Ladder diagrams for atrial flutter and atrial fibrillation

Ladder diagrams are valuable teaching and interpretive tools in both human and veterinary electrocardiography. The purpose of this paper is to demonstrate how ladder diagrams can be used to help understand the possible mechanisms underlying atrial flutter and atrial fibrillation.     

Paroxysmal atrial fibrillation in racehorses

The paper describes five cases of atrial fibrillation detected after racing. In four of them, the arrhythmia disappeared spontaneously within 24 h and they were regarded as paroxysmal in type. In the fifth case, which won its race, the arrhythmia persisted for at least 45 h after racing. It was therefore regarded as an example of persistent atrial fibrillation. It was then treated with quinidine sulphate which restored sinus rhythm. It would seem that paroxysmal atrial fibrillation may be a cause of sudden decrease in racing performance.     

Management of atrial fibrillation.

Atrial fibrillation (AF) is the most common clinically important arrhythmia in veterinary medicine. Electrical cardioversion of AF to sinus rhythm is feasible, but pharmacologic rate control is an effective and achievable treatment strategy for most veterinary patients. Recent human trials suggest that rate control and rhythm control are almost equally beneficial. Nevertheless, AF can be a challenging arrhythmia to manage, because most affected animal shave numerous other concurring problems associated with the underlying heart disease that dictate or influence the clinician's choice of treatment and monitoring strategy for each patient.     

Septicemia, atrial fibrillation, cardiomegaly, left atrial mass, and Rhodococcus equi septic osteoarthritis in a foal

A foal with vegetative bacterial endocarditis affecting the wall of the left atrium was treated successfully with cefotaxime, erythromycin, and rifampin. Bacterial isolates included Escherichia coli from blood and Rhodococcus equi from a P-type osteomyelitic lesion of the left third metatarsal bone and from synovial fluid from the left metatarsophalangeal joint. Cardiac complications included cardiomegaly and atrial fibrillation, which responded to treatment with digoxin and quinidine sulfate. Cardiac function was considered normal 18 months after treatment. Bacteriologic cure of osteoarthritis was achieved by use of surgical debridement, lavage, and local and systemic antimicrobial treatment; however, lameness developed 18 months after treatment when training for flat racing was begun. Radiography revealed chronic degenerative joint disease.     

Radiocardiography in dogs with atrial fibrillation

In 54 of 99 dogs with atrial fibrillation heart function was examined scintigraphically. Data on the ejection fraction (EF), end-diastolic volume (EDV) and regurgitation fraction (RF) are presented. Of these animals 37 had a seriously decreased EF (less than 30%) with a more or less normal RF value, whereas a smaller group (17) had a moderately decreased EF (but greater than or equal to 30%) and a seriously increased RF value. In both groups the EDV was increased.     

Radiocardiography in dogs with atrial fibrillation

Summary

In 54 of 99 dogs with atrial fibrillation heart function was examined scintigraphically. Data on the ejection fraction (EF), end‐diastolic volume (EDV) and regurgitation fraction (RF) are presented. Of these animals 37 had a seriously decreased EF (< 30%) with a more or less normal RF value, whereas a smaller group (17) had a moderately decreased EF (but ≥ 30%) and a seriously increased RF value. In both groups the EDV was increased.     

Lone atrial fibrillation in a dog

An intact male Pointer aged 9 year was found to have atrial fibrillation (AF). Thoracic radiography and echocardiography as well as routine blood work revealed no cardiac disease. Thus, the dog was diagnosed as lone AF. The arrhythmia disappeared 6 hr after the initiation of the supportive therapy, and relapse was not observed.     

The pathology of atrial fibrillation in dogs

Atrial fibrillation (AF) occurs in dogs in a number of settings, the most common of which is congestive heart failure. This paper reviews what is known about the pathology of AF in dogs, as well as its clinical relevance. We begin by discussing several experimental AF paradigms in dogs, the associated pathology, and its relevance to AF mechanisms. We then discuss clinical AF in dogs and its relationship to experimental pathology. Finally, we conclude by assessing the potential therapeutic relevance of understanding AF-related pathology in dogs, as well as its potential to have practical applications in the future.     

Chronicity of atrial fibrillation affects duration of sinus rhythm after transthoracic cardioversion of dogs with naturally occurring atrial fibrillation

BACKGROUND: Atrial fibrillation (AF) in dogs can be managed by electrical cardioversion to sinus rhythm, but early recurrence of AF occurs in some dogs. In humans, the commonly evaluated clinical variables for prediction of early relapse of AF are left atrial size and duration of AF. It is unclear whether the duration of AF affects maintenance of sinus rhythm after cardioversion in dogs with spontaneous AF. HYPOTHESIS: That duration of sinus rhythm after cardioversion is related to the chronicity of AF. ANIMALS: Forty-one consecutive dogs that had undergone successful transthoracic cardioversion for spontaneous AF were evaluated. METHODS: The relationship between the duration of documented AF and the duration of sinus rhythm after cardioversion was statistically evaluated using data obtained retrospectively. The effects of structural heart disease and pretreatment with amiodarone were also evaluated. RESULTS: The presence of structural heart disease and the duration of documented AF had significant effects on maintenance of sinus rhythm after cardioversion (P <.001 and P=.022, respectively). The duration of documented AF was inversely related to the duration of sinus rhythm (P=.022) in dogs with and without structural heart disease. CONCLUSIONS AND CLINICAL IMPORTANCE: Estimates of duration of sinus rhythm based on the duration of documented AF are provided for dogs with and without heart disease allowing prediction of risk for early AF relapse.     

