Pathologic and cardiovascular characterization of pheochromocytoma-associated cardiomyopathy in dogs.

Pheochromocytoma-associated catecholamine-induced cardiomyopathy is a well-known entity in man, nonhuman primates, and mice but has not been described in dogs. In this retrospective study, 9 dogs were identified with pheochromocytomas and concurrent cardiovascular pathology observed histologically (n = 6), echocardiographically (n = 4), and/or electrocardiographically (n = 5). Cardiac lesions included multifocal cardiomyocyte necrosis with contraction bands, cardiomyocyte degeneration, myocardial hemorrhage, lymphohistiocytic myocarditis, and interstitial fibrosis. Clinical procedures, including electrocardiographic and echocardiographic examinations, Doppler blood pressure measurement, and auscultation, were available for 5 dogs and consistently revealed concentric or mixed (eccentric and concentric) ventricular hypertrophy. Additional changes observed included arrhythmias, systemic hypertension, and heart murmurs. The myocardial lesions observed in this series of dogs are similar to those observed in humans with pheochromocytoma-associated catecholamine-induced cardiomyopathy. Since the clinical manifestations of catecholamine-induced cardiac disease are amenable to medical treatment, recognition of this cardiomyopathy has the potential to reduce morbidity and mortality in dogs with pheochromocytoma.

Clinical and pathologic responses of American crows (Corvus brachyrhynchos) and fish crows (C ossifragus) to experimental West Nile virus infection.

West Nile virus (WNV)-associated disease has a range of clinical manifestations among avian taxa, the reasons for which are not known. Species susceptibility varies within the avian family Corvidae, with estimated mortality rates ranging from 50 to 100%. We examined and compared virologic, immunologic, pathologic, and clinical responses in 2 corvid species, the American crow (Corvus brachyrhynchos) and the fish crow (C ossifragus), following experimental WNV inoculation. Unlike fish crows, which remained clinically normal throughout the study, American crows succumbed to WNV infection subsequent to dehydration, electrolyte and pH imbalances, and delayed or depressed humoral immune responses concurrent with marked, widespread virus replication. Viral titers were approximately 3,000 times greater in blood and 30,000 to 50,000 times greater in other tissues (eg, pancreas and small intestine) in American crows versus fish crows. Histologic lesion patterns and antigen deposition supported the differing clinical outcomes, with greater severity and distribution of lesions and WNV antigen in American crows. Both crow species had multiorgan necrosis and inflammation, although lesions were more frequent, severe, and widespread in American crows, in which the most commonly affected tissues were small intestine, spleen, and liver. American crows also had inflammation of vessels and nerves in multiple tissues, including heart, kidney, and the gastrointestinal tract. WNV antigen was most commonly observed within monocytes, macrophages, and other cells of the reticuloendothelial system of affected tissues. Collectively, the data support that WNV-infected American crows experience uncontrolled systemic infection leading to multiorgan failure and rapid death.

Association of age and heart rate with pulsed-wave Doppler measurements in healthy, nonsedated cats.

BACKGROUND: Associations of age and heart rate with blood flow velocities and durations assessed by pulsed-wave (PW) Doppler echocardiography in cats are incompletely understood. OBJECTIVES: To determine the effects of age and heart rate on blood flow velocities and durations of cardiac events obtained by PW Doppler echocardiography in healthy, nonsedated cats. ANIMALS: A convenience sample of 87 healthy, nonsedated cats aged 3 months to 19 years. METHODS: Prospective, observational study. PW Doppler measurements were obtained by echocardiography. Association of age and heart rate with PW Doppler values was evaluated by simple and multiple linear regressions and ANCOVA. RESULTS: Significant weak positive relationships were found between age and isovolumic relaxation time (IVRT) (R2= 0.18; P< or = .001), and between age and duration of pulmonary venous retrograde flow (R2= 0.07; P= .041). There was a significant weak negative relationship between age and transmitral peak early diastolic velocity (R2= 0.19; P< or = .001). Age and heart rate were significantly related to pulmonary venous peak systolic velocity (R2= 0.13; P= .008). Heart rate affected transmitral peak late diastolic velocity (R2= 0.11; P= .006). After adjusting for heart rate effect, the PW Doppler variables that were significantly different between age groups were transmitral peak early diastolic velocity (P< or = .001), duration of transmitral late diastolic flow (P< or = .001), IVRT (P< or = .001), and the ratio of duration of transmitral late diastolic flow to duration of pulmonary venous retrograde flow (P= .029). CONCLUSIONS AND CLINICAL IMPORTANCE: The association of several PW Doppler-derived variables and age and heart rate is weak and not clinically important.

