WHAT IS CONGENITAL CARDIAC DISEASE?
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
ADULT ONSET CARDIAC DISEASE
Adult-onset or developmental cardiac diseases develop later in life and include for example; hypertrophic, arrhythmogenic and dilatative cardiomyopathies. Because acquired disease can appear subsequent to a normal cardiac exam, adult onset clearances are only valid for one year from the time of the exam. Many 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.
ADVANCED CARDIAC EXAM
The Advanced Cardiac Database results are in a two-tiered clearance for normal dogs:
congenital cardiac disease and adult-onset cardiac disease.
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.
As of October 1, 2020 – In order to maximize the accuracy and utility of OFA cardiac certification, the
ACVIM Cardiology Specialty Group and the Orthopedic Foundation for Animals is now requiring echocardiographic examinations be submitted in order to obtain an Advanced Cardiac Database
certification. This change will help to ensure that forms of heart disease (congenital or acquired) that may be difficult or impossible to identify on auscultation alone do not go undetected. Only echocardiographic
examinations performed by a Board Certified Veterinary Cardiologist will be accepted.
BASIC CARDIAC EXAM
For the Basic Cardiac Database Certificate any licensed veterinarian can perform the examination, however, they will not be eligible for entry into the Advanced Cardiac Database.
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) and Echocardiograms
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.
DESCRIPTIONS 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.
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.
Reference: Orthopedic Foundation for Animals website: www.offa.org