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Abstract

Objective—To assess the influence of age on pulmonary hemodynamics and hemorheological properties in healthy dogs.

Animals—14 healthy Beagles.

Procedures—Dogs were placed in 2 age groups as follows: young dogs (≤ 5 years old; n = 8) and old dogs (≥ 8 years old; 6). Hematologic characteristics, plasma total protein and fibrinogen concentrations, and blood viscosity were measured. Systolic time intervals of pulmonary blood flow were recorded by pulsed-wave Doppler echocardiography. Early (E′) and late (A′) diastolic myocardial velocities, isovolumic contraction velocity, and systolic myocardial velocity of the free tricuspid annulus were recorded by pulsed-wave tissue Doppler imaging (TDI). Dogs were anesthetized and pulmonary arterial pressures (PAP) and cardiac output were recorded with a pediatric thermodilution Swan-Ganz catheter.

Results—Hemorheological measurements were not different between the 2 groups. Systolic, mean, and diastolic PAP were higher in old dogs, compared with values in young dogs; this difference was attributed to a high pulmonary vascular resistance and low arterial compliance in old dogs. Systolic time intervals of pulmonary blood flow stayed unchanged. The A′ wave of the free tricuspid annulus was increased in old, compared with that young dogs, and the E′:A′ ratio was decreased. Pulmonary vascular resistance was inversely correlated with compliance.

Conclusions and Clinical Relevance—The age of dogs should be taken into account when interpreting pulmonary hemodynamic results and TDI variables of right ventricular diastolic function.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine whether dobutamine stress tests (DST) can be used to detect cardiac dysfunction in dogs with early left ventricular dysfunction (ELVD) induced by rapid right ventricular pacing (RRVP).

Animals—7 adult male Beagles.

Procedure—A pacemaker was surgically implanted in each dog at the level of the right ventricular apex. Electrocardiography, Doppler sphygmomanometry, and Doppler echocardiography were performed before and during a DST prior to activation of the pacemaker and every 3 to 4 days during the period of RRVP. Dobutamine stress tests were performed by infusing dobutamine at incremental dosages ranging from 12.5 to 42.5 µg/kg of body weight/min.

Results—Clinical signs of congestive heart failure were not observed during the pacing period. However, all dogs developed ELVD associated with significant changes in values for most Doppler echocardiographic variables obtained prior to DST. Adverse cardiac effects were not detected during DST. Most Doppler echocardiographic indices of cardiac function were significantly altered in response to dobutamine infusion during the pacing period, compared with prepacing values. However, a dobutamine-induced 2-fold increase in cardiac output was maintained.

Conclusions and Clinical Relevance—Dobutamine stress tests can be safely performed in dogs with experimentally induced ELVD. Dobutamine stress tests may be a sensitive, noninvasive diagnostic method, complementary to standard clinical examinations, for detection of early cardiac dysfunction in dogs asymptomatic for dilated cardiomyopathy. (Am J Vet Res 2001;62:448–455)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To investigate the effects of preventive angiotensin converting enzyme inhibitor treatment with ramipril in dogs with progressively severe experimentally induced heart failure.

Animals—20 dogs.

Procedures—Dogs were randomly allocated to receive no treatment (control) or ramipril (0.125 mg/kg, PO, daily) for 7 weeks. Physical examination, repetitive catheterization of the right side of the heart, and echocardiography were performed before the study (day 0) and weekly for 7 weeks. Renal plasma flow (RPF) as determined by para-aminohippuric acid clearance and glomerular filtration rate (GFR) as determined by creatinine and iohexol clearances were measured on day 0 and at weeks 4 and 7.

Results—Overpacing induced a progressive increase in right atrial pressure (RAP) and pulmonary artery pressure, occluded (PAPO), with a decrease in systemic arterial pressure. There were progressive alterations of echocardiographic indices of diastolic and systolic ventricular function. The RPF and GFR decreased before cardiac output decreased, and filtration fraction increased. The logarithm of the urinary sodium–to–potassium concentration ratio (log10[Na+/K+]) decreased. Significant effects of ramipril included a delay in clinical signs of heart failure, a late decrease in RAP and PAPO, and increases in the sodium excretion fraction and log10(Na+/K+). There was a satisfactory agreement between the creatinine and iohexol clearance measurements.

Conclusions and Clinical Relevance—Results suggest that, in this rapid-evolving, dilated cardiomyopathy, activation of the renin-angiotensin system contributes to the pathophysiology of heart failure late in the disease and essentially by an activation of renal salt and water retention.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To assess morphologic and metabolic abnormalities in dogs with early left ventricular dysfunction (ELVD) induced by rapid right ventricular pacing (RRVP).

Animals—7 Beagles.

Procedure—Plasma carnitine concentrations were measured before and after development of ELVD induced by RRVP. At the same times, transvenous endomyocardial biopsy was performed, and specimens were submitted for determination of myocardial carnitine concentrations and histologic, morphometric, and ultrastructural examination.

Results—In 4 dogs in which baseline plasma total carnitine concentration was normal, RRVP induced a decrease in myocardial total and free carnitine concentrations and an increase in myocardial esterified carnitine concentration. In 3 dogs in which baseline plasma total carnitine concentration was low, plasma and myocardial carnitine concentrations were unchanged after pacing. Structural changes associated with pacing included perinuclear vacuolization in 3 dogs. Morphometric analyses indicated there was a decrease in myofiber cross-sectional diameter and area following pacing. Electron microscopy revealed changes in myofibrils and mitochondria following pacing.

Conclusions and Clinical Relevance—Results indicated that moderate to severe alterations in myocyte cytoarchitecture are present in dogs with ELVD induced by RRVP and that in dogs with normal plasma carnitine concentrations, myocardial carnitine deficiency may be a biochemical marker of ELVD. Results also indicated that transvenous endomyocardial biopsy can be used to evaluate biochemical and structural myocardial changes in dogs with cardiac disease. (Am J Vet Res 2001;62:889–894)

Full access
in American Journal of Veterinary Research