Noninvasive Evaluation of Coronary Reperfusion by CT Angiography in Patients With STEMI
What is the role of 64-slice multidetector computed coronary tomography (MDCT) in identifying coronary reperfusion, defined as Thrombolysis in Myocardial Infarction (TIMI) 3 flow, compared to TIMI 0-2 flow following ST-segment elevation myocardial infarction (STEMI)?
Standard coronary arteriography (SCA) was performed in 110 consecutive patients with a first STEMI. The protocol involved performing MDCT angiography prior to SCA. MDCT was excluded in 10 patients because of high-risk STEMI and 13 others were excluded because of standard contraindications to high-quality MDCT, leaving a total of 87 patients. MDCT was analyzed for presence and location of the infarct-related artery (IRA). When the IRA was visualized past the level of obstruction, a region of interest was placed in the proximal IRA as well as the most distal portion, and contrast intensity was quantified at each site, and subsequently the ratio of distal to proximal intensities was calculated (CTR).
By SCA, IRA TIMI flow grade was 0 in 55 and 1, 2, and 3 in 3, 17, and 12 patients, respectively. MDCT angiography did not visualize a distal IRA in 56 subjects, and by SCA, 53 had TIMI grade 0 flow, 2 grade 1, and 1 grade 2 flow. The distal IRA was visualized in 31 by MDCT and TIMI flow 0-3 was seen in 2, 1, 16, and 12 IRAs. The two patients with TIMI 0 flow by SCA but a visualized distal vessel by MDCT had total coronary obstruction with robust collaterals. Receiver operating curve analysis identified a CTR ≥0.54 as the best discriminator between TIMI 3 and TIMI 0-2 flow. Reperfusion was visualized in 13 patients who had a CTR ≥0.54, 11 of whom had TIMI 3 flow, 1 TIMI 0, and 1 TIMI 2 flow. Seventy-four patients had either absent reperfusion by MDCT or CTR ≤0.54, 54 of whom had TIMI 0 flow, 1 had TIMI 1 flow, and 16 had TIMI 2 flow. The sensitivity, specificity, and accuracy of CTR ≥0.54 for predicting TIMI grade 3 flow was 92%, 97%, and 97%.
This visualization of the IRA by MDCT accurately separates patients with TIMI 3 flow from patients with TIMI 0-2 flow during STEMI.
MDCT has been validated in numerous studies as an accurate means of identifying and quantifying proximal coronary artery stenosis, and for this purpose, it has become a clinically relevant tool. This study extended the observations to evaluation of patients presenting with STEMI and demonstrated, based on absence of flow distal to an obstruction and a ratio of contrast intensity in proximal and distal portions of the IRA, the ability to separate patients with TIMI 3 flow from those with grade 0-2 flow. While demonstrated in a relatively small number of patients, the results are not surprising. The exact clinical role that this less invasive method for determining the integrity of flow in an IRA will play remains conjectural, especially in view of recommended strategies for early rapid percutaneous intervention in STEMI. The precise patient population for whom delaying invasive coronary arteriography and definitive therapy would be clinically appropriate remains to be established. Conversely, using MDCT in select patients following reperfusion with lytic therapy to identify the high-risk patient with ≤TIMI 2 flow may be a more appropriate utilization of this technique.
Keywords: Myocardial Infarction, Coronary Stenosis, Coronary Angiography, Multidetector Computed Tomography, Myocardial Reperfusion
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