Observations on Surgically Induced Insufficiency of the Canine Mitral Valve

Br. vet. J. (1972), 128, 567

OBSERVATIONS ON SURGICALLY INDUCED INSUFFICIENCY OF THE CANINE MITRAL VALVE By

W. E. D.

B OUSF I ELD AND

N . L . R.

BO W D EN

D epartm ent of M edicine, T he R oyal Veterinary College, a nd G uy's H ospital M ed ical School, London

SUMMA RY

Insufficiency of the mitral valve was produced surgically in 7 young male beagles. Clinical , radiological, haemodynamic, electrocardiographical and serum biochemical parameters were measured during the pre- and postoperative periods. Following post-mortem examination, lungs were examined histologically. Individual dogs were observed post-operatively for periods ranging from I to 20 weeks and on clinical, radiological and haemodynamic assessmen t could be divided into two groups . Group I showed marked passive pulmonary hypertension and an unusual pattern of exercise intolerance. Group II resembled clinical cases of mild left heart failure with compensation . Each group showed a definite sequence of cardiomegaly. A consistent feature was localized dilatation of the main pulmonary artery. Lung histology revealed mainly vascular congestion, with a relatively high in cidence of inflammatory change.

I NT ROD UCT IO N

The creation of mitral insufficiency in the d og can p roduce a useful experimental model for study of the sequelae to left h eart failure. A recent research programme required this procedure to be undertaken in a sm all number of dogs of standard type, and provided an oppor tunity for the furth er investigation and correlation of p ara m eten relevant to this condition. Hall er & Morrow (I 95Sa, b) publish ed observations on left atrial pressure changes and lung histology in dogs following section of mitral chordae tcndineae and valve cusp damage. Moscovitz, D onoso, Gelb & ' Vilder ( 1963), using similar preparations, d escribed changes in left a trial and ventricular pressure waves and discussed some of the implications regarding pulmonary circulation. The same workers also carried out acute exp eriments in w hich thin-walled tubes were used to dilate the mitral valve ring, a nd related d egree of dilatation to gross haemodynamic disturbance. Ettinger & Buergelt (1969) h ave reported on 28 cases of spontaneous rupture of chordae tendineac of the canine mitra l valve, but in m a ny of these dogs the tricuspid chordae were also involved. The authors recorded , where pos~ibl e, clinical, electrocardiographical, radiological , and p ost-mortem findings.

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BRITISH VETERINARY JOURNAL,

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MATERIALS AND METHODS

The programme for each dog comprised the initial monitoring of chosen parameters for the establishment of control values, followed by cardiac surgery and re-monitoring over a variable period of time. The duration of the latter period was dependent upon the progress of an individual animal, criteria for euthanasia being signs of obvious distress or imminent collapse, or failure to show further significant changes. Animals and management All dogs were young mature male beagles, purpose-bred and vaccinated against canine distemper and viral hepatitis. Routine m anagement was standardized as far a~ possible, the diet consisting of a proprietary canned meat and biscuit, with free access to fluid . During the post-operative period animals were initially subjected to cagerest, restricted exercise being gradually introduced under careful supervision. ' /Vith the exception of antibiotics and analgesics, no therapeutic substances were administered. Cardiac surgery Preliminary research confirmed that in the absence of cardiac bypass or hypothermia, section of chordae tendineae remained the only reliable method of creating significant and permanent mitral regurgitation in a small dog. In spite of the preference stated by Haller & Morrow (I955a) for a ventricular approach to the valve, the left atrial route was chosen as it appeared to reduce the risk of immediate loss 01 monitored dogs. Thoracotomy via the left fourth intercostal space permitted exposure and anchorage of the left atrial appendage, which was incised within the confines of a pre-placed ligature. Using a special bistuary, sufficient chordae tendineae were sectioned to produce a thrill in the left atrial wall. Repair was conventional with the exception of complete ligation of the tip of the friable atrial appendage. The generous pericardial incision was not closed. Owing to the magnitude of haemodynamic changes, the measurement of intracardiac pressures during valvular surgery gave little indication of the degree of insufficiency being created, and the results of surgery were unpredictable at the time. Suitable general anaesthesia and careful attention to fluid and electrolyte balance limited the immediate mortality rate to approximately 25 per cent. Good nursing, with adequate antibiotic and analgesic therapy, generally resulted in a remarkably uneventful post-operative recovery. Selected parameters Clinical observations Bodyweights were checked and clinical examinations performed at regular intervals. Particular attention was paid to the effects of any exercise. H aemodynamics After standard premedication and thiobarbiturate induction, general

