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Echocardiographic phenotype of canine DCM differs based on diet type | VETgirl Veterinary Continuing Education Podcasts

In today’s VETgirl online veterinary continuing education podcast, we review whether or not echocardiographic phenotype of canine dilated cardiomyopathy differs based on canine diet types. Dilated cardiomyopathy (DCM) in dogs occurs secondary to predominantly genetic causes, but also occurs secondary to systemic disease, toxins, infectious disease and nutritional causes. DCM in association with taurine and L-carnitine deficiency is well documented and has the potential for reversal of myocardial dysfunction with appropriate supplementation.

So, Adin et al out of North Carolina State University initiated a study entitled Echocardiographic phenotype of canine dilated cardiomyopathy differs based on diet type to evaluate this due to an increase in frequency of DCM in dogs whose age and breed fall outside of the typically reported demographics, with the additional observation that many of these dogs were eating specialty meat-based grain-free (GF) diets. [This observation is currently under study at multiple veterinary institutions. What we know is that there appears to be an association of DCM with grain-free diets, and that there are two subpopulations within this group, namely those that are taurine-deficient and those that have normal taurine levels (1)]. The authors hypothesized that dogs with DCM eating grain-free (GF) diets would display a greater severity of disease assessed via echocardiogram than dogs with DCM eating grain-based diets. They also hypothesized that dogs eating a particular brand of grain-free diet (name withheld, referred to as GF-1) would have more severe disease than dogs eating all other brands of grain-free diets (GF-o).

The study was a retrospective analysis reviewing medical records over a 40-month period from 2015-2018. Inclusion required that brand and variety of food were known for each patient and that the dogs had clear echocardiographic evidence of DCM (based on decreased left ventricular shortening fraction, increased normalized left ventricular internal diameters in diastole and systole). Dogs were excluded for other forms of heart disease, unknown diet history, as well as vegan, vegetarian or home-cooked diets. Definition of grain-based (GB) diets required wheat, rice, oats, cornmeal, barley, bulgar, millet, rye, or spelt on the ingredients list. Patient signalment, weight, echocardiographic parameters of systolic function, presence or absence of congestive heart failure (CHF), radiographic vertebral heart scale (VHS), and results of testing for taurine, L-carnitine, or various infectious diseases were recorded. Echocardiography was performed by a single investigator and all dogs diagnosed with DCM that underwent a diet change had follow-up echocardiograms.

48 dogs met the study inclusion criteria. Twelve were eating GB diets at the time of diagnosis of DCM compared with 36 eating GF diets. Of the 36 dogs eating GF diets, 14 were eating GF-1 and 22 were eating GF-o. Thirteen brands of GF diets were represented overall (compared with 7 GB diets). After June 2017, a diet change from a GF diet to a GB diet manufactured by a pet food company employing veterinary nutritionists was consistently recommended for dogs eating GF diets, but was not consistently recommended prior to that time. All but one dog in the GF group received taurine supplementation following diagnosis, regardless of blood taurine level status.

So, what’d they find in this study? No significant differences in age, breed, or sex were identified among groups, but a significant difference in body weight was identified, as GF-1 dogs weighed less than GF-o and GB dogs. There were no differences among groups with respect to presence or absence of CHF or radiographic VHS. Echocardiographic data indicated that GF-1 dogs had significantly larger normalized end-diastolic and end-systolic left ventricular dimensions than GB dogs despite no difference in fractional shortening. GF-1 dogs also had lower left ventricular diastolic sphericity indexes (a marker for myocardial dysfunction) than GB dogs. No differences in echocardiographic parameters were detected between GF-o and GB dogs. Regarding taurine status, no significant differences existed among the groups with regards to blood taurine concentrations, and no dogs in the GF group were identified as taurine-deficient according to reference laboratory values at the time (which indicated low end of normal range of 200 nmol/mL, although recent data (1) suggests the low end of the normal range requires revision to 250 nmol/mL and three dogs in the GF group had values between 200-250 nmol/mL). Serial echocardiography in 7 dogs in the GF group indicated significant improvements (reductions) in normalized end-diastolic and end-systolic left ventricular dimensions, as well as reductions in left atrial-to-aortic root ratio (marker for left atrial size) at 3 months [following diet change (7/7 dogs) and taurine supplementation (6/7 dogs)].

This retrospective study suggests that diet type may affect patient body weight and severity of disease (assessed echocardiographically) in dogs with dilated cardiomyopathy. The majority of GF dogs with DCM (and in the study overall) were not taurine deficient. The demonstration of echocardiographic improvement (in those GF dogs that received serial echocardiograms) following diet change implies causality in those dogs’ diet type and the development of DCM. Although the nature of the causality has not been elucidated, the detection of differences between GF-1 and GB groups, but not GF-o and GB groups, suggests that there are differences among GF diets with respect to development and severity of DCM, which may or may not relate directly to the grain-free nature of the diet but instead perhaps to other compositional factors of these diets. This is further supported by another reported finding of the study, namely that two of the dogs in the GF-1 group demonstrating echocardiographic improvement following diet change were changed to diets that were still grain-free, but considered to be “major brands.”

The authors acknowledge that the role of taurine supplementation in improvement of disease in some of the GF dogs in the study is unclear, as although most of the dogs that improved were prescribed taurine, they also had normal blood taurine levels. [It seems less likely that their improvement would be directly attributable to taurine supplementation, as opposed to the diet change, based on this fact, however.] Furthermore, only approximately 50% of all dogs in the study had taurine level testing performed.

Although hindered by the typical limitations of a retrospective study, including inconsistent or incomplete medical records, inconsistency of testing/results obtained across the study population, and small population size (to name a few), the results themselves are noteworthy. They serve as further support that a dietary-associated form of dilated cardiomyopathy likely exists, specifically in association with (at least) certain grain-free diets, and that improvement/regression of disease is possible in these cases. They further support the premise that many of these cases do not appear to be associated with taurine deficiency. The results suggest, as has been previously suggested (1), that other compositional irregularities aside from the actual grain-free nature of these diets may play a significant role in the development of disease. Finally, they appear to identify that DCM in association with some grain-free diets may display a more severe phenotype of the disease than traditional genetic causes (i.e. idiopathic).

So, what do we take away from this VETgirl podcast? This retrospective study suggests that diet type may affect patient body weight and severity of disease (assessed echocardiographically) in dogs with dilated cardiomyopathy. In other words, dietary-associated DCM does occur with some grain-free diets, and if detected, can potentially improve with diet change. So, you should educate your owners on the risks of grain-free. And that it’s not worth the risk!

Abbreviations:
DCM: Dilated cardiomyopathy
GB: grain-based
GF: grain-free
GF-1: a particular brand of grain-free diet (name withheld)
GF-O: all other brands of grain-free diets (GF-o)

References:
1. Freeman LM, Stern JA, Fries R, et al. Diet-associated dilated cardiomyopathy in dogs: what do we know? J Am Vet Med Assoc 2018;253:1390-1394.
2. Darcy A, DeFrancesco TC, Keene B, et al. Echocardiographic phenotype of canine dilated cardiomyopathy differs based on diet type. J Vet Cardiology 2019;21:1-9.

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