Cardiac leiomyoma associated with advanced atrioventricular block in a young dog

Presumed primary cardiac mast cell tumor, pericardial effusion, and arrhythmia in a dog

A 13-year-old female spayed border collie cross presented for pericardial effusion, arrhythmia, and a suspected cardiac mass. Echocardiogram revealed severe thickening and hypokinesis of the interventricular septum with a heterogenous, cavitated myocardium, concerning for neoplasia. Electrocardiogram revealed predominantly accelerated idioventricular rhythm with frequent periods of nonsustained ventricular tachycardia. Occasional prolonged PR intervals terminating in an aberrantly conducted QRS complex were present. These beats were postulated to represent either first-degree atrioventricular block with aberrant QRS conduction or atrioventricular dissociation. Cytology of the pericardial effusion revealed atypical, suspected neoplastic, mast cells. The patient was euthanized, and postmortem examination confirmed full-thickness infiltration of the interventricular septum by a mast cell tumor, with metastasis to the tracheobronchial lymph node and spleen. Given the anatomic location of the mass, the observed atrioventricular nodal conduction delay may represent neoplastic infiltration of the atrioventricular node. Neoplastic infiltration of the ventricle was suspected to cause the accelerated idioventricular rhythm and ventricular tachycardia. To the authors' knowledge, this is the first reported case of a primary cardiac mast cell tumor causing arrhythmia and pericardial effusion in a dog.

Characteristics and outcomes of cats with and without pacemaker placement for high-grade atrioventricular block

INTRODUCTION

Available information on characteristics and outcome in cats with high-grade atrioventricular block (AVB) that receive a pacemaker is limited.

ANIMALS

Twenty-two privately owned cats presenting with high-grade AVB.

MATERIALS AND METHODS

Medical records were retrospectively examined. Cats were grouped as having received a pacemaker (PACE group) or not having received a pacemaker (non-PACE group). Clinical characteristics and outcomes of groups were evaluated.

RESULTS

There were 10 cats in the PACE group and 12 cats in the non-PACE group. At presentation, syncope or seizure-like behavior (p = 0.004) and bradycardia (p = 0.043) were more common in the PACE than the non-PACE group. Historical lethargy (p = 0.015) and dull mentation (p = 0.045) were more common in the non-PACE group, as was clinically relevant systemic disease. Pacemaker placement improved syncope or seizure-like behavior in 100% of cats. The degree of AVB at presentation was not associated with pacemaker placement nor the future degree of AVB. The major complication rate of pacemaker placement was 40%. Intergroup survival was not significantly different (PACE group 1278 days, 95% confidence interval: 0-2145 days; non-PACE group 213 days, confidence interval: 1-not available, p = 0.77).

CONCLUSIONS

Pacemaker placement improved clinical signs in cats with high-grade AVB. A difference in survival time could not be demonstrated between cats that received and did not receive a pacemaker in this retrospective study. High-grade AVB can be transient and accompanied by systemic disease in some cats.

Subendocardial nodular proliferation of myofibroblasts in a laboratory beagle

A smooth white focus was macroscopically observed in the right ventricular endocardium in a 15-month-old male beagle from a 4-week oral gavage toxicity study. This lesion likely arose from myofibroblasts and was diagnosed as subendocardial nodular proliferation of myofibroblasts. This lesion was observed only in one animal in a low dose group and was an incidental finding. Histopathologically, the well-demarcated nodule comprised abundant collagen containing spindle cells arranged in intermediate to long streams and formed broad interlacing fascicles. The spindle cells had an indistinct cell border with round to elongated hyperchromatic nuclei or nuclei with finely stippled chromatin and indistinct nucleoli. Furthermore, these cells were weakly positive for S100 and positive for α-smooth muscle actin, calponin, and vimentin. Based on the histological features, the proliferating spindle cells resembled phenotypes of smooth muscles or myofibroblasts. However, the proliferating cells lacked well-differentiated smooth muscle cells, cigar-shaped nuclei, and well-developed reticulin fibers outlining individual cells. This study describes the morphological characteristics of an endocardial proliferative lesion in the right ventricle of a beagle.

