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Association between atrial fibrillation and right-sided congestive heart failure in dogs | VETgirl Veterinary Continuing Education Podcasts

In this VETgirl online veterinary continuing education podcast, we review the association between atrial fibrillation (AF) and right-sided manifestations of congestive heart failure (CHF). Atrial fibrillation (AF) in dogs most commonly develops secondary to distension and structural remodeling of the atrial myocardium in association with either degenerative mitral valve disease (DMVD) or dilated cardiomyopathy (DCM). The lack of organized atrial activity in atrial fibrillation results in loss of the atrial contribution to left ventricular filling during diastole, with secondary effects on cardiac output (decreased) and atrial pressure (increased). These effects may destabilize a patient with existing cardiac disease. Congestive heart failure (CHF) in dogs is generally described as either left sided (L-CHF), right sided (R-CHF), or bilateral, however, the two most common forms of heart disease in dogs  both primarily effect the left sided of the heart. Prior published case series in dogs have suggested than an association with right sided or bilateral CHF and onset of atrial fibrillation may exist. So, Ward et al out of Iowa State University wanted to evaluate this in a study entitled Association between atrial fibrillation and right-sided manifestations of congestive heart failure in dogs with degenerative mitral valve disease or dilated cardiomyopathy.

In this study, the authors wanted to determine if an association existed between the occurrence of atrial fibrillation and right sided or bilateral CHF in dogs with left sided CHF secondary to DMVD or DCM. A secondary objective was to determine if particular clinical or echocardiographic parameters were specifically associated with AF or R-CHF. The study was retrospective in nature over an eleven year period (2007-2018). Criteria for inclusion were confirmation of clinical and imaging-based (e.g., radiographic, echocardiographic, necropsy) CHF and either DMVD or DCM. Dogs with any form of congenital heart disease were excluded. Various clinical, imaging (including confirmation of radiographic pulmonary edema and ultrasound-confirmed pericardial, pleural, and/or abdominal effusion), echocardiographic, and electrocardiographic data were tabulated. Diagnosis of pulmonary hypertension (including classification of severity), degenerative mitral valve disease, and dilated cardiomyopathy was based on echocardiographic parameters derived from previously published references in the veterinary literature. Dogs were grouped based on the presence or absence of AF, and the presence or absence of R-CHF. Statistical analysis was performed using appropriate methodology for normally distributed variable, non-normally distributed variables, and categorical variables.

220 dogs were included in the study. 70.5% (155/220) had DMVD, with Cavalier King Charles Spaniels the most commonly represented breed (n = 50). Almost 30% (65/220%) had DCM, with Doberman Pinscher the most commonly represented breed (n = 12). Echocardiography was completed within 24 hours of the onset of CHF in the vast majority (86.9%) of dogs. Between the two groups of underlying heart disease (DMVD and DCM), significant differences in age (younger with DCM), body weight (larger with DCM), and sex (more males in DCM group) were detected. Significant differences in breed existed between DMVD and DCM groups consistent with the known predispositions of certain large breed dogs to develop DCM vs certain small breed dogs to develop DMVD based on previously published data. Dogs with DCM also had higher baseline heart rates, greater degree of ventricular ectopic activity, and smaller left atrial-aortic-root (LA:Ao) ratios than dogs with DMVD. Almost 90% of dogs (195/220) had confirmed pulmonary edema (L-CHF), 35 of which had bilateral CHF (e.g., concurrent evidence of R-CHF). In total, 27.3% (60/220) had findings compatible with R-CHF (either alone or in combination with L-CHF). A statistically significant difference was found between underlying disease type and presence of R-CHF, with DCM dogs more likely to develop R-CHF than DMVD dogs. Type of cavity effusion present in R-CHF listed from most common to least common were: ascites (n = 40), pleural effusion (26), and pericardial effusion (13). A statistically significant difference was detected in occurrence of pleural effusion in DCM (greater occurrence) versus DMVD in those dogs with confirmed R-CHF, but not for other effusion types. For R-CHF dogs, the average number of cavities with confirmed effusions (one, two or three) was greater for dogs with atrial fibrillation but did not differ between underlying disease type.

