Sophy A. Jesty

c-kit+ precursors support postinfarction myogenesis in the neonatal, but not adult, heart

We examined the myogenic response to infarction in neonatal and adult mice to determine the role of c-kit+ cardiovascular precursor cells (CPC) that are known to be present in early heart development. Infarction of postnatal day 1–3 c-kitBAC-EGFP mouse hearts induced the localized expansion of (c-kit)EGFP+ cells within the infarct, expression of the c-kit and Nkx2.5 mRNA, myogenesis, and partial regeneration of the infarction, with (c-kit)EGFP+ cells adopting myogenic and vascular fates. Conversely, infarction of adult mice resulted in a modest induction of (c-kit)EGFP+ cells within the infarct, which did not express Nkx2.5 or undergo myogenic differentiation, but adopted a vascular fate within the infarction, indicating a lack of authentic CPC. Explantation of infarcted neonatal and adult heart tissue to scid mice, and adoptive transfer of labeled bone marrow, confirmed the cardiac source of myogenic (neonate) and angiogenic (neonate and adult) cells. FACS-purified (c-kit)EGFP+/(αMHC)mCherry− (noncardiac) cells from microdissected infarcts within 6 h of infarction underwent cardiac differentiation, forming spontaneously beating myocytes in vitro; cre/LoxP fate mapping identified a noncardiac population of (c-kit)EGFP+ myocytes within infarctions, indicating that the induction of undifferentiated precursors contributes to localized myogenesis. Thus, adult postinfarct myogenic failure is likely not due to a context-dependent restriction of precursor differentiation, and c-kit induction following injury of the adult heart does not define precursor status.

Measurement of plasma cardiac troponin I concentration by use of a point-of-care analyzer in clinically normal horses and horses with experimentally induced cardiac disease

OBJECTIVE To compare cardiac troponin I (cTnI) concentrations determined by use of a point-of-care analyzer with values determined by use of a bench-top immunoassay in plasma samples obtained from clinically normal horses with and without experimentally induced cardiac disease, and to establish a reference range for plasma equine cTnI concentration determined by use of the point-of-care analyzer. ANIMALS 83 clinically normal horses, 6 of which were administered monensin to induce cardiac disease. PROCEDURES A blood sample was collected from each of the 83 clinically normal horses to provide plasma for analysis by use of the point-of-care analyzer; some of the same samples were also analyzed by use of the immunoassay. All 83 samples were used to establish an analyzer-specific reference range for plasma cTnI concentration in clinically normal horses. In 6 horses, blood samples were also collected at various time points after administration of a single dose of monensin (1.0 to 1.5 mg/kg) via nasogastric intubation; plasma cTnI concentration in those samples was assessed by use of both methods. RESULTS The analyzer-specific reference range for plasma cTnI concentration in clinically normal horses was 0.0 to 0.06 ng/mL. Following monensin treatment in 5 horses, increases in plasma cTnI concentration determined by use of the 2 methods were highly correlated (Pearson correlation, 0.83). Peak analyzer-determined plasma cTnI concentrations in monensin-treated horses ranged from 0.08 to 3.68 ng/mL. CONCLUSIONS AND CLINICAL RELEVANCE In horses with and without experimentally induced cardiac disease, the point-of-care analyzer and bench-top immunoassay provided similar values of plasma cTnI concentration.

Clinical Findings and Serum Cardiac Troponin I Concentrations in Horses after Intragastric Administration of Sodium Monensin

Six adult horses were administered sodium monensin, 1.0–1.5 mg/kg, via gastric gavage. Anorexia and/or diarrhea occurred within 24 hr after monensin administration in all 6 horses. Cardiac disease and dysfunction were evaluated by both elevations in heart rate, echocardiography, and an increase in serum concentrations of cardiac troponin I (cTnI), occurred in 4 horses. The development and severity of cardiac disease was likely affected by the monensin dose, vehicle (water or corn oil) mixed with monensin, and/or whether the monensin was administered to fed or fasted horses. Initial increases in cTnI concentrations occurred between 24 and 72 hr after monensin administration. The 2 horses with the highest cTnI concentrations died or were euthanized within 5 days after monensin administration and had severe cardiac disease. One horse had increased cTnI concentrations from day 2 to day 16, but no apparent change in ventricular contractile function was evident on echocardiography. The fourth diseased horse did not return to cTnI reference intervals until day 27 after monensin administration, and the ventricular function was still abnormal just before euthanasia 9 months later. Cardiac troponin I measurements could be useful in managing farm outbreaks of accidental monensin feeding by the early identification of horses with cardiac disease.

