The Ancient Contraposition between Anatomy and Function: The Effectiveness of Left Atrial Volume Index and the Advantages of Left Atrial Longitudinal Strain

Dear Sir,

I read with a great interest the article published by Limongelli et al.[1] about the correlation between left atrial volume index (LAVi) at rest and during test stress LAVi (sLAVi) and clinical outcome including atrial and ventricular arrhythmias and heart failure in patients with hypertrophic cardiomyopathy (HCM). Indeed, HCM is an extremely variable disease that, in a significant percentage of cases, can be complicated by heart failure, sudden cardiac death, and arrhythmias, and it is particularly important to find elements that could indicate a subgroup of high-risk patients. It is well known that HCM is characterized by a progressive diastolic dysfunction, due to the reduced left ventricular (LV) cavity and the increased LV filling pressures. The left atrium is the accurate mirror of LV diastolic function and earlier or later, it begins to enlarge. Indeed, it has been demonstrated that HCM patients showed increased LAVi, no matter which hypertrophy phenotype they have.[2] The obvious consequence of the left atrial (LA) remodeling and dysfunction is the onset of atrial fibrillation, the most common arrhythmia in these patients. In addition, the diastolic dysfunction attested by the increased LAVi contributes to the LV remodeling and as a consequence, it favors the onset not only of atrial but also of ventricular arrhythmias. It has been reported that LAVI was an independent predictors of appropriate implantable cardioverter-defibrillator (ICD) therapy in HCM patients and that it provided incremental clinical predictive value for appropriate ICD therapy on top of conventional sudden cardiac death risk factors.[3] The effectiveness of LAVi as a predictor of poor cardiovascular outcome was already reported by Hiemstra et al.[4] and has been confirmed by Limongelli et al.[1] in their article. Interestingly, the authors chose to test the effectiveness of LAVi not only at rest but also during an exercise stress test, finding a better prognostic relevance of sLAVi compared with LAVi at rest. sLAVi has been already used as a prognostic parameter in several clinical conditions and, for example, showed to be able to predict the presence of angiographically significant and/or multivessel coronary artery disease in patients with chest pain and no resting wall motion abnormalities.[5] The effectiveness of sLAVi can be explained if one considers that during exercise, the left atrium increases its reservoir function and thus the ventricular preload to guarantee the increase of cardiac output despite a reduction in filling time. When a pathological condition such as HCM or coronary artery disease causes LA remodeling and fibrosis, the LA reservoir function cannot be increased and the atrium enlarges.

These data clearly suggest the effectiveness of LAVi as a predictor element in patients with several pathological conditions, including HCM. However, the LA dilatation is an anatomical change of the left atrium, and as occurs in every anatomical change, it needs time to develop. In the last two decades, the improvement of echocardiographic technology allows us to accurate assess the functional changes of heart chambers, using speckle tracking echocardiography (STE) strain. It has been widely demonstrated that LA two-dimensional STE longitudinal strain, and particularly, the assessment of reservoir function, provides fundamental information about subtle LA remodeling, being able to identify atrial fibrosis[6] and to characterize diastolic dysfunction.[7] Moreover, it has been reported that an impaired atrial function can predict AF onset in patients with normal LA size[8] and that a reduced LA strain in HCM patients was associated with a higher risk for adverse cardiovascular outcomes.[9] The evidence that an impaired LA function precedes LA dilatation can be clearly understood if we consider that in the first phases of diastolic dysfunction, the elevated LV filling pressure causes a subtle LA remodeling, undetectable by anatomical quantification of LA size, characterized by deposition of collagen fibers in the interstitium, with the consequent alterations in normal conduction and LA stiffening, that favor FA onset;[10] only in a following phase LA stiffness overcomes LA functional reserve and the atrium enlarges.[11] Thus, since that our main aim should be to detect subtle dysfunction as soon as possible, to have the chance of treating it and preventing its worsening, the use of functional parameters that allow us this opportunity in our opinion, should be preferred. Of course, the prognostic importance of solid and well tested parameters like LAVi cannot be questioned; only, it would be important to understand that these new functional parameters could add fundamental pieces of information that were not available before and that could allow us to significantly contrast the progression of diastolic dysfunction to the heart failure reducing mortality in our patients.

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