Veterinary Cardiology: Clinical Manifestations

Clinical Manifestations in Veterinary Cardiology and Objectives

• The following topics will be covered: cardiac auscultation, causes/characteristics of heart murmurs, valvular insufficiencies pathophysiology, common cardiomyopathies, and cardiac radiology value.

Cardiac Auscultation Overview

• Four heart sounds are possible, but usually only two are heard in normal small animals and the sounds are more audible in large animals.
• S1 is the sound of the closure of the Atrioventricular valves (left and right) which occurs at the start of ventricular systole.
• S2 is the sound of the closure of the semilunar valves (pulmonary and aortic) which occurs at the end of ventricular systole.
• S3 is the sound of rapid ventricular filling during diastole but is not normally auscultated in small animals.
• S3 can be associated with congestive heart failure and cardiomyopathy
• S4 is the sound of atrial systole, and is not normally auscultated in small animals.
• S4 can be associated with filling of non-compliant ventricles, or hypertrophic cardiomyopathy.

Describing Heart Murmurs

• Intensity is graded from I to VI, with Grade I being not distinct and Grade VI being very loud, not requiring a stethoscope.
• Position and Duration are described in relation to the cardiac cycle such as systolic, diastolic, pan-, holo-, early-, late, and continuous.
• Location matches the valve area which has the point of maximum intensity as Pulmonic, Aortic, Mitral, or Tricuspid.
• Quality can be described by the intensity profile such as plateau, crescendo, decrescendo, or diamond (crescendo-decrescendo).
• Character/Pitch/Frequency Profile is used to describe the sound as Blowing, musical, honking, harsh, or noisy.

Murmurs and Blood Flow

• Murmurs are the turbulent sound of blood flow and thus is classified as(ABNORMAL).
• Murmurs can be caused by an abnormal flow pattern such as Valvular insufficiency where the valve doesn't close completely.
• Murmurs can be caused by abnormal vessel diameter such as narrowing of the aorta (aortic stenosis).
• Murmurs can be caused by abnormal blood viscosity such as anemia causing low viscosity blood.
• Cardiac disease severity doesn't always link to the severity of the murmur.

Cardiac Output and Volume Regulation

• Cardiac pathology needs some physiology in order to understand it.
• The volume of blood moving in circulation is the responsibility of the heart along with the kidneys.
• Cardiac Output = Heart Rate X Stroke Volume.
• Stroke volume can be altered by contractility, and/or changes in blood volume.

Mitral Insufficiency Consequences

• Mitral insufficiency is where some of the blood leaks through the valve back into the left atrium.
• Cardiac output decreases as a result of mitral insufficiency.
• The body increases the heart rate in response to try and bring cardiac output bring it back to normal, but the disease progresses.
• The kidneys compensate by retaining water and electrolytes to increase blood volume and pressure, thus increasing pre-load (end diastolic volume).
• The kidneys short term compensation also increases the amount of blood regurgitated through the faulty valve.
• The heart must compensate to accommodate the increased volume and increased pressure, which results in dilated cardiomyopathy.

Mitral Insufficiency Final Result

• Without therapy, the end result of Mitral insufficiency is congestive heart failure.
• The left side of the heart can no longer enlarge and blood pressure continues to rise, causing more regurgitation and pressure in the lungs to increase eventually causing pulmonary edema.
• Myocardial failure can occur the heart muscle fails to pump fluid forward.

Mitral and Tricuspid Valve Insufficiency Effects

• Mitral Valve insufficiency eventually causes a reduction of flow to the left side of the heart
• An end result of Mitral valve insufficiency is pulmonary edema (fluid in the lungs), resulting in increased respiratory rate and effort/coughing or eventual exercise intolerance.
• Tricuspid valve insufficiency eventually causes a reduction in flow to the right side of the heart.
• Systemic circulation becomes congested because capillaries of the body cavity linings, abdomen, and chest manifest signs of disease first.
• Abdomen is lined by peritoneum, so the accumulation of fluid in the peritoneal space is called “Ascites” causing a distended abdomen.
• Chest is lined by pleura, so accumulation of fluid in the plural space is called "Plural effusion" causing respiratory effort, rate, and noise.

Tricuspid Insufficiency (Regurgitation)

• Tricuspid insufficiency is the result of a very similar disease process (pathophysiology) as mitral disease.
• There is right-sided heart congestion and pressures of the systemic circulation increases and starts “leaking”.
• The lining of the body cavities (thorax/abdomen) have tiny vessels that can become “leaky" under stress of high pressure.
• The abdominal cavity and organs are lined by the peritoneum.
• Excessive fluid in the peritoneal space is called "Ascites".
• The thoracic cavity and organs are lined with pleura.
• Excessive fluid in the plural space is called "Plural Effusion”.

Predisposed Breeds

• Mitral valve disease (acquired) predisposed breeds include Cavalier King Charles spaniel, dachshund, and any small dog breeds.
• Mitral valve disease (congenital) predisposed breeds include bull terriers and rottweilers.
• Myocardial failure predisposed breeds include boxers, cocker spaniels, Doberman pinschers, Great Danes, Irish wolfhounds, and Labrador retrievers.
• Patent ductus arteriosus predisposed breeds include cocker spaniels, English springer spaniels, German shepherds, Maltese terriers, and poodles.
• Pulmonary stenosis predisposed breeds include boxers, cocker spaniels, English bulldogs, mastiffs, miniature schnauzers, Samoyeds, and West Highland white terriers.
• Subvalvular aortic stenosis predisposed breeds include boxers, German shepherds, golden retrievers, Newfoundlands, and rottweilers.
• Tricuspid valve disease (congenital) predisposed breed is the Labrador retriever.
• Ventricular septal defect predisposed breed is the English springer spaniel.

Dilated Cardiomyopathy

• Dilated Cardiomyopathy occurs most frequently in boxers and Doberman pinchers due to a decrease in contractility of cardiac muscle because of genetics.
• Initially it is compensated by increasing heart rate and blood volume, but eventually the orientation of the mitral valve is affected resulting in mitral valve insufficiency ensues.
• Dilated cardiomyopathy is directly related to Taurine deficiency in a cat's diet.
• Dilated cardiomyopathy is very rare in household cats due to commercially available balanced nutrition.

Feline Hypertrophic Cardiomyopathy

• The exact cause of Feline Hypertrophic Cardiomyopathy is unknown, but there is a definitive genetic predisposition (Ragdoll, Maincoon).
• Ventricular walls thicken, pumps well, but cannot relax during diastole resulting in decreased Cardiac Output (CO).
• Can result in Malalignment of valves (especially the mitral).

Patent Ductus Arteriosus (PDA)

• Patent Ductus Arteriosus blood results in a a connection between the aorta vessels and the pulmonary artery.

Cardiac Silhouette on Radiographs

• Cardiac silhouette is NORMALLY about 60 to 65 percent of the thoracic width.
• VHS stands for Vertebral Heart Size
• VHS = L(ong) + S(hort)
• Normal ranges for the average dog is 8.5 - 10.9 Vertebra, and a normal range for the average cat is 6.8 - 8.1 Vertebra.
• To measure heart size on radiographs you measure the Long axis from the Carina to the Apex.
• To measure heart size on radiographs you measure the short axis from the widest part with in the cardiac silhouette.
• Measure both in cm/mm then with your measurement tool move the measurement length towards vertebrae starting at T4.
• This will give you a rough vertebral heart size
• Feline VD radiographs are more reliable than dog radiographs and can also be utilized because there is relatively little variation in cat chest shape (ratio of depth : width).
• Dogs have a large variation in shape between breeds.