Purpose: To gather data regarding heart diseases in dogs, and to identify dogs which are phenotypically normal prior to use in a breeding program. For the purposes of the registry, a phenotypically normal dog is defined as:
- One without a cardiac murmur.
- One with an innocent heart murmur that is found to be otherwise normal by virtue of an echocardiographic examination which includes Doppler studies. The OFA maintains two separate and distinct cardiac databases: The Congenital Cardiac Database and the Advanced Cardiac Database.
Congenital Cardiac Database
Congenital heart disease in dogs is a malformation of the heart or great vessels. The lesions characterizing congenital heart defects are present at birth and may develop more fully during perinatal and growth periods. Many congenital heart defects are thought to be genetically transmitted from parents to offspring; however, the exact modes of inheritance have not been precisely determined for all cardiovascular malformations. The most common congenital cardiovascular defects can be grouped into several anatomic categories. These anatomic diagnoses include:
- Malformation of the atrioventricular valves
- Malformation of the ventricular outflow leading to obstruction of blood flow
- Defects of the cardiac septa (shunts)
- Abnormal development of the great vessels or other vascular structures
- Complex, multiple, or other congenital disorders of the heart, pericardium, or blood vessels
Examination and Classification
Each dog is to be examined and classified by a veterinarian with expertise in the recognition of canine heart disease, in accordance with procedures outlined in The Cardiac Exam section.
A breed registry number will be issued for any dog found to be normal for congenital cardiac disease at 12 months of age or older. The exam must include auscultation. There is an initial OFA fee and no charge for recertification at a later age. The breed registry number will indicate the age at evaluation and the type of examiner (C-cardiologist, S-specialist, and P-practitioner).
Dogs under 12 months of age can be evaluated for the owner’s information. The most opportune time to gather this data is at 8–10 weeks of age, prior to the puppy’s release to the new owner.
Dogs with Congenital Heart Disease
The veterinarian and owner are encouraged to submit all evaluations, whether normal or abnormal, to help assure accuracy of the database and to assist in the analysis of patterns of inheritance in important canine congenital heart disease. There is no OFA fee for entering an abnormal congenital cardiac evaluations into the database. Abnormal information will not be released into the public domain unless the owner gives permission for this release by initialing the appropriate line on the application form.
Advanced Cardiac Database
The Advanced Cardiac Database results in a two-tiered clearance for normal dogs: congenital cardiac disease and adult-onset cardiac disease. Congenital heart disease in dogs is a malformation of the heart or great vessels that is present at birth and may develop more fully during perinatal and growth periods. Adult-onset or developmental cardiac diseases develop later in life and include for example; hypertrophic, arrhythmogenic and dilatative cardiomyopathies. Many congenital and adult-onset or developmental cardiac diseases may have a genetic component, however the exact modes of inheritance have not been precisely determined for all cardiovascular malformations.
Examination and Classification
Each dog is to be examined and classified by a veterinary cardiologist. Veterinary cardiologists are defined as licensed veterinarians with diplomate status in either the American College of Veterinary Internal Medicine (ACVIM) cardiology sub-specialty, or the European College of Veterinary Medicine (ECVIM) cardiology sub-specialty.
The Advanced Cardiac Database examinations results in a two-tiered clearance: congenital cardiac disease and adult-onset cardiac disease. A breed registry number will be issued for any dog found to be normal for cardiac disease (congenital disease and/or adult-onset disease) at 12 months of age or older. The congenital clearances are considered permanent. The adult-onset clearances are valid for one year from the date of the exam. In order for an adult-onset clearance to remain current, exams must be repeated periodically. The exam must be include auscultation at a minimum. Echocardiograms may be recommended following the auscultation results, or for breeds susceptible to adult-onset cardiac diseases requiring an echo for an accurate diagnosis. Additionally, for an adult-onset clearance, Boxers and Doberman Pinschers also require a Holter test within 90 days of the cardiologist’s examination.
Dogs under 12 months of age can be evaluated for the owner’s information. The most opportune time to gather this data is at 8–10 weeks of age, prior to the puppy’s release to the new owner. Preliminary exams do not result in OFA certification.
