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Infarcted Area and Residual Ischemia
of the Q and noQ Myocardial Infarct
Estimated by SPECT

Rochela Vázquez, Luis M.; Batista Cuéllar, Juan F.;
Stusser Beltranena, Rodolfo; Pérez Valdés, Marilyn;
Peña Quián, Yamile; Hernández Cairo, Abel;
Coca Pérez, Marco A.

Centro de Investigaciones Clínicas, Ciudad Habana, Cuba

SUMMARY
Myocardial perfusions SPECT with study of viability used to determines the percent of infarcted area (IFA) of the left ventricle, based in the assumptions all viable myocardium should have > 50% percent of uptake, with the advantage that with to it single study too it is possible to determined the percent of area with residual isquemia or myocardium in risk (MR).
Objective: To compare the IFA and MR between the myocardial infarcts (MI) Q and no-Q.
Material and Method: A sample of 166 patients that presented MI was studied. It was divided according to the presence (n =77) or not (n =89) of characteristic Q wave of MI in the ECG. They underwent a myocardial perfusion SPECT with study of viability using TL201 (n =83) or 99mTc-MIBI (n =83).
Results: Significant differences did not exist between the groups for same characteristics (table). Q MI has bigger significant percent and frequency of IFA as well of MR than the non-Q MI (Table 1).

Discussion: These results have the contributions that the quantification was carried in the polar image and to be a study completely quantified with stress images and viability. Nevertheless we should follow the same behavior independently of the type of IM, because even Maceira et al found to bigger incidence of multivessels illness in the IM-no Q, that which would darken the I predict of these patients.
Conclusions: The Q MI has bigger IFA and MR, nevertheless both types of MI should be studied in MR and IFA assessment that which would determine the clinical follow-up management.

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INTRODUCTION
   The infarcted area (IFA) has been to estimate for several methods like they are the electrocardiography, contrast angiocardiography, nuclear ventriculography of rest, echocardiography and the myocardial scintigraphy with 99mTc-pyrophosphate. In the case of the electrocardiography, it is supposed that the every IFA present electric signs of myocardial infarct (MI). It doesn't always happen, because sometime the IFA is covered for normal myocardial that emits normal electric signs (as it happens in the noQ-MI). It is supposed that in the ventriculographys and the echocardiography test every disfuntioning area corresponds the IFA, which spreads to overestimate it because the myocardial stunned (1, 2, 3) and hibernated (1, 4, 5) also dysfunctions. In the case of the scintigraphy 99mTc-pyrophosphate, the sensibility is 61% with specificity of 97%. Even in the case of the noQ-MI the sensibility is 37% (6), but this requires to be carried out between the 2do and 7mo day of the MI, it is not always possible. This constitutes a disadvantage of this test regarding the SPECT of myocardial perfusion, so this is the technique that will use in this work to determine the IFA, it will include study of viability. We will leave of the hypothesis that all viable myocardial although it is ischemic myocardial should have perfusion it didn't seize the necropsied myocardial. We prefer this method for its advantages like: to be able to carry out the study in any time even after discharge hospital, you can determine the ischemic residual area (IRA) or myocardial in risk simultaneously with the IFA (a decisive facto r in the prognostic); which determines the behavior to continue with the infarcted patient (revascularization or not); it permit the determination of the functional class, present arrhythmias and other parameters characteristic of the ergometry during the realization of the effort test.

GENERAL OBJECTIVES
   To know the similarities and differences b/t Q-MI and noQ-MI concerning dysfunctions of myocardial perfusion.

Specific objectives:

1- Know the differences between the Q-MI and noQ for the extension and severity of the myocardial perfusion dysfunctions with TL201 and 99mTc-MIBI.
2- Know the differences between the Q-MI and noQ for the IFA and IRA with TL201 and 99mTc-MIBI.

MATERIAL AND METHOD
   It was carried out retrospective study of 166 patients with antecedents of MI with myocardial perfusion SPECT with study of viability using TL201 (n =83) or 99mTc-MIBI of those they 138 (83.13%) were masculine with an average age of 51.73 years-old and a percent of frequency heart reached maxim of 84.96% for that's why can affirm that it was general research useful for diagnose. This sample was divided according to the presence (Group 1, n =77) or not (Group 2, n =89) of the characteristic Q wave in ECG of MI not finding significant statistically differs (SSD) among the groups (Table 1). Were excluded all patients that their antecedent enters they had some cause of false positive of the SPECT of myocardial perfusion.