EXPERIMENT AL INSUFFICIENCY OF CANI NE MITRAL VALUE

569

anaesthesia was maintained by means of a non-rebreathing positive pressure circuit incorpor ating a Fluotec * vapouriser. Hyperventilation with h alothane/ oxygen mixtures p ermitted the maintenance of a light but stable plane of anaes thesia, with satisfactory control of blood pressure. Pressures. Catheter/m anometer systems were checked for ad equa te frequency response and suitable d amping char acteristics. Manometers were set for zero at a level of IO em above the table-top. A selected pr essu re was recorded simultaneously together with femoral arterial pressure and the electrocardiogram, femoral systolic pressure being sta ndardized for a n individual animal on consecutive occasions. Routine recordings wer e ob tained of right a trial, right ventricular, main pulmonary artery, pulmonary a rtery wedge and left ventricular pressures. Although it was often possible to obtain left a trial traces by r etrograde catheterization from the left ventricle, r ecorded pressures were not r elia ble. The wedge pressure was therefore of p articular value in view of its close correlation with ,mean left atrial pressu re and probable independ ence of pulmonary vascula r r esistance (Pakrashi, Pelides, Stoker & T aylor, 1970). As changes in complianc e of the thorax produced variable elevation of recorded pressures, for the purpose of interpreta tion all pressures were adjusted to bring right and left minimal ventricula r pressures to zero. The validity of this adjustment was verified by checking that left ventricular end-diastolic pressure closely ma tched the corresponding pressure in the ,main pulmonary artery-a condition which should obtain in the unventilated subj ect (F alicov & R esnekov, 19 70). Cineangiography . Following th e method described by Gribbe, Hirdonen, Lind & Wegelius (1959) a 35-mm cinecamera was used to r ecord single-plane cardioangiogram s, using a right oblique proj ection. Contrast ,medium was administered into the m ain pulmonary artery via a cardiac catheter connected to highpressure injection equipment. ,,yhere radiographic d efinition was adequate and cardiac rhythm normal, m easurements from individual control and post-oper ative films permitted the calculation of changes in left ventricular stroke volume and minute " output", apparent increases in both values substantially reflecting the d egree of mitral regurgitation produced. From these films it was also possible to estimate changes in pulmonary circulation time.

Plain thoracic radiography In each case a series of dorsoventral and lateral radiographs was taken at appropriate intervals. Individual X-ray exposures were standardized. Dogs were positioned accurately und er general anaesthesia and endotracheal intubation permitted comparable d egrees of chest inflation. Cardiac outline was m easured on dorsoventral films and the r esults analysed according to the criteria d escribed by Hamlin (1968), but evaluation was always based upon both views. Films were assessed for pulmonary or incidental radiopathology.

* Cyprane L td.

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Electrocardiography In addition to routine monitoring during catheterization and surgical sessions, regular recordings were made oflimb leads I, II, III and A.V.F. in the conscious animal. Biochemistry Serial samples of blood were submitted for determination of serum alkaline phosphatase (SAP) and serum glutamic pyruvic transaminase (SGPT) levels. No blood was collected for these purposes for one week following cardiac catheterization or surgery. Post-mortem findings General examination of the cadaver was followed by detailed study of the heart, which was assessed for dilation and/or hypertrophy and damage to the mitral valve. Lung histopathology Lungs were fixed in natural distension by the introduction of formalin solution into the trachea and ligation of the bronchial tree. Blocks of tissue were taken from standard sites and stained by haematoxylin and eosin, Van Gieson, periodic-acid-Schiff and Lillies allochrome techniques. RESULT S

