Transvenous cardiac pacing

Transvenous pacing therapy is a life-saving technique for patients with clinically significant bradyarrhythmias. For most symptomatic bradyarrhythmias in small animals, there is no effective substitute for cardiac pacing. The methods employed for pacemaker placement, although potentially time-consuming, are not technically difficult. This article discusses the indications, techniques, clinical decision-making, and potential complications associated with temporary and permanent transvenous cardiac pacing.     

Characterisation and cardiac directed differentiation of canine adult cardiac stem cells

A multicentre study of 285 cases was performed to enhance the management of distal phalangeal fractures on the basis of clinical evidence. The outcome after treatment was available for 223 of the cases. Horses with a non-articular type I fracture had a better prognosis (91.7%) for return to original or expected level of use than horses with an articular type II or III fracture (69.6% and 74.1%, respectively). The prognosis for types IV and V fractures was fair (57.7% and 57.1%, respectively) and for type VI good (80%). Horses with a hindlimb fracture had a significantly greater chance of a successful outcome. No significant association between age or time to start treatment and success rate was noted. The best treatment option for types I-III fractures was a conservative approach (box rest). Type IV fractures were best treated by arthroscopic removal of the fragment. Immobilisation of the hoof did not seem to influence outcome. Radiological findings and clinical healing were not accurately correlated and the re-commencement of training should be based on clinical rather than radiological findings. Complete osseous union of the fracture was not essential for a successful return to athletic activity.     

Permanent transvenous cardiac pacing

Transvenous cardiac pacing is a commonly employed treatment for symptomatic bradyarrhythmias in dogs. Medical management of these conditions has not proven to be successful leaving pacing as the only viable alternative. The technique of pacemaker implantation is not difficult, but successful pacemaker therapy requires an understanding of electrophysiology, cardiac fluoroscopic anatomy, pacemaker instrumentation, and programming. Proper patient selection and identification of the underlying rhythm disturbance is essential to a successful clinical outcome. This article discusses the indications, equipment, techniques, complications, and outcome of permanent transvenous cardiac pacing.     

Non-invasive real-time measurements of cardiac vagal tone in dogs with cardiac disease

In dogs with spontaneous heart disease, an electronically generated measurement of cardiac vagal tone, the cardiac index of parasympathetic activity, was a sensitive, simple and inexpensive measure of the severity of heart failure. Dogs with cardiac disease and an index score less than 3 were at 15.8 (95 per cent confidence interval 2.9 to 87.2) times the risk of dying within a year than those with a score of 3 and over. The measurement of the index provided an objective and reliable beat-by-beat measurement of cardiac vagal tone, which was prognostically useful in dogs with heart disease.     

Changes in cardiac dimensions and indices of cardiac function during deconditioning in horses

OBJECTIVE: To investigate the effects of deconditioning on cardiac dimensions and indices of cardiac function in horses. ANIMALS: Thirteen 3-to 4-year-old Standardbred geldings. PROCEDURE: All horses had echocardiographic measurements performed at the conclusion of 9 months of intense training and at weeks 1.5, 4, 8, and 12 of deconditioning. Direct echocardiographic measurements included interventricular septal thickness, left ventricular internal dimensions, left ventricular freewall thickness, left atrial dimension, aortic diameter, diameter of the pulmonary artery, slopes of the mitral valve, heart rate, preejection period, and ejection time. Derived indices of cardiac function included fractional shortening, fractional area change, and cardiac output. RESULTS: Cardiac dimensions did not change significantly for the first 4 weeks of deconditioning but decreased significantly by week 8 and continued to decrease until week 12. Indices of cardiac function increased significantly during the first 10 days of deconditioning, remaining stable until week 4 of deconditioning. After week 4, indices of cardiac function decreased significantly until week 12. CONCLUSIONS AND CLINICAL RELEVANCE: Deconditioning resulted in a general reduction in cardiac dimensions and indices of cardiac function over 12 weeks. However, results of the study reported here indicate that following an intense period of training, cardiac function may be maintained during the first 4 weeks of deconditioning. Results indicate that trained horses may rest for up to 4 weeks without a substantial reduction in cardiac capacity as reflected by echocardiographic indices.     

Endostatin inhibits bradykinin-induced cardiac contraction

.Endogenous fragments of extracellular matrix are known to possess various biological effects. Levels of endostatin, a fragment of collagen type XVIII, increase in certain cardiac diseases, such as cardiac hypertrophy and myocardial infarction. However, the influence of endostatin on cardiac contraction has not been clarified. In the present study, we investigated the effects of endostatin on bradykinin-induced atrial contraction. Isometric contractile force of mouse isolated left atria induced by electrical current pulse was measured. Voltage-dependent calcium current of guinea pig ventricular myocytes was measured by a whole-cell patch-clamp technique. Endostatin (100–1,000 ng/ml) alone treatment had no influence on left atrial contraction. On the other hand, pretreatment with endostatin (300 ng/ml) significantly inhibited bradykinin (1 µM)-induced contraction and voltage-dependent calcium current. These data suggest that endostatin may decrease bradykinin-induced cardiac contraction perhaps through the inhibition of voltage-dependent calcium channel.     

