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.

Accelerated Idioventricular Rhythm Associated With Isoflurane Administration in a Foal: A Case Report.

A 2-day-old filly was referred to the hospital with abdominal pain and constipation. The foal presented tachycardia, tachypnea, hypoxemia, hyperlactatemia, and abdominal distension. Meconium impaction was diagnosed, and the filly underwent abdominal surgery. Diazepam and butorphanol were administered for anesthesia premedication, but sedative effects were mild. Xylazine was used to enhance sedation and ketamine was subsequently administered for induction. The foal showed swallow reflex and head movement when intubation was attempted. Consequently, isoflurane on oxygen was provided via an anesthetic face mask. After intubation, the foal was connected to the anesthetic machine and monitored. The electrocardiogram revealed accelerated idioventricular rhythm, characterized by atrioventricular isorhythmic dissociation with monomorphic wide QRS complexes. Lidocaine was administered but the arrhythmia persisted during anesthesia and was spontaneously corrected once the isoflurane was discontinued at the end of the procedure. The foal recovered from anesthesia without complications and no further cardiac events were observed before the patient being discharged. Accelerated idioventricular rhythm likely resulted from administration of isoflurane to a foal presenting hypoxemia, a condition that exacerbates the risk of arrhythmia. Proper management of this abnormal rhythm is crucial as inappropriate treatments may worsen the arrhythmia.