Clinical, haemodynamic and radiological findings These parameters are considered collectively since they permit the division of animals into two small but distinct groups. Group 1. Of the five dogs in this group, three were observed post-operatively for periods of from three to four weeks, with completion of an adequate monitoring programme prior to sacrifice. One of these three animals ("Joe") became febrile after two weeks and developed bronchopneumonia, which responded to antibiotic therapy. The remaining two dogs both succumbed to an isolated episode of peracute pulmonary oedema which occurred approximately one week after surgery. Following resolution of postoperative discomfort, clinical findings in animals subjected to cage rest with restricted exercise may be summarized as follows. General condition remained satisfactory, and malaise was minimal or absent. Pulse rates were consistently increased and were of the order of 150/min, but pulse volumes differed from day to day and could be correlated with varying degrees of pallor of mucous membranes. Respirations were normal in character but a slight increase in rates was noted. Auscultation revealed a grade III or IV mitral systolic murmur accompanied by a faint but coarse precordial thrill. Lung sounds were normal. The effects of a short period of brisk exercise were dramatic but delayed and transient. Within twelve to twenty-four hours of the exercise period symptoms of acute pulmonary oedema were present, characterized by dyspnoea,

TABLE I HAEMODYNAMIC DATA OBTAINED FROM FIVE DOGS RE-MONITORED PRIOR TO SACRIFICE t'1

Pressures· (mm Hg) Dog and GroupNoo

Stage in programme

Mean left atrium (PoAoWo)··

Mean main puimolUlry artery

X

Cineangiography

Left ventricle end-diasto

RighJ ventricle end-diasto

Stroke volume (ml)

Cardiac rate (per min)

~

Cardiac " output' (litre/min)

~

Pulmoluzry* *. eireo time (sec )

....

:;:tl

s:: ~

Z

Able (I )

Control 4 weeks pOSl-Opo

Baker (I)

Joe

Control 3 weeks post-opo Control 4 weeks post-op o

(I)

S

14

S

5

12°2

110

1°34

2 °3

19

25

20

10

23°4

130

3°04

3°9

S

16

10

4

,6°5

11 0

loS2

3°3

22

30

20

7

36 °4

130

4°73

4°9

II

IS

12

6

18°7

100

l oS7

3°3

20

25

'9

4

9

16

2'

5

11 8

100

' °,8

3°0

16

22

,6

6

27°4

120

3° 29

3°8

' 5°3

11 0

1 68

3° 8

I~

Ul'

II ~.... t>:l

Z

0

><

0

"'1

Monday

(II)

Boy (II)

Control 4 weeks post-opo 20 weeks post-opo Control 8 weeks post-opo

0

9

17

II

4

9

15

II

3

2°2

7

14

10

5

3°0

0

Noteo • The above values for pressures were obtained after application of correction factors as described under Materials and M ethodso ** Mean left atrial pressures were derived from the pulmonary artery wedge traceso .u Time for passage of contrast medium between main pulmonary artery and left atrium o

0

~ ..... Z

t'1

....o-is::

II :>~ t"'

