Effect of Transvenous Electrical Cardioversion on Plasma Cardiac Troponin I Concentrations in Horses with Atrial Fibrillation

Intracardiac ultrasound-guided transseptal puncture in horses: Outcome, follow-up, and perioperative anticoagulant treatment

BACKGROUND

Cardiac catheterizations in horses are mainly performed in the right heart, as access to the left heart traditionally requires an arterial approach. Transseptal puncture (TSP) has been adapted for horses but data on follow-up and closure of the iatrogenic atrial septal defect (iASD) are lacking.

HYPOTHESIS/OBJECTIVES

To perform TSP and assess postoperative complications and iASD closure over a minimum of 4 weeks.

ANIMALS

Eleven healthy adult horses.

METHODS

Transseptal puncture was performed under general anesthesia. Serum cardiac troponin I concentrations were measured before and after puncture. Weekly, iASD closure was monitored using transthoracic and intracardiac echocardiography. Relationship between activated clotting time and anti-factor Xa activity during postoperative enoxaparin treatment was assessed in vitro and in vivo.

RESULTS

Transseptal puncture was successfully achieved in all horses within a median duration of 22 (range, 10-104) minutes. Balloon dilatation of the puncture site for sheath advancement was needed in 4 horses. Atrial arrhythmias occurred in 9/11 horses, including atrial premature depolarizations (N = 1), atrial tachycardia (N = 5), and fibrillation (N = 3). Serum cardiac troponin I concentrations increased after TSP, but remained under the reference value in 10/11 horses. Median time to iASD closure was 14 (1-35) days. Activated clotting time correlated with anti-factor Xa activity in vitro but not in vivo.

CONCLUSIONS AND CLINICAL IMPORTANCE

Transseptal puncture was successfully performed in all horses. The technique was safe and spontaneous iASD closure occurred in all horses. Clinical application of TSP will allow characterization and treatment of left-sided arrhythmias in horses.

A randomised, controlled trial to determine the effect of levothyroxine on Standardbred racehorses

BACKGROUND

The use of thyroid supplement is pervasive in athletic horses although its effects on measures of performance are not known.

OBJECTIVES

One purpose of this study was to determine whether supra-physiologic doses of levothyroxine affect the velocities at which blood lactate was greater than 4 mmol/L (V_La4 ) and heart rate was over 150 (V₁₅₀ ) and 200 (V₂₀₀ ) beats per minute respectively. Additionally, a survey of post-race blood samples was also conducted to determine whether high thyroxine concentrations were common in racehorses.

STUDY DESIGN

A randomised, crossover, trial was performed in six healthy Standardbred racehorses.

METHODS

Study 1: T4 was determined in 50 post-race samples from a single Standardbred meet. Study 2: Research horses were trained to fitness and then randomised to one of three treatments: carrier, 0.1 mg/kg thyroxine or 0.25 mg/kg thyroxine for 2 weeks. Horses completed a standardised exercise treadmill test (SET) to fatigue on the last day of treatment. Serum free and total thyroxine and triiodothyronine were determined on the day of SET testing. Blood lactate and ECG data were collected during the SET at 6, 8, 10, 11, and 12 m/s and during recovery. The effect of treatment and SET on heart rate and blood lactate was examined using generalised linear mixed models. Post hoc analysis was adjusted for multiple comparisons using Tukey's Test. Data were expressed as mean ± standard deviation and P < .05 was considered significant.

RESULTS

Study 1: The median T4 value in this population of horses was 2.00 µg/dL (laboratory's normal range 1.5-4.5 µg/dL) and 3 of 50 racehorses had values above the laboratory reference range. Study 2: Levothyroxine at 0.25 mg/kg resulted in higher heart rates during SET (199 ± 30, 223 ± 17 and 239 ± 9 bpm at 6, 8 and 10 m/s respectively) and recovery (144 ± 20 and 119 ± 15 at 5 and 15 min) as compared to placebo (176 ± 18, 203 ± 10 and 219 ± 6 bpm at 6, 8, and10 m/s and 126 ± 5, 102 ± 11 at 5-15 minutes respectively). Three of six horses developed cardiac arrhythmias including atrial fibrillation.

