Thermodilution and Echocardiography as an Assessment of Cardiac Function in the Cat. D.G. Allenand D. Nymeyer*. ABSTRACT. A technique for the determi-.
A Preliminary Investigation on the Use of Thermodilution and Echocardiography as an Assessment of Cardiac Function in the Cat D.G. Allen and D. Nymeyer*
ABSTRACT A technique for the determination of cardiac output in the cat by the thermal dilution method is described. The values of cardiac output assessed by thermal dilution and the values of left ventricular function assessed echocardiographically are compared. Values of cardiac output obtained by thermal dilution compare favourably with values obtained by other investigators by indicator dye dilution, the Fick method and electromagnetic flowmeter technique. The technique of thermal dilution in the cat was consistent and simple to perform. The calculation of ventricular volumes and cardiac output echocardiographically using formulae suggested in man was unsuccessful. Such formulae based on assumptions of cardiac shape and contractility do not appear valid in the cat. Statistical analysis demonstrated a positive correlation between the cardiac output determined by thermodilution and the left ventricular diastolic and systolic dimensions determined echocardiographically. A positive correlation was also shown between the cardiac output and the cardiac index, the left ventricular diastolic dimension and the left ventricular systolic dimension and the percent change in minor diameter and the velocity of circumferential
fibre shortening. A negative correlation existed between the left ventricular systolic dimension and the velocity of circumferential fibre shortening and the ejection time and the velocity of circumferential fibre shortening.
Key words: Cat, echocardiography, left ventricular function, thermodilution. RESUME Cet article decrit une technique destinee a determiner le debit cardiaque, chez le chat, a l'aide de la thermodilution. II compare aussi les valeurs du debit cardiaque, telles que determinees par la thermodilution, et les valeurs de la fonction du ventricule gauche, telles que definies par l'echocardiographie. Les valeurs du debit cardiaque, obtenues par la thermodilution, se comparaient avantageusement a celles que d'autres auteurs ont d6ji obtenues par la dilution d'un indicateur colore, la methode de Fick ou celle du debitmetre electromagnetique. Chez le chat, la technique de la thermodilution donna des resultats constants et s'avera simple a utiliser. Le calcul des volumes ventriculaires et du debit cardiaque, au moyen de l'6chocardiographie, en utilisant des formules sugg6r6es pour les humains, se r6v6la infructueux. Ces for-
mules, basees sur des hypotheses de conformation et de contractilite cardiaques, semblerent inapplicables au chat. Une analyse statistique demontra une correlation positive entre le debit cardiaque, determine par la thermodilution, et les dimensions diastolique et systolique du ventricule gauche, fournies par l'echocardiographie. Cette analyse revela une autre correlation positive entre le debit et l'index cardiaques, les dimensions diastolique et systolique et systolique du ventricule gauche, le pourcentage de changement de son plus petit diametre et la velocite du raccourcissement de la circonf6rence de ses fibres. Une correlation negative existait toutefois entre la dimension systolique du ventricule gauche et la v6locite du raccourcissement de la circonference et ses fibres, ainsi qu'entre le temps d'ejection et la v6locite du raccourcissement de la circonference de ses fibres. Mots cl6s: chat, echocardiographie, fonction du ventricule gauche, thermodilution.
INTRODUCTION The cat was chosen as the research subject because of the prevalence of cardiovascular disease (1) and the paucity of research on cardiac function in this species (2, 3).
*Department of Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, Ontario NlG 2W1. Submitted September 2, 1982.
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Can J Comp Med 1983; 47: 112-117.
The assessment of cardiac function is fundamental to the diagnosis, treatment and prognosis of cardiac disease. Cardiac performance is dependent on preload, afterload, contractility and heart rate (4). Cardiac ultrasound has been used to assess preload or left ventricular end diastolic diameter (LVDd), and the contractility or the velocity of circumferential fibre shortening (VcF) and the precent change in minor diameter (% dD). A simultaneous recording of an electrocardiogram (ECG) determines heart rate (HR). The advantages of echocardiography are that it is a noninvasive, safe technique that provides quantitative information on cardiac wall thicknesses, internal cardiac dimensions, valvular motion and ventricular function (5, 6, 7, 8). Echocardiography is used to assess ventricular function in the presence of cardiac disease and while under the influence of various pharmacological agents (4, 5, 7, 8, 9, 10, 11, 12). In man it has been significantly correlated to angiocardiography, dye dilution, Fick and thermal dilution techniques of determining cardiac function (10, 13, 14, 15, 16). Thermal dilution as an indicator of cardiac output was introduced by Fegler in 1954 (17). The technique has been validated in various species by comparison with Fick, dye dilution and the electromagnetic flowmeter for the determination of cardiac output (2, 15, 17, 18, 19, 20). The advantages of thermodilution are that it may be repeated many times, it is safe, reliable and reproducible. There is no recirculation of the injectate as occurs with indicator dye dilution, it is not influenced by peripheral blood flow and there is no residual dye accumulation to adversely affect repeat studies (19, 21). The principle disadvantages of thermodilution are that it requires
general anesthesia, fluoroscopy and/or pressure studies for accurate placement of the sensing devices. Intracardiac placement of catheters has in the past been technically difficult in small
animals (22); it tends to overestimate volumes in some species (17) and may by its own presence in the heart and outflow tracts adversely affect blood flow and its measurement (23). In spite of these problems thermodilution has proved to be a consistently reliable indicator of cardiac output (7). The purpose of this research was to establish a reliable and consistent technique for determining cardiac output by thermal dilution in the cat and to compare values obtained by this method with simultaneously determined values of ventricular function recorded echocardiographically.
judged to be free of significant cardiovascular disease based on physical examination, electrocardiogram and chest radiographs were used in this research (24). Cats were anesthetized with an intravenous bolus of sodium pentobarbital (Somnotol, MTC Pharmaceuticals, Hamilton, Ontario) at a dosage of 30 mg/kg (23). Echocardiographic and thermodilution studies were begun when the cats were in stage 3, plane 1 to 2 of anesthesia as judged by the absence of corneal and pedal reflexes in the presence of a slow and regular respiration, regular heart rate and normal capillary refill (5). For echocardiographic study the MATERIALS AND METHODS Electronics for Medicine, Echo IV Recorder (Echo IV, EchocardioA population of ten mature cats graphic/Simultrace Recorder, of either sex and any breed and Pleasantville, New York) was used L E F T
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