Treatment of supraventricular tachycardia in a horse.

OBJECTIVE: To describe the treatment of persistent supraventricular tachycardia (SVT) in a young horse in endurance training. CASE SUMMARY: A 6-year-old Arab gelding in endurance training presented for a dysrhythmia and decreased performance. SVT was diagnosed and conversion to a normal sinus rhythm was achieved following administration of a constant rate infusion of amiodarone. However, reversion to SVT occurred shortly after initiation of ridden exercise. A second attempt to convert the dysrhythmia with amiodarone failed, but normal sinus rhythm was achieved with transvenous electrical cardioversion (TVEC). Postmortem examination of the heart revealed extensive fibrous replacement of most of the left atrial myocardium; these changes likely provided the structural substrate for the dysrhythmia. The underlying cause of the fibrosis was not identified. NEW OR UNIQUE INFORMATION PROVIDED: SVT is a form of supraventricular tachyarrhythmia rarely diagnosed in the horse. A recent report has described sudden death of a horse following attempted conversion of SVT with oral flecainide acetate. In the present report, we describe short-term conversion of SVT in a horse using intravenous amiodarone with no significant adverse effects. When the dysrhythmia recurred, the animal was donated for teaching purposes and conversion was achieved with TVEC. Normal sinus rhythm persisted for 2 weeks until the horse was euthanized for postmortem evaluation of the heart. Intravenous amiodarone or TVEC could be considered as treatments for supraventricular tachyarrhyhmias other than atrial fibrillation in the horse.

Cardiopulmonary Effects of Laparoscopic Ovariectomy of Variable Duration in Cats.

OBJECTIVE: To evaluate the cardiopulmonary effects of low-pressure (6 mmHg) peritoneal insufflation of varying duration in healthy cats during ovariectomy (OVE). STUDY DESIGN: Prospective, randomized study. ANIMALS: Female cats (n = 24). METHODS: After anesthesia induction, cats had short (Short LAP; n = 8) or long duration (Long LAP; n = 8) laparoscopic ovariectomy, or Open OVE (Open; n = 8) for comparison. Hemodynamic and pulmonary measurements were recorded after induction of anesthesia (T0), 5 minutes after abdominal insufflation had reached 6 mmHg of pressure (T1), after the 2nd ovary had been resected (T2), after abdominal decompression (T3), and at the end of anesthesia, after abdominal closure (T4). Hemodynamic and pulmonary variables were compared between groups. RESULTS: Low-pressure abdominal insufflation caused cardiopulmonary changes in cats. At T1 and T2, Long LAP and Short LAP caused a significant change in PvCO2 and RC when compared with Open. During T3, RC was lower only in Long LAP. At T2, there was decrease in SV, but not CO for Long LAP when compared with Open. CONCLUSIONS: Duration of insufflation was associated with worsening of negative cardiopulmonary effects; however, these effects were reversible and resolved by the end of the procedure.

Associations between 'valentine' heart shape, atrial enlargement and cardiomyopathy in cats.

'Valentine' heart shape is a common qualifier used in veterinary radiology to describe a cardiac silhouette with focal enlargement at the level of the base of the heart in feline patients. Anecdotally, this sign has been thought to be related to biatrial enlargement and also to hypertrophic cardiomyopathy (HCM). However, to our knowledge, there has been no study performed to assess the association between cardiac chamber enlargement and cardiac disease with the 'valentine'-shaped heart. The aim of this study was to verify the association between the 'valentine' heart shape observed in ventrodorsal thoracic radiographs and the presence of singular or combined cardiac chamber enlargement, and also the presence and type of cardiomyopathy (CM) in cats. A search of the database of the Small Animal Veterinary Hospital of the University of Florida for cats with a radiology report of thoracic radiographs that contained the words 'valentine' and 'biatrial', and echocardiography performed within 1 week, was undertaken; 41 cases met the inclusion criteria. Eighty-two percent of the cats of the study sample had some form of CM. The 'valentine' heart shape was associated with biatrial enlargement in 41% of the patients in our study sample that had some form of CM and just 8% of cases diagnosed with HCM, suggesting that the 'valentine' heart shape has a low association with HCM or biatrial enlargement; however, it should be considered a sign of feline CM.

