Tuesday, November 13, 2012

Clinical utility of cardiac markers in monitoring reperfusion following thrombolytic therapy

When STEAMI occurs there is thrombus responsible for the occlusion. It can be lysed by administration of thrombolytic agents (urokinase, streptokinase, tissue plasminogen activator) or pushed downward by angioplasty. This therapy is given if the onset of chest pain is <12 hours. 

Unfortunately reperfusion can cause tissue damage a syndrome known as reperfusion-ischemic injury. Normally after thrombolytic therapy occlusion should be resolved within 90-120 minutes but sometimes upto 3 days is seen. Injury usually occurs due to sudden change in environment and mediated by increase in intracellular calcium, oxidative stress, pH, etc.

During monitoring markers during reperfusion following therapy, there must be washout of markers from the circulation if reperfusion is good. The rate of increase in cardiac biomarkers (cTnI, cTnT, Mb, CK-2) concentration after thrombolytic therapy can be assessed by frequent sampling. 

Reperfusion assessment should be done within 60-120 minute after therapy because at this time there is clot resolution and marker washout. To meet this testing of markers should be rapid. For this assessment markers should be measured prior to therapy and after therapy and then at later time usually at 60 and 90 minute.

Because of low molecular weight and its rapid turnover Mb is used to assess the myocardial perfusion after thrombolytic therapy but also other are measured. Increased CK-MB after 12 hours of therapy means failed reperfusion. Raised serum CK-MB >10 IU/L/hour over the first 2.5 hour of treatment indicates successful thrombolysis. Similarly rise in troponin in first hour after therapy indicates success of therapy. Increase in Mb 2 hr after therapy indicates success. 
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