Daily Rhythms of Left Atrial Pressure in Beagle Dogs with Mitral Valve Regurgitation

Dose-dependent effects of isoflurane and dobutamine on cardiovascular function in dogs with experimental mitral regurgitation

OBJECTIVE

To investigate the dose-dependent effects of isoflurane and dobutamine on haemodynamics in dogs with experimentally induced mitral valve insufficiency (MI).

STUDY DESIGN

Experimental, dose-response study.

ANIMALS

Six healthy Beagle dogs.

METHODS

Dogs with surgically induced MI were anaesthetized once. First, anaesthesia was maintained at an end-tidal isoflurane concentration (Fe'Iso) 1.0% (ISO1.0) for 20 minutes. Then, dobutamine was infused successively at 2, 4, 8 and 12 μg kg^-1 minute^-1 (DOB2-12) for 10 minutes at each dose rate. Measurements were recorded at each stage. Dobutamine was discontinued and Fe'Iso was increased to 1.5% (ISO1.5) for 20 minutes. Dobutamine was administered similarly to ISO1.0, and cardiovascular variables were recorded. The same sequence was repeated for Fe'Iso 2.0% (ISO2.0). Aortic pressure (AoP) and left atrial pressure (LAP) were recorded by radiotelemetry. The combination method of the pressure-volume loop analysis and transoesophageal echocardiography was used to measure cardiovascular variables: end-systolic elastance (Ees), effective arterial elastance (Ea), Ea/Ees, forward stroke volume (FSV), heart rate (HR), and cardiac output (CO).

RESULTS

High isoflurane concentration resulted in reduced Ees and increased Ea/Ees, which indicated low arterial pressure. High-dose dobutamine administration resulted in increased Ees and FSV at all isoflurane concentrations. In ISO1.5 and ISO2.0, HR was lower at DOB4 than baseline (BL) but increased at DOB12 compared with DOB4. CO increased at ≥ DOB8 compared with BL. In ISO1.5 and ISO2.0, systolic and mean AoP increased at ≥ DOB4 and ≥ DOB8, respectively. LAP did not change under all conditions.

CONCLUSIONS AND CLINICAL RELEVANCE

The dose-dependent hypotensive effect of isoflurane in MI dogs was mainly derived from the decrease in contractility. Dobutamine increased AoP without increasing LAP by increasing the contractility attenuated by isoflurane. Our findings may improve the cardiovascular management of dogs with MI undergoing general anaesthesia with isoflurane.

Effects of a sustained-release form of isosorbide dinitrate on left atrial pressure in dogs with experimentally induced mitral valve regurgitation

BACKGROUND

The effects of isosorbide dinitrate (ISDN) have not been sufficiently investigated in conscious dogs with mitral valve regurgitation (MR).

OBJECTIVE

The objective was to investigate the effects of a sustained-release form of ISDN (sr-ISDN) on hemodynamics and the autonomic nervous system in dogs with MR.

ANIMALS

Six healthy Beagles weighing 11.2 ± 2.2 kg (2 years of age; 2 males and 4 females) were used.

METHODS

Experimental, crossover, and interventional study. Dogs with experimentally induced MR were administered placebo, 2, 5, and 10 mg/kg sr-ISDN PO on separate days with a 7-day washout period between randomized dosings. Left atrial pressure (LAP) had been recorded continuously from 30 minutes before administration of sr-ISDN to 12 hours after administration.

RESULTS

LAP was significantly decreased after administration in the 5 and 10 mg/kg groups. Significant decrease was observed at 3 and 4 hours after administration in the 5 mg/kg group. In the 10 mg/kg group, significant decrease was observed at 2, 3, 4, 5, 6, 7, 10, and 11 hours after administration. The lowest value was observed at 4 hours after administration in the 5 and 10 mg/kg groups (20.9 ± 4.2 to 15.9 ± 3.9 mmHg, P < .01, and 21.3 ± 4.0 to 13.6 ± 4.2 mmHg, P < .001).

CONCLUSIONS AND CLINICAL IMPORTANCE

Sustained-release form of ISDN showed significant decrease of LAP in the 5 mg/kg and 10 mg/kg groups, and duration of effect was dose related.

Comparative effects of amlodipine and benazepril on left atrial pressure in dogs with experimentally-induced mitral valve regurgitation

Background

One of the purposes of treatment for dogs with mitral regurgitation (MR) is lowering left atrial pressure (LAP). There has been few study of the amlodipine in dogs with MR and amlodipine’s effect on LAP has not been fully evaluated in a quantitative manner because of difficulties in directly measuring LAP. The objective of our study was to compare the short-term effects of amlodipine (0.2 mg/kg PO q12h) vs benazepril (0.5 mg/kg PO q12h), on LAP and echocardiographic parameters in five beagle dogs with experimentally-induced MR. LAP of eight dogs that has own control were measured using radiotelemetry system at baseline and again on days 1, 2, 3, 4, 5, 6, 7 of the drug administration.