II ~ II

U1

.....-

57 2

BRITISH VETERI NARY JOUR NAL, [28, [[

moist bronchial rales, intermittent retching cough and mild cyanosis. Spontaneous r esolution of these symptoms occurred during twenty-four hours of cage rest. The three dogs re-catheterized prior to sacrifice showed similar haemodynamic changes (T able I ). Most striking features were the rise in mean left atrial pressure (MLAP) and mean main pulmonary artery pressure (MPAP). As in all cases the rise in MLAP equalled or exceeded that in MPAP, pressure gradient across the lungs was little altered. Postoperative left atrial traces were dominated by a large C-wave fused with the V component. This was reflected to a surprising degree in the pulmonary artery trace, a nd appeared to be chiefly responsible for the rise in M PAP. The largest of these pressure changes were recorded in dog " Baker" and reproductions of the postoperative main pulmonary artery a nd left atrial traces for this animal app ear in Fig. I & 2. Partial left ventricular failure was indicated by a change of wave form in the trace and raised end-diastolic pressure (Table I ). Right ventricular performance appeared little changed or enhanced. Complete cineangiography records of fair quality were obtained in two animals in this group, revealing postoperative increases in left ventricular minute " outputs" and pulmonary circulation times- the respective factors being of the order of2 ·5 and 1·5 in both cases (Table I ). Thoracic radiographs taken within one week of surgery invariably revealed localized but significant dila tation of the root of the main pulmonary artery (Fig. 3), which persisted throughout the observation period. Cardiomegaly (T able II ) could always be discerned from two weeks and in two cases (including one of the early fatalities) was observed after a few days. Enlargement involved left atrium and usually left ventricle. With the exception of the dog which d eveloped bronchopneumonia, radiopathology oflung fields wa1> confined to a minimal increase in vascular m arking, and slight oedema was apparent in one case. (Unfortunately it was considered too hazardous to subj ect animals showing the delayed exercise syndrome to radiography until dyspnoea had abated. ) Localized radiodensity was always present adjacent to the thoracotomy site. Group II. This group consisted of only two dogs which, apart from a grade II mitral murmur, remained clinically normal throughout their respective observation periods of eight a nd twenty weeks. At sacrifice r ecorded pressures were virtually identical to control values (Table I ), but the eight-week survivor showed a small regurgitant wave in the pulmonary artery trace. The twenty-week survivor was subjected to an additional catheterization study at four weeks, when all the features found in recordings of Group I. animals were present to some extent, with the exception of left ventricular failure. At this time there was a similar increase in left ventricular minute "output" but this was less than 1·5 X the control value at sacrifice. Radiological ob8ervations closely resembled those d escribed above, but a significant difference was noted in the sequence of cardiomegaly. Enlargement was evident from two weeks, but the p attern was dominated by the right

~_ ~ ---~ ---'~- 1l" V\. ; !•. - , '- 1- -1 -1 · I

"BAKER" 9-11-70

M.P.A. mm.Hg.

::~

A

Paper Speed 2·5

40 --------'-=

10 ~

em.! sec.

BAKER mm.Hg' 30 19-10-70 _

M.P.A.

20

B 10- . - ' .

Paper Speed 2,5

em Isec .

Fig. I. A- Reproduction of main pulmonary artery trace 20 days postoperatively from dog " Baker ", with simultaneous electrocardiogram (lead II ) . The large regurgitant componen t (R ) dominates the trace. B- R eproduc tion of co ntrol trace. A lthough und erdamped , this provides an interesting comparison with A above.

"BAKER· 9- 11-70

LA. 50 - ' 30 10 Fig. 2. R eproduction of left a trial trace 20 days post· operatively from the sam e d og as in Fig. I , obtained by retrog rade catheterization from left ventricle. The regurgi. tant compone nt (R ) overshadows the A-wave. The cha nge in ampli tud e of the lead II electrocardiogram is due to reposi tioning of the animal. Bousfi eld a nd Bowden, B r. vet.]. ( 1972), 128,

I I

Fig. 3. Dorsoventra l thoracic radiograph of " Baker" taken seven days postoperatively. The arrow indicates protrusion of the pulmonary artery segment. Loss of normal rib contour a nd localized radiopacity of adjacent lung field indicate the thoracotomy site. Overl ying soft tissue reaction is still apparent.

Bousfi eld and Bowden, Br. vet.]. ( 1972), 128, 1 I

TABLE 11

RADIOLOGICAL SEQUENCE OF CARDIAC

ENLA RGEMENT AND CORRELATION

WITH

POST -MORT EM

ASSESSMENT

ttj

Dog and Group No.

2

3

4

(Sacrifice)

Able (I )

PAS +

PAS ++ LA +

No change

Baker (I)

PAS +

PAS + LA + LV + RA ± RV ±

(Sacrifice)

Joe (I )

PAS + LA + LV + RV +

'[Monday (II )

>< ~

Change in cardiac shado w with postoperative time* (weeks )

PAS +

Boy (II )

PAS +

+Mac (I )

PAS + LA + RV +

5

7

10

PAS + RV +

ttj

~

......

