sistent with previous recently reported ex vivo and in vivo findings (1–3), we highlight consistently larger LA measurements obtained with IVUS compared to FD-OCT across all segments, with a further significant reduction in these luminal measurements when measured in smaller-sized coronary segments, and when measured with 3D-QCA. This also supports recent data which has compared Terumo FD-OCT, IVUS, and conventional QCA measurements in stented coronary segments (3). Until further validation studies are conducted, specific lumen-based cut-off values previously vali- dated with IVUS and currently utilised in contemporary interven- tional practice should not be arbitrarily translated into the FD- OCT and 3D QCA hemispheres. (Fig. 1) Rishi Puri, MBBS, Adam J. Nelson, MBBS, Gary Y. H. Liew, MBBS, Stephen J. Nicholls, MBBS, PhD, Angelo Carbone, MMedSc, Dennis T. L. Wong, MBBS, James E. Harvey, MD, MSc, Kiyoko Uno, MD, PhD, Barbara Copus, RN, Darryl P. Leong, MBBS, MPH, John F. Beltrame, BMBS, PhD, Stephen G. Worthley, MBBS, PhD, Matthew I. Worthley, MBBS, PhD* *Cardiovascular Investigational Unit, Royal Adelaide Hospital, Level 6 The- atre Block, North Terrace, Adelaide, South Australia 5000, Australia, E- mail: matthew.worthley@adelaide.edu.au. doi:10.1016/j.jcmg.2011.07.012 Please note: Drs. Puri, Leong and Liew are supported by a Postgraduate Medical Research Scholarship from the National Health & Medical Research Council (565579, 519177, and 497809 respectively). Drs. Puri and Leong are jointly funded by the National Heart Foundation of Australia (PC0804045, PC07A3395). Dr. Worthley has a South Australian Early to Mid Career Practitioner Fellowship. REFERENCES 1. Gonzalo N, Serruys PW, Garcia-Garcia HM, et al. Quantitative ex vivo and in vivo comparison of lumen dimensions measured by optical coherence tomography and intravascular ultrasound in human coronary arteries. Rev Esp Cardiol 2009;62:615–24. 2. Yamaguchi T, Terashima M, Akasaka T, et al. Safety and feasibility of an intravascular optical coherence tomography image wire system in the clinical setting. Am J Cardiol 2008;101:562–7. 3. Okamura T, Onuma Y, Garcia-Garcia HM, et al. First-in-man evalua- tion of intravascular optical frequency domain imaging (OFDI) of Terumo: a comparison with intravascular ultrasound and quantitative coronary angiography. EuroIntervention 2011;6:1037– 45. Atrial Function in Patients Undergoing CRT We read with great interest the paper by Carluccio et al. (1) regarding the impact of left ventricular (LV) remodeling on the response to cardiac resynchronization therapy (CRT). In this elegant study, the authors performed a comprehensive assessment of LV function, showing that extensive LV remodeling at baseline is associated with poor improvement after CRT. We wish to raise an essential issue, which may be of keen interest to the readers. In recent years, there has been growing interest in the potential impact of CRT on atrial function, but the state of knowledge in this field is still controversial and unsettled (2–4). In the paper by Carluccio et al. (1) several baseline data concerning atrial function are presented (left atrial volume index and mitral regurgitation severity), but unfortunately there is no information related to CRT response. We believe that their excellent echocardiographic data could also be useful to better understand another debated issue (i.e., the effect of CRT on the risk of the development of atrial arrhythmias) that is clearly related to atrial remodeling (4,5). Gaetano Santulli, MD,* Salvatore D’Ascia, MD, Vittoria Marino, MD, Cristofaro D’Ascia, MD *Columbia University Medical Center, College of Physicians & Sur- geons, St. Nicholas Avenue, New York, New York, 10032. E-mail: gs2620@columbia.edu. doi:10.1016/j.jcmg.2011.11.002 Figure 1. Segmental Analysis of Coronary Lumen Dimensions With IVUS and OCT Visual representation of methodology used with corresponding horizontal views of intravascular ultrasound (IVUS) (A) and Fourier Domain-optical coherence tomography (FD-OCT) (C) and cross sectional views of IVUS (B) and FD-OCT (D) are shown. JACC: CARDIOVASCULAR IMAGING, VOL. 5, NO. 1, 2012 JANUARY 2012:123–5 Letters to the Editor 124