Results

Mean LAP decreased significantly after amlodipine (11.20 ± 4.19 mmHg vs 14.61 ± 3.81 mmHg at baseline, p < .01) but not after benazepril treatment (13.19 ± 3.47 mmHg, p > .05). LAP was lower after 7 days of amlodipine treatment than after 7 days of benazepril treatment. Significant reduction was seen for the first time 4 days after the administration amlodipine. The rate of the maximal area of the regurgitant jet signals to the left atrium area (ARJ/LAA) of the amlodipine treatment was significantly lower (p < .05) after 7 days compared to baseline. Other echocardiographic parameters did not change significantly.

Conclusions

LAP was significantly decreased after amlodipine treatment in dogs with surgically-induced MR but not after benazepril treatment. Although this study did not focus on adverse effects, amlodipine may be an effective drug for helping the patients with acute onset of severe MR, such as rupture of chordae tendinae or end stage patients were the LAP is likely to be elevated. Additional studies in clinical patients with degenerative mitral valve disease and acute chordal rupture are warranted because the blood-pressure lowering effects of amlodipine can decrease renal perfusion and this can further activate the RAAS.

The effect of pimobendan on left atrial pressure in dogs with mitral valve regurgitation

BACKGROUND

The effects of pimobendan on left atrial pressure (LAP) in dogs with mitral valve disease (MR) have not been documented in a quantitative manner.

OBJECTIVE

The objective was to document and study the short-term effects of pimobendan on LAP and echocardiographic parameters in MR dogs.

ANIMALS

Eight healthy Beagle dogs weighing 10.0-14.7 kg (3 males and 5 females; aged 2 years) were used.

METHODS

Experimental, cross-over, and interventional study. Dogs with surgically induced MR received pimobendan at either 0.25 mg/kg or 0.50 mg/kg p.o. q12h for 7 days and then, after a 7-day wash-out period, the other dosage. LAP was measured for 30 minutes at baseline and again on days 1, 2, 4, and 7 of pimobendan administration.

RESULTS

Mean LAP was significantly decreased after the administration of 0.25 mg/kg (15.81 ± 5.44 mmHg to 12.67 ± 5.71 mmHg, P < .001) and 0.50 mg/kg (15.76 ± 5.45 mmHg to 10.77 ± 5.23 mmHg, P < .001). Also, the 0.50 mg/kg group led to a significantly lower LAP (P < .01) compared with the 0.25 mg/kg group. Significant reduction was seen for the first time 4 days after the administration of 0.25 mg/kg and a day after the administration of 0.50 mg/kg.

CONCLUSIONS AND CLINICAL IMPORTANCE

Pimobendan decreased LAP in a dose-dependent manner in dogs with acute MR caused by experimental chordal rupture. This study did not evaluate adverse effects of high-dose pimobendan, and additional studies in clinical patients are warranted.

The influence of circadian variations on echocardiographic parameters in healthy people

BACKGROUND

Our aim was to investigate whether diastolic functions, myocardial velocities and pulmonary vein flow show diurnal variation within a 24-hour day.

METHOD AND RESULTS

Fourty-four healthy subjects with no history of cardiovascular or systemic diseases (32 males, 12 females; mean age 34.7 ± 8.7 years, mean BMI: 25.5 ± 3.5 kg/m(2)) were enrolled in this study. None of the subjects had a history, symptoms or signs of cardiovascular or systemic diseases or were taking drugs of any kind. All underwent echocardiographic examination at 7 a.m., 1 p.m., 7 p.m., and 1 a.m. M-mode systolic, diastolic velocities and pulmonary vein flow measurements were obtained. There were no differences in systolic and diastolic blood pressures and heart rate. The left atrial diameter was greater at 1 p.m. (3.80 ± 0.44; P = 0.031). The isovolumic contraction time (ICT) was found to be the shortest (41 ± 12 msn; P = 0.050), and ejection time (ET) the longest (290 ± 31 msn; P = 0.017) at the 1 am measurements. The mitral myocardial performance index (MPI) was lowest during the 1 a.m. measurements (0.42 ± 0.11; P = 0.001). The systolic myocardial velocities (Sm) obtained from the septum and inferior region were significantly higher at 1 p.m. and lower at 7 a.m. (9.17 ± 1.79, 10.25 ± 2.29; 8.11 ± 1.06, 8.63 ± 1.49; P < 0.05). The late diastolic velocities obtained from the lateral, inferior and anterior regions were higher at 1 p.m. and 7 p.m.

CONCLUSION

The left ventricular diameter and ejection fraction did not exhibit circadian variations. However, our data indicate that some parameters reflecting diastolic function, systolic myocardial velocities and MPI, as well as left atrial diameter change at different times of the day, independent of blood pressure and heart rate.

