Transducer orientation for Doppler echocardiography in dogs

Use of aortic flow indexes derived from transthoracic echocardiography to evaluate response to a fluid challenge in anesthetized dogs

OBJECTIVE

To evaluate the ability of transthoracic echocardiographic aortic flow measurements to discriminate response to a fluid challenge (FC) in healthy anesthetized dogs.

STUDY DESIGN

Prospective experimental study.

ANIMALS

A total of 48 isoflurane-anesthetized dogs (14.2-35.0 kg) undergoing elective surgery.

METHODS

Fluid responsiveness was evaluated before surgery by FC (lactated Ringer's 10 mL kg^-1 intravenously over 5 minutes). Percentage increases in transpulmonary thermodilution stroke volume (ΔSV_TPTD) >15% from values recorded before FC defined responders to volume expansion. A group of 24 animals were assigned as nonresponders (ΔSV_TPTD ≤15%). When ΔSV_TPTD was >15% after the first FC, additional FC were administered until ΔSV_TPTD was ≤15%. Final fluid responsiveness status was based on the response to the last FC. Percentage increases after FC in aortic flow indexes [velocity time integral (ΔVTI_FC) and maximum acceleration (ΔVmax_FC)] and in mean arterial pressure (ΔMAP_FC) were compared with ΔSV_TPTD.

RESULTS

After one FC, 24 animals were responders. For nonresponders, ΔSV_TPTD was ≤15% after one, two and three FCs in eight/24, 15/24 and one/24 animals, respectively. The FC that defined responsiveness increased ΔSV_TPTD by 29 (18-53)% in responders and by 8 (-3 to 15)% in nonresponders [mean (range)]. The area under the receiver operating characteristics curve (AUROC) of ΔVTI_FC (0.901) was larger than the AUROCs of ΔVmax_FC (0.774, p = 0.041) and ΔMAP_FC (0.519, p < 0.0001). ΔMAP_FC did not predict responsiveness (p = 0.826). Best cut-off thresholds for discriminating responders, with respective zones of diagnostic uncertainty (gray zones) were >14.7 (10.8-17.6)% for ΔVTI_FC and >8.6 (-0.3 to 14.7)% for ΔVmax_FC. Animals within the gray zone were 17% (ΔVTI_FC) and 50% (ΔVmax_FC).

CONCLUSIONS AND CLINICAL RELEVANCE

Changes in VTI induced by FC can determine responsiveness with reasonable accuracy in dogs and could play an important role in goal-directed fluid therapy.

Echocardiographic indices in normal German shepherd dogs

Sixty clinically normal German shepherd dogs, 31 males and 29 females, ranging in age from 1 and 5 years and with a body weight ranging from 22 to 37.2 kg, were examined by the two-dimensional mode, M-mode, and Doppler echocardiography. In Doppler mode, the mitral valve flows were obtained, where the aim was to determine the velocity peaks and ratios of the E and A waves and the mitral E wave deceleration time. The velocity peaks were obtained for the tricuspid, pulmonary and aortic valves. On the left ventricular outflow tract flow, the time velocity integral and aortic cross-sectional area was used to calculate the cardiac output. A statistically significant correlation with the body weight was found for the systolic left atrial and diastolic aortic diameter on two-dimensional mode. On M-mode, there was a significant correlation between the body weight and the systolic left atrium and diastolic aortic dimension, systolic and diastolic left ventricular, septal and posterior wall dimensions. Doppler echocardiography showed that there was no significant correlation between the body weight and the mitral, tricuspid, pulmonary and aortic valves flows. These results demonstrate that it is important to know the normal echocardiographic values for German shepherd dogs because there are some characteristics peculiar to this particular breed. The data obtained is expected to be helpful for studies on small animal cardiology.

Ecocardiografia modo Doppler pulsado em gatos clinicamente sadios

Estudou-se o fluxo sangüíneo através das quatro valvas cardíacas em 30 gatos clinicamente sadios, com idade entre um e cinco anos e peso médio de 4,08kg, por meio da ecocardiografia modo Doppler pulsado. Foram medidas a velocidade máxima e a velocidade média dos fluxos, e realizou-se uma análise qualitativa dos seus perfis. Os animais foram sedados pela combinação de quetamina (12mg/kg) e acepromazina (0,04mg/kg), aplicados por via intramuscular. Observou-se correlação positiva entre os parâmetros avaliados e a freqüência cardíaca, com exceção daqueles medidos no fluxo da valva aórtica. Não se observou correlação entre velocidades máxima e média e freqüência cardíaca e entre aquelas e peso corporal, e não houve diferença entre sexos.

