Equine echocardiography--sound advice at the heart of the matter

Congenital cardiac defects in neonatal foals: 18 cases (1992-2007)

BACKGROUND

Literature available regarding congenital cardiac defects in foals is limited to reports of individual cases or small case series.

OBJECTIVE

To describe the clinical, echocardiographic, and necropsy findings and breed predilection of congenital cardiac defects in neonatal foals.

ANIMALS

Eighteen foals < 15 days of age with 1 or more congenital cardiac defects.

METHODS

Medical records of foals diagnosed with congenital cardiac defects at the William R. Pritchard Veterinary Medical Teaching Hospital were reviewed. Data collected included history, signalment, clinical signs, laboratory data, diagnostic and necropsy results, and outcome.

RESULTS

Arabian foals represented 39% of cases with congenital cardiac defects and were significantly (P = .004) overrepresented (OR = 4.7 [CI: 1.8-12.4]) compared with the general hospital population. Ventricular septal defect (VSD) (14/18), tetralogy of Fallot (5/18), and tricuspid valve atresia (4/18) were the most common defects identified. A > or = 3/6 heart murmur (14/ 14) accompanied by tachycardia (14/17), tachypnea (17/17), and cyanosis of mucous membranes (7/16) were the most common clinical signs. Concurrent congenital defects were common (9/18). Two foals, both with VSD, survived for > or = 8 years after diagnosis and 1 was a successful performance horse.

CONCLUSIONS AND CLINICAL RELEVANCE

Arabian horses appear to have a predisposition for cardiac defects. The presence of a loud murmur (> or = 3/6), cyanotic membranes, and tachycardia or tachypnea in a neonatal foal should warrant thorough evaluation of the heart for congenital defects. Foals with cardiac defects should be closely evaluated for concurrent congenital defects in other body systems.

Sources and magnitude of variation of echocardiographic measurements in normal standardbred horses

The purpose of this study was to assess the intraobserver variation of various echocardiographic measures in standardbred trotters. Serial echocardiographic examinations were carried out on eight standardbred mares by one ultrasonographer for 5 separate days. During each examination, five nonconsecutive cardiac cycles (frames) were recorded and an average obtained for each individual measure. Various echocardiographic measures were obtained by use of two-dimensional (2-D), M-mode, color flow Doppler and pulsed wave Doppler echocardiography. The total variation in the echocardiographic measurements was split into three levels: the variation between horses, the day-to-day variation within individual horses, and finally the variation within horse on the same day of examination (intercardiac cycle variation). The intraclass correlation coefficient (ICC) was calculated for each measure. The ICC represents the variability of the measurements because of differences between the horses. In general the 2-D, M-mode and color flow Doppler measures had higher ICC values (ICC from 0.63 to 0.95) than the pulsed wave Doppler measures (ICC from 0.24 to 0.46), and the former measures were more repeatable than the pulsed wave measures. Exceptions to that were left ventricular free wall in diastole, the pulmonary artery in systole and the left ventricular mass, which all had low repeatability (ICC from 0.22 to 0.49). The results were used to calculate the relative differences that must be detected to diagnose a statistically significant change between two measurements in an individual horse. Differences from 4.2% to 21.8% must be achieved to document significant changes between serial measurements. A general tendency is that the color flow and pulsed wave Doppler measures require a larger relative difference (11.4-21.8%) between the measures to point out statistically significant cardiac changes than the 2-D and M-mode measures (4.2-13.9%).

Heart size estimated by echocardiography correlates with maximal oxygen uptake

Maximum oxygen uptake also appears to correlate to athletic performance in horses. In the Thoroughbred industry, there has long been an empirical theory that heart size is related to athletic performance, despite a lack of scientific evidence supporting this assertion. To investigate the relationship between peak oxygen consumption (VO2max) and cardiac size measured by echocardiography, guided M-mode and 2-dimensional echocardiography were performed in 17 conditioned Thoroughbreds with a range of VO2max from 126 to 217 ml/min/kg STPD (mean +/- s.d. 158 +/- 28 m/min/kg). Horses were age 2-10 years and weighed 430-510 kg. Echocardiography was performed using a Vingmed System V echocardiograph with a 2.25 MHz phased array ultrasound transducer. All images were obtained from the right hemithorax using a short axis view of the left ventricle (LV) at the level of the chordae tendinae. All horses were free from significant regurgitation at the aortic or mitral valves. Maximal oxygen uptake was measured during a standardised incremental treadmill exercise test to fatigue. Maximal oxygen uptake was correlated significantly with LVIDd (r = 0.71; P = 0.001), MWT (r = 0.72; P = 0.001), LV mass (r = 0.78; P = 0.0002) and LV short-axis area (r = 0.69; P = 0.003). When indices of heart size were indexed to bodyweight, the correlation between VO2max and indices of heart size were LVIDd (r = 0.57; P = 0.01), MWT (r = 0.44; P = 0.07), LV mass (r = 0.78; P = 0.0002) and LV short-axis area (r = 0.69; P = 0.003). The current study suggests there is a strong relationship between VO2max and measurements of left ventricular size in Thoroughbred horses when individuals with a range of VO2max are compared.

