Response to Letter Regarding Article, “Impact of Intravascular Ultrasound Guidance on Long-Term Mortality in Stenting for Unprotected Left Main Coronary Artery Stenosis”
We appreciate the article regarding the comments on our intravascular ultrasound (IVUS) substudy of the MAIN-COMPARE registry assessing the effectiveness of IVUS-guided stenting for unprotected left main coronary artery stenosis.1 Their interests and questions about our results are very useful for a changing substrate. We certainly agree with the comments on our limitations that occurred because of the nonrandomized registry study design. First, regarding the question on presenting symptom, which was a potential contributor to the outcomes, between patients receiving IVUS- versus angiography-guided stenting, the 2 groups had comparable characteristics, as shown in the Table. However, as pointed out in the original article, unobserved confounders were hardly adjusted despite our rigorous propensity-matching model having a good feasibility with a c statistic of 0.70 and a Hosmer-Lemeshow goodness-of-fit statistic of 0.31 in the overall group. Second, they addressed the importance of cause-specific mortality rate to illuminate causal factors of superior long-term result of IVUS-guided stenting. In fact, the pattern of difference in cardiac-cause mortality rate between IVUS- versus angiography-guided groups consistently agreed with that in all-cause mortality rate for either drug-eluting stent or bare-metal stent treatment. With or without adjustment, the incidence of cardiac mortality was likely to be lower with use of IVUS guidance. However, the plausible mechanism is still unclear because we could not capture the cause of all deaths and the incidence of very late stent thrombosis according to the ARC definition. Moreover, because of the prespecified definition of outcomes, a few deaths with ambiguous causes were considered as cardiac deaths in our registry. Finally, a higher inflation pressure applied in IVUS-guided stenting than angiography-guided stenting may be partly associated with the better long-term outcomes as a consequence of better stent expansion or better strut apposition.2
With supporting evidence reported in this letter, the benefit of IVUS guidance in left main coronary artery stenting is hoped to be more ascertained. Nevertheless, indirect consumption on the mechanism of mortality reduction by IVUS guidance should be further confirmed in the following clinical researches having prespecified IVUS criteria for optimal stent placement and systematic regulation of follow-up.
Park SJ, Kim YH, Park DW, Lee SW, Kim WJ, Suh J, Yun SC, Lee CW, Hong MK, Lee JH, Park SW; for the MAIN-COMPARE. Impact of intravascular ultrasound guidance on long-term mortality in stenting for unprotected left main coronary artery stenosis. Circ Cardiovasc Intervent. 2009; 2: 167–177.
Mintz GS. What to do about late incomplete stent apposition? Circulation. 2007; 115: 2379–2381.