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Effect of pacing-induced myocardial ischemia on platelet activation and fibrin formation in the coronary circulation
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JACC Vol. 10, No. I July 1987:40-5
Effect of Pacing-Induced Myocardial Ischemia on Platelet Activation and Fibrin Formation in the Coronary Circulation ALLEN B. NICHOLS, MD, FACC, KENNETH D. GOLD, MD, JOSEPH J. MARCELLA, MD, PAUL J. CANNON, MD, FACC, JOHN OWEN, MD New York. New York
The effect of pacing-induced myocardial ischemia on platelet activation and fibrin formation was investigated in seven patients with severe proximal lesions of the left anterior descending coronary artery to determine if acute ischemia activates the coagulation system. Fibrin formation was assessed from plasma levelsof fibrinopeptide A. Platelet activation was assessed by levels of platelet factor 4, beta-thromboglobulin and thromboxane B2• Plasma levels were measured before, during and after acute myocardial ischemia induced by rapid atrial pacing. Blood samples were collected from the ascending aorta and from the great cardiac vein through heparinbonded catheters. The occurrence of anterior myocardial ischemia was established by electrocardiography and by myocardial lactate extraction.
It is well established that acute myocardial infarction is usually associated with angiographically demonstrable coronary artery occlusion (I). Successful recanalization of occluded coronary arteries with specific thrombolytic agents such as streptokinase (2,3) and tissue plasminogen activator (4) has demonstrated that the occlusion is, in most cases, due to thrombus. The presence of coronary thrombus implies that the coagulation mechanism has been activated and thrombin has been generated to convert fibrinogen to fibrin. Several studies (5-7) in which platelet proteins, thrornboxane 8 2 or fibrinopeptides were measured have suggested that acute myocardial infarction is associated with activation of the hemostatic system. From the Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, New York. This study was supported by U.S. Public Health Service Grants HL-15486, HL-2 1006 and HL-14148 from the National Institutes of Health, Bethesda, Maryland. Dr. Nichols was a Senior Investigator of the New York Heart Association during this study. It was presented in part at the American Heart Association Annual Meeting, Dallas, Texas, November 1983. Manuscript received February 5, 1986; revised manuscript received December 17, 1986. accepted January 7, 1987. Address for reprints: Allen B. Nichols, MD, Cardiovascular Laboratory. Presbyterian Hospital. 622 West 168th Street, New York. New York 10032. © 1987 by the American College of Cardiology
No significant transmyocardial gradients in the levels of fibrinopeptide A, platelet factor 4, beta-thromboglobulin or thromboxane B2 were found at rest, during ischemia or in the recovery period, and levelsin the great cardiac vein did not change in response to ischemia. These data indicate that pacing-induced myocardial ischemia does not result in release of fibrinopeptide A, platelet factor 4, beta-thromboglobulin or thromboxane B2 into the coronary circulation, and imply that acute ischemia does not induce platelet activation or fibrin formation in the coronary circulation. (J Am Coll Cardiol1987;lO:40-S)
Whether acute myocardial ischemia can trigger the thrombotic process in the coronary circulation is an important and unresolved issue. We have previously observed (8) in patients with angiographically documented coronary artery disease who were studied at rest that activation of platelets or fibrin formation could not be detected by measurements made in peripheral blood. Fibrinopeptide A was assayed to detect fibrin I formation, and levels of platelet factor 4, beta-thromboglobulin and thromboxane 8 2 were measured to detect in vivo platelet activation. In a subsequent study (9) we observed that these levels were not significantly elevated in the peripheral venous blood of patients with coronary artery disease during exercise-induced myocardial ischemia. Although these results suggest that the hemostatic mechanism is not activated during induced myocardial ischemia, it is possible that measurements of platelet proteins and fibrinopeptides in peripheral venous blood may be inadequate for the detection of activation of the hemostatic system in the coronary circulation. A more direct approach is to selectively sample the coronary venous effluent from the ischemic myocardium, but this approach requires meticulous technique to avoid artifactual platelet activation and fibrin formation. Two groups 0735-1097/87/$3.50
JACC Vol. 10, No. I July 1987:40-5
NICHOLS ET AL. PLATELET ACTIVATION IN THE CORONARY CIRCULATION
of investigators (10, II) have reported that thromboxane B 2 levels are elevated in coronary sinus blood collected with woven Dacron catheters from patients during pacing-induced myocardial ischemia. We have demonstrated that these catheters induce fibrin formation and platelet adhesion to catheter surfaces, artifactually elevating fibrinopeptide A, platelet factor 4, beta-thromboglobulin and thromboxane B2 levels in blood samples drawn through them, We recently reported (12) the development of heparin-bonded catheters that permit selective blood sampling with minimal artifactual activation of the hemostatic system. The present study addresses the issue of whether myocardial ischemia activates platelets and induces fibrin formation in the coronary circulation, Patients with severe proximal stenoses of the left anterior descending coronary artery were studied before, during and after sustained myocardial ischemia induced by rapid atrial pacing. Catheters with heparin-bonded surfaces were used to minimize catheter-induced fibrin formation and platelet activation. To selectively sample the venous effluent from the ischemic anterior ventricular segment, catheters were positioned in the great cardiac vein. The principal aim of this study was to determine whether myocardial ischemia induced by rapid atrial pacing causes platelet activation or fibrin formation, or both, in the coronary circulation, Three independent and highly sensitive indexes (platelet factor 4, beta-thromboglobulin and thromboxane B 2 ) were used to detect in vivo platelet activation, and fibrinopeptide A was used as an index of thrombin action,
narrowing of the proximal left anterior descending coronary artery, and all except one had severe triple vessel coronary artery disease (Table I), Patients with acute myocardial infarction or congestive heart failure resulting from prior myocardial infarction were excluded from the study because previous studies (7,8) have shown that platelet factor 4, beta-thrornboglobulin and fibrinopeptide A levels are frequently elevated in these patients. Also excluded were patients receiving heparin or coumarin anticoagulants agents and patients receiving antiplatelet agents. Patients with thromboembolism, a prosthetic heart valve or a pacemaker were similarly excluded. Each patient provided informed written consent for participation in the study protocol, which was approved by the Committee on Human Investigation of Columbia University. Catheterization protocol. Patients were studied after an overnight fast, and beta-adrenergic antagonists, long-acting nitrates, and calcium channel blockers were discontinued 10 hours before catheterization. One patient received propranolol, 20 mg, 4 hours before the study and one patient continued to receive nifedipine. A 7F heparin-bonded, woven Dacron, bipolar electrode catheter (Gorlin catheter, USCI Cardiology and Radiology Division) was inserted through an 8F vascular sheath placed percutaneously into the right internal jugular vein by the Seldinger technique (13). The catheter tip was positioned in the right atrium, and a control blood sample was withdrawn. The catheter was then positioned in the coronary sinus and was advanced into the great cardiac vein under fluoroscopy. The positioning of the catheter tip in the great cardiac vein was confirmed by oximetry. A heparin-bonded, polyurethane right coronary catheter (Judkins-Schmidt type) was then introduced through a vascular sheath inserted percutaneously into the femoral artery, The catheter was advanced into the ascending aorta under fluoroscopy. Both catheters were fil1ed with saline solution before insertion and were inserted without guide wires. A previous study in our laboratory (12) has shown that catheter insertion over
Methods Patient selection. Seven patients with exertional angina and severely stenotic lesions of the proximal left anterior descending artery were studied. Included were six men and one woman with a mean age of 65 years. All patients had typical exertional angina for periods ranging from I week to 3 years, Each patient underwent diagnostic coronary arteriography for clinical indications. All patients had >70%
Table 1. Coronary Arteriographic Findings in the Seven Patients Studied Estimated Percent Coronary Stenosis
Patient No.
