Complete atrioventricular block secondary to cardiac lymphoma in a dog

Third degree atrioventricular (AV) block was observed in a patient with a roughly spherical mass measuring approximately 1 × 1 × 1 cm, visible in the basilar portion of the interventricular septum on 2-dimensional transthoracic echocardiographic examination. The patient had a brief history of lethargy and episodic collapse, and the owner elected to euthanize the dog after the mass lesion was discovered. Necropsy revealed multiple masses within the interventricular septum, ventricular free walls and atrial myocardium. The final diagnosis was large cell (T-cell) lymphosarcoma.     

Cardiac trauma and third degree AV block in a dog following a road accident

A nine-and-a-half-year-old dog was referred for investigation of bradycardia after being hit by a car. Electrocardiography revealed a third degree atrioventricular (AV) block. The dog died during a syncopal attack. Post mortem examination revealed an atrial septal tear with haemorrhage and myocardial degeneration affecting the AV bundle.     

Third degree atrioventricular block and sudden death secondary to acute myocarditis in a dog

Third degree atrioventricular (AV) block in dogs is thought to be most frequently characterized by non-specific fibrotic changes in the AV node. However, it may occur secondary to an undiagnosed inflammatory process. We report a case of third degree AV block in a dog, secondary to acute lymphocytic-plasmacytic myocarditis that resulted in sudden death. This dog had cardiac troponin I levels of 44.65 ng/mL (normal <0.11 ng/mL). The serum cardiac troponin I level was five times higher than any other AV block patient measured in our laboratory, and was also substantially higher than in dogs with chronic valve disease or dilated cardiomyopathy. The severe myocardial necrosis observed at necropsy correlated with the degree of cardiac troponin I elevation. This report suggests that measurement of cardiac troponin I may be an indicated test before pacemaker implantation in dogs with third degree AV block.     

Exploration of a third degree atrioventricular block by standard echocardiography, tissue Doppler imaging, and treatment with a cardiac pacemaker in a German wire-haired pointer

A nine-year-old intact male Drathaar was evaluated for syncope and extreme weakness, and was found to have a third degree atrioventricular (AV) block. As there were no biochemic, serologic, organic (thoracic radiographs, abdominal echography, standard and tissue Doppler echocardiographies) and histologic (interventricular septum biopsy) anomalies, the dog was treated with a permanently implanted cardiac pacemaker.     

Gerbode type defect and third degree atrioventricular block in association with bacterial endocarditis in a dog

Gerbode type defects are rare left ventricular outflow tract–right atrial communications in people that may be congenital or acquired; they have been reported only once previously in dogs. Acquired forms in humans have been reported secondary to bacterial endocarditis, trauma, and valve replacement surgery, among other causes. We report a case of left ventricular outflow tract to right atrium and right ventricle communications (Gerbode type defect) in association with aortic and tricuspid valve bacterial endocarditis in a geriatric dog. The dog also developed third degree atrioventricular block and had underlying subaortic stenosis. The authors hypothesize that the Gerbode type defect in this case was acquired secondary to invasion and destruction of the membranous interventricular septum due to bacterial endocarditis.     

Diagnosis of right coronary artery to right atrial fistula in a dog using two-dimensional echocardiography

A five-year-old boxer dog developed cardiac murmurs, complete heart block and car-diomegaly associated with vegetative bacterial endocarditis. Using two-dimensional echocardiography, vegetative lesions of the aortic valves and extension of the vegetations into the proximal right coronary artery and adjacent atrial septum were identified. The vegetation within the atrial septum appeared as a cavitated mass which protruded into the right atrium. Fistulae within the atrial septal vegetation permitting communication between the coronary artery and right atrium were observed with colour Doppler echocardiography. The dog died despite medical treatment. Post mortem examination confirmed the echo-cardiographic findings. Vegetative endocarditis with invasion into the right coronary artery and atrial septum producing fistulae and communication with the right atrium has not been reported previously in dogs. Doppler echocardiography proved useful in demonstrating the abnormal anatomy, intraluminal fistular blood flow and its communication with the right atrium.     

