Use of two- and three-dimensional echocardiography for assessment of the left ventricular outflow tract and aortic orifice areas in dogs

INTRODUCTION/OBJECTIVES

In clinical practice, dogs are screened for subaortic stenosis (SAS) using two-dimensional (2DE) and Doppler echocardiography. There is no accepted antemortem diagnostic criterion to distinguish between mild SAS and unaffected, therefore additional means of evaluating the left ventricular outflow tract (LVOT) and aorta may be desirable. This study sought to determine and compare LVOT and aortic orifice areas using 2DE and three-dimensional echocardiography (3DE) in apparently healthy dogs of various breeds and somatotypes.

ANIMALS, MATERIALS, AND METHODS

Sixty-nine healthy, privately-owned dogs. The LVOT and aortic orifice areas were determined using 2DE aortic valve (AV) diameter-derived area; the continuity equation (CE); and 3DE planimetry of the LVOT, AV, sinus of Valsalva, and sinotubular junction. Orifice areas were indexed to body surface area (BSA).

RESULTS

Obtaining 3DE images and performing planimetry were feasible in all dogs. The mean indexed area measured using the 2DE AV diameter (2.85 cm2/m2) was significantly lower than that derived from 3DE AV planimetry (3.85 cm2/m2; mean difference, 1.00 cm2/m2; P<0.001). There was poor agreement between the effective area calculated using the CE and the anatomic areas calculated using 2DE AV diameter and 3DE planimetry. The area calculated using the CE was less than all other calculations of area. Interobserver and intraobserver repeatability and reproducibility for 3DE planimetry were excellent.

CONCLUSIONS

Methods for determining aortic orifice areas in dogs are not interchangeable, and this must be taken into account if these methods are investigated in the evaluation of dogs with SAS in the future.

Effect of medetomidine on left ventricular outflow tract velocity in cats: A Doppler echocardiography study

The purpose of the present study was to evaluate effects of medetomidine on left ventricular outflow tract (LVOT) velocity in domestic short-haired cats. Eighteen healthy adult male domestic short-haired cats were used for this study. All animals were client-owned. Echocardiography machine with 7.50 MHz transducer was used. Specific veterinary two-dimensional and pulse-waved echocardiogram images in apical five chamber right parasternal view were obtained and blood velocity in LVOT was calculated. After baseline echocardiographic recordings, 0.04 mg kg^-1 of medetomidine was intramuscularly administered to each animal and LVOT velocity was calculated after 15 (T15), 50 (T30) and 80 (T80) min following drug administration. The LVOT velocity values (mean SEM) of cats in baseline were 1.06 0.04 m sec^-1. There were significant differences between baseline and T15 and T30 regarding mean LVOT values. Age and weight had no significant effect on LVOT velocity values. The LVOT velocity values of T15, T50 and T80 were 0.77 0.04, 0.80 0.02 and 0.960.03 m sec^-1, respectively. Our findings revealed significant decrease in mean LVOT velocity up to 50 min following medetomidine administration. The present study determined normal LVOT velocity range for a small population of cats before and after intra-muscular medetomidine administration.

Effects of the estrous cycle and pregnancy status on cardiovascular variables in healthy bitches

INTRODUCTION

The aim of the study was to characterize changes in maternal cardiovascular variables throughout the reproductive cycle in healthy bitches and determine whether magnitude of pregnancy-induced changes correlates to litter size.

ANIMALS

Eleven client-owned breeding bitches were included in the study.

MATERIALS AND METHODS

Bitches were enrolled prospectively and followed up longitudinally throughout a single reproductive cycle. Physical examination, echocardiography, blood pressure analysis, and plasma volume estimation were performed during proestrus, diestrus (early and late pregnancy), and anestrus. Fetal echocardiography was performed during late pregnancy. Data were compared across visits using a linear mixed-effects model, and correlation between variables was assessed.

RESULTS

Compared with proestrus, no significant changes were observed at any phase of the cycle in heart rate, blood pressure, echocardiographic measurements of left ventricular size or function, or echocardiographic calculations of stroke volume or cardiac output. Estimated plasma volume increased by 29.6% in early pregnancy (p < 0.001) and 70.7% in late pregnancy (p < 0.001). Fetal echocardiography was feasible in a subset of fetuses for each bitch. There was a significant correlation between estimated total fetal cardiac output and late pregnancy increase in maternal cardiac output (p = 0.0025). The incidence of physiologic heart murmurs ranged from 5 of 11 (45%) bitches in proestrus to 2 of 11 (18%) bitches in late pregnancy, attributed to variations in aortic outflow velocity.

CONCLUSIONS

Hemodynamic alterations in pregnant bitches do not result in consistently detectable echocardiographic changes, suggesting that cardiac screening could be diagnostic at any time during a reproductive cycle. Physiologic heart murmurs were common in this study population and not obviously associated with the reproductive cycle.

Echocardiographic evaluation of velocity ratio, velocity time integral ratio, and pulmonary valve area in dogs with pulmonary valve stenosis

Background

Velocity ratio, velocity time integral (VTI) ratio, and pulmonary valve area indexed to body surface area (iPVA) are methods of assessment of pulmonary valve stenosis (PS) severity that are less dependent on blood flow. Studies evaluating these methods are limited.

Objectives

To determine the effects of butorphanol, atenolol, and balloon valvuloplasty (BV) on velocity ratio, VTI ratio, iPVA, mean PG, and max PG.

Animals

Twenty‐seven dogs with PS (max PG >50 mm Hg).

Methods

Prospective study. All dogs underwent an echocardiogram at baseline, 5‐minutes after administration of butorphanol (0.2‐0.25 mg/kg IV), and 2‐to‐4 weeks after atenolol (1‐1.5 mg/kg q12h). Twenty‐one of these were evaluated 24‐hours after BV.

Results

There were no significant differences (P > .05) amongst any of the methods of assessment of PS severity after butorphanol. After atenolol, mean (SD) of mean (57.0 [21.0] mm Hg) and max PG (93.1 [33.8] mm Hg) were significantly decreased (P ≤ .047) compared with baseline (65.2 [26.2] mm Hg and 108 [44.4] mm Hg, respectively). After atenolol, there were no significant (P ≥ .12) differences in velocity ratio (0.29 [0.09]), VTI ratio (0.18 [0.05]), or iPVA (0.43 [0.16] cm²/m²) compared with baseline (0.30 [0.09], 0.19 [0.09], 0.44 [0.17] cm²/m², respectively).

Conclusions and Clinical Importance

Atenolol might reduce mean and max PG but does not alter less flow‐dependent methods of assessment of PS severity (velocity ratio, VTI ratio, and iPVA) in dogs with PS. Results support an integrative approach to assessment of PS severity that includes less flow‐dependent methods, particularly in states of altered flow or right ventricular function.