Background Assessment of left atrial (LA) size is important in medical decision making and prognostication in dogs with myxomatous mitral valve disease (MMVD). Real‐time 3‐dimensional (RT3DE) and 2‐dimensional echocardiographic (2DE) methods may be used to assess LA size. Objectives To compare measured LA volumes obtained by RT3DE with those calculated by biplane Simpson's modified method of discs (SMOD) and the area‐length method (ALM) using the same RT3DE acquisition with the same timing. Animals One hundred twenty‐one privately owned dogs with naturally occurring MMVD. Methods Prospective observational study comparing LA volumes indexed to body weight using RT3DE and 2DE‐based biplane SMOD and ALM. Agreement between methods was evaluated using Bland‐Altman plots and linear regression analyses. Results Estimations of LA volume using SMOD or ALM did not show good agreement with RT3DE‐derived measurements. Absolute differences between methods increased with increasing LA volume, but SMOD underestimated whereas ALM overestimated calculated volumes compared to RT3DE‐derived measurements. The difference in LA volume between RT3DE and the biplane methods showed a systematic underestimation of 7% for SMOD and a systematic overestimation of 24% for ALM. Comparison of LA volumes obtained by SMOD and ALM did not show good agreement. The ALM yielded 30% larger LA volumes compared to SMOD. Conclusion and Clinical Importance In comparison with RT3DE, SMOD systematically underestimated whereas ALM systematically overestimated LA volumes in dogs with MMVD. Because the systematic difference between RT3DE and SMOD was only 7%, SMOD might be considered the method of choice.

Background: Real-time 3-dimensional (RT3D) echocardiography provides a novel technique for assessing left atrial ejection fraction (LAEF) in dogs.Hypothesis: Left atrial ejection fraction is associated with severity of myxomatous mitral valve disease (MMVD). Animals: Privately owned dogs; 101 with MMVD and 52 healthy control dogs. Methods: Prospective observational study using RT3D echocardiographic estimations of LA volumes at atrial end-diastole and atrial end-systole to calculate LAEF in comparison with conventional 2-dimensional echocardiographic variables.Results: Left atrial ejection fraction decreased with increasing LA to aortic ratio (LA/Ao), percentage increase in left ventricular (LV) internal dimension, corrected for body weight (BW), in diastole (LVIDd inc%) and systole (LVIDs inc%), and age for MMVD dogs, and with BW for control dogs. The final models in the multiple regression analyses included LVIDd inc% and age for MMVD dogs, and BW alone for control dogs. LAEF varied widely in both MMVD dogs and control dogs.Conclusion and clinical importance: The wide variation of LAEF and the fact that LAEF does not appear to be an independent marker of disease severity suggest that the clinical importance of determining LAEF in dogs with MMVD might be limited.

BackgroundEffective regurgitant orifice area (EROA), calculated from the vena contracta width (VCW) as the narrowest portion of the proximal regurgitant jet, might be used to estimate severity of mitral regurgitation. However, this simplified assumption only holds when the EROA is circular, which might not be true in dogs with myxomatous mitral valve disease (MMVD).HypothesisEffective regurgitant orifice area in dogs with MMVD is noncircular, and using color Doppler real‐time 3‐dimensional (RT3D) echocardiography, measured EROA in the en face view will be significantly different from calculated EROA.AnimalsHundred and fifty‐eight privately owned dogs with naturally occurring MMVD.Materials and MethodsProspective observational study comparing en face view of EROA with calculated EROA using VCW in 4‐chamber (4Ch) and 2‐chamber (2Ch) view only or combined 4Ch and 2Ch views using RT3D echocardiography.ResultsThe calculated EROA using the 2Ch view showed a systematic underestimation of 17% compared with the measured en face EROA corrected for body surface area. The calculated EROA using 4Ch and 4Ch + 2Ch views showed less agreement with the en face EROA, and the difference between methods increased with increasing EROA. The difference between calculated and measured EROA showed a systematic underestimation of the calculated EROA by 36% (4Ch) and 33% (4Ch + 2Ch), respectively, compared to measured en face EROA.Conclusion and Clinical ImportanceWhen replacing measured EROA with calculated EROA using VCW measurements, the 2Ch view is preferred in dogs with MMVD.

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