Paroxysmal atrial fibrillation in seven dogs with presumed neurally-mediated syncope

Risk Factors for Atrial Fibrillation in the Dog: A Systematic Review

Different risk factors for atrial fibrillation (AF) development have been identified in numerous studies on humans, but this information is less clearly available on the dog. The aim of this systematic review is to determine the risk factors for AF in the dog. Following the PRISMA 2020 guidelines, we conducted a comprehensive search using the Web of Science and Scopus databases for articles reporting on cases of spontaneously occurring AF in dogs. The level of evidence was assessed using the Evidence Quality Grading System of the National Institute of Health. One thousand forty-three studies were initially identified, and twenty of them were included in this systematic review involving 2,359,275 dogs, of which 4807 showed spontaneously occurring AF. Genetics, for the Irish Wolfhound, increased body weight, and left atrial enlargement were the main risk factors for the development of AF in dogs with different cardiac diseases, particularly myxomatous mitral valve disease (MMVD) and dilated cardiomyopathy (DCM). However, some differences were found between these two cardiac diseases regarding additional risk factors. In particular, the presence of congestive heart failure and echocardiographic evidence of increased left atrial pressure or the presence of right atrial enlargement emerged as risk factors in dogs with MMVD or DCM, respectively. Furthermore, significant differences in risk factors were observed between dogs and humans. In particular, advanced age and male sex are not reliable indicators of an increased risk of AF in dogs.

Rhythm disturbances associated with lidocaine administration in four dogs with supraventricular tachyarrhythmias

OBJECTIVE

To describe arrhythmias associated with administration of lidocaine in dogs treated for supraventricular tachyarrhythmias.

CASE SUMMARIES

Four dogs with recent-onset supraventricular tachyarrhythmias: 3 dogs had atrial fibrillation (AF), and 1 had focal atrial tachycardia (FAT), which was thought to be AF at the time of assessment. The substrate of the supraventricular tachyarrhythmia was considered to be due to primary cardiomyopathy in 1 dog, high vagal tone in 2 dogs, and the change in hemodynamics from heavy sedation in 1 dog. Pharmacological cardioversion using lidocaine was only successful in the 2 dogs with vagally mediated AF. In these 2 cases, lidocaine administration resulted in a paroxysmal atrial flutter that was self-limiting and quickly led to sinus rhythm within 10 seconds in 1 dog but did not change over a 5-minute interval and required additional boluses in another dog. In the latter case, the dog showed severe bradycardia for 17.5 seconds prior to achieving sinus rhythm. The 2 unsuccessful cases both developed ventricular arrhythmias shortly after the lidocaine administration, with 1 case degenerating into ventricular fibrillation and cardiac arrest.

NEW OR UNIQUE INFORMATION PROVIDED

Arrhythmias associated with lidocaine should be considered when treating dogs with supraventricular tachyarrhythmia.

Heart rhythm characterization during sudden cardiac death in dogs

INTRODUCTION/OBJECTIVES

Inherited or acquired arrhythmic disorders and cardiac disease have been associated with sudden cardiac death (SCD) in dogs. The electrical mechanism related to death in most of these cases is unknown. This retrospective study aimed to describe arrhythmic events in dogs that experienced SCD during Holter monitoring.

ANIMALS, MATERIALS AND METHODS

Nineteen client-owned dogs that experienced SCD during Holter examination were included. Clinical records from a Holter service database were reviewed, and both the rhythm preceding death and the dominant rhythm causing SCD were analysed. Clinical data, Holter diaries and echocardiographic diagnosis were also evaluated.

RESULTS

Structural heart disease was identified in 12/19 dogs (dilated cardiomyopathy in five dogs, arrhythmogenic right ventricular cardiomyopathy in four dogs, myxomatous mitral valve disease in two dogs, and suspected myocarditis in one dog), five of which had concurrent congestive heart failure. Sudden cardiac death was related to ventricular premature complexes or monomorphic ventricular tachycardia degenerating into ventricular fibrillation in 42% of dogs, polymorphic ventricular tachycardia, or torsade de pointes-like inducing ventricular fibrillation in 21%, and asystole or presumptive agonal pulseless electrical activity triggered by malignant bradyarrhythmias in 37%.