Rhabdomyosarcoma associated with the lead wire of a pacemaker generator implant.

An 11-year-old female spayed Labrador Retriever was presented for a draining, painful subcutaneous mass palpated over a previously implanted pacemaker generator. Infection was suspected and the mass was removed surgically. On cut surface, the mass was friable and mottled tan to brown with firm pale tan nodules, surrounding the pacemaker lead wire adjacent to the pacemaker generator. Cytologic interpretation of impression smears was consistent with a sarcoma, and suggestive of a rhabdomyosarcoma due to the presence of strap-like cells. On histopathologic examination, a highly invasive nodular mass surrounded the pacemaker lead, composed of pleomorphic round, spindle and strap cells, and multinucleated giant cells. The population exhibited microscopic invasion into the deep portion of the fibrous capsule surrounding the pacemaker generator. There were tumor emboli within small to medium subcutaneous veins adjacent to the mass. Immunohistochemically, the neoplastic cells stained positive for α-sarcomeric actin and vimentin, and negative for α-smooth muscle actin, consistent with a rhabdomyosarcoma arising at the site of the pacemaker generator. To our knowledge, this is the first report of a rhabdomyosarcoma associated with the lead wire of a pacemaker generator in a dog.

Computed tomography angiography of coarctation of the aorta in a dog.

Coarctation of the aorta has been described previously as either a post-mortem or angiographic finding in three dogs with clinical signs related to the aortic coarctation. A 10-year-old dog was presented for evaluation of suspected laryngeal paralysis. On physical examination, femoral pulses were absent bilaterally, with an indirect systolic blood pressure difference of 60 mmHg between the ipsilateral thoracic and pelvic limbs. Coarctation of the aorta was detected on a thoracic computed tomographic angiography study. The coarctation was pre-ductal in position, with extensive dilation of the descending thoracic aorta. Characteristic rib changes that are seen in humans with coarctation were not apparent in this dog. 3D reconstructions of the thorax provided high vascular definition with exact localization of the aortic narrowing.

Pharmacokinetics of oral dichloroacetate in dogs.

We characterized the pharmacokinetics and dynamics of dichloroacetate (DCA), an investigational drug for mitochondrial diseases, pulmonary arterial hypertension, and cancer. Adult Beagle dogs were orally administered 6.25 mg/kg q12h DCA for 4 weeks. Plasma kinetics was determined after 1, 14, and 28 days. The activity and expression of glutathione transferase zeta 1 (GSTZ1), which biotransforms DCA to glyoxylate, were determined from liver biopsies at baseline and after 27 days. Dogs demonstrate much slower clearance and greater inhibition of DCA metabolism and GSTZ1 activity and expression than rodents and most humans. Indeed, the plasma kinetics of DCA in dogs is similar to humans with GSTZ1 polymorphisms that confer exceptionally slow plasma clearance. Dogs may be a useful model to further investigate the toxicokinetics and therapeutic potential of DCA.

Echocardiographic evaluation of clinically healthy Florida manatees (Trichechus manatus latirostris).

Antemortem studies pertaining to the manatee cardiovascular and cardiopulmonary systems are limited despite reports of cardiac disease in postmortem specimens. The objective of this project was to develop a technique for echocardiography in the Florida manatee (Trichechus manatus latirostris). Because of their unique anatomy, a ventral approach was employed by use of an echocardiography table designed specifically for this study. Fourteen clinically healthy, free-ranging and captive Florida manatees underwent echocardiography between the fall of 2011 and winter of 2012. Eight females and six males of various age categories were included in the study. Clear visualization of all valves and chambers was accomplished, and length and width measurements of the left atrium, peak aortic flow velocity, and ejection fraction percentage were calculated in most animals. Abnormalities observed during the study included atrioventricular regurgitation and severe right-atrial enlargement. Based on the results of this study, echocardiography in the Florida manatee is possible, which has both clinical and research implications in larger epidemiologic studies evaluating diseases of the cardiopulmonary and cardiovascular systems.

Procedure times, complication rates, and survival times associated with single-chamber versus dual-chamber pacemaker implantation in dogs with clinical signs of bradyarrhythmia: 54 cases (2004-2009).

