Advance Publication
The Journal of Veterinary Medical Science Accepted Date: 24 Nov 2016 J-STAGE Advance Published Date: 16 Dec 2016
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Internal Medicine
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FULL PAPER
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Effects of Postural Change on Transesophageal Echocardiography Views and
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Parameters in Healthy Dogs
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Seijirow Goya 1) *, Tomoki Wada 1), Kazumi Shimada 1), Daiki Hirao 1), Ryuji
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Fukushima 1), Norio Yamagishi 2), Miki Shimizu 3) and Ryou Tanaka 1)
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1)
Department of Veterinary Surgery, Faculty of Veterinary Medicine, Tokyo
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University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo, 183-
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0052, Japan
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2)
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University, 3-18-8 Ueda-cho, Morioka-shi, Iwate, 020-8550, Japan
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3)
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Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi,
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Tokyo, 183-0052, Japan
Department of Veterinary Clinical Medicine, Faculty of Agriculture, Iwate
Department of Veterinary Diagnostic imaging, Faculty of Veterinary Medicine,
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*Correspondence to
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Goya S., Department of Veterinary Surgery, Faculty of Veterinary Medicine, Tokyo
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University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo, 183-
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0052, Japan. e-mail:
[email protected]
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Running head
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EFFECTS OF POSTURAL CHANGE ON TEE PARAMETERS 1
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ABSTRACT The purpose of the present study is to investigate the effect of postural change on
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transesophageal echocardiography (TEE) views and parameters of interest anesthesia
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monitoring in healthy dogs. Twelve Beagle dogs were anesthetized and randomly
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positioned in one of four postures: right lateral-recumbency, left lateral-recumbency,
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supine position and prone position. After examinations in one posture, the same
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examination was demonstrated in another posture and repeated in all postures. In each
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posture, several standard TEE views were demonstrated: longitudinal cranial-
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esophageal aorta long-axis-view, transverse middle-esophageal mitral valve long-
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axis-view and transgastric middle short-axis-view. Additionally, echocardiographic
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parameters were attempted to measure, and direct blood pressure monitoring was
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performed in each view. As a result, oriented views, except for transgastric middle
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short-axis-view, could be obtained in all postures. Stroke volume and peak early
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diastolic velocity of mitral inflow were lower in supine position compared with those
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in right and left lateral-recumbency. Heart rate (HR) and systemic vascular resistance
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were higher in supine position compared with those in right and left lateral-
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recumbency. Left ventricular pre-ejection period/left ventricular ejection time
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corrected and uncorrected by HR were higher in supine position compared with those
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in right and left lateral-recumbency. In conclusion, longitudinal cranial-esophageal
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aorta long-axis-view and transverse middle-esophageal mitral valve long-axis-view
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provide useful information of interest anesthesia monitoring, because of their views
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enable to certainly obtain TEE parameters in various postures. Furthermore, TEE
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parameters allow to detect the changes of preload, afterload and HR that occur in
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supine position dogs. 2
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KEY WORDS: cardiovascular system, dog, echocardiography, ultrasound
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In human medicine, transesophageal echocardiography (TEE) has been recognized
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as a useful tool not only for diagnosis of congenital heart disease [14, 24] and for an
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assessment tool of interventional cardiology [1, 28], but also for a noninvasive
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intraoperative monitoring of cardiac function in patients with severe conditions, such
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as heart failure [10, 31, 34]. Although TEE has been mainly used as an assistant tool
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for catheter intervention in veterinary medicine [23, 30, 33, 35], few reports on the
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intraoperative cardiac evaluation are available in dogs with heart failure. To enhance
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anesthetic safety, intraoperative blood pressure has been monitored by way of
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prevention of acute renal disorders and cerebral ischemia [21].