Age (yr) & Sex
LMCA
LAD
LCx
RCA
I 2 3 4 5 6 7
60M 58M 73M 60M 66M 68F 69M
70 0 0 0 0 70 0
70 80 100 99 99 90 90
100 80 75 0 50 100 25
100 75 99 0 100 90 100
Ant Desc = left anterior descending coronary artery; F = female; LMCA = left main coronary artery; LAD = left anterior descending coronary artery; LCx = left circumflex coronary artery; M = male; RCA = right coronary artery.
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NICHOLS ET AL. PLATELETACTIVATION IN THE CORONARY CIRCULATION
JACe Vol. 10. No. I July 1987:40--5
guide wires causes artifactual elevation of plasma fibrinopeptide A, beta-thromboglobulin, platelet factor 4 and thromboxane B 2 levels. Saline solution (0.9%) was infused continuously at 1.0 mil min through the catheter lumen, except during blood sampling. Blood samples for baseline fibrinopeptide A, beta-thromboglobulin, platelet factor 4 and thromboxane B 2 and lactate levels were then collected from the great cardiac vein and ascending aorta. Atrial pacing was then commenced using the bipolar pacing electrodes on the Gorlin catheter. The heart rate was increased in 10 beat/min increments at I minute intervals until the patient experienced angina or attained a maximal heart rate of 150 beats/min. The tachycardia was sustained for 3 to 5 minutes while the patient experienced angina. Repeat blood samples were collected simultaneously from the great cardiac vein and ascending aorta during angina. None of the patients were given nitroglycerin during pacinginduced angina, and long-acting nitrates had been discontinued before coronary arteriography. Immediately after blood sample collection, pacing was discontinued and, after a 5 minute recovery period, blood sampling was repeated. The Gorlin catheter was then withdrawn until the tip was again positioned in the right atrium, and a final control blood sample was obtained. Three electrocardiographic leads (L, aVF and VI) were monitored continuously during pacing. The electrocardiographic (ECG) criteria for an ischemic response to pacing was horizontal or downsloping ST segment depression of ~0.1 mV in the cycles immediately after termination of pacing (14, IS). All blood samples were collected before intracardiac pressure recordings or injection of contrast medium for angiography. Blood sample processing and radioimmunoassays. For assay offibrinopeptide A, beta-thromboglobulin and platelet factor 4, blood samples (9 ml) were withdrawn from the catheters into polypropylene syringes, and immediately transferred into a chilled 10 ml siliconized glass tube containing I ml of the following anticoagulant mixture: 1,400 V/ml heparin, 1,000 V/ml aprotinin (Trasylol), 10 mM adenosine and 20 mM theophylline in N-2-hydroxyethylpiperazine-N '-2-ethane sulfonic acid (HEPES)-buffered saline solution (pH 7.4). The tubes were placed in melting ice and centrifuged within I hour at 3,000 g for 20 minutes at 4°C. The supernatant plasma was transferred to polypropylene tubes and centrifuged at 49,000 g for 15 minutes at 4°C. The resulting platelet-poor plasma was stored frozen at - 80°C until assayed. For assay ofthromboxane B2> 3 ml of blood was collected into 10 mg of disodium ethylenediaminetetraacetate. The sample was centrifuged at 3,000 g for 20 minutes at 4°C and the supernate plasma stored at - 80°C until assayed. Fibrinopeptide A, platelet factor 4, beta-thromboglobulin and thromboxane B 2 levels were measured by radioimmunoassay as previously described (9,16-18).
Lactate assay. Blood samples for lactate determination were deproteinated in iced 10% perchloric acid and assayed by a spectrophotometric technique (Sigma Chemical Company) (19). A change in the arteriovenous lactate difference of >0.8 mg/dl from control period to peak pacing was considered diagnostic of myocardial ischemia (20). Statistical analysis. Analysis of variance and other parametric tests were performed after logarithmic transformation of the fibrinopeptide A, platelet factor 4, beta-thromboglobulin and thromboxane B 2 data, because these data have been noted to be skewed in past studies (8). For this reason geometric rather than arithmetic means have been used to describe the results. Probability levels were considered to be statistically significantly different at <0.05. Because fibrinopeptide A, platelet factor 4, beta-thromboglobulin and thromboxane B 2 all reflect activation of the hemostatic system, tests of significance for four different variables were combined as described by Sokal and Rohlf (21).
Results Response to rapid atrial pacing. During rapid atrial pacing, ST segment depression diagnostic of myocardial ischemia was observed in all patients. ST segment depression was observed in lead I in all seven patients and in lead aVF in two patients. Five of the seven patients experienced angina, and pacing was terminated before 5 minutes had elapsed in three patients because of severe chest pain. During pacing, lactate extraction decreased significantly in five patients. Thus, six of the seven patients had either chest pain or altered lactate extraction, or both, confirming the occurrence of ischemia in response to pacing. Fibrinopeptide A levels (Fig. 1). The mean fibrinopeptide A level in blood withdrawn from the great cardiac vein did not change significantly in response to ischemia and did not differ significantly from levels in aortic blood samples collected simultaneously, either before or during pacing. Fibrinopeptide A levels were significantly higher (p < 0.05) in the great cardiac vein than in the right atrium before pacing. Platelet factor 4 levels (Fig. 2). Mean platelet factor 4 levels in aortic and great cardiac vein blood collected during pacing-induced ischemia and in the recovery phase did not differ significantly from levels measured during rest conditions. Platelet factor 4 levels in great cardiac vein and aortic blood samples did not differ significantly either at rest, during rapid atrial pacing or during recovery. Before rapid pacing, mean platelet factor 4 levels were significantly (p < 0.05) higher in both the great cardiac vein and the aorta than in the right atrium. Beta-thromboglobulin levels (Fig. 3). Mean betathromboglobulin levels also were not significantly elevated in the great cardiac vein or aorta during pacing-induced
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ischemia or in the recovery period. Beta-thromboglobulin levels in great cardiac vein blood samples were not significantly different from levels in the right atrium or aorta before, during or after rapid pacing. Thromboxane B2 levels (Fig. 4). Similarly, thromboxane B 2 levels did not differ significantly in the aorta, great cardiac vein or right atrium. at rest, during pacing-induced ischemia or in the recovery period, Statistical analysis. The combined test of signifi cance performed on the logarithmically transformed data indicated no net change in the variables measured during pacinginduced ischemia. Activation of the hemostatic system leading to a combined 50% increase in the measured levels would have been detectable at the I% level, The actual changes found (fibrinopeptide A, + 10%; platelet factor 4 . - 3%; beta-thromboglobulin, - II %; and thromboxane 8 2 , + 4%) indicate no detectable activation of the hemostatic system.