A retrospective analysis of stereotactic body radiation therapy for canine heart base tumors: 26 cases

INTRODUCTION

This study retrospectively evaluated outcomes and adverse radiation effects (AREs) associated with stereotactic body radiation therapy (SBRT) for canine heart base tumors (HBTs). A secondary aim was to identify any demographic or echocardiographic factors that might determine which dogs would most benefit from SBRT.

ANIMALS

Twenty-six dogs that received SBRT for an imaging-based diagnosis of a HBT were evaluated.

METHODS

Twenty-three dogs were treated with three fractions of 10 Gy delivered daily or every other day. The remaining 3 dogs received variable protocols of one to five fractions. Demographic, echocardiographic, and radiographic information, AREs, and treatment responses were collected. Correlations of these data with survival time were evaluated.

RESULTS

The median overall survival time was 404 days (95% confidence interval: 239-554 days). The majority of dogs experienced a partial response (25%) or stable disease (60%) for a median duration of 333 days (95% confidence interval: 94-526 days). Three dogs had progressive disease within six months of SBRT. Radiographic pneumonitis was identified in 7 of 23 dogs, and clinical pneumonitis was identified in 4 dogs. No other AREs were noted. The rate of distant metastasis was 13%. On multivariate analysis, it was found that vena caval obstruction, supraventricular and ventricular arrhythmias, clinical signs, and enlarged locoregional lymph nodes at presentation were negatively associated with survival time.

CONCLUSIONS

Stereotactic body radiation therapy was delivered with a low rate and degree of normal tissue complications. Asymptomatic dogs with confirmed, progressive growth of a HBT may most likely benefit from SBRT.

Pericardial Effusion in a Dog with Pericardial Hemangiosarcoma

An adult Jack Russel terrier dog presented for evaluation of large-volume peritoneal and pleural effusion. Echocardiography revealed scant pericardial effusion and abnormally thickened pericardium. Electrocardiography revealed complete atrioventricular block with junctional and ventricular escape beats and occasional ventricular premature complexes. Computed tomography of the thorax confirmed diffuse abnormal thickening of the pericardium, and a tentative diagnosis of constrictive-effusive pericarditis was made. The dog underwent subtotal pericardiectomy to remove the parietal pericardium and permanent epicardial pacemaker implantation to manage bradycardia. Based on pericardial histopathology and immunohistochemistry, a diagnosis of pericardial hemangiosarcoma was made. Systemic chemotherapy was initiated with doxorubicin 1 month after surgery. Despite initial improvement with chemotherapy, the dog was euthanized 4 months after surgery because of development of recurrent pleural effusion. To the author's knowledge, this is the first case report in dogs to describe isolated pericardial location of hemangiosarcoma resulting in constrictive-effusive pericarditis.

Indications for permanent pacing in dogs and cats

Pacemaker implantation is considered as a standard procedure for treatment of symptomatic bradycardia in both dogs and cats. Advanced second-degree and third-degree atrioventricular blocks, sick sinus syndrome, persistent atrial standstill, and vasovagal syncope are the most common rhythm disturbances that require pacing to either alleviate clinical signs or prolong survival. Most pacemakers are implanted transvenously, using endocardial leads, but rarely epicardial leads may be necessary. To decide whether a patient is a candidate for pacing, as well as which pacing modality should be used, the clinician must have a clear understanding of the etiology, the pathophysiology, and the natural history of the most common bradyarrhythmias, as well as what result can be achieved by pacing patients with different rhythm disturbances. The goal of this review was, therefore, to describe the indications for pacing by evaluating the available evidence in both human and veterinary medicine. We described the etiology of bradyarrhythmias, clinical signs and electrocardiographic abnormalities, and the choice of pacing modality, taking into account how different choices may have different physiological consequences to selected patients. It is expected that this review will assist veterinarians in recognizing arrhythmias that may require permanent pacing and the risk-benefit of each pacing modality and its impact on outcome.

