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