Discussion Many groups of investigators ( 10,22-26) have postulated that acute myocardial ischemia induces abnormal platelet Figure2. Platelet factor4 levels in plasmacollected at rest, during peak pacing and after recovery (geometric mean ::!: SEM) show no significant change during pacing-induced ischemia. Symbols and abbreviations as in Figure I.
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activation in the coronary circulation. The importance of this issue is that enhanced platelet aggregation in the coronary circulation could impede blood flow in atherosclerotic coronary arteries, resulting in further ischemia. Furthermore, thromboxane B2 generation caused by aggregated platelets may aggravate myocardial ischemia by inducing coronary vasoconstriction. Most important, platelet activation and fibrin formation in the coronary circulation could induce coronary thrombosis. resulting in myocardial infarction. Effect of pacing-induced ischemia on thromboxane B 2 levels. This issue has become controversial. however, because recent studies of the effect of pacing-induced ischemia on platelet activation in the coronary circulation have produced confl icting results. Lewy et al. (10) first reported in 1980 that thromboxane 8 2 levels were elevated in the coronary sinus blood of several patients during pacing-induced ischemia. Subsequently. other investigators (11,27) observed increased thromboxane 8 2 release in patients with coronary artery disease during pacing-induced ischemia. Recently. Martin e[ al. (28) observed positive transmyocardial thromboxane 8 2 gradients in 8 of 18 patients after pacing but in none during pacing. Lastly, Rubenstein et al. (29) reported significant transmyocardial release of beta-thromboglobulin Figure 4. Thromboxane B! levels in plasma collected at rest. during peak pacing and after recovery (geometric mean ± SEM) were not significantly elevated during pacing-induced ischemia. Symbols and abbreviations as in Figure I. I--PACING-I
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NICHOLS ET AL. Pl.ATEL ET ACTIVATION IN THE CORONARY CIRCULATION
JACC Vol. 10, No. I July 1987:40-5
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NICHOLS ET AL. PLATELET ACTIVATION IN THE CORONARY CIRCULATION
JACC Vol. 10. No. I July 1987:40-5
in patients with coronary artery disease studied at rest, but other authors (30,31) reported that beta-thromboglobulin levels are not elevated in coronary sinus blood samples in similar patients.
and suggest that pacing-induced ischemia does not activate platelets or cause fibrin formation. Although the number of patients studied was small, the combined test of significance based on all four assays enhanced the statistical power of this result. Levels of jibrinopeptide A in the coronary circulation during acute myocardial ischemia have not been reported previously. Two recent studies (30,31) have described betathromboglobulin levels in the coronary sinus blood of patients during pacing-induced myocardial ischemia. Thaulow (30) reported that these levels were not elevated in patients with pacing-induced ischemia, but were inexplicably elevated in patients without ischemia during pacing. Verheught et al. (31) reported that they were not elevated at rest or during pacing-induced ischemia in patients given 5,000 units of heparin before catheterization. In both of these studies, blood samples were collected nonselectively from the coronary sinus; with such sampling it is possible that an increased concentration of a substance released from an area of ischemia could be diluted by blood draining from a nonischemic region. To minimize this problem, in the present study we selected patients with lesions of the proximal left anterior descending artery and selectively catheterized the great cardiac vein, which drains the venous effluent of the anterior descending coronary artery. This technique should ensure that venous blood was directly sampled from the ischemic left ventricular segment without dilution by venous effluent from the nonischemic segments. To detect possible in vivo platelet activation in the present study, two platelet proteins in addition to thromboxane B2 were measured. Determination of both platelet factor 4 and beta-thromboglobulin levels in each sample is useful for distinguishing in vitro from in vivo platelet release occurring during collection and processing of blood samples (32). In previous studies, only one platelet protein assay was performed, raising the possibility that artifactual platelet activation was undetected. The observation that jibrinopeptide A and platelet factor 4 levels were slightly, but significantly, higher in the great cardiac vein and the aorta than in the right atrium raises the possibility that they were continuously released into the coronary venous effluent or released from the lungs. However, the magnitude of the elevation was slight and further studies will be necessary to distinguish intrapulmonary from intracoronary release. Recently, Mant et al. (33) presented data, obtained with heparin-filled catheters, which demonstrate that platelet factor 4 and beta-thromboglobulin levels are not elevated at rest in coronary sinus blood of patients with coronary artery disease; other investigators (30,31) reported similar findings. Summary and clinical implications. Our study demonstrates that pacing-induced ischemia does not cause platelet activation or fibrin formation in blood draining ischemic myocardial segments. The implication of our study is that
44
Fibrin formation and platelet aggregation on catheter surfaces. In all of these studies, blood samples were collected from the coronary sinus and aorta with conventional woven Dacron cardiac catheters. We have studied (12) the effect of blood contact with catheter surfaces on levels of fibrinopeptide A, platelet factor 4, beta-thromboglobulin and thromboxane B2 in blood samples withdrawn through cardiovascular catheters. We found that blood collected through woven dacron catheters showed artifactual elevation of these levels as a result of fibrin formation and platelet aggregation on the surfaces of the catheters. Progressive elevation of fibrinopeptide A and platelet proteins was observed while the catheters remained in the venous or arterial circulation, particularly if multiple blood samples were collected through the catheters. These observations may explain why elevated thromboxane B2 levels were observed in previous studies in both aortic and coronary sinus blood during and after pacing (l0, II ,27).
Role of heparin-bonded catheters for collecting blood samples. In the present study, heparin-bonded catheters were used for collection of blood samples from the great cardiac vein and aorta. We previously found (l2) that collection of blood samples through such catheters eliminated spurious elevation of fibrinopeptide A, platelet factor 4, beta-thromboglobulin and thromboxane H2 caused by fibrin formation and platelet aggregation on catheter surfaces. Scanning electron microscopy revealed fibrin strands and platelet aggregates on the surfaces of conventional catheters, but not on catheters with heparin-bonded surfaces. The passivating effect of heparin bonding was shown to last for > 30 minutes, which is a suitable time for completion of an interventional pacing study. However, elevation of the fibrinopeptide A level was consistently observed after percutaneous insertion of vascular sheaths. In the present study, multiple vascular sheaths were inserted, which accounts for the elevated baseline level of fibrinopeptide A. In both studies, the fibrinopeptide A levels were noted to decline gradually over the ensuing 20 to 30 minutes.
Effect of ischemia on fibrinopeptide A and platelet protein levels. In the present study, mean levels of fibrinopeptide A, platelet factor 4, beta-thromboglobulin and thromboxane H2 in the great cardiac vein during pacinginduced ischemia did not differ from coronary sinus levels measured at rest or in the recovery period. Furthermore, significant transmyocardial gradients of these levels were not observed at rest, during pacing-induced ischemia or in the recovery period after pacing. These data indicate that pacing-induced ischemia does not cause the release of detectable fibrinopeptide A, platelet factor 4, beta-thromboglobulin or thromboxane H2 into the coronary circulation
45
JACC Vol. 10. No. July 1987:40-5
NICHOLS ET AI.. PLATELET ACTIVATION IN THE CORONARY CIRCU LATION
stress-induced ischemia itself doe s not activate the coagulation system in the coronary circulation . Thu s, pacinginduced ischemia will not be a useful model for stud ying intracoronary platelet activation or fibrin formation associated with spontaneous myocardial ischemia. The mech anism of pacing-induced angina probabl y differs considerably from the mechanism of spont aneous angina occurring at rest. Consistent with this observation is the recent report of Fitzgerald et al. (34) that urinary metabolites of thromboxane were acutely increa sed in patients with unstable angina during chest pain, but were not increased in patient s with stable angina after exercise-induced ischemia.