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Considering fully understanding of intraoperative hemodynamics, however, blood
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pressure measurement alone is not always the answer to explain the mechanism of
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hypotension. Hypotension can be caused by several factors: decrease in preloa d,
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afterload, and contractility and echocardiographic measurements allow to reveal these
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cardiac information during surgery. For the intraoperative echocardiography
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monitoring under anesthesia, animal positions undergoing surger y usually depend on
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the operative procedure and transthoracic echocardiography is sometimes unavailable
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for evaluation. Therefore, TEE parameters should be the only option for the purpose
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of intraoperative monitoring. Several experimental reports addressing the utility of
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TEE parameters in evaluating canine cardiac function were performed only in lateral-
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recumbency [7, 13]. Postural change may alter the positional relation of the
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intrathoracic organs and influence echocardiographic views, and the effects of
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postural differences on TEE views and parameters should be considered. The present
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study was conducted to elucidate the effects of postural change on conventional TEE
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views and echocardiographic parameters.
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MATERIALS AND METHODS
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During the study, the dogs were managed and cared for in accordance with the
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standards established by the Tokyo University of Agriculture and Technology
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(TUAT) and described in its ‘‘Guide for the Care and Use of Laboratory Animals.”
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This study was approved by the Experimental Animal Committee of TUAT
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(acceptance no. 26-87).
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Animals: We used twelve, 1- to 2-year-old Beagle dogs (8 males and 4 females)
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weighing 10.0 ± 1.0 kg (range, 8.4 - 11.7 kg). The dogs were evaluated with general
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physical examination, blood and serum biochemical evaluations, electrocardiography,
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thoracic radiography and echocardiography, and then, all were declared as healthy.
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Anesthesia and preparatory procedures: Dogs were premedicated with meloxicam
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(0.2 mg/kg, SC), butorphanol tartrate (0.2 mg/kg, IV) and midazolam hydrochloride
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(0.2 mg/kg, IV). Induction was achieved with propofol (4 mg/kg, IV), after which the
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dog was intubated. Anesthesia was maintained by administering a mixture of 1.5 -
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2.0% isoflurane and oxygen. The respiratory rate and airway pressure were
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maintained with a mechanical ventilator. End-tidal CO 2 was monitored and
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maintained between 35 and 45 mmHg using a monitoring instrument. A 5 MHz rotary
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plane transesophageal probe (Aloka UST-52119S, Hitachi Aloka Medical, Tokyo,
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Japan) connected to an ultrasound machine (Prosound α10, Hitachi Aloka Medical)
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was navigated according to the technique as described in literatures [9, 19]. The dogs
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were randomly positioned in one of four postures: right lateral recumbency, left
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lateral recumbency, supine position and prone position. After the examination in a 4
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posture was finished, another posture was selected randomly, and then, the dogs were
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changed their position quietly. This process was repeated consecutively until the end
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of examination in all postures. In each posture, the examination was conducted for at
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least 10 min after hemodynamics stabilization was achieved.
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TEE measurements: In accordance with reports [9, 19], the following three views
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were attempted to be displayed in each posture. Echocardiographic measurements
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were performed at the end of the expiration period. Data was collected and analyzed
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by a single investigator. The mean value of 3 heart beats was calculated excluding the
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maximum and minimum values among the 5 consecutive cardiac cycles.
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Longitudinal cranial-esophageal aorta long-axis-view: The probe was inserted in the
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cranial esophagus in neutral position (not flexed). Then, the transducer tip was
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retroflexed (bend backward) and advanced caudally until an image of the heart base
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was produced [9]. With the array angle set to 75°-85°, longitudinal views were
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obtained. By orienting the beam centrally, the aortic arch could be seen. The sample
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volume was placed at the place between pulmonary artery and right auricle in the
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center of ascending aorta (Fig. 1). Stroke volume (SV) and cardiac output (CO) were
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calculated using the cross sectional area of the aorta. Left ventricular pre-ejection
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period (LVPEP) and ejection time (LVET) were measured, and LVPEP per LVET
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ratio (LVPEP/LVET) was calculated by using pulsed Doppler in conjunction with
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electrocardiography. The HR-corrected left ventricular ejection time (LVETc) and
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LVPEP per LVETc ratio (LVPEP/LVETc) were calculated according to the report
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[29]. HR is determined from the RR intervals of the beats immediately after preceding
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those measured.