Dogs with Congenital or Adult-Onset Heart Disease
The veterinarian and owner are encouraged to submit all evaluations, whether normal or abnormal, to help assure accuracy of the database and to assist in the analysis of patterns of inheritance in important canine congenital and adult-onset heart disease. Abnormal information will not be released into the public domain unless the owner gives permission for this release by initialing the appropriate line on the application form.
The Cardiac Exam
The clinical cardiac examination should be conducted in a systematic manner. The arterial and venous pulses, mucous membranes, and precordium should be evaluated. Heart rate should be obtained. The clinical examination should be performed by an individual with advanced training in cardiac diagnosis.
Board certification by the American College of Veterinary Internal Medicine, Specialty of Cardiology is considered by the American Veterinary Medical Association as the benchmark of clinical proficiency for veterinarians in clinical cardiology, and examination by a Diplomate of this specialty board is recommended. Other veterinarians may be able to perform these examinations, provided they have received advanced training in the subspecialty of congenital heart disease.
Types of Cardiac Exams:
- Auscultation (listening with a stethoscope)
Cardiac auscultation should be performed in a quiet, distraction-free environment. The animal should be standing and restrained, but sedative drugs should be avoided. Panting must be controlled and, if necessary, the dog should be given time to rest and acclimate to the environment. The clinician should able to identify the cardiac valve areas for auscultation. The examiner should gradually move the stethoscope across all valve areas and also should auscultate over the subaortic area, ascending aorta, pulmonary artery, and the left craniodorsal cardiac base. Following examination of the left precordium, the right precordium should be examined.
- The mitral valve area is located over and immediately dorsal to the palpable left apical impulse and is identified by palpation with the tips of the fingers. The stethoscope is then placed over the mitral area and the heart sounds identified.
- The aortic valve area is dorsal and one or two intercostal spaces cranial to the left apical impulse. The second heart sound will be most intense when the stethoscope is centered over the aortic valve area. Murmurs originating from or radiating to the subaortic area of auscultation are evident immediately caudoventral to the aortic valve area. Murmurs originating from or radiating into the ascending aorta will be evident craniodorsal to the aortic valve and may also project to the right cranial thorax and to the carotid arteries in the neck.
- The pulmonic valve area is ventral and one intercostal space cranial to the aortic valve area. Murmurs originating from or radiating into the main pulmonary artery will be evident dorsal to the pulmonic valve over the left hemithorax.
- The tricuspid valve area is a relatively large area located on the right hemithorax, opposite and slightly cranial to the mitral valve area.
- The clinician should also auscultate along the ventral right precordium (right sternal border) and over the right craniodorsal cardiac border.
- Any cardiac murmurs or abnormal sounds should be noted. Murmurs should be designated according to the descriptions below.
The echocardiographic examination should be conducted in a systematic matter. The examiner must be able to perform two-dimensional, pulsed-wave Doppler, and continuous-wave Doppler examinations of the heart. The availability of color Doppler is valuable but not essential for most examinations. The echocardiographic examination should be performed and interpreted by individuals with advanced training in cardiac diagnosis. Board certification by the American College of Veterinary Internal Medicine, Specialty of Cardiology is considered by the American College of Veterinary Medical Association as the benchmark of clinical proficiency for veterinarians in clinical cardiology, and examination by a Diplomate of this Specialty Board is recommended. Other veterinarians may be able to perform these examinations provided they have the appropriate equipment and have received advanced training in echocardiography.
Imaging the pericardial space, both atria, both ventricles, the great vessels, and the four cardiac valves should be imaged using long axis, short axis, apical, and angled image planes as necessary to perform a complete examination of the heart. Nomenclature should follow that recommended by the American College of Veterinary Internal Medicine Specialty of Cardiology. An anatomic diagnosis may be possible based on two-dimensional imaging; however, the origin of cardiac murmurs should also be evaluated using Doppler methods.
Doppler examination of all cardiac valves should be performed and recorded. Abnormal flow should be quantified using pulsed wave or continuous wave Doppler techniques. Values obtained should be compared to reference values. The depressant effects of any tranquilizers or sedative must be considered when measuring peak flow velocities. Color Doppler echocardiography should be employed if available to assess normal and abnormal blood flow patterns. Identification of abnormal flow across the cardiac septa or shunts at the level of the great vessels is best done by a combination of color and pulsed wave Doppler techniques. Typical echocardiographic features of common congenital heart defects are indicated in table one.
