ISSN:0009-7322    

出版商:OVID    

年代:1991

数据来源: OVID

ISSN:0009-7322    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

BackgroundHeparin is of limited value as an antithrombotic drug in the presence of platelet activation and residual thrombus. Greater anticoagulant activity can be achieved in vivo with more specific thrombin inhibitors. Heparin may also increase the risk of bleeding by an effect on platelets that is independent of its thrombin inhibitory activity.Methods and ResultsThe pharmacodynamic and pharmacokinetic effects of a novel thrombin inhibitor, argatroban, were examined alone and in combination with aspirin in normal male volunteers. Argatroban induced a dose-dependent prolongation of the thrombin time and the activated partial thromboplastin time (aPWT). aPTT had returned to its pretreatment value 1 hour after stopping the infusion of argatroban. Six male subjects received an infusion of 1 μg/kg/min argatroban after the administration of two doses of 162.5 mg aspirin or a matching placebo. At this dose, aspirin decreased serum thromboxane B2 by a mean of 99% and prolonged the bleeding time (230±52 versus 320±f113 seconds,p< 0.01). Argatroban given alone increased thrombin time by 454±18% and aPTT by 160±3%. Steady-state plasma concentrations were achieved at 1 hour and declined exponentially with an elimination half-life of24±4 minutes. Neither the anticoagulant effects nor the plasma concentrations of argatroban were altered by aspirin. Furthermore, argatroban did not increase the bleeding time when given alone and did not further prolong the bleeding time when combined with aspirin.ConclusionThe combination of aspirin and argatroban may prove to be an effective therapeutic strategy in the prevention of coronary thrombosis.

ISSN:0009-7322    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

BackgroundExperimental studies have demonstrated that intracoronary platelet aggregation and thrombus formation may induce marked vasoconstriction of epicardial arteries with endothelial injury.Methods and ResultsTo examine the effects of intracoronary thrombus formation on coronary vasomotor tone of human epicardial arteries in vivo, we studied 15 patients who developed intracoronary thrombi adherent to the guide wire during balloon dilatation. Epicardial artery luminal area was evaluated by quantitative coronary angiography proximal and distal to the site of intracoronary thrombus formation and in a reference vessel before and after thrombus formation as well as after intracoronary injection of 0.2–0.3 mg nitroglycerin. All artery segments distal to the site of thrombus formation showed vasoconstriction with a luminal area reduction of −27.4±17.1% (p< 0.001), whereas proximal vessel segments and reference vessels not manipulated during percutaneous transluminal coronary angioplasty did not demonstrate any significant luminal area changes during thrombus formation. Angiographic measurements after advancing the guide wire with the adherent thrombus (performed in six of the 15 patients) revealed in all patients that vasoconstriction did develop at a new site distal to the thrombus with persistence of the initial vasoconstriction now residing proximal to the thrombus. Thus, there was a sequential association between thrombus formation and subsequent distal vasoconstriction. Intracoronary injection of nitroglycerin abolished the thrombus-induced vasoconstriction. No significant luminal area changes were observed in 20 patients without angiographic evidence of intracoronary thrombus formation.ConclusionsIntracoronary thrombus formation during percutaneous transluminal coronary angioplasty causes focal vasoconstriction of epicardial arteries in patients with coronary artery disease. Although caution must be advised in the extrapolation of this phenomenon, which was observed in a manipulated artery during coronary angioplasty, the vasoconstrictor response to intracoronary thrombus formation in vivo may play an important role in the dynamic mechanisms of acute coronary heart disease syndromes.

ISSN:0009-7322    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

BackgroundThe efficacy of aspirin for prevention of thrombotic graft occlusion after coronary artery bypass grafting (CABG) depends both on the dosage and time window of administration. Early and late graft patency were therefore assessed in a prospective, double-blind, randomized, placebo-controlled trial of aspirin, 324 mg daily, given within 1 hour of CABG.Methods and ResultsAngiographic graft patency was determined at 1 week (231 patients) and year (219 patients) after CABG. The early vein graft occlusion rate was 1.6% on aspirin and 6.2% on placebo (p= 0.004), and late graft occlusion rate was 5.8% on continued aspirin and 11.6% on placebo (p= 0.01). New graft occlusion between 1 week and 1 year was less common in patients on aspirin than on placebo (4.3% versus 7.4%,p= 0.013). The protective effect of aspirin against occlusion persisted in most subgroups of graft type, graft flow, diameter of recipient artery, location of grafted artery, and endarterectomy. Mean chest tube blood loss for the first 24 hours was 571 ml for the aspirin group and 563 ml for the placebo group. Red cell transfusion requirements were 902 ml in the aspirin group and 934 ml in the placebo group (p=NS). The reoperation rate was 4.8% in the aspirin group and 1% in the placebo group (p= 0.1).ConclusionsImmediate postoperative administration of aspirin (324 mg) improves early graft patency and, with continued usage, protects against further occlusion up to 1 year after CABG. Postoperative blood loss was similar in the two groups; however, aspirin was associated with a nonsignificant higher rate of reoperation.