Effects of ketamine constant rate infusions on cardiac biomarkers and cardiac function in dogs

Objective

To evaluate the effects of ketamine continuous rate infusions (CRI) at two dose rates on cardiovascular function and serum creatine kinase MB isoenzyme (CK-MB) and troponin I in healthy conscious dogs.

Evaluation of the renin-angiotensin system in cardiac tissues of cats with pressure-overload cardiac hypertrophy

OBJECTIVE: To clarify regulation of the renin-angiotensin (RA) system in cardiac tissues by measuring angiotensin-converting enzyme (ACE) and chymase activities in cats with pressure-overload cardiac hypertrophy. ANIMALS: 13 adult cats. PROCEDURES: Pressure-overload cardiac hypertrophy was induced by coarctation of the base of the ascending aorta in 6 cats, and 7 cats served as untreated control animals. Cats were examined before and 3 months and 2 years after surgery. Two years after surgery, cardiac hypertrophy was confirmed by echocardiography, and the blood pressure gradient was measured at the site of constriction. Cats were euthanized, and ACE and chymase activities were measured in cardiac tissues. RESULTS: Mean +/- SD pressure gradient across the aortic constriction was 63 +/- 6 mm Hg. Chymase activity predominated (75% to 85%) in the RA system of the cardiac tissues of cats. Fibrosis in the wall of the left ventricle was detected in cats with hypertrophy, and fibrosis of the papillary muscle was particularly evident. CONCLUSIONS AND CLINICAL RELEVANCE: Chronic pressure overload on the heart of cats can activate the RA system in cardiac tissues. A local increase in angiotensin II was one of the factors that sustained myocardial remodeling.     

Congenital cardiac disease in dogs

Patent ductus arteriosus (PDA) is thought to be inherited and occurs twice as often in females as in males, most commonly in Poodles, Collies, Cocker Spaniels and Shetland Sheepdogs. About half of untreated dogs develop left-sided heart failure by 8 months of age. Clinical signs include coughing, decreased exercise tolerance, pulmonary edema, a "machinery" murmur in the pulmonic-aortic region, and a bounding pulse. An ECG may reveal an increased amplitude of the R wave and a lengthened P wave. Plain LAT films reveal loss of the cranial and caudal cardiac waists, increased sternal contact of the heart, increased width and straightened caudal border of the cardiac silhouette, elevated carina, and an enlarged left atrium. Changes on plain DV films include an elongated cardiac silhouette, enlarged right ventricle, and 3 bulges on the left side of the cardiac silhouette. Nonselective angiocardiography can be used for a definitive diagnosis and to demonstrate a reverse right-to-left PDA, in which the ascending aorta, brachiocephalic trunk and left subclavian artery are not opacified by contrast medium. Animals with a right-to-left shunt PDA are cyanotic in caudal body parts. Treatment of left-to-right shunt PDA involves ligation with 2 nonabsorbable sutures. A right-to-left shunt PDA should not be ligated but is treated by restricted exercise and periodic phlebotomy.     

Congenital cardiac disease in dogs

Patent ductus arteriosus, aortic stenosis, ventricular septal defect, pulmonic stenosis and tetralogy of Fallot are the most frequently reported cardiac anomalies of dogs. Systolic murmurs occur after the first heart sound but before the second, while diastolic murmurs occur after the second heart sound. Murmurs associated with the pulmonic, aortic and mitral valves are best heard at the left intercostal spaces 3, 4 and 5, respectively, and those of the tricuspid valve at the right intercostal space 3 or 4. Mucosae at both ends of the animal should be examined for cyanosis. Right ventricular enlargement is characterized by a mean electrical axis greater than 100 degrees, a Q wave amplitude greater than 0.5 mv in leads II, III and AVF, and a positive T wave in lead V10. Left ventricular enlargement causes an axis of less than 40 degrees, a QRS complex duration greater than 0.06 seconds, an R wave amplitude greater than 3 mv, and a slurred or depressed ST segment. Atrial enlargement is characterized by a P wave duration greater than 0.04 seconds and a P wave amplitude greater than 0.4 mv. The cardiac silhouette is more upright and round on DV radiographs than on VD projections.     

