TIMI perfusion grade compared to TIMI flow in prediction of infarct size and microvascular obstruction measured by contrast-enhanced MRI

Background

The TIMI perfusion grade (TMPG) and TIMI flow are angiographic parameters with prognostic impact in ST-elevation myocardial infarction (STEMI). The association of these parameters with infarct size and microvascular obstruction assessed by MRI, which also have of prognostic impact, has not been studied so far.

Methods

From 02/2006–01/2008 280 consecutive patients with STEMI underwent primary PCI. In an MRI study (day 1–4 after PCI) infarct size and microvascular obstruction in percent of left ventricular mass (%LV) were measured by delayed enhancement. In addition, post-PCI TIMI flow and TMPG were assessed from invasive angiography. All measurements were done by blinded investigators. TMPG and TIMI flow were graded as severely impaired (0–1) or mildly impaired-normal (2–3).

Results

For post-PCI TIMI flow there was a significant difference in the extent of microvascular obstruction (TIMI 0–1: 6.6 ± 5.1%LV vs. TIMI 2–3: 3.6 ± 4.6%LV, p = 0.021), but no significant difference in infarct size (TIMI 0–1: 25.9 ± 15.3%LV vs. TIMI 2–3: 21.19.3 ± 13.4, p = 0.07). For TMPG microvascular obstruction (TMPG 0–1: 5.3 ± 5.2%LV vs. TMPG 2–3: 3.5 ± 4.5%LV, p = 0.011) and infarct size were significantly different (TMPG 0–1: 25.0 ± 13.0%LV vs. 18.6 ± 13.5%LV, p = 0.002). In a multivariable model the strongest predictors of infarct size and microvascular obstruction were post-PCI TMPG, infarct location, Killip class, and 90 minute ST-segment resolution (p < 0.005 for all).

Conclusion

In STEMI patients undergoing primary PCI the TMPG is a better indicator of angiographic success compared to TIMI flow reflected by a significant difference in infarct size measured by cardiac MRI. This might explain why the TMPG has additional prognostic impact in patients with restoration of normal TIMI flow.