Preload dependency of left atrial pump function in hypertrophic cardiomyopathy

Cardiac Resynchronization Therapy and Left Atrial Remodeling: A Novel Insight?

Cardiac resynchronization therapy (CRT) restores ventricular dyssynchrony, improving left ventricle (LV) systolic function, symptoms, and outcome in patients with heart failure, systolic dysfunction, and prolonged QRS interval. The left atrium (LA) plays tremendous roles in maintaining cardiac function, being often inflicted in various cardiovascular diseases. LA remodeling implies structural-dilation, functional-altered phasic functions, and strain and electrical-atrial fibrillation remodeling. Until now, several important studies have approached the relationship between LA and CRT. LA volumes can predict responsiveness to CRT, being also associated with improved outcome in these patients. LA function and strain parameters have been shown to improve after CRT, especially in those who were positive responders to it. Further studies still need to be conducted to comprehensively characterize the impact of CRT on LA phasic function and strain, and, also, in conjunction with its impact on functional mitral regurgitation and LV diastolic dysfunction. The aim of this review was to provide an overview of current available data regarding the relation between CRT and LA remodeling.

The three integrated phases of left atrial macrophysiology and their interactions

Our understanding of the left atrium is growing, although there are many aspects that are still poorly understood. The left atrium size as an imaging biomarker has been consistently shown to be a powerful predictor of outcomes and of different cardiovascular disorders, such as, but not limited to, atrial fibrillation, congestive heart failure, mitral regurgitation and stroke. Left atrial function has been conventionally divided into three integrated phases: reservoir, conduit and booster-pump. The highly dynamic left atrium and its response to the stretch and secretion of atrial neuropeptides leaves the left atrium far from being a simple transport chamber. The aim of this review is to provide an understanding of the left atrial physiology and its relation to disorders within the heart.

Left atrial function: physiology, assessment, and clinical implications

The interest in the left atrium (LA) has resurged over the recent years. In the early 1980s, multiple studies were conducted to determine the normal values of LA size. Over the past decade, LA size as an imaging biomarker has been consistently shown to be a powerful predictor of outcomes, including major public health problems such as atrial fibrillation, heart failure, stroke, and death. More recently, functional assessment of the LA has been shown to be, at least as, if not more robust, a marker of cardiovascular outcomes. Current available data suggest that the combined evaluation of LA size and LA function will augment prognostication. The aim of this review is to provide a critical appraisal of current echocardiographic techniques for the assessment of LA function and the implications of such assessment for prediction and disease prevention.

An integrated approach to determine left atrial volume, mass and function in hypertrophic cardiomyopathy by two-dimensional echocardiography

METHODS

The study included 25 hypertrophic cardiomyopathy (HCM) patients (15 non-obstructive and 10 obstructive) and 25 controls for assessment of left atrial (LA) volume, mass and function by two-dimensional echocardiography. Measurement included mean LA diameter (LAD), LA mass = {(mean LAD + anterior LA wall + posterior LA wall)3 - mean LAD3} x 0.8 + 0.6, LA volume = [(8/3 pi L . A1 . A2), where L is LA length, A1 and A2 are LA area in 4-chambers and 2-chambers, respectively] including maximum (V max), minimum (V min), and pre-atrial contraction (V pre-A), total atrial stroke volume (TA-SV), TA emptying fraction (TA-EF), active atrial SV (AA-SV), AA-EF, passive atrial SV (PA-SV), PA-EF, atrial expansion index (AEI), and LA kinetic energy (LA-KE) = (1/2) x AA-SV x P x V2.

RESULTS

LAD, LA mass, V max, V min, and V pre-A were significantly higher in HCM than controls. TA-SV and TA-EF were comparable in both HCM subgroups and controls. AA-SV and LA-KE were significantly higher in both HCM subgroups than controls. LA-KE was significantly higher in obstructive HCM than non-obstructive (P < 0.001). PA-EF and AEI were significantly lower in obstructive HCM than controls (P < 0.05).

CONCLUSION

HCM is associated with increased LA size and augmented LA pump function especially obstructive type. LA conduit and reservoir functions are impaired in obstructive HCM.

Left atrial myopathy in idiopathic dilated cardiomyopathy

To investigate whether left atrial systolic dysfunction in dilated cardiomyopathy is the result of left atrial dilatation, atrial involvement in the myopathic process, or both, 20 patients with aortic stenosis, 14 patients with idiopathic dilated cardiomyopathy, and 10 normal control subjects were studied. Left atrial volumes (cubic centimeters) were echocardiographically measured at mitral valve opening (maximal), mitral valve closure (minimal), and onset of atrial systole (P wave of the electrocardiogram) with the biplane area-length method. Atrial systolic function was assessed by calculating the active emptying fraction, equal to (volume at onset of atrial systole minus minimal volume)/volume at onset of atrial systole. Heart rate was similar in patients with aortic stenosis and dilated cardiomyopathy (83 +/- 11 vs 86 +/- 15 beats/min, respectively). Maximal volume was similar in patients with aortic stenosis (74.8 +/- 26.4 cm3) and dilated cardiomyopathy (79.7 +/- 25.3 cm3) but greater (p < 0.0001) than in control subjects (46.4 +/- 11.9 cm3). Active emptying fraction was inversely related to volume at onset of atrial systole and to tension at end of atrial systole (aortic stenosis r = -0.61 and r = -0.81, respectively; dilated cardiomyopathy r = -0.79 and r = -0.66, respectively). At any given level of volume at onset of atrial systole and tension at end of atrial systole, however, active emptying fraction was lower in patients with dilated cardiomyopathy compared with those with aortic stenosis.(ABSTRACT TRUNCATED AT 250 WORDS)