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Determinants of infarct size after thrombolytic treatment in acute myocardial infarction
C J Bruce1, T F Christian, G L Schaer
1Division of Cardiovascular Diseases and Internal Medicine, Mayo Clinic, Rochester, Minnesota 55905, USA.
Insights
Myocardium at risk and collateral flow are key factors determining final infarct size in myocardial infarction patients. Multicenter tomographic imaging reliably assesses these parameters, crucial for thrombolytic therapy trials.
Area of Science:
- Cardiology
- Nuclear Medicine
- Medical Imaging
Background:
- Myocardium at risk, collateral flow, and occlusion duration influence infarct size.
- Previous studies confirmed these factors in single-center trials.
Purpose of the Study:
- To validate findings of infarct size determinants in a multicenter setting.
- To assess the reliability of perfusion imaging across different camera and computer systems.
- To demonstrate the utility of technetium-99m sestamibi imaging in multicenter thrombolytic therapy trials.
Main Methods:
- Sequential tomographic myocardial perfusion imaging with technetium-99m sestamibi in 74 first-time myocardial infarction patients.
- Patients received thrombolysis within 6 hours of chest pain onset.
- Myocardium at risk assessed early; collateral flow estimated noninvasively; final infarct size determined at discharge.
Main Results:
- Myocardium at risk (r=0.61) and collateral flow estimates (r=0.58-0.66) significantly correlated with final infarct size (p<0.0001).
- These associations were independent of treatment center.
- Multivariate analysis identified myocardium at risk, collateral flow, and treatment arm as independent infarct size determinants.
Conclusions:
- Myocardium at risk and collateral flow are significant, center-independent determinants of infarct size.
- Tomographic technetium-99m sestamibi imaging provides reliable, noninvasive assessment of these parameters in multicenter settings.
- This imaging technique is valuable for multicenter trials evaluating thrombolytic therapy.
Abstract:
Both experimental and single-center clinical studies have shown that myocardium at risk, residual collateral flow, and duration of coronary occlusion are important determinants of final infarct size. The purpose of this study was to replicate these results on a multicenter basis to demonstrate that perfusion imaging using different camera and computer systems can provide reliable assessments of myocardium at risk and collateral flow. Sequential tomographic myocardial perfusion imaging with technetium-99 (Tc-99m) sestamibi was performed in 74 patients with first time myocardial infarction, who were enrolled in a multicenter, randomized, double-blind, placebo-controlled pilot study of poloxamer 188 as ancillary therapy to thrombolysis. All patients underwent thrombolysis within 6 hours of the onset of chest pain. Tc-99m sestamibi was injected intravenously at the initiation of thrombolytic therapy, and tomographic imaging was performed 1 to 6 hours later to assess myocardium at risk. Collateral flow was estimated noninvasively from the acute sestamibi images by 3 methods that assess the severity of the perfusion defect. Final infarct size was determined at hospital discharge by a second sestamibi study. Myocardium at risk (r = 0.61, p <0.0001) and radionuclide estimates of collateral flow (r = 0.58 to 0.66, all p <0.0001) were significantly associated with final infarct size. These associations were independent of the treatment center. On a multivariate basis, myocardium at risk (p = 0.003), the radionuclide estimate of collateral flow (p = 0.03), and treatment arm (p = 0.04) were all independent determinants of infarct size. Time to thrombolytic therapy showed only a trend (p = 0.10). The treatment center was not significant (p = 0.42). Myocardium at risk and collateral flow are important determinants of infarct size that are independent of treatment center. Tomographic imaging with Tc-99m sestamibi can provide noninvasive assessments of these parameters in multicenter trials of thrombolytic therapy.