Effects of experimental cardiac volume loading on left atrial phasic function in healthy dogs

Incremental Prognosis by Left Atrial Functional Assessment: The Left Atrial Coupling Index in Patients With Floppy Mitral Valves

Background Emerging data suggest important prognostic value to left atrial (LA) characteristics, but the independent impact of LA function on outcome remains unsubstantiated. Thus, we aimed to define the incremental prognostic value of LA coupling index (LACI), coupling volumetric and mechanical LA characteristics and calculated as the ratio of left atrial volume index to tissue Doppler imaging a', in a large cohort of patients with isolated floppy mitral valve. Methods and Results All consecutive 4792 patients (61±16 years, 48% women) with isolated floppy mitral valve in sinus rhythm diagnosed at Mayo Clinic from 2003 to 2011, comprehensively characterized and with prospectively measured left atrial volume index and tissue Doppler imaging a' in routine practice, were enrolled, and their long-term survival analyzed. Overall, LACI was 5.8±3.7 and was <5 in 2422 versus ≥5 in 2370 patients. LACI was independently higher with older age, more mitral regurgitation (no 3.8±2.3, mild 5.1±3.0, moderate 6.5±3.8, and severe 7.8±4.3), and with diastolic (higher E/e') and systolic (higher end-systolic dimension) left ventricular dysfunction (all P≤0.0001). At diagnosis, higher LACI was associated with more severe presentation (more dyspnea, more severe functional tricuspid regurgitation, and elevated pulmonary artery pressure, all P≤0.0001) independently of age, sex, comorbidity index, ventricular function, and mitral regurgitation severity. During 7.0±3.0 years follow-up, 1146 patients underwent mitral valve surgery (94% repair, 6% replacement), and 880 died, 780 under medical management. In spline curve analysis, LACI ≥5 was identified as the threshold for excess mortality, with much reduced 10-year survival under medical management (60±2% versus 85±1% for LACI <5, P<0.0001), even after comprehensive adjustment (adjusted hazard ratio, 1.30 [95% CI, 1.10-1.53] for LACI ≥5; P=0.002). Association of LACI ≥5 with higher mortality persisted, stratifying by mitral regurgitation severity of LA enlargement grade (all P<0.001) and after propensity-score matching (P=0.02). Multiple statistical methods confirmed the significant incremental predictive power of LACI over left atrial volume index (all P<0.0001). Conclusions LA functional assessment by LACI in routine practice is achievable in a large number of patients with floppy mitral valve using conventional Doppler echocardiographic measurements. Higher LACI is associated with worse clinical presentation, but irrespective of baseline characteristics, LACI is strongly, independently, and incrementally determinant of outcome, demonstrating the crucial importance of LA functional response to mitral valve disease.

Effect of pimobendan on left atrial function in dogs with preclinical myxomatous mitral valve disease

Background

Left atrial (LA) function is an important determinant of the left ventricular (LV) filling, playing a key role in maintaining optimal cardiac performance. Pimobendan is a phosphodiesterase III inhibitor with positive inotropic and vasodilator effects. The present study aims to investigate the effects of pimobendan on LA function in dogs with stage B2 myxomatous mitral valve disease (MMVD).

Aim

The aim of this investigation was to study the effects of pimobendan on LA function in dogs with preclinical MMVD.

Methods

Twenty-seven dogs with stage B2 MMVD were retrospectively included. LA function was assessed before and 1-6 months following pimobendan initiation. For each dog, two-dimensional (2D) echocardiography was performed to assess LA diameter and volume for each phase of the LA cycle and to assess complete, passive, and active LA function. Pulsed-wave tissue Doppler imaging (TDI) of the left ventricular longitudinal myocardial velocity associated with atrial contraction (A'), both at the level of the interventricular septum and the LV free wall, was also used as an indicator of LA function.

Results

There were no significant differences in any of the left atrial variables pre- and posttreatment.

Conclusion

Echocardiographic estimates of LA function by 2D diameters and volumes and TDI A' in dogs with MMVD do not change after treatment with pimobendan.