Combination Therapy with Digoxin and Diltiazem Controls Ventricular Rate in Chronic Atrial Fibrillation in Dogs Better than Digoxin or Diltiazem Monotherapy: A Randomized Crossover Study in 18 Dogs

BACKGROUND Atrial fibrillation (AF) with excessively high ventricular rates (VR) occurs in dogs with advanced heart disease. Rate control improves clinical signs in these patients. Optimal drug therapy and target VR remain poorly defined. HYPOTHESIS Digoxin-diltiazem combination therapy reduces VR more than either drug alone in dogs with high VR AF. ANIMALS Eighteen client-owned dogs (>15 kg) with advanced heart disease, AF, and average VR on 24-hour Holter > 140 beats per minute (bpm). METHODS After baseline Holter recording, dogs were randomized to digoxin or diltiazem monotherapy, or combination therapy. Repeat Holter evaluation was obtained after 2 weeks; dogs were then crossed over to the other arm (monotherapy or combination therapy) for 2 weeks and a third Holter was acquired. Twenty-four hour average VR, absolute and relative VR changes from baseline, and percent time spent within prespecified VR ranges (>140, 100-140, and <100 bpm) were compared. Correlations between serum drug concentrations and VR were examined. RESULTS Digoxin (median, 164 bpm) and diltiazem (median, 158 bpm) decreased VR from baseline (median, 194 bpm) less than the digoxin-diltiazem combination (median, 126 bpm) (P < .008 for each comparison). With digoxin-diltiazem, VR remained <140 bpm for 85% of the recording period, but remained >140 bpm for 88% of the recording period with either monotherapy. Serum drug concentrations did not correlate with VR. CONCLUSIONS AND CLINICAL IMPORTANCE At the dosages used in this study, digoxin-diltiazem combination therapy provided a greater rate control than either drug alone in dogs with AF.

Effect of transvenous electrical cardioversion on plasma cardiac troponin I concentrations in horses with atrial fibrillation.

BACKGROUND Whether electrical cardioversion of cardiac arrhythmias results in cardiomyocyte damage is unknown. OBJECTIVE To describe effect of transvenous electrical cardioversion (TVEC) on plasma cardiac troponin I (cTnI) concentration in horses. ANIMALS All horses presented to the Cornell University Hospital for Animals for cardioversion of atrial fibrillation between May 2006 and October 2008 were eligible for inclusion in the study. Owners of 14 horses elected for TVEC and each horse was then enrolled (16 procedures). METHODS Prospective observational study measuring concentrations of plasma cTnI before and after TVEC. RESULTS Median cTnI concentration increased from 0.045 ng/mL at baseline (range 0.0-0.20 ng/mL) to 0.11 ng/mL after TVEC (range 0.0-3.73 ng/mL) (P= .036). This increase was not associated with the number of shocks delivered, maximal energy delivered, cumulative energy delivered, chronicity of atrial fibrillation before cardioversion, or positioning of the pulmonary artery catheter. CONCLUSIONS The increase in cTnI is unlikely to be clinically important. The increase might be correlated with persistent atrial dysfunction after TVEC, suggesting that a longer convalescent period after the procedure could be warranted.

The effects of pentoxifylline on equine platelet aggregation.

