Cardiac interventionists have now veered around to the view that it is not sufficient to bust the big clot that produces a heart attack; ensuring that the small vessels supply blood to the heart muscle is as crucial.
When interventionists attempt to thrombolyse or bust the clot that has triggered a heart attack, in most cases pieces of the blood clot travel down the micro vessels and get lodged there, cutting off supply to that portion of the heart muscle, explains G. Sengottuvelu, consultant interventional cardiologist, Apollo Hospitals.
“If there is good micro-circulation, then there is no problem. But, in instances where there is improper flow of blood right to the end of the vessel, it has to be corrected. If we don't, then the amount of permanent damage will be higher.”
Cardiologists operate with the aim of saving as much muscle as possible after a heart attack has occurred. In an acute myocardial infarction, there is interest only in the block that caused the attack, but once that has been thrombolised it is essential to check for the myocardial blush score – to see if the blood flow has been restored.
The longer a blush lasts it means the block has not been successfully removed — that there may be blocks in the smaller vessels, he explains.
Recently, a 70-year-old man was brought to the emergency unit with a massive attack. “Even as we sent in a catheter through the hand (radially) to thrombolyse the clot, it turned out that the re-perfusion was not so smooth. The angiogram showed segments of the smaller vessels being cut off.”
Through the traditional method of passing drugs through a catheter to bust those clots, it has been proven that over 50 per cent of the drug would be washed away and a further 20-25 per cent delivered to unwanted branches of the small vessels (that have no clots).
“In effect that means that less than 20 per cent of the drug will reach the target area,” he says.
Sudhir Vaishnav, director, Asian Heart Institute, Mumbai, explains that the idea is to use a device that will prevent the microvasculature from clogging. “The flow should be brisk, and the blush should be good. The ideal, then, would be to use any equipment that will be able to deliver the drug to the site of the smaller blocks.”
Dr. Sengottuvelu's 70-year-old was lucky. The hospital had at hand a state-of-the-art device a local therapeutic infusion device, the ClearWay catheter. It has a balloon at its end that “gently weeps” the drug into the targeted area, dissolving the clot.
Typically such an Occlusion Containment Infusion (OCI) equipment removes the occlusion (block) in the vessel.
It contains the thrombus (clot) at the site itself and infuses the drug gently so that the clot dissolves, according to Dr. Vaishnav. The prognosis for the patient is also better, and saves a larger area of the heart muscle, he adds.
