Which is the most important factor that determines thrombolysis failure in STEMI ?
- Thrombus load .
- Drug efficiency
- Time delay
- Presence of a mechanical lesion
- Hemodynamic instability
Answer : 3 .(Though all 5 factors operate )
Failed thrmbolysis occur in about 40-50% after streptokinase and slightly less with TPA and TNK-TPA . Delayed arrival and late thrombolysis are most common cause of failed thrombolysis. As the time flies , the myocardium gets damaged and the intra coronary thrombus gets organised .Both these processes make delayed thrombolysis a futile exercise.
Not all STEMI patients have large thrombus burden. There need to be a critical load of thrombus for thrombolytic to be effective
Some may have a major mechanical lesion in the form of plaque fissure, prolapse and it simply blocks the coronary artery mechanically like a boulder on the road . The poor streptokinse or the rich Tenekteplace ! nothing can move this boulder .The only option here is emergency PCI .
How will you know when the patient arrives in ER with STEMI whether his/ her coronary artery is blocked with soft thrombus or hard mechanical boulder ?
It is impossible to know.That’s why primary PCI has a huge advantage. But still thrombolysis is useful as some amount of thrombus will be there in all patients with STEMI.Lysing this will provide at least a trickle of blood flow that will jeep the myocardium viable and enable us to take for early PCI.
Final message
The commonest cause for thrombolytic failure is the time of administration and the degree of underlying mechanical lesion . So it does not make sense to blame streptokinase always !
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Dr.S.Venkatesan MD 