There is an increasing amount of breed specific information about canine dilated cardiomyopathy. Because of differences the specific breed should be considered when considering etiology, developing treatment plans, and providing prognostic information.
Occasionally, atypical breeds of dogs develop dilated cardiomyopathy. The etiology of the disease in these cases is unknown.
Dilated cardiomyopathy has been reported in both American and English cocker spaniels; however, dilated cardiomyopathy occurs less commonly in this breed than valvular endocardiosis.
An association between the development of dilated cardiomyopathy and low plasma taurine levels has been reported in some American cocker spaniels. Dogs provided taurine and i.carnitine supplementation showed an increase in FS% and a decrease in LVEDD and LVESD over a 4-month period, although myocar-dial function did not return to normal. This study suggests that at least some Cocker spaniels with dilated cardiomyopathy may benefit from supplementation with taurine and, perhaps I.carnitine. The current recommendations for American cocker spaniels with dilated cardiomyopathy are to measure plasma taurine levels (normal >50 µg/ml) and to treat with 500 mg of taurine orally every 12 hours and 1.0 gram of l.camitine orally every 12 hours. Additional treatment should be given as needed to address such conditions as congestive heart failure and arrhythmias. The investigators suggest that supportive cardiovascular medications can be gradually withdrawn after the FS% increases to more than 20% (usually 3 to 4 months of supplementation). Supplementation with taurine, and L-camitine if possible, should be continued for life. If taurine deficiency is not identified the prognosis is poorer.
English cocker spaniels also get a form of dilated cardiomyopathy but a relationship to taurine or camitine levels has not been well studied. Many reported dogs were from the same kennel, which may suggest a heritable component. Profound evidence of left ventricular enlargement on the electrocardiogram with R wave amplitudes more than 3.0 mV in lead II was frequently observed. Some of the reported dogs died suddenly, but many have had a prolonged, fairly asymptomatic course of disease, or a long survival (years) with medical management.
Male dogs appear to be over represented in Dalmatian dilated cardiomyopathy, although large studies have not been performed. All dogs had adult onset disease and presented for signs consistent with left heart failure (cough, dyspnea) or syncope. None of the dogs had evidence of biventricular heart failure. Electrocardiography frequendy demonstrated sinus rhythm or sinus tachycardia with occasional ventricular ectopy. Atrial fibrillation was not observed in any of the dogs. Duration of survival ranged from 1.5 to 30 months with euthanasia due to refractory congestive heart failure. None of the dogs died suddenly. Interestingly, the majority (8/9) of reported dogs had been fed a low protein diet for all or part of their lives for prevention or treatment of urate stones. The cause and effect of these diets on the development of dilated cardiomyopathy is not known, but Dalmatians that develop dilated cardiomyopathy that are being fed a low protein diet should be switched to a more balanced diet if possible.
Occasionally Dalmatians develop acquired AV valve disease, so this should be considered as an important differential diagnosis.
The Doberman pinscher is one of the most commonly reported breeds of dogs to be affected with dilated cardiomyopathy in North America. It is characterized as an adult disease that results in the development of left and/or biventricular failure, often with atrial fibrillation. However, about 30% of the dogs develop ventricular tachyarrhythmias and may present for syncope or die of sudden death before the development of heart failure, and in some cases, before the development of ventricular dilation and systolic dysfunction.
Dilated cardiomyopathy in this breed is believed to be familial, although the pattern of inheritance is not well documented.
The clinical stage of dilated cardiomyopathy in the Doberman pinscher appears to be malignant in comparison to the disease in other breeds. The median survival time for dogs once heart failure has developed is 9.6 weeks. Atrial fibrillation and bilateral congestive heart failure are poor prognostic signs. However, the occult stage appears to be slowly progressive (2 to 3 years), and some affected dogs die from noncardiac disease before they become symptomatic from dilated cardiomyopathy. Although there is only a small amount of evidence, there may be some benefit to early diagnosis and initiation of treatment in the occult stage (as discussed below).
Some Doberman pinschers develop syncope or die suddenly before left ventricular dilation or systolic dysfunction ever develops. In most cases, these symptoms are associated with the presence of ventricular tachyarrhythmias. However, bradycardia-associated episodic weakness and syncope has also been observed in cardiomyopathic Doberman pinschers. Therefore Holter monitoring should be performed on the syncopal dog to document the causative arrhythmia before treatment is initiated.
The timing and procedure for treatment of ventricular arrhythmias in the affected dog is not clear cut. Rapid ventricular tachycardia, complex ventricular arrhythmias, or the combination of ventricular arrhythmias, ventricular dilation, and systolic dysfunction is thought to be associated with a higher risk of sudden cardiac death and to be indications for treatment, but this has not been well documented. Additionally, some dogs die suddenly without having any of these arrhythmias documented. If treatment is warranted, consideration might be given to the use of one of several ventricular antiar-rhythmics. Sotalol, a combination beta-blocker and potassium channel Mocker, may be beneficial in some cases but should be used with caution if systolic dysfunction is present. Amiodarone has been studied in the affected Doberman pinscher at a dose of 10.0 mg/kg orally every 12 hours for 1 week, followed by 8.0 mg/kg every 24 hours. After 6 months the dose may be reduced to 5.0 mg/kg every 24 hours. Careful evaluation of serum concentrations, complete blood counts (neutropenia has been reported), and liver enzymes monthly is suggested. Although the goals of treatment include decreasing the number of VPCs, decreasing symptoms, and decreasing the risk of sudden death. The ability of any antiarrhythmic to reach these goals for these cases has not been proven.
