• Review the pathophysiological changes associated with the common congenital and acquired cardiac defects in small animal medicine.
• Discuss the characteristics of anesthetic drugs that may make them desirable of undesirable for each problem.
Canine Valvular Heart Disease (Endocardiosis, myxomatous valve degeneration):
• CVHD/Mitral insufficiency is a relatively common finding. 10% of all dogs that present to veterinarians have heart disease. Of these, 75% have CVHD.
• Older, small breed dogs are especially prone to this acquired condition.
• Males are more commonly affected than females.
• Usually more rapidly progressive in large dogs.
• Mitral insufficiency is associated with chronic left ventricular volume overload. The left ventricle at end diastole contains blood that has passed though the atria into the ventricle (normal antegrade filling) AND blood that flowed in a retrograde fashion across the mitral valve during ventricular contraction.
• The ventricle responds by increasing volume and wall thickness (eccentric hypertrophy). This change is compensatory and helps to maintain function. Atrial dilation occurs as a result of increased volume.
• Over time, ventricular systolic function decreases.
• The relationship between atrial pressure and aortic pressure determines the direction and quantity of blood flow.
• Increased aortic diastolic pressure tends to increase regurgitation of blood into the atria.
• Patients with mitral regurgitation are in a state of chronic volume overload and sympathetic stimulation. The degree of alteration is related to the severity of disease.
• Animals with mitral regurgitation are sensitive to volume overload, decreased heart rate, and increased afterload.
• Thoracic radiographs provide an indication of cardiac enlargement and may indicate the onset of congestive heart failure.
• Ultrasonic evaluation will confirm the diagnosis of mitral insufficiency, and can provide an indication of myocardial function.
• Central venous pressure can be useful in determining volume status or onset of congestive heart failure.
• Exercise tolerance, and other historical and physical findings can provide a good indication of cardiac function and anesthetic risk.
• The practitioner should be familiar with the ACVIM's guidelines for diagnosis and treatment of canine valvular heart disease:
Summary: ACVIM Consensus Statement, Guidelines for the Diagnosis and Treatment of Canine Valvular Heart Disease (CVHD) 2009