Cardiomyopathy is a non-specific term meaning diseased heart muscle. There are several different types of cardiomyopathy; for example, one type is hypertrophic cardiomyopathy where the muscle of the heart thickens and the internal chambers of the heart are small due to encroachment of the excess muscle. In contrast, with dilated cardiomyopathy the muscular heart is actually thinned from stretching to accommodate abnormally large, dilated heart chambers. While in other species and in other breeds of dogs there are many
causes of dilated cardiomyopathy (DCM), in the Doberman the disease is primary, a genetic predisposition, not caused by other medical problems. The primary problem in Doberman DCM is within the heart muscle cell, an inability to contract normally which leads to abnormal function of the heart. To compensate for the poor contractile ability the heart dilates increasing the chamber size which in the early stages of disease will improve output of the heart (stroke volume). At this time the disease is in the asymptomatic or occult stage. However, with further progression of disease, there comes a time when further dilation of the heart no longer improves stroke volume but in fact leads to increasing pressure within the heart (heart failure). This in turn causes a back up of blood in the blood vessels in the lungs and in turn causes fluid to leak out into the lungs leading to difficulty breathing, and eventually death. Another potential cause of death with Doberman DCM is arrhythmias. With the abnormal stretching of the heart electrical abnormalities can occur, some are of a benign nature but may aid in early detection of disease, but malignant forms can occur leading to sudden death.
Diagnosis of DCM
Overt disease: When the disease is in the symptomatic or overt stage, diagnosis is not difficult. Symptoms may include shortness of breath, coughing, poor appetite and weight loss, fainting episodes. Physical examination will reveal a heart murmur, a gallop (an extra heart sound which indicates heart failure) and often irregular beats. Chest X-ray will show an enlarged heart and fluid in the lungs. Echocardiogram (ultrasound of the heart) will show a dilated left ventricle and atrium, with poor function and mitral valve insufficiency (leaking of the valve).
Occult disease: When the disease is in an asymptomatic or occult stage, the diagnosis maybe suspected by testing, but at this date these criteria are not uniform from center to center. Echocardiography of healthy Dobermans recently studied at the UDC nationals and it was found that the average fractional shortening of these healthy dogs was 26% using a short axis view, and 22.5% using a long axis view. In other breeds a fractional shortening of 25% or less in the short axis view is considered abnormal. This either indicates that a large percentage of healthy Dobermans have occult DCM or that the Doberman heart at baseline is not comparable to that of most breeds. As such, to diagnose occult DCM, most centers now require not only a depressed fractional shortening, but some evidence of functional impairment such as dilated heart chambers or frequent ventricular arrhythmias. While diagnostic criteria may vary from center to center, the largest ongoing study is being performed by Dr. Michael O’Grady at the University of Guelph, and his criteria are the best defined and studied to date. To diagnose occult DCM, Dr. O’Grady requires the following echocardiographic findings, measured in the parasternal long axis view/ A fractional shortening of less than 20% with the following left ventricular chamber measurements: greater than 49 mm at the end of diastole (when the ventricle is completely filled), greater than 42 mm at the end of systole (when the ventricle has completed emptying). This diagnosis is collaborated by a progression of 3-5 mm since a prior examination. Alternatively, the diagnosis can be suspected by frequent ventricular arrhythmia €“ the criteria currently in use by Dr. O’Grady is greater than 50 PVCs (premature ventricular contractions) per hour, however this study is on-going. This is measured by a Holter monitor, which is and ECG running continuously for a 24 hour period.
Treatment of DCM
Overt disease: Once heart failure has occurred, treatment is symptomatic and palliative. Life expectancy is limited, generally less than six months. Treatment usually consists of diuretics to rid the lungs of fluid and an angiotensin converting exzyme (ACE) inhibitor to decrease the workload of the failing heart. Some veterinary cardiologists also use digoxin to attempt to increase the contractility of the heart muscle, others do not believe it is helpful in this setting. If the dog has an arrhythmia than a drug will be used specifically for this purpose, there are several different types of drugs which may be chosen. A newer medication, Pimobendan (increases contractility of the heart and decreases workload) is currently undergoing trials. While nutritional supplements such as L-carnitine, co-enzyme Q are sometimes recommended, there is no scientific evidence that these are helpful in treatment of Doberman DCM.
Occult disease: There is some evidence that treatment with ACE inhibitors in the asymptomatic or occult stage will slow progression of the disease, prolonging life and time until the onset of symptomatic disease.
Prevention of DCM
The cause of this disease is unknown. Many theories (such as carnitine or taurine deficiency) have been tested with no positive results. It is likely a heritable disease but the mode of genetic transmission is still unknown. There is not known preventative strategy for Doberman DCM. The best strategy for an individual Doberman is to have annual cardiac screening to diagnose the disease in its early occult stage. With diagnosis treatment with ACE inhibitors will not only prolong life but improve the quality of life.
Dr. Meurs review of canine dilated cardiomyopathy
Helayne Silver MD
DPCA Public Education Committee