Evidence that the disease is familial and that early intervention may increase survival has lead to significant interest in screening asymptomatic dogs for signs of early disease. Annual echocardiography and ambulatory electrocardiography (Holter monitoring) are believed to be the best predictors of early dilated cardiomyopathy. Criteria that are believed to be indicators of occult disease include an echocardiographically determined LVEDD more than 4.6 cm and a LVESD more than 3.8 cm, even in the absence of systolic dysfunction. These numbers are based on average sized dogs and may not be valid for very large dogs. Annual Holter monitoring has also been recommended to detect Doberman pinschers that may develop ventricular arrhythmias before ventricular dilation and systolic dysfunction. Adult Doberman pinschers with greater than 50 ventricular premature complexes (VPCs) per 24 hours, or with couplets or triplets are suspect for the development of dilated cardiomyopathy,< Owners should be advised that since this is an adult onset disease with variability in the age of onset, screening tests should be performed annually.
Dilated cardiomyopathy in the Great Dane appears to be a familial disease. Affected male dogs were overrepresented, which suggests an X-linked pattern of inheritance in at least some families. If this is true, sons of affected females are at high risk of developing the disease; daughters of affected fathers are likely to be silent carriers.
Affected Great Danes presented most commonly for weight loss and/or coughing. Left-sided heart murmurs, gallops, and ascites were frequently observed. The most common electro-cardiographic findings included atrial fibrillation with occasional ventricular premature complexes. In some cases, atrial fibrillation may develop before any other evidence of underlying myocardial disease (chamber enlargement or systolic dysfunction). These dogs should be carefully followed for the possible development of dilated cardiomyopathy.
Atrial fibrillation frequently preceded the development of a heart murmur, clinical signs, and congestive heart failure in the Irish wolfhound with dilated cardiomyopathy and was present in the majority of dogs by the time they developed dilated cardiomyopathy.’ The progression of the disease is not well understood but appears to be slow, with the development of atrial fibrillation preceding the development of congestive heart failure by an average of 24 months. Occasionally, additional electrocardiographic abnormalities have been described, which include ventricular premature complexes and left anterior fas-cicular block patterns. Echocardiography is useful for separation of normal dogs, dogs with occult disease, and dogs with clinical evidence of heart failure. Affected Irish wolfhounds occasionally died suddenly but more commonly were euthanized due to heart failure, most commonly biventricular and sometimes with chylothorax.
Adult-onset dilated cardiomyopathy without a gender predisposition has been reported in the Newfoundland. Clinical presentation included dyspnea, cough, inappetance, and ascites with left or biventricular heart failure. Interestingly a heart murmur was auscultable in a very small percentage of the dogs (4 out of 37). The most common electrical abnormality was atrial fibrillation, but isolated ventricular premature complexes were also observed.
Portuguese Water Dogs
A juvenile form of familial dilated cardiomyopathy has been reported in the Portuguese water dog. Affected puppies were from apparently unaffected parents. Puppies died from congestive heart failure at an average age of 13 weeks after a very rapid course of disease.
Treatment of the Dog with Occult Dilated Cardiomyopathy
Administration of angiotensin converting enzyme (ACE) inhibitors may have some benefit for the dog with early ventricular dilation, with or without systolic dysfunction. Specifically, the use of angiotensin-converting enzyme inhibitors (enalapril, lisinopril, captopril) in the Doberman pinscher with ventricular dilation was found to prolong the amount of time before die onset of CHE Although this study was limited to evaluation of Doberman pinschers, the use of angiotensin-converting enzyme inhibitors for other breeds of dogs with occult dilated cardiomyopathy may be considered. This information provides additional support for the practice of screening adult dogs that are at increased risk of developing dilated cardiomyopathy because of their breed, and perhaps a family history, to allow early medical intervention.
Administration of beta-blockers at this stage is still being evaluated. The addition of low-dose beta-blockers to the treatment of human patients with dilated cardiomyopathy and stable heart failure has demonstrated a reduction in both mortality and morbidity. However, many human patients with dilated cardiomyopathy cannot tolerate even very low doses of beta-blockers and demonstrate rapid cardiac decompensation. The use of beta-blockers for the canine patient with dilated cardiomyopathy has not yet been well studied and a consensus opinion on use of these drugs for patients is not yet available.
Beta-blockers might be considered for the patient with occult disease, but they should be very carefully monitored and should not be given once there is evidence of fluid retention and heart failure until it is very well stabilized. The optimal beta-blocker for this purpose appears to be carvedilol because of its effects on both alpha and beta-receptors. It cannot be overemphasized that the addition of beta-blockers in canine dilated cardiomyopathy patients should be done very cautiously with gradual increases in dosing after a 2-weck period and careful monitoring of heart rate, blood pressure, and symptomology.
Treatment of the Dog with Dilated Cardiomyopathy and CHF
There are no specific therapeutic recommendations for the treatment of dilated cardiomyopathy other than those mentioned above. Nonspecific treatments, including surgery and nutritional supplementation, have been reported but have not yet been shown to have significant long-term benefits for most dogs. As discussed above, early diagnosis and intervention may be of the most benefit. A thorough discussion of treatment of the dog with congestive heart failure is provided elsewhere in this textbook.