~

LAD ± RVD ± LAD ± RVD ±

ttj

Z

;! r

Z c::

IJJ

PAS + LA + LV ++ (Sacrifice) RV + PAS + RV +

Post-mortem assessment*

No change

PAS + + LA + RA + RV +

LAD ++ LVD + RVD + PAS + LA + LV + RV +

PAS + PAS + LA + LV + LA + RA + RV + + RV +

PAS + LA + LV + RV ++

PAS + (Sacrifice RV + at 8 weeks)

LVH ± RVH ++

I-rj I-rj

......

o......

ttj

Z

o

><

o

I-rj

LAD + LVH + D ± RVD + RAD ++ RVD + +

o;J> Z

Z tTl ~

::j Notes.

* PAS =

pulmonary artery segment; LA = left atrium; LV = left ventricle; RA = right atrium; RV = right ventricle. + symbols indicate the degree of regional enlargement on radiographs or of abnormality at post-mortem examination. They refer to changes relative to the heart as a whole at the particular time of examination and should be interpreted as follows: ± = slight. + = obvious. + + = very obvious. D = dilation. H = hypertrophy. t No significant change after 10 weeks-sacrificed at 2 0 weeks. + Early fata lity-rad iographed at 4 days.

~

r

< ;J>

r

c::ttj

'-" "-I <..>:>

574

BRITISH VETERINARY JOURNAL, 128,

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ventricle (Table II ). The long-term survivor showed moderate distension of th e posterior vena cava from ten weeks.

Electrocardiography and serum biochemistry Marginal changes in voltage and electrical axes of some hearts were noted, but the information was of little practical value. Cardiac arrhythmi as were not a feature of this experimental series. All animals showed moderate elevation of SAP levels following surgery, an d although tending to fall with time, they remained above 50 i.u. and wer e considered to be consistent with hepatic congestion. SGPT rises tended to be small or absent and indicated minimal liver damage. Post-mortem findings and lung histopathology Cadavers of both early fatalities showed generalized passive venous congestion and severe pulmonary oedema. This was associated with considerable dilation of right ventricle in one case and of left atrium in the other. Apart from obvious pulmonary oedema persisting in the animal which had survived bronchopneumonia, general findings in the remaining dogs were unremarkable. Moderate cardiac enlargement was always apparent. Mild hepatic congestion was sometimes present, but hepatomegaly was not observed. As a result of surgery, extensive pleural adhesions persisted at thoracotomy sites and localized pericardial adhesions had formed in three animals. Cardiomegaly in Group I dogs appeared to be due entirely to dilatation. Ventricular hypertrophy was an obvious feature in Group II, involving left ventricle in the eight-week and right ventricle in the twenty-week survivor. Correlation with previous radiological observation was fair (Table II ) but the degree of left heart dilatation was difficult to assess post mortem. Section of primary chordae tendineae in all Group I dogs had resulted in detachment of approximately one half of the free boarder of either anterior (aortic) or posterior (mural) cusp of the mitral valve, but the extent of detachment was greater in both fatalities. Minor tears in cusps and accessory leaflets were generally present. Haemodynamic sequelae were not found to be dependant upon which of the two cusps had been involved, probably because section was substantially limited to a few primary chordae. No chordae tendineae had, in fact, been sectioned in either of the group II dogs, the insufficiency resulting principally from a completely divided cusp, with subsequent development of left atrial jet lesions. Both hearts showed nodular fibrous thickening of the mitral valve, probably due to extensive minor trauma inflicted at surgery and the longer survival times. Microscopically all lungs showed evidence of congestion throughout the arterial and venous network and alveolar wall capillaries were extensively involved. Fibrosis was never apparent. Oedema was confined to sections of lung from the three dogs in which the condition had been obvious macroscopically. In these sections there was also evidence of bronchopneumonia, characterized by collapse of alveoli with cellular infiltration of their walls.

EXPERIMENT AL INSUFFI CIENCY OF CANINE M ITRAL VALUE

575

In one early fatality the infec tion appeared to be associated with an ascending p eriarteritis- possibly a complication of surgery or catheterization.