13. Seldinger SI. Catheter replaceme nt of the needle in percutaneous arteriography: a new techn ique. Acta Rad iol 1953;39:368-70.
We acknowledge the invaluable techni cal ass istance of Betty Grossman. who performed the fibrinopeptide A, platelet factor 4 and beta-thromboglobulin assays. and we thank Leonard L. Norbert for expert preparation of this manuscript.
14 . O' Brian KP. Higgs LM . Glancy DL , Epstein SE . Hemod ynam ic acco mpaniments of angin a: a co mpar ison during angina induced by exercise and by atrial pacing. Circulation 1969;39:735-43 . 15. Parker 10. Chiong MA . West RO. Case RB . Sequential alterati ons in myocardial lactate metaboli sm, ST seg ments, and left ventricul ar function during angina induced by atrial pacing. Circulation 1969;40: 11 3- 31. 16. Nossel HL. Yudelman I, Canfield RE. et al. Measurement of fibrinopeptide A in human blood. 1 Clin Invest 1974;54:43-53. 17. Kaplan KL. Owen J . Radio immuno assay of platelet factor 4 . Methods Enzymol 1982 ;84:83- 92 . 18. Kaplan KL. Owen 1. Radioimmun oassay of beta-thromboglobulin . Methods Enzymol 1982;84:93-102. 19 . Marboch EP. Weil MH. Rapid enzym atic measurement of blood lactate and pyruvate. Clin Chern 1967;13:314-20. 20 . Jackson G. Atkinson L. Clark M, Crook B, Armstrong P. Oram S. Diagnosis of coronary artery disease by estimation of coronary sinus lactate . Br Heart J 1978;40 :979-83. 2 1. Sokal RR. Rohlf FJ. Biometr y. 2nd ed . San Francisco: WH Freeman , 1981:779- 82.
References I. DeWood MA, Spores J. Notske R. et al. Prevalence of total co ronary artery occlusion durin g the early hours of transmural myocardial infarction. N Engl J Med 1980 ;303:897-902. 2. Rentrop P, Blanke H, Karsch KR , Kaiser H, Kostering H. Leitz K. Selecti ve intracoron ary thrombolysis in acute myocardial infarction and unstable angina pectori s. Ci rculation 1981:63:307-17 . 3. Kennedy JW , Ritchie JL. Davis KB, Fritz JK . Western Washington randomi zed trial of intracoronary strep tokin ase in acute myocardi al infarction . N Engl J Med 1983;309 : 1477 - 82. 4 . The TIMI Stud y Group . The thrombol ysis in myocardial infarction (T IM/) trial: phase I findings . N Engl J Med 1985;312:932-6. 5. Mombelli B, 1m Hoff V, Haeberl i A, Straub PW. Effect of heparin on plasma fibrinopeptid e A in patients with acute myocardial infarction . Circulation 1984;69:684 - 9 . 6. O'Brien JR, Etherington MD. Shuttleworth RD. Caldwell WHo Platelet function in acute myocardi al infarction patients compared with co ntrols. Thromb Haemost 1980;44:96-9 . 7. Eisenberg PR, Sherman LA , Schectman K. Perez J. Sobel BE. Jaffe AS . Fibrinopeptide A: a marker of acute coronar y thrombosi s. Circulation 1985;71:9 12- 8 8. Nichols AB. Owen J. Kaplan KL. Sciacca RR. Cann on PJ, Nossel HL. Fibrinopeptide A. platelet factor 4 . and beta-thromboglobul in levels in co ronary heart disease . Blood 1982;60:650-4 . 9 . Marcella 11, Nichol s AB , Johnson LL. et al. Exercise- induced myocardial ischemia in patient s with coronary artery disease: lack of evidence for platelet activation or fibrin formation in peripheral venous blood . J Am Coil Cardi ol 1983;1:1185-93. 10. Lewy RI. Weiner L. Walinsky P. Lefer AM , Silver MJ. Smith JB . Thr omboxane release durin g pacing-induced angina pectoris: possible vasoconstrictor influence on the coronary vasculature. Circulation 1980;61: 1165- 7 1. II. Mehta J, Mehta P. Feldman RL, Horalek C. Thr omboxane release in coro nary artery disease : spontaneous versus pacing-induced angina . Am Heart J 1984;107;286-92 . 12. Nichols AB, Owen I , Gro ssman BA, Marcella 11. Fleisher LN. Lee MM . Effect of heparin bondin g on catheter-induced fibrin formation and platelet activation . Circulation 1984 ;70:843-50.
22. Sobel M, Salzman EW . Davies GC. et al. Circulating platelet products in unstable angina. Circulat ion 198) ;63:300 - 6. 23. Smitherman TC , Milam M . Woo 1. Willerson IT, Frenkel EP . Elevated beta-thromb o-globul in in peripheral venous blood of patients with acute myocardial ischemia: direct evidence for enhan ced platelet reactivity in vivo. Am J Card io! 1981 ;48:395-402. 24. Hirsh PD. Hillis LD . Campbell WB. Firth BG. Willerson IT. Release of prostaglandins and thrornboxane into the coronary circulation in patients with ischemic heart disease. N Engll Med 1981;304:685- 90. 25. Mehta J . Mehta P, Pepine CJ . Platelet agg regation in aortic and coro nary venous blood in patient s with and without coronary disease . 3. Role of tachycardia stress and propranolol. Circulation 1978;58:881-6. 26. Gall ino A, Haeberl i A, Bauer HR, Straub PW. Fibrin format ion and platelet aggregation in patient s with severe coronary artery disease : relationship with the degree of myocardial ischemia. Circulation 1985;72: 27- 30. 27. Tada M. Kuzuya T. Inoue M. et al. Elevation of thromboxane B2 levels in patients with classic and variant angina pectoris. Circulation 1981:64: 1107-15. 28 . Martin Jl. , Wilson JR, Burch JW, et al. Effect of atrial pacing on intracoronary thromboxane production in coronary artery disease . J Am Coli Cardiol 1983; I:1194- 200. 29. Rubenstein MD , Wall RT, Bairn DS, Harrison DC . Platelet acti vation in cl inical coro nary artery disease and spasm. Am Heart J 1981;102: 363-8. 30. Thaulow E. Effects induced on blood platelets in ischemi c and nonischemic myocardium. Am 1 Cardiol 1983 ;52:466-9 . 31. Verheugt FW. Serru ys PW, van Vliet H, Spijkers A, Hugenh oltz PG. lntracoronar y platelet release in patients with and without coronary artery disease . Thromb Haemost 1983 ;49:28-31. 32. Kaplan KL, Owen J . Plasma levels of bcta-thromboglobulin and platelet factor 4 as indices of platelet activation in vivo. Blood 1981 ;57: 199- 202. 33. Man! Ml, Kappagoda CT , Taylor RF, Quinl an IE . Tran scorona ry platelet activation and consumption in coronary artery disease (CAD): studies at rest (abstr). Blood I984 ;64(suppl ):249a . 34 . Fitzgerald D1. Roy L. Catell a F. Fitzgerald GA . Platelet activation and unstable coronary disease . N Engll Med 1986;315:983-9 .
