Secondary right atrial thrombosis in three dogs: Antithrombotics therapy and echocardiographic follow-up.

Three dogs were diagnosed with right atrial thrombosis, thought to be secondary to systemic diseases. Specifically, two cases had hyperadrenocorticism and one case was diagnosed with pancreatitis with acute renal injury. In all cases, the thrombi were found within the right atrium, necessitating a differentiation from cardiac neoplasia. In all three cases, the structures assumed to be thrombi had irregular margins with interspersed hypoechoic regions, which were later confirmed as thrombi based on the responsiveness to therapy. All three cases were prescribed with the combination of clopidogrel and rivaroxaban.The thrombi gradually disappeared after initiation of the combination therapy. Complete resolution of right atrial thrombosis was noted in each dog treated with clopidogrel and rivaroxaban. This combination therapy appears to be safe and well tolerated. Diligent observation of the echocardiographic findings and clinical course allows the diagnosis of thrombosis.

Transient P' waves in a hyperkalemic cat: artifact or dissociation?

A 15-year-old Sphynx cat was referred for cervical ventroflexion, ataxia, and lethargy associated with hypokalemia. After administration of supplemental potassium, the cat became severely hyperkalemic. Transient P' (vs. pseudo P' waves) were detected on the electrocardiogram. Over the course of hospitalization, the cat's potassium normalized, and the abnormal P' waves did not recur. These images are presented to highlight the differential diagnoses for this type of electrocardiogram. Diagnostic considerations included complete or transient atrial dissociation (as a rare consequence of hyperkalemia), atrial parasystole, and various electrocardiographic artifacts. Definitive diagnosis of atrial dissociation requires an electrophysiologic study or echocardiographic documentation of two independent atrial rhythms with associated mechanical activity, but these were unavailable in this case.

Cardiovascular changes in horses with atrial fibrillation and high thyroid hormone concentration: a case-control study.

INTRODUCTION: Hyperthyroidism is a predisposing factor for atrial fibrillation (AF) in humans. The relationship between high thyroid hormone (TH) and AF in horses has not been evaluated. OBJECTIVES: The aim of this study is to identify whether (1) high TH concentrations were present in horses with AF, (2) other cardiovascular effects were observed in horses with high TH and AF, and (3) TH status affected recurrence rate. ANIMALS: Twenty-three horses presented with naturally occurring AF. METHODS: Prospective case-control clinical study. Thyroid hormone concentration was measured in horses presenting with AF. Heart rate, electrocardiogram, blood pressure, and an echocardiogram were recorded as part of their clinical workup. Recurrence rate was determined by owner/veterinarian follow-up. RESULTS: High TH concentration was found in 60% of horses with AF. Horses in the high TH group had a higher heart rate (P=0.001), systolic blood pressure (P=0.019), left ventricular free wall thickness (P=0.026), relative wall thickness (P=0.041) and were more likely to have periods of AF with a rapid ventricular response rate (P=0.022). All horses were successfully converted to normal sinus rhythm. The likelihood of recurrence was not different between groups. CONCLUSION: Elevated TH concentration can be found in horses with AF. Other cardiovascular effects of high TH concentrations in other species were also present in horses with AF and elevated TH concentrations. This study recommends measuring TH concentrations in horses presenting for AF with a history of thyroid or iodine supplementation. This study also cautions against TH or iodine supplementation in healthy performance horses.

Pulmonary vein firing initiating atrial fibrillation in the horse: Oversized dimensions but similar mechanisms.

Atrial fibrillation is triggered by the pulmonary veins in humans. Although atrial fibrillation is known to occur in other species, the mechanisms of disease in these are not known. Here we present evidence for pulmonary vein triggers in the horse, where 3D HD Grid mapping was undertaken in the conscious state in the absence of fluoroscopy.

Oxidative stress creates a unique, CaMKII-mediated substrate for atrial fibrillation in heart failure.

The precise mechanisms by which oxidative stress (OS) causes atrial fibrillation (AF) are not known. Since AF frequently originates in the posterior left atrium (PLA), we hypothesized that OS, via calmodulin-dependent protein kinase II (CaMKII) signaling, creates a fertile substrate in the PLA for triggered activity and reentry. In a canine heart failure (HF) model, OS generation and oxidized-CaMKII-induced (Ox-CaMKII-induced) RyR2 and Nav1.5 signaling were increased preferentially in the PLA (compared with left atrial appendage). Triggered Ca2+ waves (TCWs) in HF PLA myocytes were particularly sensitive to acute ROS inhibition. Computational modeling confirmed a direct relationship between OS/CaMKII signaling and TCW generation. CaMKII phosphorylated Nav1.5 (CaMKII-p-Nav1.5 [S571]) was located preferentially at the intercalated disc (ID), being nearly absent at the lateral membrane. Furthermore, a decrease in ankyrin-G (AnkG) in HF led to patchy dropout of CaMKII-p-Nav1.5 at the ID, causing its distribution to become spatially heterogeneous; this corresponded to preferential slowing and inhomogeneity of conduction noted in the HF PLA. Computational modeling illustrated how conduction slowing (e.g., due to increase in CaMKII-p-Nav1.5) interacts with fibrosis to cause reentry in the PLA. We conclude that OS via CaMKII leads to substrate for triggered activity and reentry in HF PLA by mechanisms independent of but complementary to fibrosis.