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.

Recurrent supraventricular arrhythmias in a dog with atrial myocarditis and gastritis.

This report describes a dog with recurrent atrial fibrillation and atrial flutter associated with chronic gastritis. Although no underlying structural heart disease was apparent antemortem or on gross post-mortem examination, chronic atrial myocarditis was seen on histopathological examination. Atrial myocarditis is a recognised cause of atrial fibrillation in human beings with presumed lone fibrillation, and an association between supraventricular tachyarrhythmias and infectious agents has been made.

Patent ductus arteriosus in cats (Felis catus): 50 cases (2000-2015).

OBJECTIVES: To describe signalment, clinical characteristics, diagnostic, treatment, and outcome data in a large case series of cats with patent ductus arteriosus (PDA). ANIMALS: Fifty cats with confirmed PDA. METHODS: Retrospective review of medical records from five referral veterinary hospitals for cats with PDA between 2000 and 2015. Cats were included if a PDA was visualized echocardiographically, during surgery, or on post-mortem examination. RESULTS: Median age at presentation was 6 months (range: 36 days-9.7 years; n = 50), and sex distribution was approximately equal (27 male, 23 female). Most cats did not have clinical signs (70.2%; 33/47) at the time of presentation. Murmurs were classified as continuous (55%; 22/40) or systolic (45%; 18/40). Echocardiography confirmed left-to-right shunting in 33 cats (82.5%; 33/40) and right-to-left shunting in 7 (17.5%; 7/40). Concurrent cardiac anomalies were identified in 54.5% (18/33) and pulmonary hypertension in 45.7% (16/35). Closure was pursued in 68% (34/50), and complications associated with the procedure occurred in 14.7% (5/34) of cats, including one intraoperative mortality. Long-term follow up was available in 80% (40/50) of cats. CONCLUSIONS: Cats with PDA often do not display clinical signs and may not have the characteristic physical examination findings typical of PDA in dogs. An increased prevalence of concurrent cardiac anomalies and pulmonary hypertension were found relative to previous reports. Thoracic radiographs and echocardiogram may provide the most comprehensive information for making a diagnosis and treatment recommendations. PDA closure was associated with a favorable long-term outcome in cats included in this study.

Ischemic dysfunction and impaired recovery in hypertensive hypertrophied hearts is associated with exaggerated intracellular sodium accumulation.

The primary objectives of this study were to determine if hypertrophied spontaneously hypertensive rat (SHR) hearts exhibited a greater increase in intracellular sodium (Na+i) compared with Wistar-Kyoto (WKY) control rats during low flow ischemia, and to determine whether Na+i accumulation in these hearts was associated with greater ischemic dysfunction and damage. In addition, intracellular pH and high energy phosphates were monitored to assess the relationships between changes in these variables and changes in Na+i. Interleaved 31P and 23Na spectra were acquired in perfused hearts from 8- to 10-month-old rats during low flow ischemia and reperfusion, while left ventricular pressures were monitored continuously. The majority of SHR (n = 13) exhibited an increase in Na+ similar to that for WKY and did not demonstrate exaggerated ischemic dysfunction or damage. However, a subgroup of SHR (n = 7) exhibited exaggerated Na+i accumulation during ischemia, compared with WKY, that was associated with contractile failure and a greater increase in left ventricular end diastolic pressure during ischemia, and slower recovery of developed pressure during reperfusion. Greater Na+i accumulation in this SHR subgroup preceded significantly greater depletion of high energy phosphates compared with WKY. In conclusion, increased Na+i accumulation was observed in all hypertrophied hearts with greater ischemic dysfunction compared with WKY. These results suggest that impaired Na+i handling may indeed contribute to the greater susceptibility of hypertrophied hearts to ischemic dysfunction and damage.