5
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Transverse middle-esophageal mitral valve long-axis-view: From cranial-esophageal
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position, by further advancing the probe in neutral position until the point in which
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interference by the trachea was no longer present, middle-esophageal position views
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could be produced. A 4 chamber long axis view could be achieved with 0° array angle
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from this position [9, 19]. Doppler inflow across the mitral valve was measured by
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use of this view, with the 2 mm sample volume positioned at the tip of the mitral
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valve (Fig. 2). The transmitral flow velocities were measured to determine the pe ak
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early diastolic velocity (E) and peak atrial systolic velocity (A), and peak early
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diastolic velocity per peak atrial systolic velocity ratio (E/A) was calculated. After
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that, tissue Doppler echocardiographic examination was performed by use of the same
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view. The sample volume was placed at the septal mitral annulus, and the peak
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systolic velocity of mitral annulus (Sm), the peak early diastolic velocity of mitral
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annulus (Em), peak atrial systolic velocity of mitral annulus (Am) and peak early
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diastolic velocity per peak early diastolic velocity of mitral annulus ratio (E/Em) were
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determined.
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Transgastric middle short-axis-view: The probe was advanced into the stomach until
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the liver image was seen on the screen. The transducer tip is then completely
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anteflexed (bend forward), and the whole probe is slightly pulled to have the stomach
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wall adhere [9, 19]. Loyer and Thomas reported [19] that there is a short-axis-view of
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the left ventricle at the level of the papillary muscles. The short-axis-view image of
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the left ventricle was attempted to measure certain parameters.
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Arterial blood pressure measurements: In a total of dogs, 24-gauge intravenous
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catheter was inserted into the dorsalis pedis artery for direct pressure monitoring [40].
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The invasive arterial blood pressure was directly recorded by means of a pressure 6
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transducer (DX-300, Nihon Kohden, Tokyo, Japan) connected to the catheter. Systolic
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arterial pressure (SAP), mean arterial pressure (MAP) and HR were determined from
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the arterial pulse and recorded by use of the monitoring instrument. Systemic vascular
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resistance (SVR) was calculated as SVR (Wood) = (MAP - central venous
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pressure)/CO [41]. Central venous pressure was defined as 5 mmHg, considering a
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lack of right atrium enlargement or jugular distension.
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Statistical analysis: All data are reported as mean ± standard deviation (SD). The
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differences among postures in normally distributed data were analyzed using one -way
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repeated measures analysis of variance and Tukey’s multiple comparisons test. Non -
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normally distributed data were analyzed using the Kruskal -Wallis test and Dunn’s
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multiple comparisons test. Linear regression analysis for R and P values was
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conducted to determine the Pearson correlation coefficient. Statistical significance
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was defined as P < .05. GraphPad Prism (GraphPad Prism version 5.0a, GraphPad,
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San Diego, CA, U.S.A.) was used to perform these statistical analyses.
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RESULTS
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Longitudinal cranial-esophageal aorta long-axis-view was obtained by the same
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technique among any posture in all dogs. In regard to the effects of postural change
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on echocardiographic parameters, SV and LVET in supine position were significantly
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lower compared with those in right and left lateral-recumbency. LVPEP was
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significantly prolonged in supine position compared with that in right and left lateral-
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recumbency. LVPEP/LVET and LVPEP/LVETc were significantly higher in supine
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position compared with those in right and left lateral-recumbency (Table 1).
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Transverse middle-esophageal mitral valve long-axis-view was obtained by the same technique among any posture in all dogs. E was significantly lower in supine position 7
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compared with that in right and left lateral-recumbency. Em was significantly lower
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in supine position compared with that in right and left lateral-recumbency, and
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significantly lower in prone position compared with right lateral -recumbency (Table
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2).
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Transgastric middle short-axis-view was not obtained by the clear image among any posture in all dogs.
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HR and SVR increased significantly in supine position compared with those in right
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and left lateral-recumbency. SAP, MAP and DAP did not show significant differences
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among postures (Table 3). Fig. 3-1 and 3-2 shows the correlation between HR and
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SV, LVET. HR was weakly correlated with SV (P < 0.0001, R= -0.55) and LVET (P
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= 0.0005, R = -0.48).
