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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 the 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:

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 suspected 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.
  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 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.
  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 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 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.

Limitations


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 to the examinations described above are most reliable when performed by an experienced individual with advanced training an 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 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 1 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. 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 (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 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).

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