Echocardiographic estimation of left atrial pressure in beagle dogs with experimentally-induced mitral valve regurgitation

Non-invasive and immediate estimation of left atrial pressure (LAP) is very useful for the management of mitral regurgitation (MR), and many reports have assessed echocardiographic estimations of LAP to date. However, it has been unclear of which examination and evaluate article possess the best accuracy for the MR severity. The present research aims to establish the echocardiographic estimation equation of LAP that is well applicable for clinical MR dogs. After the chordae tendineae rupture was experimentally induced via left atriotomy in six healthy beagle dogs (three males and three females, two years old, weighing between 9.8 to 12.8 kg), a radio telemetry transmitter catheter was inserted, which allows the continuous recordings of LAP without the use of sedation. Approximately 5 weeks after the surgery, echocardiographic examination, indirect blood pressure measurement, measurement of plasma atrial natriuretic peptide (ANP) and LAP measurement by way of the radio telemetry system was performed simultaneously. Subsequently, simple linear regression equations between LAP and each variable were obtained, and the equations were evaluated whether to be applicable for clinical MR dogs. As a result, the ratio of early diastolic mitral flow to early diastolic lateral mitral annulus velocity (E/Ea) had the strongest correlation as maximum LAP=7.03*(E/Ea)-54.86 (r=0.74), and as mean LAP=4.94*(E/Ea)-40.37 (r=0.70) among the all variables. Therefore, these two equations associated with E/Ea should bring more precise and instant estimations of maximum and mean LAP in clinical MR dogs.

Detection of congestive heart failure in dogs by Doppler echocardiography

BACKGROUND

Echocardiographic prediction of congestive heart failure (CHF) in dogs has not been prospectively evaluated.

HYPOTHESIS

CHF can be predicted by Doppler echocardiographic (DE) variables of left ventricular (LV) filling in dogs with degenerative mitral valve disease (MVD) and dilated cardiomyopathy (DCM).

ANIMALS

Sixty-three client-owned dogs.

METHODS

Prospective clinical cohort study. Physical examination, thoracic radiography, analysis of natriuretic peptides, and transthoracic echocardiography were performed. Diagnosis of CHF was based upon clinical and radiographic findings. Presence or absence of CHF was predicted using receiver-operating characteristic (ROC) curve, multivariate logistic and stepwise regression, and best subsets analyses.

RESULTS

Presence of CHF secondary to MVD or DCM could best be predicted by E:isovolumic relaxation time (IVRT) (area under the ROC curve [AUC]=0.97, P<.001), respiration rate (AUC=0.94, P<.001), Diastolic Functional Class (AUC=0.93, P<.001), and a combination of Diastolic Functional Class, IVRT, and respiration rate (R2=0.80, P<.001) or Diastolic Functional Class (AUC=1.00, P<.001), respiration rate (AUC=1.00, P<.001), and E:IVRT (AUC=0.99, P<.001), and a combination of Diastolic Functional Class and E:IVRT (R2=0.94, P<.001), respectively, whereas other variables including N-terminal pro-brain natriuretic peptide, E:Ea, and E:Vp were less useful.

CONCLUSION AND CLINICAL IMPORTANCE

Various DE variables can be used to predict CHF in dogs with MVD and DCM. Determination of the clinical benefit of such variables in initiating, modulating, and assessing success of treatments for CHF needs further study.

The effect of angiotensin-converting enzyme inhibitors of left atrial pressure in dogs with mitral valve regurgitation

BACKGROUND

Despite many epidemiological reports concerning the efficacy of angiotensin-converting enzyme (ACE) inhibitors in dogs with mitral regurgitation (MR), the hemodynamic effects of ACE inhibitor administration have not been fully evaluated.

OBJECTIVES

To document left atrial pressure (LAP) in dogs with MR administered ACE inhibitors, in order to obtain interesting information about daily LAP changes with administration of ACE inhibitors.

ANIMALS

Five healthy Beagle dogs weighing 9.8 to 14.2 kg (2 males and 3 females; aged 2 years).

METHODS

Experimental, crossover, and interventional study. Chordae tendineae rupture was induced, and a radiotelemetry transmitter catheter was inserted into the left atrium. LAP was recorded for 72 consecutive hours during which each of 3 ACE inhibitors--nalapril (0.5 mg/kg/d), temocapril (0.1 mg/kg/d), and alacepril (3.0 mg/kg/d)--were administered in a crossover study.

RESULTS

Averaged diurnal LAP was significantly, but slightly reduced by alacepril (P = .03, 19.03 +/- 3.01-18.24 +/- 3.07 mmHg). The nightly drops in LAP caused by alacepril and enalapril were significantly higher than the daily drops (P = .03, -0.98 +/- 0.19 to -0.07 +/- 0.25 mmHg, and P = .03, -0.54 +/- 0.21-0.02 +/- 0.17 mmHg, respectively), despite the fact that the oral administrations were given in the morning. Systolic blood pressure (122.7 +/- 14.4-117.4 +/- 13.1 mmHg, P = .04) and systemic vascular resistance (5800 +/- 2685-5144 +/- 2077 dyne x s/cm5, P = .03) were decreased by ACE inhibitors.

CONCLUSIONS AND CLINICAL IMPORTANCE

ACE inhibitors decrease LAP minimally, despite reductions in left ventricular afterload. ACE inhibitors should not be used to decrease LAP.