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DISCUSSION In the present study, conventional TEE techniques allowed to display longitudinal
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cranial-esophageal aorta long-axis-view and transverse middle-esophageal mitral
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valve long-axis-view and to measure echocardiographic parameters in any posture.
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On the other hand, the present study also revealed the difficulty of obtaining
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transgastric middle short-axis-view with TEE in any posture. Loyer and Thomas
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reported [19] that transgastric middle short-axis-view could seldom be obtained by
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TEE in dogs, lacking image or additional useful information. Unlike in humans, the
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anatomical spatial gap between the heart and stomach results from the vertical
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positional relationship between the cardiac longitudinal axis and esophagus. This is
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why the transgastric middle short-axis-view was not available in dogs.
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In human medicine, transgastric middle short-axis-view is used for the calculation of
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fractional area change, which is a reliable, quick index of cardiac contractilit y [32].
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Fractional shortening, an index of contractility, measured in transgastric middle short-
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axis-view, is also obtained using transthoracic echocardiography in veterinary
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medicine. Sm, which correlated with the peak value of the positive first derivative of
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left ventricular pressure, is detectable in transverse middle-esophageal mitral valve
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long-axis-view. Longitudinal cranial-esophageal aorta long-axis-view also can show
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SV and CO and provides the important information related to anesthesia monitoring.
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The longitudinal cranial-esophageal aorta long-axis-view and transverse middle-
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esophageal mitral valve long-axis-view are views available for contractility
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monitoring in any postures in dogs.
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The decrease in SV and the increase in LVPEP/LVET and LVPEP/LVETc were
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observed in supine position compared with that in right and left lateral-recumbency in
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the present study. Several studies have reported that the corrected and uncorrected
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LVPEP/LVET are better correlated with the ejection fraction, dP/dt and SV [6, 11,
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12, 22]. These results show a reduction in pump function in supine position. This
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hemodynamic change could be considered to be caused by several factors: an increase
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in afterload, a decrease in preload and a reduction in cardiac contractility. However,
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the effect of the reduction in contractility is likely negligible, because a significant
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difference was not observed in Sm. The increase in SVR shows the increase in
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afterload in supine position than right and left lateral -recumbency. The preload was
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decreased in supine position, as shown by the reductions in E and Em [26]. LVETc is
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a preload indicator [16, 20]; however, LVETc is also affected by afterload [36] and
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cardiac contractility [2, 18]. Unchanged LVETc indicates the simultaneous decrease 9
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of preload and/or the increase of afterload. A prolonged LVPEP indicates the increase
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in afterload and/or depression of cardiac contractility [4, 42]. To summarize the
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above, the reduction of pump function in supine position was caused by the increase
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in afterload and the decrease in preload. Postural change significantly affects
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hemodynamics in human [8, 17, 37-39] and animals [3, 15, 27]. In normal pregnant
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women, cardiac output was increased by postural change from supine to lateral
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position [17, 38, 39]. Compression and relief of the inferior vena cava by the gravid
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uterus caused this physiological phenomenon. Furthermore, the decrease in cardiac
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output was observed in not only pregnant women but also anesthetized dogs [27].
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Nakao et al. suggested that the preload reduction in supine position resulted from the
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compression of the inferior vena cava by intra-abdominal organs [27]. Hoffman et al.
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also observed altered SV caused by postural change, which is associated with the
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Frank-Starling mechanism [15]. If the compression of the inferior vena cava by intra-
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abdominal organs occurs also in our study, the increase in afterload might also be
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derived from the compression of the celiac artery. The reduction of SV along with
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postural change is a physiological change, detected and assessed by TEE parameters.
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Furthermore, the postural change influenced the modulation of the cardiac
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autonomic nervous system [5, 25]. Cardiac vagal activity is greatest in right lateral-
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recumbency, and the sympathetic tone is increased in supine position in normal
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human subjects [5] and patients with congestive heart failure [25]. The finding that
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HR was higher in supine position than in lateral-recumbency concurs with the canine
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study made by Bornscheuer et al [3]. Consequently, CO was unchanged due to the
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rise of HR compensating for the reduction in SV. The rise of HR along with postural
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change related to the variation of several TEE parameters, such as SV and LVET, and 10
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significant difference is not found in CO and LVETc among 4 postures. The effect of
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HR should be considered when assessing cardiovascular function using TEE.