Pericardial Hemangiosarcoma in a 10-Year-Old Papillon

A 10 yr old papillon was evaluated for lethargy, inappetence, tachypnea, and labored breathing. Physical examination findings included dehydration, tachypnea, tachycardia, and muffled heart sounds. Thoracic radiographs revealed an enlarged cardiac silhouette. Echocardiography revealed a mild volume of pericardial effusion and no evidence of right atrial tamponade or a cardiac-associated mass. Cytological analysis of the pericardial effusion was consistent with blood. There was no evidence of neoplasia. Coagulation parameters were within normal limits. Initial treatment consisted of pericardiocentesis. A subtotal pericardiectomy was later performed. No surgical complications were noted, and the dog was discharged 2 days following surgery. Results of the histological examination of the pericardium revealed hemangiosarcoma. Treatment with doxorubicin was initiated 12 days after surgery, at which time, pulmonary metastasis was suspected. The dog survived for 18 days after subtotal pericardiectomy, when it was euthanized because of complications presumably related to pulmonary metastatic disease. This is the first published report of primary pericardial hemangiosarcoma. The dog had a short survival time; thus, the response to subtotal pericardiectomy combined with adjuvant doxorubicin treatment could not be determined. Pulmonary metastatic disease was suspected 12 days following surgery. Based on this case report, pericardial hemangiosarcoma carries a guarded prognosis.

Long-term Intrinsic Rhythm Evaluation in Dogs with Atrioventricular Block

Background

Atrioventricular block (AVB) is a conduction abnormality along the atrioventricular node that, depending on etiology, may lead to different outcomes.

Objectives

To evaluate variations of intrinsic rhythm (IR) in dogs that underwent pacemaker implantation (PMI).

Animals

Medical records of 92 dogs affected by 3rd degree atrioventricular block (3AVB), advanced 2nd degree AVB (2AVB), paroxysmal 3AVB, 2:1 2AVB, or 3AVB with atrial fibrillation (AF) were retrospectively reviewed.

Method

The patient IR was documented with telemetry on the day of 1 – (95% CI, 1–2), 33 – (95% CI, 28–35), 105 – (95%CI, 98–156), and 275 days (95%CI, 221–380) after PMI. According to AVB grade at different examinations, AVB was defined as progressed, regressed, or unchanged.

Results

In 48 dogs, 3AVB remained unchanged, whereas in 7 it regressed. Eight cases of 2AVB progressed, 3 regressed and 2 remained unchanged. Eight cases of paroxysmal 3AVB progressed and 3 remained unchanged. Four dogs affected by 2:1 2AVB progressed, 2 regressed, and 1 remained unchanged. All cases with 3AVB with AF remained unchanged. Regression occurred within 30 days after PMI, whereas progression was documented at any time. Variations in IR were associated with type of AVB (P < .03) and time of follow‐up (P < .0001).

Conclusions and clinical importance

The degree of AVB assessed at the time of PMI should not be considered definitive because more than one‐third of the cases in this study either progressed or regressed. Additional studies would be necessary to elucidate possible causes for transient AVB in dogs.

A descriptive review of cardiac tumours in dogs and cats

Cardiac tumours are uncommon in the canine and feline population and often an incidental finding. Common types include haemangiosarcoma (HSA), aortic body tumours (chemodectoma and paraganglioma) and lymphoma. These neoplasms can cause mild to severe, life-threatening clinical signs that are independent of the histological type and may be related to altered cardiovascular function or local haemorrhage/effusion into the pericardial space. Cardiac tumours may require symptomatic treatment aimed at controlling tumour bleeding and potential arrhythmias, and other signs caused by the mass effect. Additional treatment options include surgery, chemotherapy and radiotherapy. For all medical therapies, complete remission is unlikely and medical management, beyond adjunctive chemotherapy in HSA, requires further investigation but combination chemotherapy is recommended for lymphoma. The aim of this report is to summarize and critically appraise the current literature in a descriptive review. However, interpretation is limited by the lack of definitive diagnosis and retrospective nature of most studies.

Myocardial infarct associated with a partial thickness left atrial tear in a dog with mitral insufficiency

A 10-year-old male neutered cavalier King Charles Spaniel with a 1-year history of degenerative mitral valve disease presented for dyspnea and severe weakness. He was diagnosed with congestive heart failure, systolic dysfunction, presumptive myocardial infarction and a left atrial thrombus based on thoracic radiographs, electrocardiogram and echocardiographic findings. Clinical signs also suggested right foreleg embolism. The dog was euthanized due to the grave prognosis and a postmortem evaluation was performed. The postmortem examination confirmed myocardial infarction and was thought to be due to embolic showering from the thrombus attached to a partial thickness left atrial endocardial tear.