    For the realization of these studies the following protocols of SPECT of myocardial perfusion were used:

1- Effort, Redistribution and Reinjection with TL201: One carries out diagnoses ergometry under the protocol of Bruce with injection from 2,5 to 3mci of TL201 (and continuation of the effort during one minute) when the percent of reached heart frequency was > 85% and/or some approach of detention of the teas appeared, later on spent to the gammacamera (SOPHA DS7) where 32 images of 40 seg each one were acquired, when traveling 180grados in circular orbit from the position right anterior oblique (RAO) until the position left posterior oblique (LPO). The visual field of the gammacamera was equipped with 61 tubes photomultipliers, a thickness of the glass of NaI (Tl) of 3/8inch, and a collimator of general purpose, low energy and parallel holes. The window of energy of 20% was centered on the 80 Kev of the pick of rays X 4 hours were expected to allow the redistribution of the product and they took images of redistribution under equal conditions, then it was reinjected 1mci additional of TL201 20min were expected and was carried out the acquisition of the images of the reinjection in the same form, later on all the projections were stored in a magnetic disk using a womb of 64 x 64 (16 bit). The images were processed using a filter Hamming-Hann, in a system Sopha-Medical. The cuts tomographics was obtained in the three axes for each phase of the test as well as the corresponding polar images. The algorithm developed in language Forth in a prosecution station SOPHY 20P, divided the image in 13 sectors, calculating the quantity of absolute counts for each segment and comparing them with the maximum value determining, this way the percent that represents the value of the counts of each sector with regard to the maximum that represents 100% of that image.
2- Rest, Redistribution and Reinjection with TL201: Executed in the patients that had contraindicated the ergometry and only differs in that the initial dose was injected in rest.
3- Exercise, Rest and Rest-nitroglycerine: (different day) with 99mTc-MIBI: Was carried out diagnoses ergometry it and injection of the radioisotope in similar conditions and requirements (that for the TL201) injecting a dose from 25 to 30mci of 99mTc-MIBI, later on at the 30min. of the injection the patients drink 8oz of milk rich in fat, beginning the acquisition 60min. after the injection the one which only differs (of the TL201) in that the taking of each image lasted 20seg. the journey was LPO to RAO and the energy window was centered in the 140kev of the pick of rays X. After 48 hours you proceeded to take the images of rest for that which repeated same procedure of administration of the 99mTc-MIBI and acquisition of the images (except the effort that is not carried out) and later at 48hours you proceeded to the study of viability for that which were administered via sublingual 2 pills of NTG 0,4mg and after 10min. then you proceeded to the administration of the 99mTc-MIBI, later proceeded the same as for the taking of rest. As for the storage, prosecution, and interpretation of the images the only difference (with regard to the TL201) it was the use of the filter Butterworth 5/23.
4- Rest and Rest-NTG (different day) with 99mTc-MIBI: Executed in the patients that had contraindicated the ergometry, and only differs of the previous one in that the stress image is obviated.

   The images obtained with these protocols are comparable due to having been carried out with the same radioisotope (those that are compared to each other) and to use filter chord with the dose and the administered radioisotope, our work also used the percents of uptake of each sector with regard to that same image not the number of absolute counts of each sector.

   Later on in both patients groups, on the polar image of viability by means of software of DETERMINATION OF AREAS (version 1,0) the perfusions defects corresponding to the percents of uptake < 30% and >30 < 50% were looked for to determine the percent that represents the area of the defect of uptake of the area of the polar image of the LV that you considers percent of IFA, nevertheless to make sure that those defects were not reversible so much the polar images of stress like of viability they were subjected to a quantification program that divides this in 13 sectors giving the percent of uptake of each sector and that every sector that don't improve more of 10% in the image of viability with regard to the stress you considers fixed or not reversible defect (that correspond with the IFA) therefore for each sector that was reversible and their final uptake was >30% is subtracted 7.69% to the AIF (therefore is added the AIR) it stops later on to compare both RT for types of IM and to observe if SSD exist as for this aspect. With the objective of determining the percent of IRA calculates the percentage difference (differs among the percent that represents the area of the defect of stress perfusion and the percent that it represents the area of the defect of perfusion of viability) among the perfusion defects with uptake < 50% stress and viability. With the objective of quantifying the severity of the defects of perfusion of the polar image of viability take the smallest uptake percent inside the ranges that we settled down, in the event of not having any defect of perfusion < 50% we take the existent minor.

