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Cardiovascular disease in general, and cardiac arrhythmias specifically, is common in great apes. However, the clinical significance of arrhythmias detected on short-duration electrocardiograms is often unclear. Here we describe the use of an implantable loop recorder to evaluate cardiac rhythms in 4 unanesthetized adult chimpanzees (Pan troglodytes), 1 with a history of possible syncope and 3 with the diagnosis of multiform ventricular ectopy (ventricular premature complexes) and cardiomyopathy. The clinical significance of ventricular ectopy was defined further by using the implantable loop recorder. Arrhythmia was ruled out as a cause of collapse in the chimpanzee that presented with possible syncope because the implantable loop recorder demonstrated normal sinus rhythm during a so-called syncopal event. This description is the first report of the use of an implantable loop recorder to diagnose cardiac arrhythmias in an unanesthetized great ape species.

Objectives: Cardiac arrhythmias as a cause of syncope, collapse, or intermittent weakness can be challenging to diagnose. The purpose of this paper is to retrospectively review the diagnosis and outcome of 23 cases of syncope or collapse in dogs that had a Reveal Plus ILR recorder placed as part of the diagnostic evaluation., Animals, Materials and Methods: Medical records of 23 client-owned dogs that were presented for evaluation of syncope, collapse, or intermittent weakness were retrospectively reviewed., Results: Recurrent syncope occurred in 13/23 (57%) and a positive diagnosis of the cause of the event was made in 11/13 (48% of all dogs). Diagnoses included 6/11 with prolonged periods of sinus arrest with slow ventricular escape rate and one each of sub-optimal fixed heart rate by endocardial pacing, high grade second degree atrioventricular block, supraventricular tachycardia, normal ECG during multiple episodes, and high grade second degree atrioventricular block or sinus arrest., Conclusions: The Reveal Plus ILR device was successful in diagnosing a high percentage of cases of syncope or collapse in which signs recurred and implantation had a low complication rate. The Reveal Plus ILR device is a useful tool to diagnose the etiology of recurrent syncope, collapse, or intermittent weakness in the dog., (Copyright 2010 Elsevier B.V. All rights reserved.)

Objective: To evaluate the diagnostic value of an implantable loop recorder (ILR) in dogs with unexplained syncope., Design: Prospective case series., Animals: 12 dogs with recurrent unexplained syncope., Procedures: An ILR was surgically inserted in a pocket created in the subcutaneous tissues of the left hemithorax of each dog. The ILRs were programmed for manual and automatic activation, and event analysis and programming were performed at 3-month intervals and after each syncopal episode., Results: The ILR was manually activated in 7 of 12 dogs at least once within 45 to 218 days (median, 120 days) after implantation. Four dogs had syncopal episodes associated with sinus tachycardia followed by sinus bradycardia and asystolic pauses. Two dogs had ventricular tachycardia, and 1 dog had sinus node dysfunction with prolonged sinus arrest that coincided with loss of consciousness and falling. Four dogs had no additional syncopal episodes after implantation of the ILR. In the remaining dog, the owner was unable to activate the ILR during the only syncopal episode observed for that dog after ILR implantation. In all 12 dogs, analysis of ECG traces after automatic activation of recording revealed normal cardiac rhythms., Conclusions and Clinical Relevance: Data gained after manual activation of an ILR provided valuable diagnostic and prognostic information in almost all dogs with unexplained syncopal episodes by confirming or disproving an association between syncope and arrhythmias. However, detection of disturbances in cardiac rhythm after automatic activation did not appear to improve the diagnostic value for an ILR implanted in dogs.

The Reveal is an implantable loop recorder. It is increasingly being used in humans for the diagnosis of unexplained syncope where it is believed that cardiac arrhythmias may play a role, and may have great potential for investigating syncope in veterinary patients. The purpose of this report is to describe the first use of the device in the diagnosis of unexplained syncope in a cat.

