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Atrioventricular
Valve Dysplasia
Basics
OVERVIEW
• The heart of the dog or cat is composed of four cha mbers; the
top two chambers are the left and right atria and t he bottom two
chambers are the left and right ventricles; heart v alves are
located between the left atrium and the left ventri cle (mitral
valve); between the right atrium and the right vent ricle
(tricuspid valve); from the left ventricle to the a orta (the main
artery of the body; valve is the aortic valve); and from the right
ventricle to the main pulmonary (lung) artery (pulm onary valve)
• The mitral valve and the tricuspid valves are the
“atrioventricular valves”; that is, they are the va lves between the
left atrium and ventricle and between the right atr ium and
ventricle, respectively
• In order to pump blood to the lungs and body, the h eart must
work in a coordinated fashion; the normal control o r
“pacemaker” of the heart is the sinoatrial (SA) nod e, which
starts the electrical impulse to begin the coordina ted contraction
of the heart muscles—the electrical impulse causes the atria to
contract, pumping blood into the ventricles; the el ectrical impulse moves through the atrioventricular (AV) node
and into the ventricles, causing the ventricles to contract and to pump blood to the lungs (right vent ricle) and
the body (left ventricle)
• “Dysplasia” is the medical term for abnormal develo pment of a tissue
• “Atrioventricular valve dysplasia” is a congenital (present at birth) malformation of the mitral or tr icuspid valve;
may be referred to as “mitral valve dysplasia” or “ tricuspid valve dysplasia” to indicate which valve is affected
• It is not uncommon for mitral and tricuspid valve d ysplasia to occur together in the same pet
GENETICS
• Tricuspid valve dysplasia is inherited as an autoso mal recessive trait in Labrador retrievers
• Heritability and pattern of inheritance has not bee n established in other breeds
SIGNALMENT/DESCRIPTION OF PET
Species
• Dogs
• Cats
• One of the most common congenital (present at birth ) heart defects in cats; less frequently diagnosed in dogs

Breed Predilections
• Mitral valve dysplasia—bull terriers, Newfoundlands , Great Danes, golden retrievers, Dalmatians, and S iamese
cats; perhaps the most common congenital (present a t birth) heart defect of cats
• Mitral valve malformations often are noted in cats with hypertrophic cardiomyopathy (disease character ized by
inappropriate enlargement or thickening of the hear t muscle of the left ventricle)
• Tricuspid valve dysplasia—Labrador retrievers, Germ an shepherd dogs, Great Pyrenees, possibly Old Engl ish
sheepdogs; common in cats
Mean Age and Range
• Variable
• Signs most often seen within the first few years of life
Predominant Sex
• Males are more likely than females to have signs of heart failure
SIGNS/OBSERVED CHANGES IN THE PET
• Exercise intolerance is the most common problem in dogs and cats with atrioventricular valve dysplasia
• Abdominal swelling or distention, weight loss, and stunting of growth may be observed with severe tric uspid
valve dysplasia
• Labored breathing is common in dogs or cats with mi tral valve dysplasia
• Fainting (known as “syncope”) and collapse, if crit ical mitral or tricuspid valve narrowing (known as “stenosis”),
or if blood flow through the valves is blocked (kno wn as “outflow obstruction”), or if the pet has irr egular
heartbeats (known as “arrhythmias”), or the pet has congestive heart failure (CHF) from poor functioni ng of the
abnormal heart valve; “congestive heart failure” is a condition in which the heart cannot pump an adeq uate
volume of blood to meet the body’s needs
Mitral Valve Dysplasia (Involves the Valve between the Left Atrium and the Left Ventricle)
• Heart murmur; with severe disease, may be able to f eel vibrations caused by abnormal blood flow (known as
“thrills”) when placing hand against the chest wall , or may hear a sequence of three heart sounds (kno wn as a
“gallop rhythm”) when listening to the heart with a stethoscope; heartbeat sounds like a galloping hor se instead
of normal “lub dub”
• Evidence of left-sided congestive heart failure—pet s with severe defects may have rapid breathing (kno wn as
“tachypnea”); increased breathing efforts; rough sn apping sounds (known as “crackles”) may be heard wh en
listening to the chest with a stethoscope; and blui sh discoloration of the skin and moist tissues (muc ous
membranes) of the body caused by inadequate oxygen levels in the red blood cells (known as “cyanosis”) ;
congestive heart failure is a condition in which th e heart cannot pump an adequate volume of blood to meet the
body’s needs
Tricuspid Valve Dysplasia (Involves the Valve betwe en the Right Atrium and the Right Ventricle)
• Heart murmur; with severe disease, may be able to f eel vibrations caused by abnormal blood flow (thril ls) when
placing hand against the chest wall or may hear a s equence of three heart sounds (gallop rhythm), when
listening to the heart with a stethoscope; heart be at sounds like a galloping horse instead of normal “lub dub”
• The external jugular veins (located on either side of the neck) may be enlarged or distended and may h ave a
pulse
• Evidence of right-sided congestive heart failure—fl uid buildup in the abdomen (known as “ascites”), an d, more
rarely, fluid buildup in the tissues, especially th e legs and under the skin (known as “peripheral ede ma”) in pets
with severe malformations of the tricuspid valve
CAUSES
• Congenital (present at birth) malformation of the m itral or tricuspid valve
Treatment
HEALTH CARE
• Inpatient treatment required for congestive heart f ailure; congestive heart failure is a condition in which the
heart cannot pump an adequate volume of blood to me et the body’s needs

