Boxer cardiomyopathy

Last updated

Boxer cardiomyopathy (also known as "Boxer arrhythmogenic right ventricular cardiomyopathy") is a disease of the myocardium primarily affecting Boxer dogs. It is characterized by the development of ventricular tachyarrhythmias, resulting in syncope and sudden cardiac death. Myocardial failure and congestive heart failure are uncommon manifestations of the disease. [1]

Syncope (medicine) transient loss of consciousness and postural tone

Syncope, also known as fainting, is a loss of consciousness and muscle strength characterized by a fast onset, short duration, and spontaneous recovery. It is caused by a decrease in blood flow to the brain, typically from low blood pressure. There are sometimes symptoms before the loss of consciousness such as lightheadedness, sweating, pale skin, blurred vision, nausea, vomiting, or feeling warm. Syncope may also be associated with a short episode of muscle twitching. When consciousness and muscle strength are not completely lost, it is called presyncope. It is recommended that presyncope be treated the same as syncope.

Contents

Overview

Boxer cardiomyopathy shares striking similarities to a human myocardial disease called arrhythmogenic right ventricular cardiomyopathy (ARVC). [1] On histopathology, the disease is characterized by the progressive replacement of ventricular myocardium (primarily right ventricular myocardium) with fatty or fibro-fatty tissue. [2] 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. [2]

Ventricular tachycardia Fast heart rhythm that originates in one of the ventricles of the heart

Ventricular tachycardia is a type of regular, fast heart rate that arises from improper electrical activity in the ventricles of the heart. Although a few seconds may not result in problems, longer periods are dangerous. Short periods may occur without symptoms, or present with lightheadedness, palpitations, or chest pain. Ventricular tachycardia may result in cardiac arrest and turn into ventricular fibrillation. It is found initially in about 7% of people in cardiac arrest.

Ventricular fibrillation disorganized electrical activity in the ventricles. It is a type of cardiac arrhythmia Ventricular fibrillation results in cardiac arrest

Ventricular fibrillation is when the heart quivers instead of pumping due to disorganized electrical activity in the ventricles. It is a type of cardiac arrhythmia. Ventricular fibrillation results in cardiac arrest with loss of consciousness and no pulse. This is followed by death in the absence of treatment. Ventricular fibrillation is found initially in about 10% of people in cardiac arrest.

Cause

Boxer cardiomyopathy is a genetic disease inherited in an autosomal dominant pattern. [3] The presentation in affected offspring is quite variable, suggesting incomplete penetrance. [3] 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 [4] [5] 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. 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. [2]

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. [6]

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. [6]

Diagnosis

Physical examination The physical examination is often unremarkable, although an arrhythmia characterized by premature beats may be detected. [6]

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. [2] [6]

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. [2] Boxer breeders are encouraged to Holter their breeding stock annually to screen out affected dogs. [7]

Genetic test: A genetic test for Boxer cardiomyopathy is now commercially available. [8] 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. [2]

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. [9] 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. [6] [9] 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. [9] It is likely that these medications also reduce syncopal episodes, and it is hoped this extends to a reduced risk of sudden death. [6] [10] Consequently, antiarrhythmic therapy is typically recommended by veterinary cardiologists for Boxer dogs with ARVC. [10] Although relatively rare, oral antiarrhythmic medications may be proarrhythmic in some dogs; consequently, appropriate monitoring and follow-up is recommended. [2] [11]

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. [12] 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. [12]

Related Research Articles

Cardiomyopathy A heart disease and a myopathy that is characterised by deterioration of the function of the heart muscle

Cardiomyopathy is a group of diseases that affect the heart muscle. Early on there may be few or no symptoms. Some people may have shortness of breath, feel tired, or have swelling of the legs due to heart failure. An irregular heart beat may occur as well as fainting. Those affected are at an increased risk of sudden cardiac death.

Brugada syndrome heart conduction disease that is characterized by abnormal electrocardiogram (ECG) findings and an increased risk of sudden cardiac death

Brugada syndrome (BrS) is a genetic disorder in which the electrical activity within the heart is abnormal. It increases the risk of abnormal heart rhythms and sudden cardiac death. Those affected may have episodes of passing out. The abnormal heart rhythms seen in those with Brugada syndrome often occur at rest. They may be triggered by a fever.