DI SCUSS I ON

Findings in Group I bear a r esemblance to those describ ed by Ettinger & Buergelt ( 1969) in certain of their clinical cases of ruptured chordae tendineae, a nd to those recorded by H aller & Morrow (I955a, b) in experimental cases. It must be emphasized, however, th at observa tions on this present series a re based upon a small number of young and otherwise healthy dogs, und er conditions of partial cage-rest. The three survivors in Group I are of particula r interest because they show that a large degree of mitral regurgitation can be tolerated under favourable conditions. Moreover, it is possible for considerable p assive pulmonary hypertension to exist without obvious evidence on either clinical or plain r adiographical examination. A further surprising feature in this group was the delay in onset of th e pulmonary oedema following brisk exercise and its spontaneous resolution in the fac e of gross hae,modynamic disturbance. General absence of p ersistent oede,ma, and hence minimal secondary trauma from coughing, could well account for the limited lung p athology in this experimental series. The thickening of alveolar walls and haemosiderinladen phagocytes described by H aller & Morrow ( I955a) in experimental cases, and by Das & Tashjian (1965) in fatal clinical cases of mitral insufficiency, were not observed. However, in view of the provision of adequa te antibiotic cover, the histological evidence of infection in lungs fro,m three out of five dogs in Group I cannot pass without com,ment and probably reflects weakened defence mechanism in the congested lung. It is inter esting to note that two of these ani,mals comprised the early fatalities. The literature makes no reference to distension of the m ain pulmon ary artery of the dog as an early sequel to isolated mitral regurgitation. The localized dilatation noted in this series was a re,markable feature and could be dependant upon the age group. On more than one occasion pulmonary artery dilatation was seen to occur prior to closure of the thorax at surgery, rather than the left atrial swelling reported by Haller & Morrow ( I955a). To wha t extent this elastic structure is capable of acting as a hydraulic damper, thus possibly providing some protection to the pulmonary vascular tree, is a ma tter for speculation. Indirect evidence of damping at this site was found in control pressure traces, where the main pulmonary artery peak systolic pressure was consistently several mm Hg below the corresponding right ventricular pressure - a result which did not appear to be entirely d ependent upon venturi effect a t the catheter tip. It is apparent that early dilatation of the left heart was an indication of a critical haemodyna,mic situation. Conversely, the ability of the right ventricle to undergo considerable dilatation without loss of perfor,mance was clearly demonstrated. I t is interesting to note that Laks, Garner & Swan (1967),

BRITISH VETERI NARY JOUR AL, 128, II

reporting on post-mortem studies of the canine heart, found that compliance of th e right ventricle always exceed ed that of the left. A C K N OWLE D G E l\!E N T S

We wish to thank the Wellcome T rust for fi nancial support a nd Professor F. R. Bell for help and encouragem ent. \Ve are indebted to M. G. D ear for advice and to m emb ers of the Royal Veterinary College and D epartmen t of Physics, Guy's Hospital Medical School, for valua ble technical a5sistance. REFEREN C ES

DAS, K . M. & TASHJIAN, R. J. ( 1965). Vet. M ed., 60, 1209. ETTINGER, S. & BUERGELT, C. D . (1969) . J. Am. vet. med. Ass. 155,535. FALICOV, R. E. & RESNEKOV, L. (1970) . Circulation, 42, 65. GRlBBE, P., HIRDONEN, L., LIND,]. & WEGELlUS, C. (1959). Cardiologia, 34, 348. HALLER,]. & MORROW, A. (I955a). Ann. Surg. 142, 37. HALLER, ]. & MORROW, A. (I955b). Surgery, 38, 518. HAMLIN, R. L. (1968). J. Am. vet. med. Ass., 153, 1446. LAKS, M. M., GARNER, D. & SWAN, H.]. C. (1967). Circ. R es. 20, 565. MoscovlTZ, H., DONOSO, E., GELB, 1. & WILDER, R. (1963) . In An Atlas of Haemody namics of the Cardiovascular System. New York : Grune & Stratton. PAKRASHI, B. C., PELlDES, L., STOKER,]. P. & TAYLOR, S. H. (1970). 6th WId Congo Cardiol., Cardiovascular R esearch, 243. (Acceptedfor publication 19 June 1972 )

