This retrospective study showed that loss of the main D flow before primary PCI of anterior STEMI was associated with worse one-month and long-term adverse clinical outcomes, even after the active revascularization. It suggested need to pay more attention to the treatment and follow-up of these patients.
In general, LAD supplies 40% of the myocardium in the left ventricle, including the anterior ventricular septum and the anterior wall of the left ventricle [9]. Prognosis of LAD occlusion is related to the location of the lesion [3, 10]. The main D, usually referring to the first D, is the most important branch of the LAD supplying blood to the anterior and anterolateral wall of the left ventricle. Because the D has different diameters, lengths, and range distributions in different populations, the degree of influence of occlusion on cardiac function is different when the D is occluded. Generally, the number of D ranges from 2 to 9; a D with diameter larger than 2 mm is regarded as the main supply branch of the LAD. The previously published researches on the D were mostly about the bifurcation lesion of LAD/D, with scarce study of the D itself [11].
The proximal LAD was defined as the segment spanning from the ostium of the LAD to that of the first main branch (usually referring to the significant diagonal branch) [12]. Generally, both proximal LAD and D occlusion can cause loss of D flow. Loss of D flow might be associated with poor prognosis of patents with STEMI. However, the clinical significance of the two occlusion scenarios is quite different, with the former being most common, of greater severity, and with worse prognosis [11, 13, 14], while isolated D occlusion is relatively rare and appears mainly inconsequential [15]. Therefore, distinction between the two scenarios is of clinical relevance. Electrocardiographic findings may provide clues [16, 17], and coronary angiography can basically distinguish between the two scenarios. Regarding therapy, proximal LAD occlusion compromising the main D flow should undoubtedly be treated by revascularization as soon as possible. In contrast, the treatment of isolated D occlusion is currently a matter of debate [7, 18]. It is not possible to generalize about the need to perform further revascularization for the D after intervention of the target vessel, because different individuals have different D blood flow conditions and the target lesions are different. However, published studies showed that complete revascularization is a reasonable strategy to improve outcomes in patients with STEMI [19, 20]. In clinical practice, we are inclined to perform PCI for the side branch with diameter ³2mm. The benefit and risk should be comprehensively weighed according to various factors like age, lesion severity, renal function and procedure duration. The decision that whether treating side branch are supposed to be made carefully.
Isolated D occlusion has been reported to have a lesser effect on cardiac function[5]. In our study, the proportion of patients with normal LVEF in the group with D flow loss was lower than that in the group without D flow loss. Therefore, the group with D flow loss had a larger myocardial infarct size, lower cardiac function and a higher Killip class grade. Regarding the potential cause of worse clinical outcomes, we speculated that it could be explained partly by the proximal LAD occlusion. Almost all the patients with D flow loss in our study presented with LAD lesions involving the D. However, we believed that for the proximal LAD occlusion patients, those with D flow loss were still more likely to have a larger myocardial infarct size and worse outcomes compared with those without D flow loss. The cardiac MRI test could accurately measure infarct size and verify our viewpoint. Regrettably, we failed to obtain the MRI data in this retrospective study. As the loss of the main D often results from proximal LAD lesions, the average diameter of LAD and the stent implanted in the group with D flow loss might be larger, which was verified in the present study.
Due to the relatively large sample size difference between the two groups, we performed multivariate analysis using two COX models, which presented the stable and close results. The sensitivity analysis further demonstrated that the loss of the D was independently associated with clinical adverse events at one month and 18-month follow-up. In the Kaplan-Meier survival curves, clinical adverse events, particularly all-cause mortality, occurred in the group with D flow loss, mainly within 30 days after the intervention, underscoring the relevance of appropriate early postprocedural care. The landmark analysis further showed that the differences in the incidences of MACEs and all-cause death between the two groups mainly resulted from in-hospital events. However, the incidences of MACEs and all-cause death after discharge were similar between groups.
Limitations
The present study has several limitations including those inherent to its retrospective, single center design. First, LVEF within the first 24 hours of STEMI was unable to reflect the exact cardiac function and we did not follow up LVEF. Moreover, infarct size was not estimated on admission. Besides, there might be recallbias about the drug usage during follow-up. As thus, large, prospective, randomized clinical trials are required to confirm our findings in the present study.