Special attention should be directed to the assessment of flow patterns and velocities in the left ventricular outlet and descending aorta. Optimal alignment with blood flow should be sought for accurate velocities to be reported. This may require the use of sub-xiphoid (subcostal) transducer positions as well as left apical (caudal parasternal) transducer placements. In addition to measurement of peak velocity using pulsed or color wave Doppler, the pulsed wave sample volume should be gradually advanced from the subaortic area into the ascending aorta in order to identify sudden accelerations inflow velocity, turbulence, or aortic regurgitation.
Echocardiographic studies should be recorded on video for subsequent analysis and a written record of abnormal findings should be entered into the medical record. See chart of Echocardiographic Findings.
Description of Cardiac Murmurs
A full description of the cardiac murmur should be made and recorded in the medical record.
- Murmurs should be designated as systolic, diastolic, or continuous.
- The point of maximal murmur intensity should be indicated as described above. When a precordial thrill is palpable, the murmur will generally be most intense over this vibration.
- Murmurs that are only detected intermittently or are variable should be so indicated.
- The radiation of the murmur should be indicated.
Effects of Heart Rate, Heart Rhythm, and Exercise
Some heart murmurs become evident or louder with changes in autonomic activity, heart rate, or cardiac cycle length. Such changes may be induced by exercise or other stresses. The importance of evaluating heart murmurs after exercise is currently unresolved. It appears that some dogs with congenital subaortic stenosis or with dynamic outflow tract obstruction may have murmurs that only become evident with increased sympathetic activity or after prolonged cardiac filling periods during marked sinus arrhythmia. It also should be noted that some normal, innocent heart murmurs may increase in intensity after exercise. Furthermore, panting artifact may be a problem after exercise.
It is most likely that examining dogs after exercise will result in increased sensitivity to a diagnosis of soft murmurs but probably decreased specificity as well. Auscultation of the heart following exercise is at the discretion of the examining veterinarian.
Abnormal Cardiac Grades
Grade 1: A very soft murmur only detected after very careful auscultation
Grade 2: A soft murmur that is readily evident
Grade 3: A moderately intense murmur not associated with a palpable precordial thrill (vibration)
Grade 4: A loud murmur; a palpable precordial thrill is not present or is intermittent
Grade 5: A loud cardiac murmur associated with a palpable precordial thrill; the murmur is not audible when the stethoscope is lifted from the thoracic body wall
Grade 6: A loud cardiac murmur associated with a palpable precordial thrill and audible even when the stethoscope is lifted from the thoracic wall
Other descriptive terms may be indicated at the discretion of the examiner; these include such timing descriptors as: proto(early)-systolic, ejection or crescendo-decrescendo, holosystolic or pansystolic, decrescendo, and tele(late)-systolic and descriptions of subjective characteristics such as: musical, vibratory, harsh, and machinery.
Cardiac Guidelines for Breeders
A careful clinical examination that emphasizes cardiac auscultation is the most expedient and cost-effective method for identifying Congenital Heart Disease in dogs. While there are exceptions, virtually all common congenital heart defects are associated with the presence of a cardiac murmur. Consequently, it is recommended that cardiac auscultation be the primary screening method for initial identification of CHD and the initial classification of dogs. Murmurs related to CHD may at times be difficult to distinguish from normal, innocent (also called physiologic or functional) murmurs. Innocent cardiac murmurs are believed to be related to normal blood flow in the circulation. Innocent murmurs are most common in young, growing animals. The prevalence of innocent heart murmurs in mature dogs (especially in athletic dogs) is undetermined. A common clinical problem is the distinction between innocent murmurs and murmurs arising from CHD.
Definitive diagnosis of CHD usually involves one or more of the following methods:
- Echocardiography with Doppler studies
- Cardiac catheterization with angiocardiography
- Post-mortem examination of the heart (necropsy).
- Other methods of cardiac evaluation, including electrocardiography and thoracic radiography, are useful in evaluating individuals with CHD, but are not sufficiently sensitive nor specific to reliably identify or exclude the presence of CHD.
