SP ON TA N EOU S CONTRAST AND M A S S LESIONS

IN THE HEARTS OF RACE HORSES: U L T R A S O U N D

D I A G N O S I S - P R E L I M I N A R Y D A T A

Norman W. Rantanen DVM, MS1; T. Douglas Byars DVM2;

Michael L. Hauser, DVM, MS1 and Rob D.Gaines, RDMS ~

S U M M A R Y

The association of cardiac changes and decreased performance indicates that many horses have occult, but significant cardiac abnormality that may be a limiting factor. Many of these horses bad no outward signs of disease, it is interesting to speculate on the etiology of endothelial damage with subsequent platelet aggregation to produce visible echogenic contrast passing through the right heart and measurable mass lesions within the right atrium or attached to the tricuspid valve. The potential therapeutic value of platelet inhibitors, such as aspirin, appears to be worthy of clinical investigations in the horse.

I N T R O D U C T I O N

Echocardiography has been used to examine the horse heart. One-dimensional M-Mode instruments have been used most frequently.~

This report describes two-dimensional real time echoca rd iog raph i c f indings in the hearts of 103 Thoroughbred horses in training and racing. Emphasis is placed upon the description of the right heart findings. Many of the horses were examined because of clinical evidence of cardiac disease, while others were examined because of a reported decrease in racing or training performance. Seventy of the horses surveyed had no reported clinical evidence of cardiac disease, and results

were correlated with past and future perlormance. Only ultrasonographic findings will be reported here.

M A T E R I A L S A N D M E T H O D S

A mechanical sector scanner with a 3.0 MHz ninety- degree sector scanhead with a maximum of 20 cm penetration was utilized. ~ Images were recorded on 1/2 inch VHS videotape with commercially available video cassette recorder.t The horses were examined from both the right and left sides without removing the hair over the cardiac notch. Gain and threshold settings were adjusted to minimal levels necessary to visualize card iac structures. Mitral, tricuspid, pulmonic, and aortic valves as well as left and right atria and ventricles were imaged and recorded in multiple planes. Some horses were circled on a lead shank several times in the stall or jogged a short distance to elevate the heart rate and the right heart was scanned a second time. The videotapes were reviewed using frame-by-frame analysis and polaroid photographs were made of the findings.

Horses were evaluated and placed into four different categories: (1) No abnormalities found (2) Spontaneous contrast (mild, moderate or heavy echogenic particulate material) in the right heart (3) Spontaneous contrast plus a measurable mass in the right atrium or tricuspid valve lesion, and (4) mitral valve lesions. Other parameters were determined on a large number of the horses and will be the subject of a further report.

Author's addresses: t Echo Affiliates, Inc. 376 S. Broadway, Lexington, Ky 40508 2 Hagyard-Davidson-McGee, 848 V Nandino

Blvd, Lexington, Ky 40511

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a ATL 4600 Mechanical Sector Scanner and 722 3.0 MHz Scanhead. Pie Data Medical, PO Box 10663, Riviera Beach, FL 33404. bpanasonic Videocassette Recorder NV 8200, Matsushita Electric Industrial Co., Ltd., Japan.

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Figure 1. Photograph made from a videotape of a normal right heart of a normal horse (category one). The base of the heart is to the left and the tricuspid valve is open. RA: Right atrium; RV: Right ventricle; T: Tricuspid valve; Ao: Aortic outflow tract; S: Septum Note abscence of echogenic particles in the inflow tract.

Figure 3. Same horse as figure 2 after a slight increase in heart rate. Note the marked increase in echogenic particles in the right atrium and ventricle (arrows).

Figure 2. Photograph made from a videotape of a horse from category two. Note the presence o f echogenic particles in the right atrium and ventricle (arrows).

RESULTS

Forty-one horses had no evidence of cardiac lesions and were placed in the first category. Atrioventricular valves were distinct and well-defined and had a normal excursion. Aortic and pulmonic cusps were visualized and were considered within normal limits. Normal blood turbulence, a swirling softly echogenic pattern, was seen throughout the examination and no mass lesions were found. Volume 4, Number 5

Figure 4. Horse from category three with a 4.0 cm mass lesion (m) attached to the right atrial wall superior to the tricuspid valve (arrows). The base of the heart is to the right. This mass was seen best during the diastolic filling phase of the right ventricle.

Twenty-nine category 2 horses had evidence of echogenic particulate material passing through the tricuspid valve from the right atrium. This spontaneous contrast differed from normal turbulence in that it was brightly echogenic and passed through the tricuspid valve during diastole and was visible in the right ventricle and atrium during systole. These echoes were seen at rest in some horses and increased markedly with minimal increases in heart rate. Figure I is a photograph of the appearance of the right heart of a normal horse (category one) taken from the videotape. Figure 2 and 3 are the

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Figure 5. Horse from category three with a mass (m) attached to the base o f the tircuspid valve (T) on the ventricular side. An oblique plane was needed to document the attachment of this lesion (arrows).