Syncope associated with paroxysmal atrioventricular block an ventricular standstill in a cat

A four-and-a-half-year-old neutered male shorthair cat was presented with a three-week history of episodic fainting. Twenty-four hour electrocardiographic (Holter) recording revealed frequent prolonged episodes of complete atrioventricular (AV) block with ventricular standstill. The fainting episodes coincided with the longest periods of ventricular inactivity. A permanent transjugular pacemaker was placed to prevent further life-threatening episodes of syncope. Three months after discharge, the patient was re-presented with sudden onset dyspnoea associated with chylothorax and electrocardiography showed a third degree (complete) AV block. The pacemaker was reprogrammed in view of the third degree AV block and the chylous effusion was successfully treated by repeated thoracocentesis and long-term diuresis. However, the patient's general condition deteriorated progressively and the cat was euthanased five and a half months after implantation of the pacemaker.     

Transvenous pacemaker placement in a dog with atrioventricular block and persistent left cranial vena cava

The case reported herein describes the placement of a permanent transvenous pacemaker in an older dog with a previously undiagnosed persistent left cranial vena cava (PLCVC) and recent onset symptomatic third-degree atrioventricular (AV) block. On presentation the dog was found to have atrial flutter and third-degree AV block and echocardiography demonstrated evidence of chronic valvular disease and pulmonary arterial hypertension. The persistent left cranial vena cava was discovered via angiography when difficulties were encountered with pacemaker placement. Successful right ventricular pacing necessitated passage of the lead through the coronary sinus. The attendant complications in pacemaker placement in the presence of a PLCVC are well-described in man but, to the authors' knowledge, have not been described in companion animals.     

Trifoliate left atrioventricular valve with and without intact septal structures in four dogs: echocardiographic findings and surgical repair

Trifoliate left atrioventricular (AV) valve with common atrioventricular junction is considered part of the spectrum of atrioventricular septal defect. This valve morphology is typically associated with defects in the AV septum resulting in communication at the atrial or ventricular level, but has also been described as an isolated defect in the setting of a common AV junction without AV septal defect. Trifoliate left AV valve exhibits a line of apposition between the bridging leaflets that is directed toward the inlet interventricular septum, distinguishing it from isolated mitral valve cleft in which the orientation of the bridging leaflets are toward the left ventricular outflow tract. The echocardiographic findings of four dogs with trifoliate left AV valve are described; two with intact septal structures and two with large ostium primum defects. Three dogs underwent open surgical repair using different approaches depending on the presence or absence of a septal defect. One of these underwent concurrent surgical repair for right AV valve dysplasia. One dog with intact septal structures underwent interventional closure of a concurrent patent ductus arteriosus. Current terminology associated with trileaflet left AV valve malformations is reviewed.     

Temporary transvenous cardiac pacing in a dog with diltiazem intoxication

Objective: This case report presents the clinical findings of a dog with diltiazem intoxication and the utilization of temporary transvenous pacing for management of high‐grade second‐degree atrioventricular (AV) block with associated bradycardia and hypotension. Case summary: A nine‐year‐old spayed female Basset Hound, who ingested between 95 and 109 mg/kg of sustained‐release diltiazem exhibited clinical signs of cardiac arrhythmias, bradycardia, hypotension, mental depression and gastrointestinal (GI) upset. Bradycardia was present initially, then was followed by high‐grade second‐degree AV block with ventricular escape. Traditional medications to treat calcium channel blocker (CCB) intoxication, including atropine, calcium gluconate, dopamine and glucagon were initially successful in managing the cardiac rhythm disturbances and hypotension. Twenty‐two hours post‐ingestion, however, the dog became refractory to these medications following sedation for GI decontamination and a temporary transvenous pacemaker was placed. The dog was paced for 19 hours. Transvenous pacing effectively increased heart rate, which increased blood pressure into an acceptable range. The dog was successfully discharged from the hospital following treatment. New or unique information provided: The use of a temporary pacemaker should be considered an acceptable treatment for bradycardia, AV block and hypotension associated with CCB intoxication when conventional medical therapy fails.     

