Left atrial expansion index and renal deterioration-causality or epi-phenomenon?

In this issue of the journal, Hsiao and Chiou assessed and followed, over 5 years, a relatively large cohort referred for a tertiary cardiology clinic, mostly for the evaluation of dyspnoea. These subjects had no diabetes, no previous myocardial infarction, and had normal renal function and normal or preserved ejection fraction. After 5year follow-up, 57 of the original 804 patients showed a decline in their renal function. Those with renal function decline were older, more often hypertensive, and had larger left ventricular (LV) mass and left atrium (LA) volume; however, the authors show that one of the strongest predictors for renal function decline was LA expansion index—a simple LA functional test, which had already been described by the authors and others previously. These observations are interesting and of potential practical clinical significance. It is now well recognized that left atrial function plays a significant role in both systolic and certainly diastolic heart failure. The contribution of left atrial contraction to stroke volume and cardiac output is up to 30%. Left atrial volume index is an important parameter in the assessment of diastolic function and is listed among the three most important echocardiographic measurements in the recent European and American Guidelines on echocardiographic measurements in heart failure with preserved LV function (the other two being tricuspid gradient and E/e’ > 14). Renal function is closely related to cardiac function. Patients with both systolic and/or diastolic heart failure are prone to deterioration of their renal function. Both heart failure itself, and certainly some medications often administered in this situation, may affect renal function. Therefore, it should come as no surprise that in a cohort, such as that described in the current manuscript, including patients complaining of dyspnoea, those with clear risk factors to develop heart failure, and who already have larger left atrial volume, will have an altered expansion index, the calculation of which is based on the largest and smallest left atrial volumes. Left atrial function has been assessed by several modalities. It is now well accepted that the left atrium contributes to filling through its reservoir, conduit, and booster pump function, and is affected by LV function throughout the cardiac cycle. During systole and isovolumic relaxation periods, the left atrium functions as a reservoir, receiving blood from the pulmonary veins, and the process is maintained by increased pressure in the left atrium, which is modulated by ventricular systole, associated with a decrease in the basal part of the LV (LV longitudinal shortening), by right ventricular pressure conducted into the pulmonary arteries and by left atrial properties such as stiffness. During diastole, the left atrium functions as a conduit. During early diastole, blood enters the LV due to pressure gradient between the two chambers. During diastasis, blood flows directly from the pulmonary veins through the left atrial conduit into the LV. This phase is modulated primarily by LV properties. During late diastole, the left atrium functions as a booster pump, and this phase contributes significantly to the total cardiac output. This phase is modulated by LV compliance, LV enddiastolic pressure, and atrial function. These complex phases and functions, each contributing to LV filling, have been demonstrated and extensively investigated by conventional echocardiography/Doppler and by more advanced techniques including tissue Doppler imaging and in particular speckle tracking, the latter has recently shown to predict recurrence of atrial fibrillation. In this article, none of these advanced techniques were used, and the complex three-phase atrial function was united into the much more simple and simplified left atrial expansion index. Nevertheless, the authors have been able to demonstrate that this simple and easy to use technique may be a useful clinical tool and is associated with future renal function decline. Is it really a true and reliable marker to be used routinely in all relatively high risk individuals? Or is atrial expansion function is simply yet another factor associated with altered left atrial function. This will still need to be further evaluated in future studies.