Figure 7. Horse from category three taken during systole. The tricuspid valve (T) is closed. The mass lesion (m) can be seen on the atrial (RA) aspect o f the valve. The base of the heart is to the right.

Figure 6. Horse from category three with a mass lesion (m) attached to the atrial surface of the tricuspid valve (T). The base of the heart is to the right.

Figure 8. Horse from category four with a mass lesion (m) on the mitral valve leaflet (M). LV: Left ventricle; S: Septum; MV: mitral valve. The base o f the heart is to the left.

appearance of a horse in category two at rest and after moderate increase in heart rate.

Thirty category 3 horses had the same evidence of particulate material in the right heart as horses in category two plus the presence of a mass lesion seen during the cardiac cycles. The mass lesions varied in size and location and had well defined borders. The majority were attached to the right atrial wall. (Figure 4). Usually, the site of attachment could be found if the scanning plane was varied during the study. Some of the masses would pass in and out of the scanning plane during the filling phase of the ventricle. Some of these horses had a

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diastolic murmur on auscultation. Horses with lesions attached to the tricuspid valve had systolic murmurs (Figures 5 and 6). Most of the masses were best seen during the diastolic filling phase of the cardiac cycle, while others could be observed during both systole and diastole. (Figure 7)

Mitral valve lesions (category four) were found in five horses. (Figure 8) Two of them had concomitant right- sided mass lesions. These horses had detectable murmurs best heard over the mitral valve area. No evidence of particulate showering was present in the left heart of horses with mitral lesions.

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D I S C U S S I O N

Horses in category one did not demonstrate decreased performance. With no clinically significant auscultable murmurs and negative ultrasound examination, it was assumed that cardiac abnormalities were not present.

A large number of category two, three, and four horses on the other hand had decreased performance as a common history. Systolic murmurs were present in those with valvular lesions and diastolic murmurs were heard in some with the right atrial masses, though not consistently in the same horses during all periods of examination. Some of the horses with the right sided mass lesions were also febrile, anorectic, depressed, had atelectic lung and clinical evidence of pneumonia suggesting the lesion was most likely septic (vegetative endocarditis).

The ultrasonic reflectances seen in the right hearts p r o b a b l y r e p r e s e n t a g g r e g a t e d p la te le t s or b lood components. 2 This would suggest some event or lesion that could cause platelet aggregation. Many of the horses were outwardly normal and showed no overt clinical evidence of cardiac disease. The most common complaint was decreased performance. Those horses with particles in the right heart without evidence of a mass lesion in the right ventricle (category two) could have lesions of the endothelium in the right atrium (not visualized during the scan) or involvement of the vena cava or jugular veins.

Platelets have been described as a participant in the development ofendoearditis lesions.3 Abnormalb lood t u r b u l e n c e , h e m o c o n c e n t r a t i o n of p l a t e l e t s or coagulation proteins can result in eventual aggregation and adhesion of platelets, especially if the prostaglandin- t h r o m b o x a n e p a t h w a y were to be i n t e rmi t t en t l y activated. The significance of the particles, if indeed they are platelet aggregates, is not known in conjunction with those horses that eventually develop mass lesions of endocarditis.

Damage to the endothelial surfaces is one explanation for the presumed platelet aggregation. These could result from multiple venapunctures of the jugular veins. The lesions in the right atrium and tricuspid valve could result from injections of compounds producing direct damage to endothelial surfaces or from excessive turbulence

Figure 9. Photograph taken of a scan of a horse receiving IV fluids under pressure. Note the microbubbles produced from the injection (arrows).

created with smaller volumes of fluids given under pressure. Ultrasound scans of the right heart made during the administration of fluids under pressure showed excess ive tu rbu lence with m i c r o b u b b l e f o r m a t i o n (Figure 9.)

The presence of mitral valve lesions in two horses with right sided mass lesions and spontaneous contrast could indicate a previous episode of septic endocarditis. None of the five horses with mitral valve lesions had clinical evidence of sepsis at the time they were examined.

R E F E R E N C E S

I. Pipers FS, Hamlin RL: Echocardiography in the horse. JA VMA 170:815-19 (1977)

2. DeMaria Anthony: Department of Cardiology, University of Kentucky. Personal Communication.

3. Weinstein L, Schlesinger J J: Pathoanatomic, pathophysiologic, and clinical correlation in endocarditis New Eng J Med 29 !-i 6, 832-836 (1974)

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