Influence of detomidine on atrial fibrillation cycle length measured by intracardiac electrogram recording and by colour tissue Doppler imaging in horses.

REASONS FOR PERFORMING STUDY: Shortening of atrial fibrillation cycle length (AFCL) is a marker of atrial electrical remodelling due to atrial fibrillation (AF). OBJECTIVES: To investigate the effect of administration of detomidine on AFCL measured invasively from an intra-atrial electrogram (AFCLEGM) and noninvasively by tissue Doppler imaging (AFCLTDI). We hypothesised that detomidine would have no effect on AFCL but would improve the ease of TDI measurements and facilitate noninvasive AFCL determination. STUDY DESIGN: Prospective clinical study. METHODS: Measurements were performed before and after i.v. administration of 7.5 µg/kg bwt detomidine in 33 episodes of AF in 32 horses (582 ± 64 kg bwt, 10 ± 3 years old) referred for electrical cardioversion. The AFCLEGM was measured from a right atrial intracardiac electrogram. The AFCLTDI was measured from atrial colour tissue velocity curves in 5 atrial wall regions. Mean AFCLEGM and AFCLTDI without and with sedation were compared using a repeated-measures linear mixed model with Bonferroni correction for multiple comparisons and calculation of the Bland-Altman mean bias and limits of agreement between AFCLEGM and AFCLTDI. RESULTS: The mean AFCL was significantly increased after sedation, but this increase was very small (mean difference +4 ms). For AFCLTDI measurements, sedation significantly improved the quality of the atrial myocardial velocity curves and the number of AF cycles that could be measured per cardiac cycle. The Bland-Altman bias between AFCLEGM without sedation and AFCLTDI with sedation ranged from -18 to +15 ms depending on wall region. Bland-Altman limits of agreement were similar between AFCLEGM without sedation and AFCLTDI without and with sedation. Therefore, noninvasive AFCLTDI measurements with sedation can be used to estimate the atrial fibrillatory rate. CONCLUSIONS: Sedation facilitates noninvasive AFCL measurements but causes a slight increase in AFCL. Noninvasive AFCL measurements can be used as an indicator of atrial electrical remodelling, to study AF pathophysiology and to investigate the effect of anti-arrhythmic drugs.

Atrial Fibrillation in Eight New World Camelids.

BACKGROUND: There is limited information on the incidence of clinical signs, concurrent illness and treatment options for atrial fibrillation (AF) in New World Camelids (NWC). OBJECTIVE: Describe clinical signs and outcome of AF in NWC. ANIMALS: Eight New World Camelids admitted with AF. METHODS: A retrospective observational study of camelids diagnosed with AF based on characteristic findings on electrocardiogram (ECG). RESULTS: All animals had an irregularly irregular heart rhythm detected on physical examination and 4 cases had obtunded mentation on admission. Three camelids were diagnosed with AF secondary to oleander intoxication, 3 animals had underlying cardiovascular disease, 1 was diagnosed with lone AF and 1 had AF diagnosed on examination for a urethral obstruction. Five of eight animals survived to discharge and nonsurvivors consisted of animals which died or were euthanized as a result of cardiovascular disease (2/8) or extra-cardiac disease unrelated to the AF (1/8). CONCLUSIONS AND CLINICAL IMPORTANCE: Atrial fibrillation occurs in NWC in association with cardiovascular disease, extra-cardiac disease or as lone AF. Amiodarone and transthoracic cardioversion were attempted in one llama with lone AF, but were unsuccessful. Atrial fibrillation was recorded in 0.1% of admissions.

Atrial paroxysmal tachycardia in dogs and its management with homeopathic Digitalis--two case reports.

Homeopathic Digitalis 6c was evaluated in two clinical cases of atrial paroxysmal tachycardia in dogs. Tachycardias are common cardiac problems in dogs, and atrial paroxysmal tachycardia is a serious cardiac arrhythmia that may lead to syncope. Both adult dogs (Labrador and German Shepherd) were treated with Digitalis 6c, 4 drops orally four times daily for 7 days. Following treatment with Digitalis 6c heart rate stabilised and synchronized atrial and ventricular electrical activity was restored in 7 days.

Pacing techniques in assessing cardiac function in the horse.

The problem of transitory cardiac arrhythmias in equidae is discussed particularly with regard to the referral of suspect cases to specialist institutions for second opinion. Recently developed electro-stimulation techniques designed to uncover problem arrythmias, are briefly described and their potential in the analysis of cardiac electrical function under varying conditions is reviewed. The author cautions on the too rapid evaluation of the techniques for this purpose while remaining optimistic of the potential of electro-stimulation in the objective analysis of cardiac electric parameters.