Author + information
We enjoyed the study by Thomas et al. published in the Journal(1); however, we have some concern regarding the absolute value of the calculated mean left atrial maximal and minimal volume. In patients without mitral regurgitation, the reservoir volume (left atrial total emptying volume) of the left atrium represents the amount of blood coming from the pulmonary vein during ventricular systole. In the case of the younger group of the present study, 22.5 ml of blood fills the left atrium from the pulmonary vein during systole. Because the systolic fraction of the pulmonary vein is 56% (of the systo-diastolic flow), we can assume that the total flow coming from the pulmonary vein (which reflects the total forward stroke volume) is 40 ml. Consequently, for the reported heart rate and body surface area, the cardiac index is 1.5 l/min/m2, which is surprisingly low for a normal patient population. This rough calculation is enforced by the observation during transesophageal echocardiography that the diameter of the pulmonary vein does not change so much during the entire cardiac cycle. It has been shown that left atrial volume measured by echocardiography is underestimated compared with both cine-computed tomography (2)and magnetic resonance imaging (3). Would it not be useful to consider a physiologic variable such as cardiac output to evaluate the accuracy of volume measurement?
- American College of Cardiology Foundation