RESULTS
   In the comparison between types of MI without keeping in mind the radioisotope see the Q-MI has a bigger percent and frequency of IFA that the noQ as well as bigger percent and frequency of IRA (Table 2 and graph 1).

   Comparing both types of MI in the patients carried out with TL201 observes that the Q-IM presented bigger uptake defects and more severe as well as bigger IRA and IFA. Although it was not presented the SSD the % of uptake < 30%. (Table 3 and graph 2).

   Comparing both types of MI in the patients carried out with 99mTc-MIBI also observes that the Q-MI presented bigger uptake defects and more severe as well as bigger IRA and IFA. Only it not was presented SSD the % of uptake < 30%. (Table 4 and graph 3).

   Making a general analysis of the results observes that independently of the analysis carried out the IM-Q always present bigger uptake defects and more severe as well as bigger IRA that which doesn't depend on the product used in the test.

DISCUSSION
   In the comparison among the two types of MI carried out in general observe that the Q-MI presents bigger uptake defects and more severe (IFA) that the noQ-MI the same as other authors (7, 8, 9, 10, 11), but in this work with the contribution that the quantification was carried out in the polar image (that was already used by other authors [12, 13]) which gives a global image of the LV and on the base of the uptake percent, the areas were determined with that uptake percent, that is to say a completely quantified study. Also this work one carries out with two radioisotopes (TL201 and 99mTc-MIBI) both with stress images and viability (which facilitates not to underestimate the IRA and therefore neither to overvalue the IFA) aspects that don't contain the works to that we make reference, and they are very important because this demonstrated the importance of the reinjection in the case of the TL201 (12) and the NTG in the case of the 99mTc-MIBI for the study of the viability (13, 14, 15, 16, 17,18).

   We find bigger IRA in the Q-MI, but in this case with the contribution that we don't only value the ischemia perinfarct like Maceira et al (7), but rather we value the IRA in all the LV (perinfarct and/or at distance). The presence of this defines the behavior of revascularization since independently of its localization it is myocardial in risk that is necessary to save. It is demostrated that anyone of the types of MI can have it, for what to both types of MI the same importance should be granted and to even maintain the same behavior. Since Maceira et al they found in its work a bigger incidence of multivessels illness in the mi-MI (that which would darken the even predict of these patients with smaller IFA and even without significant differences as for the LVEF between both types of MI according to Maceira et al).

   The theory of considering the Q-MI like complete and the mi-MI like incomplete (7) we don't share it, since it spreads to minimize the possibility of presence the myocardial in risk in the Q-MI, that which would exclude to these patients of the search of possibility of revascularization that we also demonstrate in this work that is just the opposite, also in autopsy studies carried out to infarct patients was observed with Q-MI with necrosis subendocardial and patients with mi-MI with necrosis transmural (19, 20, 21, 22, 23).

   We consider that this work has limitations, like it is this reported by other authors that the SPECT of myocardial perfusion the IFA overestimates (24). However it was not our objective to determine the absolute % of IFA of the LV, but characterizing the perfusion defects taken place for that reason by both types of MI. For that we always make reference to percent of IFA of the polar image of the LV (never of the LV) and also the error margin is in any event the same one for both types of MI for what we consider that this limitation doesn't invalidate the results.

CONCLUSIONS
   The Q-MI has bigger IFA and IRA that the mi-MI (but both have IRA) for what we recommend that both types of MI should always be studied in search of the myocardial in risk and the IFA, which would determine the behavior and the medical prognostic.

REFERENCES

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2nd Virtual Congress of Cardiology

Dr. Florencio Garófalo
Steering Committee
President
Dr. Raúl Bretal
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Dr. Armando Pacher
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President
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