pISSN 1598-298X / eISSN 2384-0749J Vet Clin 32(4) : 330-333 (2015)http://dx.doi.org/10.17555/jvc.2015.08.32.4.330

330

Idiopathic Atrial Standstill in an Old English Sheepdog Cross Dog

Sang-il Suh, Ran Choi and Changbaig Hyun1

Section of Small Animal Internal Medicine, College of Veterinary Medicine, Kangwon National University, Chuncheon 201-701, Korea

(Accepted: August 20, 2015)

Abstract : An 1 year old intact male mixed dog (weighing 20 kg) was presented with primary complaints of abdominaldistension and severe exercise intolerance. Electrocardiogram found profound bradycardia (46-79 beats/min) with atrialstandstill. Laboratory studies found no particular abnormalities. Serum cortisol and T4 concentration were within normalrange. Diagnostic imaging studies revealed generalized cardiomegaly, ascites, dilation in all cardiac chambers, absenceof atrial contraction, absence of transmitral A-peak, mitral and tricuspid valve insufficiency and normal left ventricularsystolic dimension. Based on diagnostic findings, the case was diagnosed as idiopathic atrial standstill. The dog wastreated with conventional therapy for heart failure.

Key words : Atrial standstill, bradycardia, arrhythmia, sinoatrial arrest, dog.

Introduction

Atrial standstill (AS) is a rare bradyarrhythmia character-

ized by the absence of atrial contraction (no P-wave) (10).

Transient AS can be occurred by hyperkalemia and myo-

carditis, while persistent AS can be occurred by atrioventricu-

lar muscle dystrophy (4,6), cardiomyopathy, hypothyroidism,

hypoadrenocorticism, immune-mediated polymyositis (10),

nemaline myopathy (8,9) and dilated cardiomyopathy (1,2).

Inherited AS has been reported in English Springer Spaniels

(4,6). Weakness, exercise intolerance and occasional synco-

pal episodes are major clinical signs of this disease, although

clinical signs can be differed by underlying diseases. Pace-

maker implantation is the choice of therapy for this disease,

if the AS is persistent. This case report described a rare case

of idiopathic atrial standstill in an Old English Sheep dog

cross dog.

Case

An 1 year old intact male Old English Sheep dog cross dog

(weighing 20 kg) was presented with primary complaints of

abdominal distension and severe exercise intolerance. The

owners reported the dog was only survivor from his 6 litter-

mates. According to the referring veterinarian, the dog might

have dilated cardiomyopathy. The dog was treated with con-

ventional medical therapy for heart failure including furo-

semide, digoxin and enalapril. On presentation, the dog was

depressed and lethargic with marked abdominal distension. On

physical examination, mucous membranes were pale (CRT

> 2s) and respiration was rapid and shallow (65 breaths / min)

with normal femoral pulsation. The heart rhythm was regu-

lar but bradycardic (45 beats/min). Cardiac auscultation found

IV/VI systolic decrescendo type left apical and II/VI systolic

decrescendo type right apical murmurs. There was no abnor-

mal respiration sound in the lung fields. Laboratory studies

including complete blood cell counts, serum biochemistry

and serum electrolytes found no particular abnormalities.

Serum cortisol and T4 concentration were also within nor-

mal range. Electrocardiogram revealed the absence of P waves

with regular bradycardic supraventricular rhythm (46-79 beats/

min; Fig 1). Atropine response test found no acceleration of

heart rate. Thoracic radiography revealed generalized cardi-

omegaly, dorsal displacement of trachea and abdominal fluid

accumulation (Fig 2). There was no pulmonary infiltration,

indicating no pulmonary edema. The 2D and M-mode echo-

cardiogram revealed biatrial dilation, absence of left atrial

1Corresponding author.E-mail : hyun5188@kangwon.ac.kr

Fig 1. The 6-lead electrocardiogram (ECG) of this case. There

is no P-wave on this ECG tracing, although ventricular beats

were regular escape beats in supraventricular origin.

Idiopathic Atrial Standstill in an Old English Sheepdog Cross Dog 331

Fig 3. Echocardiography of this case. A: The 2D-echocardiogram taken at left apical long axis of four chamber view revealed dilation

of right and left atria and left ventricle. There were no abnormalities in mitral and tricuspid valvular cusps and annulus. B: The M-

mode echocardiogram taken at right parasternal short axis of left ventricular (LV) papillary muscle revealed intact left ventricular sys-

tolic function.

Fig 2. Ventrodorsal (A) and right lateral (B) projection of thoracic radiography revealed generalized cardiomegaly, dorsal displacement

of trachea and abdominal fluid accumulation. There was no pulmonary infiltration, indicating no pulmonary edema.

Fig 4. Echocardiography of this case. A&C: Color and continuous wave Doppler echocardiogram taken at left apical long axis of four

chamber view revealed mild tricuspid regurgitation (peak velocity 2.34 m/s; pressure gradient 21.9 mmHg). B&D: Color and con-

tinuous wave Doppler echocardiogram taken at left apical long axis of four chamber view revealed severe mitral regurgitation (peak

velocity 4.66 m/s; pressure gradient 87.8 mmHg).

332 Sang-il Suh, Ran Choi and Changbaig Hyun

contraction, weak residual right atrial contraction, mild

biventricular dilation, and intact left ventricular contractility

(Fig 3). Color and continuous wave Doppler echocardio-

gram also revealed mild tricuspid regurgitation (peak veloc-

ity 2.34 m/s; pressure gradient 21.9 mmHg) and severe mitral

regurgitation (peak velocity 4.66 m/s; pressure gradient 87.8

mmHg; Fig 4). The A-peaks were absent in mitral flow and

residual in tricuspid flow. Aortic and pulmonic flows were all

normal. There were no shunts or intracardiac abnormalities.