JACC Vol. 10, No. I July 1987:40-5
Effect of Pacing-Induced Myocardial Ischemia on Platelet Activation and Fibrin Formation in the Coronary Circulation ALLEN B. NICHOLS, MD, FACC, KENNETH D. GOLD, MD, JOSEPH J. MARCELLA, MD, PAUL J. CANNON, MD, FACC, JOHN OWEN, MD New York. New York
The effect of pacing-induced myocardial ischemia on platelet activation and fibrin formation was investigated in seven patients with severe proximal lesions of the left anterior descending coronary artery to determine if acute ischemia activates the coagulation system. Fibrin formation was assessed from plasma levelsof fibrinopeptide A. Platelet activation was assessed by levels of platelet factor 4, beta-thromboglobulin and thromboxane B2• Plasma levels were measured before, during and after acute myocardial ischemia induced by rapid atrial pacing. Blood samples were collected from the ascending aorta and from the great cardiac vein through heparinbonded catheters. The occurrence of anterior myocardial ischemia was established by electrocardiography and by myocardial lactate extraction.
It is well established that acute myocardial infarction is usually associated with angiographically demonstrable coronary artery occlusion (I). Successful recanalization of occluded coronary arteries with specific thrombolytic agents such as streptokinase (2,3) and tissue plasminogen activator (4) has demonstrated that the occlusion is, in most cases, due to thrombus. The presence of coronary thrombus implies that the coagulation mechanism has been activated and thrombin has been generated to convert fibrinogen to fibrin. Several studies (5-7) in which platelet proteins, thrornboxane 8 2 or fibrinopeptides were measured have suggested that acute myocardial infarction is associated with activation of the hemostatic system. From the Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, New York. This study was supported by U.S. Public Health Service Grants HL-15486, HL-2 1006 and HL-14148 from the National Institutes of Health, Bethesda, Maryland. Dr. Nichols was a Senior Investigator of the New York Heart Association during this study. It was presented in part at the American Heart Association Annual Meeting, Dallas, Texas, November 1983. Manuscript received February 5, 1986; revised manuscript received December 17, 1986. accepted January 7, 1987. Address for reprints: Allen B. Nichols, MD, Cardiovascular Laboratory. Presbyterian Hospital. 622 West 168th Street, New York. New York 10032. © 1987 by the American College of Cardiology
No significant transmyocardial gradients in the levels of fibrinopeptide A, platelet factor 4, beta-thromboglobulin or thromboxane B2 were found at rest, during ischemia or in the recovery period, and levelsin the great cardiac vein did not change in response to ischemia. These data indicate that pacing-induced myocardial ischemia does not result in release of fibrinopeptide A, platelet factor 4, beta-thromboglobulin or thromboxane B2 into the coronary circulation, and imply that acute ischemia does not induce platelet activation or fibrin formation in the coronary circulation. (J Am Coll Cardiol1987;lO:40-S)
Whether acute myocardial ischemia can trigger the thrombotic process in the coronary circulation is an important and unresolved issue. We have previously observed (8) in patients with angiographically documented coronary artery disease who were studied at rest that activation of platelets or fibrin formation could not be detected by measurements made in peripheral blood. Fibrinopeptide A was assayed to detect fibrin I formation, and levels of platelet factor 4, beta-thromboglobulin and thromboxane 8 2 were measured to detect in vivo platelet activation. In a subsequent study (9) we observed that these levels were not significantly elevated in the peripheral venous blood of patients with coronary artery disease during exercise-induced myocardial ischemia. Although these results suggest that the hemostatic mechanism is not activated during induced myocardial ischemia, it is possible that measurements of platelet proteins and fibrinopeptides in peripheral venous blood may be inadequate for the detection of activation of the hemostatic system in the coronary circulation. A more direct approach is to selectively sample the coronary venous effluent from the ischemic myocardium, but this approach requires meticulous technique to avoid artifactual platelet activation and fibrin formation. Two groups 0735-1097/87/$3.50
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NICHOLS ET AL. PLATELET ACTIVATION IN THE CORONARY CIRCULATION
of investigators (10, II) have reported that thromboxane B 2 levels are elevated in coronary sinus blood collected with woven Dacron catheters from patients during pacing-induced myocardial ischemia. We have demonstrated that these catheters induce fibrin formation and platelet adhesion to catheter surfaces, artifactually elevating fibrinopeptide A, platelet factor 4, beta-thromboglobulin and thromboxane B2 levels in blood samples drawn through them, We recently reported (12) the development of heparin-bonded catheters that permit selective blood sampling with minimal artifactual activation of the hemostatic system. The present study addresses the issue of whether myocardial ischemia activates platelets and induces fibrin formation in the coronary circulation, Patients with severe proximal stenoses of the left anterior descending coronary artery were studied before, during and after sustained myocardial ischemia induced by rapid atrial pacing. Catheters with heparin-bonded surfaces were used to minimize catheter-induced fibrin formation and platelet activation. To selectively sample the venous effluent from the ischemic anterior ventricular segment, catheters were positioned in the great cardiac vein. The principal aim of this study was to determine whether myocardial ischemia induced by rapid atrial pacing causes platelet activation or fibrin formation, or both, in the coronary circulation, Three independent and highly sensitive indexes (platelet factor 4, beta-thromboglobulin and thromboxane B 2 ) were used to detect in vivo platelet activation, and fibrinopeptide A was used as an index of thrombin action,
narrowing of the proximal left anterior descending coronary artery, and all except one had severe triple vessel coronary artery disease (Table I), Patients with acute myocardial infarction or congestive heart failure resulting from prior myocardial infarction were excluded from the study because previous studies (7,8) have shown that platelet factor 4, beta-thrornboglobulin and fibrinopeptide A levels are frequently elevated in these patients. Also excluded were patients receiving heparin or coumarin anticoagulants agents and patients receiving antiplatelet agents. Patients with thromboembolism, a prosthetic heart valve or a pacemaker were similarly excluded. Each patient provided informed written consent for participation in the study protocol, which was approved by the Committee on Human Investigation of Columbia University. Catheterization protocol. Patients were studied after an overnight fast, and beta-adrenergic antagonists, long-acting nitrates, and calcium channel blockers were discontinued 10 hours before catheterization. One patient received propranolol, 20 mg, 4 hours before the study and one patient continued to receive nifedipine. A 7F heparin-bonded, woven Dacron, bipolar electrode catheter (Gorlin catheter, USCI Cardiology and Radiology Division) was inserted through an 8F vascular sheath placed percutaneously into the right internal jugular vein by the Seldinger technique (13). The catheter tip was positioned in the right atrium, and a control blood sample was withdrawn. The catheter was then positioned in the coronary sinus and was advanced into the great cardiac vein under fluoroscopy. The positioning of the catheter tip in the great cardiac vein was confirmed by oximetry. A heparin-bonded, polyurethane right coronary catheter (Judkins-Schmidt type) was then introduced through a vascular sheath inserted percutaneously into the femoral artery, The catheter was advanced into the ascending aorta under fluoroscopy. Both catheters were fil1ed with saline solution before insertion and were inserted without guide wires. A previous study in our laboratory (12) has shown that catheter insertion over
Methods Patient selection. Seven patients with exertional angina and severely stenotic lesions of the proximal left anterior descending artery were studied. Included were six men and one woman with a mean age of 65 years. All patients had typical exertional angina for periods ranging from I week to 3 years, Each patient underwent diagnostic coronary arteriography for clinical indications. All patients had >70%
Table 1. Coronary Arteriographic Findings in the Seven Patients Studied Estimated Percent Coronary Stenosis
Patient No.
