Abstract: Preinfarction angina and early reperfusion of the infarct-related artery are major determinants of reduced infarct-size in patients with acute myocardial infarction. The beneficial effects of preinfarction angina on infarct size have been attributed to the development of collateral vessels and/or to post-ischemic myocardial protection. However, recently, a relation has been found between prodromal angina, faster coronary recanalization, and smaller infarcts in patients treated with rt-PA: those with preinfarction angina showed earlier reperfusion (p = 0.006) and a 50% reduction of CKMB-estimated infarct-size (p = 0.009) compared to patients without preinfarction angina. This intriguing observation is consistent with a subsequent observation of higher coronary recanalization rates following thrombolysis in patients with prodromal preinfarction angina compared to patients without antecedent angina. Recent findings in dogs show an enhanced spontaneous lysis of platelet-rich coronary thrombi with ischemic preconditioning, which is prevented by adenosine blockade, suggesting an antithrombotic effect of ischemic metabolites. Understanding the mechanisms responsible for earlier and enhanced coronary recanalization in patients with preinfarction angina may open the way to new reperfusion strategies.
Abstract: A limitation of current fibrinolytic drugs is the procoagulant activity induced by their administration. TNK is a mutant of tissue plasminogen activator (t-PA) with high fibrin specificity, resistance to plasminogen activator inhibitor-1 and slow plasma clearance, which is administered in a single intravenous bolus. In this study we investigated the procoagulant effect of TNK-t-PA compared to streptokinase, rt-PA or no thrombolysis. Twenty-nine patients with acute myocardial infarction, treated within 6 hours of symptom onset with 1.5 MU streptokinase over 1 hour (n = 12), 100 mg rt-PA in 1.5 hours (n = 12) or 30-40 mg TNK-t-PA in 15 s (n = 5), were studied and compared to 7 patients with contraindications to thrombolysis (control group). All patients received a similar i.v. heparin regimen for at least 24 hours. Blood samples were drawn before the start of treatment (time 0) and after 2 hours. Thrombin formation was assessed as plasma concentrations of thrombin-antithrombin complex (TAT). The four patient groups did not differ significantly in age, sex, time to treatment, infarct location, and TAT values at time 0 (mean value +/- standard error of the mean 9 +/- 2 micrograms/l). Mean TAT levels at 2 hours were 26 +/- 6 micrograms/l in streptokinase treated patients (p = 0.005 vs time 0), 21 +/- 4 micrograms/l in rt-PA treated patients (p < 0.05 vs time 0), 5 +/- 0.6 micrograms/l in TNK treated patients, and 4 +/- 0.4 micrograms/l in controls (NS vs time 0 for TNK and controls). In conclusion, our data suggest that, in patients with acute myocardial infarction, bolus TNK-t-PA, unlike streptokinase or rt-PA infusions, is devoid of procoagulant effects, evaluated 2 hours after its administration.