OBJECTIVE: To compare procedure times and major and minor complication rates associated with single-chamber versus dual-chamber pacemaker implantation and with 1-lead, 2-lead, and 3-lead pacemaker implantation in dogs with clinical signs of bradyarrhythmia. DESIGN: Retrospective case series. ANIMALS: 54 dogs that underwent pacemaker implantation because of clinical signs of bradyarrhythmia. PROCEDURES: Medical records of dogs that received pacemakers between July 2004 and December 2009 were reviewed for information regarding signalment, diagnosis, pacemaker implantation, pacemaker type, complications, and survival time. Analyses were performed to determine significant differences in anesthesia time, procedure time, and outcome for dogs on the basis of pacing mode and number of pacing leads. RESULTS: 28 of 54 (51.9%) dogs received single-chamber pacemakers and 26 (48.1%) received dual-chamber pacemakers. Mean ± SD procedural time was significantly longer for patients with dual-chamber pacemakers (133.5 ± 51.3 minutes) than for patients with single-chamber pacemakers (94.9 ± 37.0 minutes), and procedure time increased significantly as the number of leads increased (1 lead, 102.3 ± 51.1 minutes; 2 leads, 114.9 ± 24.8 minutes; 3 leads, 158.2 ± 8.5 minutes). Rates of major and minor complications were not significantly different between dogs that received single-chamber pacemakers and those that received dual-chamber pacemakers or among dogs grouped on the basis of the number of pacing leads placed. CONCLUSIONS AND CLINICAL RELEVANCE: Although dual-chamber pacemaker implantation did result in increased procedural and anesthesia times, compared with single-chamber pacemaker implantation, this did not result in a higher complication rate.

How to perform combined cutting balloon and high pressure balloon valvuloplasty for dogs with subaortic stenosis.

Subvalvular aortic stenosis (SAS) is one of the most common congenital cardiac malformations in dogs. Unfortunately, the long term success rate and survival data following either open heart surgery or catheter based intervention has been disappointing in dogs with severe subaortic stenosis. Medical therapy is currently the only standard recommended treatment option. A cutting balloon dilation catheter has been used successfully for resistant coronary artery and peripheral pulmonary arterial stenoses in humans. This catheter is unique in that it has the ability to cut, or score, the stenotic region prior to balloon dilatation of the stenosis. The use of cutting balloon valvuloplasty combined with high pressure valvuloplasty for dogs with severe subaortic stenosis has recently been reported to be a safe and feasible alternative therapeutic option. The following report describes this technique, outlines the materials required, and provides some 'tips' for successful percutaneous subaortic balloon valvuloplasty.

Assessment of cardiac output measurement in dogs by transpulmonary pulse contour analysis.

OBJECTIVE: To determine if metatarsal artery pressure (COmet) is comparable to femoral artery pressure (COfem) as the input for transpulmonary pulse contour analysis (PiCCO) in anesthetized dogs, using the lithium dilution method (LiDCO) as a standard for cardiac output (CO) measurement. DESIGN: Prospective randomized study. SETTING: University research laboratory. ANIMALS: Ten healthy purpose-bred mixed breed dogs were anesthetized and instrumented to measure direct blood pressure, heart rate, arterial blood gases, and CO. INTERVENTIONS: The CO was measured using LiDCO and PiCCO techniques. Animals had their right femoral and left distal metatarsal artery catheterized for proximal (COfem) and distal (COmet) PiCCO analysis, respectively. Measurements were obtained from each animal during low, normal, and high CO states by changing amount of inhalant anesthetics and heart rate. Measurements were converted to CO indexed to body weigh (CI(BW) =CO/kg) for statistical analysis. Agreement was determined using Bland and Altman analysis and concordance correlation coefficients. MEASUREMENTS AND MAIN RESULTS: Thirty paired measurements were taken. The LiDCO CI(BW) (± SD) was 68.7 ± 30.3, 176.0 ± 53.0, and 211.1 ± 76.5 mL/kg/min during low, normal, and high CO states, respectively. There was a significant effect of CI(BW) state on bias and relative bias with COmet (P<0.001 and P=0.003, respectively). Bias of the COmet method (± SD) was -116.6 (70.5), 20.1(76.4), and 91.3 (92.0) mL/kg/min at low, normal, and high CI(BW), respectively. Bias of the COfem (± SD) was -20.3 (19.0), 8.6 (70.9), and -2.9 (83.0) mL/kg/min at low, normal, and high CI(BW) , respectively. The mean relative bias for COfem was -6.7 ± 44% (limits of agreements: -81.2 to 67.9%). CONCLUSION: Compared with lithium dilution, the pulse contour analysis provides a good estimation of CO, but requires femoral artery catheterization in anesthetized dogs.