Age (yr) & Sex
LMCA
LAD
LCx
RCA
I 2 3 4 5 6 7
60M 58M 73M 60M 66M 68F 69M
70 0 0 0 0 70 0
70 80 100 99 99 90 90
100 80 75 0 50 100 25
100 75 99 0 100 90 100
Ant Desc = left anterior descending coronary artery; F = female; LMCA = left main coronary artery; LAD = left anterior descending coronary artery; LCx = left circumflex coronary artery; M = male; RCA = right coronary artery.
41
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NICHOLS ET AL. PLATELETACTIVATION IN THE CORONARY CIRCULATION
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guide wires causes artifactual elevation of plasma fibrinopeptide A, beta-thromboglobulin, platelet factor 4 and thromboxane B 2 levels. Saline solution (0.9%) was infused continuously at 1.0 mil min through the catheter lumen, except during blood sampling. Blood samples for baseline fibrinopeptide A, beta-thromboglobulin, platelet factor 4 and thromboxane B 2 and lactate levels were then collected from the great cardiac vein and ascending aorta. Atrial pacing was then commenced using the bipolar pacing electrodes on the Gorlin catheter. The heart rate was increased in 10 beat/min increments at I minute intervals until the patient experienced angina or attained a maximal heart rate of 150 beats/min. The tachycardia was sustained for 3 to 5 minutes while the patient experienced angina. Repeat blood samples were collected simultaneously from the great cardiac vein and ascending aorta during angina. None of the patients were given nitroglycerin during pacinginduced angina, and long-acting nitrates had been discontinued before coronary arteriography. Immediately after blood sample collection, pacing was discontinued and, after a 5 minute recovery period, blood sampling was repeated. The Gorlin catheter was then withdrawn until the tip was again positioned in the right atrium, and a final control blood sample was obtained. Three electrocardiographic leads (L, aVF and VI) were monitored continuously during pacing. The electrocardiographic (ECG) criteria for an ischemic response to pacing was horizontal or downsloping ST segment depression of ~0.1 mV in the cycles immediately after termination of pacing (14, IS). All blood samples were collected before intracardiac pressure recordings or injection of contrast medium for angiography. Blood sample processing and radioimmunoassays. For assay offibrinopeptide A, beta-thromboglobulin and platelet factor 4, blood samples (9 ml) were withdrawn from the catheters into polypropylene syringes, and immediately transferred into a chilled 10 ml siliconized glass tube containing I ml of the following anticoagulant mixture: 1,400 V/ml heparin, 1,000 V/ml aprotinin (Trasylol), 10 mM adenosine and 20 mM theophylline in N-2-hydroxyethylpiperazine-N '-2-ethane sulfonic acid (HEPES)-buffered saline solution (pH 7.4). The tubes were placed in melting ice and centrifuged within I hour at 3,000 g for 20 minutes at 4°C. The supernatant plasma was transferred to polypropylene tubes and centrifuged at 49,000 g for 15 minutes at 4°C. The resulting platelet-poor plasma was stored frozen at - 80°C until assayed. For assay ofthromboxane B2> 3 ml of blood was collected into 10 mg of disodium ethylenediaminetetraacetate. The sample was centrifuged at 3,000 g for 20 minutes at 4°C and the supernate plasma stored at - 80°C until assayed. Fibrinopeptide A, platelet factor 4, beta-thromboglobulin and thromboxane B 2 levels were measured by radioimmunoassay as previously described (9,16-18).
Lactate assay. Blood samples for lactate determination were deproteinated in iced 10% perchloric acid and assayed by a spectrophotometric technique (Sigma Chemical Company) (19). A change in the arteriovenous lactate difference of >0.8 mg/dl from control period to peak pacing was considered diagnostic of myocardial ischemia (20). Statistical analysis. Analysis of variance and other parametric tests were performed after logarithmic transformation of the fibrinopeptide A, platelet factor 4, beta-thromboglobulin and thromboxane B 2 data, because these data have been noted to be skewed in past studies (8). For this reason geometric rather than arithmetic means have been used to describe the results. Probability levels were considered to be statistically significantly different at <0.05. Because fibrinopeptide A, platelet factor 4, beta-thromboglobulin and thromboxane B 2 all reflect activation of the hemostatic system, tests of significance for four different variables were combined as described by Sokal and Rohlf (21).
Results Response to rapid atrial pacing. During rapid atrial pacing, ST segment depression diagnostic of myocardial ischemia was observed in all patients. ST segment depression was observed in lead I in all seven patients and in lead aVF in two patients. Five of the seven patients experienced angina, and pacing was terminated before 5 minutes had elapsed in three patients because of severe chest pain. During pacing, lactate extraction decreased significantly in five patients. Thus, six of the seven patients had either chest pain or altered lactate extraction, or both, confirming the occurrence of ischemia in response to pacing. Fibrinopeptide A levels (Fig. 1). The mean fibrinopeptide A level in blood withdrawn from the great cardiac vein did not change significantly in response to ischemia and did not differ significantly from levels in aortic blood samples collected simultaneously, either before or during pacing. Fibrinopeptide A levels were significantly higher (p < 0.05) in the great cardiac vein than in the right atrium before pacing. Platelet factor 4 levels (Fig. 2). Mean platelet factor 4 levels in aortic and great cardiac vein blood collected during pacing-induced ischemia and in the recovery phase did not differ significantly from levels measured during rest conditions. Platelet factor 4 levels in great cardiac vein and aortic blood samples did not differ significantly either at rest, during rapid atrial pacing or during recovery. Before rapid pacing, mean platelet factor 4 levels were significantly (p < 0.05) higher in both the great cardiac vein and the aorta than in the right atrium. Beta-thromboglobulin levels (Fig. 3). Mean betathromboglobulin levels also were not significantly elevated in the great cardiac vein or aorta during pacing-induced
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ischemia or in the recovery period. Beta-thromboglobulin levels in great cardiac vein blood samples were not significantly different from levels in the right atrium or aorta before, during or after rapid pacing. Thromboxane B2 levels (Fig. 4). Similarly, thromboxane B 2 levels did not differ significantly in the aorta, great cardiac vein or right atrium. at rest, during pacing-induced ischemia or in the recovery period, Statistical analysis. The combined test of signifi cance performed on the logarithmically transformed data indicated no net change in the variables measured during pacinginduced ischemia. Activation of the hemostatic system leading to a combined 50% increase in the measured levels would have been detectable at the I% level, The actual changes found (fibrinopeptide A, + 10%; platelet factor 4 . - 3%; beta-thromboglobulin, - II %; and thromboxane 8 2 , + 4%) indicate no detectable activation of the hemostatic system.
Discussion Many groups of investigators ( 10,22-26) have postulated that acute myocardial ischemia induces abnormal platelet Figure2. Platelet factor4 levels in plasmacollected at rest, during peak pacing and after recovery (geometric mean ::!: SEM) show no significant change during pacing-induced ischemia. Symbols and abbreviations as in Figure I.
