Liza Thomas

Echocardiographic evaluation of left atrial size and function: Current understanding, pathophysiologic correlates, and prognostic implications

Left atrial (LA) volume has recently been identified as a potential biomarker for cardiac and cerebrovascular disease. However, evidence regarding the prognostic implications of LA volume still remains unclear. Evaluation of LA size and function using traditional and more recent echocardiographic parameters is potentially feasible in the routine clinical setting. This review article discusses the conventional and newer echocardiographic parameters used to evaluate LA size and function. Conventional parameters include the assessment of phasic atrial activity using atrial volume measurements, transmitral Doppler peak A velocity, atrial fraction, and the atrial ejection force. Newer parameters include Doppler tissue imaging (DTI) including segmental atrial function assessment using color DTI, strain, and strain rate. In addition, an overview of the implications and clinical relevance of the findings of an enlarged left atrium, from currently available literature, is presented.

Compensatory changes in atrial volumes with normal aging: is atrial enlargement inevitable?

OBJECTIVES The aim of this study was to evaluate left atrial volume and its changes with the phases (active and passive) of atrial filling, and to examine the effect of normal aging on these parameters and pulmonary vein (PV) flow patterns. BACKGROUND Atrial volume change with normal aging has not been adequately described. Pulmonary vein flow patterns have not been volumetrically evaluated in normal aging. Combining atrial volumes and PV flow patterns obtained using transthoracic echocardiography could estimate shifts in left atrial mechanical function with normal aging. METHODS A total of 92 healthy subjects, divided into two groups: Group Y (young <50 years) and Group O (old > or =50 years), were prospectively studied. Maximal (Vol(max)) and minimal (Vol(min)) left atrial volumes were measured using the biplane method of discs and by three-dimensional echocardiographic reconstruction using the cubic spline interpolation algorithm. The passive filling, conduit, and active emptying volumes were also estimated. Traditional measures of atrial function, mitral peak A-wave velocity, velocity time integral (VTI), atrial emptying fraction, and atrial ejection force were measured. RESULTS As age increased, Vol(max), Vol(min), and total atrial contribution to left ventricle (LV) stroke volume were not significantly altered. However, the passive emptying volume was significantly higher (14.2 +/- 6.4 ml vs. 11.6 +/- 5.7 ml; p = 0.03) whereas the active emptying volume was lower (8.6 +/- 3.7 ml vs. 10.2 +/- 3.8 ml; p = 0.04) in Group Y versus Group O. Pulmonary vein flow demonstrated an increase in peak diastolic velocity (Group Y vs. Group O) with no corresponding change in diastolic VTI or systolic fraction. CONCLUSIONS Normal aging does not increase maximum (end-systolic) atrial size. The atrium compensates for changes in LV diastolic properties by augmenting active atrial contraction. Pulmonary vein flow patterns, although diastolic dominant using peak velocity, demonstrated no volumetric change with aging.

Abnormalities of left atrial function after cardioversion: an atrial strain rate study

Background and objectives: The role of atrial myocardial dysfunction after cardioversion is unclear. In a comparison of patients after successful cardioversion from chronic atrial fibrillation (CAF) and normal controls, we sought to determine whether Doppler-derived atrial strain rate (A-sr) could be used to measure global left atrial function and whether A-sr was reduced in patients with CAF. Methods: A-sr was measured from the basal septal, lateral, inferior and anterior atrial walls from the apical four-chamber and two-chamber views in 37 patients with CAF who had been cardioverted to sinus rhythm and followed up for 6 months, and in a cohort of 37 healthy people. Conventional measures of atrial function included peak transmitral A-wave velocity, A-wave velocity time integral, atrial fraction and the left atrial ejection fraction. Doppler tissue imaging was used to estimate atrial contraction velocity (A′ velocity). In addition to amplitude parameters, the time to peak A-sr was measured from aortic valve closure. Results: Immediately after cardioversion, A-sr in the CAF cohort (baseline) was significantly lower than in controls (mean (SD) −0.53 (0.31) v −1.6 (0.75) s−1; p<0.001); the A-sr correlated with A′ velocity (r = 0.63; p<0.001) in patients. Atrial function improved over time, with maximal change observed in the initial 4 weeks after cardioversion. The time to peak A-sr was increased in the CAF group compared with controls (0.55 (0.15) v 0.46 (0.12) s), but this failed to normalise over time. Conclusion: A-sr is a descriptor of atrial function, which is reduced after cardioversion from CAF and subsequently recovers.