Computed tomography angiography of bilateral peripheral pulmonary arterial stenoses in a dog.

Computed tomographic angiography (CTA) is a useful diagnostic modality that is becoming more widely available in veterinary medicine. Its three-dimensional imaging capabilities allow a template for planning surgical procedures, accurate lesion measurements, and it is considerably less expensive than other comparable modalities. Selective CTA is described here, in a case of canine bilateral peripheral pulmonary artery stenoses.

Successful closure of left-to-right patent ductus arteriosus in three dogs with concurrent pulmonary hypertension.

Closure of reversed patent ductus arteriosus (PDA) is generally accepted to be contraindicated due to case based evidence of worsened outcomes, but little is known about closure of left-to-right PDA with concurrent pulmonary hypertension (PH). This report describes three dogs presenting with varying severity of PH and clinical signs, all with documented left-to-right PDA. The PDA was closed in each case; either by surgical ligation or transarterial device occlusion, and follow up was available for a minimum of 8 months. Every case had a successful outcome with improvement or resolution of PH and associated clinical signs.

Evaluation of pacing site in dogs with naturally occurring complete heart block.

OBJECTIVE: To compare left ventricular synchronization and systolic performance with transvenous pacing of the right ventricular apex (RVA), left ventricular free wall (LVF) or simultaneous pacing of the RVA and LVF (BiV). ANIMALS, MATERIALS AND METHODS: Seven canine patients with complete heart block. Prospective study evaluating effect of pacing site. Twenty four hours following implantation of transvenous BiV pacing systems, electrocardiograms and echocardiograms were assessed during pacing from the: (1) Right Atrial Appendage/RVA (RAA/RVA), (2) RAA/LVF, and (3) RAA/BiV. RESULTS: QRS duration was significantly shorter with BiV pacing versus LVF pacing (p<0.001), or RVA pacing (p<0.001). Echocardiographic indices of systolic performance fractional shortening (FS), ejection fraction (EF), cardiac output (CO) were significantly higher with BiV pacing than with pacing from the RVA (P=0.023, 0.006, and 0.002 respectively). Cardiac output, measured by the biplane Simpson's method, was higher with LVF versus RVA pacing (P=0.036). There was no difference in FS or EF when comparing LVF to RVA pacing. Tissue Doppler measurements of synchronization and systolic performance did not show any difference between pacing mode, but a significantly increased number of segments were seen to contract following aortic valve closure during LVF pacing (P=0.0268) and RVA pacing (P=0.0197) as compared to BiV pacing. CONCLUSIONS: Findings suggest that BiV pacing improves cardiac output and systolic performance versus RVA pacing. This improvement however, is not reflected in tissue Doppler indices of synchronization and systolic performance.

Intracardiac foreign body in a dog.

A dog that was referred to the University of Florida Veterinary Medical Center was discovered to have a bamboo skewer within the right atrium and right ventricle, traversing the tricuspid valve. The skewer was ingested approximately four months prior to referral and was partially removed via gastrotomy. The presenting complaint at the time of referral included coagulopathy, anemia and leukocytosis. A linear, hyperechoic structure was identified in the right heart during an echocardiogram. The foreign body was suspected to be a portion of the skewer that the patient had previously ingested. Cardiopulmonary bypass was performed and the foreign body was removed successfully. Complications following surgery included the development of tricuspid valve and ventricular wall thrombi, atrial flutter and amiodarone toxicity. Many indications have been described in the veterinary literature for cardiopulmonary bypass. However, to the best of the authors' knowledge, successful removal of an intracardiac foreign body with cardiopulmonary bypass has not been reported in a veterinary patient. This represents a new indication for cardiopulmonary bypass in veterinary medicine.

Evaluation of the effects of transvenous pacing site on left ventricular function and synchrony in healthy anesthetized dogs.