Right ventricular outflow obstruction caused by primary cardiac neoplasia. Clinical features in two dogs.

Obstruction to pulmonary blood flow as a result of neoplasia in the right ventricular outflow tract is described in two dogs. Whereas one dog had exertional syncope and a systolic ejection murmur, the other had signs of congestive failure and hypoxia. In both animals the mass was detected in the right ventricle with two-dimensional echocardiography and confirmed angiographically. Although rare, primary right ventricular neoplasia represents a potentially treatable form of cardiac disease and should be considered as a cause of acquired outflow tract obstruction.

The effects of n-3 fatty acid supplementation on bleeding time, plasma fatty acid composition, and in vitro platelet aggregation in cats.

Dietary supplementation with fish and fish oils rich in the n-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) has been shown to alter eicosanoid metabolism and impair platelet function in several species. As an initial step in evaluating the antithrombotic effect of these n-3 fatty acids in cats, purified EPA and DHA were administered daily to 8 clinically normal cats for 2 months. Platelet function was evaluated biweekly by determining mucosal bleeding time and in vitro platelet aggregation parameters. Plasma fatty acid profiles were obtained before fish oil supplementation and at the termination of the study. In spite of significant increases (P < .0001) in the plasma concentrations of EPA and DHA after n-3 fatty acid supplementation, there were no significant changes in platelet aggregation or bleeding times. Although it is tempting, based on extrapolation of data from other species, to recommend dietary supplementation with fish oil for cats prone to arterial thromboembolism, these results indicate that administration of large doses of purified EPA and DHA once daily does not inhibit platelet function in normal cats and is unlikely to prevent thrombosis in cats with cardiovascular disease. Additional studies are recommended to ascertain whether more frequent administration of these purified n-3 fatty acids or continual feeding of diets high in n-3 fatty acid content will impair platelet function.

Evaluation of the calcium channel-blocking agents diltiazem and verapamil for treatment of feline hypertrophic cardiomyopathy.

To determine the efficacy of and clinical response to several pharmacologic agents for treatment of idiopathic hypertrophic cardiomyopathy in cats, 17 symptomatic cats were randomized to treatment with either propranolol, diltiazem, or verapamil. Clinical, laboratory, radiographic, electrocardiographic, and echocardiographic data were obtained before treatment and after 3 and 6 months of chronic oral therapy. Too few of the cats receiving propranolol or verapamil survived long enough to obtain long-term data needed to make statistical comparisons between groups. However, all 12 cats ultimately treated with diltiazem became asymptomatic, and no adverse effects from this drug were noted in any of these cats. Treatment with diltiazem was associated with a significant reduction of pulmonary congestion assessed radiographically (P less than 0.01), and improved ventricular filling based on echocardiographic measurements of left atrial size (P less than 0.05), left ventricular internal diastolic dimension (P less than 0.05), and relaxation time index (P less than 0.001). There was also a drug-related improvement in jugular venous oxygen tension (P less than 0.001) and blood lactate concentration (P less than 0.01) suggesting improved peripheral perfusion in the cats receiving diltiazem. The results indicate that diltiazem provides an effective and apparently safe treatment for the management of feline hypertrophic cardiomyopathy.

A comparison of dobutamine infusion to exercise as a cardiac stress test in healthy horses.

