DEFINITIONS AND GENERAL COMMENTS
What is Cogenital Heart Disease(CHD)?
Method of False Diagnosis
METHODS OF EXAMINATION
Salient Auscultatory & Echocardiographic Findings in Canine Congenital Heart Disease
1. Purposes - To gather data regarding congenital 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 currently defined as:
1) one without a cardiac murmur, or as
2) one with an innocent heart murmur that is found to be otherwise normal by virtue of an echocardiographic examination which includes Doppler studies.
2. Examination and Classification - Each dog is to be examined and classified by a veterinarian with expertise in the recognition of canine congenital heart disease in accordance with procedures out-lined in the enclosed Application and General Instructions.
3. Certification - A certificate and breed registry number will be issued for any dog found to be nor-mal at 12 months of age or older. The OFA fee is $ 15.00 and no charge will be made for recertification at a later age. The breed registry number will indicate the age at evaluation.
4. Provisional Certification* - Evaluation of dogs under 12 months of age is possible if requested by the owner. OFA will enter the information in a data bank at a fee of $10.00 for those found to be nor-mal. Full certification, however, requires subsequent examination at 12 months of age or older.
5. Dogs with congenital heart disease - The veterinarian and owner are encouraged to submit all evaluations, whether normal or abnormal, for the purpose of completeness of data collection and to assist in the analysis of inheritance of important canine congenital heart defects. There is no OFA fee for entering an abnormal evaluation of the heart into the data bank.
* Such provisional certification may be of value to breeders prior to the sale of any dog or for assessment of the breeding potential of a dog.
Definitions and General Comments
A. Congenital Heart Disease (CHD) in dogs is a malformation of the heart or great vessels. The lesions characterizing congenital heart defects are pre-sent at birth and may develop more fully during the 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.
B. The most common congenital cardiovascular defects can be grouped into several general anatomic categories. These anatomic diagnoses include:
1. Malformation of the atrioventricular valves
2. Malformations of ventricular outflow leading to obstruction of blood flow
3. Defects of the cardiac septa (shunting defects)
4. Abnormal development of the great vessels or other vascular structures
5. Complex, multiple, or other congenital disorders of the heart, pericardium, or blood vessels
C. A careful clinical examination that emphasizes cardiac auscultation is the most expedient and cost-effective method for identifying CHD 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 classi-fication of dogs.
D. Murmurs related to CHD may at times be difficult to distinguish from normal, innocent (also called physiologic orfunctiofial) murmurs. Innocent cardiac murmurs are believed to be related to normal blood flow in the circulation. Innocent murmurs are most common in young, grow-ing animals. The prevalence of innocent heart murmurs in mature dogs (and especially in athletic dogs) is undetermined. A common clinical problem is the distinction between innocent murmurs and murmurs arising from CHD.
E. Definitive diagnosis of CHD usually involves one or more of the following methods: 1) Echocardiography with Doppler studies; 2) Cardiac catheterization with angiocardiography; or 3) 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.
1. The noninvasive method of echocardiography with Doppler is the preferred method for establishing a definitive diagnosis in dogs when CHD is suspectedfrom 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 examination suggest a definite or potential cardiovascular abnormality.
2. 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 of dogs) may not be identifiable by this method alone.
3. Doppler studies, including pulsed-wave and continuous wave spectral Doppler, and two-dimensional color Doppler demonstrate the direc-tion 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 con-tinuous 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 velocity in discrete anatomic areas.
4. Cardiac catheterization is an invasive method for 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 of CHD, this method has been supplanted by echocardiography with Doppler for routine evaluation of suspected CHD.
5. Necropsy examination of the heart should be done in any breeding dog that dies or is euthanatized. 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.
F. Each of the methods of evaluation indicated above 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:
1. The results of the examinations described above are most reliable when performed by an experienced individual with advanced training and experience 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.
2. 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 8 weeks and I year of age, final certification, prior to breeding, should be obtained in mature dogs at 12 months of age or older.
3. Examination conditions must be appropriate for recognition of subtle cardiac malformations. The identification of soft cardiac murmurs is impeded by extraneous noise or by poorly restrained, anxious, or panting dogs.
4. 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. If the clinical examination is nor-mal, no further liagnostic studies are recommended. If the clinical examination is abnormal, a tentative diagnosis may be made, but the definitive diagnosis generally requires other diagnostic studies (as indicated above).
5. 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 hospi-tal and by the veterinary scientific community, including standards published by the American College of Veterinary Internal Medicine, spe-cialty of Cardiology (J Vet Internal Med 1993; 7:247-252).
G. Examination of dogs for CHD is aimed at the identification and classification of phenotypic abnormalities. Heritable aspects of CHD cannot be addressed unless suitable genetic studies have been conducted.
METHODS OF EXAMINATION
A. Clinical Examination
1. 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 cardiolo gy, 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.
2. Cardiac auscultation should be performed in a quiet, distraction-free environment. The animal should be standing and restrained, but seda-tive drugs should be avoided. Panting must be controlled, and if necessary, the dog should be given time to rest and acclimate to the environ-ment. The clinician should be 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 subuortic area, ascending aorta, pulmonary artery, and the left craniodorsal cardiac base. Following examination of the left precordium, the right precordium should be examined.
