Response to Letters Regarding Article, “Presence of Older Thrombus Is an Independent Predictor of Long-Term Mortality in Patients With ST-Elevation Myocardial Infarction Treated With Thrombus Aspiration During Primary Percutaneous Coronary Intervention”
We agree with Testa et al that it may be clinically relevant that we used different aspiration devices. In our dataset, subanalysis showed that aspiration success was similar for the procedures in which the Rescue catheter, Export catheter, and Proxis device were used (73%, 74%, and 82%, respectively).1 We are in the process of evaluating the results with different devices in more detail.
We also agree that classification into 6 groups (fresh, lytic, organized, thrombus, and with or without plaque), such as we reported previously in Circulation in 2005, may better represent histopathological complexity.2 In the present analysis, we observed similar outcomes in patients with lytic and organized thrombus, and therefore we chose a dichotomous analysis. In addition, smaller sample sizes reduced statistical power. We stated clearly the limitation that postprocedural thrombolysis in myocardial infarction flow grade was not assessed by an independent core laboratory.3 Finally, all-cause mortality was available to us from the Dutch Central Bureau of Statistics, but cardiovascular cause of death was not.
Dr Niccoli suggests that the association between thrombus age and outcome observed in our study may be explained by distal embolization and the no-reflow phenomenon. In addition, Dr Niccoli would like to see additional data on myocardial blush grade and ST-segment resolution as measures of the no-reflow phenomenon. We would like to reiterate that we observed an association between the presence of older thrombus and outcome, but we were uncertain about a causal relationship, as we stated in our article.3 We agree that the presence of older thrombus may be associated with more extensive microvascular obstruction and no-reflow at the cellular level. However, we could not demonstrate independent contribution of measures of no-reflow to outcome. Thus, although no-reflow may be an explanation for our findings, our data do not sufficiently support that conclusion. Myocardial blush grade has been shown to be associated with outcome. To assess myocardial blush, standardized images in low-power magnification from the correct projection angle with longer exposure duration are required. Unfortunately, we do not record these types of images routinely in our practice. Following Dr Niccoli’s suggestion, we looked at ST-segment resolution in the subset of patients in whom we had reliable electrocardiography data. No difference was found in ST-segment resolution in patients with fresh compared with older thrombus. Therefore, although this potential explanation is important for our findings, our data do not substantiate this notion.
Kramer MC. The efficacy of thrombus aspiration during primary PCI: evaluation of three devices. Paper presented at: Transcatheter Cardiovascular Therapeutics Scientific Sessions; October 16, 2008; Washington, DC.
Rittersma SZ, van der Wal AC, Koch KT, Piek JJ, Henriques JP, Mulder KJ, Ploegmakers JP, Meesterman M, de Winter RJ. Plaque instability frequently occurs days or weeks before occlusive coronary thrombosis: a pathological thrombectomy study in primary percutaneous coronary intervention. Circulation. 2005; 111: 1160–1165.
Kramer MC, van der Wal AC, Koch KT, Ploegmakers JP, van der Schaaf RJ, Henriques JP, Baan J Jr, Rittersma SZ, Vis MM, Piek JJ, Tijssen JG, de Winter RJ. Presence of older thrombus is an independent predictor of long-term mortality in patients with ST-elevation myocardial infarction treated with thrombus aspiration during primary percutaneous coronary intervention. Circulation. 2008; 118: 1810–1816.