Not All Heart Attacks Are Created Equal

Not All Heart Attacks Are Created Equal

The type of heart attack can control the prognosis very much. A heart attack can be recognized by clinical features of chest pain or shortness of breath, ECG or cardiac imaging findings and elevated biochemical markers including the cardiac troponin, the so-called “heart attack blood test”.

The development of ever more sensitive and heart tissue specific cardiac bio markers and more sensitive imaging techniques now allows for detection of very small amount of heart damage or myocardial necrosis. The use of high sensitive troponin assays allows for the detection of low levels of troponin even in normal healthy subjects. The majority of cardiac troponin is inside the cardiac cell. The release of cardiac troponin into the bloodstream can involve several mechanisms including cell necrosis, formation of blebs or leakage of the cardiac cell membrane or release of enzymes that can break down troponin. Sometimes rapid heartbeat (tachycardia) or transient myocardial ischemia (angina) can release intact cardiac troponin into the blood.

It is recognized that in the presence of the clinical history suggestive of acute coronary syndrome and ECG abnormality, an elevated troponin result greater than the 99th percentile compared to a reference group is indicative of myocardial necrosis. However, what is more significant are those serial troponin measurements can help establish whether the patient’s chest pain is of cardiac origin and whether the patient is having a true myocardial infarction. The patients presenting in the emergency room with chest pain do not all have a myocardial infarction. A higher sensitivity troponin test can help differentiate earlier and more accurately whether the patient is having a myocardial infarction or not. Consequently, serial negative troponin tests have a very good predictive value attesting that these patients can be discharged safely and have a good outcome post discharge. The troponin measurements must be interpreted in the context of the probability of coronary artery disease.

Not all heart attacks are created equal

Because of the new techniques for detection of MI and the ever evolving treatment of MI, the WHO (World Health Organization) has been updating the universal definition and classification of MI recognizing the diverse conditions that cause a heart attack. The diagnosis of MI requires evidence of myocardial necrosis in a clinical setting consistent with acute myocardial ischemia. It necessitate the detection of a RISE and/ or FALL in cardiac troponin with at least one value above the 99th percentile upper reference limit AND at least one of the following: 1) symptoms of myocardial ischemia (chest pain, shortness of breath…), 2) new ECG changes or development of a Q wave, 3) imaging evidence of MI or new wall motion abnormality (MRI, echo or nuclear), 4) a clot or thrombus by angiogram. Understanding that different types of MI are treated differently, 5 types of MI have been recognized.

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