional cardiology should address the issue of case mix.

Spinal epidural abscess: a report of nine cases and the use of intra-operative ultrasonography

BACKGROUND

Spinal epidural abscess is an uncommon and dangerous lesion. Once neurological complications occur the damage is often irreversible.

METHODS

The clinical presentation, operative findings, management and follow up of nine cases of spinal epidural abscess were reported. Four patients were diabetic and four others were intravenous drug addicts. The last patient had a history of a protracted stay in an intensive care unit complicated by pneumonia and pleural effusion. Ultrasonography was used intraoperatively to guide and to assess the adequacy of drainage and decompression of the epidural abscess.

RESULTS

Multiple level laminectomy was necessary and Staphylococcus aureus was the most common organism cultured. None of the five patients presenting with acute complete paralysis regained neurological function. Two of the four patients with incomplete paralysis were able to walk with an aid.

CONCLUSIONS

Spinal epidural abscess usually presents late and the prognosis is generally poor. Ultrasound may be useful in determining the extent of the abscess during operation to drain the collection.

First case of haemolytic disease of the newborn due to anti-Mur in Hong Kong

The fifth child of a Hong Kong Chinese mother developed moderate jaundice, attributable to antibodies (anti-Mi) against antigenic determinants in GP.Mur (Miltenberger, class III) red cells. Both the father and the eldest sister were of the phenotype GP.Mur. Testing of maternal serum against a red cell panel including cells known to carry the antigenic determinants of some Miltenberger phenotypes revealed the presence of anti-Mur. This report documents the first case of haemolytic disease of the newborn (HDN) due to anti-Mur in Hong Kong.

Subacute stent thrombosis: evolving issues and current concepts

During percutaneous coronary revascularization, intracoronary stents are effective in the treatment of abrupt vessel closure and improvement of suboptimal angioplasty results, and compared to balloon angioplasty, they reduce stenosis recurrence. Opposing these benefits, subacute thrombosis of stents is associated with a substantial increase in periprocedural morbidity and mortality. To review factors associated with stent thrombosis and to study the impact of evolving procedural techniques on the incidence of stent thrombosis, we reviewed all English articles from MEDLINE (1988 to 1995) with key words "stent" and "thrombosis." Stent registry data and recent abstracts from scientific meetings were also reviewed. Factors related to the clinical setting, the lesion, the stent and the procedural technique that affect the risk of stent thrombosis were identified. Sixty clinical studies were reviewed and include 7,914 patients receiving intracoronary stents. Studies were separated into those reporting stents placed emergently or electively without adjunct high-pressure balloon inflations, stents placed in saphenous vein graft conduits, and stents placed with high-pressure balloon inflations but without subsequent oral anticoagulants. Overall, subacute thrombosis was substantially higher in stents placed emergently (10.1%) compared to those placed electively (4.3%). Among contemporary trials employing high-pressure balloon inflations, the rate of stent thrombosis appears markedly lower (1.3%) despite reduced postprocedural anticoagulation. Taken together, these studies suggest factors associated with a heightened risk of stent thrombosis, many of which can be avoided with proper case selection and contemporary techniques.

A case of hydrops fetalis, probably due to antibodies directed against antigenic determinants of GP.Mur (Miltenberger class III) cells

The GP.Mur (Miltenberger class III) phenotype was found to occur in about 6.3 percent of Hong Kong (HK) Chinese blood donors. The incidence of antibodies directed against antigenic determinants of GP.Mur cells (anti-Mi) among patients was 0.34 percent, similar to that in Taiwan Chinese. A case of hydrops fetalis probably attributable to maternal anti-Mi was encountered in an HK Chinese woman during her sixth pregnancy. The anti-Mi was potent (titer 512, score 99). It fixed complement and was a mixture of IgG1 and IgG3. Two biological assays, the monocyte monolayer assay and the chemiluminescence test, were strongly positive. The father was found to be heterozygous for the GP.Mur gene.

Hemolytic transfusion reaction due to Rh antibodies detectable only by manual polybrene and polyethylene glycol technique

The authors report two cases of severe hemolytic transfusion reaction (HTR) attributable to Rh antibodies, which were not detectable by the saline indirect antiglobulin test (SIAT), low ionic strength saline solution technique (LISS), or two-stage enzyme (Enz) indirect antiglobulin test (IAT), but were readily detectable by the manual polybrene technique (MPT), MPT-IAT, and polyethylene glycol (PEG) IAT. With rare exceptions, Rh antibodies can usually be easily detected by the SIAT or Enz-IAT, and seldom cause intravascular HTR. The two cases in this report illustrate the value of the MPT and PEG-IAT in the detection of clinically significant Rh antibodies that would not otherwise be detectable by conventional methods.

Comparison of platelet counts in simultaneous venous and capillary blood samples using an automated platelet analyser

Platelet counts (PC) obtained simultaneously from capillary blood (CB) are generally lower than those from venous blood (VB). We quantified this difference in 17 patients with low platelet counts (LPC) and 18 healthy volunteers with normal platelet counts (NPC). The reproducibility of the counts in these 2 groups of subjects was also evaluated. The mean venous platelet count (VPC) and the mean capillary platelet count (CPC) were 67 +/- 30 x 10(3)/ul (+/- SD) and 61 +/- 23 x 10(3)/ul (p = 0.012) in the LPC, and 264 +/- 44 x 10(3)/ul and 234 +/- 45 x 10(3)/ul (p = 0.00016) in the NPC respectively. The mean difference (d) in the PC between VB and CB were 9.4 +/- 13.1 x 10(3)/ul and 19.4 +/- 17.6 x 10(3)/ul in the LPC and NPC respectively. The coefficients of variation (CV) of double counts for VB and CB were 8.1 +/- 8.3% and 9.8 +/- 8.6% for LPC, and 2.3 +/- 1.6% and 2.5 +/- 2.2% for NPC respectively. In conclusion, VPC was frequently (82.9% or 29/35 cases) higher than CPC. In addition, in patients with LPC, the agreement between VPC and CPC was poor and the counts were less reproducible.