MAIN LIMITATIONS

A relatively small number of animals were used and a SET is not identical to actual racing conditions.

CONCLUSIONS

Supra-physiologic thyroxine supplementation caused a decreased V₂₀₀ during a standard exercise test and may result in cardiac arrhythmias.

Atrial fibrillation in horses Part 2: Diagnosis, treatment and prognosis

Atrial fibrillation (AF) is suspected by an irregularly irregular rhythm during auscultation at rest and should be confirmed by electrocardiography. Heart rate monitoring is potentially interesting for AF detection by horse owners, based on the disproportionally high heart rate during exercise or increased heart rate variability. Echocardiography and laboratory analysis are useful to identify underlying cardiac disease. Horses with severe cardiac disease should not undergo cardioversion due to the risk of recurrence. Cardioversion is recommended especially in horses performing high intensity exercise or showing average maximal heart rates higher than 220 beats per min or abnormal ventricular complexes during exercise or stress. Pharmacological cardioversion can be performed using quinidine sulphate administered orally, with an overall mean reported success rate around 80%. Other therapeutic drugs have been described such as flecainide, amiodarone or novel atrial specific compounds. Transvenous electrical cardioversion (TVEC) is performed by delivering a shock between two cardioversion catheters positioned in the left pulmonary artery and right atrium, with a success rate of >95%. After cardioversion, most horses return to their previous level of performance. However, the recurrence rate after pharmacological or electrical cardioversion is up to 39%. Recurrence has been related to previous unsuccessful treatment attempts, valvular regurgitation and the presence of atrial premature depolarisations or low atrial contractile function after cardioversion. Large atrial size and long AF duration have also been suggested as risk factors. Different approaches for preventing recurrence have been described such as the administration of sotalol, however, large clinical studies have not been published.

Clinical Pathology of the Racehorse

The assessment of blood analytes in racehorses can provide useful data on performance and health. The horses' adaptive responses to training that occur to optimize performance should be considered when interpreting alterations seen on laboratory results. Similarly, the alterations observed in laboratory test results can identify subclinical and clinical disease and be helpful for identifying organ dysfunction and, in many cases, monitoring progress and response to treatment. This article discusses hematologic and biochemical tests that are important in the evaluation of performance and health in racehorses.

Myocardial insult and arrhythmias after acute hemorrhage in horses

OBJECTIVE

The objectives of this investigation were to: (1) Determine if acute hemorrhage is associated with increased plasma cardiac troponin I (cTnI) concentration or cardiac arrhythmias, (2) to describe the types of arrhythmias and their clinical course in horses following acute hemorrhage, (3) to determine the ability of clinical or clinicopathological variables to predict an increase in cTnI concentration and the presence of arrhythmias, and (4) to determine the associations of cTnI and cardiac arrhythmias with outcome.

DESIGN

Prospective observational study.

SETTING

Large animal veterinary teaching hospital.

ANIMALS

Eleven client-owned adult horses admitted for treatment of acute hemorrhage (HG) and 4 adult horses undergoing controlled blood collection (BDG).

METHODS

Serial cTnI concentrations were measured and continuous ECGs were obtained from the HG and BDG groups. Statistical tests were used to determine associations among acute hemorrhage and plasma cTnI concentrations, the presence of cardiac arrhythmias, clinicopathologic data (heart rate [HR], packed cell volume [PCV], total plasma protein [TPP], plasma lactate, and plasma creatinine concentrations), and outcome.

RESULTS

Plasma cTnI concentration and ECG were within reference intervals at all time points in the BDG. All horses in the HG had increased cTnI (ranging from 0.1-29.9 ng/mL). Arrhythmias were detected in 8 of these horses. There was an association between acute hemorrhage and increased cTnI (P = 0.004, ρ = 0.77), and the presence of arrhythmias (P = 0.026, ρ = 0.64). There were associations among plasma cTnI concentration and the presence of arrhythmias (P = 0.005), arrhythmias requiring treatment (P = 0.036), and poor outcome (P = 0.024).

CONCLUSIONS

Acute hemorrhage results in myocardial injury that can be detected by measuring cTnI concentration. Arrhythmias were frequent in hospitalized horses following acute hemorrhage.

