Three cases of ruptured mitral valve chordae in the horse

Morphological variability of the atrioventricular valve cusps in the equine heart

BACKGROUND

The morphometric studies of the atrioventricular valves are still limited in the horse.

OBJECTIVES

To investigate the anatomy of the atrioventricular valves in the horse, focusing on the morphometric features of the valvular leaflets and the tendinous cords. We hypothesised that accessory leaflets occur commonly and exist as independent structures in the atrioventricular valves of the horse.

STUDY DESIGN

Descriptive anatomical study.

METHODS

Twenty normal hearts from slaughtered half-bred horses were used. The cardiac weight and circumference were recorded. The atrioventricular valves were exposed by excision of the atria, and the tricuspid and mitral annular diameters and circumferences were measured; the number of leaflets and tendinous cords for each atrioventricular ostium were then counted. The atrioventricular valves were isolated and the width, height and thickness of each leaflet were measured.

RESULTS

In addition to the principal leaflets, accessory leaflets were identified in 39 of 40 cardiac valves, 2 to 6 accessory leaflets for the mitral valve and 1 to 4 for the tricuspid valve. All the accessory leaflets were separated from the adjacent leaflets at their insertion. They were narrower and thinner than the principal leaflets, and were attached to a single papillary muscle; 95% of the accessory leaflets had two tendinous cords shared with the adjacent leaflets while a minority (34%) had their own specific tendinous cord.

MAIN LIMITATIONS

Lack of signalment data from the study population.

CONCLUSIONS

Supernumerary leaflets occurred commonly in the atrioventricular valves of the horse and appeared as independent structures. The clinical relevance of increased numbers of commissures that result from accessory leaflets and their relationship with valvular regurgitation are currently unknown.

Equine Acquired Valvular Disease

Degenerative myxomatous disease is common and is associated with aging. Poor prognostic indicators for equine aortic regurgitation specifically include ventricular ectopy, increased pulse pressure, and hyperkinetic pulses. Valvular prolapse is a functional abnormality diagnosed echocardiographically, about which knowledge is limited. A better understanding of its role in valvular regurgitation is needed. Infective endocarditis presents with fever and other systemic signs accompanying valvular regurgitation. The prognosis is poor, warranting aggressive therapy. Other forms of valvular disease occur rarely, but often presenting with severe regurgitation. Management of horses with valvular disease is focused on assessment of severity and regular clinical, echocardiographic, and electrocardiographic monitoring.

Cardiac and Respiratory Disease in Aged Horses

Respiratory and cardiac diseases are common in older horses. Advancing age is a specific risk factor for cardiac murmurs and these are more likely in males and small horses. Airway inflammation is the most common respiratory diagnosis. Recurrent airway obstruction can lead to irreversible structural change and bronchiectasis; with chronic hypoxia, right heart dysfunction and failure can develop. Valvular heart disease most often affects the aortic and/or the mitral valve. Management of comorbidity is an essential element of the therapeutic approach to cardiac and respiratory disease in older equids.

Clinical and echocardiographic features of mild mitral valve regurgitation in 108 horses

The clinical and echocardiographic characteristics of 108 horses with echocardiographically confirmed mild mitral valve regurgitation (MR) were investigated along with its clinical progression. Follow-up consisted of a re-examination of 28 horses and questionnaires were used to obtain information on a further 43 cases. Thirty-seven horses with mild MR were lost to follow-up. Horses with mild MR were re-examined between 2 and 9 years (3.8+/-1.8 years) following first presentation, with mild MR still present and a small, but statistically significant (P=0.049) increase of left ventricular diameter in end-diastole. These results suggested that mild MR has a good mid-term prognosis in sport and pleasure horses.

Cardiac disease in the geriatric horse

Almost all equine cardiac diseases may affect the geriatric horse. This article focuses on those cardiac diseases that are most common in the older horse, including degenerative valve disease, aortocardiac fistula, and congestive heart failure. Other cardiac diseases, such as bacterial endocarditis, pericarditis, and arrhythmias, are seen in all age groups of horses and are beyond the scope of this article.

Severe mitral regurgitation in horses: clinical, echocardiographic and pathological findings

Forty-three horses with mitral regurgitation (MR) and congestive heart failure were examined, using M-mode, 2-dimensional real-time and Doppler echocardiography. There was no breed or sex predisposition when compared to the general hospital population. The mean +/- s.d. age of affected horses was 7.6 +/- 8.1 years. Horses with MR and congestive heart failure had significant increases in mean values for left ventricular chamber size, left atrial size and heart rate and significant decreases in interventricular septal and left ventricular free wall thickness. Significant increases in pulmonary artery diameter were detected compared to aortic diameter. Mean values for fractional shortening were not significantly different from normal. All horses had a Grade 3-6/6 holosystolic or pansystolic murmur with its point of maximal intensity in the mitral to aortic valve area. Atrial fibrillation was found at presentation in 24 horses with MR and congestive heart failure. One horse presented with atrial tachycardia and subsequently developed atrial fibrillation. Seven horses had ventricular premature contractions. Exercise intolerance (n = 34), respiratory signs (n = 31), and fever (n = 21) were the most common presenting signs. Thickening of the left atrioventricular valve leaflets, endocarditis, flail valve leaflets, rupture of a chorda tendineae, and mitral valve prolapse were detected echocardiographically. Doppler echocardiography confirmed the presence of a large systolic regurgitant jet in the left atrium in all horses in which it was used, and in many horses, concurrent tricuspid and pulmonary regurgitation was detected. All horses died or were subjected to euthanasia due to the severity of their MR and/or lack of response to therapy. Post mortem examinations were performed in 35 horses and confirmed the echocardiographic findings. The echocardiographic detection of a flail mitral valve leaflet was significantly associated with the detection of a ruptured chorda tendineae at post mortem examination. There was a significant association between echocardiographic detection of a dilated pulmonary artery and its presence at post mortem examination. M-mode, 2-dimensional real-time, and Doppler echocardiography should be used to accurately characterise the valvular abnormalities and assess the severity of mitral regurgitation. Pulmonary artery dilatation, an echocardiographic indication of severe pulmonary hypertension, should be considered a grave prognostic indicator and may indicate impending pulmonary artery rupture.