This study was done to determine whether administration of dobutamine would produce echocardiographic and electrocardiographic alterations comparable to those induced by treadmill exercise in healthy horses. Fourteen horses received maximal treadmill exercise and, separately, intravenous dobutamine infusion up to a maximum rate of 50 microg/kg/min. Ten of the 14 horses were euthanized, and the myocardial tissues were examined grossly and histopathologically. No significant differences were found in the chronotropic effects of dobutamine and exercise (P = .905). Dobutamine induced greater interventricular septal thickening during systole (dobutamine = 4.78 cm, exercise = 4.03 cm; P = .004). and greater left ventricular diameters during diastole (dobutamine = 9.73 cm, exercise = 9.26 cm; P = .037), than did exercise treatment. Horses exhibited transient signs of sweating and restlessness during infusion of moderate to maximum doses of dobutamine. Ventricular ectopy seen in 11 of 14 horses was attributed to the arrhythmogenic properties of dobutamine, as well as to increased vagal tone present at low dobutamine doses. Myocardial lesions characteristic of catecholamine myotoxicity were present in 2 of the 10 horses examined. Although dobutamine induces chronotropic and inotropic changes similar to those induced by exercise, the use of high-dose dobutamine as a cardiac stressor in horses cannot be advocated because of potential development of arrhythmias or myotoxicity.

Use of relaxation half-time as an index of ventricular relaxation in clinically normal cats and cats with hypertrophic cardiomyopathy.

Relaxation half-time (t1/2) was evaluated as a measure of isovolumic ventricular relaxation in clinically normal cats and cats with hypertrophic cardiomyopathy. Relaxation half-time was determined directly from the left ventricular pressure tracing as the time required for the left ventricular pressure at the beginning of isovolumic relaxation to decrease by half. The value of t1/2 was unaffected by moderate changes in heart rate, inotropic state, and afterload in clinically normal cats. However, t1/2 increased significantly (P = 0.003) with increased preload. The value of t1/2 was significantly higher (P = 0.0003) in a group of cats with hypertrophic cardiomyopathy, compared with that of a group of clinically normal cats. Although t1/2 must be interpreted in the context of changes in loading conditions, the index is useful as a measure of relaxation in clinically normal cats and cats with hypertrophic cardiomyopathy.

Cardiac electrophysiologic measurements in dogs before and after intravenous administration of atropine and propranolol.

OBJECTIVES: To assess baseline cardiac electrophysiologic (EP) measurements in dogs undergoing a clinically used anesthetic protocol, and to study the effects of i.v. administered atropine and propranolol on these EP variables. ANIMALS: 15 adult dogs with cardiac function within reference ranges, as assessed by physical examination, electrocardiography, and echocardiography. PROCEDURE: 13 cardiac EP variables were measured in isofluorane-anesthetized dogs before and after i.v. administration of atropine and propranolol. Multipolar electrode catheters were positioned against the endocardium of the dorsal portion of the right atrium, His bundle region, and right ventricular apex. Incremental pacing and pacing-extrastimulus techniques were used to obtain EP measurements of the sinoatrial node, atrioventricular node, and atrial and ventricular myocardia in the control state and after i.v. administration of 0.04 mg of atropine and 0.2 mg of propranolol/kg of body weight. RESULTS: Only the atrial effective refractory period changed significantly after muscarinic and beta-adrenergic receptor antagonism. Marked individual variation in response to these agents, however, was apparent. Two dogs had substantial decreases in sinoatrial and/or atrioventricular nodal measurements, and 7 dogs had notable increases in atrioventricular nodal measurements. CONCLUSIONS: Cardiac EP measurements vary widely among clinically normal, isofluorane-anesthetized dogs. Individual dogs can have variable degrees of autonomic tone, which can be minimized by pharmacologic receptor antagonism. CLINICAL RELEVANCE: Although effects of receptor antagonism at clinically applicable dosages were not significant for 12 of 13 measurements, withdrawal of vagal tone can induce marked EP changes and may be important during a clinical study.