Paroxysmal atrial fibrillation in a dog that was presented for neck wounds

A 12-year-old spayed female German shorthaired pointer dog sustained extensive bite wounds around the neck. At presentation, atrial fibrillation was identified with a rapid ventricular response rate of 300 beats per minute (bpm). The ventricular response rate rapidly decreased to 130 bpm following administration of hydromorphone and oxygen. Based on the rate, antiarrhythmic therapy was not initiated. The heart rhythm converted back to sinus rhythm by the time of the first recheck evaluation 2 days later, and the dog remained in sinus rhythm at all subsequent evaluations. With the resolution of the arrhythmia, paroxysmal atrial fibrillation was suspected. The underlying etiology of the arrhythmia was not determined; however, imbalances in autonomic tone associated with trauma and/or direct trauma to the heart were hypothesized.Key clinical message:This report indicates a possible role of imbalances in autonomic tone due to trauma in the development of paroxysmal atrial fibrillation and suggests that it should be a differential diagnostic consideration in patients with atrial fibrillation following trauma. Primary treatment of atrial fibrillation may not be needed in these cases if the ventricular response rate is not rapid, or if there is spontaneous conversion to sinus rhythm.     

Fossa ovalis tear causing right to left shunting in a Cavalier King Charles Spaniel

Left atrial tear is an infrequent sequela of severe mitral regurgitation due to myxomatous mitral valve degeneration. Interatrial septal tear due to mitral regurgitation causing a left-to-right shunt is uncommon. Right to left shunting secondary to acute interatrial septal tear is very rarely reported in the human literature, and has not been reported in the veterinary literature in a dog. This case describes the clinical, radiographic, echocardiographic, gross pathologic, and histopathologic features of a dog presented in acute respiratory distress secondary to acute onset right to left shunting through the interatrial septum. This was later documented to be due to a tear in the septum secondary to tricuspid regurgitation and pulmonary hypertension. The presence of an acquired right to left shunting atrial septal defect is of clinical and prognostic significance, and should be considered in cases of acute respiratory distress.     

Suspected lily-of-the-valley (Convallaria majalis) toxicosis in a dog

Objective: To describe successful treatment of third-degree atrioventricular (AV) block using temporary noninvasive transthoracic pacing and placement of a permanent transvenous pacemaker in a case of suspected lily-of-the-valley ( Convallaria majalis ) intoxication in a dog.
Case summary: A 2-year-old neutered male Beagle weighing 17.8 kg was presented to the emergency service for treatment of bradycardia, vomiting, and lethargy. An electrocardiogram revealed third-degree AV block that was nonresponsive to atropine. Ten hours after admission, the dog became obtunded. Treatment initially consisted of temporary noninvasive transthoracic pacing and eventually placement of a permanent transvenous pacemaker. The initial history did not suggest that the dog had access to any known cardiotoxins. However, C. majalis , which contains cardiac glycosides, was identified within the dog's environment and the dog's serum did contain digoxin or an immunologically cross-reactive compound.
New or unique information provided: This is the first reported successful management of C. majalis toxicosis in a dog. Temporary noninvasive transthoracic pacing was used in the management of this case as a safe and effective bridge to permanent pacemaker implantation.     

Successful use of an acceleration rate response pacemaker with a transvenous steroid-eluting screw-in lead for third-degree atrioventricular block in a labrador retriever

Permanent pacemakers are commonly used in veterinary practice and can have a dramatic effect on the treatment of heart block. A Labrador Retriever dog suffering from exercise intolerance secondary to third degree atrioventricular block was treated with a new pacemaker system. A steroid-eluting screw-in type lead that has the advantage of being more fixed to the myocardial wall without increasing the pacing threshold was used. The heart rate was regulated with an acceleration sensing pacemaker generator that included several automatic modulation systems. Nineteen months after implantation, the dog has a normal level of activity. The present case suggests that this pacemaker design may offer important advantages for canine patients.     

Malignant pheochromocytoma presenting as a bradyarrhythmia in a dog

Objective: To describe a case of atrioventricular block and syncope secondary to systemic hypertension in a dog with malignant pheochromocytoma. Case Summary: A 13‐year‐old spayed female mixed‐breed dog presented following an acute onset of collapse. The dog was hypertensive and had paradoxical high‐grade second‐degree atrioventricular block with concurrent syncope. Initial emergent therapy included a nitroprusside infusion for the systemic hypertension and vagolytic therapy for the bradyarrhythmia. A left adrenal mass was seen on abdominal ultrasound and was further characterized by MRI. Following medical stabilization with phenoxybenzamine and propantheline, a left adrenalectomy was performed. Histological diagnosis was consistent with a malignant pheochromocytoma. Following tumor removal there has been no further hypertension, atrioventricular block or syncope. Unique information provided: This is the first documented case of a malignant pheochromocytoma presenting as syncope secondary to hypertension induced atrioventricular block.     