Aorto-cardiac fistulas in seven horses

This report describes the history, clinical, electrocardiographic and echocardiographic findings, treatment, outcome and post-mortem findings in seven horses with aorto-cardiac fistula. Affected horses included 5 stallions, one gelding and one mare; 2 each of the Thoroughbred, Arabian and Standardbred breeds and one Thoroughbred-cross with a mean +/- s.d. age of 12 +/- 4 years, range 6-18 years. The presenting signs were acute distress (four horses), exercise intolerance (two horses) and the lesion was detected during a routine examination in one horse. Five horses had monomorphic ventricular tachycardia on admission and one other had a history of this arrhythmia. Five horses had a characteristic continuous murmur loudest in the right fourth intercostal space. Echocardiography (six horses) and/or post-mortem examination (four horses) revealed the horses had aorto-cardiac fistulas arising from the right aortic sinus in all five horses in which the site was recorded. Two horses had ruptured aneurysmal dilatations of the aortic wall at this site. Fistulas extended into the right ventricle in four horses; the right atrium in two horses, the left ventricle in one horse, and five horses had dissecting tracts in the septal myocardium. Horses survived for periods ranging from 24 h to 4 years. Aorto-cardiac fistula should be considered in the differential diagnosis for horses presenting with acute distress, bounding arterial pulse, a right-sided continuous murmur and/or monomorphic ventricular tachycardia, particularly in middle-aged or older stallions. Echocardiography is the technique of choice for confirming the diagnosis and demonstrating accompanying cardiac changes.

Heart murmurs in horses: determining their significance with echocardiography

Physiological flow murmurs occur frequently in horses and may be difficult to distinguish from murmurs associated with underlying cardiac disease. The significance of heart murmurs auscultated in horses is often difficult to determine if the horse is not exhibiting any clinical signs or if the signs, such as poor performance, are nonspecific. A complete echocardiographic examination (M-mode, 2-dimensional (2-D) and Doppler) provides an objective assessment of the severity of the horse's underlying cardiac disease. Valvular regurgitation and ventricular septal defects (VSDs) occur frequently and may impair performance, result in the horse's premature demise or have no apparent effect on the horse's life expectancy or performance capabilities. The echocardiographic findings that are used to formulate a prognosis for longevity and performance in horses with valvular regurgitation include the abnormalities detected on the valve leaflets, degree of cardiac chamber enlargement, severity of the resultant volume overload, size of the regurgitant jet, and relative relationship of jet size to chamber size. The echocardiographic findings that are used to formulate a prognosis for horses with VSDs are the number, size and location of the defect(s), degree of left ventricular volume overload, maximal velocity and direction of shunt flow through the defect and the presence and severity of concurrent valvulus regurgitation. Knowledge of the natural progression of the common types of cardiovascular disease in horses, coupled with the echocardiographic findings, clinical history and owner's or trainer's expectations can help the veterinarian form an accurate prognosis for life and performance in horses with heart murmurs.

Acquired cardiovascular disease

This article reviews the etiology, clinical findings, and significance of diseases of the heart valves, myocardium, pericardium, and great vessels of the horse. Each valve is considered separately from the point of view of murmur production. In addition, the role of the cardiovascular system in the etiology of sudden and unexpected death is considered.

Observations on seven cases of mitral insufficiency in the horse

Observations on seven cases of mitral insufficiency are described. Three of the horses had recent histories of cardiac failure and formed a separate group in which there were marked haemodynamic changes which varied in relation to heart rate but were associated with pulmonary hypertension, elevated right ventricular pressure and low peak left ventricular pressure. In the other four horses the heart appeared to be compensating at rest but to be unable to cope with severe exertion. On auscultation, a widespread pansystolic murmur and a prominent third heart sound were characteristic of the left ventricular volume overload. Microscopic changes were found in one left papillary muscle. The possibility that changes in the position of the papillary muscles consequent upon left ventricular dilatation may lead to or exaggerate mitral valve eversion is discussed.

Observations on structure and function of the equine mitral valve

The anatomy of the equine mitral valve and certain variations observed in 60 adult horses are described. The functional role of this valve, sited between the left atrium and the high pressure-generating left ventricle, is discussed in relation to its anatomical structure. A method of examining the left side of the heart post mortem is described.