What Causes Heart Attack?
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It is so unfortunate that your partner had to suffer so much because of the cardiac problem. I will explain you in following paragraphs that how it happens.
1. Whenever a heart attack occurs, most common mechanism is formation of a clot in one of the blood vessels (arteries) supplying the heart. This clots totally occludes the artery and the blood supply to concerned muscle region is totally stopped. This clots almost always forms on a pre-existing cholesterol plaque. In studies, it has been found that 85% of such clots (causing heart attack) forms on plaques which were causing less than 60% stenosis or obstruction prior to clot formation.
2. Second fact is that whatever stress tests we have designed are meant to detect the significant plaques (i.e. those causing ~70% obstruction or more). Hence when a stress test (like TMT, stress ECHO or a stress thallium) comes out to be negative or normal, it only means that on that given day the individual does not have a significant plaque causing more than 70% obstruction. The stress test in no way can predict the occurrence of a future heart attack, nor a normal stress test gives any kind of assurance about non-occurrence of future attack. Moreover, these tests, at best, has accuracy of ~85-90%.
3. Unfortunately, medical sciences as yet are not able to device a test which can predict the formation of clot on a plaque in blood vessel.
4. I hope, by now, it is clear to you that the cardiac arrest suffered by your partner was only a manifestation of a massive heart attack which can not be predicted by any tests. The damaged caused to the heart happened during the process of that event only which led to cardiac arrest.
5. All preventive measures like cessation of smoking, avoiding fatty meals, daily exercise and good compliance to drug lower your risk of plaque formation but do not 100% prevent it.
6. 25%-30% left ventricular function means that his heart is pumping with a lower capacity. This results when heart muscle is damaged by process of heart attack. Normal LV function is ~55%-70%. Some part of it may recover over a period of time by use of guideline based therapy.
7. None can exactly predict the life of a given patient. However lower pumping capacity of left ventricle is a bad prognostic indicator. People have done well with guidelines based therapy even after massive heart attacks. Stick to the treatment prescribed by your doctor. Try to live a stress free life.
Hope this provides some insight. Feel free to discuss further.