Two-dimensional myocardial strain imaging detects changes in left ventricular systolic function immediately after anthracycline chemotherapy

AIMS The efficacy of anthracyclines is undermined by potential life-threatening cardiotoxicity. Cardiotoxicity is dependent upon several factors and the timing to its development is variable. Moreover, as adjuvant therapy with trastuzumab often follows, a close monitoring of cardiac function in those treated with anthracyclines is mandatory. Left ventricular ejection fraction (LVEF) by echocardiography is currently used for monitoring cardiotoxicity; however, LVEF has numerous limitations. Two-dimensional strain imaging may provide a more sensitive measure of altered LV systolic function, so the aim of the present study was to compare LVEF and LV systolic strain before and after anthracyclines. METHODS AND RESULTS Fifty-two women with histologically confirmed breast cancer were prospectively studied. Echocardiographic LVEF (by Simpsons method), global and regional peak longitudinal, radial, and circumferential 2D systolic strain were measured 1 week before and 1 week after chemotherapy. Global and regional longitudinal LV systolic strain was significantly reduced after treatment; global longitudinal strain decreased from -17.7 to -16.3% (P < 0.01) with 48% of global measurements reduced by >10%. Global and regional radial LV systolic strain after treatment was also significantly reduced; global radial strain dropped from 40.5 to 34.5% (P < 0.01) with 59% of global measurements reduced by >10%. In contrast, no reduction in LVEF >10% after chemotherapy was observed. CONCLUSION Reduced LV systolic strain immediately after anthracycline treatment may indicate early impairment of myocardial function before detectable change in LVEF.

Impact of Mild Hypertension on Left Atrial Size and Function

Background—Left atrial (LA) enlargement has been documented to occur in moderate and severe hypertension. Methods and Results—One hundred twelve mild hypertension patients were prospectively recruited and compared with 198 healthy volunteers. All recruits had a transthoracic echocardiogram. Maximum LA biplane volume, minimum LA biplane volume, and pre ‘p’-LA biplane volume were measured, and left atrial passive, active emptying, and conduit volumes were calculated at baseline and in a subgroup of patients after 12 months. After adjusting for age, gender, and body mass index, maximum LA biplane volume, pre ‘p’-LA biplane volume, and their indexed volumes were increased in the hypertension group. Active emptying volume and fraction were significantly increased in the hypertension group, with no change in conduit and passive volumes. Subgroup analysis comparing hypertensives with normal/mildly increased left ventricular mass (group 1) with those with moderate/severely increased left ventricular mass (group 2) at baseline demonstrated that maximum LA biplane volume (62.8±17.9 mL versus 45.4±13.7 mL; P<0.001) was significantly increased in group 2. Active emptying volume was also increased. Conclusion—Even mild hypertension seems to be associated with a reduction in early diastolic filling. This results in augmented late left ventricular diastolic filling due to active atrial contraction and may be the mechanism for the increase in left atrial size.

Atrial dilation and altered function are mediated by age and diastolic function but not before the eighth decade.

