Organs and Tissues vary according to their sensitivity to blockage in their blood supply.
The heart, the brain, and the kidneys are highly susceptible, getting ‘infarcted‘ within seconds to minutes after onset of ischemia; muscles and bones are relatively resistant, remaining viable even hours after ischemia has set in, provided certain conditions are met. Most other tissues are somewhere in between.
Damage to heart muscle from ischemia is called Myocardial Infarct. Damage to brain tissue differs in some respects.
The heart is a muscle, being uniform all over; damage to any part produces similar effect. The volume of damage is critical in that situation: the larger the Infarct, the more serious the consequence. In some situations, damage to some specific areas may have a more profound effect even if the volume of damage is small; for example, when the electrical circuit within the heart is damaged, or one of the valves suffers ischemia.
The brain, on the other hand, is a very heterogeneous organ; every millimeter of its landscape has a different function. As a result, the effect of ischemic damage may differ widely depending on which part of the brain is affected.
If a very large area of brain is infarcted, then the increase in size of the tissue and the pressure effects may jeopardize the life of the victim.
[caption id="attachment_384" align="aligncenter" width="300"] Infarct with some bleeding into it, called a hemorrhagic infarct[/caption]
With smaller-sized infarcts, the effect will differ greatly based on where the damage has occurred. That is why victims of brain ischemia and Infarct present with varied complaints, and some infarcts may even be silent in that they produce no effect at all.
This has major implications to success in treating a given situation; ‘Silent Infarcts‘ may accumulate over time to compromise the function over long periods of time, without the sufferer ever being aware of this. This is not very common, though it does happen a lot.
The MOST important point to be made here is that treatment of a brain stroke (or even a heart attack, for that matter) is time-critical. In the minutes that follow the blockage of a blood vessel, the response of the victim, his family, the Emergency Response Team’ at the hospital, and the Specialist, will determine how much of the tissue is salvaged. Thrombolytic Therapy, or clot-buster therapy, is now available – in specialized centers. The reason this clot-buster therapy cannot be done at smaller centers is that brain strokes are not only difficult to identify – but the Neurologist also has to be sure he is dealing with an Ischemic stroke and not the other variety – a Hemorrhagic Stroke – which accounts for about 15% of all brain strokes.
[caption id="attachment_380" align="alignleft" width="300"] Area of massive hemorrhage with mass effect and mid-line shift[/caption]
[caption id="attachment_379" align="alignright" width="300"] Thalamic hemorrhage with pressure effect on the adjacent ventricle and upper mid-brain[/caption]
For this, an emergency CT scan of the Brain is mandatory; there is no ‘clinical’ way that these can be differentiated reliably, and a mistake here can cost the patient his life. For example, if a Hemorrhagic Stroke is treated with clot-buster therapy, or even Aspirin, the hemorrhage may worsen and lead to the patient’s death.
Even if the CT scan shows there is no hemorrhage – in the early hours of the ischemic stroke, CT scan remains normal – there is another issue to be resolved. The patient should have no bleeding tendency.
If someone has had a recent bleeding, is on some treatment which blocks clotting, has had a major surgery recently, or has a known bleeding disorder, then he or she is not a candidate for clot-buster therapy.
This decision has to be taken by the treating Neurologist, hence the family should attend the ER as early as possible and provide all the information to the doctor.
There are many other details on clot-buster therapy that I will cover separately. Here I will deal with other questions about brain blood supply that I commonly come across.
Sometimes the patient has an attack – say weakness of one half of the body, or blindness in one eye – which recovers, sometimes within minutes.
In the past, this was labelled as TIA – Transient Ischemic Attack – or mini- Stroke, and much controversy surrounded this entity.
This kind of label led to a false sense of assurance among many stroke victims, and sometimes even medical professionals; because the patient recovered, it was considered a ‘false alarm’. But this can lead to serious neglect of the problem; a TIA or mini- Stroke should be dealt with exactly as a full-blown Stroke is – except that clot-buster therapy cannot be administered.
Some family members then worry about the clot still being inside, and whether a certain proposed treatment would be successful in dissolving this clot.
The answer is – in a mini-Stroke, there is no role for clot-buster therapy.
Even in full-blown Stroke, once the initial phase is over, the patient is already improving from the effects of the stroke (though this may not always be visible to the family), and at this stage also, there is no role for clot-buster therapy.
In a mini- Stroke, by definition, the clot has already moved on, or migrated and dissolved in technical parlance, and that is the reason the person improved. In some instances, the clot may remain but flow from alternate channels may restore the local blood supply and relieve the effects of ischemia. In either situation, there is no treatment to dissolve the clot.
The use of clot-buster therapy beyond the 6-hour window after the onset of stroke has been shown to worsen outcomes due to bleeding in the infarcted tissue.
Stroke Prevention strategies initiated at this stage are the only treatments available. Once an Infarct has occurred, it is not possible to reverse the process. Despite this, patients of stroke do improve after a stroke, and this happens mostly because all of the ischemic tissue does not become infarcted. That is why a stroke victim is always worse on the first day and improves over time.