Cardiac responses to training in 2-year-old thoroughbreds: an echocardiographic study

Guided M-mode echocardiography was performed in seven 2-year-old Thoroughbreds before commencement of commercial flat-race training, and 18 weeks later, when all horses were either racing regularly (5 horses), or at racing fitness (2 horses). M-mode echocardiography was performed using a 2.5 MHz annular phased array ultrasound transducer and a Vingmed 800 Supervision echocardiograph. Images were obtained from the right hemithorax; a short axis view of the left ventricle (LV) at the level of the chordae tendinae was used to position the M-mode cursor. The following variables were measured: left ventricular (LV) internal diameter in diastole (LVIDd) and systole (LVIDs) and interventricular septal (IVS) and left ventricular free wall thickness (LVFW) in systole and diastole. The following variables were also calculated: LV fractional shortening (%FS), LV ejection fraction (EF), LV relative and mean wall thickness and muscle mass. Values before and after training were compared using a paired Student's t test. Training resulted in significant reductions in %FS and EF. Left ventricular internal diameter increased from 11.38 s.d = 0.58) cm before training to 12.16 (s.d. = 0.7) cm after training (P < 0.001). Calculated left ventricular mass also increased significantly (mean increase of 33% P < 0.001). Bodyweight was unchanged in the present study. Relative wall thickness was significantly increased in all horses, suggesting that eccentric cardiac hypertrophy occurs in response to commercial flat-race training. The mean post training value for relative wall thickness of 0.45 (s.d. = 0.05) for the horses in the present study is similar to that of human athletes in power/endurance disciplines.

Measurement of cardiac function by transthoracic echocardiography: day to day variability and repeatability in normal Thoroughbred horses

In order to assess the reliability and repeatability of transthoracic echocardiography for detecting serial changes in cardiac function in horses, day to day variability of a number of echocardiographic indices of ventricular function were studied. The variables investigated were, from 2-dimensional (2-D) and M-mode echocardiography - aortic diameter in systole (Aos), pulmonary artery diameter in systole (Pas), left ventricular internal diameter in systole (LLVIDs) and diastole (LLVIDd), and left ventricular fractional shortening (%FS) and estimated ejection fraction (EF). From pulsed Doppler echocardiography - maximum velocity (Vmax) and acceleration (dv/dtmax) of aortic and pulmonary arterial blood flow, left and right ventricular velocity time integral (AoVTI and PAVTI) and estimated cardiac output (COLV, and CORV), left and right ventricular ejection time (LVET and RVET) and pre-ejection period (LVPEP and RVPEP), and heart rate. Maximum velocity of early rapid right ventricular filling (ETV) and late right ventricular filling due to right atrial contraction (ATV) were measured. Maximum deceleration and time for deceleration of early rapid filling (dv/dtTV and dt TV) were also determined. Seven healthy mature Thoroughbred horses weighing 490-600 kg were studied. The horses' management regimes and environment were standardised and an echocardiographic examination was carried out on each horse at the same time every day for 6 consecutive days. Two statistical measures of repeatability were calculated for each variable: the intraclass correlation coefficient (rI) and the 95% confidence intervals for error free value of a single measurement. In general, the dimensions and indices of cardiac function derived from 2-D and M-mode echocardiography showed better repeatability for individual horses than did the indices derived from Doppler echocardiography. Overall the 95% confidence intervals for an error-free value of all variables derived from Doppler echocardiography were wide. This must be appreciated when attributing serial measured changes of Doppler echocardiographic variables in an individual animal to effects of a treatment or disease.