OBJECTIVE-To compare the acute effects of cardiac pacing from various transvenous pacing sites on left ventricular (LV) function and synchrony in clinically normal dogs. ANIMALS-10 healthy adult mixed-breed dogs. PROCEDURES-Dogs were anesthetized, and dual-chamber transvenous biventricular pacing systems were implanted. Dogs were paced in single-chamber mode from the right atrial appendage (RAA) alone and in dual-chamber mode from the right ventricular apex (RVA), from the left ventricular free wall (LVFW), and simultaneously from the RVA and LVFW (BiV). Standard ECG and echocardiographic measurements, cardiac output measured with the lithium dilution method (LiDCO), and tissue Doppler-derived measurements of LV synchrony were obtained during each of the pacing configurations. RESULTS-Placement of the biventricular pacing systems was possible in 8 of the 10 dogs. The QRS duration was significantly different among all pacing sites, and the order of increasing duration was RAA, BiV, LVFW, and RVA. Pacing sites did not differ with respect to fractional shortening; however, pacing from the RVA resulted in a significantly lower ejection fraction than pacing from all other sites. During RVA and LVFW pacing, LiDCO was significantly lower than that at other sites; there was no significant difference between RAA and BiV pacing with respect to LiDCO. Although the degree of dyssynchrony was significantly lower during pacing from the RAA versus other ventricular pacing sites, it was not significantly different among sites. CONCLUSIONS AND CLINICAL RELEVANCE-Ventricular activation by RAA pacing provided the best LV function and synchrony. Pacing from the RVA worsened LV function, and although pacing from the LVFW improved it, BiV pacing may provide additional improvement.

Effect of routine cardiovascular catheterization on cardiac troponin I concentration in dogs.

OBJECTIVE: To determine changes in cardiac troponin I concentration (cTnI) associated with cardiovascular catheterization in dogs. ANIMALS, MATERIALS AND METHODS: cTnI was measured after transarterial coil embolization of patent ductus arteriosus (PDA), balloon valvuloplasty (BV), and pacemaker implantation (PACE). Dogs undergoing ovariohysterectomy (OHE) were used as a control, with 15 animals in each group. Blood for the cTnI assay was collected at baseline (T0), at 5h (T5), 24h (T24) and 10 days (T240) post-procedure. The effects of age, duration and difficulty of the procedure were evaluated. RESULTS: There was no difference in cTnI concentration at T0 for any of the groups. There was a significant increase in cTnI concentration for BV and PACE, but not PDA at T5 and T24. PACE at T24 and T240 also had higher cTnI than control. Dogs with longer procedure times had significantly higher concentration of cTnI. There was no correlation between the difficulty of the procedure or peri-procedure complications and cTnI. CONCLUSION: cTnI increased during some cardiovascular catheterization procedures, but returned to normal values at 24-240 h. Patients undergoing long catheterization procedures have increased risk for myocardial injury, but this was not related to short-term prognosis.

Cardiac evaluation of anesthetized Grevy's zebras (Equus grevyi).

OBJECTIVE: To determine ECG and echocardiographic measurements in healthy anesthetized Grevy's zebras (Equus grevyi). ANIMALS: 20 healthy zebras. PROCEDURES: Auscultation, base-apex ECG, and echocardiography were performed on anesthetized zebras. RESULTS: Low-grade systolic murmurs were detected in the left basilar region in 4 of 20 zebras. Evaluation of ECGs from 19 zebras revealed sinus rhythm with a predominantly negative QRS complex and a mean +/- SD heart rate of 67 +/- 10 beats/min. Echocardiograms of sufficient image quality were obtained for 16 zebras. Interventricular septal thickness in diastole, left ventricular chamber in diastole and systole, left atrial diameter, and left ventricular mass were significantly and moderately correlated with estimated body weight (r values ranged from 0.650 to 0.884). Detectable swirling of blood in the right and sometimes the left ventricles was detected in 9 of 16 zebras, whereas physiologic regurgitation of blood was detected for the aortic valve in 3 zebras, pulmonary valve in 2 zebras, mitral valve in 2 zebras, and tricuspid valve in 1 zebra. CONCLUSIONS AND CLINICAL RELEVANCE: Results of this study provide reference information for use in the cardiac evaluation of anesthetized Grevy's zebras.