Dilated cardiomyopathy (DCM): Dilated cardiomyopathy is a degenerative disease of the heart muscle, which can lead to heart failure, abnormal heart rhythms, and sudden cardiac death. DCM is known to be inherited in the Doberman, Boxer dog, Great Dane, Newfoundland, Irish Wolfhound, Cocker Spaniel and the Portuguese Water Dog. It is believed to be inherited in many other breeds also, but scientific data on this is currently lacking. There are no reliable genetic tests for DCM, and we do not yet understand whether or not measurement of cardiac biomarkers (NT-proBNp or cardiac troponin I) is a helpful thing to screen for DCM, which means that a heart scan (echocardiography) is the only way to diagnose the condition in most breeds; a 24h ECG, or “Holter” can be used in Dobermans, but is recommended in conjunction with echocardiography rather than as an alternative. The age at which to start screening ranges from 3 years (Doberman) to 6 years (Newfoundland), and is dependent upon which breed club scheme is used.
Mitral valve disease (MVD): Mitral valve disease (also known as myxomatous mitral valve disease, and chronic degenerative mitral valve disease) is the commonest heart disease in dogs, affected mainly older, small breed dogs. A process of progressive damage occurs within the cells of the mitral valve, leading to a leak of blood backwards in the heart, reducing cardiac output and triggering volume overload and enlargement of the heart – eventually resulting in heart failure and breathing difficulties. It is inherited in the Cavalier King Charles Spaniel, Miniature Dachshund, and many more. Screening for MVD in the Cavalier using a scheme in Denmark has recently been proven to successfully reduce the prevalence of disease in the offspring of screened dogs. The “Danish Scheme” – used to measure mitral valve prolapse in dogs with and without heart murmurs – will be used in the UK by VCS-accredited cardiologists (trained by the Danish team who pioneered the screening system) from Spring 2018, and is approved by the UK Kennel Club for Cavalier King Charles Spaniels.
Congenital heart diseases – present from early in life
Pulmonic stenosis (PS): Dogs with pulmonic stenosis have narrowing of the valve leading from the right side of their heart to the main artery in the lungs (the pulmonic valve). This is often caused by a fusion of the valve leaflets, because the valve failed to properly develop in the womb. Occasionally, and more common in some breeds, the narrowing is caused by a small pulmonary artery, or a valve which failed to develop at all. This increases pressure on the right side of the heart, leading to abnormal heart rhythms and heart failure, if affected dogs do not sadly suffer fatal arrhythmias first. Predisposed breeds include the Cocker Spaniel (3x higher risk than non-pedigree dogs), Beagle, Terrier breeds, Chihuahua, Boxer dog, English Bulldog, and the French Bulldog (11x higher risk of PS than the Cocker Spaniel). Most dogs have a loud heart murmur at the time of first vaccination, so dogs without murmurs can be classified as free of pulmonic stenosis. Those with murmurs should undergo Doppler echocardiography by a cardiologist with experience of congenital heart disease. Dogs with severe PS can undergo a minimally invasive procedure to dilate the narrowed valve using a specialised balloon.
Subaortic stenosis (SAS): Although dogs can have valvular fusion of the aortic valve causing stenosis (see above re. PS), the most common form of aortic stenosis in dogs is subaortic stenosis (SAS), where a fibromuscular ring of tissue develops below the entrance to the aorta, the body’s main artery from the heart. Because of an increased pressure on the heart, the muscle thickens, becomes starved of oxygen because of its increased workload, and abnormal heart rhythms are commonplace. If these are not fatal in the first years of life, dogs with SAS can develop heart failure. Boxer dogs, Newfoundlands, the German Shepherd dog, English Bull Terriers and Pugs are predisposed to SAS, and we know that it is definitely heritable in Boxers and Newfoundlands. All affected dogs have a heart murmur, but frustratingly the condition seems to worsen over the first year of life. In this scenario, a dog may have a quiet murmur (grade I-II) at the time of first vaccination and vet check, only to develop a much louder murmur at 12-18 months old, representative of severe, life-limiting disease. Screening for this disease therefore is important after maturity, and breeds over-represented with SAS should not be tested before 1 year old. Treatment is more challenging than in cases of PS, but balloon procedures are possible as a means of relieving clinical signs and improving quality of life in some dogs.
Patent ductus arteriosus (PDA): The ductus arteriosus is a blood vessel that is normally open in the foetus, and allows blood to bypass the lungs, which are not inflated in utero. In normal dogs, the ductus closes in the first days of life, owing to contraction of smooth muscle surrounding the vessel, in response to increased hormone levels around the time of birth. In some dogs, a lack of this smooth muscle leads to persistence of blood flow through the ductus – a patent ductus arteriosus (PDA). After birth, flow through a PDA overloads the lungs and the heart, and eventually leads to heart failure. Predisposed breeds include Newfoundlands, Chihuahuas, Poodles (standard and miniature), Spaniel, Terrier and Toy breeds. Survival rates to 1 year old are estimated at 50%, but some dogs are not diagnosed until well into adulthood. Affected dogs have a loud murmur, present constantly during auscultation. Animals with a murmur suggestive of a PDA should undergo echocardiography. Dogs with a PDA have a very good long-term prognosis if it is closed, either surgically or using a more modern, minimally invasive technique (considered the gold-standard because of high success rates and a low level of risk).