Congenital cardiac disease in dogs

Thoracic conformation, age, amount of body fat, and stage of respiration and cardiac contraction affect the cardiac silhouette. Deep-chested dogs have an upright, narrow cardiac silhouette about 2 1/2 intercostal spaces wide, while barrel-chested dogs have a round, wide silhouette about 3 1/2 intercostal spaces wide. On LAT films the vessels to a lung lobe should be of equal size and 0.25-1.2 times the diameter of the upper third of the 4th rib at the 4th intercostal space. On DV projections, vessels to the caudal lung lobe should be no larger than the diameter of the 9th rib. Signs of right ventricular enlargement include loss of the cranial waist, increased width of the cardiac silhouette, increased sternal contact of the heart, and an elevated cardiac apex. Signs of left ventricular enlargement include an elevated carina, loss of the caudal waist, and a more perpendicular caudal cardiac border. Signs of left atrial enlargement include separation of mainstem bronchi, compression of the bronchus to the left caudal lung lobe, and an increased distance from the carina to the dorsal border of the caudal vena cava. Enlargement of the aorta and main pulmonary artery segment on a LAT view appears as a soft tissue density obscuring the cranial waist. Pulmonary vascular fields are usually hypervascular in patent ductus arteriosus and interventricular septal defects, normal in uncomplicated aortic or pulmonic stenosis, and hypovascular in tetralogy of Fallot.     

Serum cardiac troponin I and cardiac troponin T concentrations in dogs with gastric dilatation-volvulus

OBJECTIVE: To determine whether serum concentrations of cardiac troponin I (cTnI) and cardiac troponin T (cTnT) are increased in dogs with gastric dilatationvolvulus (GDV) and whether concentrations correlate with severity of ECG abnormalities or outcome. DESIGN: Prospective case series. ANIMALS: 85 dogs with GDV. PROCEDURE: Serum cTnl and cTnT concentrations were measured 12 to 24, 48, 72, and 96 hours after surgery. Dogs were grouped on the basis of severity of ECG abnormalities and outcome. RESULTS: cTnl and cTnT were detected in serum from 74 (87%) and 43 (51%) dogs, respectively. Concentrations were significantly different among groups when dogs were grouped on the basis of severity of ECG abnormalities (none or mild vs moderate vs severe). Dogs that died (n = 16) had significantly higher serum cTnI (24.9 ng/ml) and cTnT (0.18 ng/ml) concentrations than did dogs that survived (2.05 and < 0.01 ng/ml, respectively). Myocardial cell injury was confirmed at necropsy in 4 dogs with high serum cardiac troponin concentrations. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that concentrations of cTnI and cTnT suggestive of myocardial cell injury can commonly be found in serum from dogs with GDV and that serum cardiac troponin concentrations are associated with severity of ECG abnormalities and outcome.     

Congenital cardiac disease in dogs

Aortic stenosis is a heritable cardiac anomaly most common in German Shepherds, Boxers and Newfoundlands, and less common in Pugs, English Bulldogs, Boston Terriers, Fox Terriers, Schnauzers and Bassets. Clinical signs are associated with secondary left-sided heart failure and include coughing, moist rales, exercise intolerance, arrhythmias and a weak femoral pulse. It causes an ejection-type crescendo-decrescendo, systolic murmur best heard on the left side near the elbow. The ECG may be normal or may show signs of left ventricular hypertrophy, including an axis of less than 40 degrees, a QRS complex of greater than 60 seconds in duration, R waves greater than 3 mv in amplitude, ST segment slurring or depression, or T waves of an amplitude greater than 25% of that of R waves. A LAT radiograph usually reveals an enlarged cardiac silhouette, loss of the cranial cardiac waist, and normal pulmonary vasculature, while DV projections show an elongated cardiac silhouette, rounding of the left ventricular border, and a normal descending aorta. Nonselective angiocardiography reveals poststenotic dilatation of the aorta. Treatment of severely affected dogs involves surgical correction.     

Congenital cardiac disease in dogs

Ventricular septal defect (VSD) generally occurs high in the membranous septum rather than lower in the muscular portion. The English Bulldog and Siberian Husky may be predisposed. Clinical signs include a holosystolic or crescendo-decrescendo murmur best heard low on the right side at the 3rd-4th intercostal space and, with large defects, pulmonary congestion, exercise intolerance, cyanosis and ascites. The ECG is normal unless the right ventricle is hypertrophied, which causes right axis deviation and other electrocardiographic signs of right-sided heart enlargement. Plain film thoracic radiographs reveal signs of right-sided heart enlargement but often are not diagnostic. Nonselective angiocardiography is often not useful in diagnosing VSD with a left-to-right shunt of blood. Selective angiocardiography, in which contrast medium is injected directly into the left ventricle via a catheter, is the method of choice for diagnosis of VSD. Dogs with a small VSD remain asymptomatic, but those with large defects require surgical correction with a prosthetic septal pathic or pulmonary artery band.