Premature ventricular contraction Human disease

A premature ventricular contraction (PVC) is a relatively common event where the heartbeat is initiated by Purkinje fibers in the ventricles rather than by the sinoatrial node, the normal heartbeat initiator. PVCs may cause no symptoms at all, but they may also be perceived as a "skipped beat" or felt as palpitations in the chest. Single beat PVC abnormal heart rhythms do not usually pose a danger.

Palpitations are the perceived abnormality of the heartbeat characterized by awareness of cardiac muscle contractions in the chest, which is further characterized by the hard, fast and/or irregular beatings of the heart. It is both a symptom reported by the patient and a medical diagnosis.

Arrhythmogenic Cardiomyopathy (ACM), formerly called arrhythmogenic right ventricular dysplasia (ARVD), or arrhythmogenic right ventricular cardiomyopathy (ARVC), is an inherited heart disease.

Hypertrophic cardiomyopathy (HCM) is a condition in which a portion of the heart becomes thickened without an obvious cause. This results in the heart being less able to pump blood effectively. Symptoms vary from none to feeling tired, leg swelling, and shortness of breath. It may also result in chest pain or fainting. Complications include heart failure, an irregular heartbeat, and sudden cardiac death.

Dilated cardiomyopathy intrinsic cardiomyopathy that is characterized by an an enlarged heart and damage to the myocardium causing the heart to pump blood inefficiently

Dilated cardiomyopathy (DCM) is a condition in which the heart becomes enlarged and cannot pump blood effectively. Symptoms vary from none to feeling tired, leg swelling, and shortness of breath. It may also result in chest pain or fainting. Complications can include heart failure, heart valve disease, or an irregular heartbeat.

Short QT syndrome heart conduction disease that is characterized by heart arrhythmia defined as a short QT interval on an EKG (less than 300 ms) that does not significantly change with heart rate, tall and peaked T waves, and a structurally normal heart

Short QT syndrome (SQT) is a very rare genetic disease of the electrical system of the heart, and is associated with an increased risk of abnormal heart rhythms and sudden cardiac death. The syndrome gets its name from a characteristic feature seen on an electrocardiogram (ECG) – a shortening of the QT interval. It is caused by mutations in genes encoding ion channels that shorten the cardiac action potential, and appears to be inherited in an autosomal dominant pattern. The condition is diagnosed using a 12-lead ECG. Short QT syndrome can be treated using an implantable cardioverter-defibrillator or medications including quinidine. Short QT syndrome was first described in 2000, and the first genetic mutation associated with the condition was identified in 2004.

Flecainide Antiarrhythmic medication used to prevent and treat tachyarrhythmias

Flecainide is a medication used to prevent and treat abnormally fast heart rates. This includes ventricular and supraventricular tachycardias. Its use is only recommended in those with dangerous arrhythmias or when significant symptoms cannot be managed with other treatments. Its use does not decrease a person's risk of death. It is taken by mouth or injection into a vein.

Andersen–Tawil syndrome Human disease

Andersen–Tawil syndrome, also called Andersen syndrome and Long QT syndrome 7, is a rare genetic disorder affecting several parts of the body. The condition is associated with a disturbance of the electrical function of the heart, characterised by a feature of an electrocardiogram known as a long QT interval. This abnormality increases the risk of experiencing abnormal heart rhythms. Unlike those with other forms of Long QT syndrome, those with Andersen–Tawil syndrome often have characteristic physical features including low-set ears and a small lower jaw, and may experience intermittent periods of muscle weakness known as hypokalaemic periodic paralysis.

T wave alternans

T wave alternans (TWA) is a periodic beat-to-beat variation in the amplitude or shape of the T wave in an electrocardiogram TWA was first described in 1908. At that time, only large variations could be detected. Those large TWAs were associated with increased susceptibility to lethal ventricular tachycardias.

Tachycardia-induced cardiomyopathy (TIC) is a disease where prolonged tachycardia or arrhythmia causes an impairment of the myocardium, which can result in heart failure. People with TIC may have symptoms associated with heart failure and/or symptoms related to the tachycardia or arrhythmia. Though atrial fibrillation is the most common cause of TIC, several tachycardias and arrhythmias have been associated with the disease.