CONCLUSIONS

The most common rhythm associated with SCD in our population of dogs was ventricular tachycardia leading to ventricular fibrillation, although bradyarrhythmia-related SCD, possibly related to inappropriate vagal reflexes, was also a notable cause.

Canine atrial fibrillation: Pathophysiology, epidemiology and classification

Atrial fibrillation (AF) is the most common non-physiological arrhythmia in dogs and humans. Its high prevalence in both species and the impact it has on survival time and quality of life of affected patients, makes it a very relevant topic of medical research. Significant developments in understanding the mechanisms underlying this arrhythmia in humans has occurred over the last decades and some of this knowledge is being applied to veterinary medicine, despite the many differences between species. This article reviews the current understanding of the pathophysiology of AF. The epidemiology and classification of AF in dogs will also be discussed.

Heart rhythm during episodes of collapse in boxers with frequent or complex ventricular ectopy

OBJECTIVES

To describe heart rhythm during collapse events in boxer dogs using ambulatory electrocardiogram and determine the predictive value of frequent or complex ventricular ectopy for collapse associated with ventricular tachycardia.

MATERIALS AND METHODS

A total of 659 ambulatory electrocardiogram recordings from 429 boxer dogs were identified from a database in the UK. Summary statistics described the frequency and complexity of ventricular ectopy during all recordings, recordings in which collapse occurred and associated boxer demographics. Positive predictive values were calculated to investigate whether frequent ventricular ectopy was useful to predict heart rhythm during episodes of collapse.

RESULTS

Of the 659 ambulatory electrocardiogram recordings, 250 recordings showed <50 single ventricular beats (Group 1), and frequent (≥50) or complex ventricular ectopy were observed in 409 recordings (Group 2). A total of 90 collapse events were observed in 72 ambulatory electrocardiograms from 68 dogs, comprising 30 dogs in Group 1 and 38 dogs in Group 2. In both groups, sinus rhythm was the most frequent collapse rhythm, followed by neurally mediated collapse and then ventricular tachycardia. The proportion of dogs that displayed ventricular tachycardia-associated episodic collapse given that they had frequent (≥50) or complex ventricular ectopy in the study population was 0.11 [95% confidence interval = 0.01 to 0.21].

CLINICAL SIGNIFICANCE

These results challenge the preconception that UK boxer dogs with collapse will have ventricular tachycardia and, consequently, the authors recommend definitive diagnosis of the cause of episodic collapse to guide selection of therapeutic drugs.

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.

Typical vasovagal syncope as a "defense mechanism" for the heart by contrasting sympathetic overactivity

Many observations suggest that typical (emotional or orthostatic) vasovagal syncope (VVS) is not a disease, but rather a manifestation of a non-pathological trait. Some authors have hypothesized this type of syncope as a "defense mechanism" for the organism and a few theories have been postulated. Under the human violent conflicts theory, the VVS evolved during the Paleolithic era only in the human lineage. In this evolutionary period, a predominant cause of death was wounding by a sharp object. This theory could explain the occurrence of emotional VVS, but not of the orthostatic one. The clot production theory suggests that the vasovagal reflex is a defense mechanism against hemorrhage in mammals. This theory could explain orthostatic VVS, but not emotional VVS. The brain self-preservation theory is mainly based on the observation that during tilt testing a decrease in cerebral blood flow often precedes the drop in blood pressure and heart rate. The faint causes the body to take on a gravitationally neutral position, and thereby provides a better chance of restoring brain blood supply. However, a decrease in cerebral blood flow has not been demonstrated during negative emotions, which trigger emotional VVS. Under the heart defense theory, the vasovagal reflex seems to be a protective mechanism against sympathetic overactivity and the heart is the most vulnerable organ during this condition. This appears to be the only unifying theory able to explain the occurrence of the vasovagal reflex and its associated selective advantage, during both orthostatic and emotional stress.