Cardiovascular effects of the alpha2-adrenergic receptor agonist medetomidine in clinically normal cats anesthetized with isoflurane.

OBJECTIVE: To assess the cardiovascular effects of the alpha2-adrenergic receptor agonist medetomidine in healthy cats anesthetized with 2% isoflurane. ANIMALS: 11 clinically normal cats. PROCEDURE: Cats were anesthetized with isoflurane, and catheters were inserted for measurement of aortic, left ventricular, and right atrial pressures. For data collection, end-tidal isoflurane concentration was reduced to 2%, and end-tidal CO2 was maintained at 35 to 40 mm of Hg by use of positive-pressure ventilation. After measurement of baseline data, medetomidine (0.01 mg/kg of body weight, i.m.) was administered and data were collected continuously for 75 minutes. At the end of data collection, incisions were closed and cats were allowed to recover from anesthesia. RESULTS: Medetomidine significantly increased mean arterial pressure and systemic vascular resistance. The increase in mean arterial pressure was maximal at 17.8 +/- 7 minutes after medetomidine administration. Medetomidine also increased left ventricular peak systolic pressure, left ventricular end diastolic pressure, and right atrial pressure. Medetomidine significantly decreased heart rate and mean aortic flow. CONCLUSIONS: The low dosage of medetomidine (0.01 mg/kg, i.m.) promoted severe vasoconstriction in isoflurane-anesthetized cats, and resulted in sustained increases in left ventricular preload and afterload.

Transcatheter modification of the atrioventricular node in dogs, using radiofrequency energy.

OBJECTIVE: To develop a protocol for reliably inducing atrioventricular (AV) block (ideally first- or second-degree), using radiofrequency energy. DESIGN: An electrosurgical unit was coupled to an ammeter, which was connected to the distal pole of an electrode catheter positioned at the AV node. Control settings had previously been calibrated to the power output in a circuit with a 100-ohm resistance. ANIMALS: 10 clinically normal dogs. PROCEDURE: Transcatheter AV nodal modification was attempted, using progressive power applications of 10 to 20 W for progressive durations of 10 to 30 seconds. Atrioventricular nodal conduction and refractivity were measured before and 20 minutes and 1 month after ablation. Electrocardiograms were monitored throughout the 1-month period. RESULTS: Eight of the 10 dogs developed complete AV block, I developed stable 2:1 AV block, and another had no long-term change in AV nodal conduction. Four dogs attained their maximal degree of AV block in 2 to 5 days. Three of these had no AV nodal conduction changes until 2 to 4 days after ablation. CONCLUSIONS: An electrosurgical unit can be economically modified for radiofrequency transcatheter ablation. Stable, incomplete AV block was rarely induced using this protocol, whereas complete AV block often developed. A major finding was frequent delay between energy delivery to the AV nodal region and induction of AV block. CLINICAL RELEVANCE: Induction of complete AV block using this technique, followed by permanent pacemaker placement, is an effective alternative to long-term antiarrhythmic treatment in animals with chronic atrial arrhythmias. Transcatheter ablation could be used to treat other forms of tachycardia, as it is in human medicine.

Volatility of radiopharmacy-prepared sodium iodide-131 capsules.