Based on diagnostic findings, the case was diagnosed as idio-

pathic atrial standstill. Three liter of light reddish fluid was

removed by abdominocentesis. Cytological studies revealed

red cells with a few methothelial cells indicating modified

transudate. We requested pacemaker implantation to the own-

ers. The request was declined by financial reason. The dog was

released with prescription of furosemide (2 mg/kg, q12hr, PO;

Lasix, Handok, Korea), spironolactone (1 mg/kg, q12hr, PO;

Aldactone, Pfizer, Korea), enalapril (0.5 mg/kg, q12hr, PO;

Enalapril, Seokwang, Korea), and aminophylline (10 mg/kg,

q12hr, PO; Daewon, Korea). According to phone call to own-

ers, the clinical condition of dog was improved but ascites

was re-occurred. The dog was medically treated for 80 days

to date. The dog is currently survived with medical therapy

and occasional abdominocentesis.

Discussion

Several etiologies for persistent AS have been reported (1-

10). Atrioventricular muscular dystrophy in English Springer

spaniels is a known cause of persistent AS in dogs (4,6). It is

a putative familial disease characterized by the replacement of

cardiomyocytes with fibrous tissue at the atria subsequently

with ventricles. Some affected English Springer spaniels may

have also muscular dystrophy in facial and shoulder mus-

cles. Inherited facioscapulohumeral muscular dystrophy and

Duchenne muscular dystrophy in humans have similar fea-

tures of atrioventricular muscular dystrophy in English Springer

spaniels (3,7,9). Similar disease has been also reported in Old

English Sheep dogs (4). The presented case has similar clin-

ical features of AS in English Springer spaniels, although

there were no remarkable findings in either facial or shoul-

der muscles. However there was no evidence for other causes

(e.g., cardiomyopathy, hypothyroidism, hypoadrenocorticism,

and congenital cardiac anomalies) of persistent AS in this

case. Hypothyroidism and hypoadrenocorticism were ruled

out by hormone assays. There were no evidences for cardi-

omyopathies and congenital cardiac anomalies in this case.

Serum potassium level was also within normal range in this

case. Therefore we could rule out hyperkalemia (major cause

of transient AS in dogs). Because the AS in this dog was per-

sistent after discontinuing the administration of digoxin, we

could also rule out digoxin toxicity. Because this case of dog

was Old English Sheep cross dog, we suspected familial atri-

oventricular muscular dystrophy which is a known cause of

persistent AS in dogs. Familial ASs have been also reported

in human and were caused by genes mutation involved in ion

channel (SCN5A and NPPA; ref) and gab junction (connexin-

40) (3,7).

Atrial standstill causes lack of atrial contraction activity

resulting from the absence of atrial depolarization, although

ventricular contraction occurs normally by either junctional

or ventricular subsidiary pacemakers (10). The notched QRS

in this case suggested the ventricular escape beats might be

originated from the supraventricular site. The absence of

transmitral A-peak on the echocardiogram in this case sup-

ported the diagnosis of AS. Atrial dilation, mitral valve insuf-

ficiency and thrombotic events in humans are major com-

plications from persistent AS (9). Therefore, left and right

atrial dilation and mitral and tricuspid regurgitation in this

case might be secondary to persistent AS. Normal range of

%fractional shortening and left ventricular ejection fraction

could rule out dilated cardiomyopathy for cause of persistent

AS in this case. However, the AS in English Springer Span-

iels dogs has progressive nature leading to ventriclular systolic

dysfunction. Therefore, acute pulmonary edema is generally

consequence of persistent AS in English Springer Spaniels

(5). Unlike AS in English Springer Spaniels, ascites was a pri-

mary complaint in this case. Tricuspid regurgitation and right

atrial dilation might be the cause of abdominal fluid accumu-

lation in this case.

Therapy should be directed to manage underlying causes if

the cause of AS was identified. However, in case of idio-

pathic or familial AS, therapy should be direct to manage

congestive heart failure and to maintain proper heart rate by

implanting pacemaker (5). Xathine derivate such as theo-

phylline and aminophylline can be used as adjunct therapy

for accelerating heart rate (5). Because the owners refused

pacemaker implantation, therapy was focused on managing

heart failure (i.e., abdominocentesis, diuretics) and increas-

ing heart rate (i.e., aminophylline) in our case.

In conclusion, this case report described a rare case of per-

sistent AS complicated with congestive heart failure. Although

familial atrioventricular muscular dystrophy was strongly sus-

pected, further genetic analysis was unable to carry out,

because all other littermates were died right after birth.

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Old English Sheepdog Cross Dog에서의 특발성 심방정지

서상일·최란·현창백1

강원대학교 수의학과 소동물 내과교실

요 약 : 1년령 intact male mixed dog(체중 20 kg)가 복부 팽창과 심각한 운동불내성을 주증으로 내원하였다. 심전도

검사에서 심방정지와 함께 두드러진 서맥(46-79회/분)이 관찰되었다. 실험실 검사상 특별한 이상 소견은 관찰되지 않

았다. 혈청 cortisol과 T4농도는 정상 범위였다. 영상검사상 심장비대, 복수, 모든 심장 chamber의 확장, 심방정지,

transmitral A-peak 소실, 이첨판과 삼첨판 역류, 정상 좌심실 수축기 직경이 관찰되었다. 검사결과에 근거하여 특발성

심방정지로 진단되었으며 심부전에 준한 일반적인 치료를 실시하였다.

주요어 :심방정지, 서맥, 부정맥, 동방정지, 개