Cardiac troponin I in calves with congenital heart disease

BACKGROUND

The association between plasma cardiac troponin I (cTnI) and the magnitude of cardiac enlargement in calves with congenital heart disease (CHD) are not well defined.

OBJECTIVE

To investigate the relationship between plasma cTnI concentrations and cardiac size in healthy calves and calves with CHD.

ANIMALS

A total of 19 healthy calves (control) and 12 Holstein calves with CHD (patent ductus arteriosus, ventricular septal defect, tetralogy of Fallot or double outlet right ventricle).

METHODS

Case control study. All animals underwent a comprehensive transthoracic echocardiographic study to document cardiac health or presence of CHD. The vertebral heart score (VHS) was determined in each animal using right lateral survey radiographic images. Blood samples were collected via jugular venipuncture and plasma cTnI concentration and creatine kinase (CK) activity were determined by a 3rd generation immunoassay and an automatic biochemical analyzer, respectively. Groups were compared using Mann-Whitney U-test and receiver-operating characteristics (ROC) curve analysis.

RESULTS

Calves with CHD had significantly larger VHS values and higher plasma cTnI concentrations (P < .001) compared to control. Creatine kinase activity was not different between the control and CHD groups of calves. Diagnostic cutoffs of VHS and plasma cTnI for discrimination of groups were 8.9 vertebrae and 0.035 ng/mL, respectively. The cTnI concentration in plasma was significantly correlated with VHS (r (2) =0.512, P < .001).

CONCLUSION AND CLINICAL RELEVANCE

Our results suggest that determination of plasma cTnI concentrations in calves with clinical signs compatible with CHD might prove useful as a guide to quantify cardiac remodeling associated with increased cardiac size.

Cardiac changes in horses with atypical myopathy

BACKGROUND

Atypical myopathy (AM) is an acute, fatal rhabdomyolysis in grazing horses that mainly affects skeletal muscles. Postmortem examinations have shown that myocardial damage also occurs. Limited information is available on the effect of AM on cardiac function in affected and surviving horses.

OBJECTIVES

To describe electrocardiographic and echocardiographic changes associated with AM in the acute stage of the disease and after follow-up.

ANIMALS

Horses (n = 12) diagnosed with AM in which cardiac ultrasound examination and ECG recording were available.

METHODS

All horses underwent clinical examinations, serum biochemistry, electrocardiography, and echocardiography. Four surviving horses underwent the same examinations after 2-10 weeks.

RESULTS

All but 1 horse had increased cardiac troponin I concentrations and 10 horses had ventricular premature depolarizations (VPDs). All horses had prolonged corrected QT (QT(cf) ) intervals on the day of admission and abnormal myocardial wall motion on echocardiography. One of the surviving horses still had VPDs and prolonged QT(cf) at follow-up after 10 weeks.

CONCLUSIONS AND CLINICAL IMPORTANCE

The AM results in characteristic electrocardiographic and echocardiographic changes and may be associated with increased cardiac troponin I concentrations and VPDs. In survivors, abnormal cardiac function still may be found at follow-up after 10 weeks. Additional research in a larger group of horses is necessary to identify the long-term effects of AM on cardiac function.

Elimination half-life of intravenously administered equine cardiac troponin I in healthy ponies

REASONS FOR PERFORMING STUDY

To date, no information is available on the true biological elimination half-life (T(1/2) ) of cardiac troponin I (cTnI) in the equine species. Such data are required to better evaluate the optimal time to acquire the cTnI sample following acute myocardial injury.

OBJECTIVE

To determine the T(1/2) of equine cTnI.

METHODS

Four healthy ponies received i.v. injections of recombinant equine cTnI. Plasma cTnI concentrations were measured with a point-of-care cTnI analyser at multiple time points after injection. Standard pharmacokinetic analysis was performed to establish the T(1/2) of cTnI.

RESULTS

The average T(1/2) of cTnI was determined to be 0.47 h using a single rate elimination model.

CONCLUSION

The elimination of recombinant equine cTnI following i.v. administration is very rapid. Establishing the T(1/2 ) of troponin provides critical information in understanding the clinical application of this cardiac biomarker in equine practice.