OBJECTIVE: The aims of this study were to quantify the extent of volatilization from 131I-NaI therapeutic capsules prepared in a centralized radiopharmacy and to quantify the amount of volatile 131I released from a dispensing vial containing a compounded 131I-NaI therapy capsule. METHODS: Therapy capsules were prepared by injecting 131I oral solution into capsules containing anhydrous dibasic sodium phosphate. Volatilized activity was obtained by filtering air drawn across samples that were placed open on the bottom of a sample holder cup. Volatile 131I was captured by filtering it through 3 triethylenediamine-impregnated carbon cartridge filters, arranged in series. To quantify the amount of volatile 131I released from a dispensing vial during a simulated patient administration, a vial containing a compounded 131I therapy capsule was opened inside a collapsible plastic bag and all the air was drawn across TEDA-impregnated carbon cartridge filters. RESULTS: The 370-MBq (10-mCi) 131I capsules from the first part of the experiment released an average of 0.035% (SD 0.031%) of the capsule activity on the first day, 0.012% (SD 0.002%) on the second day, and 0.012% (SD < 0.001%) for days 3 through 5. The 37-MBq (1-mCi) 131I capsules released an average of 0.058% (SD 0.025%) on the first day, 0.029% (SD 0.009%) on the second day, and 0.020% (SD 0.004%) on the third day. The activity released from the vial during a simulated patient administration was 0.00093% of the 131I capsule activity. CONCLUSION: The amount of 131I, which volatilized daily from the exposed therapy capsules, was a small percentage of the capsule activity. The volatile 131I that would be released during a patient administration was much less than the activity that volatilized from the exposed therapy capsules.

Pancreatic adenocarcinoma in a dog with a maldigestion syndrome.

Maldigestion caused by a pancreatic enzyme insufficiency was diagnosed in a 10-year-old Scottish Terrier on the basis of clinical signs and gastrointestinal function test results. The histologic diagnosis was pancreatic adenocarcinoma. Maldigestion is an unusual manifestation of this malignancy, particularly in the absence of other clinical signs. However, pancreatic neoplasia should be considered in aged dogs that develop exocrine insufficiency.

Isolated right ventricular cardiomyopathy in a dog.

Right-sided heart failure was diagnosed in a young dog with clinical and pathologic features of isolated right ventricular cardiomyopathy. This disorder, also referred to as right ventricular dysplasia, is an infrequent cause of heart failure and sudden death in people. Echocardiography of this dog revealed right ventricular and right atrial dilatation and severe right ventricular systolic dysfunction. Left ventricular size and function were normal. Electrocardiography revealed ventricular bigeminy. The configuration of the ectopic beats was similar to that seen with left bundle branch block. The dog died suddenly, and histologic examination of the heart revealed fibroadipose replacement of right atrial and right ventricular myocardium.

Clinical usefulness of cardiac event recording in dogs and cats examined because of syncope, episodic collapse, or intermittent weakness: 60 cases (1997-1999).

OBJECTIVE: To determine the clinical usefulness of cardiac event recording in evaluating dogs and cats with unexplained syncope, episodic collapse, or intermittent weakness. DESIGN: Retrospective study. ANIMALS: 58 dogs and 2 cats. PROCEDURE: Medical records and electrocardiographic rhythm strips obtained by cardiac event recordings were reviewed. Cardiac rhythm data from the event recordings were classified as diagnostic or nondiagnostic. Diagnostic yield was calculated by dividing the number of animals for which cardiac event recording was diagnostic by the total number of animals undergoing cardiac event recording. RESULTS: For 51 animals, cardiac event recording was classified as diagnostic; therefore, overall diagnostic yield was 85%. Diagnostic yield was lower for animals without underlying structural heart disease (75.5%) than for animals with structural heart disease (95.6%). A specific arrhythmia was identified as the cause of clinical signs in 18 of the 51 (35%) animals for which cardiac event recording was diagnostic. Cardiac arrhythmia was definitively excluded as the cause of clinical signs in the remaining 33 (65%) animals in which cardiac event recording was diagnostic. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that cardiac event recording had a high diagnostic yield in dogs and cats examined because of unexplained syncope, episodic collapse, or transient weakness and ataxia, regardless of whether animals did or did not have an underlying structural heart disease. Diagnostic yield of cardiac event recording was higher than that reported previously for Holter monitoring.

Percutaneous balloon valvuloplasty for treatment of pulmonic stenosis in a dog.

A 2.5-year-old dog with congenital pulmonary valve dysplasia was treated by percutaneous balloon dilation of the stenotic orifice. Clinical and hemodynamic improvement was apparent immediately and for 9 months after the valvuloplasty procedure.