Metabolic and structural abnormalities in dogs with early left ventricular dysfunction induced by incessant tachycardia.

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.

Usefulness of dobutamine stress tests for detection of cardiac abnormalities in dogs with experimentally induced early left ventricular dysfunction.

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 microg/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.

Hormonal response to dobutamine cardiac stress testing in a conscious canine model of early left ventricular dysfunction induced by chronic rate overload.

The aims of this study were to investigate (1) hormonal activation before and during dobutamine cardiac stress testing (DST) in a canine model of early left ventricular dysfunction (ELVD) induced by rapid right ventricular pacing (RRVP) and (2) the relationship between this hormonal profile and carnitine concentrations. Before the pacing period, the 6 dogs were assigned to 2 groups according their baseline total plasma carnitine concentration. A DST was performed on each dog before activation of the pacemaker and every 3 to 4 days during development of 3 progressive stages of ELVD (stages 1, 2 and 3). Plasma atrial natriuretic factor (ANF), angiotensin II (ANG II) and endothelin-1 (ET-1) levels were measured at the start and at the end of each DST. Effects of ELVD, DST and plasma carnitine concentration on these measurements were tested. The RRVP induced a significant increase of ANF and ANG II and a non significant trend toward increase of ET-1 in all dogs. Before the pacing period, ANF remained constant during the DST in dogs with normal total plasma carnitine concentration, while it significantly decreased in dogs with low total plasma carnitine concentration. Dobutamine stress testing induced a significant decrease in ANF in all dogs in ELVD. Dobutamine infusion induced a significant increase in ANG II in all dogs before as well as during the pacing period while ET-1 was unchanged. These results suggest that investigation of the hormonal profile before and after a dobutamine challenge might provide important diagnostic information in dogs with asymptomatic or mildly symptomatic cardiac dysfunction of different origins.