Dogs with MMVD have progressive mitral valve degeneration. With every heartbeat, the abnormal valve allows blood to leak backward, or regurgitate, into the left atrium. Over time, mitral valve regurgitation (MR) leads to left atrial enlargement, compensatory left ventricular remodeling and, potentially, heart failure.
The mechanisms that cause MMVD are not completely understood. However, studies by Purina scientists demonstrate that a specific blend of nutrients can help improve heart function and slow disease progression – long before dogs with MMVD develop heart failure.
Read on to learn about the science behind a novel nutritional intervention that could transform the management of cardiac health for dogs with early stage MMVD.
The highest incidence of MMVD occurs in older, small- to medium-sized dogs weighing less than 20 kilograms.4, 5
The rate of MMVD progression, from one stage to the next, is variable and hard to predict. However, about 30% of dogs will develop advanced heart disease.6
Dogs appear normal until stage C, when they show signs of congestive heart failure.
Based on the ACVIM consensus guidelines, current nutritional recommendations focus on dogs in later stages of MMVD, after clinical signs of congestive heart failure occur.4
Discovering an intervention that is effective in the earlier stages of this disease could help dogs live better, longer lives.
Knowing that dogs with MMVD who develop congestive heart failure have a shorter life span and reduced quality of life, Purina scientists identified a blend of nutrients that could slow disease progression and help improve cardiac function in dogs with early stage MMVD.
The heart cannot store energy for future use – it can only keep beating as long as cardiac mitochondria continue to generate ATP.
Studies show that dysfunctional mitochondria, which use less efficient pathways for energy production, contribute to heart failure.7
Current nutritional recommendations for dogs in heart failure are focused on nutrient deficiencies or excesses. But emerging research shows that nutrition can provide alternative energy substrates and cardiac health benefits before the heart starts to fail.7-9
In previous omics studies, Purina scientists found that dogs with MMVD had altered energy metabolism, increased oxidative stress and inflammation.10 Based on these scientific insights, they identified nutrients that could address these metabolic changes.
The cardiac protection blend of nutrients includes:
A 6-month placebo-controlled, dietary intervention study, feeding a complete and balanced diet with the cardiac protection blend (CPB) slowed progression of disease in dogs with preclinical MMVD and demonstrated beneficial clinical effects.11
This blinded, randomized feeding trial enrolled 19 dogs in stage B1 or B2 heart disease. The dogs were divided into two groups randomized by age, sex, breed, body weight, and murmur grade, then fed either a control diet (CON) or the CPB-supplemented diet.
Although MMVD is considered a slowly advancing disease, during the 6-month study the dogs fed the control diet showed progression of disease while those fed the CPB diet did not progress.
The CPB-fed dogs also showed improvement in key measures: left atrial size and mitral regurgitation.
The most reliable independent indicator for MMVD progression is left atrial enlargement, as measured by left atrial diameter (LAD) and the ratio of left atrium to aortic root measurements (LA/Ao) with echocardiography.6,12
Echocardiographic measurement of left atrial diameter (LA) and Aortic root (Ao)
Image courtesy of: Rebecca L. Stepien, DVM, MS, ACVIM (Cardiology) University of Wisconsin, USA
In CON dogs the left atrial size increased by an average of 10%.
In CPB dogs the left atrial size actually decreased by an average of 3%.
Importantly, these changes in left atrial size occurred as early as three months into the study.
Adapted from Li et al., 2019
Mitral regurgitation (MR) is often the first indication of MMVD in dogs. Progressive mitral regurgitation, which increases cardiac work, can lead to both atrial and ventricular remodeling, and heart enlargement. Increasing mitral regurgitation is a clinical indicator of worsening, or progression, of MMVD.
In this study, the severity of mitral regurgitation was assessed by echocardiogram. During the study, 30% of the dogs fed CPB had less murmur severity, while none of the CON dogs improved. Only 10% of the CPB dogs worsened, while 25% of the CON dogs had more severe MR.
This graph shows the percentage of dogs that showed changes of at least one grade in mitral regurgitation after 6 months, compared with baseline. P=0.041
In addition, researchers observed that the CPB-fed dogs who had reduced left atrial size also had a decrease in blood pressure. This observation was not statistically significant, however the downward trend correlated with reduced left atrial size.
In a separate, published Purina study,13 metabolomic analysis showed that clinical benefits seen in dogs fed the cardiac protection blend of nutrients were associated with improved fatty acid use for energy and reduced markers of inflammation and oxidative stress. This showed that improvements in cardiac measurements of MMVD dogs were also reflected in positive changes at the molecular level.
This series of studies demonstrates that dietary intervention, with a blend of specific nutrients developed to address key metabolic changes associated with MMVD in dogs, was able to slow progression of the heart disease and help improve heart function in dogs with preclinical MMVD. Importantly, these nutrients act synergistically to achieve the documented efficacy.