ACTIVITY
• Restricted in accordance with severity of clinical signs
DIET
• Sodium-restricted diet, if in or likely to develop congestive heart failure; congestive heart failure is a condition in
which the heart cannot pump an adequate volume of b lood to meet the body’s needs
SURGERY
• Heart valve repair or replacement surgery is availa ble in a few centers
• Surgical treatment is expensive
Medications
Medications presented in this section are intended to provide general information about possible treat ment. The
treatment for a particular condition may evolve as medical advances are made; therefore, the medicatio ns should
not be considered as all inclusive
• Mitral or tricuspid dysplasia with insufficiency—me dications to remove excess fluid from the body (kno wn as
“diuretics,” such as furosemide), heart medications (such as angiotensin converting enzyme [ACE] inhib itors
and pimobendan) for pets in or likely to develop co ngestive heart failure; digoxin to control rapid he art rhythms
(known as “supraventricular tachyarrhythmias”); con gestive heart failure is a condition in which the h eart
cannot pump an adequate volume of blood to meet the body’s needs
• Mitral or tricuspid narrowing (stenosis)—medication s to remove excess fluid from the body (diuretics, such as
furosemide) to control fluid buildup (known as “ede ma”); heart rate should be maintained near 150 beat s per
minute, using digoxin, a calcium channel blocker (s uch as diltiazem), or a beta-receptor blocking drug (such as
atenolol)
• Dynamic blockage of blood flow through the valves ( known as “dynamic outflow tract obstruction”)—beta-
receptor blocking drug (such as atenolol) to decrea se severity of outflow obstruction; a “dynamic” pro cess is one
in which the lumen of the chambers changes with the movements of the heart (relaxation and contraction )
• Medications to remove excess fluid from the body (d iuretics, such as furosemide), if the pet is in con gestive
heart failure
Follow-Up Care
PATIENT MONITORING
• Recheck yearly, if no signs of congestive heart fai lure; congestive heart failure is a condition in wh ich the heart
cannot pump an adequate volume of blood to meet the body’s needs
• Recheck at a minimum of every 3 months, if signs of congestive heart failure—chest x-rays (radiographs ),
electrocardiogram (ECG, a recording of the electric al activity of the heart), and echocardiography (us e of
ultrasound to evaluate the heart and major blood ve ssels)
PREVENTIONS AND AVOIDANCE
• Do not breed affected pets
POSSIBLE COMPLICATIONS
• Congestive heart failure—left-sided with mitral val ve dysplasia; right-sided with tricuspid valve dysp lasia;
congestive heart failure is a condition in which th e heart cannot pump an adequate volume of blood to meet the
body’s needs
• Collapse or fainting (syncope) with exercise
• Sudden onset (known as “paroxysmal”) supraventricul ar tachycardia or atrial fibrillation with severe d isease;
“supraventricular tachycardia” is a rapid heart rat e caused by electrical impulses that originate from a site other
than the sinoatrial node, the normal pacemaker of t he heart; “atrial fibrillation” is a rapid, irregul ar heart
rhythm involving the top two chambers of the heart (atria)
EXPECTED COURSE AND PROGNOSIS
• Depends on severity of underlying defect
• Prognosis is guarded to poor with serious defects

Key Points
• “Atrioventricular valve dysplasia” is a congenital (present at birth) malformation of the mitral or tr icuspid valve
• Potentially an inherited disorder; affected pets sh ould not be used for breeding

Enter notes here

Blackwell's Five-Minute Veterinary Consult: Canine and Feline, Fifth Edition, Larry P. Tilley and Francis W.K. Smith, Jr. © 2011 John Wiley & Sons,
Inc.