Objective: To evaluate the effect of 4 antiarrhythmic treatment protocols on number of ventricular premature complexes (VPC), severity of arrhythmia, heart rate (HR), and number of syncopal episodes in Boxers with ventricular tachyarrhythmias., Design: Randomized controlled clinical trial., Animals: 49 Boxers., Procedure: Dogs with > 500 VPC/24 h via 24-hour ambulatory ECG (AECG) were treated with atenolol (n = 11), procainamide (11), sotalol (16), or mexiletine and atenolol (11) for 21 to 28 days. Results of pre- and posttreatment AECG were compared with regard to number of VPC/24 h; maximum, mean, and minimum HR; severity of arrhythmia; and occurrence of syncope., Results: Significant differences between pre- and posttreatment number of VPC, severity of arrhythmia, HR variables, or occurrence of syncope were not observed in dogs treated with atenolol or procainamide. Significant reductions in number of VPC, severity of arrythmia, and maximum and mean HR were observed in dogs treated with mexiletine-atenolol or sotalol; occurrence of syncope was not significantly different between these 2 treatment groups., Conclusions and Clinical Relevance: Treatment with sotalol or mexiletine-atenolol was well tolerated and efficacious. Treatment with procainamide or atenolol was not effective.

Objective: To determine the clinical usefulness of cardiac event recording in evaluating dogs and cats with unexplained syncope, episodic collapse, or intermittent weakness., Design: Retrospective study., Animals: 58 dogs and 2 cats., Procedure: Medical records and electrocardiographic rhythm strips obtained by cardiac event recordings were reviewed. Cardiac rhythm data from the event recordings were classified as diagnostic or nondiagnostic. Diagnostic yield was calculated by dividing the number of animals for which cardiac event recording was diagnostic by the total number of animals undergoing cardiac event recording., Results: For 51 animals, cardiac event recording was classified as diagnostic; therefore, overall diagnostic yield was 85%. Diagnostic yield was lower for animals without underlying structural heart disease (75.5%) than for animals with structural heart disease (95.6%). A specific arrhythmia was identified as the cause of clinical signs in 18 of the 51 (35%) animals for which cardiac event recording was diagnostic. Cardiac arrhythmia was definitively excluded as the cause of clinical signs in the remaining 33 (65%) animals in which cardiac event recording was diagnostic., Conclusions and Clinical Relevance: Results indicate that cardiac event recording had a high diagnostic yield in dogs and cats examined because of unexplained syncope, episodic collapse, or transient weakness and ataxia, regardless of whether animals did or did not have an underlying structural heart disease. Diagnostic yield of cardiac event recording was higher than that reported previously for Holter monitoring.

The objective of this study was to evaluate retrospectively the clinical utility of ambulatory (Holter) electrocardiographic monitoring in syncopal dogs and to compare the Holter recording with the clinic electrocardiogram (ECG) in these animals. Fifty Holter reports and 44 medical records from 44 dogs were evaluated. A syncopcal episode occurred during monitoring in 24% of the recordings. No obvious relationship was found between the frequency of syncope occurring before Holter recording and the likelihood of a dog having an episode during recording. Holter recordings were helpful in establishing a diagnosis 42% of the time, but no relationship was detected between the frequency of episodes occurring before Holter recording and the likelihood of a diagnostically useful Holter. An arrhythmia was ruled out as the cause of syncope in 12% of the recordings and was implicated as the cause of syncope in 30% of recordings. Of these, 20% were ventricular tachyarrhythmias and 10% were bradyarrhythmias including pacemaker failure. Ambulatory electrocardiographic recordings led to a therapeutic change in 38% of cases. A comparison of the Holter recordings and clinic ECGs documented the expected increased sensitivity for Holter detection of arrhythmias. The average clinic ECG heart rate consistently exceeded the average Holter heart rate with a mean difference between the average heart rates recorded by the two techniques of 31 bpm (range -8-87 bpm).