Relationship of dual time point myocardial SPECT-CT with peak creatine kinase and cardiac troponin I levels

AIM: The aim of this sub-study of a randomized clinical trial was to evaluate the relationship of peak creatine kinase (CK) and peak sensitive cardiac Troponin I (sc-TnI) levels with perfusion defect and left ventricular ejection fraction (LVEF) by gated single-photon emission computed tomography myocardial perfusion imaging (SPECT-MPI) in patients with ST-elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (pPCI) during the acute phase and one month later. METHODS: Patients who were admitted with STEMI within 8 hours of symptom onset underwent gated SPECT-MPI acquisition (SPECT-LDCT, Siemens Symbia T6, Erlangen) within 24 hours (timepoint (TP) 1) after pPCI and one month later (TP 2). The MPI SPECT data were reconstructed and analyzed using 4DM-SPECT software. The infarct size was defined as percentage of the total left ventricular myocardium (%LV). Serial CK (U/L) und sc-TnI (μg/L) levels were evaluated at presentation and 2, 6, 12, 24 and 48 hours after pPCI, respectively. Both, peak NT-proBNP (ng/L) values and LVEF in ECHO were assessed during day 2 and 5 after admission. RESULTS: Twenty-four consecutive patients (mean age 60±12 years, 8 females) were included in this analysis. All patients had TIMI 3 flow in the culprit vessel after pPCI. In total 19 patients underwent SPECT on TP1 and 17 on TP2. The median perfusion defect was significantly larger on TP1 compared to TP2 (34%LV (IQR 16-54) vs. 16%LV (IQR 4-22), p=0.008). We found significant correlations for peak sc-TnI and peak CK levels with the perfusion defect assessed on TP1 (r=0.5, p=0.031; r=0.51, p=0.026; respectively) and on TP2 (r=0.88, p<0.001; r=0.92, p<0.001, respectively). Nt-proBNP values did not significantly correlate with the perfusion defect on either TP1 or TP2 (r=0.486, p=0.056; r=0.329, p=0.297), respectively. However, we found good correlations for LVEF between ECHO and SPECT assessment at TP1 and TP2 (r=0.7, p=0.005 and r=0.68, p=0.007). CONCLUSION: The results of this pilot study demonstrate a significant correlation between infarct size assessed by use of SPECT-MPI and peak values of the more specific cardiac biomarkers CK and sc-TnI. This correlation was much higher one month compared to 24 hours after pPCI. LVEF calculated with SPECT-MPI showed good correlation to echocardiography irrespective of the TP. However, Nt-proBNP, a marker of left ventricular function, was not correlated with infarct size, which might be explained by stunning of potentially vital myocardium.