Lorcainide chemical compound

Lorcainide is a Class 1c antiarrhythmic agent that is used to help restore normal heart rhythm and conduction in patients with premature ventricular contractions, ventricular tachycardiac [7] and Wolff-Parkinson-White syndrome. [9] Lorcainide was developed by Janssen Pharmaceutica (Belgium) in 1968 under the commercial name Remivox and is designated by code numbers R-15889 or Ro 13-1042/001. [2] It has a half-life of 8.9 +- 2.3 hrs which may be prolonged to 66 hrs in people with cardiac disease [9].

Signal-averaged electrocardiography (SAECG) is a special electrocardiographic technique, in which multiple electric signals from the heart are averaged to remove interference and reveal small variations in the QRS complex, usually the so-called "late potentials". These may represent a predisposition towards potentially dangerous ventricular tachyarrhythmias.

The following outline is provided as an overview of and topical guide to cardiology:

DSC2 protein-coding gene in the species Homo sapiens

Desmocollin-2 is a protein that in humans is encoded by the DSC2 gene. Desmocollin-2 is a cadherin-type protein that functions to link adjacent cells together in specialized regions known as desmosomes. Desmocollin-2 is widely expressed, and is the only desmocollin isoform expressed in cardiac muscle, where it localizes to intercalated discs. Mutations in DSC2 have been causally linked to arrhythmogenic right ventricular cardiomyopathy.

Heart arrhythmia Group of conditions in which the heartbeat is irregular, too fast, or too slow

Heart arrhythmia is a group of conditions in which the heartbeat is irregular, too fast or too slow. A heart rate that is too fast – above 100 beats per minute in adults – is called tachycardia, and a heart rate that is too slow – below 60 beats per minute – is called bradycardia. Many types of arrhythmia have no symptoms. When symptoms are present, these may include palpitations or feeling a pause between heartbeats. In more serious cases, there may be lightheadedness, passing out, shortness of breath or chest pain. While most types of arrhythmia are not serious, some predispose a person to complications such as stroke or heart failure. Others may result in cardiac arrest.

Frank I. Marcus is an American cardiologist and Emeritus Professor of Medicine at the University of Arizona Health Sciences Center, the author of more than 290 publications in peer-reviewed medical journals and of 90 book chapters. He is considered a world expert on arrhythmogenic right ventricular cardiomyopathy (ARVC) and has been or is a member of the Editorial/Scientific Board of 14 Cardiovascular Journals as well as a reviewer for 26 other medical publications.

References

  1. 1 2 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
  2. 1 2 3 4 5 6 7 Meurs KM. Boxer dog cardiomyopathy: An update. Vet Clin North Am Small Anim Pract 2004;34:1235–1244.
  3. 1 2 Meurs KM, Spier AW, Miller MW, et al. Familial ventricular arrhythmias in boxers. J Vet Intern Med 1999;13:437–439.
  4. ↑ Meurs et al. Abstract: Boxer Cardiomyopathy Journal Veterinary Internal Medicine 2009;23:687-688)
  5. ↑ Powell, C. Vet cardiologist discovers gene for heart disease. April 2009. URL: http://www.wsutoday.wsu.edu/pages/publications.asp?Action=Detail&PublicationID=14446 Accessed: 12 Dec 2009
  6. 1 2 3 4 5 6 Kittleson MD, Kienle RD. Arrhythmogenic Right Ventricular Cardiomyopathy. In: Small Animal Cardiovascular Medicine. St Louis, MO:Mosby; 1998.
  7. ↑ American Boxer Club. "Recommendations for Health Screening of Boxers in Breeding Programs".
  8. ↑ Anon. “Boxer Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)” Veterinary Cardiac Genetics Lab, North Carolina State University URL: http://www.ncstatevets.org/genetics/boxerarvc/ Accessed: 9 Oct 2013
  9. 1 2 3 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.
  10. 1 2 Meurs, K.M. Arrhythmogenic Right Ventricular Cardiomyopathy; Kirk's Current Veterinary Therapy XV 2014
  11. ↑ Roden, DM., Mechanism and management of proarrhythmia. Am J Cardiol 20 August 1998;82(4A):49I-57I.
  12. 1 2 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
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.