General Cardiac Information

Congenital Heart Disease

Congenital heart diseases in dogs are malformations 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.

Developmental Inherited Cardiac Diseases (SAS and Cardiomyopathy)

At this time inherited, developmental cardiac diseases like subaortic stenosis and cardiomyopathies are difficult to monitor since there is no clear cut distinction between normal and abnormal. The OFA will modify the congenital cardiac database when a proven diagnostic modality and normal parameters by breed are established. However at this time, the OFA cardiac database should not be considered as a screening tool for these diseases.

Purpose of Cardiac Database

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 database, a phenotypically normal dog is defined as:
  1. One without a cardiac murmur -or-

  2. One with an innocent heart murmur that is found to be otherwise normal by virtue of an echocardiographic examination which includes Doppler echocardiography

Congenital Cardiac Disease Physical Exam

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.

Ascultation

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 1 or 2 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 be right craniodorsal cardiac border.

  • Any cardiac murmurs or abnormal sounds should be noted. Murmurs should be described as indicated below.

Description of Cardiac Murmurs

A full description of the cardiac murmur should 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 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.

Congenital Cardiac Disease Echocardiographic Exam

The Echocardiographic Exam

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 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

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.

Assessment

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 acsending aorta in order to identify sudden accelerations in flow velocity, turbulence, or aortic regurgitation.

Videotape

Echocardiographic studies should be reported on videotape for subsequent analysis and a written record of abnormal findings should be entered into the medical record.

Echocardiographic Findings


Congenital Defect Typical Auscultatory Features Diagnostic Echocardiographic and Doppler Echocardiographic Features
Patent ductus arteriosus Continuous heart murmur with maximal intensity over the left cranial dorsal cardiac base Continuous retrograde flow from the patent ductus arteriosus 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. Abnormal, 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. Abnormal blood flow may be identified across the septal defect into the right atrium.
Pulmonic stenosis Systolic murmur with maximal intensity over the pulmonic valve area and pulmonary artery Abnormal 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 murmur may also be prominent over the right cranial thorax. Abnormal subvalvular or aortic valvular anatomy may be evident. Sudden acceleration of blood flow into 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 left 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 murmur at the left base is often detected; cyanosis is an important clinical sign Abnormal anatomy related to the cardiac malformations examples include: tetralogy of Fallot, patent ductus arteriosus with pulmonary hypertension, pulmonary or tricuspid valves stenosis with atrial septal defect. Right to left shunting may be documented by Doppler techniques and/or by contrast echocardiography.

Congenital Cardiac Grades

The Congenital Cardiac Database is for dogs 12 months and over. Examinations performed on dogs less than 12 months will be treated as Consultations and no OFA breed numbers will be assigned.

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 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, holo-systolic or pan-systolic, decrescendo, and tele(late)-systolic and descriptions of subjective characteristics such as: musical, vibratory, harsh, and machinery.

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