Author + information
- Julio A. Chirinos, MD, PhD∗ (, )
- Scott R. Akers, MD, PhD,
- Bilal Ansari, MD and
- Snigdha Jain, MD
- ↵∗South Tower, Room 11-138, Perelman Center for Advanced Medicine, 3400 Civic Center Boulevard, Philadelphia, Pennsylvania 19104
We appreciate the comments by Dr. Khanji and colleagues, and the opportunity to clarify our methods. We estimated right atrial volume (RAV) using a single-plane area-length measurement in the 4-chamber view. We traced the inner edge of the right atrial wall/India-ink artifact, excluding the Eustachian valve and the interatrial septum (as well as any segments of lipomatous interatrial septal hypertrophy). The cavity projection sometimes seen basal to the lateral tricuspid annulus in this plane was included only if it was clearly visualized in this plane and not heavily trabeculated.
Dr. Khanji and colleagues note that other studies have reported larger values for RAV; however, there has been wide variability in the published data, and previous studies have also reported values similar to ours or even smaller. For example, Rheinheimer et al. (1) has reported RAV indices as small as 23 ml/m2 using magnetic resonance imaging. Similarly, much smaller RAV indices compared to the studies cited by Dr. Khanji and colleagues were reported in studies using computed tomography (25 to 32 ml/m2, depending on the method) (1) and 3-dimensional echocardiography (23 ml/m2) (2).
With magnetic resonance imaging, a full short-axis stack covering the entire right atrium (RA) should provide the most reliable measurements; however, this method may overestimate RA size due to partial-volume effects, requires additional imaging/post-processing time, and is rarely applied clinically. Area-length methods in 2 orthogonal planes (4-chamber view and right-sided 2-chamber view) have been used. Interestingly, the transverse RA diameter in the right-sided 2-chamber view can be substantially different than in the 4-chamber view. Therefore, it should not be expected that single-plane area-length measurements in the 4-chamber view (assuming axisymmetric geometry) would produce volumes similar to those obtained with bi-plane or short-axis stack methods. More inclusive versus exclusive segmentation methods using a single 4-chamber plane will produce different absolute estimated volumes, but this is unlikely to affect the correlation between the estimated volumes and the in vivo reality (more likely, there is only a shift in the intercept of the relationship).
Our study assessed the interindividual variability in RAV estimated from the 4-chamber plane as a predictor of death. As shown in Table 3 of our manuscript, RAV index predicted the risk of death (hazard ratio: 1.35; 95% confidence interval: 1.12 to 1.63; p = 0.0015), indicating that such variability was informative. However, this was dependent on clinical factors, such that RAV index was not an independent predictor in adjusted models. In contrast, RA phasic function, obtained from the same images (and subject to the same limitations), was independently predictive. Our findings show that RA phasic function is an independent predictor of death and a useful adjunct to RA volume estimations.
Please note: Dr. Chirinos has received personal fees from Bristol-Myers Squibb, OPKO Healthcare, Fukuda Denshi, Microsoft, Ironwood Pharmaceuticals, Sanifit, Pfizer, Merck, and Bayer; has received grants from the National Institutes of Health, the American College of Radiology Network, Fukuda Denshi, Bristol-Myers Squibb, and Microsoft; and is named as inventor in a University of Pennsylvania patent application for the use of inorganic nitrates/nitrites for the treatment of Heart Failure and Preserved Ejection Fraction. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.
- 2019 American College of Cardiology Foundation