Observations a propos de l'induction chirurgicale d'insuffisance de la valve IDitrale des chiens (Bousfield et Bowden) Reswne. L'insuffisance de la valve mitrale fut produite chirurgicalement chez 7 jeunes chiens briquets d e sexe masculin. Les parametres cliniques, radiologiques, hemodynamiques, electrocardiographiques et biochimiques du serum furent mesures en pre et post-operatoire. Apres examen post-mortem, les poumons furent examines histologiquement. Les chi ens furent observes individuellement en post-operatoire pour des periodes allant d ' l a 20 semaines et d'apres l'evaluation clinique, radiologique et hemodynamique pouvaient ~tre divises en deux groupes. Le groupe I montrait une hypertension passive marquee ainsi qu'une intolerance inhabituelle a l'exercice. Le groupe II ressemblait aux cas cliniques d'insuffisance cardiaque gauche moderee avec compensation. Chaque groupe montra comme consequence bien definie une cardiomegalie. Un caractere constant fut localise la dilatation de l'artere pulmonaire principale. L'histologie pulmonaire mit en evidence principalement une congestion pulmonaire, avec une incidence relativement elevee de modification inflammatoire. Beobachtungen bei chirurgisch verursachter Mitralinsuffiizienz bei Hunden (Bousfield und Bowden) Zusanunenfassung. Bei 7 mannlichen Beaglehunden wurde durch chirurgischen Eingriff eine Mitralinsuffizienz angelegt. In der prae- und post-operativen Zeit wurden klinische, rontgenologische, hamodynamische, elektro-kardiographische Untersuchungen angestellt und Messungen d es serumbiochemischen Parameters vorgenommen. Nach der Sektion wurden die Lungen histologisch untersucht. Die einzelnen Hunde wurden post-operativ fUr Zeiten von einer bis zu 20 Wochen beobachtet und es konnten aufgrund der klinischen, rontgenologischen und hamodynamischen Resultate zwei Gruppen unterschieden werden: Bei Gruppe I fand sich deutliche passive pulmonale Hypertonie und eine ungewohnliche Art von Unnihigkeit mit Anstrengungen

EXPERIMENTAL INSUFFICIENCY OF CANINE MITRAL VALUE

577

fertig zu werden. Die Gruppe II ahnelte klinischen Fallen von linksseitigem Herzversagen mit entsprechenden Kompensationserscheinungen, Beide Gruppen hatten eine definitive Kardiomegalie. Eine lokale Dilatation der A. Pulmonalis trat regekmassig auf. Die histologische Untersuchung der Lungen zeigte hauptsachlich vaskulare Kongestion mit relativ haufiger Vorkommen von entzundlichen Veranderungen. Observaciones sobre la insuficiencia de la valvula tnitral inducida quiriirgicatnente en los caninos (Bousfield y Bow den) ResUInen. Se produjo por metodos quirurgicos insuficiencia de la valvula mitral en 7 sabuesos machos jovenes. Se midieron durante los period os pre y post-operatorios los para metros clinicos, radiologicos, hemodimimicos, electrocardiograficos y bioquimicos del suero. A seguidasdel examen post-mortem, se estudio histologicamente los pulmones . Los perros individualmente fueron observados post-operativamente por period os que oscilaron d e I a 20 semanas y la evaluacion clinica radiologica y hemodinamica se pudo dividir en dos grupos . El Grpo I mostro una acusada hipertension pulmonar y una forma fuera de 10 usual de intolerancia al ejercicio. E l Grpo II se parecio a los casos clinicos de insuficiencia cardiaca izquierda ligera con estado de compensacion. Los dos grupos mostraron una secuencia definid a de cardiomegalia. Una caracteristica consistente fue la dilatacion localizada de la arteria pulmonar principal. La histologia del pulmon revelo principalmente congestion vascular con una incidencia relativamente alta de cambios inflamatorios.