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Longitudinal cranial-esophageal aorta long-axis-view and transverse middle-
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esophageal mitral valve long-axis-view provide the same views and stable parameters
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in any posture: however, some parameters are influenced by the physiological
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changes in supine position.
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A limitation of the study reported here is that no catheter examination was
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performed for the accurate assessment of cardiac function. There may be some
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differences between the actual values obtained using a catheter and the TEE
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parameters. Therefore, the dogs in this study are all normal, so we cannot reveal
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whether the healthy dogs are the same as the dogs with cardiovascular disease. Also,
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we cannot exclude the possibility of the anesthetic effect on the TEE parameters.
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Finally, only 1 breed of 1 particular body weight and chest conformation was assessed
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in our study. The results might not be automatically transferable to dogs of different
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breeds, age, body weights and chest conformations.
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Although postural effects on TEE parameters must be considered, longitudinal
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cranial-esophageal aorta long-axis-view and transverse middle-esophageal mitral
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valve long-axis-view obtained using TEE provide useful information for monitoring
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intraoperative hemodynamics in dogs.
257 258
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FIGURE LEGENDS
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Fig. 1. Longitudinal cranial-esophageal aorta long-axis-view was obtained with the
396
array angle set to 75-85°. The sample volume was set at 2 mm and was located in the
397
center of the ascending aorta between PA and Rau. LVPEP was the duration from Q
398
of ECG to left ventricular ejection onset. LVET was duration of the blood flow from
399
the left ventricular. PA: pulmonary artery; Rau: right auricle; LVPEP: left ventricular
400
pre-ejection period; LVET: left ventricular ejection time.
401 17
402
Fig. 2. Transverse middle-esophageal mitral valve long-axis-view was obtained with
403
the array angle set to 0°. The sample volume was set at 2 mm and was placed at the
404
tip of mitral valve. LA: left atrium; LV: left ventricle; MV: mitral valve; RA: right
405
atrium; RV: right ventricle; E: the peak early diastolic velocity; A: the peak atrial
406
systolic velocity.
407 408
Fig. 3-1. Relationship between SV and HR in all postures. A significant negative
409
correlation was found between SV and HR. SV: stroke volume; HR: heart rate.
410 411
Fig. 3-2. Relationship between LVET and HR in all postures. A significant negative
412
correlation was found between LVET and HR. LVET: left ventricular ejection time;
413
HR: heart rate.
414
18
FIG. 1
FIG. 2
FIG. 3-1
FIG. 3-2
Table 1. Mean ± SD values for the aortic flow parameters obtained from longitudinal cranial-esophageal aorta long-axis-view in 4 postures (n = 12)
Posture Left lateralRight lateralVariable Supine position Prone position recumbency recumbency SV (ml) 14 ± 3 14 ± 2 13 ± 3 10 ± 3a,b) CO (l/min) 1.3 ± 0.3 1.3 ± 0.3 1.0 ± 0.3 1.2 ± 0.2 a,b) LVPEP (ms) 61 ± 5 59 ± 5 66 ± 9 72 ± 11 a,b) LVET (ms) 210 ± 9 212 ± 15 201 ± 20 185 ± 11 LVPEP/LVET 0.29 ± 0.03 0.28 ± 0.03 0.33 ± 0.06 0.40 ± 0.08a,b) LVETc (ms) 338 ± 21 337 ± 17 338 ± 29 335 ± 25 a,b) LVPEP/LVETc 0.29 ± 0.02 0.28 ± 0.02 0.31 ± 0.03 0.35 ± 0.04 SV: stroke volume; CO: cardiac output; LVPEP: left ventricular pre-ejection period; LVET: left ventricular ejection time; LVPEP/LVET: a ratio of PEP to ET; LVETc: HR-corrected LVET; LVPEP/LVETc: a ratio of LVPEP to LVETc. a) Significant difference with left lateralrecumbency (p