Effect of milrinone on echocardiographic parameters after single dose in Beagle dogs and relationship with drug-induced cardiotoxicity

The aim of this study was to further investigate the mechanism of development of cardiac lesions occurring under treatment with milrinone in dogs, by using echocardiography for assessing the effects of this drug on cardiac function. Milrinone is a cAMP phosphodiesterase 3 inhibitor having positive inotropic and vasodilatory effects. We treated groups of three dogs with milrinone at a single dose of 0.5 or 1 mg/kg and recorded M-mode and Doppler parameters at different time points before and after treatment. The hearts of the high-dose animals were histopathologically examined. The treatment with milrinone at 1 mg/kg produced mild cardiac lesions at two different locations. In the left ventricle, haemorrhages in the subendocardium and myocardium occurred in all three dogs. In the right atrium, subepicardial haemorrhages occurred in one dog and inflammation of the epicardium was observed in two dogs. These lesions were considered to be related to changes in the cardiac function, which were investigated by echocardiography. Milrinone treatment produced a moderate tachycardia and changes in M-mode parameters indicating an increase in contractility, in particular, a decrease in end-systolic volume, an increase in ejection fraction and an increase in the rate of circumferential fiber shortening. In addition, there was an increase in the maximal aortic flow velocity evaluated by Doppler measurements, which is thought to represent a haemodynamic correlate of an increase in left ventricular contractility. This increase in myocardial work is considered to play a key role in the development of the lesions observed in the left ventricle. Doppler measurements also revealed changes in the right atrioventricular flow, probably resulting from cardiac stimulation produced by milrinone. In particular, there was an increase in the Vmax of the A-wave of the tricuspid flow, suggesting an increase in contractility of the right atrium. This change, by increasing blood flow in atrial wall, may be involved in the induction of the lesions observed in the right atrium. In conclusion, Doppler and M-mode echocardiography are useful tools to assess haemodynamic changes occurring upon treatment with vasodilators or cardiac stimulants in order to further understand the mechanism of development of cardiac lesions produced by such compounds.

Long-term follow-up of dogs with patent ductus arteriosus

Postocclusion survival data from dogs with left-to-right shunting patent ductus arteriosus (PDA) was available from 80 dogs, diagnosed from 1990 to 2000. Of these, 37 had undergone a procedure to close the ductus and were re-evaluated at the time of this study; clinical data from the follow-up examination was compared with that from the original examination. Radiographically, the right ventricle remained apparently enlarged, and the aortic bulge associated with dilation of the descending aorta did not disappear after closure. On M-mode echocardiography, left ventricular chamber diameter in diastole and systole and left ventricular posterior wall in systole decreased significantly. Mitral endocardiosis was a common feature. Residual flow was evident in 46 per cent of the animals. Late closure occurred in 8 per cent of the dogs, and trivial recanalisation in 19 per cent. The maximum survival time postclosure was 168 months and, after non-occlusion, 114 months, suggesting that dogs with PDA follow an unpredictable course. However, there was a significant difference in survival times between the corrected and non-corrected group.

Ecocardiografia Doppler em cães neonatos

Utilizaram-se 10 cães neonatos (cinco machos e cinco fêmeas), obtidos a partir de cinco ninhadas (um casal de cada) com o objetivo de estabelecer o perfil ecodopplercardiográfico normal durante a fase neonatal (de um até 30 dias). Por meio do Doppler pulsado foram mensurados os picos de velocidade dos fluxos sangüíneos através das valvas mitral, tricúspide, aórtica e pulmonar. Observou-se correlação positiva de todas as mensurações com o peso corporal e a idade dos neonatos de ambos os sexos. Não houve diferenças significativas no padrão de velocidade dos fluxos sangüíneos estudados entre machos e fêmeas durante a fase neonatal.

Doppler echocardiography. II. Color Doppler imaging

Color Doppler imaging (CDI) is a sophisticated form of ultrasound technology that overlays blood flow and velocity information onto a B-mode, two-dimensional, gray-scale image. This imaging technique--also called color Doppler echocardiography, color-coded Doppler, Doppler color-flow imaging, and color-flow imaging--is a type of pulsed-wave Doppler echocardiography. Because the anatomical site of received Doppler-shift information can be readily determined, CDI is useful for documenting normal blood flow patterns and screening the heart and great vessels for areas of abnormal flow.

Doppler echocardiography. I. Pulsed-wave and continuous-wave examinations

Doppler echocardiography is a specialized processing of cardiac ultrasound that is characterized by a continuously updated display of blood velocity during the cardiac cycle. Doppler examinations, which include color-coded Doppler echocardiography, pulsed-wave examination, and continuous-wave studies, are readily applicable to veterinary patients.

Pulmonary venous flow characteristics as assessed by transthoracic pulsed Doppler echocardiography in normal dogs

Transthoracic Doppler echocardiography was used to evaluate the technique of measuring and normal patterns of pulmonary venous flow in fourteen normal dogs. Polyphasic pulmonary venous flow profiles were obtained in all dogs, consisting of one (S) or two (SE and SL) systolic forward flow waves, one early diastolic forward flow wave (D), one reverse flow wave (R) related to atrial contraction, and one reverse flow wave (R2) observed after cessation of systolic flow. Pulmonary venous flow was laminar in 9 dogs (65%). Maximal flow velocity during systole (0.39 +/- 0.14 m/sec) was significantly lower (P < 0.01) than in early diastole (0.56 +/- 0.14 m/sec). During late diastole peak flow velocity was 0.20 +/- 0.08 m/sec and maximum R2 velocity was 0.17 +/- 0.05 m/sec. Duration of mitral A-wave was significantly greater (P < 0.05) than R-wave duration in all dogs (0.075 +/- 0.010 vs 0.058 +/- 0.012 sec). These results can be used for comparison with patterns found in disease states.