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activation in the coronary circulation. The importance of this issue is that enhanced platelet aggregation in the coronary circulation could impede blood flow in atherosclerotic coronary arteries, resulting in further ischemia. Furthermore, thromboxane B2 generation caused by aggregated platelets may aggravate myocardial ischemia by inducing coronary vasoconstriction. Most important, platelet activation and fibrin formation in the coronary circulation could induce coronary thrombosis. resulting in myocardial infarction. Effect of pacing-induced ischemia on thromboxane B 2 levels. This issue has become controversial. however, because recent studies of the effect of pacing-induced ischemia on platelet activation in the coronary circulation have produced confl icting results. Lewy et al. (10) first reported in 1980 that thromboxane 8 2 levels were elevated in the coronary sinus blood of several patients during pacing-induced ischemia. Subsequently. other investigators (11,27) observed increased thromboxane 8 2 release in patients with coronary artery disease during pacing-induced ischemia. Recently. Martin e[ al. (28) observed positive transmyocardial thromboxane 8 2 gradients in 8 of 18 patients after pacing but in none during pacing. Lastly, Rubenstein et al. (29) reported significant transmyocardial release of beta-thromboglobulin Figure 4. Thromboxane B! levels in plasma collected at rest. during peak pacing and after recovery (geometric mean ± SEM) were not significantly elevated during pacing-induced ischemia. Symbols and abbreviations as in Figure I. I--PACING-I
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NICHOLS ET AL. Pl.ATEL ET ACTIVATION IN THE CORONARY CIRCULATION
JACC Vol. 10, No. I July 1987:40-5
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NICHOLS ET AL. PLATELET ACTIVATION IN THE CORONARY CIRCULATION
JACC Vol. 10. No. I July 1987:40-5
in patients with coronary artery disease studied at rest, but other authors (30,31) reported that beta-thromboglobulin levels are not elevated in coronary sinus blood samples in similar patients.
and suggest that pacing-induced ischemia does not activate platelets or cause fibrin formation. Although the number of patients studied was small, the combined test of significance based on all four assays enhanced the statistical power of this result. Levels of jibrinopeptide A in the coronary circulation during acute myocardial ischemia have not been reported previously. Two recent studies (30,31) have described betathromboglobulin levels in the coronary sinus blood of patients during pacing-induced myocardial ischemia. Thaulow (30) reported that these levels were not elevated in patients with pacing-induced ischemia, but were inexplicably elevated in patients without ischemia during pacing. Verheught et al. (31) reported that they were not elevated at rest or during pacing-induced ischemia in patients given 5,000 units of heparin before catheterization. In both of these studies, blood samples were collected nonselectively from the coronary sinus; with such sampling it is possible that an increased concentration of a substance released from an area of ischemia could be diluted by blood draining from a nonischemic region. To minimize this problem, in the present study we selected patients with lesions of the proximal left anterior descending artery and selectively catheterized the great cardiac vein, which drains the venous effluent of the anterior descending coronary artery. This technique should ensure that venous blood was directly sampled from the ischemic left ventricular segment without dilution by venous effluent from the nonischemic segments. To detect possible in vivo platelet activation in the present study, two platelet proteins in addition to thromboxane B2 were measured. Determination of both platelet factor 4 and beta-thromboglobulin levels in each sample is useful for distinguishing in vitro from in vivo platelet release occurring during collection and processing of blood samples (32). In previous studies, only one platelet protein assay was performed, raising the possibility that artifactual platelet activation was undetected. The observation that jibrinopeptide A and platelet factor 4 levels were slightly, but significantly, higher in the great cardiac vein and the aorta than in the right atrium raises the possibility that they were continuously released into the coronary venous effluent or released from the lungs. However, the magnitude of the elevation was slight and further studies will be necessary to distinguish intrapulmonary from intracoronary release. Recently, Mant et al. (33) presented data, obtained with heparin-filled catheters, which demonstrate that platelet factor 4 and beta-thromboglobulin levels are not elevated at rest in coronary sinus blood of patients with coronary artery disease; other investigators (30,31) reported similar findings. Summary and clinical implications. Our study demonstrates that pacing-induced ischemia does not cause platelet activation or fibrin formation in blood draining ischemic myocardial segments. The implication of our study is that
44
Fibrin formation and platelet aggregation on catheter surfaces. In all of these studies, blood samples were collected from the coronary sinus and aorta with conventional woven Dacron cardiac catheters. We have studied (12) the effect of blood contact with catheter surfaces on levels of fibrinopeptide A, platelet factor 4, beta-thromboglobulin and thromboxane B2 in blood samples withdrawn through cardiovascular catheters. We found that blood collected through woven dacron catheters showed artifactual elevation of these levels as a result of fibrin formation and platelet aggregation on the surfaces of the catheters. Progressive elevation of fibrinopeptide A and platelet proteins was observed while the catheters remained in the venous or arterial circulation, particularly if multiple blood samples were collected through the catheters. These observations may explain why elevated thromboxane B2 levels were observed in previous studies in both aortic and coronary sinus blood during and after pacing (l0, II ,27).
Role of heparin-bonded catheters for collecting blood samples. In the present study, heparin-bonded catheters were used for collection of blood samples from the great cardiac vein and aorta. We previously found (l2) that collection of blood samples through such catheters eliminated spurious elevation of fibrinopeptide A, platelet factor 4, beta-thromboglobulin and thromboxane H2 caused by fibrin formation and platelet aggregation on catheter surfaces. Scanning electron microscopy revealed fibrin strands and platelet aggregates on the surfaces of conventional catheters, but not on catheters with heparin-bonded surfaces. The passivating effect of heparin bonding was shown to last for > 30 minutes, which is a suitable time for completion of an interventional pacing study. However, elevation of the fibrinopeptide A level was consistently observed after percutaneous insertion of vascular sheaths. In the present study, multiple vascular sheaths were inserted, which accounts for the elevated baseline level of fibrinopeptide A. In both studies, the fibrinopeptide A levels were noted to decline gradually over the ensuing 20 to 30 minutes.
Effect of ischemia on fibrinopeptide A and platelet protein levels. In the present study, mean levels of fibrinopeptide A, platelet factor 4, beta-thromboglobulin and thromboxane H2 in the great cardiac vein during pacinginduced ischemia did not differ from coronary sinus levels measured at rest or in the recovery period. Furthermore, significant transmyocardial gradients of these levels were not observed at rest, during pacing-induced ischemia or in the recovery period after pacing. These data indicate that pacing-induced ischemia does not cause the release of detectable fibrinopeptide A, platelet factor 4, beta-thromboglobulin or thromboxane H2 into the coronary circulation
45
JACC Vol. 10. No. July 1987:40-5
NICHOLS ET AI.. PLATELET ACTIVATION IN THE CORONARY CIRCU LATION
stress-induced ischemia itself doe s not activate the coagulation system in the coronary circulation . Thu s, pacinginduced ischemia will not be a useful model for stud ying intracoronary platelet activation or fibrin formation associated with spontaneous myocardial ischemia. The mech anism of pacing-induced angina probabl y differs considerably from the mechanism of spont aneous angina occurring at rest. Consistent with this observation is the recent report of Fitzgerald et al. (34) that urinary metabolites of thromboxane were acutely increa sed in patients with unstable angina during chest pain, but were not increased in patient s with stable angina after exercise-induced ischemia.