ISSN:0009-7322    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

BackgroundThis study addressed the need for heparin administration to be continued for more than 24 hours after coronary thrombolysis with recombinant tissue-type plasminogen activator (rt-PA).Methods and ResultsA total of 241 patients with acute myocardial infarction were treated with100 mg rt-PA and a bolus of 5,000 units i.v. heparin followed by 1,000 units/hr i.v. heparin for 24 hours. At 24 hours, 202 patients were randomized to continue intravenous heparin therapy (n=99) in full dosage or to discontinue heparin therapy and begin an oral antiplatelet regimen of aspirin (300 mg/day) and dipyridamole (300 mg/day) (n=103). On prospective recording, there were no differences in the pattern of chest pain, reinfarction, or bleeding complications. Coronary angiography on cardiac catheterization at 7–10 days showed no differences in patency of the infarct-related artery. The proportion of patients with total occlusion (TIMI grade 0–1) of the infarct-related artery was 18.9% in the heparin group and 19.8% in the aspirin and dipyridamole group. In the patients with an incompletely occluded infarct-related artery, the lumen was reduced by 69±2% of normal in the heparin group and 67±2% in the aspirin and dipyridamole group. Left ventricular function assessed on cardiac catheterization and radionuclide study at day 2 and at 1 month showed no differences between the two groups. Left ventricular ejection fraction on radionuclide ventriculography at 1 month was 52.4± 1.2% in the heparin group and 51.9±1.2% in the aspirin and dipyridamole group.ConclusionsWe conclude that heparin therapy can be discontinued 24 hours after rt-PA therapy and replaced with an oral antiplatelet regimen without any adverse effects on chest pain, reinfarction, coronary patency, or left ventricular function.

ISSN:0009-7322    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

BackgroundThe efficacy of aspirin for prevention of thrombotic graft occlusion after coronary artery bypass grafting (CABG) depends both on the dosage and time window of administration. Early and late graft patency were therefore assessed in a prospective, double-blind, randomized, placebo-controlled trial of aspirin, 324 mg daily, given within 1 hour of CABG.Methods and ResultsAngiographic graft patency was determined at 1 week (231 patients) and 1 year (219 patients) after CABG. The early vein graft occlusion rate was 1.6% on aspirin and 6.2% on placebo (p= 0.004), and late graft occlusion rate was 5.8% on continued aspirin and 11.6% on placebo (p= 0.01). New graft occlusion between 1 week and 1 year was less common in patients on aspirin than on placebo (4.3% versus 7.4%,p= 0.013). The protective effect of aspirin against occlusion persisted in most subgroups of graft type, graft flow, diameter of recipient artery, location of grafted artery, and endarterectomy. Mean chest tube blood loss for the first 24 hours was 571 ml for the aspirin group and 563 ml for the placebo group. Red cell transfusion requirements were 902 ml in the aspirin group and 934 ml in the placebo group (p=NS). The reoperation rate was 4.8% in the aspirin group and 1% in the placebo group (p= 0.1).ConclusionsImmediate postoperative administration of aspirin (324 mg) improves early graft patency and, with continued usage, protects against further occlusion up to 1 year after CABG. Postoperative blood loss was similar in the two groups; however, aspirin was associated with a nonsignificant higher rate of reoperation.

ISSN:0009-7322    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

BackgroundTo quantify the duration of postexercise hypotension at different exercise intensities, we studied six unmedicated, mildly hypertensive men matched with six normotensive controls.Methods and ResultsEach subject wore a 24-hour ambulatory blood pressure monitor at the same time of day for 13 consecutive hours on 3 different days. On each of the 3 days, subjects either cycled for 30 minutes at 40% or 70o maximum Vo2 or performed activities of daily living. There was no intensity effect on the postexercise reduction in blood pressure, so blood pressure data were combined for the different exercise intensities. Postexercise diastolic blood pressure and mean arterial pressure were lower by 8±1 (p< 0.001) and 7±1 mm Hg (p< 0.05), respectively, than the preexercise values for 12.7 hours in the hypertensive group. These variables were not different before and after exercise in the normotensive group. Systolic blood pressure was reduced by 5±1 mm Hg (p< 0.05) for 8.7 hours after exercise in the hypertensive group. In contrast, systolic blood pressure was 5±1 mm Hg (p< 0.001) higher for 12.7 hours after exercise in the normotensive group. When the blood pressure response on the exercise days was compared with that on the nonexercise day, systolic blood pressure (135 + 1 versus 145± 1 mm Hg) and mean arterial pressure (100±1 versus 106±1 mm Hg) were lower (p< 0.05) on the exercise days in the hypertensive but not in the normotensive group. We found a postexercise reduction in mean arterial pressure for 12.7 hours independent of the exercise intensity in the hypertensive group. Furthermore, mean arterial pressure was lower on exercise than on nonexercise days in the hypertensive but not in the normotensive group.ConclusionThese findings indicate that dynamic exercise may be an important adjunct in the treatment of mild hypertension.