Effect of acute volume loading on left atrial strain values derived from two-dimensional speckle tracking echocardiography in dogs

The purpose of this study was to evaluate the cardiac acute volume loading effect on left atrial (LA) strain and strain rate (SR) parameters derived from two-dimensional speckle tracking echocardiography (2D-STE) in healthy dogs. Six healthy beagles were anesthetized and subjected to increase cardiac preload by intravenous infusion with lactated Ringer solution at 150 ml/kg/hr for 90 min. A Swan-Ganz catheter was placed to directly measure the mean pulmonary capillary wedge pressure (PCWP). Echocardiography was performed before (baseline) and at 15, 30, 45, 60, 75, and 90 min after acute volume loading began. Apical 4-chamber images focused on the LA were digitally recorded for later strain and SR analysis via 2D-STE. Acute volume loading significantly increased from baseline during LA strain and SR as assessed by the speckle tracking–based technique during reservoir and conduit function at 15 to 90 min after volume load began, and strain indices representing booster pump function were enhanced at 45 to 90 min. In addition, acute volume loading resulted in a significantly greater PCWP after fluid infusion. On multiple regression analysis, quadratic regression analysis was a better fit for the relationship between PCWP and all LA functional indices. Our findings indicated that LA function analyzed by strain and SR was enhanced during cardiac acute volume loading in healthy dogs. The change in strain and SR during acute volume loading should be interpreted with caution during the diagnosis of heart diseases related to volume overload.

Prognostic value of echocardiographic indices of left atrial morphology and function in dogs with myxomatous mitral valve disease

Background

The prognostic relevance of left atrial (LA) morphological and functional variables, including those derived from speckle tracking echocardiography (STE), has been little investigated in veterinary medicine.

Objectives

To assess the prognostic value of several echocardiographic variables, with a focus on LA morphological and functional variables in dogs with myxomatous mitral valve disease (MMVD).

Animals

One‐hundred and fifteen dogs of different breeds with MMVD.

Methods

Prospective cohort study. Conventional morphologic and echo‐Doppler variables, LA areas and volumes, and STE‐based LA strain analysis were performed in all dogs. A survival analysis was performed to test for the best echocardiographic predictors of cardiac‐related death.

Results

Most of the tested variables, including all LA STE‐derived variables were univariate predictors of cardiac death in Cox proportional hazard analysis. Because of strong correlation between many variables, only left atrium to aorta ratio (LA/Ao > 1.7), mitral valve E wave velocity (MV E vel > 1.3 m/s), LA maximal volume (LAVmax > 3.53 mL/kg), peak atrial longitudinal strain (PALS < 30%), and contraction strain index (CSI per 1% increase) were entered in the univariate analysis, and all were predictors of cardiac death. However, only the MV E vel (hazard ratio [HR], 4.45; confidence interval [CI], 1.76‐11.24; P < .001) and LAVmax (HR, 2.32; CI, 1.10‐4.89; P = .024) remained statistically significant in the multivariable analysis.

Conclusions and Clinical Importance

The assessment of LA dimension and function provides useful prognostic information in dogs with MMVD. Considering all the LA variables, LAVmax appears the strongest predictor of cardiac death, being superior to LA/Ao and STE‐derived variables.

Left Atrial Strain at Different Stages of Myxomatous Mitral Valve Disease in Dogs

Background

Decreased function of the left atrium (LA) is a useful prognostic indicator in dogs with myxomatous mitral valve disease (MMVD). In humans, LA strain is a novel severity indicator of mitral regurgitation, but its clinical utility in dogs has not been confirmed.

Objectives

To examine whether LA strain as evaluated with speckle‐tracking echocardiography is associated with MMVD stage in dogs.

Animals

Fifty‐two client‐owned dogs with MMVD.

Methods

Cross‐sectional study. Dogs were classified as stage B1, B2, C, or D, according to the American College of Veterinary Internal Medicine consensus. Physical examination findings and echocardiographic variables were compared among the groups. To assess the comparative accuracy of echocardiographic variables in identifying dogs with the presence or history congestive heart failure (CHF), receiver operating characteristic curves and multivariate logistic analysis were used.

Results

There were no significant differences in parameters of LA strain between B1 and B2 groups. However, LA longitudinal strain during atrial contraction (ε_A) (median, 19.1%; interquartile range, 15.3–24.3% in B1, 19.6%; 14.1–21.4% in B2, 6.2%; 3.18–11.2% in C/D) and during ventricular systole (ε_S) (32.7%; 28.9–39.2% in B1, 35.6%; 31.7–41.9% in B2, 23.6%; 16.9–26.1% in C/D) were significantly lower in stages C/D than in stages B1 and B2. In multivariate logistic regression analysis, ε_A and peak early diastolic mitral inflow velocity were identified as independent indicators of stage C/D.

Conclusions and Clinical Importance

ε_A was the best predictor of the presence or history of CHF. Further studies are needed to determine the clinical implications of these findings for treatment decisions and prognosis determination.