Frame counting improves the assessment of post-reperfusion microvascular patency by TIMI myocardial perfusion grade: Evidence from cardiac magnetic resonance imaging

Abstract

Background: Quantitative modification of TIMI myocardial perfusion grade (TMPG) by the method of frame counting may improve its sensitivity and the false negative rate for post-reperfusion microvascular dysfunction (MVD) in ST segment-elevated myocardial infarction (STEMI) patients.

Methods: The durations of contrast-washout from infarction area of 139 patients were measured by counting the cine-frame numbers between the appearance and disappearance of myocardial blush. The achieved new index, TMP Frame Counting (TMP-FC) was referenced by cardiac magnetic resonance, by which MVD was defined as microvascular obstruction on gadolinium late-enhancement imaging.

Results: Median TMP-FC differed significantly between patients with and without MVD (126 frames, IQR 105-160 vs. 86 frames, IQR 75-100, p<0.001). By receiver-operating characteristic analysis, the cutoff of TMP-FC at ≥ 95.5 frames represented an independent predictor of MVD (OR=11.61, p<0.001). TMP-FC had similar specificity (75%) and positive predictive value (88%), but significantly improved sensitivity (85.3%) and negative predictive value (70.2%) for MVD compared with TMPG (88.6%, 86.5%, 33.7% and 38.2%, respectively) and other traditional angiographic assessments, leading to a better overall accuracy (area under the curve: 0.801 compared with 0.612 from TMPG, p<0.001) for the evaluation of microvascular patency. TMP-FC was positively correlated with MVD extent (r=0.5, p<0.001). Abnormal TMP-FC was associated with larger infarction size (28.67 ± 13.72% vs. 16.51 ± 10.68% of left ventricular mass, p<0.001) and lower LVEF (49.37 ± 11.06% vs. 56.84 ± 9.72%, p<0.001).

Conclusion: Frame counting can improve the accuracy of TMPG for MVD. Moreover, TMP-FC is correlated with the degree of MVD and cardiac detriments, which is useful for risk stratification.

Keywords: Angiographic assessment; CMR; Microvascular dysfunction; Reperfusion; STEMI.