- The noninvasive method of echocardiography with Doppler is the preferred method for establishing a definitive diagnosis in dogs when CHD is suspected during the clinical examination. Echocardiography is an inappropriate screening tool for the identification of congenital heart disease and should be performed only when the results of clinical examinations suggest a definite or potential cardiovascular abnormality.
- Two-dimensional echocardiography provides an anatomic image of the heart and blood vessels. While moderate to severe cardiovascular malformations can generally be recognized by two-dimensional echocardiography, mild defects (which are often of great concern to breeders) may not be identifiable by this method alone.
- Doppler studies, including pulsed-wave and continuous-wave spectral Doppler, and two-dimensional color Doppler, demonstrate the direction and velocity of blood flow in the heart and blood vessels. Abnormal patterns of blood flow are best recognized by Doppler studies. Results of Doppler studies can be combined with those of the two-dimensional echocardiogram in assessing the severity of CHD. Color Doppler echocardiography is used to evaluate relatively large areas of blood flow and is beneficial in the overall assessment of the dog with suspected CHD. Turbulence maps employed in color Doppler imaging are useful for identifying high velocity or disturbed blood flow but are not sufficiently specific (or uniform among manufacturers) to quantify blood velocity. It is emphasized that quantitation of suspected blood flow abnormalities is essential and can only be accomplished with pulsed or continuous wave Doppler studies. Pulsed wave and continuous wave Doppler examinations provide a display of blood velocity spectra in a graphical format and are the methods of choice for assessing blood flow patterns and blood flow velocity in discrete anatomic areas.
- Cardiac catheterization is an invasive method for the identification of CHD that is considered very reliable for the diagnosis of CHD. Cardiac catheterization should be performed by a cardiologist, usually requires general anesthesia, carries a small but definite procedural risk, and is generally more costly than noninvasive studies. While cardiac catheterization with angiocardiography is considered one of the standards for the diagnosis CHD, this method has been supplanted by echocardiography with Doppler for routine evaluation of suspected CHD.
- Necropsy examination of the heart should be done in any breeding dog that dies or is euthanized. The hearts of puppies and dogs known to have cardiac murmurs should always be examined following the death of the animal. A post mortem examination of the heart is best done by a cardiologist or pathologist with experience in evaluating CHD. While it is obvious that necropsy cannot be used as a screening method, the information provided by this examination can be useful in guiding breeders and in establishing the modes of inheritance of CHD.
Each of the methods of evaluation may be associated with false positive and false negative diagnoses. It must be recognized that some cases of CHD fall below the threshold of diagnosis. In other cases, a definitive diagnosis may not be possible with currently available technology and knowledge. These limitations can be minimized by considering the following general guidelines:
- The results of the examinations described above are most reliable when performed by an experienced individual with advanced training in cardiovascular diagnosis. Echocardiography with Doppler, cardiac catheterization, and post-mortem examination of the heart for CHD requires advanced training in cardiovascular diagnostic methods and the pathology and pathophysiology of CHD.
- Examinations performed in mature dogs are most likely to be definitive. This is especially true when considering mild congenital heart defects. Innocent heart murmurs are less common in mature animals than in puppies and are less likely to be a source of confusion. Furthermore, the murmurs associated with some mild congenital malformations become more obvious after a dog has reached maturity. While it is quite reasonable to perform preliminary evaluations and provide provisional certification to puppies and young dogs between eight weeks and one year of age, final certification, prior to breeding, should be obtained in mature dogs at 12 months of age or older.
- Examination conditions must be appropriate for recognition of subtle cardiac malformations. Identification of soft cardiac murmurs is impeded by extraneous noise or by poorly restrained, anxious, or panting dogs.
- A standardized cardiac clinical examination must be performed according to a predetermined and clearly communicated protocol. Physical examination and cardiac auscultation should be used as the initial method of cardiac evaluation.
- Examiners who perform echocardiography with Doppler must use appropriate ultrasound equipment, transducers, and techniques. Such individuals should have advanced training in noninvasive cardiac diagnosis and should follow diagnostic standards established by their hospital and by the veterinary scientific community, including standards published by the American College of Veterinary Internal Medicine, specialty of Cardiology (J Vet Internal Med 1993;7:247-252).