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Abstract
It recently has been demonstrated that thrombolytic therapy has circadian pattern
of efficacy, as assessed by the ability to rapidly provide coronary patency. A study
of 692 patients receiving intravenous tPA and undergoing acute coronary arteriography
demonstrated a substantial diurnal pattern in patency with a peak at 8:00 pm. The
heightened tendency for a coronary artery to be opened in the evening correlates well
with the substantial tendency demonstrated in the same study and in multiple other
studies for coronary arteries to thrombose and cause myocardial infarction in the
morning hours. Circadian variations have been defined for a number of hemostatic and
physiologic factors that would predispose toward clotting in the late morning, and
converse circadian patterns have been described for a number of factors associated
with thrombolysis that would predispose towards enhanced fibrinolysis in the evening
hours. Methods by which efficacy of lytic therapy potentially could be enhanced include
development of tPA variants or adjunctive agents that eliminate the circadian nadirs
of efficacy, modification of dosage or choice of lytic agent as a function of time
of treatment, and selection between pharmacologic lysis and direct angioplasty as
a function of time of day.