OBJECTIVES This study investigated changes in left atrial (LA) volumes and phasic atrial function, by deciles, with normal aging. BACKGROUND LA volume increase is a sensitive independent marker for cardiovascular disease and adverse outcomes. To use this variable more effectively as a marker of pathology and a gauge of outcome, physiological changes due to aging alone need to be quantitated. METHODS A detailed transthoracic echocardiogram was performed in 220 normal subjects; 89 (41%) were male and their age ranged from 20 to 80 years (mean 45 ± 17 years). Maximum (end-ventricular systole), minimum (end-ventricular diastole), and pre-a-wave volumes were measured using the biplane method of disks. LA filling, passive emptying, conduit and active emptying volumes, and fractions were calculated. Transmitral inflow, pulmonary vein flow, and pulsed-wave Doppler tissue imaging parameters were measured as expressions of left ventricular diastolic function. For purposes of analysis, subjects were divided by age deciles. RESULTS LA indexed maximum (0.05 ml/m(2) per year) and minimum (0.06 ml/m(2) per year) volume increased with age but only became significant in the eighth decade (26.0 ± 6.3 ml/m(2), p = 0.02, and 13.5 ± 3.9 ml/m(2), respectively; p < 0.001). Impaired left ventricular diastolic relaxation was apparent in decade 6 and was associated with a shift in phasic LA volumes so that LA expansion index and passive emptying decreased with increasing age, whereas active emptying volume increased. CONCLUSIONS In normal healthy subjects, LA indexed volumes remain nearly stable until the eighth decade when they increase significantly. Therefore, an increase in LA size that occurs before the eighth decade is likely to represent a pathological change. Changes in phasic atrial volumes develop earlier consequent to age-related alteration in LV diastolic relaxation.

Atrial strain rate is a sensitive measure of alterations in atrial phasic function in healthy ageing

Objective Strain and strain rate measure local deformation of the myocardium and have been used to evaluate phasic atrial function in various disease states. The aim of this study was to define normal values for tissue Doppler-derived atrial strain measurements and examine age-related changes by decade in healthy individuals. Methods Transthoracic echocardiograms were performed on 188 healthy subjects. Tissue Doppler-derived strain and strain rate were measured from the apical four and two-chamber views of the left atrium, and global values were calculated as the mean of all segments. Measurements included peak systolic strain, systolic strain rate, early and late diastolic strain rate. Phasic left atrial volumes and fractions were calculated. Mitral inflow and tissue Doppler imaging were employed to estimate left ventricular diastolic function. Results A significant reduction in global systolic strain was observed from decade 6. Alterations in atrial strain rate were apparent from decade 5; systolic strain rate and early diastolic strain rate decreased, while late diastolic strain rate increased significantly. Changes in phasic atrial volume and function occurred in conjunction with age-related changes in left ventricular diastolic function. Importantly, age-related changes in global atrial systolic strain rate and early diastolic strain rate occurred a decade before corresponding changes in atrial phasic volume parameters. Conclusion Atrial strain and strain rate can be used to quantify atrial phasic function and appear to be altered before traditional parameters with ageing. Strain analysis may therefore be more sensitive in detecting subclinical atrial dysfunction with alterations in strain rate parameters observed before traditional parameters.

Strain rate evaluation of phasic atrial function in hypertension

Background: Strain (SI) and strain rate (SR) measure regional myocardial deformation and may be a new technique to assess phasic atrial function. Objective: To examine the feasibility of using SI and SR to evaluate phasic atrial function in patients with mild hypertension (HT). Patients and methods: The study group comprised 54 patients with mild essential HT (29 women) and 80 age-matched normal controls (47 women). Standard two-dimensional and Doppler echocardiography was performed as well as Doppler tissue imaging. The following left atrial (LA) volumes were measured: (a) maximal LA volume or Volmax; (b) minimal LA volume or Volmin; (c) just before the “p” wave on ECG (Volp). Phasic LA volumes were also calculated. Systolic (S-Sr), early diastolic (E-Sr), late diastolic (A-Sr) strain rate and SI were measured. Results: Despite no differences in indexed maximal LA volume with only mild increases in left ventricular mass in the HT cohort compared with normal subjects (mean (SD) 86 (18) g/m2 vs 67 (14) g/m2; p = 0.001), E-Sr was significantly lower in the HT cohort. There was a corresponding reduction in indexed conduit volume in the HT cohort compared with normal subjects (10.5 (7.5) ml/m2 vs 13.8 (6.1) ml/m2; p = 0.006). Global E-Sr showed modest negative correlations with LA Volmax and LA ejection fraction. No significant difference was present in S-Sr, A-Sr or global atrial strain between the normal and HT cohorts. Conclusion: Mild HT results in a reduction in LA conduit volume, although maximal LA volume is unchanged. This is reflected by a reduction in E-Sr with preserved S-Sr and A-Sr.