Idiopathic atrial fibrillation in a champion Standardised racehorse

Atrial fibrillation is described in a champion pacer which earlier had been named Australian Harness Horse of the Year as a 3-year-old in 1986-87. Prior to conversion atrial fibrillation had been present for at least 6 weeks, during which the horse had not raced. Successful treatment was achieved with two 10g doses of quinidine sulphate per oesophageal tube, after slow digitalisation with intravenous digoxin over 4d. Four hours after commencement of quinidine therapy the arrhythmia had regressed to atrial flutter and converted to sinus rhythm 10 min later. Considering his age, standard of racing and high reputation the horse's overall performance as a 5-year-old after conversion from atrial fibrillation appeared comparable to his previous performance as a 4-year-old before the disorder occurred. In one of the wins since his return to sinus rhythm, the horse recorded his fastest winning speed and created a new track record at the major Melbourne racetrack. The absence of abnormalities of atrial and atrio-ventricular conduction after the cessation of the arrhythmia, together with the horse's return to successful racing, indicate that this was case of atrial fibrillation occurring as a functional disorder without persistent atrial pathology.     

Spontaneous resolution of hypothermia-induced atrial fibrillation in a dog

Objective: To report a case of spontaneous resolution of atrial fibrillation secondary to hypothermia in a dog without detectable heart disease. Case summary: An 8‐year‐old female spayed mixed breed dog presented with a history of prolonged exposure to below freezing environmental temperatures. The dog presented hypothermic (<32°C or <90°F) and minimally responsive to stimuli. The heart rate was 80 beats per minute (bpm) and irregular. Atrial fibrillation was diagnosed. The dog had pale mucous membranes, absent femoral pulses, and no obtainable blood pressure via indirect Doppler technique. Resuscitation fluids were administered and active external warming was instituted. Peripheral edema was observed during the rewarming phase and the irregular heart rate was noted to increase. The atrial fibrillation spontaneously resolved with no specific anti‐arrhythmic therapy. No underlying myocardial disease was found. The recovery of this dog was complete with a subsequent repeat of the echocardiogram and electrocardiogram (ECG) 8‐months later found to be within normal limits.     

Transvenous electrical cardioversion of atrial fibrillation in two dogs

Atrial fibrillation is characterized by uncoordinated electrical activation of the atria that leads to the loss of atrial mechanical function and atrial fibrosis as a substrate promoting maintenance of rhythm abnormality. Transvenous electrical cardioversion has not been previously reported in the dog. The authors demonstrate the use of this technique for successful cardioversion of atrial fibrillation in two dogs with dilated cardiomyopathy.     

Successful conversion of equine atrial fibrillation using oral flecainide

Atrial fibrillation is the most common arrhythmia affecting performance in horses. Conversion to sinus rhythm carries a good prognosis if no significant underlying cardiac disease is present and horses commonly return to performance at the previous level or above. The drug most commonly used to convert equine atrial fibrillation is quinidine. However, quinidine has the potential for a number of adverse effects including colic, nasal mucosal edema, dyspnea and laminitis. Quinidine also requires administration through a nasogastric tube, as the drug is very bitter and acidic and may cause oral ulcerations if administered PO. Flecainide is an antiarrhythmic agent of Singh-Vaughan Williams class Ic, whereas quinidine belongs to class Ia. Intravenously administered flecainide has been reported to be a safe and effective drug for treatment of induced atrial fibrillation in the horse, with fewer adverse effects compared to quinidine, but has been less effective when administered to horses with naturally occurring atrial fibrillation. The pharmacokinetics of oral flecainide and the oral dosage required to treat equine atrial fibrillation have been determined. To the authors' knowledge, there are no reports describing treatment of equine atrial fibrillation with oral flecainide. This report describes the successful conversion of naturally occurring atrial fibrillation, by means of oral flecainide, in a horse.     

Cardiac lesions in dairy cows with idiopathic atrial fibrillation

Histopathological examination of the heart, particularly the right atrium including the sinoatrial (SA) node, was carried out in 9 Holstein dairy cows with idiopathic atrial fibrillation (AF; AF group) and 12 healthy cows of the same breed (control group) in order to establish the correlation between idiopath