ISSN:0009-7322    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

BackgroundTwo catheter electrode systems were compared for delivering radiofrequency current for ablation of the atrioventricular junction. Seventeen patients with drug-resistant supraventricular tachyarrhythmias were studied.Methods and ResultsA 6F or 7F catheter with six or eight standard electrodes (1.25 mm wide, 2.5-mm spacing) was used in the first seven patients (group 1). A 7F quadripolar catheter with a large-tip electrode (4 mm long; surface area, 27 mm2) was used in the final 10 patients (group 2). Both ablation catheters were positioned to record a large atrial potential and a small but sharp His bundle potential from the distal bipolar electrode pair. Radiofrequency current was applied between a large skin electrode on the left posterior chest and either 1) each individual electrode on the standard-tip electrode catheter at 40 V (group 1) or 2) the large-tip electrode at 50–60 V (group 2). Radiofrequency current was limited to 40 V in group patients because of the strong potential for an early impedance rise when higher voltage is applied through tandard electrodes. Complete atrioventricular block was achieved in six of seven group 1 patients and all 10 group 2 patients. A junctional escape rhythm followed ablation in five or six group 1 patients (mean cycle length, 1,066±162 msec) and eight of 10 group 2 patients (mean cycle length, 1,281±231 msec). Atrioventricular block was produced in a mean of 4.7±4.6 radiofrequency current applications delivered over a period of 42±45 minutes using thelarge-tip electrode (group 2) compared with 46±22 applications using standard electrodes (15.9±10.2 applications delivered through the standard-tip electrode) over a period of 147±59 minutes (group 1). For the application producing atrioventricular block, the large-tip electrode used higher voltage (58±17 versus 38 + 5 V, p <0.03) and had lower impedance (103±22 versus 148 + 40Qk, p <0.01), resulting in greater power (33.0±13.0 versus 10.2 ±0.6 W, p <0.003) and shorter time to block (8±3 versus 22±3 seconds, p <0.001). Current delivery through standard electrodes was limited by an impedance rise occurring 7±7 seconds after the onset of one or more radiofrequency current applications at 10±1 W in six of seven patients. Using the large-tip electrode, an impedance rise occurred in five of 10 patients, but at 25±10 W and after 21±9 seconds. Atrioventricular block occurred before the impedance rise in three of these five patients. Complete atrioventricular block persisted in 15 of 16 patients at a mean follow-up of 8.7 months. Atrioventricular conduction returned at 1 month in one group 2 patient and was successfully ablated by a second procedure. Three group 1 patients died 0.5–2 months after ablation, and a fourth patient underwent cardiac transplantation after 10 months. Pathological examination of the heart in two of these patients showed necrosis of the atrioventricular node and origin of the His bundle, without injury to the middle or distal His bundle. All 10 group 2 patients are alive and subjectively improved after ablation.ConclusionsWe conclude that catheter-delivered radiofrequency current effectively produces complete atrioventricular block (94%) without requiring general anesthesia or the risk of ventricular dysfunction or cardiac perforation. The large-tip electrode allows a threefold increase in delivered power and markedly decreases the number of pulses and time required to produce atrioventricular block.

ISSN:0009-7322    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

BackgroundConventionally, monomorphic sustained ventricular tachycardia in patients with remote myocardial infarction is believed to originate from the subendocardium. In a previousstudy, we demonstrated that electrical activation patterns during ventricular tachycardia occasionallysuggest a subepicardial rather than subendocardial reentry.Methods and ResultsThis study prospectively evaluated the functional role of the epicardium inpostinfarction ventricular tachycardia with complex intraoperative techniques including computerizedelectrical activation mapping, entrainment, observation of changes in activation patternduring successful epicardial laser photoablation, and histological study. Five of 10 consecutive patients undergoing intraoperative computerized activation mapping had 10 ventricular tachycardia morphologies displaying epicardial diastolic activation. These 10 “epicardial” ventricular tachycardias revealed the following global activation patterns: monoregional spread (two), figure-eight activation (five), and circular macroreentry (three). Entrainment of ventricular tachycardia using epicardial stimulation was successfully performed froman area of slow diastolic conduction in four tachycardia morphologies. During entrainment, global activation remained undisturbed with recordings showing a long stimulus toQRS interval, unchanged QRS morphology, and pacing capture of all components of the reentrycircuit. Neodymium:yttrium aluminum garnet laser photocoagulation was delivered duringventricular tachycardia to epicardial sites of presumed reentry. Epicardial photoablation terminatedfive of five figure-eight tachycardias, two of three circular macroreentry tachycardiasbut not the monoregional tachycardias. Electrophysiological recordings during epicardiallaser photocoagulation demonstrated progressive prolongation of ventricular tachycardia cyclelength and apparent interruption of the presumed reentrant circuit. Histological evaluationof the reentrant region (three patients) showed a rim of surviving myocardium under the epicardial surface.ConclusionsThis study suggests that 1) chronic postinfarction ventricular tachycardia may resultfrom subepicardial macroreentry, 2) slow conduction within the reentry circuit can be localizedby computerized mapping and epicardial entrainment, and 3) ventricular tachycardia interruptionby laser photocoagulation results from conduction delay and block within critical elementsof the reentrant pathway. Viable subepicardial muscle fibers may constitute the underlyingpathology.

ISSN:0009-7322    

出版商:OVID    

年代:1991

数据来源: OVID