Objective—To evaluate the effects of the pacemaker funny current (If) inhibitor ivabradine on heart rate (HR), left ventricular (LV) systolic and diastolic function, and left atrial performance in healthy cats and cats with hypertrophic cardiomyopathy (HCM).
Animals—6 healthy cats and 6 cats with subclinical HCM.
Procedures—Anesthetized cats underwent cardiac catheterization and were studied over a range of hemodynamic states induced by treatment with esmolol (200 to 400 μg/kg/min, IV), esmolol and dobutamine (5 μg/kg/min, IV), ivabradine (0.3 mg/kg, IV), and ivabradine and dobutamine. Left ventricular systolic and diastolic function, cardiac output, and left atrial function were studied via catheter-based methods and echocardiography.
Results—Treatment with ivabradine resulted in a significant reduction of HR, rate-pressure product, and LV contractile function and a significant increase in LV end-diastolic pressure, LV end-diastolic wall stress, and LV relaxation time constant (tau) in cats with HCM. Concurrent administration of ivabradine and dobutamine resulted in a significant increase of LV contractility and lusitropy, with blunted chronotropic effects of the catecholamine. Left atrial performance was not significantly altered by ivabradine in cats with HCM. Regression analysis revealed an association between maximum rate of LV pressure rise and tau in cats with HCM.
Conclusions and Clinical Relevance—Ivabradine had significant effects on several cardiovascular variables in anesthetized cats with HCM. Studies in awake cats with HCM are needed to clinically validate these findings.
Objective—To evaluate the accuracy of a commercial ultrasonographic cardiac output (CO) monitoring system (UCOMS) in anesthetized Beagles as assessed by comparison with thermodilution CO (TDCO).
Animals—8 healthy anesthetized Beagles.
Procedures—Simultaneous UCOMS and TDCO measurements of CO were obtained during 4 hemodynamic states: baseline anesthesia (0.5% to 1.5% isoflurane), a higher depth of anesthesia (2% to 3.5% isoflurane) to yield a ≥ 15% reduction in systolic arterial blood pressure, IV infusion of colloidal solution to a mean right atrial pressure of ≥ 15 mm Hg, and IV infusion of dobutamine at 5 μg/kg/min. Measurements were obtained at 2 probe positions: the subxiphoid region and the right thoracic inlet. Correlation and agreement of results between methods were determined via linear regression analysis and Bland-Altman plots.
Results—A significant positive correlation was detected between UCOMS andTDCO measurements obtained at the subxiphoid (R = 0.86) and thoracic inlet (R = 0.83) positions. Bland-Altman plots revealed minimal bias between methods (bias ± SD, −0.03 ± 0.73 L/min and −0.20 ± 0.80 L/min for subxiphoid and thoracic inlet measurements, respectively). However, the percentage error associated with UCOMS measurements made at the 2 positions was > 45%.
Conclusions and Clinical Relevance—When compared with the results of TDCO, CO measured with the UCOMS exceeded commonly accepted limits of error in healthy dogs. The UCOMS was, however, able to track changes in CO across hemodynamic states. Additional research is needed to assess the usefulness of the UCOMS for monitoring CO in critically ill dogs.
Objective—To determine aortic ejection velocity in
healthy adult Boxers with soft ejection murmurs without
overt structural evidence of left ventricular outflow
tract obstruction and in healthy Boxers without
Procedure—Dogs were examined independently by
2 individuals for evidence of a cardiac murmur, and a
murmur grade was assigned. Maximal instantaneous
(peak) aortic ejection velocity was measured by
means of continuous-wave Doppler echocardiography
from a subcostal location. Forty-eight dogs were
reexamined approximately 1 year later.
Results—A soft (grade 1, 2, or 3) left-basilar ejection
murmur was detected in 113 (56%) dogs. Overall
median aortic ejection velocity was 1.91 m/s (range,
1.31 to 4.02 m/s). Dogs with murmurs had significantly
higher aortic ejection velocities than did those
without murmurs (median, 2.11 and 1.72 m/s, respectively).
Auscultation of a murmur was 87% sensitive
and 66% specific for the identification of aortic ejection
velocity > 2.0 m/s. An ejection murmur and aortic
ejection velocity > 2.0 m/s were identified in 73
(36%) dogs. For most dogs, observed changes in
murmur grade and aortic ejection velocity during a follow-up examination 1 year later were not clinically
Conclusions and Clinical Relevance—Results
suggested that ejection murmurs were common
among healthy adult Boxers and that Boxers with
murmurs were likely to have high (> 2.0 m/s) aortic
ejection velocities. The cause of the murmurs in
these dogs is unknown. (J Am Vet Med Assoc
Objective—To compare measurements of blood flow
in the common femoral artery obtained by duplex
Doppler ultrasonography (DDU) and a reference ultrasonic
transit-time flow (TTF) method and to examine
the impact of Doppler spectral waveform measurement
techniques on volumetric estimates.