BACKGROUND Pentoxifylline (PTX) possesses a number of vasomotor, immunomodulatory, and hemorheologic properties. Based upon the hypothesis that equine laminitis and navicular disease result from microthrombosis, the inhibitory effects of PTX on inflammatory cytokines, and its inhibitory effects on human platelet aggregation, PTX has been widely used to treat equine endotoxemia, navicular disease, and laminitis. Despite this, the effects of PTX on equine platelet aggregation have not been investigated previously. HYPOTHESIS PTX decreases platelet aggregation in equine whole blood at concentrations approximating those achieved in horses given clinically relevant doses of PTX. ANIMALS Seven healthy adult horses from a research herd. METHODS Whole blood impedance aggregometry using whole equine blood incubated with varying concentrations of PTX. Adenosine diphosphate (ADP) and collagen were used to initiate aggregation. RESULTS The onset time of collagen-induced equine platelet aggregation was significantly shortened by PTX. The maximum slope of resistance change (dR/dt) and total resistance change of collagen-induced platelet aggregation were unaffected by PTX. No effects of PTX on ADP-induced onset time of aggregation, dR/dt, or total resistance change were observed. CONCLUSIONS AND CLINICAL IMPORTANCE Our hypothesis is not supported by the results. PTX hastens the onset of collagen-induced platelet aggregation in equine whole blood, but has no effect on the rate of collagen-induced aggregation. PTX does not affect ADP-dependent equine platelet aggregation. Given these findings, PTX may not be a reasonable therapeutic option to decrease platelet aggregation in horses.

Cardiomyocyte calcium cycling in a naturally occurring German shepherd dog model of inherited ventricular arrhythmia and sudden cardiac death.

OBJECTIVE To further characterize arrhythmic mechanisms in German shepherd dogs (GSDs) affected with inherited ventricular arrhythmias by evaluating intracellular calcium cycling and expression of calcium handling genes. ANIMALS Twenty five GSDs, 9 backcross dogs, and 6 normal mongrel dogs (controls) were studied. The GSDs and backcross dogs were from a research colony of inherited ventricular arrhythmias. The control research dogs were purchased. METHODS Action potentials (APs) and pseudo-electrocardiograms (ECG) were recorded from left ventricular (LV) wedge preparations of GSDs and normal dogs. Midmyocardial (Mid) LV cells from GSDs and normal mongrels were isolated by enzymatic digestion. Cells were either field stimulated or voltage clamped and calcium transients were measured by confocal microscopy using the indicator Fluo-3AM. Expression of calcium handling genes was measured by quantitative RT-PCR. RESULTS Mean calcium transient decay (tau) was not different between affected GSDs and control dogs, but striking cell-to-cell variability for tau was observed within affected GSDs and between affected GSDs and controls (P < 0.0001 each); within-dog variability accounted for 75% of total variability. Calcium sparks and afterdepolarizations occurred in GSD but not control cells. ATP2A2/SERCA2a expression was significantly reduced (P = 0.0063) in affected GSDs and inversely correlated (P = 0.0006) with severity of ventricular arrhythmias. CONCLUSIONS German shepherd dogs with inherited ventricular arrhythmias have electrophysiologic abnormalities in calcium cycling associated with reduced ATP2A2/SERCA2a expression. These animals provide a unique opportunity to study calcium remodeling at the genetic and molecular level in familial ventricular arrhythmias.

An accessory bypass tract masked by the presence of atrial fibrillation in a horse

Accessory bypass tracts are rarely documented in horses. Here, we present a case of an accessory bypass tract which was initially masked by the presence of atrial fibrillation. Evidence of ventricular pre-excitation was recognized after cardioversion to normal sinus rhythm and the horse was diagnosed with Wolff-Parkinson-White Syndrome. In people, atrial fibrillation in the presence of an accessory bypass tract is considered dangerous due to the risk of sudden cardiac death. Although we did not consider this horse safe to ride, he continues to compete successfully and has not had recurrence of clinically significant tachyarrhythmias.