· The Initral 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 1or 2 intercostal spaces cranial to the left apical impulse. The second heart sound will be become most intense when the stethoscope is centered over the aortic valve area. Murmurs originating from or radiating to the suboortic 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 precorrhum (right stemal border) and over the r ight craniodorsal cardiac border.
· Any cardiac murmurs or abnormal sounds should be noted. Murmurs should be described as indicated below.
3. 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.
· Grading of heart murmurs is as follows:
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 - 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 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 sueh timing descriptors as: proto(early)-sys-tolic, ejection or crescendo- decr~scendo, holo-systolic or pan-systolic, decrescendo, and tele(late)-systolic and descriptions of subjec-tive characteristics such as: musical, vibratory, harsh, and machinery.
4. 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 diagnosis of soft murmurs but probably decreased specificity as well. Auscultation of the heart following exercise is at the discretion of the examining veterinarian.
· At this time the OFA does not require a post exercise examination in the assessment of heart murmurs in dogs; however, this practice may be modified should definitive information become available
1. The echocardiographic examination should be conducted in a systematic manner. 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 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 appropriate equipment and have received advanced training in echocardiography.
2. 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 recom-mended 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.
3. Doppler examination of all cardiac valves should be performed and recorded. Abnormal flow should be quantified using pulsed or continuous wave Doppler techniques. Values obtained should be compared to reference values. The depressant effects of any tranquilizers or sedatives must be considered when measuring peak flow velocities. Color Doppler echocardiography should be employed if available to assess normal and abnormal blood flow panems. 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 I.
4. Special attention should be directed to the assessment of flow patterns and velocities in the left ventricular outlet and ascending aorta. Optimal alignment with blood flow should be sought for accurate velocities to be recorded. This may require the use of subxiphoid (sub-costal) transducer positions as well as left apical (caudal parasternal) transducer placements. In addition to measurement of peak velocity using pulsed or CW Doppler, the pulsed wave sample volume should be gradually advanced from the subaortic area into the ascending aorta to order to identify sudden accelerations in flow velocity, turbulence, or aortic regurgitation.
5 Echocardiographic studies should be recorded on videotape for subsequent analysis and a written record of abnormal findings should be entered into the medical record.,
|CONGENITAL DEFECT||TYPICAL AUSCULTATORY FEATURES *||DIAGNOSTIC ECHOCARDIOGRAPHIC and DOPPLER ECHOCARDIOGRAPHIC FEATURES|
|Patent Ductus Arteriosus||Continuous heart murmur with maximal intensiry over the left, craniodorsal cardiac base.||Continuous retrograde flow from the patent ductus aneriosus into the pulmonary artery.|
|Ventricular Septal Defect||Systolic murmur with maximal intensity over the right ventral precordium: less often maximal intensity is over the pulmonic valve area and pulmonary artery||The septal defect can often be imaged in multiple imaging planes Abnonmal, generally high velocity systolic flow across the septal defect is evident.|
|Atrial Septal Defect||Systolic murmur with maximal intensity over the pulmonic valve area and pulmonary artery. The second heart sound may be widely split||The septal defect can generally be imaged in multiple imaging planes. Abnommal, blood flow may be identified crossing the septal defect into the right atrium.|
|Pulmonic Stenosis||Systolic murmur with maximal intensity over the pulmonic valve area and pulmonary artery.||Abnonmal pulmonary valve and/or subvalvular anatomy. Sudden acceleration, of blood flow in the right ventricular outlet with turbulent, high velocity systolic flow across the pulmonary valve and into the main pulmonary artery.|
|Valvular and Subvalvular Aortic Stenosis||Systolic murmur with maximal intensity over the subaortic or aortic valve area and radiating into the ascending aorta. The mummur may also be prominent over the right cranial thorax||Abnonmal subvalvular or aortic valvular anatomy may be evident. Sudden acceleration of blood flow in the left ventricular outflow tract with turbulent, high velocity systolic flow across the aortic valve and into the ascending aorta. Concurrent aortic regurgitation is usually present.|
|Mitral Valve Dysplasia||Systolic murmur with maximal intensity over the lei't apex and mitral area.||Abnormal anatomy of the mitral valve apparatus. High velocity retrograde systolic flow across the mitral valve into the left atrium. Concurrent mitral valve stenosis may be present.|
|Tricuspid Valve Dysplasia||Systolic murmur with maximal intensity over the tricuspid valve area.||Abnormal anatomy of the tricuspid valve apparatus. High velocity retrograde systolic flow across the tricuspid valve into the right atrium. Concurrent tricuspid valve stenosis may be present.|
|Right-to-Left Cardiac Shunt||Variable - a systolic munmur at the left base is ohen detected: cyanosis is an important clinical sign.||Abnormal anatomy related to the cardiac malformations: examples include: tetralogy of Fallot, patent ductus aneriosus with pulmonary hypertension; pulmonary or tricuspid valve stenosis with atrial septal defect. Right to left shunting may be documented by Doppler techniques and/or by contrast echocardiography.|
* See text for description of valve and auscultation areas