Page 295 - Clinical Small Animal Internal Medicine

26 Canine Myocardial Disease 263

Arrhythmogenic Right Ventricular Rather, an 8‐base pair deletion in the striatin gene has
VetBooks.ir Cardiomyopathy been linked to ARVC in some American boxers, though
its causal role has been challenged. Striatin is an interca-
lated disc protein that co‐localizes with three of the des-
Etiology/Pathophysiology
mosomal proteins implicated in ARVC in people. There
Arrhythmogenic right ventricular cardiomyopathy is a is also some suggestion that the RyR2 is involved as
progressive myocardial disorder characterized by partial affected boxers have a deficiency of calstabin2, a RyR2
to complete replacement of the right ventricular (RV) protein.
myocardium with fatty or fibro‐fatty tissue, presence of Arrhythmogenic right ventricular cardiomyopathy in
ventricular arrhythmias, and risk of SD. The distribution dogs manifests as ventricular tachyarrhythmias predom-
of pathologic changes is greater in the subepicardium, and inantly of RV origin (left bundle branch block [LBBB]
the left ventricle is not spared despite being a predomi- configuration) and patients are at risk of SD from
nantly RV disorder. In humans, a majority of cases are ventricular fibrillation (Figure 26.5).
familial or inherited and genetic mutations in at least 20 Supraventricular tachyarrhythmias may also occasion-
genes encoding mostly proteins of the desmosome (region ally be noted. In boxers, the hearts are most often struc-
of intercalated discs between myocardial cells involved in turally normal on gross examination, unlike in humans
mechanical and electrical coupling) have been implicated. where RV dilation, systolic dysfunction, and aneurysms
A few nondesmosomal genes, including the cardiac ryan- are common. A small percent of boxers experience systolic
odine receptor (RyR2, calcium release channel of the sar- dysfunction and heart failure, whereas this may be more
coplasmic reticulum), have also been involved. common in English bulldogs, another affected breed.
Arrhythmogenic right ventricular cardiomyopathy is
likewise a familial (inherited) disorder in the boxer. The Epidemiology
disease, once referred to as “boxer cardiomyopathy,” has
been reclassified as ARVC due to its similarities with The true prevalence of ARVC in the boxer is unknown,
the human disease. To date, none of the mutations but anecdotally it would appear to be quite common.
described in people have been found in the boxer. The prevalence in other breeds is very low.

Figure 26.5 Nine‐lead ECG, 25 mm/s, 5 mm/mV. Right ventricular VPCs (left bundle branch block configuration) in a boxer with ARVC.
There are periods of ventricular bigeminy (alternating VPCs and sinus beats) and several VPC couplets.