SYSTEMIC FIBRINOLYSIS AND PLASMA VISCOSITY REDUCTION: A SECOND BENEFIT

The aim of this study on a small cohort of patients (N = 30) with acute myocardial infarction (AMI) receiving systemic streptokinase (STK) thrombolytic therapy was to measure the decrease in plasma viscosity concomitant with fibrinogen depletion.

Serial measurements of plasma viscosity, plasma fibrinogen and haematocrit were undertaken in treatment and control groups at times t = 0, 1 hour, 6 hours, 12 hours, 24 hours and daily thereafter over a period of six days. Viscosity was measured at 25°C using a Wells-Brookfield cone/plate digital viscometer, and fibrinogen determination was by the method of Clauss.

Results indicated a mean percentage drop in plasma viscosity of −17% in the STK-treated group with a maximum drop in any one patient in excess of −30%. This contrasted with a mean viscosity rise of almost +20% in the control group with a maximum rise in any one patient of almost +44%, parallelling the rise in plasma fibrinogen as an acute phase reactant.

Correlation studies between viscosity and plasma fibrinogen were strongly positive with mean r-values of 0.74 and 0.66 respectively. Interestingly, mean plasma viscosity in the STK-treated group was still reduced by −5% at 6 days post-therapy.

The conclusions drawn from these data are that the benefit of systemic STK treatment in AMI may in part be due to reduced myocardial workload and oxygen consumption at a critical time through afterload reduction, and improved collateral circulation and microcirculation consequent on the reduced plasma viscosity. Clearly there may be implications for newer tissue-specific agents which do not have a substantial systemic effect.