Animals—5 healthy female pigs.
Procedure—Femoral arterial blood flow was measured
simultaneously in anesthetized pigs by use of a
TTF probe (left femoral artery) and transcutaneous
DDU (right femoral artery). A range of flow states was
induced pharmacologically by using xylazine,
bradykinin, dobutamine, and isoflurane. Volumetric
blood flow was calculated from DDU waveforms,
using the product of the flow velocity integral (FVI),
the cross-sectional vessel area, and heart rate. Three
calculations of FVI were obtained by manually tracing
the Doppler spectral envelopes at the outer envelope,
the modal, and the inner envelope of the spectral dispersion
pattern. Data analysis included calculation of
Pearson correlation coefficients and Bland-Altman
limits of agreement.
Results—Blood flow measured by DDU was more
closely correlated with TTF measurements when the
modal or inner envelope tracing method was used
( r, 0.76 and 0.78; limits of agreement, –100 to 54.2
and –48.5 to 77.0 mL/min, respectively). Limits of
agreement for the outer envelope tracing method
were –238.5 to 64 mL/min.
Conclusion and Clinical Relevance—Transcutaneous
DDU is a reliable noninvasive technique for
measuring blood flow in the femoral artery of pigs
over a range of flow states. Tracing the inner envelope
of the Doppler spectral dispersion pattern provided
the best estimate of blood flow in this study.
(Am J Vet Res 2003;64:43–50)
Objective—To evaluate the effects of treatment on respiratory rate, serum natriuretic peptide concentrations, and Doppler echocardiographic indices of left ventricular filling pressure in dogs with congestive heart failure (CHF) secondary to degenerative mitral valve disease (MVD) and dilated cardiomyopathy (DCM).
Design—Prospective cohort study.
Animals—63 client-owned dogs.
Procedures—Physical examination, thoracic radiography, analysis of natriuretic peptide concentrations, and Doppler echocardiography were performed twice, at baseline (examination 1) and 5 to 14 days later (examination 2). Home monitoring of respiratory rate was performed by the owners between examinations.
Results—In dogs with MVD, resolution of CHF was associated with a decrease in respiratory rate, serum N-terminal probrain natriuretic peptide (NT-proBNP) concentration, and diastolic functional class and an increase of the ratio of peak velocity of early diastolic transmitral flow to peak velocity of early diastolic lateral mitral annulus motion (E:Ea Lat). In dogs with DCM, resolution of CHF was associated with a decrease in respiratory rate and serum NT-proBNP concentration and significant changes in 7 Doppler echocardiographic variables, including a decrease of E:Ea Lat and the ratio of peak velocity of early diastolic transmitral flow to isovolumic relaxation time. Only respiratory rate predicted the presence of CHF at examination 2 with high accuracy.
Conclusions and Clinical Relevance—Resolution of CHF was associated with predictable changes in respiratory rate, serum NT-proBNP concentration, and selected Doppler echocardiographic variables in dogs with DCM and MVD. Home monitoring of respiratory rate was simple and was the most useful in the assessment of successful treatment of CHF.
Objective—To identify clinical, echocardiographic,
and electrocardiographic abnormalities in Boxers with
cardiomyopathy and echocardiographic evidence of
left ventricular systolic dysfunction.
Animals—48 mature Boxers.
Procedure—Medical records were reviewed for information
on age; sex; physical examination findings;
and results of electrocardiography, 24-hour ambulatory
electrocardiography, thoracic radiography, and
Results—Mean age of the dogs was 6 years (range, 1
to 11 years). Twenty (42%) dogs had a systolic murmur,
and 9 (19%) had ascites. Congestive heart failure was
diagnosed in 24 (50%) dogs. Seventeen (35%) dogs
had a history of syncope. Mean fractional shortening
was 14.4% (range, 1% to 23%). Mean left ventricular
systolic and diastolic diameters were 4.5 cm (range, 3
to 6.3 cm) and 5.3 cm (range, 3.9 to 7.4 cm), respectively.
Twenty-eight (58%) dogs had a sinus rhythm
with ventricular premature complexes (VPCs), and 20
had supraventricular arrhythmias (15 with atrial fibrillation
and 5 with sinus rhythm and atrial premature complexes).
Sixteen of the dogs with supraventricular
arrhythmias also had occasional VPCs. Morphology of
the VPCs seen on lead II ECGs was consistent with left
bundle branch block in 25 dogs, right bundle branch
block in 8, and both in 11.
Conclusions and Clinical Relevance—Results suggest
that Boxers with cardiomyopathy and left ventricular
dysfunction frequently have arrhythmias of supraventricular
or ventricular origin. Whether ventricular dysfunction
was preceded by electrical disturbances could
not be determined from these data, and the natural history
of myocardial disease in Boxers requires further
study. (J Am Vet Med Assoc 2005;226:1102–1104)