Spontaneous closure of a ventricular septal defect in a horse

A 2-month-old Quarter Horse Paint colt was referred to the University of Pennsylvania, Widener Hospital for Large Animals for evaluation of bilateral cardiac murmurs. The murmurs had been detected during a routine neonatal physical examination when the colt was 3 days old. There had been no changes in the cardiac murmurs and no other signs of cardiac disease during the first 2 months of life. Physical examination at presentation to the hospital identified a grade 5/6 pansystolic coarse band-shaped murmur with point of maximal intensity over the tricuspid valve region and a grade 4/6 holosystolic coarse band-shaped murmur with point of maximal intensity over the pulmonic to aortic valve regions. Physical examination was otherwise unremarkable. A ventricular septal defect (VSD) with relative pulmonic stenosis was considered the most likely cause of the cardiac murmurs. A complete echocardiographic examination (2D, Mmode, and Doppler [color flow, continuous wave, pulsed wave] echocardiography) was performed using a variable frequency 2.5–3.5mHz cardiac transducer. A small defect in the caudoapical portion of the interventricular muscular septum was detected. The diameter of the defect was 1.23 0.95 cm on longand short-axis views, respectively. Color flow Doppler echocardiography revealed blood flow across the interventricular septum from left to right during systole at the site of the defect. Color flowDoppler also indicated that the shunted blood flow from the VSD coursed dorsocranially within the right ventricle, along both the right ventricular free wall and the right side of the interventricular septum. Continuous wave Doppler echocardiography from the right cardiac window revealed high-velocity blood flow from left to right across the defect with a peak velocity of 4.27m/s. The apex of the right ventricle appeared mildly rounded and the tricuspid, mitral, and aortic valves appeared mildly thickened. All 4 cardiac valves were thoroughly examined by Doppler echocardiography and no evidence of regurgitation was detected. The echocardiographic findings were consistent with an isolated restrictive caudoapical muscular VSD. Prognosis for a normal life expectancy and use as a western pleasure horse were considered to be good. Annual echocardiographic reevaluation was recommended. It was recommended that the foal not be bred as an adult because there is evidence for a hereditary component with VSDs in a few animal species and in some human families. Approximately 8 months later, the referring veterinarian evaluated the colt for mucopurulent, bilateral nasal discharge and an occasional cough. At this time, the colt’s cardiac murmurs had decreased in intensity. The colt was treated with trimethoprim sulfamethoxazole and its respiratory signs improved. However, because of the decrease in intensity of the cardiac murmurs the colt was readmitted to the Widener Hospital for Large Animals for cardiac reexamination. On physical examination, the colt was in good body condition and had grown appropriately, weighing 348 kg. An occasional cough was present. Pulmonary auscultation disclosed harsh bronchovesicular sounds cranioventrally. An occasional wheeze was auscultated over the right midthorax with a rebreathing examination. Cardiac auscultation revealed that both cardiac murmurs had decreased in intensity by 1 grade and the right-sided murmur was holosystolic rather than pansystolic. Physical examination findings were otherwise unremarkable. The small caudoapical muscular VSD was still discernable on echocardiographic examination. The defect measured 1.32 1.04 cm on longand short-axis views, respectively. Color flow Doppler echocardiography identified a very narrow jet of blood flow through the interventricular septum, which continued dorsocranially along the right side of the interventricular septum (Fig 1). A velocity of 3.48m/s was obtained with continuous wave Doppler echocardiography, but the measurement was thought to be an underestimate of the peak shunt velocity because of poor alignment with shunt flow. Increased right ventricular pressure because of increased pulmonary vascular resistance secondary to the colt’s respiratory tract disease also could explain the decreased shunt velocity across the VSD and decreased intensity of the cardiac murmurs. Right-sided cardiac catheterization was recommended because the lack of tricuspid regurgitation precluded noninvasive estimation of pulmonary arterial pressure. Thoracic radiographs and thorough evaluation of the colt’s respiratory disease also was recommended. The owner declined these diagnostic procedures and elected to continue monitoring the colt From the Department of Clinical Studies, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, KennettSquare, PA (Short, Seco, Reef); and the Department of Clinical Studies, College of Veterinary Medicine, Cornell University, Ithaca, NY (Jesty). This work was performed at the New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA. Corresponding author: Dr Diana M. Short, DVM, Veterinary Clinical Science, College of Veterinary Medicine, Washington State University, P.O. Box 646610, Pullman WA 99164-6610; e-mail: dshort@vetmed.wsu.edu. Submitted April 2, 2010; Revised June 2, 2010; Accepted July 20, 2010. Copyright r 2010 by the American College of Veterinary Internal Medicine 10.1111/j.1939-1676.2010.0589.x Abbreviations: