Dogs With MMVD May Develop Reductions In PCV
4 years ago 
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A new study, published in the latest issue of the Journal of Small Animal Practice (JSAP), identified an inverse relationship between packed cell volume (PCV) and the severity of myxomatous mitral valve disease (MMVD) in dogs. The study was funded by BSAVA-PetSavers, the charitable division of the British Small Animal Veterinary Association.
The study titled “The effect of myxomatous mitral valve disease severity on packed cell volume” was a retrospective analysis of prospectively collected data. Clinical data were selected from a population of dogs (n=289) on more than one occasion (n=1465 visits) between 2004-2017 at a research clinic conducted by the Royal Veterinary College in two primary-care practices in London, UK. A control population of normal, unaffected patients seen at the same research clinic were included in the study.
To be included in the study, dogs were required to have received an echocardiographic diagnosis of MMVD by a board-certified cardiologist and have a measurement of PCV available from the same examination. Dogs underwent repeated examinations approximately every 6 months and at each visit a jugular blood sample was taken. PCV (% whole blood), total solids (TS, g/L) and blood urea nitrogen (BUN, mmol/L) concentration were measured. Standard right parasternal echocardiographic views were obtained, from which the left atrial to aortic root ratio and the normalised left ventricular internal diameter at end diastole were calculated. Heart disease was staged according to American College of Veterinary Internal Medicine (ACVIM) guidelines.
Dr Jenny Wilshaw, corresponding author for the paper, said: “In this study, PCV appeared to decrease with increasing severity of preclinical disease, producing a significant difference when stages B1 and B2 were compared. Interestingly, this inverse relationship with ACVIM stage did not continue through to stage C. PCV in stage C was significantly greater than either preclinical stage, lying closer to that of the unaffected dogs.”
Dr Wilshaw continued: “A second analysis indicated that the increased PCV in stage C disease may be due to diuresis reducing plasma volume, as dogs receiving furosemide had higher values of PCV. We therefore concluded that dogs with MMVD may develop small reductions in PCV as a result of haemodilution. This study adds to our understanding of the pathophysiology of MMVD by suggesting that plasma volume is expanded as early as stage B1.
“Similar associations between left ventricular internal diameter at end diastole, furosemide administration and TS were observed when TS was analysed as the dependant variable. Haemodilution would not be expected to affect PCV in isolation, so finding these results for another component of blood provides further support for our interpretation.”
“In addition to ACVIM stage, several demographic factors also remained in the model. When grouped as Cavalier King Charles Spaniel (CKCS) or non-CKCS, PCV was significantly lower in CKCS.”
Nicola Di Girolamo, Editor of JSAP concluded: “Although retrospective, this study included a large population of dogs and appropriate statistical techniques to account for repeated measures from the same individual. Studies like this one are particularly welcome to the JSAP, as a base for further prospective research.”
BSAVA-PetSavers is funded solely by charitable donations and has invested more than £2 million in vital clinical research and training programmes over the past 40 years to advance clinical investigations into pet animal medicine and surgery. For further information on BSAVA-PetSavers visit: http://www.petsavers.org.uk
The full article can be found in the June issue of the Journal of Small Animal Practice and can be read online here: https://onlinelibrary.wiley.com/doi/10.1111/jsap.13308. It is open access and can be freely accessed by anyone.
The Journal of Small Animal Practice is published monthly and access to all articles is free for BSAVA members. For information on how to become a BSAVA member visit https://www.bsava.com/Membership/Member-categories
1J. Wilshaw, M. Stein, N. Lotter, J. Elliott and A. Boswood (2021) The effect of myxomatous mitral valve disease severity on packed cell volume in dogs. Journal of Small Animal Practice, 62 (5). Available at: https://onlinelibrary.wiley.com/doi/10.1111/jsap.13308
Further information relating to the ACVIM consensus guidelines for the diagnosis and treatment of MMVD in dogs can be found here. Briefly, the staging system for MMVD is outlined below.
The ACVIM consensus guidelines for MMVD in dogs describes 4 basic stages of heart disease and heart failure:
· Stage A identifies dogs at high risk for developing heart disease but that currently have no identifiable structural disorder of the heart (e.g. every Cavalier King Charles Spaniel or other predisposed breeds without a heart murmur).
· Stage B identifies dogs with structural heart disease (e.g. the typical murmur of mitral valve regurgitation, accompanied by some typical valve pathology, is present), but that have never developed clinical signs caused by heart failure. In a change from the 2009 recommendations, strong evidence now supports initiating treatment to delay the onset of clinical signs of heart failure in a subset of stage B patients with more advanced cardiac morphological changes (outlined below).
o Stage B1 describes asymptomatic dogs that have no radiographic or echocardiographic evidence of cardiac remodelling in response to their MMVD, as well as those in which remodelling changes are present, but not severe enough to meet current clinical trial criteria that have been used to determine that initiating treatment is warranted (see specific criteria detailed below)
o Stage B2 refers to asymptomatic dogs that have more advanced mitral valve regurgitation that is haemodynamically severe and long-standing enough to have caused radiographic and echocardiographic findings of left atrial and ventricular enlargement that meet clinical trial criteria used to identify dogs that clearly should benefit from initiating pharmacologic treatment to delay the onset of heart failure (specific criteria detailed below).
· Stage C denotes dogs with either current or past clinical signs of heart failure caused by MMVD. Because of important treatment differences between dogs with acute heart failure requiring hospital care and those in which heart failure can be treated on an outpatient basis, these issues have been addressed separately by the panel. It is important to note that some dogs presented with heart failure for the first time may have severe clinical signs requiring aggressive treatment (e.g., with additional afterload reducers or temporary ventilatory assistance) that more typically would be reserved for those patients refractory to standard treatment (see Stage D below).
· Stage D refers to dogs with end-stage MMVD, in which clinical signs of heart failure are refractory to standard treatment (defined later in this consensus statement). Such patients require advanced or specialized treatment strategies to remain clinically comfortable with their disease, and at some point, treatment efforts become futile without surgical repair of the valve. As with Stage C, the panel has distinguished between dogs in Stage D that require acute, hospital-based treatment and those that can be managed as outpatients.
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