Individual lytic efficacy of recombinant tissue plasminogen activator in an in vitro human clot model: rate of "nonresponse".

Objectives Recombinant tissue plasminogen activator (rt-PA) is a lytic medication widely used in the emergency department to treat acute thrombotic disorders such as ischemic stroke and myocardial infarction. It is known in the clinical use of this drug that it can be less effective in approximately 25% of individuals receiving such treatment. However, there are no data on the variation of lytic efficacy of rt-PA in decreasing individuals' clot size over time. In this study, in vitro lytic efficacy was determined by measuring the decrease in clot diameter after 30 minutes of drug exposure. The authors sought to explore whether there are individuals who do not respond to this lytic therapy and to estimate the rate of nonresponse. Methods Human whole blood clots were made from blood drawn from 22 adult volunteers. The only exclusion criterion was the use of aspirin within 72 hours of the blood draw. Blood clots were allowed to spontaneously form at room temperature and were then incubated at 37°C for 3 hours to ensure complete clot retraction. Sample clots from the same individuals were then exposed to human fresh-frozen plasma (hFFP) control or rt-PA in hFFP (rt-PA) at a concentration of 3.15 μg/mL. All clots were exposed at 37°C for 30 minutes, and clot diameter was measured as a function of time, using a microscopic imaging technique. The fractional clot loss (FCL), which is the percentage decrease in clot diameter at 30 minutes, was used as a measure of lytic efficacy. Results Means with standard deviation (SD) FCL values were 8.6% (±3.0%) for control and 20.6% (±9.3%) for rt-PA–treated clots. The mean (±SD) difference in FCL values was 12.0% (±8.8%) and was significant (p < 0.05, paired t-test). Five of the 22 subjects (23%) were “rt-PA nonresponders,” in that their FCL (rt-PA) values fell within that of the FCL control values. Conclusions Overall, rt-PA does not produce clot lysis in vitro in clots from a substantial minority of the population, likely due to individual variations in clot composition and structure. Resumen Eficacia Litica Individual del Activador Tisular de Plasminogeno Recombinante en un Modelo de Coagulo Humano in Vitro: El porcentaje de “No Respuesta” Objetivos El activador tisular de plasminogeno recombinante (Recombinant tissue plasminogen activator o rt-PA) es una medicacion litica utilizada ampliamente en el servicio de urgencias (SU) para tratar enfermedades tromboticas agudas como el ictus isquemico o el infarto de miocardio. El uso clinico de este medicamento pone en evidencia que puede ser menos efectivo en aproximadamente un 25% de los individuos que lo reciben. Sin embargo, no hay datos sobre la variacion de la eficacia litica de rt-PA en la disminucion del tamano del coagulo en los individuos a lo largo del tiempo. Es este estudio, la eficacia litica in vitro se determino midiendo el descenso en el diametro del coagulo tras 30 minutos de exposicion al medicamento. Se exploro si hay individuos que no responden a esta terapia litica, y se estimo el porcentaje de no respuesta. Metodologia Se hicieron coagulos sanguineos humanos con sangre extraida de voluntarios tras la aprobacion del protocolo de estudio por el comite etico de investigacion. El unico criterio de exclusion fue la toma de aspirina en las 72 horas previas a la extraccion de sangre. Los coagulos de sangre de los 22 adultos voluntarios se formaron espontaneamente a temperatura ambiente y despues se incubaron a 37°C durante 3 horas para asegurar la retraccion completa del coagulo. Los coagulos de la muestra de un mismo individuo se expusieron posteriormente a plasma fresco humano congelado (hFFP) control, o a rt-PA en hFFP a la concentracion de 3,15 μg/ml. Todos los coagulos se expusieron a 37°C durante 30 minutos. El diametro del coagulo se midio en funcion del tiempo usando tecnicas de imagen microscopicas. La fraccion de coagulo perdida (fractional clot loss (FCL)), que es el porcentaje que disminuye el diametro del coagulo en 30 minutos, se uso como medida de la eficacia litica. Resultados Las medias con desviacion estandar (DE) de los valores de FCL fueron 8,6% (DE ±3,0%) para el grupo control y 20,6% (DE ±9,3%) para los coagulos tratados con rt-PA. La diferencia media en los valores de FCL fue del 12,0% (DE ±8,8%) y fue significativa (p < 0,05, t-test para datos apareados). Cinco de los 22 sujetos (23%), fueron “no respondedores a rt-PA,” ya que sus valores FCL (rt-PA) se encontraron dentro de sus valores de FCL control. Conclusiones En general, el rt-PA no funciona para una minoria considerable de la poblacion, probablemente debido a variaciones individuales en la composicion y estructura del coagulo.