13. Seldinger SI. Catheter replaceme nt of the needle in percutaneous arteriography: a new techn ique. Acta Rad iol 1953;39:368-70.
We acknowledge the invaluable techni cal ass istance of Betty Grossman. who performed the fibrinopeptide A, platelet factor 4 and beta-thromboglobulin assays. and we thank Leonard L. Norbert for expert preparation of this manuscript.
14 . O' Brian KP. Higgs LM . Glancy DL , Epstein SE . Hemod ynam ic acco mpaniments of angin a: a co mpar ison during angina induced by exercise and by atrial pacing. Circulation 1969;39:735-43 . 15. Parker 10. Chiong MA . West RO. Case RB . Sequential alterati ons in myocardial lactate metaboli sm, ST seg ments, and left ventricul ar function during angina induced by atrial pacing. Circulation 1969;40: 11 3- 31. 16. Nossel HL. Yudelman I, Canfield RE. et al. Measurement of fibrinopeptide A in human blood. 1 Clin Invest 1974;54:43-53. 17. Kaplan KL. Owen J . Radio immuno assay of platelet factor 4 . Methods Enzymol 1982 ;84:83- 92 . 18. Kaplan KL. Owen 1. Radioimmun oassay of beta-thromboglobulin . Methods Enzymol 1982;84:93-102. 19 . Marboch EP. Weil MH. Rapid enzym atic measurement of blood lactate and pyruvate. Clin Chern 1967;13:314-20. 20 . Jackson G. Atkinson L. Clark M, Crook B, Armstrong P. Oram S. Diagnosis of coronary artery disease by estimation of coronary sinus lactate . Br Heart J 1978;40 :979-83. 2 1. Sokal RR. Rohlf FJ. Biometr y. 2nd ed . San Francisco: WH Freeman , 1981:779- 82.
References I. DeWood MA, Spores J. Notske R. et al. Prevalence of total co ronary artery occlusion durin g the early hours of transmural myocardial infarction. N Engl J Med 1980 ;303:897-902. 2. Rentrop P, Blanke H, Karsch KR , Kaiser H, Kostering H. Leitz K. Selecti ve intracoron ary thrombolysis in acute myocardial infarction and unstable angina pectori s. Ci rculation 1981:63:307-17 . 3. Kennedy JW , Ritchie JL. Davis KB, Fritz JK . Western Washington randomi zed trial of intracoronary strep tokin ase in acute myocardi al infarction . N Engl J Med 1983;309 : 1477 - 82. 4 . The TIMI Stud y Group . The thrombol ysis in myocardial infarction (T IM/) trial: phase I findings . N Engl J Med 1985;312:932-6. 5. Mombelli B, 1m Hoff V, Haeberl i A, Straub PW. Effect of heparin on plasma fibrinopeptid e A in patients with acute myocardial infarction . Circulation 1984;69:684 - 9 . 6. O'Brien JR, Etherington MD. Shuttleworth RD. Caldwell WHo Platelet function in acute myocardi al infarction patients compared with co ntrols. Thromb Haemost 1980;44:96-9 . 7. Eisenberg PR, Sherman LA , Schectman K. Perez J. Sobel BE. Jaffe AS . Fibrinopeptide A: a marker of acute coronar y thrombosi s. Circulation 1985;71:9 12- 8 8. Nichols AB. Owen J. Kaplan KL. Sciacca RR. Cann on PJ, Nossel HL. Fibrinopeptide A. platelet factor 4 . and beta-thromboglobul in levels in co ronary heart disease . Blood 1982;60:650-4 . 9 . Marcella 11, Nichol s AB , Johnson LL. et al. Exercise- induced myocardial ischemia in patient s with coronary artery disease: lack of evidence for platelet activation or fibrin formation in peripheral venous blood . J Am Coil Cardi ol 1983;1:1185-93. 10. Lewy RI. Weiner L. Walinsky P. Lefer AM , Silver MJ. Smith JB . Thr omboxane release durin g pacing-induced angina pectoris: possible vasoconstrictor influence on the coronary vasculature. Circulation 1980;61: 1165- 7 1. II. Mehta J, Mehta P. Feldman RL, Horalek C. Thr omboxane release in coro nary artery disease : spontaneous versus pacing-induced angina . Am Heart J 1984;107;286-92 . 12. Nichols AB, Owen I , Gro ssman BA, Marcella 11. Fleisher LN. Lee MM . Effect of heparin bondin g on catheter-induced fibrin formation and platelet activation . Circulation 1984 ;70:843-50.
22. Sobel M, Salzman EW . Davies GC. et al. Circulating platelet products in unstable angina. Circulat ion 198) ;63:300 - 6. 23. Smitherman TC , Milam M . Woo 1. Willerson IT, Frenkel EP . Elevated beta-thromb o-globul in in peripheral venous blood of patients with acute myocardial ischemia: direct evidence for enhan ced platelet reactivity in vivo. Am J Card io! 1981 ;48:395-402. 24. Hirsh PD. Hillis LD . Campbell WB. Firth BG. Willerson IT. Release of prostaglandins and thrornboxane into the coronary circulation in patients with ischemic heart disease. N Engll Med 1981;304:685- 90. 25. Mehta J . Mehta P, Pepine CJ . Platelet agg regation in aortic and coro nary venous blood in patient s with and without coronary disease . 3. Role of tachycardia stress and propranolol. Circulation 1978;58:881-6. 26. Gall ino A, Haeberl i A, Bauer HR, Straub PW. Fibrin format ion and platelet aggregation in patient s with severe coronary artery disease : relationship with the degree of myocardial ischemia. Circulation 1985;72: 27- 30. 27. Tada M. Kuzuya T. Inoue M. et al. Elevation of thromboxane B2 levels in patients with classic and variant angina pectoris. Circulation 1981:64: 1107-15. 28 . Martin Jl. , Wilson JR, Burch JW, et al. Effect of atrial pacing on intracoronary thromboxane production in coronary artery disease . J Am Coli Cardiol 1983; I:1194- 200. 29. Rubenstein MD , Wall RT, Bairn DS, Harrison DC . Platelet acti vation in cl inical coro nary artery disease and spasm. Am Heart J 1981;102: 363-8. 30. Thaulow E. Effects induced on blood platelets in ischemi c and nonischemic myocardium. Am 1 Cardiol 1983 ;52:466-9 . 31. Verheugt FW. Serru ys PW, van Vliet H, Spijkers A, Hugenh oltz PG. lntracoronar y platelet release in patients with and without coronary artery disease . Thromb Haemost 1983 ;49:28-31. 32. Kaplan KL, Owen J . Plasma levels of bcta-thromboglobulin and platelet factor 4 as indices of platelet activation in vivo. Blood 1981 ;57: 199- 202. 33. Man! Ml, Kappagoda CT , Taylor RF, Quinl an IE . Tran scorona ry platelet activation and consumption in coronary artery disease (CAD): studies at rest (abstr). Blood I984 ;64(suppl ):249a . 34 . Fitzgerald D1. Roy L. Catell a F. Fitzgerald GA . Platelet activation and unstable coronary disease . N Engll Med 1986;315:983-9 .