The 2016 EPIC Study of administering pimobendan to dogs diagnosed with myxomatous mitral valve disease (MMVD) defined dilatation for its echocardiograph enrollment criteria as LA/Ao ≥ 1.6 and LVIDDN ≥ 1.7. Should those criteria also be used to diagnose MMVD-affected dogs as being in ACVIM Stage B2 and started on pimobendan? If not, how should cardiomegaly be determined in MMVD-affected patients?
LVID parameter is of great help in the direct assessment of cardiomyopathies. In case of hypertrophic cardiomyopathy, left ventricular internal diameter decreases in both systole and diastole while in dilation cardiomyopathy, both these parameters increase. Unlike ventricles, left atrium increases in size in response to both pressure and volume overload. For confirmatory diagnosis, primary abnormality which is causing the increase in atrial pressure and volume should be identified. Absolute increase in the left atrial diameter is not confirmatory of left atrial dilation and left atrium to aortic root ratio (LAD/AoD) is a better parameter to assess this abnormality. Instead of going for comparison of absolute measurement in a normogram or with a regression equation, this ratio can be solely relied upon to assess left atrial enlargement. A significant increase in left atrial dimension results in a greater left atrial to aortic root ratio with advancing age, as aortic root significantly diminished with age. Decreased systolic function evidenced by reduced fractional shortening (FS%) and ejection fraction (
All parameters of echocardiography in MMVD can be very misleading. They also depend on many conditions, even from the hour of the day when the study is being done. The my current study compares the possibilities of some M-mode echocardiographic and radiographic dimensions to determine the extent of the progression of MVD. There is also a new LA/AO x VHS ratio that 100% separates the dogs included in the study in regard to the absence or presence of pulmonary edema, due to the development of decompensated heart failure. The size we are introducing LA / AO x VHS multiplies the heart enlargement from the X - rays and the M - mode ultrasound imaging. I think combining the more stable radiographic dimensions with the more erratic echocardiographic dimensions is the solution to the problem.
Atanas, is not cardiomegaly a fairly reliable measure of mitral regurgitation? And, is not the rate of increase of cardiomegaly a measure of the rapidity of progression to heart failure?
Yes - to both questions. But treatment also depends on the adequacy of the remodeling.
I understand. Thank you. I know of cardiologists who classify the degree of enlargement of the LA and/or LV as mild, moderate, and severe, and they tend to classify the degree of mitral regurgitation (MR) by the same terms.
The cardiologists I follow will recommend starting pimobendan if the MR and enlargement is severe, and if moderate, they will either start the pimobendan at that time or re-check the moderate levels within a few months for any changes, and they will not consider starting pimobendan if the degree is mild but will re-check it in six months or a year.
As for their reasoning, they have found that as many as 70% or more of small dogs with mild MMVD cardiomegaly will not ever progress to heart failure, so they see no point in prescribing an expensive drug for the purpose of delaying the onset of heart failure to dogs which most likely will not ever reach that stage anyway. So, they wait for progression and if they observe it, they also pay attention to the speed of that progression.
Hello, if we comment on diameters at DMVD, it is more correct to comment on the systolic diameter.
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