Title: Boxer cardiomyopathy

{{Use dmy dates|date=February 2023}}
'''Boxer cardiomyopathy''' (also known as &quot;Boxer arrhythmogenic right ventricular cardiomyopathy&quot;) is a disease of the [[myocardium]] primarily affecting [[Boxer dogs]]. It is characterized by the development of ventricular tachyarrhythmias, resulting in [[Syncope (medicine)|syncope]] and [[sudden cardiac death]]. Myocardial failure and congestive heart failure are uncommon manifestations of the disease.&lt;ref name=&quot;Basso&quot;&gt;Basso C, Fox PR, Meurs KM, et al. Arrhythmogenic right ventricular cardiomyopathy causing sudden cardiac death in Boxer dogs: A new animal model of human disease. Circulation 2004;109:1180–1185&lt;/ref&gt;

==Overview==
Boxer cardiomyopathy shares striking similarities to a human myocardial disease called [[arrhythmogenic right ventricular cardiomyopathy]] (ARVC).&lt;ref name=&quot;Basso&quot;/&gt; On histopathology, the disease is characterized by the progressive replacement of ventricular [[myocardium]] (primarily right ventricular myocardium) with fatty or fibro-fatty tissue.&lt;ref name=&quot;update&quot;&gt;Meurs KM. Boxer dog cardiomyopathy: An update. Vet Clin North Am Small Anim Pract 2004;34:1235–1244.&lt;/ref&gt; Clinically, the disease is characterized by the development of ventricular tachyarrhythmias, including [[ventricular tachycardia]] and [[ventricular fibrillation]]. Affected dogs are at risk of syncope and sudden cardiac death.&lt;ref name=&quot;update&quot;/&gt;

==Cause==
Boxer cardiomyopathy is a [[genetic disease]] inherited in an [[autosomal dominant]] pattern.&lt;ref name=&quot;familial&quot;&gt;Meurs KM, Spier AW, Miller MW, et al. Familial ventricular arrhythmias in boxers. J Vet Intern Med 1999;13:437–439.&lt;/ref&gt; The presentation in affected offspring is quite variable, suggesting incomplete penetrance.&lt;ref name=&quot;familial&quot;/&gt; In 2009, a group led by Dr. Kathryn Meurs at Washington State University announced that they had identified one genetic anomaly associated with Boxer cardiomyopathy&lt;ref&gt;Meurs et al. Abstract: Boxer Cardiomyopathy Journal Veterinary Internal Medicine 2009;23:687-688)&lt;/ref&gt;&lt;ref&gt;Powell, C. Vet cardiologist discovers gene for heart disease. April 2009.  URL: http://www.wsutoday.wsu.edu/pages/publications.asp?Action=Detail&amp;PublicationID=14446 {{Webarchive|url=https://web.archive.org/web/20110718111811/http://www.wsutoday.wsu.edu/pages/publications.asp?Action=Detail&amp;PublicationID=14446 |date=18 July 2011 }}  Accessed: 12 December 2009&lt;/ref&gt; but as of 2012 there is still debate over the significance of the discovery.

==Clinical presentation==
Boxer cardiomyopathy is an adult-onset disease with three distinct clinical presentations:

The '''concealed''' form is characterized by an asymptomatic dog with [[premature ventricular contractions]] (PVCs).

The '''overt''' form is characterized by ventricular tachyarrhythmias and [[Syncope (medicine)|syncope]]. Dogs with overt disease may also have episodic weakness and exercise intolerance, but syncope is the predominant manifestation.

The third form, which is recognized much less frequently, is characterized by '''myocardial systolic dysfunction'''. This may result in left-sided, right-sided, or bi-ventricular [[congestive heart failure]]. It is not known if this form represents a separate clinical entity, or whether it is part of the continuum of disease.&lt;ref name=&quot;update&quot;/&gt;

==Sudden cardiac death==
All dogs with Boxer cardiomyopathy are at risk of [[sudden cardiac death]]. This includes asymptomatic dogs, meaning that sudden death may be the first sign of disease.&lt;ref name=&quot;kittleson&quot;&gt;Kittleson MD, Kienle RD. Arrhythmogenic Right Ventricular Cardiomyopathy. In: Small Animal Cardiovascular Medicine. St Louis, MO:Mosby; 1998.&lt;/ref&gt;

Sudden cardiac death is usually caused by the degeneration of ventricular tachycardia to ventricular fibrillation. Unless terminated promptly by [[defibrillation]], death usually occurs within minutes.&lt;ref name=&quot;kittleson&quot;/&gt;

==Diagnosis==

'''Physical examination'''
The physical examination is often unremarkable, although an arrhythmia characterized by premature beats may be detected.&lt;ref name=&quot;kittleson&quot;/&gt;

