Success of acute thrombolytic therapy in acute myocardial infarction: what does it demand from cardiac imaging in the 1990s?

Article Abstract:

An intensive study of the treatment of heart attack victims has been underway for several years. The study conducted by the Thrombolysis in Myocardial Infarction Study Group recommends that the treatment of an acute myocardial infarct (heart attack) be an aggressive intervention to open the blood vessels of the heart itself (coronary arteries). This usually means the intravenous injection of various thrombolytic agents, or products which dissolve clots. This method has been successful in opening the clogged coronary arteries and restoring good circulation to the heart. In spite of this treatment, the rate of vessels becoming clogged again is approximately 20 percent. Because of this reocclusion rate, patients are subjected to coronary angiography, an X-ray of the coronary vessels using a dye, to document which vessel is involved in the heart attack and to evaluate its status. However, recent studies have shown that the invasive nature of coronary angiography together with aggressive treatments with thrombolytic compounds offers no advantage over more conservative treatment. It is likely in light of this study that the number of coronary angiographies performed during the immediate post-coronary period might be expected to decline. The desire for documentation, however, remains and will likely be filled by noninvasive measures such as magnetic resonance imaging (MRI), coupled with new dyes and other procedures. Already there are indications that MRI and manganese pyridoxal phosphate, a contrast dye, can provide reliable information on the status of blood flow (perfusion) of the heart. The greatest remaining problem with the use of MRI is the inability to localize precisely the affected area, leaving clinical questions unanswered. Questions also remain about the effect of these relatively new contrast materials on the damaged heart cells and vessels.

Care and treatment, Heart, Thromboembolism, Infarction, editorial

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Occlusive and reperfused myocardial infarcts: differentiation with Mn- DPDP-enhanced MR imaging

Article Abstract:

The increasing use of thrombolytic therapy, the injection of drugs to break apart blood clots, as an immediate measure during or soon after a heart attack (myocardial infarction) makes the development of a method to determine the survival of heart muscle vital. Thrombolytic therapy often restores the flow of blood to the heart tissue, but the possibility exists that this reperfusion has occurred too late to save the heart muscle. Magnetic resonance imaging (MRI), which is a noninvasive method involving the use of a strong magnetic field to obtain images of internal organs, was used to assess the condition of the heart muscle, following an experimental blockage of blood flow to the hearts of rats. An experimental dye which is able to be concentrated by heart tissue, Mn-DPDP, or manganese N,N'-bis(pyridoxal-5-phosphate)ethelenediamine- N,N'-diacetic acid, was used to detect the physiologic status of the rat hearts by MRI. After 30 minutes Mn-DPDP was distributed in the heart so as to allow the detection of normal areas of heart, damaged areas, and reperfused regions which had experienced damage (infarct). Although many such contrast agents are under investigation at the current time, they are unlikely to be widely used because of difficulties with toxicity, lack of tolerance by the body or rapid excretion. Although some safety questions still exist in regard to Mn-DPDP, it is taken up in higher concentration by the heart than the surrounding skeletal muscle, and remains within the body for an extended period of time, thus allowing studies to be easily performed.

EDTA, Ethylenediaminetetraacetic acid, Contrast media, Contrast media (Chemicals)

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Reperfused-viable and reperfused-infarcted myocardium: differentiation with in vivo P-31 MR spectroscopy (magnetic resonance)

Article Abstract:

The increasing use of thrombolytic therapy (the injection of drugs to break apart blood clots) as an immediate measure during or soon after a heart attack (myocardial infarction) makes the development of a method to determine the survival of heart muscle vital. Thrombolytic therapy often restores the flow of blood to the heart tissue, but the possibility exists that this reperfusion has occurred too late to save the heart muscle. Beagle dogs had the blood supply to an area of the heart interrupted by a surgical clamp placed across a main coronary artery. The effect of this procedure, and the subsequent restoration of blood flow or reperfusion, was correlated with physiologic or biochemical measurements and with data obtained from a magnetic resonance imaging (MRI) device equipped to measure the level of a phosphorus isotope, P-31 (MR Spectroscopy). Sophisticated statistical analysis showed that measurements of P-31 correlated perfectly with viable reperfused cardiac muscle. This animal investigation shows that P-31 MR spectroscopy can successfully clarify the areas of the heart which remain viable after an induced period of ischemia. Other techniques are either not economically feasible or unable to make this determination. The technique remains experimental and costly and was performed on the dogs in an invasive manner. The results presented here hold great promise and should provide impetus for the development of a noninvasive method suitable for humans.

Usage, Nuclear magnetic resonance

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