LA volume is one of the critical parameters that define (as well as determines the symptoms) both diastolic and systolic LV dysfunction.Still, we are tentative in the true estimates about the normal range of LA volume. (Upper limit 40ml/m²) .We are surprised to note, the difference between MRI derived and Echo measured LA volume showed a disturbing variation nearing 80 %.
How to measure LA volume?
While the timing of LA volume measurement has not much controversy (end-systole), and the shape errors are largely eliminated by 3D echo, still why this variation?
It is a telltale error, of either including (or excluding ) the pulmonary vein ostium and complete blindness to LAA during LA border tracing. We know, LAA is physiologically, pathologically, and electrically is a critical accessory of LA. Still, we have so for excluded it from routine LA volume calculations. Is that a right-thinking in the overall evaluation of LA volume?
Normal LAA volume
Though the LAA volume is directly related to its size, shape much great confounder, since it precludes in arriving any mathematical calculation of volume from the area. Direct casts ofLAA and 3D echo to a certain extent will help measure LAA volume. MRI may also do the same.The normal LAA volume is calculated to be up to 20 ± 9 ml. Whatever be the LAA volume, one estimate suggests it will reach 25 % of total LA volume. This is very important to know. In fact, In significant LV dysfunction, LAA is expected to stretch, efface, and dilate and contribute more to LA volume. Both static and dynamic LAA volume status also gives us an idea about potential thrombus formation risk.
Are we justified to Ignore the LAA volume during routine LA function assesment ?
I don’t know. It may be wise to routinely add LAA volume to LA chamber volume to truly assess 1.Overall LA function, 2.Estimate the risk of thrombus formation and 3.Risk of developing AF. Meanwhile, its found LAA appendage volume might even approach that of LA volume when it’s pathologically enlarged. (Left Atrial Appendage Volume as a New Predictor of Atrial Fibrillation Recurrence After Catheter AblationPedro Pinto Teixeira et al. J Interv Card Electrophysiol. 2017 August)
LAA volume is Important for one more reason
We are getting new data about dynamic LAA volume status during LAA closure.In fact , this particular study (JACC: Cardiovascular Interventions Volume 8, Issue 15, December 2015) documented how LAA appendage balloons out during volume loading of LA.This study suggests we have to be careful about the hidden potential of LAA to expand and if ignored the device is likely to get dislodged with volume overloading. These observations make it clear we can’t isolate LAA volume when calculating LA volume.
Final message
There is a strong case for measuring LAA size & volume separately and preferably be added in the net LA volume Index. We can’t simply Ignore this vital and inherent part of LA , just because its called as an appendage. Of course, even a novice will rank LAA first, as the pathological hot spot within the entire LA.
Reference
Everything about LAA
Giuseppe Patti, Vittorio Pengo, Rossella Marcucci,The left atrial appendage: from embryology to prevention of thromboembolism European Heart Journal, Volume 38, Issue 12, 21 March 2017, Pages 877–887, https://doi.org/10.1093/eurheartj/ehw159
Dr.S.Venkatesan MD 