Almost 23% of dogs (50/220; DCM = 33 dogs, DMVD = 17 dogs) were diagnosed with AF at the time of onset of CHF. Atrial fibrillation was significantly more common in DCM dogs than DMVD dogs. In both DMVD and DCM dogs, dogs in the AF group were larger, younger and had higher heart rates than the non-AF dogs in their disease-type groups. Additionally, DMVD dogs with AF were more likely to be male, had lower left ventricular fractional shortening (marker of systolic function), decreased severity of tricuspid regurgitation, and larger right atrial and ventricular dimensions than non-AF DMVD dogs. DCM dogs with AF also had reduced frequency of ventricular ectopy than non-AF DCM dogs. Importantly, dogs with AF were more likely to develop signs of R-CHF than dogs without AF, regardless of underlying type of heart disease.

In this study, the parameters that retained statistical significance in their association with AF were heart rate (increased) and body weight (larger). The parameters that retained statistical significance in their association with R-CHF included presence of AF, diagnosis of DCM (vs DMVD), and presence of moderate-severe tricuspid regurgitation. Certain statistical differences detected in the study were not surprising and consistent with previously published data on the typical demographics of dogs with DMVD vs dogs with DCM, including signalment, body size, heart rate, and left atrial size. The significantly greater occurrence of AF and R-CHF in dogs with DCM vs DMVD is also consistent with previously published data. The key finding in this study, however, is the significant association of AF with the presence of R-CHF, regardless of underlying type of disease. Dogs with AF were 14.4X more likely to have R-CHF than non-AF dogs. When examined further, approximately 75% of dogs in the study with AF also had R-CHF, indicating that the two developments commonly occurred together, which significantly reduces the likelihood that cavitary effusions are occurring from non-cardiac causes in this type of patient population. These findings lend credibility to the premise that the negative hemodynamic effects of the atrial fibrillation itself may be a driving force in the development of R-CHF. It has long been established that chronic, pacing-induced tachycardia (in the absence of primary underlying cardiac disease) results in CHF (i.e. tachycardia-induced cardiomyopathy).

So it was nice to see this study make a more definitive statement about the long-suspected association of AF with R-CHF. It was also interesting to note in this study that although moderate-severe concurrent tricuspid regurgitation was independently associated with the onset of R-CHF, the authors did not find an association of echocardiographically-derived pulmonary hypertension with R-CHF in this population. It cannot be determined with certainty if this lack of association is real or an artifact based on study design, statistical power (or lack thereof), etc. The authors did acknowledge a variety of limitations inherent with the retrospective nature of the study. Whether such an association does or does not exist between pulmonary hypertension and R-CHF in dogs with primary left sided heart disease warrants further investigation.

So, what do we take away from this VETgirl study? There is a significant association of AF with the presence of R-CHF, regardless of underlying type of disease. Remember, for a dog with left sided heart disease/left sided heart failure to develop right-sided heart failure, there usually has to be “something” else that has to occur, and that “something else” is usually one or more of the following:

-Development of persistent/sustained tachyarrhythmias (atrial fibrillation or otherwise)
-Severe concurrent tricuspid valve disease or right ventricular myocardial disease
-Pulmonary hypertension
-Left atrial rupture (free wall, cardiac tamponade)
-Atrial septal rupture (acquired atrial septal defect)

More importantly, before blowing off that chronic 4/6 heart murmur in that dog with DMVD – or – if you just diagnosed a dog with DCM – please make sure to educate the pet owner on the importance of an echocardiographic workup with a cardiologist, chest radiographs, work up, ECG, and long term management. We want to be able to pick up on some of these arrhythmias and related complications sooner than later. The sooner we can diagnose some of these diseases, the sooner we can potentially prevent secondary complications.

Abbrevations:
AF: Atrial fibrillation
DCM: Dilated cardiomyopathy
DMVD: Degenerative mitral valve disease

References:
Ward J, Ware W, Viall A. Association between atrial fibrillation and right-sided manifestations of congestive heart failure in dogs with degenerative mitral valve disease or dilated cardiomyopathy. J Vet Cardiology 2019;21:18-27.

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