'''Electrocardiogram:'''
An [[ECG]] often shows premature ventricular complexes (PVCs). These typically have an upright morphology on lead II (left bundle branch morphology). This occurs as the ectopic impulses usually arise in the right ventricle. In some case, the ECG may be normal. This is due to the intermittent nature of ventricular arrhythmias, and means that the diagnosis should not be excluded on the basis of a normal ECG.&lt;ref name=&quot;update&quot;/&gt;&lt;ref name=&quot;kittleson&quot;/&gt;

'''Holter monitor:'''
A [[Holter monitor]] allows for 24-hour ambulatory ECG monitoring. It facilitates quantification of the frequency and severity of ventricular ectopy, and is important in the management of affected dogs.&lt;ref name=&quot;update&quot;/&gt; Boxer breeders are encouraged to Holter their breeding stock annually to screen out affected dogs.&lt;ref name=abc&gt;{{cite web|last=American Boxer Club|title=Recommendations for Health Screening of Boxers in Breeding Programs|url=http://www.americanboxerclub.org/health-screening.html}}&lt;/ref&gt;

'''Genetic test:'''
A genetic test for Boxer cardiomyopathy is now commercially available.&lt;ref&gt;Anon. &quot;Boxer Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)” Veterinary Cardiac Genetics Lab, North Carolina State University URL: http://www.ncstatevets.org/genetics/boxerarvc/  Accessed: 9 October 2013&lt;/ref&gt; The genetic test is not yet accepted as a definitive test and additional diagnostic testing continues to be essential to characterize the [[phenotype]], and to help direct therapeutic interventions.

'''Echocardiogram:'''
[[Echocardiography]] is recommended to determine if structural heart disease is present. A small percentage of dogs have evidence of myocardial systolic dysfunction, and this may affect the long-term prognosis.&lt;ref name=&quot;update&quot;/&gt;

==Treatment==
Current treatment options for Boxer cardiomyopathy are largely restricted to the use of oral [[anti-arrhythmic medications]]. The aim of therapy is to minimize ventricular ectopy, eliminate syncopal episodes, and prevent sudden cardiac death.&lt;ref name=&quot;treatments&quot;&gt;Meurs KM, Spier AW, Wright NA, Atkins CE, DeFrancesco T, Gordon S, et al. Comparison of the effects of four antiarrhythmic treatments for familial ventricular arrhythmias in Boxers. J Am Vet Med Assoc 2002;221:522–7.&lt;/ref&gt; A number of medications have been used for this purpose, including atenolol, procainamide, sotalol, mexiletine, and amiodarone. Combinations can also be used. [[Sotalol]] is probably the most commonly used antiarrhythmic at this time.&lt;ref name=&quot;kittleson&quot;/&gt;&lt;ref name=&quot;treatments&quot;/&gt; It has been demonstrated that sotalol alone, or a combination of mexiletine and atenolol, results in a reduction in the frequency and complexity of ventricular ectopy.&lt;ref name=&quot;treatments&quot;/&gt; It is likely that these medications also reduce syncopal episodes, and it is hoped this extends to a reduced risk of sudden death.&lt;ref name=&quot;kittleson&quot;/&gt;&lt;ref name=&quot;MeursCVT&quot;&gt;Meurs, K.M. Arrhythmogenic Right Ventricular Cardiomyopathy; Kirk's Current Veterinary Therapy XV 2014&lt;/ref&gt; Consequently, antiarrhythmic therapy is typically recommended by veterinary cardiologists for Boxer dogs with ARVC.&lt;ref name=&quot;MeursCVT&quot; /&gt; Although relatively rare, oral antiarrhythmic medications may be [[proarrhythmic]] in some dogs; consequently, appropriate monitoring and follow-up is recommended.&lt;ref name=&quot;update&quot;/&gt;&lt;ref&gt;Roden, DM., Mechanism and management of proarrhythmia. Am J Cardiol 20 August 1998;82(4A):49I-57I.&lt;/ref&gt;

The ideal therapy for Boxer cardiomyopathy would be implantation of an [[implantable cardioverter-defibrillator]] (ICD). This has been attempted in a limited number of dogs.&lt;ref name=&quot;nelson&quot;&gt;O. Lynne Nelson, Sunshine Lahmers, Terri Schneider, and Pam Thompson. The Use of an Implantable Cardioverter Defibrillator in a Boxer to Control Clinical Signs of Arrhythmogenic Right Ventricular Cardiomyopathy J Vet Intern Med 2006;20:1232–1237&lt;/ref&gt; Unfortunately, ICDs are programmed for humans and the algorithms used are not appropriate for dogs, increasing the risk of inappropriate shocks. In the future, reprogramming of ICDs may allow them to emerge as a viable option in the treatment for Boxer cardiomyopathy.&lt;ref name=&quot;nelson&quot;/&gt;

==References==
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[[Category:Genetic dog diseases]]