Changes in left atrial volume in diabetes mellitus: more than diastolic dysfunction?

AIM To evaluate left atrial (LA) volume and function as assessed by strain and strain rate derived from 2D speckle tracking and their association with diastolic dysfunction (DD) in patients with diabetes mellitus (DM). METHODS AND RESULTS Seventy three patients with DM were compared with age- and gender-matched normal controls; 30 patients with DM alone were compared to those with hypertension (HT) alone. The maximum LA volume, traditional measures of atrial function, 2D strain and strain rate were analysed. The LA indexed volume (LAVI) was larger in DM group than that in normal controls (38.2 ± 9.9 vs. 20.5 ± 4.8 ml/m(2), P< 0.0001), as well as in DM alone compared with hypertensive patients (33.9 ± 10 vs. 25.7 ± 8 ml/m(2), P< 0.0001). Global strain was significantly reduced in the DM group compared with that in normal controls (22.5 ± 8.67 vs. 30.6 ± 8.27%; P< 0.0001) but was similar with HT. There was a weak correlation between LAVI and global strain with increasing grades of DD (r= 0.439, P< 0.0001 and r= - 0.316, P< 0.0001, respectively) in the diabetic group. However, there was no significant difference in LAVI between these groups. A logistic regression analysis for predictors of LAVI demonstrated that only diabetes was a determinant of LAVI. Patients with diabetes showed a significant reduction in global strain compared with normal controls but no difference with increasing grades of diastolic function. CONCLUSIONS LA enlargement in DM is independent of associated HT and diastolic function. LA enlargement is associated with LA dysfunction as evaluated by 2D strain. It is likely that a combination of DD and a diabetic atrial myopathy contribute to LA enlargement in patients with DM.

Clinical StudiesPeak Mitral Inflow Velocity Predicts Mitral Regurgitation Severity 12

OBJECTIVES Mitral regurgitation (MR) is a common echocardiographic finding; however, there is no simple accurate method for quantification. The aim of this study was to develop an easily measured screening variable for hemodynamically significant MR. BACKGROUND The added regurgitant volume in MR increases the left atrial to left ventricular gradient, which then increases the peak mitral inflow or the peak E wave velocity. Our hypothesis was that peak E wave velocity and the E/A ratio increase in proportion to MR severity. METHODS We performed a retrospective analysis of 102 consecutive patients with varying grades of MR seen in the Adult Echocardiography Laboratory at the University of California, San Francisco. Peak E wave velocity, peak A wave velocity, E/A ratio and E wave deceleration time were measured in all patients. The reference standard for MR was qualitative echocardiographic evaluation by an expert and quantitation of regurgitant fraction using two-dimensional and Doppler echocardiography. RESULTS Peak E wave velocity was seen to increase in proportion to MR severity, with a significant difference between the different groups (F = 37, p < 0.0001). Peak E wave velocity correlated with regurgitant fraction (r = 0.52, p < 0.001). Furthermore, an E wave velocity >1.2 m/s identified 24 of 27 patients with severe MR (sensitivity 86%, specificity 86%, positive predictive value 75%). An A wave dominant pattern excluded the presence of severe MR. The E/A ratio also increased in proportion to MR severity. Peak A wave velocity and E wave deceleration time showed no correlation with MR severity. CONCLUSIONS Peak E wave velocity is easy to obtain and is therefore widely applicable in clinical practice as a screening tool for evaluating MR severity.