Permanent Transvenous Pacemaker Implantation in Forty Dogs

Permanent transvenous cardiac pacemakers were implanted in 40 dogs. Electrocardiographic diagnoses included persistent atrial standstill (3 dogs), sick sinus syndrome (8 dogs), and high-grade second-degree or third-degree atrioventricular (AV) block (29 dogs). Thirteen dogs were alive and well 4 to 42 months after pacemaker implantation (mean, 16.9 months). The mean and median survival times of the 26 dogs that died or were euthanatized during the study were 17.9 months and 13 months, respectively. Most of these dogs succumbed to problems unrelated to the arrhythmia and pacemaker implant. One dog was lost to follow-up. Complications associated with permanent transvenous pacemaker implantation included lead dislodgement, infection, hematoma formation, skeletal muscle stimulation, ventricular arrhythmia, migration of the pulse generator, and skin erosion. Lead dislodgement was the most common complication, occurring in 7 of 9 dogs paced using untined electrode leads and in 6 of 30 dogs paced using tined leads. Lead dislodgement did not occur in the only dog paced using an actively fixed endocardial lead. It was concluded that permanent transvenous cardiac pacing is a feasible, less traumatic alternative to epimyocardial pacing in dogs, but that successful use of this technique requires careful implantation technique and anticipation of the potential complications.     

Complete atrioventricular canal defect in a foal: Clinical and pathological features

Atrioventricular (AV) canal defects comprise a rare category of congenital heart disease associated with abnormal development of the endocardial cushions. These anomalies include a broad spectrum of lesions involving the atrial septum primum, the inlet portion of the ventricular septum, and the atrioventricular valves. In severe cases heart failure may result. The present report describes cardiopulmonary findings in a six-week-old, female Thoroughbred foal with persistent tachypnea and tachycardia since birth. Clinical, echocardiographic, cardiac catheterization, and pathologic findings were compatible with complete AV canal defect with bi-directional shunting, congestive heart failure, and pulmonary hypertension. Gross cardiac pathologic findings included a large atrioventricular septal defect, a common atriovalvular orifice, five atrioventricular leaflets, with two free-floating bridging leaflets. Histopathologic lesions in the lung included hypertrophy of the pulmonary arteriolar walls due to thickening of the tunica media. This represents a well documented case of complete endocardial cushion defect with anomalous development of the atrioventricular valves and resultant pulmonary hypertension and heart failure.     

Cardiac fibrosarcoma in a dog

A cardiac fibrosarcoma involving the right ventricular free wall, the interatrial septum, and proximal portion of the interventricular septum, with a 2-cm diameter protrusion into the right atrial lumen, was found at necropsy of a 2-year-old Miniature Schnauzer. Severe distortion of the tricuspid valve and narrowing of the aortic and pulmonic outflow tracts had caused the dog to develop right-sided cardiac failure and to have syncopal episodes. A tentative antemortem diagnosis of congenital pulmonic stenosis had been made on the basis of results of physical examination and diagnostic work-up. Evaluation of the case exemplifies the difficulty encountered in diagnosing cardiac tumors before the patient's death.     

Incomplete atrioventricular canal complicated by cardiac tamponade and bidirectional shunting in an adult dog

An incomplete atrioventricular (AV) canal with bidirectional shunting and cardiac tamponade in a 6-year-old dog was initially diagnosed echocardiographically as a common atrium. The dog failed to respond to medical therapy and was euthanized. Upon necropsy, the defect was confirmed as an incomplete AV canal. A mechanism for the potential sequence of clinical events demonstrated in this dog is proposed.     

Heart arrhythmias in horses caused by delays of conduction in the atrioventricular nodes and in the bundle of His]

The clinical importance of the AV blocks in horses discussed. The second degree AV block is a symptom of the adaptation of the heart to increased workload and it is not an indication of a good performance.