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Arrhythmogenic Right Ventricular Cardiomyopathy, Dog 77

with higher numbers of arrhythmias and ○ S 3 gallop sound • 24-hour ambulatory ECG results showing
are more likely to develop structural heart ○ Hypokinetic pulse quality > 300 single VPCs or complex ventricular
VetBooks.ir ○ ARVC is occasionally reported in dogs represented as persistent tachycardia or diagnosis and particularly important for Diseases and Disorders
○ Auscultable arrhythmia, which may be
arrhythmias in boxers are consistent with a
disease (type III ARVC, dilated cardio-
myopathy [DCM]–like phenotype)
intermittent premature beats with post-
breed screening.
free of the striatin mutation, suggesting
deficits
50-300 single VPCs in boxers is equivocal
at least one other cause of this disease. extrasystolic pauses and possible pulse • 24-hour ambulatory ECG results showing
• Bulldogs have a genetic predisposition to a ○ Left apical systolic heart murmur due to for a diagnosis of ARVC.
similar disease that usually involves structural annular stretch and secondary mitral • 24-hour ambulatory ECG results showing
change to the heart, including dilation of regurgitation, which is not to be confused < 50 single VPCs is considered normal in
the right and/or left ventricle in addition to with left basilar ejection murmurs present the boxer.
arrhythmias. A causative genetic mutation in many healthy boxers and boxers with
has not yet been identified. aortic or subvalvular aortic stenosis Differential Diagnosis
○ Possible signs of left-sided CHF, including • Type I: consider all causes of ventricular
RISK FACTORS fine pulmonary crackles, increased respira- arrhythmias, including the following:
• Because it is an inherited cardiomyopathy, tory effort or rate ○ Metabolic disturbance: endocrinopathy,
familial history is the most important risk ○ Possible signs of right-sided CHF, acid-base derangements, immune-
factor. including a palpable abdominal fluid mediated disease or inflammation,
• Positive genetic test status for the striatin wave (ascites), jugular venous pulsation/ neoplasia, and electrolyte derangements
mutation, particularly homozygous status, distention, positive hepatojugular reflux (commonly hypercalcemia, hypokalemia,
indicates clear risk. and hypomagnesemia)
• Increased age is also associated with higher Etiology and Pathophysiology ○ Underlying cardiac disease: acquired
risk for disease. • The hallmark histopathologic lesions include valvular disease, congenital cardiac disease,
fibrofatty infiltration of the right ventricle other cardiomyopathy, cardiac neoplasia,
Clinical Presentation and myocytolysis, which may spread more or myocarditis
DISEASE FORMS/SUBTYPES broadly in some cases to include the atria ○ Abdominal disease: abdominal neoplasia,
• Type I (occult or concealed) is characterized and left ventricle. The events that lead to splenic or hepatic disease, gastric dilation/
by ventricular arrhythmias without clinical the observed myocardial change are unclear. volvulus, and peritonitis
signs. These changes explain the characteristic ○ Autonomic imbalance: stress/pain or a
• Type II (overt) is characterized by ventricular right-sided ventricular premature complexes pathologic increase in sympathetic tone
arrhythmias with clinical signs (e.g., syncope). (VPCs) noted on the electrocardiogram (e.g., pheochromocytoma)
• Type III (myocardial dysfunction) is char- (ECG) (predominantly upright in lead II). ○ Drugs/toxins: digoxin, methylxan-
acterized by ventricular and/or supraven- • A deletion mutation in the striatin gene, which thines, oleander, catecholamines, and
tricular arrhythmias and cardiac dilation with codes for a desmosomal protein, has been chemotherapeutics (most commonly
systolic dysfunction. This form resembles implicated in this disease. This mutation leads doxorubicin)
DCM, and dogs may have clinical signs of to disruption of cardiac desmosomes and may • Type II: consider all causes of ventricular
left or biventricular congestive heart failure trigger loss of normal cell-to-cell adhesion. arrhythmias as described for type I and all
(CHF) and/or syncope. Prognosis is signifi- • ARVC is also associated with calstabin 2 causes of episodic weakness/syncope, includ-
cantly worse than for types I and II. deficiency and alterations in beta-catenin. ing the following:
Calstabin 2 is an important regulator of ○ Causes of syncope: neurocardiogenic
HISTORY, CHIEF COMPLAINT the ryanodine receptor in the myocardium (reflex-mediated) syncope, poor cardiac
• Type I patients may be diagnosed during and helps prevent calcium leakage from the output (DCM, severe mitral valve
breed screening or because an arrhythmia sarcoplasmic reticulum; without it, calcium regurgitation), congenital heart disease,
was incidentally identified on examination. leakage can potentiate arrhythmias seen in bradyarrhythmias, tachyarrhythmias, and
• Type II patients present for evaluation this disease. Beta-catenin alterations suggest pulmonary hypertension (which is unlikely
of clinical signs relatable to a ventricular possible involvement of the canonical Wnt in the boxer)
tachyarrhythmia, most commonly syncope or pathway, a driver of adipocyte differentiation. ○ Episodic weakness that may be mistaken
presyncope (collapse, weakness, or transient • A similar disease that is also referred to as for syncope (e.g., hypoglycemia, splenic
ataxia). The first clinical sign may be sudden ARVC has been described in cats, bulldogs, tumor hemorrhage)
death. and several other breeds of dogs, and it usually ○ Seizure disorder
• Type III patients present for evaluation of involves dilation of the right and sometimes ○ Narcolepsy (rare)
clinical signs related to a tachyarrhythmia, left ventricles in addition to arrhythmias. • Type III: consider all causes of a dilated
including syncope or presyncope, or may cardiomyopathy phenotype and CHF.
present with signs related to left or biven- DIAGNOSIS ○ Primary structural cardiac disease with
tricular CHF, including cough, respiratory resultant cardiac dilatation and systolic
distress, increased respiratory rate, exercise Diagnostic Overview dysfunction (e.g., acquired valvular disease,
intolerance, abdominal distention (ascites), • No single antemortem diagnostic test is congenital cardiac lesions)
and weakness. confirmatory; ARVC is a presumptive ○ Myocarditis
diagnosis based on findings of ventricular ○ Severe systemic disease (e.g., sepsis) with
PHYSICAL EXAM FINDINGS arrhythmias (most commonly right sided or resultant systolic dysfunction
• In types I and II, physical examination may upright in lead II) with exclusion of other ○ Hypothyroid cardiomyopathy
be normal. causes of ventricular arrhythmias. ○ Nutritional cardiomyopathy (taurine-
○ Possible physical exam findings include • Diagnosis is strongly supported by positive deficient or carnitine-deficient DCM)
an auscultable arrhythmia with post- genetic testing (heterozygote or homozygote
extrasystolic pauses and possible pulse for the striatin mutation). Initial Database
deficits. • Diagnosis is also supported by a family • Documentation of ventricular arrhythmia
• In type III, possible findings include the history of the disease and the presence of on ECG in the absence of the above comor-
following: supraventricular or ventricular arrhythmias. bidities supports ARVC in boxers. VPCs are

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